Archives for category: marine biology

The Pufferfish is considered the second deadliest vertebrate in the world, after the Golden Poison Frog. The common image we have of this creature is that it inflates when threatened. I have kept these fish in an aquarium, and in my experience they rarely puff out in captivity.

What makes the Pufferfish, also called the Fugu so popular is the lethal toxin in its liver, skin and the ovaries, and the fact that the Japanese treat it as a delicacy. Pretty ironic I guess? By the way it is extremely expensive and prepared only by trained, licensed chefs who, like all humans, occasionally make mistakes.


Almost all pufferfish contain tetrodotoxin, a substance that makes them foul tasting and often lethal to fish. To humans, tetrodotoxin is deadly, up to 1,200 times more poisonous than cyanide. The toxin paralyzes the muscles, including the muscles in our diaphragm, which is essential for breathing. The victim eventually dies of asphyxiation. There is enough toxin in one pufferfish to kill 30 adult humans, and there is no known antidote. Tetrodotoxin has been isolated from widely differing animal species, including western newts of the genus Taricha (where it was formerly termed “tarichatoxin”), pufferfishtoads of the genus Atelopus, several species of blue-ringed octopuses of the genusHapalochlaena (where it was called “maculotoxin”), several sea stars, certain angelfish, a polyclad flatworm, several species of Chaetognatha (arrow worms), several nemerteans (ribbonworms) and several species of xanthid crabs.

Tetrodotoxin molecule


Negative aspects aside, Puffer Fish makes cute companion.

Of course, don’t go around scaring puffer fish because a puffer fish could only perform a limited number of inflation in its life.


When a Pufferfish is threatened, it will pump itself up by taking 35 gulps or so in the course of 14 seconds. Each gulp draws in a big load of water thanks to some peculiar anatomic changes in the muscles and bones. The entire fish balloons as it continuously takes water into its stomach.

The stomach expands to nearly a hundred times its original volume, and the fish’s spine, already slightly curved, bends into an upside-down U shape, and all other internal organs become squeezed between the fish’s backbone and its rapidly expanding stomach. Meanwhile, the fish’s skin is pushed out, obscuring most of the puffer’s features-

Image: Sally J. Bensusen. American Museum of Natural History.

Sometimes they have difficulties expelling water from their stomach, and hence they actually risk dying every time they inflate. I guess we should record a default video showing one individual inflating itself on a public website to prevent curious divers/swimmers/fishers going around harming more Pufferfish. Pufferfish belong to family Tetraodontidae is a family of primarily marine and estuarine fish of the order Tetraodontiformes. The family includes many familiar species, which are variously called pufferfishpuffersballoonfishblowfishbubblefishglobefishswellfishtoadfishtoadies,honey toadssugar toads, and sea squab. They are morphologically similar to the closely related porcupinefish, which have large external spines (unlike the thinner, hidden spines of Tetraodontidae, which are only visible when the fish has puffed up). The scientific name refers to the four large teeth, fused into an upper and lower plate, which are used for crushing the shells of crustaceans and mollusks, their natural prey.

With all of this, many people still consider Fugo to be a delicacy , especially in Japan.



Tridacna Clams
Clams of the family Tridacnidae are some of the most amazing and beautiful animals available in the aquarium trade. Of the nine known species of tridacnids, only six are available to hobbyists. These magnificent creatures are native only to Pacific waters.
The presence of endosymbionts in the mantle of these clams has made them relatively easy to keep and to feed due to their ability to photosynthesize. Unlike corals however, the clam does not have these symbionts in the planktonic stage and must capture free-floating symbionts released by an adult clam.  
These clams are regarded as a delicacy in Chinese cuisine, many considering them to be an aphrodisiac.  This, along with their popularity in the aquarium hobby, has caused some species to become extinct in certain Pacific Islands.
The idea of propagating these clams was started by the Micronesian Mariculture Center (MMDC) in Palau.  Soon, organizations such as The International Center for Living Aquatic Resource Management (ICLARM) jumped in the game.  They founded the Coastal Aquaculture Center in the Solomon Islands and began producing clams and other marine organisms as well. Now, several species of clams are bred in captivity and available to hobbyists.
 Phylum:      Mollusca
 Class:         Bivalvia
 Order:         Veneroidea
 Family:       Cardiacea
 Subfamily:  Tridacnidae
 Genus:        Tridacna & Hippopus
                    1. Tridacna crocea
                    2. Tridacna derasa
                    3. Tridacna gigas
                    4. Tridacna maxima
                   5. Tridacna squamosa
                   6. Tridacna rosewateri
                   7. Tridacna tevoroa
                   8. Hippopus hippopus
                   9. Hippopus porcellanus

Of the nine species known, only the following six are commonly found in the hobby:

Tridacna crocea

Tridacna Crocea, which grows only to about 6”, is the smallest of the Tridacna species. These clams are found in colonies and live in shallower waters where more light is present. T. crocea is also noted as the “boring clam” because it can be found burrowed into rocks and coral heads.  The shell is relatively smooth with small furrows. This particular species has a relatively large byssus opening. This larger opening makes this species of Tridacna a little harder to keep due to the susceptibility of predation. It is also more light demanding than other species. The distribution of these clams ranges from Thailand to New Caledonia.

Tridacna maxima

T. Maxima can reach about the same size as T. squamosa, but is typically smaller. T. maxima is fairly easy to keep. In comparison to T. squamosa, the shell of T. maxima is asymmetrical with closer rows of scales and has a smaller hinge. T. maxima can be found from East Africa to Polynesia.

Tridacna squamosa

T. Squamosa can grow up to 16″ and are fairly easy to keep. The shells are very distinct in that the have rows of scales. The byssal opening of T. squamosa is fairly wide, but not like that of T. crocea.  These clams can live at depths of up to 18 meters and are found from East Africa through Polynesia.

Tridacna derasa

T. derasa is the second largest clam and can grow to about 24″. These are one of the easiest clams to keep. They can be collected in waters as deep as 20 meters and are commonly found in Australia, Philippines, and Indonesia.

Tridacna gigas

The giant of all clams, this species can grow up to one meter. Like T. derasa, this species is easy to keep. It can also be easily misidentified as a T.derasa. However, T. derasa has six to seven vertical folds where as T. gigas usually has four to five vertical folds. T. gigascan be found at depths of up to 20 meters. T. gigas can be found in the Indo-Pacific, but due to it’s overharvesting, this species is becoming endangered.

