How climate change is messing up the ocean’s biological clock, with unknown long-term consequences

By Frédéric Cyr, Memorial University of Newfoundland

Every year in the mid-latitudes of the planet, a peculiar phenomenon known as the phytoplankton spring bloom occurs. Visible from space, spectacular large and ephemeral filament-like shades of green and blue are shaped by the ocean currents.

The phytoplankton blooms are comprised of a myriad of microscopic algae cells growing and accumulating at the ocean’s surface as a result of the onset of longer days and fewer storms — often associated with the move into spring.

The timing of the phytoplankton spring bloom is, however, likely to be altered in response to climate change. Changes which will affect — for good or ill — the many species that are ecologically adapted to benefit from the enhanced feeding opportunity that blooms represent at crucial stages of their development.

Fine-tuned ecological adaptation

Phytoplankton blooms are, in some aspects, metronomes of the annual oceanic cycles around which many species’ biological clocks are synced to.

One example is the zooplankton Calanus finmarchicus, a class of micro-organism only capable of swimming up and down through the water column. Calanus finmarchicus usually spend the winter in diapause — the marine version of hibernation — surviving on their accumulated energy reserves in the deep ocean. At the moment they deem appropriate in the spring, they raise from the abyss to graze on the bloom and reproduce.

Fish and shellfish, too, are adapted to this natural metronome.

For some species, such as shrimp, females strategically lay their eggs in the water in advance of these blooms so their young will have ample food supplies from the moment they hatch

As incredible as it seems, some species can “calculate” the egg incubation period so that eggs hatch on average within a week of the expected spring bloom.

A question of timing

This, unfortunately, is where climate change is entering into the equation. What was normal in the past may well be changing more rapidly than marine species can adapt.

Zooplankton and fish larvae constitutes the bulk of what ocean scientists call secondary production.

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