Extinction vortex

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There are many reasons why we should care about biodiversity, as scientists in Sweden have discovered: loss of the most sensitive species makes the remaining ecosystem more vulnerable to the effects of climate change.

It was previously thought that losing some species merely meant that others would take over their role, whether that role is water filtration (aquatic plants), pollination (insects and birds), or preventing some species from growing to plague proportions (predator species such as lizards and some mammals).

But the team of Swedish researchers discovered that small changes may badly destabilise a whole ecosystem. Since the 1980s, the prevalence of eelgrass meadows, which provide a nursery environment for young cod, has reduced dramatically all along parts of the Swedish coastline, being replaced by mats of algae.

Meadows of Posidonia oceanica.
Pictures (a) illustrating the individual shoots (ramets), (b) hosting the largest (15 km) clones detected in this study. Photograph by M. San Félix.
from Implications of Extreme Life Span in Clonal Organisms: Millenary Clones in Meadows of the Threatened Seagrass Posidonia oceanica by Sophie Arnaud-Haond et. al. http://www.plosone.org/article/

Several factors are at work here:

  • Overfishing has drastically reduced the numbers of cod;
  • This has led to a huge increase in numbers of smaller predatory fish;
  • These fish eat the herbivorous crustaceans which graze on the algae;
  • This, combined with eutrophication, fosters the growth of the ‘nuisance’ algae which shades and suffocates out the eelgrass;
  • This in turn reduces the number of cod as their young have no place to hide from predators, and crustaceans, and eelgrass, and the cycle goes on.

Eelgrass, like many other aquatic plants, is vulnerable to the growth of the algae which suffocates the plants, thereby depriving a variety of marine creatures a haven in which to grow and hide.

There’s some fine short videos of eelgrass meadows here, should you want to see the variety of life that inhabits eelgrass.

* You can find out about extinction vortices here

[Featured image: Dodo reconstruction (Raphus cucullatus) reflecting new research at Oxford University Museum of Natural History. Photographer: Ballista. Licensed under the GNU Free Documentation License, version 1.2 or later]

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