Additionally, chance photographs of intact mammal carcasses and skeletons on the deep-sea floor were also reported –, prompting discussion of the role that food-falls play in deep-sea food chains.
Early investigation of this phenomenon looked at the utilisation of wood and other plant remains in the deep-sea –, while baited camera traps revealed a host of scavengers that consumed animal carcasses. While most detritus reaches the seafloor as millimetre sized particles of marine snow, the remains of large plants, algae and animals arrive as bulk parcels that create areas of intense organic enrichment. Temporal fluctuations in the quantity and quality of POC can have marked effects on the benthic community below, and some animals appear to be specially adapted to respond to these changes. Particulate organic carbon (POC) export to the deep-sea decreases exponentially with depth and is believed to play a key role in structuring deep-sea communities –. This is mainly composed of dead plankton and fecal pellets produced by zooplankton, which are exported to the deep seafloor as fine particles of ‘marine snow’. In the absence of sunlight, most animals in the deep ocean (below 200 m) are reliant on detritus from the surface waters as their primary source of food. We postulate that these food-falls are the result of a local concentration of large marine vertebrates, linked to the high surface primary productivity in the study area. Rapid flux of high-quality labile organic carbon in fish carcasses increases the transfer efficiency of the biological pump of carbon from the surface oceans to the deep sea. Using best estimates of carcass mass, we calculate that the carcasses reported here represent an average supply of carbon to the local seafloor of 0.4 mg m −2d −1, equivalent to ∼4% of the normal particulate organic carbon flux. No evidence of whale-fall type communities was observed on or around the carcasses, with the exception of putative sulphide-oxidising bacterial mats that outlined one of the mobulid carcasses. Based on a global dataset of scavenging rates, we estimate that the elasmobranch carcasses provided food for mobile scavengers over extended time periods from weeks to months. The carcasses supported moderate communities of scavenging fish (up to 50 individuals per carcass), mostly from the family Zoarcidae, which appeared to be resident on or around the remains.
These observations come from industrial remotely operated vehicle video surveys of the seafloor on the Angola continental margin. Here were report on the first observations of three large ‘fish-falls’ on the deep-sea floor: a whale shark ( Rhincodon typus) and three mobulid rays (genus Mobula). The carcasses of large pelagic vertebrates that sink to the seafloor represent a bounty of food to the deep-sea benthos, but natural food-falls have been rarely observed.
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