New research tracks fate of detritus on coral reefs
Aug 8, 2013 –Palmyra Atoll, a ring-shaped coral reef (shown right) located approximately half way between Hawaii and American Samoa, is virtually uninhabited except for temporary populations of staff and scientists. Having largely been spared the affects of human disturbance, it is an optimal location for studying how coral reefs, and the fish communities they support, function. One key factor of food web function that is often overlooked is the role of benthic detritus in coral reef food webs. You know, benthic detritus, the ocean floor mélange of fish droppings, deceased organisms, and mucus produced by corals or other invertebrates. Whether you perceive detritus to be offensive or not, it plays a significant role in cycling energy and nutrients through a complex food web, linking pelagic (open ocean) and reef ecosystems.
Detritus is an important food source for reef fishes, but how important has been mostly unknown to date. And we know little about how the amount of detritus varies from one reef habitat to the next…until now. Steve Gaines and Robert Warner of CMAP, along with scientists from Moss Landing Marine Laboratories, found significant differences between the compositions and amount of detritus that is produced and remains in exposed forereef and protected backreef habitats of Palmyra Atoll, with the latter experiencing a higher amount of standing stock detritus than the former.
The differences were a result of a variety of factors. For example, the study found that Palmyra’s backreefs supported a higher mass of detrivorous fish than the forereef because the backreef was protected from the physical disruption of waves. An intriguing finding is that Palmyra’s detrital resources do not occur in large enough quantities to meet the nutritional requirements of the detritivorous fish, begging the question: “what else are they eating?” It may be bits of algae, small invertebrates, or seaweed but the uncertainty warrants further study.
So the coral reefs of Palmyra are a bit like a fish city in which the garbage men (detritivores) routinely pick up the trash (detritus) of the residents (reef fish) as well as the visiting tourists (pelagic fish). Many mysteries remain, though. It is crucial to understand the mechanics of coral reef detritus in order to understand the ocean as a whole.