[Mr.Reefer]

by J. Charles Delbeek M.Sc.

The nutritional requirements of the various organisms that can occur
in reef systems is extremely varied and/or difficult to ascertain. We
are no longer dealing only with the different feeding habits of the
fish that we are keeping but also various orders of invertebrates, each
with their own peculiarities. Add to this mass of confusion the fact
that very little is known about the nutritional requirements of these
organisms and one can quickly see that the topic of nutrition in reef
systems is a most intimidating one. That is why I find the type of
advertising used by some manufacturers of "reef foods" rather
distressing. Very few of these products are based on any form of
original research and some appear to contain additional chemical
additives (e.g. glutamic acid, proline or alanine) that will elicit a
feeding response in some invertebrates but have questionable
nutritional value.

It will not be the purpose of this article to tell you what to feed
each organism but more to outline the various feeding modes that one
will encounter and to help you decide how best to deal with them. To
go into detail on the diet of each organism would require a complete
book. There are a few references that I will give at the end of this
article that will help you get started. Read as much as you can, ask
questions of your dealer and friends. Don't be afraid to experiment
when it comes to feeding but remember to ALWAYS FEED IN MODERATION.

The general approach taken in feeding organisms in captivity is to
closely study the diets of these organisms in the wild and to
duplicate this as much as possible. This approach works quite well
with most fish and some invertebrates. However, many natural diets are
almost impossible to duplicate e.g. coral polyps and sponges which are
fed on by a multitude of fish and invertebrates. Another problem comes
with corals where there are few studies published on the diets of
corals and indeed, much debate on how much and even if corals need to
feed.

There are various feeding mechanisms used by the inhabitants of our
reef aquariums. In some instances the same organism may use more than
one feeding strategy which is probably an adaptation to ensure that as
much nutrition as possible can be extracted from the nutrient poor
area that a reef is. This is the case with many coral species and for
this reason, coral feeding strategies will be dealt with separately.

Many organisms actually trap and/or catch and digest other organisms
such as shrimp, copepods and marine worms. Some organisms, commonly
known as filter feeders, feed by trapping much smaller particles
ranging in size from copepods and other zooplankton to detritus and
feces. Those that feed on detritus either digest the bacteria living
on them or the particulate organics that coat such particles (Wotton
1988). The method of feeding that has probably elicited the most
debate is the one involving the relationship between organisms such as
corals, bivalves, sponges and the symbiotic algae that live in their
tissues. Contrary to popular belief these algae (usually referred to
as zooxanthellae) are not green but are in fact gold-coloured
dinoflagellates of the genus Symbiodinium. At one point it was
thought that there was only a single species, Symbiodinium
microadriaticum but it has recently been shown that there are in fact
several strains of zooxanthellae; some fast growing, some slow (Blank
and Trench, 1985; Trench 1979). The final method of feeding that we
will examine in this article is the direct uptake of nutrients such as
ammonia, phosphate, proteins and dissolved organics from the water,
through the body wall.

The majority of the animals that we keep in our aquariums, such as
fish, shrimp, starfish and urchins fall into the first category of
feeding. These organisms may be omnivorous, herbivorous or
carnivorous in nature and depending on their size and appetite may be
able to fend for themselves in a reef tank. More common though is the
situation where additional feedings are required. For those organisms
that are carnivorous or omnivorous good quality flake foods with low
amounts of carbohydrates, large amounts of protein and the proper
lipids (fish oils as opposed to plant oils) should suffice. The same
goes for frozen foods. The problem with any prepared food is the issue
of vitamins, pigments and other micronutrients. Many of these are
destroyed during the manufacturing process and need to be added to the
feed later. The problem is that these substances have a limited shelf
life. By the time the food has gone through the hands of the
manufacturer, wholesaler, retailer and finally to you, the majority of
these substances may have been lost through oxidization. As a result,
your organisms will not be getting the full nutritional value that you
may think. Fortunately, recent developments in aquaculture are making
their way into the pet industry and many foods are now available that
contain vitamins stabilized against deterioration. The main vitamin
available in this form is vitamin C and there are a number of foods
and vitamin supplements now advertising its use.

