Ronald L. Shimek, Ph D.

The Why's and How's of Sand Beds

The Role of the Benthos in the Reef Aquarium Ecosystem

September 6, 1998 on #reefs

My basic assumption is that the natural way is best. Emulating nature

facilitates predictability and prevents organism stress.

I claim that our reef aquarium systems are artificial ecosystems, and

function as do natural ones. To assess this claim, we need to define the term

"ecosystem" and see if our systems meet that definition.

What is an ecosystem and why is a reef aquarium system one?

An ecosystem has fours basic components: energy, a physical environment,

a biota (or the living creatures), and predictable pathways for energy and material

transfer.

The energy found in such a system can be electromagnetic (basically

solar energy), chemical (basically food energy) or kinetic (basically the energy inherent

in water motion). The last is important, but relatively few communities can harvest

kinetic energy, so I will concentrate on the first two.

In photosynthesis solar energy is used to convert water and carbon

dioxide to sugar. In this conversion, a lot of solar energy is stored in the sugar as

chemical energy: the energy of chemical bonds. It is this energy that is important in

ecosystems as chemical energy.

Solar energy is fixed in the coral reef ecosystem by the action of

"producers:" phytoplankton, algae, and zooxanthellae. All other organisms are

"consumer" and must either eat producers or producer byproducts. The pathway of

energy through a system is called a food web. And food webs pass energy and materials

through the ecosystem. The passage of materials through a system is NOT efficient. At any

given step, up to 90 percent of both the food and the energy in it is not used by the

organisms. This is a result of the Second Law of Thermodynamics which states that no

transfer of energy or materials is 100 percent efficient.

This means when a coral utilizes the byproducts of zooxanthellae, for

example, only about 10-20 % of those products are converted into coral or coral products.

The rest leave the coral via diffusion or as waste. This kind of ratio holds for any

energy transfer, such as a fish eating a planktor, or a deposit feeding worm eating a

piece of detritus. In all cases, the efficiency is low. Eventually in a food web, the

amount of food remaining of an initial amount is too low to support another transfer of

energy. However, the matter remains in the system.

An example of such a food chain be the following. To make 1 pound of a

killer whale requires 10 pounds of salmon, which in turn requires 100 pounds of small

fish, which in turn requires about 1000 pounds of large zooplankton, which in turn

requires about 10,000 pounds of small zooplankton, which in turn requires about 100000

pounds phytoplankton. This latter requires a LOT of ocean. In even the most productive of

marine ecosystems, there is not enough ocean to produce enough phytoplankton to support a

predator on killer whales.

However, although only 10 percent of the transfer makes it through the

process, the rest remains in the system as dissolved organic material and detritus. This

has to be processed.

In our aquaria, we short circuit some of the food webs by supplying food

(compressing the plankton end), however the aquaria follow all other pathways found in the

normal ecosystem.

So... we are ecosystem managers.

What is the benthos? The benthos is simply a term describing all the

organisms living on or in the ocean bottom. There are two types of benthos in our systems

as there are nature.

The first are the Epifauna, those organisms that live on substrates.

These include corals, sponges, and algae. The organisms found in the epifauna are

regulated by several factors,

such as the physical factors of light and depth. However, the most

important factors are probably the controls instituted by predators and herbivores.

The ecological structure of the reef community is not what most folks

tend to think. Coral reefs are algal dominated communities; up to 80 percent of the living

matter on coral reefs is algal tissue.

These algal distributions determined by light, available nutrients, and

herbivores. In experiments done in the laboratory, and in work done in the field the

following points are confirmed:

1) Sea urchin grazing promotes calcareous algae.

2) Fish grazing promotes filamentous algae.

3) Low water flow inhibits algal growth.

4) Oscillatory flow stimulates filamentous algae.

In effect, a reef aquarium with oscillating flow (timed power heads,

wave makers, etc) with fish predators such as tangs

is effectively an algal garden.

Now, on a natural reef - and in our tanks the algal growth is due to

dissolved organic material in the water. This in turn is due to the feeding of animals all

along the food chain.

Aquarists tend to forget that corals are predatory animals. In fact, of

all the predators on the Earth's surface, corals have the largest percentage of their

body devoted to food capture. If the food were not important to them, natural selection

would have optimized them to utilize other energy sources.

