ABSTRACT
The absence of any obvious cellular or morphological structures in EAM detritus suggests that non-cellular organic matter is a key component of the detritus and that aggregation of dissolved organic matter (DOM) may be an important process in the formation of EAM detritus (Wilson & Bellwood 1997, Wilson 2000). Both living and dead organisms are potential sources of dissolved nutrients on coral reefs and measures of dissolved nutrients in reef waters suggest that natural levels are much higher than has previously been assumed (Szmant 1997). The DOM from these sources may be exported from the reef, or converted to particulate organic matter (POM) via biotic and abiotic processes. Biotically, bacteria use DOM and are an important component of the microbial loop (Azam et al. 1983). Bacterial productivity, however, cannot account for all the DOM produced on coral reefs (Ducklow 1990). Furthermore, the microbial loop is energetically inefficient, because energy must pass through many levels before it is consumed by apex predators (Mann 1988). The microbial loop alone is therefore unable to sustain a high abundance of detritivorous fishes. Abiotically, organic particulates can form from DOM when they are adsorbed on surfaces, such as carbonates (Otsuki & Wetzel 1973), which may be especially important on coral reefs. Bubbling through nutrient rich water will also produce organic particulates (e.g. Alber & Valiela 1994), as can laminar shearing of water (Passow 2000) and it is possible that DOM can spontaneously form particulates in the form of polymer gels (Chin et al. 1998).