There are a number of precautions you should take when purchasing and
using prepared foods. First of all only buy food from a dealer who
regularly rotates their stock and who buys direct from the
manufacturer or from a wholesaler who rotates their stock. Most flake
foods have a shelf live of about 6 months if not refrigerated.
Secondly, as soon as you open your food make sure you do not leave it
close to the tank or in other warm, humid areas. Keep the container
tightly sealed and in the frige. Some hobbyists soak their foods in
vitamin supplements before feeding. This is a good idea only if the
vitamins are fresh of course. Baby vitamins have been used with some
success and have the added benefit of having expiry dates on the jars.
Of course the best foods are those that are as fresh as possible such
as raw shrimp, clams, mussels and marine fish. For large predators
such as groupers and lionfish, it is extremely important to avoid
feeding them freshwater fish as a staple food. Try and wean them from
these foods and onto prepared marine foods or fresh shrimp etc. The
reason for this is that freshwater fish lack certain essential fatty
acids that are mandatory for marine fish. A lionfish may live for
years on a diet of goldfish then one day it will inexplicably die.
When these fish are examined they are usually found to have fatty
livers caused by the abundance of improper fatty acids in their diet.

Most omnivorous invertebrates can be fed on prepared foods
supplemented with pieces of shrimp, mussels or clams. Organisms that
fall into this category include Brittle Stars, Fromia sp. starfish,
sea urchins, shrimps and crabs. Some of these will supplement their
diet with the algae found in the system.

Herbivores, in some systems, can get enough to eat from the various
micro- and macroalgae in the aquarium. In some cases though, such as
with tangs, surgeons and sea urchins, they will quickly strip the tank
of algae and will require additional feedings. These animals can be
fed a variety of fresh greens such as green peas, spinach, romaine
lettuce, bok choy and various marine algae that can be found in
oriental food markets. I have found that blanching the greens for 30
seconds or so helps to soften them and fish that would not touch them
before will devour the same greens when blanched. Additional feedings
of vitamin enriched prepared foods are recommended too.

Organisms that feed on smaller particles such as detritus and its
associated components, as well as zooplankton, can either be fed or,
in some cases, ignored entirely. It has been my experience that many
forms of fanworm will exist quite well in aquariums, where the fish
are fed regularly, without any additional feedings. If you find that
the crowns of these fanworms decrease in size, then this may be a sign
that they are not getting enough to eat and supplemental feeding would
then be required. Liquid foods work well for the smaller species while
live baby brine shrimp will be accepted by the larger species i.e.
Sabellastarte magnifica. Other such feeders include Sea Cucumbers,
clams (other than Tridacna spp.), tunicates and crinoids. Given that
large amounts of detritus are produced in reef systems and that this
detritus is often found as a fine suspension in the water due to the
actions of burrowing worms in the rock, fish, bacterial action and
water movement, most filter feeders receive more than enough to eat
and do not need any additional feeding.

Zooxanthellae bearing corals (hermatypic), both hard and soft,
including mushroom anemones, zoanthids, anemones and gorgonians, can
utilize a wide variety of feeding techniques. Not only can they
utilize the photosynthetic products of their algal symbionts but they
can also feed directly on plankton, bacteria, detritus and fish feces.
Some corals have even been shown to be able to directly absorb glucose
from the water (Stephens, 1962). Other zooxanthellae bearing organisms
include some sponges and Tridacna spp. clams.

As mentioned above, most corals contain symbiotic algae in their
tissues which can supply some of their nutritive needs. I say some
because the degree to which zooxanthellae contribute to a coral's
nutrition has been the subject of much research over the past 40
years. It seems that the amount varies between species. In some
species of zoanthids over 90% of their nutrition can be met by the
zooxanthellae while in others this figure is much lower (60%) (Steen
and Muscatine, 1984). However, the general consensus is that
zooplankton do not contribute a major portion of the caloric or carbon
requirements of hermatypic corals (Muscatine and Porter, 1977).

