|Marine carrion and scavengers|
Britton, J.C.; Morton, B. (1994). Marine carrion and scavengers. Oceanogr. Mar. Biol. Ann. Rev. 32: 369-434
In: Oceanography and Marine Biology: An Annual Review. Aberdeen University Press/Allen & Unwin: London. ISSN 0078-3218, more
|Authors|| || Top |
New definitions of marine carrion and scavengers are provided, the incidence of scavenging as a feeding strategy among marine animals is discussed and important sources of marine carrion are considered. Most major phyla have scavenging members, many of which feed opportunistically. Carrion is a spatially and temporally infrequent food resource in the sea. In the absence of human interference, we suggest that few marine animals die as a consequence of natural senescence, thereby becoming consistently available as carrion for scavengers. Instead, most death results from predation, so that only scraps are available, ephemerally, to scavengers. Even when a carrion windfall follows a natural mass mortality, e.g. as the result of either a pandemic disease or environmental excesses, i.e. temperature or natural toxins produced during red tides, the resulting available biomass is still an unpredictable addition to the nutrient mosaic of the sea. Carrion, as an infrequent food source has, thus, favoured the evolution of facultative rather than obligate marine scavengers. Notwithstanding, lysianassid amphipods and nassariid gastropods most closely approximate our concept of a marine scavenger. Many species in both groups readily detect, move purposely towards and consume carrion. They also have feeding structures and a digestive system capable of rapid processing and digestion of large amounts of such food. A single meal sustains individuals for long periods. Such scavengers are likely derived from otherwise predatory lineages. Human interference in marine ecosystems probably has contributed to an overestimation of the importance of marine scavengers as a definable feeding guild. Lysianassid amphipods thus feed on and benefit from fish constrained by fishing nets and nassariid populations increase on polluted, carrion-littered, beaches. Many human activities, e.g. discarded trawler bycatches, channel dredging and oceanic gill netting, influence our perception of the importance of marine scavengers. It is possible, for example, that fluxes in sea bird numbers, especially of gulls, may be related to changing ways in which commercial fisheries dispose of discards and the degree to which landfills are either open or sanitized. Human-engendered carrion in the sea is now a significant source of food for a large variety of opportunistic scavengers and has promoted new fisheries, e.g. those for buccinid whelks and portunid crabs. Pollution promotes greater levels of available carrion both directly and indirectly. Lethal and sub-lethal effects of pollutants kill or weaken organisms, thereby making them susceptible to predators and/or scavengers. Indirectly, eutrophication fosters excessive plankton enrichment, e.g. red tides, which, in turn, can lead to marine mass mortalities; alternately, human-induced diseases bring about episodic deaths of large marine mammals. The present success of marine scavengers can be attributed to human interference in the sea.