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Explainer: Marine predators as climate sentinels

How can marine predators act as climate sentinels? Watch Dr. Kylie Scales explain.
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In this section you will learn about how marine invertebrates such as seabirds and seals can be climate sentinels providing valuable information about climate impacts on the marine environment. Hi, I’m Dr. Kylie scales. I’m a specialist in marine ecology from the University of the Sunshine Coast Australia. The world is warming marine ecosystems are changing, we need to measure and monitor those changes if we are to find ways to mitigate and adapt to the impacts of climate change. There are various technologies that we can use to measure the physical properties of the ocean. For example, research vessels, Earth observation satellites, gliders, and Argo floats, which are a fleet of robotic instruments that float with ocean currents.
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These all directly measure properties such as temperature and salinity, and we have ocean models now to fill the gaps. However, this can’t tell us everything about how ecosystems are changing. We can also find ways to listen to what the animals that inhabit the ocean are telling us about how their habitats are changing. And this is the concept of marine predators as climate sentinels. You may be familiar with the concept of the canary in the coal mine. 19th century coal miners would take a caged Canary with them down the pit as an indicator of the presence of noxious gases. If the canary fell off the perch, it was time to get out of there.
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In this way, the canary was a living indicator of change that might otherwise be difficult to detect. And marine predators can act as our canaries for climate impacts on the marine environment. Marine predators make good climate sentinels because they’re high trophic level, which means they sit at the top of the food web. As climate change alters aspects of the biophysical environment like water temperature, and pH, the effects ripple up through food webs. Marine predators also range over ocean basin scales, and they can therefore amplify the signal of those disturbances to a signal that we can detect.
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It can be easier to observe air-breathing marine predators that breed in colonies on land, for example, then whole ocean populations of fish and squid. There are several ways in which marine predators can operate as climate sentinels. The first that we’ll discuss is changing distributions. Each species has particular requirements. For example, they might only be able to live in a certain temperature range, or they might need to eat specific prey that only exist in certain places. As the oceans warm and change, unusual conditions can open up new areas or close off regions that they used to inhabit.
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For example, in 2010, the summer melt of Arctic sea ice allowed bowhead whales from separate Atlantic and Pacific populations to mix and forage in the Northwest Passage, which has historically been a major barrier between different ocean populations. Another is changing populations themselves. We can measure population size by counting animals at breeding colonies, breeding success by counting surviving offspring, and individual health status by analysing tissue or blood samples, for instance. In recent years, there have also been a number of unusual mortality events that are strong indicators of changing ecosystems.
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For example, a marine heatwave off the US West Coast in 2015 to 16 that was known as The Blob was associated with 10s of 1000s - perhaps a million - dead seabirds, and over three and a half thousand California sea lions stranding on beaches. The hypothesis is that the blob of hot water on top of the northwest Pacific push the usual prey out of their reach, causing mass starvation and emaciation in these populations. Marine predators can also be climate sentinels by allowing us to monitor changes to their behaviour at sea.
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For example, we can use animal attached electronic tags to track their movements in three dimensions, a field known as biologging, and to monitor how behaviour changes with changing ocean conditions. And we can even use bio logging technologies to sample ocean conditions directly from the same tags using tagged animals like elephant seals as oceanographers themselves. There are many ways in which marine predators can act as climate sentinels. And if you’re interested to read more, please follow the link to the article in the course materials.

Want to read more about marine top predators as climate and ecosystem sentinels?

This paper discusses climate sentinels and ecosystem sentinels in more detail

In a nutshell:

Marine top predators are often conspicuous and wide ranging, and integrate information from the bottom to the top of the food web

Such predators could act as “sentinels” of an ecosystem’s response to climate variability and change

We define the terms “climate sentinel” and “ecosystem sentinel”, and describe the features of marine predators that would make them useful in these roles

Choosing one or more appropriate sentinels can provide insight into ecosystem processes and help to manage changing ecosystems into the future

This article is from the free online

Life Below Water: Conservation, Current Issues, Possible Solutions

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