The general rule seems to be the smaller the polyps, the more
important zooxanthellae are in the diet (Porter, 1976). Corals
feed in a variety of ways. The larger polyped forms (e.g. Euphyllia
spp.) can actually feed on shrimp-sized prey which they capture with
their tentacles. Other forms collect the slime that forms on the
polyps and swallow the microorganisms and detritus trapped in it
(Kuhlmann, 1985). Still others can directly absorb nutrients
(ammonium, nitrate and phosphate used by the zooxanthellae as well as
various amino acids) from the water (Franzisket, 1974; Muscatine and
Porter, 1977; D'Elia, 1978; Muscatine and D'Elia, 1978). The problem
comes when deciding when and how much to feed. In my own personal
opinion many coral species do not need direct feeding. Many get more
than enough from natural sources in the tank. Every time you feed your
fish, particles of food and nutrients are added to the water. The
presence of live rock and their associated algae and bacteria produce
copious amounts of nutrients, vitamins and other products. Even in the
presence of a highly efficient skimmer, Wilkens (1987) found that the
levels of amino acids in the aquarium were many times higher than on
the reef. It would be safe to assume that many other "nutrients" are
just as abundant, despite our best efforts.

Those polyps that are large enough to be fed small pieces of shrimp
can be fed once a week or so by directly placing pieces of food on
some of the polyps. Zooxanthellae require phosphate and although they
may be able to absorb this from the water it is generally felt that
the main source is from the prey captured by the polyps. However, some
soft corals (e.g. Xenia) have never been observed feeding. Lacking
stinging cells in their tentacles, Xenia may absorb phosphate and
other nutrients directly from the water. Judging from the large number
of successful aquariums that I have seen in which the corals are never
directly fed, indicates to me that most zooxanthellae bearing corals
do not require direct feeding to survive, grow and multiply.

If you do decide to try and feed your corals be very careful about
overfeeding i.e. feed SPARINGLY. An occasional feeding of live baby
brine shrimp or one of the better liquid foods, may be appropriate for
some specimens but not others. Pay careful attention when feeding, if
it looks like the coral is not ingesting any food then perhaps it does
not require additional feeding.

For example, some species of mushroom anemones will feed if food is
placed on their discs but others are never observed to feed. A general
rule with mushroom anemones is that if they have large bumps or
tentacle-shaped protrusions, you should try and feed them. Smooth
surfaced forms, however, generally obtain enough nutrition from their
zooxanthellae. However, Elliott and Cook (1989) showed that the
Caribbean corallimorpharian Discosoma sanctithomae relied both on
their zooxanthellae and on nocturnal morphological changes to capture
prey. Even in those species that have short tentacles, the tentacles
are non-retractile, non-motile, practically devoid of musculature and
lack significant numbers of nematocysts (Den Hartog 1980). Those
mushroom anemones (e.g. Elephant Ear Mushrooms, Rhodactis howesii
sp.) that do feed, do so primarily by envelopment where the prey is
trapped in the disc cavity and digested by mysenterial filaments
extruded through the mouth.

When one is dealing with corals that do not contain zooxanthellae
(ahermatypic) then feeding takes on extreme importance. Examples of such
organisms include certain gorgonian species, Dendronepthya sp. soft
corals and Orange Cup Coral (Tubastrea aurea). In these cases live
or prepared foods should be used. Live foods such as baby brine shrimp
and rotifers are excellent for most gorgonians and Dendronepthya sp.
while Tubastrea should be fed larger items such as live adult brine
shrimp or small pieces of shrimp, scallop or fish. Prepared foods
can be used as well. Dried or freeze-dried foods can be finely ground
and soaked in a vitamin preparation. This sludge is then fed directly
to the coral through a pipette or baster. You should not feed such
food by simply placing it into the water. This only results in added
pollution as most of it ends up in the filter, in the gravel or under
rocks.

The final method of feeding in reef tanks is through the direct uptake
of organic compounds through the body walls of various marine worms,
ascidians (i.e. Tunicates), bryozoans, etc. (Sepers, 1977). The
mechanisms, importance and role of such feeding in marine ecosystems
is not well understood and certainly bears more extensive research.
Whether or not such feeding is an important component of our aquariums
is certainly an unknown area but I feel that the majority of the
nutrient needs of these organisms can be met by other means.
Certainly, the addition of extra amounts of nutrients would be both
unfounded and unnecessary given the lack of knowledge in this area. It
would first have to ascertained exactly what substances were required
by each organism and if these were depleted in an aquarium before any
consideration could be given to additions.

As I mentioned at the beginning of this article the topic of nutrition
in aquariums is poorly understood at best. This is an area where the
experiences of hobbyists can be of utmost importance to scientific
researchers. There are a lot more hobbyists out there than there are
people actively researching this area. It would be a shame if this
tremendous pool of information and experience went unused. Share your
information with others, write articles for club or national
magazines, keep detailed notes on each of your specimens, spread your
knowledge and experience, we will be all better off in the long run.
The more we can demonstrate the value of our hobby, the less likely
that it will be shut down.