Corals need a lot of nutrients for mucus production. About 40% of the

material obtained each day by the corals from their zooxanthellae is lost as mucus. This

means that corals are "snot factories" filling our systems with dissolved mucus.

Much the same happens with any algae in the systems.

Corals also need a lot of energy for nematocyst production; these are

metabolically expensive structures and need both materials and energy to produce - and

they have a lot of them, up to 10,000/sq. mm. Additionally, they need both raw materials

and energy to produce their skeletons. Aquarists often forget that the coral skeleton is

not just calcium carbonate, but that it contains a significant amount of organic material

in the form of a matrix that the mineral is deposited on.

The bottom line is that corals must feed! Based on numerous studies it

appears that about 70% of a coral's nutrition needs is met by the zooxanthellae.

Predation makes up about 25% of the needs, and about 5% is met by the absorption of

dissolved organic materials. These needs are NOT trivial. Corals need a lot of nutrition

to survive.

The animal-algal symbiosis common in reef areas is a solution to the

problem of insufficient high-quality nutrients. These high-quality foods are basically

animal tissues. One of the statements that is often bantered about is that the water

flowing over a coral reef is nutrient poor. This is true - BUT ONLY FOR DISSOLVED

NUTRIENTS!!!

Is the impinging ocean water really nutrient poor? The following data

were derived from:

Hamner, et al. 1988. Zooplankton, planktivorous fish and water currents

on a windward reef face, Great Barrier Reef, Australia. Bulletin of Marine Science.

42:459-478.

The water flow over a reef was calculated at: 6,000 cubic meters of

water/1 linear m of reef crest in 12 hr. If we assume a depth of 1 m on the reef crest,

and using U. S. gallons, this is a flow rate of 2201 gallons/min.

Adjusted to the volume of a 100 gallon aquarium: This is 834

gallons/minute. Such water flow brings 416,142 food items to the reef crest in a 12 hour

period. This is equivalent to 5 oz. Wet weight of food per day.

Now, fish get to the food first. There are several layers of plankton

feeding fishes between the ocean and the reef face, and

these fish remove effectively all living planktonic organisms during the

day.

However, fish feces and debris from the feeding reach the reef. Assuming

a processing efficiency of 10% to 20%, this means 4 to 4.5 oz of debris and dissolved

organic material pass through the volume of a 100 gallon tank during the daylight. At

night, the zooplankton do impact the reef.

Total planktonic nutrition arriving at the reef (For a volume of a 100

gallon aquarium): 4 to 4.5 ounces per day of debris and dissolved material during the day.

Approximately 5 ounces of zooplankton at night.

BASICALLY A TANK THAT APPROXIMATES A NATURAL REEF CREST ENVIRONMENT

(WHERE SPS CORALS PREDOMINATE) SHOULD BE BEING FED ABOUT 10 OUNCES (WET WEIGHT) OF FOOD IN

A 24 HOUR PERIOD.

I suspect this is just a little eeny teeny bit more than most reef

aquarists feed their tanks....<G>.

This amount of food is necessary for good growth and health of the

animals of the reef crest. Now even if you don't have a reef crest aquarium the

animals need to be fed. - AND FED A LOT!

Such feeding or predation and herbivory result in detritus and dissolved

organic materials. Processing and utilization of detritus and dissolved organic materials

is a property of the benthos, particularly the infauna.

The infauna are those organisms that live in substrates. The infauna in

natural communities includes worms (several groups)

(Annelids, Enteropneusts, Sipunculans, Flatworms, etc), clams,

echinoderms (burrowing sea cukes and sea urchins), crustaceans,

protozoa (many types but dominated by foraminiferans), and bacteria.

In my examination of the sediments from my systems I found all of the

above with the exception clams and echinoderms. The worm diversity in my tanks was lower

than the highest diversities found in natural systems, but greater than the least diverse.

In other words, it was about the middle of the range. Based on what I saw at the Sand

workshops given at the 1998 WMC held last April, I would guess most aquarists have far

less.

Types of infauna that we should strive for.

