Sea urchin proliferation threatens seaweed forests

Researchers from the Higher Council for Scientific Research (CSIC) and the University of Barcelona participated in an international study aimed at analyzing the dynamics of marine ecosystems and the factors causing the transformation of underwater seaweed forests into submarine chalkpit.

The scientists explain that sea urchins play an important role in this process. These invertebrates act as agent models of biological richness of the ocean floor, but when they proliferate excessively, can cause serious ecological damage.

The sea urchin proliferation reduces seaweed cover and limits the survival of other marine species.

The researcher Bernat Hereu, of the Department of Ecology of the University of Barcelona explains that the urchins are at an intermediate level in the food web, since they feed on seaweed and are preyed upon by fish such as bream and others.

“In the event of overfishing, for example, the urchin population can skyrocket to the point of turning algal carpets and meadows into submarines chalkpits, having low productivity and low biodiversity,” he explains.

Anyway, the projections of the general model relating marine areas with a lot of fishing activity, urchin overcrowding and low algal cover are not always met.

“This general correlation fish-urchin-seaweed is not always true”, Hereu observed.

He adds: “There are marine reserves that are rich in fish, sea urchins and chalkpits, and others in which, however, fish or sea urchins are rare, and seaweed forests are well preserved. This indicates that there are unknown interactions that can alter the dynamics of the system and divert these processes.”

Seaweed is also ecologically valuable species in marine ecosystems because they are primary producers, fix the substrate, change the environment and create microhabitats for other species.

To decipher what processes affecting the transformation of kelp forests in oceanic chalkpits, the scientists implemented a common study protocol in 13 temperate marine areas of the world.

The process is not linear, but responds to sudden changes on marine ecosystems. Therefore, at some point the ecological system collapses, it changes abruptly and significant biodiversity loss is recorded.

According to Hereu, “these changes, which must be addressed from the theory of change of alternative stable states follow a graphical model of hysteresis”.

The researchers determined that a number of feedback mechanisms maintains the stability of marine forests over time. But when urchin density reaches a critical value, the ecological system collapses and becomes a chalkpit.

Scientists involved in these studies argue that it is essential to know what the key factors are in order to prevent the collapse of natural systems and the destruction of algal forests.

“Prohibiting the fishing activity is not enough to recover these marine habitats. If we want to restore marine chalkpits and recover the algal systems, we can act on sea urchin stocks or generate structures to accelerate the recovery of these marine habitats,” Hereu concludes.

The findings of this research were published in the journal Philosophical Transactions of the Royal Society B.


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