Magazine article Science News

Early Shift: North Sea Plankton and Fish Move out of Sync

Magazine article Science News

Early Shift: North Sea Plankton and Fish Move out of Sync

Article excerpt

As ocean temperatures in the North Sea have warmed in recent decades, the life cycles of some species low in the food chain have accelerated significantly, sometimes setting off ecological havoc, new analyses suggest.

Many marine microorganisms bear chlorophyll, which lets them capture the sun's radiation and use it to grow. Each spring, as the sun rises higher in the sky, these so-called phytoplankton experience a population explosion. Small crustaceans such as copepods graze on this bounty, and they, in turn, nourish larger organisms such as fish larvae.

The number of juvenile fish produced each year depends on the synchrony of these population booms, says Martin Edwards, a marine ecologist at the Sir Mister Hardy Foundation for Ocean Science at Plymouth, England.

Edwards and his colleague Anthony J. Richardson have analyzed more than 4 decades of census figures for 66 species that appear in the lowest three levels of the food chain in the central North Sea. Between 1958 and 2002, the timing of the spring bloom of diatoms--one group of phytoplankton--didn't shift significantly.

However, peak populations of copepods, the next level up the food chain, occurred in recent years about 10 days earlier than they did in 1958. Overall numbers offish larvae, which consume both phytoplankton and copepods, recently crested about 27 days earlier than they did when the census began, says Edwards.

The life cycles and growth rates of copepods and fish larvae are influenced by both daily sunlight and average water temperature, which in the central North Sea has risen about 0. …

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