Role of Different Microbes and Substrates as Potential Suppliers of Specific, Essential Nutrients to Marine Detritivores

All animals must obtain (in addition to sources of energy and protein) certain specific essential nutrients in order to survive, grow, and reproduce. Most research concerning the nutrition of marine detritus feeders has focussed on caloric and protein needs, but requirements for certain specific nutrients, including essential fatty acids, sterols and essential amino acids, have been defined in recent aquaculture research. This paper raises the question of how marine detritus feeders are likely to obtain these required nutrients in their food. I argue that the distribution of required specific nutrients in different components of the detrital “trophic complex” is predictable, and that procurement of these nutrients could influence feeding strategy. Bacteria, for example, lack long-chain linolenic (ω3) series polyunsaturated fatty acids (PUFA) that are essential in the diet of most marine metazoans; they also lack sterols, which are essential for some invertebrates, including all crustaceans and some bivalves. Diatoms, in contrast, characteristically exhibit high proportions of PUFA, especially 20:5ω3, which should make them an excellent source of dietary essential fatty acids. Eukaryotic cells contain sterols, many of which can probably be converted to cholesterol (or other characteristic forms) by marine invertebrates. Bacteria may be important as suppliers of other specific essential nutrients, such as B-complex vitamins, and consumption of a mixed diet including different microbes and substrates could help to remedy nutritional deficiencies of specific detrital components (e.g., by protein complementarity). Studies of the nutritional value of detritus and factors affecting trophic transfer in detritus food webs should explicitly consider the importance of animal requirements for specific, essential nutrients as well as energy and protein.