Hermed lidt interessant læsning jeg faldt over ifbm min søgen om Plankton/næring - omkring fodring af
SPS. Forfatter er Sanjay Joshi
Feeding a Coral Reef Aquarium
This the text of the article that appears in the Marine Fish and Reef Annual 2000 published by Fancy Publications.
In the past, the generally accepted practice advocated minimal feeding of reef aquariums. This was based primarily on the notion that reefs are very nutrient poor, reef inhabitants especially corals could generate all their energy requirements through photosynthesis and fish could survive by picking off of live rocks. Adding food would only increase the bio load of the tank, increase nutrients and dissolved organic matter. Feeding regimes were oriented towards feeding the top of the food chain - the fish, and the recommended practice was to feed sparingly once every 2-3 days.
The natural coral reef is an ecosystem with a complex food web, comprising
primary producers (phytoplankton, zooxanthelle, algae) that convert the solar energy, carbon dioxide and water into chemical energy stored as sugar, and
consumers which either eat the producers, or the by products of producers, or consumers lower in the food web
Food provides the energy necessary for vital functions to sustain life, for growth and reproduction. For an organism to thrive, the total energy demand must be met. Only a small portion (10-20%) of the food energy is converted into useful energy, with most being lost as waste and heat. Thus as we move up the food web, the amount of lower forms of food energy required to sustain the organisms higher in the food chain increases dramatically.
In a typical reef aquarium, the complete food web does not exist in quantities large enough to sustain the ecosystem without any additional energy input. We typically provide this in the form of food that we add to the aquarium. However, in the past we have focussed only on feeding the highest members of the food web - namely the fish, leaving the other inhabitants of the reef to derive their energy requirements through other channels in the food web. This model assumes that the rest of the organisms can either derive all their energy through other pathways in the food web, or their demise or reduction in numbers is inconsequential to the proper functioning of a reef aquarium. This model of reef keeping also makes it difficult to keep organisms with specialized feeding needs - sponges, filter feeders, etc.
Over the last year or so, there has been a significant shift in the feeding approach to reef aquariums. The trend now is to try to feed the complete range of life forms that inhabit the reef aquariums - fish, corals, filter feeders, microscopic life forms, etc. Contributing to this shift in paradigm are several factors:
a better understanding of the feeding and metabolic requirements
availability of "better" protein skimmers
availability of a wider range of foods that can meet the requirements of the range and variety of reef organisms
better understanding of the role of detrivores, micro fauna
The feeding and nutritional requirements of the organisms in a reef tank is varied and often very little is known about the specific nutritional needs of the organisms. As we strive for greater biodiversity in our reef aquariums, the role of feeding may play an important role. It is often difficult to duplicate the diet of the organisms in the wild, and substitutes have to be found. In fact, it is not even clear how much, how often, should corals and other organisms be fed.
This article will present some information on feeding habits of reef organisms (gathered from research articles), along with a discussion on some "new" products that have recently hit the aquarium hobby and may have the potential to increase the range of food available to the entire food web.
For the purpose of looking at the feeding requirements of the reef life forms, this article will divide them into several broad categories (based on type and size of food particles ingested), and look at how an aquarist can try to meet their feeding requirements. The broad categories are: Fish, Hermatypic corals (with zooxanthalle), Ahermatypic corals (without zooxanthelle), filter feeders and detrivores.
Corals
Corals can be classified into two types.
Hermatypic - those housing symbiotic zooxanthelle
Ahermatypic - those without symbiotic zooxanthelle
Hermatypic scleractinian corals (primarily
SPS corals) use two modes of feeding - Autotrophic and Hetrotrophic.
Zooxanthelle are unicellular algae that live within the coral polyp, and are the primary producers that produce food energy via photosynthesis. The autotrophic mode of feeding involves the translocation of the photosynthetic products produced by the symbiotic zooxanthallae to the coral polyp tissues. Research has shown that the total energy demand cannot be met by photosynthesis alone. The corals spend energy for the following functions: respiration, mucus production, growth and reproduction. Respiration accounts for 60-70% of the energy budget of the coral, and for most hermatypic corals the ratio of gross photosynthesis to respiration is slightly greater than one. Hence corals need to provide the additional energy needs via other means.
The other mode of feeding used by the corals is the hetrotrophic mode of feeding. Hermatypic corals posses the unique ability of making use of all hetrotrophic modes of feeding known in sedentary benthic animals. These modes of feeding are:
Predatory prey capture by the polyps (zooplankton capture)
Sedimentary filter feeding using mucus nets (bacterioplankton)
Consume DOM (dissolved organic matter) via active transport of molecules through cell membranes
To determine what corals feed on in the wild, researchers evaluate the gut content of corals in the wild and also experiment with the animals in laboratory. Evaluation of the gut contents of a Monastrea coral contained copepods, ostracods, mysids, menatodes, polychaetes and other zooplankton. Suspended organic material ingested by corals via sedimentary filtration included bacteria, protozoans, detritus, feces of fish, etc. Interestingly, research indicates that the scleractinian corals rejected algae and other plant material. Research indicated that even if plant material was ingested it was not digested and regurgitated. The size of prey captured by the polyps can be larger than the polyps, with the general rule being - the smaller the polyps the more important the role of autotrophic feeding. Some of the laboratory experiments were conducted using artemia nauplii as food. These are basically a form of zooplankton. The polyps easily captured nauplii of size 0.7-0.9mm. Corals with larger polyps (e.g
pocillopora,
stylophora) also captured Artemia nauplii up to 1.4mm. Research in predatory feeding has shown that, even in corals with polyps active in the daytime, polyps hunt more efficiently at night.
In ambient conditions on the reef (with wet bio mass of zooplankton ranging from 0.5-4 mg/L, bacteria 1.5-3 X 106 cells/mL, and DOM ranging from 0.5-2 mg of C/L ), as a rough average - scleractinian corals could compose their energy balance as follows: 60-70% via photosynthesis, 10-20% predation, and 10-20% by feeding on DOM and bacterioplankton (Sorokin 1995).
The hermatypic soft corals are basically similar in respect to the scleractinians, but there is a wider range on the degree to which autotrophic sources of nutrition are used. Most researchers are of the opinion that octocorals are in general weak predators compared to the scleractinians, and may ingest passively floating particles of detritus, forminifera, eggs of slow moving larvae of inverts, etc.
For the purpose of feeding we can further classify the hermatypic corals into small polyped and large polyped corals. The large polyped corals (eg. Euphillia species, cataphylia species, etc.) also typically have large mouths and can be fed small pieces of shrimp and other chunky food (silversides, chopped sea food - fish, shrimp, squid, scallops, etc). Anemones and mushroom anemones (e.g. Rhodactics species) can also be fed in a similar manner. Feeding the small polyped corals is a more challenging task, and one that is more open to debate.
For dem som er interesseret i at læse hele artiklen, er hermed link
http://www.personal.psu.edu/faculty/s/b ... eeding.htm" onclick="window.open(this.href);return false;
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