The European flat oyster (Ostrea edulis), a species native to European and Mediterranean regions and regarded as having an unfavourable conservation status, is known for building reefs offshore, to such an extent that these areas are often referred to as the coral reefs of temperate zones.
These reefs, in the past, covered areas as extensive as football fields and, in aggregate, reached more than 1.7 million hectares. However, overfishing, pollution and disease have caused the ecological collapse of these zones, according to a team of researchers in a paper published in the journal Conservation Letters (Conservation Letters). Now, European flat oyster reefs are degraded and fragmented, with an average density estimated at fewer than one oyster per square meter. In places where they still persist, such as off the Scandinavian coast, these reefs tend to be no larger than 0.1 hectares.
This reef-building oyster species is considered a pivotal element for a diversity of other animals, with their marine structures supporting vibrant communities of fish, crabs, starfish and even seabirds and humans, who have developed livelihoods and ways of subsistence around these reefs.
Moreover, they provide important coastal protection against the erosive force of tides and the effects of storms, and being filter-feeding animals they are essential for maintaining the health of marine ecosystems. With the collapse of these habitats, everything else is swept toward a precipice of instability and ecological risks.
Thus, with the collapse of the ecosystem of this European native oyster, “we have also lost a huge filtration engine in the northeast Atlantic,” notes Joanne Preston, a lecturer at the University of Portsmouth and one of the article’s authors, adding that “even more grave” could be “the loss of biodiversity that fed on or lived in these reefs.”
Philine zu Ermgassen admits that “we were shocked by our findings.” The University of Edinburgh researcher and the study’s first author says that the work of compiling information about the historical evolution of European flat oyster reefs, as well as their contributions to the marine ecosystem as a whole, allowed us to understand “the indispensable role these reefs once played.”
Although several habitat restoration projects for this European native species are already underway in the United Kingdom and Ireland, the scientist warns that, by themselves, they may not be sufficient.
“The current recovery efforts will be insufficient,” states zu Ermgassen, who contends that, first of all, we need to look to the history of these reefs to understand what conditions enable better recovery, and not based solely on the present scenario, already influenced by factors such as pollution, overfishing and other human activities. Moreover, more funding is needed.
“The current state of collapse of the European native oyster reef ecosystem is, therefore, a powerful warning that the state of the European seas is more grave than is usually recognised when our assessments are limited to more recent reference baselines,” the article reads.
