whereas juveniles more typically have three. Recent studies also show a possible trend of "dual niche partitioning", in which scavengers tend to reach peak densities on the carcass during the day and predators are more present during the night, reducing competition between the two trophic groups. There is also a possible trend in tidal patterns and species occurrence, indicating that tides play a role in niche partitioning as well. Similar ecosystems exist when other large volumes of nutrient-rich material fall to the sea floor. Sunken beds of kelp create kelp falls, and large trees can sink to create wood falls. In more recent years, shipwrecks have also provided bases for deepwater communities. In ecosystems formed following a whale fall event, there are four stages of ecological succession. Ecosystem stages There are four stages of decomposition associated with a whale fall. These stages vary in duration and overlap with one other with the size of the carcass, water depth, and other environmental variables, such as tidal flow. Large, intact whale falls appear to pass through the four decomposition stages, while the stages on smaller or partial carcasses may be truncated. Smaller cetaceans, such as porpoises and dolphins, do not undergo the same ecological succession stages due to their small size and lower lipid content. Researchers believe the presence of Osedax worms may also be a contributing factor in the observed successional differences. Stage 1 The initial period begins with "mobile scavengers" such as hagfish and sleeper sharks actively consuming soft tissue from the carcass. Consumption can be at a rate of per day. This stage typically lasts months up to 1.5 years. Stage 2 The second stage introduces the "enrichment opportunists". These are animals which colonize the bones and surrounding sediments that have been contaminated with organic matter from the carcass and any other tissue left by the scavengers. This stage can last months up to 4.5 years. Stage 3 In the third stage, sulfophilic bacteria anaerobically break down the lipids embedded in the bones. Instead of oxygen, they reduce dissolved sulfate () and excrete hydrogen sulfide. Due to the toxicity of , only resistant chemosynthetic bacteria survive. The bacterial mats provide nourishment for mussels, clams, limpets and sea snails. As whale bones are rich in lipids, representing 4–6% of its body weight, the final digestion stage can last between 50 and possibly 100 years. Stage 4 Some scientists postulate a