A recent review of the most up-to-date scientific information about marine reserves, spearheaded by PISCO, revealed global trends in the effects of marine reserves. Considerable research—from over 200 publications in peer-reviewed journals—provides a clear picture of what has happened after the establishment of marine reserves.
As of 2010, scientists have studied more than 150 marine reserves in at least 61 countries around the world and monitored biological changes inside the reserves. The number of species in each study ranged from 1 to 250 and the reserves ranged in size from 0.006 to 800 square kilometers (0.002 to 310 square miles).
As indicated in the graph above, a 2009 study documented a wide range of changes inside marine reserves, but nearly all of the effects were positive. This global review of peer-reviewed marine reserve studies revealed that fishes, invertebrates, and seaweeds had the following average increases inside marine reserves:
These increases were similar between tropical and temperate reserves, indicating that marine reserves can be effective regardless of latitude.
Heavily fished species often showed the most dramatic increases. Some fished species had more than 1000% higher biomass or density inside marine reserves. Even small changes in species diversity and individual body size are important. These two indicators have less potential for change than do biomass or density. Additionally, in some studies such as ones conducted in Florida, USA and Kenya, reserves produced greater increases than MPAs that allowed some fishing.