Hippopus hippopus

H. hippopus can reach 16″. The one distinguishing characteristic about this clam is that the mantle does not overhang the shell. The clams are relatively easy to keep. It is found in the Indo-Pacific region.

Positioning Your Clam

• Be sure not to place your clam close to any aggressive corals.
• Place your clam in an area of good light and low current. Too much current will cause your clam not to open. Light is very important to these animals. It is best to provide them with metal halide, PC, or VHO lighting.  Juvenile clams adapt to lighting variables more readily than adult clams.
• T. crocea and T. maxima are found in rocky habitats, so it is best to place them on rocks. Be sure not to place them in an area where they cannot fully open. T. squamosa, T. derasa, and T. gigas are best placed on a sandy substrate
• It is very important to place the clam on its byssus orifice and in the upright position. Failure to do so can cause death of the clam. If a clam falls over, re-position it as soon as possible. A clam can easily suffocate itself if not in the proper position. The byssus gland is a very important part of the clam. The gland secretes threads, which help the clam to position itself and to keep it from falling off of rocks. It also allows the clam to attach itself tightly to the substrate to prevent predators from attacking the clam. T. crocea, T. maxima, and T. squamosa use bysuss threads through out most of their life, others use them as juveniles. If you remove a clam from the substrate that is attached by its bysuss thread, it is important that you cut the thread and not pull the clam. Failure to do so can cause damage of the bysuss gland and cause death to the clam.

Water Quality

Water quality is important to clams. High pH and high temperature can be problematic.  Do not let the aquarium exceed 82 degrees or a pH beyond 8.3. Maintain a calcium level of at least 400ppm and dkh of 7-9. Salinity is also important, too high or low a salinity can cause the demise of a clam. Try to keep specific gravity between 1.023 -1.025.
The number one cause of a clam’s demise is usually water quality. Signs of an unhealthy clam include gaping (inhalant siphon remains wide open), listlessness (does not respond to shadows), or if the mantle does not fully extend beyond the shell (except in H. hippoppus). If your clam exhibits any of these symptoms, be sure to check your water quality first.

Clam Diseases and Predators

Damage to the bysuss gland can be a problem. Besides mishandling of the clam, predators can also attack the gland and cause a quick demise. If this is the case, there is not much you can do to help the clam. Predators of clams include certain wrasses, pygmy angels, shrimp, crabs, caulerpa, and crabs. Check your clam for parasitic snail, so which can burrow a hole through the shell and attack the clam. Also, be sure not to place the clam too close to any aggressive corals. Some corals can sting the clam, which will keep the mantle from fully expanding.  Air bubbles can be a problem too. They can become trapped inside the clam and cause the clams demise.

Purchasing a Clam

There are several things to look for when purchasing a clam. First, be sure that the inhalant siphon is closed and that the clam is not showing any signs of “gaping.” The clam should be responsive to changes in light. Clams are photosensitive and will close when shadows occur over the clam. If the clam is listless and does not respond to shadows, it is usually a sign that there is something wrong with the clam. Also be sure to check the bysuss gland for damage. There should be no fleshy tissue hanging from the opening.
If you take all these factors into consideration before purchasing a clam, you will have much success in keeping them alive. 

