Ecological effectiveness of marine protected areas across the globe in the scientific literature

A systematic literature review (SLR) of scientific articles on the effectiveness of marine protected areas (MPAs) to conserve biodiversity in the 2010-2019 decade using Scopus was done. Only studies that used Before-After-Control-Impact (BACI-type) research designs and at least one marine biodiversity indicator were included. The 23 studies included in the review were published in 19 journals and comprised 66 MPAs from 18 countries from the five continents. Fifty-seven percent of the studies used species-specific indicators of MPA effectiveness, chiefly density/abundance and size of organisms. Over 90% of the studies used incomplete research designs, with just 9% using BACI-type designs or over. Just over half of the studies reported positive or slightly positive ecological outcomes from MPAs, with 17.4% of them reporting negative or slightly negative outcomes, and 30.4% reporting mixed or inconclusive outcomes. Legally stringent reserves clearly outperformed multiple-use MPAs ecologically. The major stated pressures to both types of MPAs related to fishing, whereas the main mentioned MPA effectiveness factors included managerial and regulatory issues. Our results add to the existing evidence that the global ocean coverage by legally stringent reserves should be expanded if effective marine biodiversity conservation is to be achieved.