The bacteria mentioned above were vitally important as they constitute

the biological filter of your aquarium basically allowing the export of nitrogenous animal

waste (ammonia) as nitrogen gas. These bacteria can only do this while they are growing.

They can grow fastest when uncrowded. Most of the infaunal animals eat bacteria or

bacterially covered sediment (which is cleaned of bacteria in the animals' guts).

This opens new space for more bacteria and facilitates the nitrogen production.

Other infauna:

Foraminiferans = shelled amoebae.

Foraminiferans prey on bacteria and thus are necessary for continued

bacterial growth. This facilitates the functioning of the biological filter, as this works

best only when the bacteria in it are actively reproducing.

Flatworms cruise through the sediments eating detritus and bacteria.

They facilitate more energy flow through the system.

Polychaete worms are probably the most numerous and diverse of the

visible infauna in most soft-sediment ecosystems and we should strive for significant

diversity in our tanks to provide multiple pathways for material flow. In my systems, as

an example, the following polychaete annelid families were represented in the sediment:

Amphinomidae, Capitellidae, Chaetopteridae, Cirratulidae, Dorvilleidae, Eunicidae,

Lumbrineridae, Maldanidae, Sabellidae, Spionidae, and the Syllidae.

Particularly important are the scavenging fire worms. These worms are

common in the sediments and are juveniles of the common fire worms Eurythoe or

Pareurythoe. Eurythoe is reef safe and an excellent scavenger and is an important

component of the benthos.

Although they can cause irritation when handled, they do not prey on

live animals and are good members of the "clean-up" crew.

In addition to being the major detritus processing component of the

benthos, the benthic infaunal polychaetes produce microplankton in the form of

reproductive products such as eggs, sperm, and larvae. Larval polychaetes are found in the

plankton of my reef system and they are produced by reproduction of animals living in the

sediments. Additionally there are "epibenthic or demersal zooplankton" which may

include larvae from annelids, but has as a major component harpacticoid copepods(both

animals and fecal pellets). Harpacticoid copepods are important in the detritus food

pathway and additionally produce fecal pellets which are used as food by many sps corals,

and other filter feeders.

It is important to consider that all of the material that goes into a

reef aquarium stays there unless it is somehow exported. Given that corals and other

animals need to feed and feed a lot, then it is important that excess nutrients resulting

from feeding be exported.

Export = Gas discharge + Filtrate + Organism removal

We can utilize one of the properties of coral reef ecosystems for export

of nutrients. That properties is the presence of significant amounts of algae. Such

organisms grow easy and may be harvested. In natural systems the larger predators would

periodically crop the algae. In our miniature worlds, the aquarist must fulfill that

ecological role and periodically harvest excess algal growth. Such algal growth should be

encouraged as it is an easy way to remove excess recycled nutrients from a system.

Thus: Organism removal = Algal removal

The importance of aquarium benthos, then is that the sediment infauna

maintains energy and material flow. Additionally epibenthic algae provide convenient

material export.

The sediment infauna process organic material turning it into organism

tissue, gas, or dissolved organic material.

A healthy and diverse sediment infauna

- prevents the accumulation of organic material in the sediment.

• feeds the filter-feeding organisms in the system.
  
• promotes and maintains the biological filter

Promotion and maintenance of the biological filter is accomplished by

feeding and movement. Feeding on the filter bacteria continually stimulates growth and

utilization of dissolved nitrogen and phosphorus compounds. Movement through the sediments

aerates the sediment and prevents clumping and clogging of the sediment.

Sediment disturbances caused by a single organism (in cubic mm per day)

Burrowing: 100 to 10,000,000

Predation on infauna: 100 to 1,000,000,000.

Deposit feeding: 100 to 100,000

These are rates for SINGLE organisms.

In normal sediments infaunal densities (for animals more than 1 mm long)

range from about 2,000 to about 500,000 animals per square meter of sediment surface.

In my aquariums, the infaunal densities range between 10,000 to 40,000

animals per square meter. These animals are distributed in a mosaic of patches throughout

the bottom of the aquaria. Nonetheless, the densities seen in my systems are perfectly

normal and well within the natural ranges found in equivalent habitats.

