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date: 21 July 2017

Sentinel Species of Marine Ecosystems

This is an advance summary of a forthcoming article in the Oxford Research Encyclopedia of Environmental Science. Please check back later for the full article.

In the past, the use of large marine vertebrates in marine ecosystem monitoring and assessment has been criticized. The fact that these species are pelagic and highly mobile has led some to suggest that they are not useful indicator species. However, in recent years a contrary view has emerged suggesting that when we gain sufficient understanding of differences in species distribution and behavior, at different times of the year, they can be extremely valuable sentinels of environmental quality. Among large vertebrates, top predators play a crucial role in maintaining the structure and function of pelagic marine ecosystems. Among top predator species, 90% have been lost from the world’s oceans. Pelagic ecosystems may undergo collapse when large marine vertebrates are lost. It is crucial to know the status of large vertebrate populations and to establish mitigation measures for their conservation. For example, it is well known that the various cetacean species exhibit different home ranges and occupy different habitats. This knowledge can be exploited in hot-spot areas, such as the Mediterranean basin, where different species could serve as sentinels of marine environmental quality at different times during the annual cycle. In this contest, the bottlenose dolphin, a coastal species, could be an indicator of various anthropogenic pressures on the coastal environment. Similarly, the striped dolphin, the most abundant odontocete in the Mediterranean region, is distributed in deeper offshore waters and could be a sentinel of the pelagic environment. Finally, due to its broad-ranging seasonal movements across the whole basin, the fin whale could represent an integrated indicator of the whole Mediterranean area.

In this case, it seems that there is usually a particular large marine vertebrate species that provides the best opportunity for detecting and monitoring specific types of pollutants in particular marine areas at different times of the year. For example, swordfish and tuna are valuable for monitoring mercury concentrations and organochlorines, while turtles are especially useful for monitoring the occurrence of plastics, and mysticete cetaceans for looking at microplastics. It also emerged that large pelagic fish may be especially useful for monitoring short- to medium-term changes in pelagic ecosystems, while marine mammals such as whales provided a more integrated view over the long-term.