Live Sand
by
Jonathan Lowrie
Some definitions to begin with:
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Infauna
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Animals that live within sediments on seafloor bottom.
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Epifauna
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Benthic animals that crawl along the bottom or are firmly attached to bottom structures.
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Macrofauna
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Macroscopic animals that live on or in sediment.
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Microfauna
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Those animals less than 50 microns that live within the sediments.
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Meiofauna
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The animals between sizes. Also between spaces- these animals live within the interstitial spaces of the sediments.
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Closed System
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System which has no connection with outside environment. A typical home aquaria.
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Open System
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A system with a direct interchange with the outside environment.
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NNR
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Natural Nitrate Reduction. A concept of ‘natural’ filtration using a plenum and live san layers.
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Plenum
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A space or cavity. In the case of san beds, a raised space off the bottom of the aquarium with a barrier covered with a thickness of sand.
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‘Natural’
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A process that occurs in captivity in much the same fashion as in nature.
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Ecosystem
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All the organisms in a biotic community and the abiotic environmental factors they interact with.
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Live Sand
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Simply put: sand with living organisms contained within the interstitial spaces, or on the sand grains.
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SeaFloor Characteristics
• Seafloor characteristics are a crucial part of the habitat of benthic organisms. As the substrate supports the weight of many animals considerably more dense than seawater.
• The seafloor also acts as a mechanical barrier to collect and accumulate plankton, waste material, and detritus. A variety of worms, echinoderms, mollusks, and crustaceans obtain their nourishment from this organic matter.
• Benthic organisms are adapted for a particular bottom type; and character of life there, to a large extent, is dependent on the properties of bottom substrate.
• This bottom material varies from very solid rock to very soft, loose deposits.
• The actual composition of the seafloor is determined principally by the amount of energy available. In nature this is through wind driven waves primarily.
• In an aquarium, it can be from the use of auxiliary pumps.
• Benthic animals play an important role in mixing and sorting of sediments by their burrowing and sorting of the sediments by their burrowing and feeding activities.
• Oxygen and water from the sediment surface are transported down into the sediment through these tubes and burrows.
• Further modification of sedimentary characteristics is accomplished via cementing particles together to form tubes, and by compacting sediments together as fecal pellets and castings.
• The distributional patterns of benthic animals and plants are strongly influenced by the form and texture of their substrate.
• These factors determine effectiveness of locomotion, or for non-motile species, the persistence of attachment to bottom.
Animal Substrate Interaction
Because of the different distributions, unique adaptations have developed allowing for specialization to those environments.
• The particle size and organic content of the bottom material limits the versatility; and thus the distribution of specialized feeding habits.
Before you say ‘huh?’, allow me to explain in terms of our captive closed systems. All the diverse habitat types in nature all support a selective array of animal life.
• What exists in one biotope, most probably will not exist in another. In our aquariums, this translates well into the discussion of live rock and live sand.
• Live rock is a solid substrate. It has a variety of live within and about it. From small sponges, tunicates, to corals.
• Within may be algaes, bacteria, and more. All of these animals and plants have adapted to life on a hard substrate such as the live rock. Sand on the other hand is a totally different environment
• It is much softer, and will not offer the same advantages to most of the animals. Yes, some will be able to make the transition, and tolerate the new habitat, but many will not migrate to the new habitat. Hence the reason why adding live rock to ‘dead’ sand will not ultimately lead to a ‘live’sand bed.
Before the critics jump up and yell, let me explain my opinion of ‘live’. Yes, the sand will have life in it.
But will it have the typical life found within that format of sediment? No.
It has to come from somewhere, and sand animals and plants as a rule don’t live on rock, and vice versa.
• Suspension feeders depend on small plankton or detritus for nutrition. Filtering devices or sticky mucous nets are employed to collect minute suspended food from the water. Suspension feeders generally require clean water to prevent accumulation of indigestible particles.
• Deposit feeders engulf masses of sediments and process them through their digestive tract. They extract nourishment through their digestive tract from the organic matter of the sediment in much the same manner as an earthworm.
If we are to keep obligate suspension feeders, or deposit feeders in our aquariums, we must be sure to provide them the proper and suitable habitat to thrive in.
Sediment Types and Sorting
Many reef sediments are terrigenous in origin (in Atlantic reefs). Terrigenous sediments are those originating from terrestrial origins, and entering the ocean through streams and rivers.
The Atlantic Ocean has more large volume rivers that dump literally millions of cubic feet per hour of terrigenous sediments into the oceans. Much of this falls along the Continental shelf, but some does reach the reef zones.
In the Pacific Ocean, there are fewer rivers with huge outflows, as well as deep trenches to collect and accumulate this sediment.
Another sediment type of reefs is biogenic sediment. Biogenic sediment is derived from living animal and plants. These are sediments formed from diatoms skeletons, and skeletons of other animals and plants that have passed through the water column.
Biogenic sediments usually contain a high level of Calcium Carbonate.
Now, again, how does all this relate to the home aquarium? Coarse sediments are very difficult for animals to inhabit.
