Abstract

The massive pelagic animal carcasses that descend to the ocean floor provide an abundance of food for the deep-sea benthos, although natural food-falls have only occasionally been seen. Here are reports about the first sightings of a whale shark and three mobula rays as enormous “fish-falls” on the deep sea floor. These findings are the result of commercial remotely controlled vehicle video studies of the seafloor along the continental margin of Angola. Up to 50 scavenger fish, predominantly from the family Zoarcidae, appeared to live on or around the carcasses, which supported moderate congregations of scavenger fish. We calculate that the elasmobranch carcasses served as food for travelling scavengers for extended periods of time, ranging from weeks to months, based on a global dataset of scavenging rates. With the exception of possible sulphide-oxidizing bacterial mats that surrounded one of the mobulid carcasses, no signs of whale-fall type communities were seen on or near the carcasses. We determine that the corpses described here constitute an average supply of carbon to the nearby seabed of 0.4 mg m2d1, which is equivalent to 4% of the typical particulate organic carbon flux, using the best estimations of carcass mass. The biological pump that moves carbon from the surface oceans to the deep sea operates more effectively when there is a rapid flux of high-quality labile organic carbon in fish carcasses. We hypothesise that the high surface primary productivity in the study area, coupled with a local concentration of large marine animals, is what causes these food-falls.