Sea urchin harvest inside marine protected areas: an opportunity to investigate the effects of exploitation where trophic upgrading is achieved

Abstract

Background Marine protected areas (MPAs) usually have both positive effects of protection for the fisheries’ target species and indirect negative effects for sea urchins. Moreover, often in MPAs sea urchin human harvest is restricted, but allowed. This study is aimed at estimating the effect of human harvest of the sea urchin Paracentrotus lividus within MPAs, where fish exploitation is restricted and its density is already controlled by a higher natural predation risk. The prediction we formulated was that the lowest densities of commercial sea urchins would be found where human harvest is allowed and where the harvest is restricted, compared to where the harvest is forbidden. Methods At this aim, a collaborative database gained across five MPAs in Sardinia (Western Mediterranean, Italy) and areas outside was gathered collecting sea urchin abundance and size data in a total of 106 sites at different degrees of sea urchin exploitation: no, restricted and unrestricted harvest sites (NH, RH and UH, respectively). Furthermore, as estimates made in past monitoring efforts (since 2005) were available for 75 of the sampled sites, for each of the different levels of exploitation, the rate of variation in the total sea urchin density was also estimated. Results Results have highlighted that the lowest sea urchin total and commercial density was found in RH sites, likely for the cumulative effects of human harvest and natural predation. The overall rate of change in sea urchin density over time indicates that only NH conditions promoted the increase of sea urchin abundance and that current local management of the MPAs has driven towards an important regression of populations, by allowing the harvest. Overall, results suggest that complex mechanisms, including synergistic effects between natural biotic interactions and human pressures, may occur on sea urchin populations and the assessment of MPA effects on P. lividus populations would be crucial to guide management decisions on regulating harvest permits. Overall, the need to ban sea urchin harvest in the MPAs to avoid extreme reductions is encouraged, as inside the MPAs sea urchin populations are likely under natural predation pressures for the trophic upgrading.

Protection effectiveness and sea urchin predation risk: The role of roving predators beyond the boundaries of a marine protected area in the Western Mediterranean Sea

“…A partially protected area is generally established as a buffer zone between fully protected and intensively exploited areas, but this trade‐off occasionally leads to very limited ecological benefits (e.g. Caselle, Davis & Marks, 2018; Ceccherelli et al, 2022). In fact, the moderate fishing in this area seems to generate detrimental effects on the ecosystem functioning (e.g.…”

Predation risk of the sea urchin Paracentrotus lividus juveniles in an overfished area reveal system stability mechanisms and restocking challenges

“…Therefore, P. lividus is now regarded as one of the most exploited benthic invertebrate species for commercial and recreational purposes [28,29]. In Sardinia (Italy) sea urchin harvest has been so intense that populations have drastically regressed, as highlighted by annual monitoring of P. lividus populations [30]: despite various restrictions imposed by the Sardinia Region to minimize the risk of over-exploitation [30], sea urchin populations have not recovered and concerns have arisen regarding the efficacy of harvest restrictions over the last several years [26]. Particular attention was dedicated to effectiveness of recruitment as if it was hindered by some stabilizing feedback mechanisms, and it could explain the lack of population recovery although sea urchin harvest has been managed and occasionally interrupted.…”