• The sand grains are cutting, and have a considerable mass that can easily crush the soft bodied animals. Most life here tends to be tube burrowing worms, and mollusks.
• Many are considered meiofauna as they exist in between sediment partakes as to prevent this destruction from abrasion.
• Finer sediments from sandy silt to mud typically have a rich fauna. Thousands of species can be found in healthy sheltered mud flats and grass beds.
• These natural sediment beds have another role as well. That role is as a mineral source. In nature, marine sediments will sometimes release minerals that will precipitate to form irregular deposits on the seafloor.
• Coral skeletons, and Halimeda is composed of calcium carbonate is composed of calcium carbonate in the form of aragonite. While many of the red algaes, and forams have CaCO3 in the form of calcite.
• Calcium carbonate can exist in three forms- two of which are important to reef systems. Those are calcite and aragonite.
In the Aquarium
So now I am back to the nature of the sand bed of the home aquarium. Typically, folks dump in a uniform size gravel of aragonite based sand.
Problems:
• Inadequate habitat
Using a fine sand and a medium sand and a coarse sand you can replicate the diversity of sediments to a limited extent.
Layers:
• Good, Bad, or indifferent
Depth:
• Deep?
• Shallow?
• Slopped?
A Mixed Sediment Filtration System:
Another more complex method is to have a mixed sediment system. This is involves using a sump and or refugium as well. Rather than go into great detail and stir up controversies, I will say this: Refugia with seagrasses and mangroves serve many useful purposes.
As a habitat for small shrimp, fish, mollusks, etc. And as a means to filter the aquarium. When I say filter- I also include mechanical and biological filtration.
Seagrasses in nature act as a baffle for sediment suspended in water, and will draw these sediments down to their bases. In a properly flowing system the seagrasses can serve much the same purpose at home.
NNR
Wait! Someone is bound to ask why? Why do we want to increase diversity if our current NNR or other systems seem to work?
A few comments:
• Live sand will not form from dead sand.
Period.
Louis Pasteur proved the world wrong on spontaneous generation, and it won’t happen in your reef tank. No matter how good the live rock is, it won’t provide what is necessary for a healthy sand bed.
Does NNR work?
• In many cases yes.
Is it the best system for me?
• Most often, no.
• Degrades over time
• Does not allow for diversification
• Artificial means to accomplish a natural function
On shipping live sand.
Sand is rough Its cuts, it grinds. And have you ever lifted 50 pounds of it?! Imagine being a soft bodied annelid or a think shelled mollusk. And being grated, smashed, and smooshed by the sand.
• Collection
• wait
• Box
• Tranship- in airplane
• Wholesalers- stored
• Fedex to you or stored
• Retail channels
Ways to Improve your Sand Bed:
• Add more benthic animals
Some sources may include Inland Aquatics Detrivore kits
Indo Pacific Sea Farms shrimp cultures
Brittle stars, Holothurians, worms, etc.
• Increase particle type diversity
Add more sand sizes
Add deeper sediment layers
• Add sifters
Gobies, other fish, etc.
• Feed and skimming
In established reef, can consider skimmerless operation
Heavy feeding of phytoplankton and zooplankton
Will help establish microfaunal population
• Depth
At least 6 to 8 inches. More if you can fit it.
Can be hidden with bottom.
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Wentworth Geometric Scale
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The phi scale is based on the logarithmic transformation of a particle diameter (phi = logbase2 particle size in mm)
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Particle Type
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Size (mm)
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Phi units
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Gravel
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Boulder
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>256
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beyond -8.0
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Cobble
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256-64
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-8.0 to -6.0
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Pebble
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64-4
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-6.0 to -2.0
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Fine Gravel
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4-2
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-2.0 to -1.0
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Sand
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Very coarse sand
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2-1
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-1.0 to 0
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Coarse sand
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1-0.5
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0 to 1.0
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Medium Sand
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0.5 – 0.2
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1.0 to 2.0
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Fine Sand
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0.25 – 0.125
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2.0 to 3.0
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very fine sand
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0.125 – 0.063
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3.0 to 4.0
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Silt
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coarse silt
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0.063 – 0.020
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4.0 to 5.0
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medium silt
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0.020 -0.005
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5.0 to 7.0
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fine silt
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0.004 -0.002
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7.0 to 8.0
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Clay
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clay
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<0.004
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beyond 8
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Composition of Reef Sand Communities
(Scoffin, et. al.,1985)
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depth
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region
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composition
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165 m
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reef shelf edge slope
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soft compacted sediment, medium to fine sand
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98 m
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shelf edge
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medium to coarse compacted sediments
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71 m
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outer shelf
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coarse loose sediments, mainly Halimeda
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63 m
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inter-reef location 1
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mixed sediment sizes
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69 m
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inter-reef location 2
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soft loose fine sand
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46 m
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leeward reef talus
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well worn coarse sediments
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40 m
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lagoon, near reef
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coarse unsorted sand
lagoon, away from reef medium to fine sediments with much macrolife
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