Demystifying Mud (Sediment Filtration)
By Jonathan Lowrie
Without question, there has been more than a bit of curiosity regarding the use of mud in reef aquariums in the past few months.  Mud has been used in freshwater biotopes for decades in certain applications with good success, but where does mud fit in to a coral microcosm?  Perhaps some of the allure lies in the fact that many want a “miracle”…something new and exciting, without requiring any explanation.  Others tend to look at such “advances” with a skeptical eye, requiring information, and viewing such “discoveries” with a touch of skepticism.  The bottom line is that mud is not a new subject or a novelty.  The study of sediment ecology and biology is well rehearsed in great depth and has been for many decades.  While aspects of sediments and their populations are being discovered almost daily, the literature abounds with immense volumes of the nature of “mud.”  In fact, to adequately cover the aspects of sediments in the marine environment would take a lifetime.  We would like to examine and clarify some aspects of mud, present some information concerning mud biotopes that are beneficial to reef aquariums, and finally present some experiences witht he use of such soft substrates.
What is Mud?
Mud, by definition, is wet soft earth or earthy matter.  
         Earth: dirt and soil, as distinguished from rock and sand. 
                  Soil is defined as the portion of the earth composed of                                  disintegrated rock and humus. 
                           Humus: the dark, organic matter in soil, produced                                 by the decomposition of vegetable or animal                               matter that results in the fertility of the                                     earth.
                  Dirt is defined as earth or soil, especially when loose.
Mud is not basically complicated, but certainly not magic, either.  However, mud does become quite complex when one looks at it from a geologist’s point of view.  There are over 13 classifications, based on the Wentworth scale.  These classification schemes to desrcibe differences in sediment texture are based on the proportion of silt, clay, sand, and water.  Commonly used categories are shown below.
Wentworth Geometric Scale
The phi scale is based on the logarithmic transformation of a particle diamer (phi = logbase2 particle size in mm)
Particle Type
Size (mm)
Phi units
beyond -8.0
-8.0 to -6.0
-6.0 to -2.0
Fine Gravel
-2.0 to -1.0
Very coarse sand
-1.0 to 0
Coasrse sand
0 to 1.0
Medium Sand
0.5 – 0.2
1.0 to 2.0
Fine Sand
0.25 – 0.125
2.0 to 3.0
vey fine sand
0.125 – 0.063
3.0 to 4.0
coarse silt
0.063 – 0.020
4.0 to 5.0
medium silt
0.020 -0.005
5.0 to 7.0
fine silt
0.004 -0.002
7.0 to 8.0
beyond 8
Meiofauna species might be expected to be more sensitive to alterations in sediment texture because of thier diminuative size.  McIntyre (1969) reviewed aspects of marine meiobenthos ecology which indicated that certain characteristic fauna occur in particular sand and mud deposits. Wieser (1960) determined that a certain Nematode only resided in muddy depostis, and Warwick and Buchannan (1970) showed that Nematode diversity decreased as particle size, increased or became more saturated with silts.  The proportion of silt and c;ay is of direct importance to many microorganisms and their distribution.  The porosity 9water content) and interstitial space are controleld directly by relative abunadanceof different sized particles.  Driscoll and Brandon (1973) observed that the distribution of Macoma tanta was directly related to the silt:clay ratio.  Also, sediment porosity, or ‘interstitial space’ is critical for small organisms living ewithin sediment.  Webb (1969) and Gray (1974) discussed the numerous types of marine sediments.  Many of the classificiatuions they developed were based on water movement through the sediment, which is dependant on particle shape and size.
Sediment water content (weight loss ofter dessication) or pore volumw (amount of water to achieve saturation) have been used to measure available space within sediments.  Frazer (1935) suggested that in systemically packed spheres:
Where permeability (P) varies directly with the square of the diameter of a spehere (D). 
Thewre are correlations of animal biomass and pre size within marine sediments (Parsons 1990)  Although total biomass of interstitial fauna was the same in all grades of sediment, the estimated volume of animals/voids was higher in samples which contained silts.
Now that we have desribed the sediment, how about animals?  Animals and plants are also classified based on size.  Macrofauna include animals whose shortest dimension is greater than or equal to 0.5 mm.  Meiofauna are less than 0.5 mm, but greater than microfauna, who are less than 0.1 mm in size.
Since benthic organisms affect and are themselves affetced by the chemical com[osition of bottom deposits, it is useful to brielfly consider chemical characteristics of marine sediments as they relates to biological processes within benthic communities. In all, but well flushed sediments, the concentrations of biologically important nutrients (silicates, nitrate, ammonia, phospahte) increase with depth to levels which are high relative to those in overlying water (Parsons, et all 1990)  Morse (1974) has develope a model for the transport process for exchange accross a sediment surface.  Its by simple diffusion.  Difussion accross a stagnant boundry layer (I cm think) may control flus into a layer where turbulent mixing ocurrs.  Waves also cause sediment/boundry layer mixing.  This action does release gases out of sediment in addition to the difussion at work.  Zeitzschel (1980) concluded that in shallow water (reef systems) up to 100% of the nutrient requirements for phytoplankton prioduction can be provided for.Becaue many nutrients are trapped within these sediments, they can be called on to provide for the reef community.  The action of the variosu detrivores within the ‘mud’ layers and thier interaction at the boundry layer will facillitate this mixing.
In an estuarrine habitat- a near shore community where an influx of seawater mixes with an outflow of freshwater, the transport of sedimentary compunds is regulkated by tidal action and estuarine flow.  These estuarine communites, commonly situated withing 300 yards of many carribean reef systems, are all associated with soft bottom, nmuddy bethic substartes.
However, not all muds are created by defintion.  In fact, a bag of top soil, one of the least humus enriched types of soil commonly available at nurseries, is composed of a perhaps quite surprising mixture.  If a bag of topsoil is added to a bucket of water, well over half of the volume will float to the surface as wood and plant debris.  Many of the fine “dirt components” cloud the water and will not easily settle out. Several washings later, the only thing that remains at the bottom of the bucket is sand and fine bits of rock of mixed types and origins. 
Of course, all this assumes that the mud is of some composition relative to its definition.  There is a special “mud” that is formed when certain bacteria decompose coral skeletons into a fine grayish mud-like carbonate based detrital sediment that has an organic content of 12%.  This was described as a “regenerative” sediment by DiSalvo in 1969.  Is this a magic mud?  No, but it is an interesting mud and does lead to the next topic.
When one begins to add mud to a reef aquarium, the addition is composed of various rock types which would not ordinarily be something added to a reef habitat, silicaceous sand (not aragonite, though limestone may be present to some degree), and a large volume of organic material.  Such organic material will continue to be decomposed by bacteria until it is finally totally released into the water column.  Most reef hobbyists spend great amounts of money and effort in order to maintain low organic content in their water, so purposely adding further organics would not seem prudent.  Furthermore, fine sedimentation of the clouded particulates comprises a stress that has many negative effects on marine life, including coral bleaching, fouling of filter feeding apparatus in invertebrates and multiple modalities in fish health.  Heavier organic loads also contribute to the eutrophication of reef communties, where algae outpace and overtake calcifying organisms.  Many of the decomposition products of the humus will also increase the nitrate and phosphate content of the water.  So why would it be advantageous at all?