Most aquaria probably don't have such a diverse benthic population,

at least based on my examination of sediments at the WMC.

To maintain a diverse benthos you need the appropriate sediments.

The sediment particle distribution should not be uniform. Particle

diameters should range from coarse sand (2.0+ mm) to fine sand(0.063 mm). The sediments

should be skewed so that about 60 percent of the sediment is between 0.5mm and 0.062 mm in

diameter (coarse sand to very fine sand). As far as the animals are concerned the sediment

mineral composition is unimportant. This sediment particle distribution facilitates water

percolation and promotes organism utilization.

There should be a appropriate innoculum of organisms from live sand. The

appropriate fauna will not be found on live rock. The aquarist should avoid of major

infaunal predators except in the largest of systems. This means NO

"sand-sifting" animals. These are sifting the sand to feed on the organisms in

it. You want those organisms - so the predators should not be added. On the other hand,

burrowing sand swallowers such as sea cucumbers or sea urchins are fine. They disturb the

sediments and primarily eat bacteria not animals.

It is normal for sand beds to accumulate fine particulate matter. This

is mostly fecal pellets and is utilized by both the sediment infauna and bacteria as food

and substrate.

Siphoning, disturbing or cleaning of the sediments will result in

significant removal or mortality of sediment organisms and may severely damage the

functional aspect of the sand bed.

Examining the morphology of both the individual organisms and the whole

system will allow aquarists to treat their captive reefs as biological systems and

facilitate their maintenance.

The message of the functional morphology of reef organisms

The role of the benthos in the reef aquarium ecosystem is to maintain

energy and material flow through the system allowing a more normal captive reef to develop

Can you get the coral to use a larger percent of those products?

No. The limitations of the product use are set by the First and Second

Laws of thermodynamics and about a billion years of evolution.

how old are his systems with all this stuff in the sand?

My system is about 2 years old.

And what kinda sand is it?

The sand is aragonitic sand, a mixture of oolitic sand, live sand and

general goo...

How much do you feed your tank per day, and what size is your

tank?"

I have three systems; 42 hex (low light), 60 gal hex (Carpet Anemone

tank) and a 42 gal. reef.

I feed about 1-2 table spoons of thawed frozen plankton, and diced fish and krill per day.

What are your recommendations on sand bed depth and sand composition?

The composition was given in the body of the talk so I will leave that

up to you to dig out. I think the minimum depth should be about 4 inches (10 cm).

The maximum depth, between 6-8 in (15-20 cm).

You want a good deep bed or the sand fauna will not set up housekeeping and survive. rs

In starting a new tank what percentage live vs dead sand would you use

to promote good growth of sand dwelling organisims?

Get as much live sand as your budget can support and get a little from

several sources to maximize the diversity of the sand critters. rs

Any specific instructions for seeding dead sand with live sand?

Not really. I generally have just added live sand to the surface of a

dead sand bed. You don't have to mix the stuff up. The animals will find their way into it

just fine.

Ron, can you please define sand sifters and burrowers a bit further with

some examples?

Good question. These are terms that are floating around a couple of

mailing lists.

Sand sifters - animals that sift sand to get food out of it. Sleeper

gobies, etc. Also some burrowing sea stars.

These animals are sifting through the sand to eat the sand fauna that

you want to maintain... bad news for the sand critters.

Burrowers are animals like burrowing sea cucumbers that move through the sediment and eat

it. They eat off the bacteria and leave the sediment

The sediment is recolonized by bacteria and this growth stimulates the function of the

biological filter.

So burrowers are good guys - burrowing sea cukes, sea urchins, some worms. The only

problem is that if they are happy, you never see 'em.

Kinda hard to spend $$$ on animals you never see. But, it is a good investment.rs

At what point,(months, years, etc) would you consider a sand bed mature?

Depending on the stability of the tank, probably after about 18 months.

Many of the animals reproduce freguently, on the order of months.

But some are annuals. The bed is mature if it remains stable through a few reproductive

cycles.

These cycles, by the way, feed the corals with larvae, etc. Good food. Yumm.

Have you ever had a problem with hydrogen sufate (sulfide? Im not a

chemist) and if so, what he does about it?

