Low Connectivity between Mediterranean Marine Protected Areas: A Biophysical Modeling Approach for the Dusky Grouper Epinephelus marginatus

Abstract

Marine protected areas (MPAs) are major tools to protect biodiversity and sustain fisheries. For species with a sedentary adult phase and a dispersive larval phase, the effectiveness of MPA networks for population persistence depends on connectivity through larval dispersal. However, connectivity patterns between MPAs remain largely unknown at large spatial scales. Here, we used a biophysical model to evaluate connectivity between MPAs in the Mediterranean Sea, a region of extremely rich biodiversity that is currently protected by a system of approximately a hundred MPAs. The model was parameterized according to the dispersal capacity of the dusky grouper Epinephelus marginatus, an archetypal conservation-dependent species, with high economic importance and emblematic in the Mediterranean. Using various connectivity metrics and graph theory, we showed that Mediterranean MPAs are far from constituting a true, well-connected network. On average, each MPA was directly connected to four others and MPAs were clustered into several groups. Two MPAs (one in the Balearic Islands and one in Sardinia) emerged as crucial nodes for ensuring multi-generational connectivity. The high heterogeneity of MPA distribution, with low density in the South-Eastern Mediterranean, coupled with a mean dispersal distance of 120 km, leaves about 20% of the continental shelf without any larval supply. This low connectivity, here demonstrated for a major Mediterranean species, poses new challenges for the creation of a future Mediterranean network of well-connected MPAs providing recruitment to the whole continental shelf. This issue is even more critical given that the expected reduction of pelagic larval duration following sea temperature rise will likely decrease connectivity even more.

Geographic isolation and larval dispersal shape seascape genetic patterns differently according to spatial scale

“…For marine species with a pelagic larval phase, such as M. surmuletus , dispersal capacity is primarily determined by pelagic larval duration (PLD), as the possible distance traveled by larvae increases with PLD (Andrello et al., 2013; Selkoe & Toonen, 2011). For example, larvae of the dusky grouper ( Epinephelus marginatus ), which has a similar PLD as M. surmuletus (30 days), disperse over distances of about 90 km on average (Andrello et al., 2013). At such scale, oceanic circulation, and thus larval dispersal, is expected to differ from Euclidian geographic distances due to the existence of small‐scale features such as gyres and fronts.…”

Efficacy of an established marine protected area at sustaining a queen conch Lobatus gigas population during three decades of monitoring

“…For example, variable patterns of local retention have been described using parentage analysis (SaenzAgudelo et al 2012) and marked recruits (Cuif et al 2015). There is also direct evidence of locations with primarily exogenous recruitment sources (Andrello et al 2013(Andrello et al , N anninga et al 2015) that would be poor MPA candidate locations. Habitat quality and environmental conditions certainly interact with larval supply in replenishing benthic populations (Lipcius et al 2008).…”

Geographic distance, water circulation and environmental conditions shape the biodiversity of Mediterranean rocky coasts

“…In this vein, current connectivity was defined as the minimum particle transit time between pairs of sites. A detailed description of the hydrodynamic simulations can be found in Andrello et al (2013).…”

“…Efforts to protect marine biodiversity through designation of Marine Protected Areas (MPAs) have been underway for decades, although designation of MPAs has often been based on opportunity rather than knowledge of ecosystem functioning (Fraschetti et al 2002), leading to ad hoc systems rather than networks of MPAs (Guilhaumon et al 2015). The importance of connected networks of reserves has been recognised as a critical requirement to protecting the Mediterranean marine ecosystem as a single interconnected entity (Andrello et al 2013, Lagabrielle et al 2014, leading to internationally coordinated efforts to plan for ecological connectivity between reserves (Lubchenco et al 2003, Grorud-Colvert et al 2014.…”

“…Recent refinement of ocean circulation models and improvements in computing power have allowed for a better understanding of the degree of hydrodynamic connectivity between populations (Andrello et al 2013(Andrello et al , 2015 and communities (Watson et al 2011a). Similarly, ocean color satellite imagery provides synoptic information on the distribution of biologically relevant environmental conditions across temporal and geographic scales not readily attainable by direct sampling alone.…”