Mud is Valuable
Most coral reefs are never found with muddy bottoms, though mixed calcareous and soft silted bottoms do occur in lagoons and nearby communties (covered later). Terrestrial based sand from multiple origin rock is rare, as is clay, which is mainly kaolinate.
165 m depth, reef shelf edge slope, soft compacted sediment, medium to fine sand
98 m depth, shelf edge, medium to coarse compacted sediments, 
71 m depth, outer shelf, coarse loose sediments, mainly Halimeda
63 m depth, inter-reef, mixed sediment sizes
69 m depth, inter reef, soft loose fine sand
46 m depth, leeward reef talus, well worn coarse sediments
40 m depth, lagoon, near reef, coarse unsorted sand
                  , lagoon, away from reef, medium to fine sediments with                 much macrolife
(Scoffin, et. al.,1985)
Nonetheless, the calcareous and non-humus containing sand bottoms that surround coral reefs have been part of the reason for their success.  Such nitrogen and phosphorous enriched sediments would quickly cause fleshy and microalgaes to overwhelm coral growth (Delgado, 1994, and others). Although the previous section would lead one to believe that mud would certainly not be beneficial to a marine aquarium, this is not the case.   In fact, the microbial (bacterial) fauna present in organically rich muds such as those of estuarine systems can be one of the most productive regions on earth in terms of their decomposition abilities and their primary productivity.  However, mud and other habitat specific sediments cultivate their own flora and fauna, composing a community uniquely adapted to that environment. 
What happens in the sediments?
The sediments that surround and lie adjavent to coral reefs, as mentioned, are not muddy.  However lagoonal sediments are quite high in organic matter.  Mud, as with other carbonate sediments, can play an integral role in denitrification and nutrient processing.  The highest rates of denitrification on reef found in dead coral heads (live rock), Thalassia sea grass beds and lagoon sediments (Seitzinger and D’Elia, 1984) Most aquarists using live sand beds in natural nitrate reduction (NNR), believe that the top aerobic (oxic) layers overlay the anoxic layers where denitrification takes place.  However, denitrification can also take place in oxic areas, and some of the highest rates of denitrification have been found in the top 1 cm of sediments where nitrate and oxygen levels are highest (Oren and Blackburn, 1979).  Nonetheless, anoxia commonly develops in the top 1/2″ to 1″ (5mm – 10 mm) of reef sediments, though this depth varies according to the grain size and composition of the substrate.  It can occur from the top millimeter down to 10-15 cm or more, such as the sediment areas near the Bermuda shelf. Areas without bioturbation may become anoxic within millimeters of the (carbonate) mud surface of shallow water sediments (Matson, 1985).
Methanogenesis can also occur often within centimeters of the surface of lagoonal sediments(Matson 1985).
The amount of bacterial populations present depend to a large degree on sediment particle size ( Rublee, 1982, etc.)
They are the highest in very fine sand year round and in very coarse sand  sediments during the winter (Johnstone, 1990 and Matson, 1985).  Sediments have been found to be generally oxidized in winter, and reduced in summer since higher temperatures favor higher anearobic activity.  Coarse sand has higher photosynthesis rates of algae within the sediments and in overall respiration of the community (Johnstone, 1990). Even such coarse grained muds. have a rate of anoxic catabolism that equals oxygen reduction .(Matson, 1985)  Bacterial populations in sediments may even be nutrient limited (Hansen, 1987) by phosphorous or nitrate; in other words, they are so effective that they could theoretically process more organic material than that to which they are exposed.
Anoxic decomposition, via reduction, is the most completely regenerative method of disposing of excess nutrients, and could account for the decomposition of all deposited organic matter to the lagoon (Matson, 1985). The energy web of most sediments in and around coral reefs revolves around detritus.
detritus and DOM–>bacteria and fungi—>mixed detrital consumers (omnivores/herbivores)—>lower carnivores—> higher carnivores (Ogden, 1988)  -include diagram of nutrient cycling, D’Elia
Biogenic sorting ocurrs as well withing a mudbed.  Burrowing organisms often generate a strong verticla inhomogeniciyty (maybe a too technical word?) in the sedimentert column.  Tyically, a sediment ingesting organisms consume preferentially small particles and transfer them to the surface or boundry layer.  The Atlantic Polychate, Clymenella torquatta, resides in its tude head down.  Particles less than 1 mm are ingested and defacated at the sediment surface.  This allows for a mixing and transport of nutrients accorss layers.
A microbiota adapted to the anoxic zone below the RPD (Redox potential discontinuity) environment can decompose organic material through fermentation, where some organics are used as hydrogen acceptors for the oxidation of other compiunds, yileding end oroiducts, such as fatty acids, or dissolved sulphates, nitrates, carbonates, and water can be used as hydrogen acceptors by different bacteria, yileding compounds liek H2S, NH3, CH4 ,H2.  This is NOT what we are looking for, yet our typical fauna in a live rock system, thrives on these compounds.  The mineralization of organic matter, although dependant on anaerobic oprocess, can be significant.  In an experiemnt using Zostrea detrituds and living plants, over half the oxidation and reduction of organic matter couldbe atributed to sulfate and nitrate reducing bacteria (Jorgenson and Fenchel, 1974)
This organic detritus (mostly algae matter and coral mucus) is decomposed primarily by microbial action. Up to 80% of dissolved organic compounds (DOC) pass through and are absorbed by the lagoon communtiy, and most of particluate organic sompounds (POC) settle on the lagoon sediments (Ogden, 1988).  Sandy lagoons also account for more than 70% of the nitrogen fixation in the reef (Shasar, 1994).  A slow downward flux of O2 appears to be at least partly responsible for sedimentary anoxia (Matson, 1985), lending further credence to the use of a plenum in sand beds.  The end products of anoxic deomposition are returned to near the sediment surface where they feed a diverse microflora involved, once again, in primary productivity.
What are the fates of nitrate?  There are many, but among the most prominent are assimilation by algae and bacteria and dissimilation by bacteria. The upper oxic layers of bacteria oxidize organics to CO2 while the anaerobic fermeners and denitrifiers oxidize organics to CO2 and convert nitrate to ammonia and nitrogen gas (N2).
Terrestrial and estuarine muds have higher rates of dissimilatory nitrate reduction back to ammonia and not nitrogen gas, thereby conserving nitrogen in the system for use by photosythesizers within the sediments.  In the reduction of nitrate to nitrogen gas, nitrogen is simply removed from the system by release into the environment, and these products can then be used by sulfate reducers and methanogenic bacteria. There is a low pH in muds, and therefore carnon dioxide (CO2) and organic acids (humic and fulvic) produced by the N2 community may then be shunted to sulfide (SO4) reduction and methanogenesis only if anoxic conditons exist. In fact, these sulfide and methanogenesi goups do exist, with redox levels as low as -450 mV.  In general, redox levels lower than 200 indicates these processes are taking place.   Sulfate reducers occur primarily in enriched lagoon sediments and are also associated with cyanobacterial mats in the reef flats (Kinsey, 1985).  The end product of their decomposition is carbon dioxide which contributes greatly to the CO2 content of the water. This carbon source can be used by algae or corals for calcification and/or respiration (Skyring, 1985). (…good or bad?  good for community, but is it good for closed systems?)
microbes: viruses, bacteria, fungii, actinomycetes, molds, yeasts,
         algae **very important
meiofauna : protozoans, crustaceans, polychaetes, annelids,
Furthermore, there are many specific areas of sediments in and around coral reefs that all support a unique benthic fauna and flora.  In the most simple of terms, these adjacent communities all play a role in the entire macrocosm of coral reefs, and in their nutrient regulation and recycling. 
