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

PeerJ. 2022 Mar 7:10:e12971. doi: 10.7717/peerj.12971. eCollection 2022.

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.

Keywords: Coastal management; Cumulative effects; Exploitation; Harvest; Marine protected areas; Mediterranean Sea; Multiple use areas; Natural predators; Predation; Restrictions.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Conservation of Natural Resources* / methods
  • Fishes / physiology
  • Humans
  • Italy
  • Paracentrotus* / physiology
  • Population Dynamics

Grants and funding

This research was funded by AGRIS Sardegna, supported by the Sardinian Regional Government, and by various commitments of the Sardinian MPAs funded by the Italian Ministry of the Environment. IG and SF were funded by the Interreg V a Italy France Maritime 2014-2020 Cooperation Program, project “Gestione Integrata delle Reti ecologiche attraverso i Parchi e le Aree Marine - GIREPAM” (Asse 2 - Lotto 3 - PI 6C-OS 1). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.