Only when I tried a plenum. Bad news, there. In my sand beds, never have

had a problem.

Should people run a sand bed zone, seperate from the main tank? any

benefit/disadvantage to that approach?

The only place I could see this as an advantage would be in a very high

current tank.

In normal tanks, you need to feed the animals, and you need the sand bed to accumulate,

process, and export the excess food, and debris.

So, I would say, keep the sand bed in the main tank. One in the sump would be a good

refugium, but it would not work as well as material processing site.

If most aquariums have far less organisms in the sand than they should,

and the appropriate fauna will not be found on live rock, Where would you suggest getting

good live sand from?

Any and all sources. Try to get some coming in from a real reef.

Floridian or Gulf of Mexico sand is okay for starters, but these animals are primarily

temperate.

They won't survive long at reef temperatures. Check around with newsgroups about the most

recent sand orders, though. There is a lot of variation.

How can we check our own sand beds for infaunal population densities?

Hard to do.

I take about tube about 1 cm in diameter and remove a plug of sand. This I examine with a

microscope.

You can remove about a cubic cm of sand with a turkey baster or some other such tool. Put

it in a flat bottomed glass dish.

Cover with sea water and swirl to spread the sand out. Put it on piece of black paper. Let

it stand for about 5 minutes with no disturbance.

Then shine a bright light on it and examine with a hand lens. You should find at least 4

or 5 worms in the sediments, you will be able to see them by the movement they cause in

the sand.

Any less than 2 worms is not good news...

Any advice on how to siphon waste out of the sand without screwing up

the fauna? or should you even mess with the sand bed?

Never siphon it out. It is the food for the sand bed fauna.

Many people would like to know the specifics of your tanks do you have a

web site?

No. I have too much going on to maintain a web site. Too klutzy, too.

I will be glad to talk about my systems on reeflist, though.

Or by email at: rshimek@imt.net

What would be the optimal flow rate over the sand (cm/s)?

It should and will be variable. In most tanks if the water flow is

strong enuf to disturb the sand surface, you can armor it with mini-riprap such as GARF

grundge or crushed coral.

It is hard to get too much flow, but you also want areas of very slow flow. This way you

maximize the number of ecological niches in your system.

That maximization facilitates the material exchange processes.

So.. vary it a lot. rs.

If a LFS has live sand with no obvious to the naked eye sand fauna,

could it still be good live sand?

Yes, but it is unlikely. I would order my sand by mail order. Every

transfer step filters and kills some of the sand fauna. rs.

It has been said that live sand does not ship well and most animals in

the sand die. Is this true and what can be done to make sure this does not happen?

It certainly can happen. Generally, you expect a fair mortality.

Howsoever, sand animals are adapted to disturbance.

Sand is a harsh environment, and generally the animals are pretty rugged. Often enough

will survive to repopulate the sand, and innoculate the rest of the bed in short order.

If the sand were shipped moist, not wet, in tightly packed bags, kept cool, and given a

blast of O2 before the shipping mortality would be minimized.

Not much we as recipients can do though, except get it into the tanks ASAP.

So in recommending no sand sifters, should one sift their own sand using

their hand, spoon etc?

No. No sifting is necessary. I have done some calculations (for an

upcoming sand bed article) that show the normal activities of the worms in my tank are

sufficient to turn all the sediment over every two days.

This doesn't happen, of course, but there is sufficient disturbance that the sand never

clumps, etc. rs.

Do you have any expierence with the kits offerend by Inland Aquatics?

No.

They sound good, but a friend near here got one that was not particularly rich. So I think

there is a bit of a quality control problem.rs.

I have seen some black sand for sale, is it any good to use in the

aquarium and where does it come from?

Damifino where it is from. It might be lava sand, and it would probably

be fine for aquaria.

However, aragonitic sand has the advantange of providing a reservoir of dissolvable

calcium carbonate, and that is often a good thing.

The starfish commonly known as the whitle linkia burrowing starfish,

good, bad, indifferent?

Bad. It is eating the sand fauna. I don't think anyone can maintain one

successfully with a functional sand bed in any less than maybe a 500 gallon system.

They are really bad news for a lot of worms.

Thanks Ron!

© 1998 www.reefs.org