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Calanus and Climate Change

Mar 1, 2011
Winter 2011

A small zooplankton species called Calanus finmarchicus plays a key role in the Gulf of Maine food web. Herring, mackerel, northern right whales, and other species rely on Calanus as a major food source, feeding on it seasonally along the coastal shelf, banks, and ledges. Changes in the abundance of Calanusover time could have significant effects on these species and the ecosystem as a whole. With the potential impacts of climate change on the horizon, understanding the implications is critical.

Biological Oceanographer Jeffrey Runge of the Gulf of Maine Research Institute and the University of Maine is leading an effort to deepen our understanding of Calanus. Using field measurements, time series data, and population dynamics modeling, they are researching the abundance ofCalanusin coastal waters, how climate change might affect the population, and the subsequent potential impact on the Gulf of Maine ecosystem.

"My hope is that this research will inform decisions about the type of observing system we need in order to understand how the Gulf of Maine is changing," said Jeff.

At higher latitudes and in colder waters, Calanus is adapted to survive seasonal periods of low food through an initial dormant, pre-adult stage that begins in the summer. During this stage, the organism is rich with lipids, which store a high level of energy. These lipids are what make Calanus a preferred prey source. Calanus remains dormant through the winter, after which it molts (sheds its outer layer) into the reproductive adult stage in the spring.

In the Gulf of Maine, Calanus resides at the southern edge of its range. Jeff and his research partners have found that it is productive in this region. However, there is evidence that temperatures in the Gulf of Maine are too warm for Calanus to stay dormant for such an extended period through the winter. Instead, many break out of dormancy in late summer to late fall, at which time they produce a fall generation that currently contributes to sustaining the Calanus stock in the region.

If Gulf of Maine surface waters were to become even warmer - a predicted impact of climate change - Calanus populations could be substantially reduced. Surface temperatures are likely already near the upper limit for this species. The reduction may be amplified by ocean acidification, a decrease in the ocean's pH caused by absorption of carbon dioxide from the atmosphere, which may interfere with reproductive success.

Scientists are working to understand whether the Gulf of Maine is likely to experience a biogeographic shift at the base of the food web, with Calanus shifting its range even further north and another warmer water zooplankton moving in to replace it. The extent to which other zooplankton species would fulfill the role ofCalanus in the food web is currently unknown but no other prominent, resident species have equivalent lipid content in the summer.

These factors put the regional population of Calanus, and therefore the larger ecosystem, in a vulnerable place.