User:TimParsons2/sandbox

Diet[edit]
High energetic requirements of sea otter metabolism require them to consume at least 20% of their body weight a day. Surface swimming and foraging are major factors in their high energy expenditure due to drag on the surface of the water when swimming and the thermal heat loss from the body during deep dives when foraging. Sea otter muscles are specially adapted to generate heat without physical activity.

Sea otters consume over 100 prey species. In most of its range, the sea otter's diet consists almost exclusively of marine benthic invertebrates, including sea urchins, fat innkeeper worms, a variety of bivalves such as clams and mussels, abalone, other mollusks, crustaceans, and snails. Its prey ranges in size from tiny limpets and crabs to giant octopuses. Where prey such as sea urchins, clams, and abalone are present in a range of sizes, sea otters tend to select larger items over smaller ones of similar type. In California, they have been noted to ignore Pismo clams smaller than 3 inches (7 cm) across.

In a few northern areas, fish are also eaten. In studies performed at Amchitka Island in the 1960s, where the sea otter population was at carrying capacity, 50% of food found in sea otter stomachs was fish. The fish species were usually bottom-dwelling and sedentary or sluggish forms, such as Hemilepidotus hemilepidotus and family Tetraodontidae. However, south of Alaska on the North American coast, fish are a negligible or extremely minor part of the sea otter's diet. Contrary to popular depictions, sea otters rarely eat starfish, and any kelp that is consumed apparently passes through the sea otter's system undigested.

The individuals within a particular area often differ in their foraging methods and prey types, and tend to follow the same patterns as their mothers. The diet of local populations also changes over time, as sea otters can significantly deplete populations of highly preferred prey such as large sea urchins, and prey availability is also affected by other factors such as fishing by humans. Sea otters can thoroughly remove abalone from an area except for specimens in deep rock crevices, however, they never completely wipe out a prey species from an area. A 2007 Californian study demonstrated, in areas where food was relatively scarce, a wider variety of prey was consumed. Surprisingly, though, the diets of individuals were more specialized in these areas than in areas where food was plentiful.

It has been observed, however, some otters may prey on seabirds resting on the surface of the ocean. This behaviour of active hunting and the targeting of animals within higher trophic levels varies largely with the usual collection of sedentary benthic food sources. These incidences appear to include select individuals and do not express the behaviour of the general otter species as a whole. This is fitting with the idea that sea otter individuals have preferences and unique variations within their own diets.This behaviour is one that opposes many natural instincts of otters which tend to rely on touch and smells to hunt their slow moving and largely sessile prey apart of lower trophic levels. The hunting of sea birds instead uses mainly visual cues and fast responses to capture large and strong birds floating on the surface of the water. This implies the strong adaptive ability that is shown by the otter species. This type of behaviour expresses the impacts that individual otters can have within the trophic cascade of their isolated habitats. Each area will possess variations within the relationships of organisms as well as between trophic levels and be specific to the feeding habits and behaviours of the otters inhabiting the space.

As a keystone species[edit]
Sea otters control herbivore populations, ensuring sufficient coverage of kelp in kelp forests Sea otters are a classic example of a keystone species; their presence affects the ecosystem more profoundly than their size and numbers would suggest. They keep the population of certain benthic (sea floor) herbivores, particularly sea urchins, in check. Sea urchins graze on the lower stems of kelp, causing the kelp to drift away and die. Loss of the habitat and nutrients provided by kelp forests leads to profound cascade effects on the marine ecosystem. North Pacific areas that do not have sea otters often turn into urchin barrens, with abundant sea urchins and no kelp forest. Kelp forests are extremely productive ecosystems. Kelp forests sequester (absorb and capture) CO2 from the atmosphere through photosynthesis. Sea otters also affect the growth and respiration of seagrass. The otters feed on species of crab that feed on seagrass and compete with other marine invertebrates, reducing competition for marine slugs and snails. These gastropods prefer to feed on the algae that grow on seagrass instead of the seagrass itself, allowing the seagrass to more efficiently capture sunlight and carbon dioxide. The feeding activity of sea otters and marine gastropods allows some seagrasses to extend their range into eutrophic environments. Sea otters also benefit the genetic diversity of eelgrass. As the otters dig for clams, they disturb and uproot existing eelgrass and leave sandy pits in their wake. These conditions favour sexual reproduction of eelgrass over asexual reproduction, which enhances the genetic diversity of the eelgrass. In areas where otters have been present for 20 years, the genetic diversity of eelgrass is up to 30% greater than areas without otters and areas where otters have been present for only 10 years. This increase in genetic diversity may help eelgrass adapt to changing environmental conditions, such as increased temperature and acidity. All of these species are effective in storing carbon. In 2012, a team of ecologists found that a 51,000 square kilometer area of kelp forest where sea otters are present is capable of capturing up to 8 million tonnes more carbon than a similar sized area lacking sea otters. Sea otters may help mitigate effects of climate change by their cascading trophic influence.

Reintroduction of sea otters to British Columbia has led to a dramatic improvement in the health of coastal ecosystems, and similar changes have been observed as sea otter populations recovered in the Aleutian and Commander Islands and the Big Sur coast of California However, some kelp forest ecosystems in California have also thrived without sea otters, with sea urchin populations apparently controlled by other factors. The role of sea otters in maintaining kelp forests has been observed to be more important in areas of open coast than in more protected bays and estuaries.

Sea otters affect rocky ecosystems that are dominated by mussel beds by removing mussels from rocks. This allows space for competing species and increases species diversity.

Sea otters and their highly targeted prey, sea urchins, have a dynamic relationship within the ecosystem. Kelp barren patches within a habitat encourage urchins to take an active foraging and feeding strategy. This opposes urchins within healthy kelp forest which instead feed passively through grazing. Passively feeding urchins possess “higher energy profitability” (Smith 2021) and are therefore the target of sea otters. These predators do not commonly hunt from urchin barrens for this reason. It is this behaviour that maintains the health of kelp forest while also indirectly allowing recovery of urchin barrens. Kelp forests are the main source of spores which can migrate to barrens and begin a regrowth of the area. The sea otters' maintenance of matured and healthy forested areas allows for the potential of regrowth in barrens even without the active hunting of urchins.