Adjacent Communties
The description of nutrient flow (flux) over a coral reef is complex and not entirely known.  However, a brief description is necessary.  Basically, upwellings and currents bring plankton rich water across a coral reef.  There, the incredible array of life strips the water of its “food.”  Much of the energy from this food is recycled and conserved within the reef habitat though the food chain within the community. Primary production of food by sunlight creating plants and algae which are in turn eaten by progressively higher consumers is not considered here. Bottom sediments and their accompanying flora and fauna are among the most important ways of recycling organic reef material. (Sorokin, 1981) The coral reef and its adjacent communties are very effective in absorbing nutrients and recycling them within the community, preventing loss of such energy sources back to the ocean, and therefore allowing the vast complex web of species to exist (Crossland and Barnes, 1983).  They are largely dependent upon each other. Kinsey states that, “Gross production and calcification in coral reefs are, nevertheless, clearlydominated by benthic processes…”
As waves and currents wash over the reef, waste, mucus, sediment, and particulate organic matter (detritus) is carried across the reef and deposited into near shore communties.  These communities depend to some degree on the organic input of the coral reef community to fuel their own growth and productivity.  To some degree, like the reef, they are self sufficient.  Nonetheless, the flow of nutrients does foster and influence these adjacent communties (Hansen, 1987, Johsnstone, 1990).  To illustrate their importance, Ogden (1988) states, “Mangrove and seagrass systems are sinks, trapping and accumulating organic and inorganic material and permitting the growth of coral reefs offshore (while) coral reefs buffer the physical influence of the ocean and permit the development…of lagoon and sedimentary environments suitable for mangroves and seagrasses.” 
Sea Grass Beds
Sea Grass Beds receive large amounts of detritus from nearby coral reefs and are thus the site of large microbial and microalgal populations.  The seagrasses, commonly known as turtle grass (Thallasia sp.), mangrove grass (syringodium sp.),  and eel grass (Zostera sp.), are not algae, but true grasses (rooted plants gaining nutrients from the sediments (Ogden and Zieman) that grow underwater.  They may be exposed to air during low tides, and play a key role in both contributing to and stablilizing the sediments in which they live.  They are also relatively free of predation.  Reef sediments in sea grass beds are predominantly calcium carbonate debris from (in order) foraminiferans, Halimeda algae, mollusks, and corals. The sea grass sediments are mostly anoxic, and are primarily carbonate reef sand with small amounts of clay and silt.    Bacterial production an populations are the highest near the sea grass roots and are significantly higher than “normal” reef sediments.  Furthermore, bacterial production in the water column is very high in sea grass beds.  Considering that corals and sponges filter bacteria from the water column at up to 95% efficiency (Morairty, 1985, Sorokin, 1978, Reiswig, 1971, Wilkinson, 1978), the loss of this microbial community from the water column could be excessive, especially in closed aquaria with high coral coverage.  Thus, sediments become even more critical.  Sulfate reduction is also at a high level, occurring at its greatest rate in the top 1 cm of  sediment (Skyring, 1985), and is dominant as the final step in decomposition of material. (Moriarty, et. al. 1985) The sediments are finer than those around the reef, and mostly oxidative (Williams, 1985), though Matson found reduction rates to also be greatest in the fine particled sand of Thallasia beds. Therefore, it appears that all types of decomposition, buth oxidative and reductive are high in sea grass beds. 
Though the sea grasses and bacteria may compete for some of the same nutrients, it is the unique sediment and species composition that accounts for the productivity and their ability to manage the surplus effluent of the reef community.  Phosphorus seems to be the limiting nutrient in Thallasia beds (Ogden, 1988), no small benefit for the often excessive phosphate levels in reef aquaria.  Seagrass beds and lagoonal areas with their associated infauna have up to ten times the area of the reef and are (by most references, conservatively) capable of denitrifying and nitrogen fixing all of the accumulated organic material from the reef (Seitzinger and D’Elia 1983).  They are even dependent on organic decay from within the community and from terrestrial runoff, making tham a highly effective “filter” in the wild, and potentially in the aquarium.
There has recently been an increase in the interest of maintaining mangrove trees as an interesting and functional addition to reef aquariums.  Not only are they quite beautiful, but their roots are quite adept at removing nutrients from the sand and water.  Therefore, the nutrients which can stunt coral growth are used to feed the growth of the mangrove instead.  Mangroves are unique habitats where many fish come to spawn in the protected waters.  Unique flora and fauna abound in these rich habitats, including many species of gastropods and mollusks.  Within the sediments of a mangrove, algal mass is low, because the mangrove forest shades the soft bottom and prevents sunlight from reaching their chloroplasts.  Terrestrial runoff and fallen branches and leaves provide a rich organic sediment that is the cause of very high bacterial productivity, and they can compose over 90% of the biomass (Alongi, 1988). These bacteria act as a sink for nutrients, and can thus be very important in aquarium nutrient control.  Mangroves, except for the occasional tidal inputs, are surprisingly self-sufficient, and do not appear to be significant in terms of export of coral reef nutrients
(Ogden, 1988).  Still, given an environment free from terrestrial, supplemental, organic inputs, mangroves would certainly be capable of utilizing and exporting reef material. 
An Effective Sediment
From the preceeding information, it should be obvious that an effective sediment in terms of decomposing and denitrifying abilities is one which is high in organic material to support copious microbial populations.  However, such rich benthos also support communties of meiofaunal and flora, and macrofauna and flora.  Other organisms, like the seagreasses, mangrove trees and macroalgaes will not be the only competition for the desirable by products of bacterial metabolism.  Other infauna occurs as well.  Primary deposit feeding macroinfauna of lagoonal systems include the sea cucumbers (Holothuria), gastropods (Tellina, Rhinoclavis),  mollusks, echinoderms, and certain fish such as the tommyfish (Limnichthys) and gobies (Amblyeleotris) (Ogden, 1988).  One particular animal which has been found repeatedly to dramatically influnce the productivity of lagoonal sediments are the thalasinid shrimp (Callianassa).  These shrimp, which burow into the sand and create small mounds of substrate around their burrows, are both prolific and efficient.  Thallasinids are very effective “substrate sifters,” and they significantly reduce the micro and mieofuanla populations.  “(Callianassa) play a major role in the restructuring and functioning of lower trophic groups in lagoonal sediments.” (Hansen, et. al. 1987, Johnstone, 1990).
The meiofaunal consumers such as protozoans, ciliates, nematodes, copepods, turbellarias, polychaetes also scavenge the sediments for detritus, algal remains, and may even forage on bacteria directly.
Many macroalgaes may be present that vie for the rcih organic content of lagoonal sediments.  The most competitive are member sof the genera Microdictyon and Caulerpa.  Caulerpa may significantly uptake ammonia produced from microbial action via their rhizoids  (Williams , 1985). 
In general, bioturbation and competition negatively affects microbial populations.  therefore, the overall effectiveness of a sediment area is reduced over what would be present throught he actions of microbes alone.  It is interesting that many proponenets of “live sand beds” still recommend the use of “substrate sifting” organisms such as sea cucumbers, sleeper gobies (Valencienna sp.) and other burrowing animals.  Such bioturbation does mix the upper layers of the sand and, in effect, clean it of excess organic matter.  However, it also removes substrate for microbes, changes the oxygen composition of the sand, and therefore alters resident bacterial populations.  The normal populations of meiofauna, coupled with perhaps a few lightly bioturbasive animals should be all that is required for a well functioning substrate.  Keeping the sand “clean” as has been assumed in the past, should not be a priority. 
