Organisms that live in the deep must be adapted to extreme conditions. There is no light, high pressure and low food availability which creates an ecosystem where opportunistic scavenging and foraging is prevalent (Iken et al., 2001). The deep ocean is a food limited environment and it is a well-known concept that many deep sea ecosystems rely upon energy in the form of organic material known as marine snow. The continuous flurry of organic material is able to sustain a somewhat limited array of marine life. The eight largest species of cetacean range in size from 30t to 160t (Lockyer, 1976). Consequently, when a whale dies and sinks to the Abyssal zone it provides a vast but localised input of energy. For example, the carbon input from a single 40t whale (~2×106gC) sinking to the sea bed is the equivalent of the organic carbon from marine snow over a hectare of the abyssal sea floor for 100-200 years (Smith and Demopoulos, 2003). It is suggested that the mean annual whale fall biomass flux to the sea floor is ~3.8×10-4g Corgy-1 (Krogh, 1934a) as a result of the annual death of approximately 69 000 great whales (>5t) per year (Lockyer, 1976; Smith and Baco, 2003). Also, if whale falls were evenly distributed across the sea floor, there would be one per 300km2 (Smith et al., 1989).
The first hint of an intricate whale fall ecosystem arised in 1854 when a floating piece of blubber was discovered off the Cape of Good Hope which harboured a new mussel species- Adipicola pelagica (Dell, 1987). In 1956, it was concluded that whale falls must support scavengers for reasonably long periods from ear bone analysis which were often retrieved by deep sea trawling (Bruun, 1956). In 1977 the first natural whale fall carcass of a grey whale was accidently discovered using the Bathyscaphe Trieste II submersible in the Santa Catalina Basin. More recently, whale falls have been accidently stumbled upon or seeked using side-scan sonar and multibeam bathymetry. Once a whale shaped anomaly shows up in the sea bed scans, submersibles such as ALVIN are used to take a closer look (Smith et al., 1989). It is uncommon for scientists to locate a whale fall event, however, this doesn’t mean that whale falls are necessarily a rare occurrence as much of the sea bed is yet to be discovered. Scientists have also actively sunk whales which were found stranded for research purposes (Fujiwara et al., 2006; Glover et al., 2010).
Whale falls create intricate ecosystems which are heavily dependent on the successional stages of decomposition. They are extremely diverse with records indicating a macrofaunal community of up to 12 490 individuals from 43 different species (Bennett et al., 1994), however, the species present change with the progression of decomposition. There are organisms present at whale falls and other vertebrate carcasses that haven’t been documented in any other ecosystem such as the bone-eating worms Osedax spp., which, despite the ephemeral conditions of a whale fall, are remarkably diverse with a wide geographical range (Rouse et al., 2004). The organisms present at an abyssal whale fall event can range from large vertebrates such as the sleeper shark (Somniosus pacificus) to bacterial mats. Whale falls that occur in shallower shelf sea areas are characterised predominantly by smaller vertebrates and crustaceans (Glover et al., 2010). The commercial whaling in the 1960s and 1970s caused major decrease in the flux of whale detritus matter to the sea floor. It has been suggested that this caused a 40% reduction in species richness in relation to preexploitation levels (Whitehead 2002).
As my blog progresses and I collate more information, I hope to take you on the journey of a dead whale, through successional stages of decomposition and looking at other aspects of their importance such as, acting as a “stepping stones” between chemosynthetic ecosystems and whale fall specialist species. I will eventually conclude whether there is any real benefit to a whale fall, how long these benefits might last and whether they are actually vital for the preservation of species in the deep ocean.
The first step of the journey is with the initial whale death and “sinking process”.