References



Blank, R. and R.K. Trench 1985. Speciation in symbiotic
dinoflagellates. Science 229:656-658.

D'Elia, C.F. 1977. The uptake and release of dissolved phosphorus by
reef corals. Limnol. Oceanogr. 22:301-315.

Den Hartog, J.C. 1980. Caribbean shallow water corallimorpharia. Zool.
Verhand. 176:1-83.

Elliott, J. and C.B. Cook 1989. Diel variation in prey capture
behaviour by the Corallimorpharian Discosoma sanctithomae:
Mechanical and chemical activation of feeding. Biol. Bull. 176:218-
228.

Franzisket, L. 1974. Nitrate uptake by reef corals. Int. Rev. Gesamten
Hydrobiol. 59:1-7.

Kuhlmann, D. 1985. Living Coral Reefs of the World. Arco Publ.

Muscatine, L. and C.F. D'Elia 1978. The uptake, retention, and release
of ammonium by reef corals. Limnol. Oceanogr. 23:725-734.

Muscatine, L. and J.W. Porter 1977. Reef Corals: Mutualistic symbioses
adapted to nutrient-poor environments. BioScience 27:454-460.

Sepers, A.B.J. 1977. The utilization of dissolved organic compounds in
aquatic environments. Hydrobiologia 52:39-54.

Steen, R.G. and L. Muscatine 1984. Daily budgets of photosynthetically
fixed carbon in symbiotic zoanthids. Biol. Bull. 167:477-487.

Stephens, G.C. 1962. Uptake of organic material by aquatic
invertebrates. I. Uptake of glucose by the solitary coral Fungia
scutaria. Biol. Bull. 123:648-657.

Trench, R.K. 1979. The cell biology of plant-animal symbiosis. Annu.
Rev. Plant Physiol. 30:485-532.

Wilkens, P. 1987. Niedere Tiere: Steinkorallen, Scheiben- und
Krustenanemonen. Engelbert Pfriem Verlag, Wuppertal, Germany.

Wotton, R.S. 1988. Dissolved organic material and trophic dynamics:
What is the food of filtering collectors in aquatic ecosystems?
BioScience 38: 172-178.


The following references contain information on feeding marine
invertebrates:

Colin, P.L. 1978. Caribbean Reef Invertebrates and Plants. TFH
Publ., Inc., Neptune City, NJ.

de Graaf, F. 1973. The Marine Aquarium Reference. The Pet Library,
LTD., Harrison, NJ.

Freshwater and Marine Aquarium Magazine. R.C. Modeller Corp., Sierra
Madre, CA.

Haywood, M. and S. Wells 1989. The Manual of Marine Invertebates.
Tetra Press.

Kaplan, E.G. 1982. A Field Guide to Coral Reefs, Caribbean and
Florida. Houghton Mifflin Co., Boston, MA.

Marine Fish Monthly. Publ. Concepts Corp., Luttrell, TN.

Marine Reef Newsletter, Aardvark Press, Bridgeport, CT.

Moe, M.A. Jr. 1989. The Marine Aquarium Reference: Systems and
Invertebrates. Green Turtle Publ., Plantation, FL.

Teh, Y.F. 1974. Keeping live corals. Marine Aquarist 5(1):19-24.

Wilkens, P. 1973. The Saltwater Aquarium for Tropical Marine
Invertebates. 2nd. Extended Ed., Engelbert Pfriem, Wuppertal-
Elberfeld, Germany.

Wilkens, P. 1976a. Mini-Reef. Marine Aquarist 7(5):37-42.

Wilkens, P. 1976b. Flower animals. Marine Aquarist 7(9):32-43.

Wilkens, P. 1976c. More flower animals. Marine Aquarist 7(10):31-44.

Wilkens, P. and J. Birkholz 1986. Niedere Tiere: Rohren-, Leder- und
Hornkorallen. Engelbert Pfriem Verlag, Wuppertal, Germany.

Wilkens, P. 1987. Niedere Tiere: Steinkorallen, Scheiben- und
Krustenanemonen. Engelbert Pfriem Verlag, Wuppertal, Germany.