Reasons to Use Mud?
The recently publicized “Ecosytstem” method has been received with great and great skepticism.  In fact, the principles behind it are not as “novel” as they may seem. From descriptions in the trade, the Caulerpa present in this method would  uptake ammonia from sedimentary breakdown and be theoretically used in nutrient export, provided it is harvested.  Certainly the use of algae for effective filtration has been used (and with more effective species than Caulerpa) for many years successfully.  Algae turf scrubbers, despite certain negative reviews in the popular literature, are highly effective filtration devices capable, in our expereince, of sustaining all manner of coral reef aquaria. Caulerpa aside, what are the reasons to use mud?
Sediments high in organic matter are capable of a greater diversity and level of microbial growth.  Fine silty particles also increase the amount of sulfide reduction within their depths.  Anoxia is, arguably, the most important condition of effective decomposition and denitrification.  As will be discussed in the next section, conditions favorable to sulfide reduction are not necessarily deleterious to the auqatic environement.  The production of hydrogen sulfide (H2S) has appeared many times in the popular literature to be a dangerous and unwanted consequence of those using “live sand” beds.  The production of hydrogen sulfide is not, in fact, likely to be a great risk, and the end products of sulfide reduction, carbond dioxide and organic acids, will be used by other animals and algae both within adn exterior to the sediments, servincg to increase biodiversity and stability of a system.  The organic acids (humic and others) have also been described in a negative light in the literature as being harmful through their light absorptive qualities, etc.  Excess humic acids do not seem to occur to any great degree in long term established sand systems.  The periodic use of activated carbon would remove accumulated organic acids from the water column, should they occur.
A new sense of sediements may be initiating at this time.  However, one caveat exists in the use of any organically enriched “mud.”  The organic and mineral material present, which supports the microbial biota, should theoretically, in time, be exhausted.  It is doubtful that sedimentary deposit of detritus and reef “wastes” would be of a similar composition to sustain the specialized community.  If it were, lagoonal and reefal sediments would resemble estuarine or terrestrial infl coastal communities.  theyd o not.  furthermore, the initial populations of specialzied communtities would not be present merely by adding, for example, a soil to the substrate.  An incoculum of flora and fauna would need to be introduced to the sediments.  therefore, we question whether or not peridodic replacement of some of the original mineral and organic content of any mud would be required.  It seems likely that this woudl be the case.  Perhaps the most important role of “mud” would be in its ability to establish sufficient levels of anoxia, and to support a diverse and possibly more unique population of meiofaunal and meiofloral components.
Experiences with Mud, Adjacent Communites, and Other Sediments
Finding the commercial allure of the complexities of mud, along with their basic neccesity and influence over coral reef growth, somewhat objectionable, we would like to offer our own past and current experiences with different sediments.  We do this in hopes that a more complete uynderstanding occurs, and a basis on which to evaluate the use of calcareous or organic sediments in an aquarium. 
In a recent internet sequence, Dr. Ron Shimek proposed that the use of live sand in aquariums probably fulfills the samd function as the use of more recent arrivals in “the sediment scene.”  Indeed, the most active sediments of the lagoonal and adjacent reef communites are, in essence, an almost completely calcareous “live sand” enriched with large amounts of detritus and other organic matter.  They have been shown to be capable of complete recycling and decomposition of organic matter oin the wild, and our own experience with unskimmed “Jaubert” style reef aquariums would indicate similar functioning of a live sand bed in the captive environment.  We have found that methanogenesis and sulfide reduction are occurring within the sand bed.  After dismantling one sand bed, in particular, deeper layers were noticeably warmer (approximately 100 degrees F) than upper layers.  Subsurface stratification of productive algal mats and cyanobacterial layers establish their critical function much the same as they do in nature. The results of our experiences with such sand beds in maintaing water quality can equal or exceed the use of more “traditional” methods employing heavy foam fractionation.  Inland Aquatics in Terre Haute,  currently have systems with sand beds depths in excess of twenty inches without the much vaunted deleterious effects of “deep sand beds.”  In fact, the populations and reductive aspects of such depths can make them even more effective.  The use of “remote” sand beds can also be a very effective way to utilize benthic microbial “filtration,” since such relatively undisturbed areas will be free of significant bioturbation and competition allowing full development of microbial populations.  In summary of live sand, there is no doubt that the use of “live sand” is a capable and important component of the total captive reef environment.  But, can it get better?  We feel it can.
The recent use of refugiums to provide a culture of zooplankton and food for the aquarium is a wonderful example of how a functional separate communtiy can be established in connection with a main reef display.  Given the nature of the adjacent communties of sea grass beds and mangroves, establishing a separate, but connected microhabitat is of great benefit.  Not only are these sub-communties an interesting and attractive display in their own right, but when coupled with a detrital producing reef in need of nutrient export, they become even more valuable.  While we are incapable of duplicating nature, we feel that the understanding of nutrient flow in nature has provided us with a unique way of natural, non-mechanical nutrient regulation.  If designed so that the flow of water from a reef display enters a seagrasss or mangrove community, the native populations are capable of complete “denitrification” deemed so valuable to reef aquarists.  The removal of foam fractionation devices and other mechanical filtration will further allow for headier populations of planktonic organisms.  Indeed, the seagrass and mangrove communties are natural spawning habitats for many vertbrates and invertebrates.  Over time, it is likely that such areas will be exploited by reef organisms for that purpose, lending a hopefully better opportunity for breeding marine organisms, as well as increasing water column plankton.  We hope to cover the establishment and care of such communties in a future article.
In summary, the use of adjacent communtites and organically rich sediments can become an exciting area for reef aquarists.  The composition of the sediments, whether they are calcareous, silty muds, or combinations, can be used in different functional manners.  The procurement of non-traditional sediments should be weighed carefully.  While finding a non-polluted natural source for estuarine mud might be ideal, the compositon of such sediments may be of a nature where unwanted toxins, chemical compounds and mineral makeups create potentially great problems.  Furthermore, for any sedimentary community to be fully effective, the complment of niche organisms, both indigenous and habitat attrracted, must be present.  To merely add an organic sediment to an established or new system without understanding its nature or function could easily be as harmful to the aquatic environment as it could be beneficial.  However, with proper use, organic rich sediments can be exploited to increase biodiversity and total function of a natural reef aquarium.

