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Biology

The far-reaching benefits of marine reserves

Paper: José Martin Pujolar, Marcello Schiavina, Antonio Di Franco, Paco Melià, Paolo Guidetti, Marino Gatto, Giulio A. De Leo and Lorenzo Zane. Understanding the effectiveness of marine protected areas using genetic connectivity patterns and Lagrangian simulations. Diversity and Distributions, (2013) 19, 1531–1542. DOI: 10.1111/ddi.12114

 

There are about 5,000 marine protected areas (MPAs) in the world but they represent only 2.3 % of the world’s oceans. MPAs are very important for marine conservation, and well designed and managed MPAs benefit not only the ecosystem and species but also generate important social, economic and cultural improvements. They provide areas where fish are able to spawn and grow to their adult size and also increase fish catches in neighboring fishing spots. Therefore, it is important to understand the patterns of connectivity or movement of organisms between MPAs and nearby non-protected areas. Connectivity is shaped by the movement of larvae, juveniles and/or adults and can be affected by different environmental factors such as ocean currents.

Figure 1: Diplodus sargus sargus (Wikipedia commons)

Figure 1: Diplodus sargus sargus (Wikipedia commons)

Using the white seabream Diplodus sargus sargus as the model species (Figure 1), Pujolar and others compiled genetic and oceanographic data to study the degree of connectivity between the MPA of Torre Guaceto (TGMPA) in Italy and its neighboring non-protected areas. The TGMPA (Figure 2) has a coastline of about 8 km and extends from the shoreline to 50 m depth. The authors collected a total of 298 settlers (juvenile white seabreams of 1-1.5 cm length) from 5 locations: one inside the TGMPA, two northward and two southward. Additionally, they caught 84 adults at the marine reserve.

 

Figure 2: Aerial view of the marine protected area of Torre Guaceto (www.pugliaevents.it)

Figure 2: Aerial view of the marine protected area of Torre Guaceto (www.pugliaevents.it)

Genetic differences between the 5 locations sampled were quantified using genetic markers called microsatellites. The authors found an overall genetic similarity within the studied area, which suggests that there is movement of individuals in and out of the MPA. The results obtained with the genetic tools were supported by larvae dispersal simulations (Figure 3) based on an oceanographic model of the region and life history characteristics of the species.

 

 

Figure 3: Simulations of particles released at 10 m depth at three locations (Torre a Mare, TGMPA and San Foca) on four dates. Black dots show the release location and red dots indicate the final position of each larval trajectory after 17 days.

Figure 3: Simulations of particles released at 10 m depth at three locations (Torre a Mare, TGMPA and San Foca) on four dates. Black dots show the release location and red dots indicate the final position of each larval trajectory after 17 days.

Simulations started at four dates according to the spawning period of the species and particles were tracked for 17 days, which is the average time pelagic larvae stay in the water column. Particles released at three locations, north of the MPA, in the TGMPA and south of the MPA, flowed from north to south, brought by the Western Adriatic Coastal Current and dispersed all throughout the study area (Figure 3). Some particles that were released at the TGMPA stayed within the TGMPA but there was also some export to the southern locations.

Interestingly, none of the simulations suggested movement of particles towards north. However, another study (Abecasis et al, 2009) suggests that juvenile D. sargus can cover large distances when they move from nurseries to adult locations. Therefore the movement of juveniles towards the north could explain the genetic similarity observed between the TGMPA and the northern sites.

 

 

 

 

This study suggests that the positive effect of the TGMPA extends beyond the limits of the marine reserve and could supply the fisheries located south of the TGMPA. However, the design of new MPAs should be considered case by case. MPAs can only be effective if they guarantee a good level of self-recruitment (larvae returning to their natal sites) and connectivity among MPAs and adjacent areas. These benefits are dependent on environment characteristics and species life history traits, so it is important to study how the connectivity of MPAs changes for different geographical areas and species.

Catarina Silva
Hi! I am a PhD candidate at Victoria University of Wellington. I study the genetic structure of organisms and how the environment influences genetics. Check out my website for more information!

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