A fascinating and rare discovery off the western coast of southern Africa has captivated ocean scientists and researchers. A team exploring potential oil and gas deposits beneath the seafloor has stumbled upon four large “fish-falls”—the carcasses of a whale shark and three mobulid rays. This discovery, reported by Nicholas Higgs, Andrew Gates, and Daniel Jones in a paper published in PLoS ONE, is significant because finding vertebrate carcasses on the deep ocean floor is incredibly rare. This so-called “graveyard” offers a unique and valuable opportunity to gain insights into the impact that the death of large marine creatures has on marine ecosystems, particularly in terms of the nutrients and food it provides to various smaller marine species.
Historically, only nine vertebrate carcasses have been discovered and studied on the ocean floor, with this recent finding raising the total to just thirteen. These carcasses are classified according to “fall” type, with fish falls, such as those found in this instance, being less common and less discussed compared to the more well-known and studied “whale falls.” Whale falls, where the carcasses of massive whales provide sustenance to deep-sea organisms for extended periods, have garnered significant scientific attention in the past, but fish falls, like the one discovered off Africa, are much rarer.
The research team noted that, along with the carcasses, they observed various scavengers that had arrived to feast on the remains. A key observation in their findings is that sharks are usually the first to appear at the scene of a carcass, though they typically do not feed on the remains themselves. Instead, crabs, amphipods, and other smaller scavengers soon arrive, beginning to consume the flesh and other parts of the carcasses. Over time, organisms such as Osedax worms, which are known to feed on bones, eventually make their appearance. In this particular case, however, the researchers noted that no Osedax were present, which led them to conclude that the carcasses had likely been on the seafloor for a relatively short time—possibly only a month or two.
While the discovery of these carcasses is intriguing, it raises more questions than it answers. The rarity of such findings has led scientists to conduct controlled experiments in the past, such as deliberately dropping dead animals into the ocean to observe the processes that unfold. This has provided valuable data, but finding four natural, undisturbed carcasses in one location is an unprecedented event. The research team was left wondering why so many large creatures appeared to have died at roughly the same time. One possibility the scientists suggest is that while the finding itself is rare, there may be many such “graveyards” on the ocean floor that have simply not been discovered yet. The ocean floor is vast, and the chances of encountering a specific “fall” while studying a given area are slim. It is also conceivable that the graveyard the researchers found is not an isolated case, as sharks, rays, and whales are abundant in the oceans, and they all eventually die.
The study of such carcasses has broader implications for marine food webs. Scientists estimate that about 4 percent of the food consumed in the ocean comes from the remains of fallen animals, including fish, rays, and whales. This is a significant amount, particularly when compared to the vast amount of marine snow—tiny particles of organic matter that fall from the surface and provide food to deep-sea organisms. The discovery of these four fish-falls highlights the important role that large vertebrate carcasses play in providing nutrients to deep-sea creatures, many of which rely on this sudden influx of food to survive in the nutrient-poor environment of the deep ocean.
In this particular instance, the researchers observed large numbers of fish surrounding the carcasses, the majority of which were eel pouts. Interestingly, eel pouts do not feed directly on the carcasses themselves but instead prey on other fish that feed on the remains. This adds a layer of complexity to our understanding of how carcasses on the ocean floor can influence local ecosystems, as the “fall” provides a complex food chain that supports multiple levels of scavengers.
The presence of scavengers around the carcasses provides crucial data on the dynamics of marine life in the deep ocean, particularly the ways in which different species interact with one another. The study of these interactions can offer valuable insights into how nutrient cycling works in the deep ocean and how various species have adapted to survive in one of the most extreme environments on Earth.
Despite the rarity of such discoveries, the researchers suggest that it is likely that more fish-falls exist, just waiting to be discovered. The ocean floor, after all, is a vast and largely unexplored frontier. The scientists who made this discovery speculate that other similar “graveyards” are likely scattered across the world’s oceans, and this find could be the first of many more to come. They acknowledge that, given the size of the oceans and the relatively small area studied by researchers, it is entirely possible that the ocean floor is full of these natural “feeding grounds” that provide sustenance to deep-sea creatures.
The findings of this research also raise the importance of continuing to study the deep-sea environment, particularly as the oceans are increasingly impacted by human activities such as oil exploration, fishing, and climate change. The delicate balance of life on the ocean floor could be disrupted by these activities, and understanding the role of carcasses in maintaining the health of marine ecosystems is more important than ever. Researchers believe that these discoveries offer new opportunities to study not only the biology of deep-sea creatures but also the long-term ecological processes that govern life in these dark, cold depths.
More information: Higgs ND, Gates AR, Jones DOB (2014) Fish Food in the Deep Sea: Revisiting the Role of Large Food-Falls. PLoS ONE 9(5): e96016. DOI: 10.1371/journal.pone.0096016