How Do Sea Jellies Sting?

the science of cnidocytes and nematocysts

Sea jellies don’t sting through electricity or by touch. A sea jelly sting through a special type of cell called a Cnidocyte, there are three types of cnidocytes currently known. Spirocysts which entangle their prey, Ptychocysts which build tubes for tube anemones and the most well known Nematocysts. Nematocysts consist of a toxic barb which is coiled on a thread inside the cindocyte, when triggered the barb is ejected almost instantly taking only 700 nanoseconds to fire and firing with a force of five million g’s. A cindoctye can only fire once, and must be replaced when fired a process that could take 2 days.

Sea jellies sting their prey using nematocysts, also called cnidocysts, stinging structures located in specialized cells called cnidocytes, which are characteristic of all Cnidaria. Contact with a jellyfish tentacle can trigger millions of nematocysts to pierce the skin and inject venom, yet only some species’ venom cause an adverse reaction in humans. When a nematocyst is triggered by contact by predator or prey, pressure builds up rapidly inside it up to 2,000 pounds per square inch (14,000 kPa) until it bursts. A lance inside the nematocyst pierces the victim’s skin, and poison flows through into the victim. Touching or being touched by a jellyfish can be very uncomfortable, sometimes requiring medical assistance; sting effects range from no effect to extreme pain to death. Even beached and dying jellyfish can still sting when touched.

Scyphozoan jellyfish stings range from a twinge to tingling to agony. Most jellyfish stings are not deadly, but stings of some species of the class Cubozoa and the Box jellyfish, such as the famous and especially toxic Irukandji jellyfish, can be deadly. Stings may cause anaphylaxis, which can be fatal. Medical care may include administration of an antivenom.

Detailed Video of firing nematocysts

Jellyfish are the major non-polyp form of individuals of the phylum Cnidaria. They are typified as free-swimming marine animals consisting of a gelatinous umbrella-shaped bell and trailing tentacles. The bell can pulsate for locomotion, while stinging tentacles can be used to capture prey.

Jellyfish are found in every ocean, from the surface to the deep sea. A few jellyfish inhabit freshwater. Large, often colorful, jellyfish are common in coastal zones worldwide. Jellyfish have roamed the seas for at least 500 million years, and possibly 700 million years or more, making them the oldest multi-organ animal.

I Bought What I was Told, Why Are My Fish Still Sick?
Successful resolution of an aquarium health problem involves one of the following:  either blind luck; or the fish would have recovered whether you did (or in spite of what you did) anything or not; or else a correct series of events involving diagnostic and treatment choices.  Since we can’t do much about the first two, I’m going to talk about the last one.
The steps involved in successful treatment of problems are:
1) correct identification of the problem
2) correct choice of therapy
3) therapy (such as drugs) contain sufficient active ingredient
4) therapy is actually getting to the pathogen, in sufficient quantity to kill it without being of harm to the patient
5) problem is treated for adequate length of time
6) conditions are optimized for the patient (this is not absolutely necessary but will definitely increase your chances of success)
As you can see, this makes the whole thing a little more complicated than it seems on the surface.  I’m going to discuss each of these points in more detail.
1) Correct identification of the problem.  This is WAY harder than you might imagine.  Many things look like many other things, and especially when one is going by a description given by another person, it’s difficutl to be accurate.  Access to a microscope and a book with good pictures helps; also, common things are common (that’s why most people can identify ich, for instance).  Not all red streaky fins mean septicemia, though, and not all cases of septicemia are caused by the same bacteria.  So if a disease isn’t responding as expected, the first step is to rethink the diagnosis.
2) Correct choice of therapy.  This step contains several implications – that it has any effective therapy at all, or that this particular strain is susceptible to the same things the usual strains are.  Bacterial infections, particularly in freshwater aquarium fish, are becoming increasingly resistant to the average antibiotics used (and this is partly the fault of being bombarded with antibiotics on a random basis).  Aeromonas and Pseudomonas, for instance, are common pathogens, and are notorious for developing resistance to drugs.  You might read in a book that most bacterial problems in fish are caused by Aeromonas, and that Drug  So and so kills it, but that may no longer be the case. 
3) The therapy you have now acquired is actually any good.  If you’ll notice, treatments (especially antibiotics) are labeled “for ornamental fish use only”.   There’s a good reason for this – the purity and strength of the drug may not be being monitored particularly closely, and indeed it’s possible that it is outdated or contaiminated. 
4) Proper delivery mode and adequate strength.  By and large, treating an internal infection (such as septicemia) with an external bath (putting meds in the water) is useless.  The fish’s skin is designed to keep foreign substances out, and the therapy simply isn’t getting to where the problem is.  Either buying a prepared medicated food or making your own (if the fish will eat) is more likely to be of help.  An exception to this is certainly problems like flukes, or columnaris while it is still external; baths may well help here.  As for adequate strength – commercial preparations are made with the idea of avoiding problems associated with overdose, so they are deliberately made to dose on the low side.  This may well be inadequate for treating many problems.  And realistically, little is known about adequate dosing in fish – absorption, drug breakdown, drug toxicity is probably different from species to species, and very little is known in non food type fishes.  Things tend to be extrapolated from trout and catfish  and salmon, and may not be truly valid.
And some things work just fine, but can be toxic easily – formalin (formaldehyde solution) is a good example.  It’s a pretty effective killer of many bad things, but unless used very carefully, can be pretty hard on the fish (the environment as well).  So you really have to know what you’re doing to use it.
5) Problem treated for adequate length of time.  Often, the signs go away, but some of the bad guys are still present; if treatment is stopped too soon, they can come back with a vengeance (since it tends to be the sturdier one who are killed last).
6) And finally, the fish with the immune system that is functioning at its best will have the best chance of getting it over the problem.  Optimal living conditions will help the immune system. 
So, as you can see, a failure in one of these steps will lead to treatment failure.  Develop a systematic way of looking at problems and formulating a treatment plan, and you will have the most likely chance for success.


What is phytoplankton? Lets take a moment to break the word down into its parts. We have Phyto and plankton Phyto is greek for plant and plankton means free swimming. Technically, plankton is any orgamisn, plant or animals that cannot swim against the current of the ocean. So, phytoplankton is plankton life that is comrpised of plants, and algaes.

It is known that green plants liberate oxygen and produce carbohydrates, a basic link in the food chain of plants to animals to people. Collectively, this chemical process is referred to as photosynthesis (photo = light, synthesis = to make). In these tiny food factories, there is a chemical compound called chlorophyll that, in combination with sunlight, converts carbon dioxide, water, and minerals into edible carbohydrates, proteins, and fats. Thus, these phytoplankton are the basis for the oceanic food chain.
Sea animals cannot perform this biological food-making process. Two-thirds of all the photosynthesis that takes place on this earth occurs in the oceans that yearly create 80 to 160 billion tons of carbohydrates. So numerous are these tiny plant forms that they often turn the water green, brown, or reddish, and are called red tides.

