By David Braun
Overfishing remans the most important threat to Mediterranean underwater ecosystems, “more than pollution, invasive species, or climate change”, says Enric Sala, one of the authors of the most comprehensive study made of the sea, published this week in the science journal PLOS ONE.
The research, published in a paper entitled Large-Scale Assessment of Mediterranean Marine Protected Areas Effects on Fish Assemblages, was co-authored by a dozen researchers. A marine ecologist and a National Geographic Explorer-in-Residence, Sala is actively engaged in exploration, research and communications to advance ocean policy and conservation.
In an interview for Ocean Views, Sala says the new study confirms the prognosis that the Mediterranean is on a trajectory to become a sea dominated by small tropical species that no one likes to eat. “Fishes will not be abundant, and the native species that the Greeks and Romans started to fish commercially will be rare — and most fisheries and the jobs they support will collapse. But this could change if we stop all the irrational overfishing, including both legal and illegal fishing, and protect a large chunk of the Mediterranean. Without these radical changes, we’re just going to reduce the Mediterranean Sea to a soup of microbes and jellyfish.”
The full interview:
What are the most important findings of this research?
The bottom line here is that the only protected areas that universally and successfully restore marine life are no-take reserves where fishing is prohibited. “Protected” areas that allow some types of fishing, evidently, are not very effective at saving marine life.
How does this inform future ocean policy with regard to protected areas as well as fishing?
Our results clearly indicate that dedicating public resources to “paper parks,” or areas that are protected only in the imagination of some, is a waste. If we want the fish back, and if we want a future for coastal fisheries, we need to create more no-take marine reserves. They are investment accounts.
What does the research tell us about non-indigenous species?
The Mediterranean is a sea with hundreds of alien species, most of which have come through the Suez Canal. We thought that native predators would keep the invaders in check, but that’s not what we have found. Current reserves in the Mediterranean have not been able to stop species invasions. There are factors other than fishing that make this a complex story. Or maybe it is that most reserves are too small and have not yet developed the large biomass of predators needed to control the populations of the alien species.
Does the research tell us anything about the changing marine environment with regard to climate change? Does this study set a new baseline to monitor the impact of warming seas?
Climate change is warming Mediterranean waters, and thus facilitating the spread of tropical species that use the Suez Canal to migrate from the Red Sea. In other words, climate change is “tropicalizing” the Mediterranean, and displacing native species that prefer colder waters. Our study provides the first quantitative baseline across the Mediterranean to track how alien species increase in abundance over time.
What have you learned about the assemblage of species in different parts of the Mediterranean Sea, specifically with regard to the impact of fishing, protection, and climate change?
Our major finding was that overfishing is the most important factor affecting Mediterranean underwater ecosystems, more than pollution, invasive species, or climate change. Taking fish out of the sea in massive quantities is what changes the underwater landscape the most. More than anything else. Period.
Can this research give you a glimpse into what the future of the Mediterranean might look like, specifically with regard to the species that might decline or become extinct and those species that might have an opportunity to survive and flourish? What is your prognosis for the future of fisheries in the Mediterranean if nothing is done? What might it be if we opt for the remedies available to us?
If we project from our current baseline, the Mediterranean of the future will be a poor sea, dominated by small tropical species that no one likes to eat. Fishes will not be abundant, and the native species that the Greeks and Romans started to fish commercially will be rare — and most fisheries and the jobs they support will collapse. But this could change if we stop all the irrational overfishing, including both legal and illegal fishing, and protect a large chunk of the Mediterranean. Without these radical changes, we’re just going to reduce the Mediterranean Sea to soup of microbes and jellyfish.
This study is part of your ongoing global research. What investigations do you have in the pipeline?
I continue research in two main areas: 1) the most pristine marine habitats, to understand what the ocean was like before humans (pristineseas.org), and 2) the benefits of marine reserves, in terms of both restoration of marine life and economic benefits.
Large-Scale Assessment of Mediterranean Marine Protected Areas Effects on Fish Assemblages was co-authored by Enric Sala and Paolo Guidetti, Pasquale Baiata, Enric Ballesteros, Antonio Di Franco, Bernat Hereu, Enrique Macpherson, Fiorenza Micheli, Antonio Pais, Pieraugusto Panzalis, Andrew A. Rosenberg, and Mikel Zabala.
Abstract: Marine protected areas (MPAs) were acknowledged globally as effective tools to mitigate the threats to oceans caused by fishing. Several studies assessed the effectiveness of individual MPAs in protecting fish assemblages, but regional assessments of multiple MPAs are scarce. Moreover, empirical evidence on the role of MPAs in contrasting the propagation of non-indigenous-species (NIS) and thermophilic species (ThS) is missing. We simultaneously investigated here the role of MPAs in reversing the effects of overfishing and in limiting the spread of NIS and ThS. The Mediterranean Sea was selected as study area as it is a region where 1) MPAs are numerous, 2) fishing has affected species and ecosystems, and 3) the arrival of NIS and the northward expansion of ThS took place. Fish surveys were done in well-enforced no-take MPAs (HP), partially-protected MPAs (IP) and fished areas (F) at 30 locations across the Mediterranean. Significantly higher fish biomass was found in HP compared to IP MPAs and F. Along a recovery trajectory from F to HP MPAs, IP were similar to F, showing that just well enforced MPAs triggers an effective recovery. Within HP MPAs, trophic structure of fish assemblages resembled a top-heavy biomass pyramid. Although the functional structure of fish assemblages was consistent among HP MPAs, species driving the recovery in HP MPAs differed among locations: this suggests that the recovery trajectories in HP MPAs are likely to be functionally similar (i.e., represented by predictable changes in trophic groups, especially fish predators), but the specific composition of the resulting assemblages may depend on local conditions. Our study did not show any effect of MPAs on NIS and ThS. These results may help provide more robust expectations, at proper regional scale, about the effects of new MPAs that may be established in the Mediterranean Sea and other ecoregions worldwide.
The paper was published on April 16, 2014.