Hotspots of predation persist outside marine reserves in the historically fished Mediterranean Sea

Boada, Jordi, Arthur, Rohan, Farina, S., Santana, Yaiza, Mascaró, Oriol . Biological Conservation 191 : 67-74 (2015). DIGITAL.CSIC

The Mediterranean Sea has sustained historically high levels of fishing since pre-Roman times. This onceabundant sea has witnessed major declines in apex predators, now largely restricted to isolated pockets within marine reserves. This depletion could critically impact macrophyte communities that are strongly structured by top-down processes.We evaluated rates of predation on the sea urchin Paracentrotus lividus, a key herbivore of macroalgal and Posidonia oceanica seagrass seascapes, across a large stretch of the Western Mediterranean coastline. Fish predation was generally higher inside reserves, but was equally high at several locations outside these boundaries. Although critically low at some locations compared to reserves, predation was functionally ubiquitous in most habitats, seasons and sites. Fish were still primarily responsible for this predation with no clear evidence of meso-predator release. Macroalgal habitats were consistently subject to higher predation than in seagrass meadows, functionally critical given the vulnerability of macroalgal systems to overgrazing. Predation hotspots were clearly associated with high fish predator numbers and low refuge availability. Taken together, these results suggest that long-term overfishing may not necessarily reflect a complete loss of trophic function. Pockets of fish predation may still persist, linked to habitat complexity, predator behavioral adaptations and landscape-level features. Given the essential role top-down control plays in macroalgal communities, regulating fishing at these predation hotspots is vital to effectively conserve habitats from future hysteretic shifts. Even historically fished seas may retain areas where trophic function persists; identifying these areas is critical to preserving the remaining ecological integrity of these coastlines.