No-take marine protected areas (MPAs) have been promoted as effective tools for preserving biodiversity and permitting species recovery. However, MPA efficacy can be hindered by small size, enforcement shortfalls, and unfavorable life-history characteristics of target species. In 2004, eight MPAs were established around the island of Moorea, French Polynesia, in response to a decline in fish and invertebrate stocks. One species of particular conservation concern was the ecologically and economically important giant clam, Tridacna maxima. Current MPA catch-regulations on Moorea encourage extraction of reproductively mature giant clams, thereby potentially hindering repopulation efforts. In addition, the iridescent coloration of some T. maxima morphs confers increased economic value and therefore potentially stronger selective pressures on these genotypes. Whereas several post-establishment surveys have demonstrated positive effects of Moorea’s MPAs on fish stocks, little is reported about the recovery status of T. maxima giant clams. To address this knowledge gap, I conducted 29 surveys across six of Moorea’s MPAs and integrated this data with historical population estimates in order to assess collection-driven demographic alterations and status of recovery in Moorea’s T. maxima populations.
Although historical surveys revealed similar population growth rates in T. maxima between MPAs and controls this likely reflects positive spill-over effects on unprotected sites. Overall, giant clams were 6x more abundant within MPAs and population demography differed greatly between MPA and control sites. Densities of mature and brightly-colored clams were 17x and 6x higher within MPAs, respectively. In addition, brightly-colored adults were only found within MPA sites. Taken together, these results suggest that, despite small size and minimal enforcement, Moorea’s MPA network effectively maintains T. maxima population diversity and promotes sustainable population demography in this threatened giant clam species.