Plankton in general are passivlely drifting or weakly swimming organisms found in both freshwater and marine environments. They can be microscopic single celled organisms, to giant jellyfish tha are meteres in total length. They can be plankton their whole life, like copepods and are called holoplankton. Or they can be plankton just for the larval stages, as is the case with certain fish, arthropods and molluscs and they are called meroplankton. As we have learned, there is plant plankton, aka phytoplankton, and there is also zooplanlton, or animal plankton. Zooplankton are all the larval fishes, mollsuks, and copepods to name a few species.
Plankton make up the basis of the food chain throughout the ocean. These single cell phytoplankton are the main food for millions of other organisms that in turn are food for larger predators, and we can follow this all the way up the food chain to humans. The role of phytoplankton, or microalgae is to cycle andconvert nutrients. Because phytoplankton can utilize sunlight for energy, photosynthesis, they can take minerals and nutrients from their surroundsing and use the light enegry and make enegery. One of the end products of photosynthesis is the production of oxygen. Because the biomass of phytoplankton is so large, the end result oxygen production helps keep our planet hispoitable for us humans to live here.
Like all plants, phytoplankton play a role in nutrient cycling as well. They utilize inorganic minerals and organic compiunds to help themselves grow. By utilizing compounds like ammonia, urea, nitrates, phosphates and potasium and metals like iron, zinc and copper they help distribute these to other organsims and help remove them from the water column. However, this removel is not permanent, as its constantly rereleased by the death and decomposition of the algae cells.
Microalages are the main source of nutrients for many smaller organisms like zooplankton. Because phytoplankton are a rich source of carbohydrates, proteins and fats they are the building block of life in the seas. In a balanced ecosystem, phytoplankton provide food for a wide range of sea creatures including whales, shrimp, snails, and jellyfish. When too many nutrients are available, phytoplankton may grow out of control and form harmful algal blooms (HABs). These blooms can produce extremely toxic compounds that have harmful effects on fish, shellfish, mammals, birds, and even people.
Why do we care? For one, phytoplankton absorb a lot of CO2. In this link, it supports that without phytoplankton the world would be a very different place. This is important to us on land because we can influence the balance of these micro organisms. Our pollution, run off and fertilizers can unbalance this ecosystem and cause the harmful blooms and knock out of whack this balanced system.When conditions are right, phytoplankton populations can grow explosively, a phenomenon known as a bloom. Blooms in the ocean may cover hundreds of square kilometers and are easily visible in satellite images. A bloom may last several weeks, but the life span of any individual phytoplankton is rarely more than a few days.

We all need to be aware of what we put into the ocean and how it can impact the systems. Afterall we depend on the ocean for our health and comfort too.

The Mariana Trench is the deepest place on Earth. It is located to the east of Mariana Islands, running for about 2550 kilometers but has a mean width of only 69 kilometers.
The deepest point, known as the Challenger Deep, which had hitherto been measured at 10919 meters, is now estimated to be 10994 meters.

From WikipediaThe Challenger Deep is the deepest known point in the Earth‘s sea floor hydrosphere, with a depth of 10,898 m (35,755 ft) to 10,916 m (35,814 ft) by direct measurement from submersibles, and slightly more by sonar bathymetry (see below). It is in the Pacific Ocean, at the southern end of the Mariana Trench near the Mariana Islandsgroup. The Challenger Deep is a relatively small slot-shaped depression in the bottom of a considerably larger crescent-shaped oceanic trench, which itself is an unusually deep feature in the ocean floor. Its bottom is about 11 km (7 mi) long and 1.6 km (1 mi) wide, with gently sloping sides. The closest land to the Challenger Deep isFais Island (one of the outer islands of Yap), 287 km (178 mi) southwest, and Guam, 304 km (189 mi) to the northeast. It is located in the ocean territory of the Federated States of Micronesia, 1 mi (1.6 km) from its border with ocean territory associated with Guam.

The depression is named after the British Royal Navy survey ship HMS Challenger, whose expedition of 1872–1876 made the first recordings of its depth. According to the August 2011 version of the GEBCO Gazetteer of Undersea Feature Names, the location and depth of the Challenger Deep are 11°22.4′N 142°35.5′E and 10,920 m (35,827 ft) ±10 m (33 ft).
June 2009 sonar mapping of the Challenger Deep by the Simrad EM120 (sonar multibeam bathymetry system for 300–11,000 m deep water mapping) aboard the RV Kilo Moana indicated a depth of 10,971 metres (35,994 ft; 6.817 mi). The sonar system uses phase and amplitude bottom detection, with a precision of better than 0.2% of water depth; this is an error of about 22 metres (72 ft) at this depth.[4][5] Further soundings made by the US Center for Coastal & Ocean Mapping in 2011 are in agreement with this figure, placing the deepest part of the Challenger Deep at 10,994 m (36,070 ft), with a vertical precision of approximately 40 m (130 ft).
Only four descents have ever been achieved. The first descent by any vehicle was by the manned bathyscaphe Trieste in 1960. This was followed by the unmanned ROVs Kaikō in 1995 and Nereus in 2009. In March 2012 a manned solo descent was made by the deep-submergence vehicle Deepsea Challenger. These expeditions measured very similar depths of 10,898 to 10,916 metres (35,755 to 35,814 ft).”
The Challenger Deep is well, deep. Inverted it dwarfs Mt. Everest in comparison.

To put the figures into perspective;
The tallest mountain in the world, Mount Everest, is only 8848 meters.
The world record for scuba diving is 330 meters.
Let’s do some calculation.
Water pressure, P is given by hρg 
since h = 10994 m, g = 9.81 m/s^2, and  ρ = 1097 kg/m^3
Therefore P = 110763120.78 Pa, or 110.7 MPa. For those that are not as well versed in physics that is a LOT of pressure.  Bone crushing pressure.
So it’s really dark,  cold and pressurized down there. One might not expect to see any living organism here. Afterall life needs sunlight and something less than bone crushing pressures 24 hours a day- right?
Not here.  In the Challenger Deep, along with other deep water life biomes some life does exist.  Deep sea shrimp, seacucumbers, and a plentiful assortment of plankton and marine micro fauna exist.  Not unlike the deep sea hydrothermal vent zonesthere is life, for example the Vent Crab, and bacterias. Lots of them. These animals are kept alive probably by hydrothermal vents, which release hydrogen sulfide and other minerals, as well as heat.
Scientists are still not sure of the food chain in the Challenger Deep, but the abudnance of small shelled animals and a hierarchy of food chain organisms suggests life does just fine down there.
Pretty cool isn’t it?