Patterns of Connectivity and Isolation in Marine Populations

There is ongoing debate about the levels of connectivity among marine populations and despite its importance, there is limited information on the levels of population connectivity in most geographic locations. This lack of information severely limits our ability to adequately manage the marine environment including the design and implementation of Marine Reserve (MRs) networks. The specific objectives of this thesis were to: 1) Develop polymorphic microsatellite loci for my model species, the intertidal gastropod Austrolittorina cincta; 2) Conduct population genetic studies across A.cincta populations within the Cook strait region to asses the levels of connectivity within the regional marine reserve network; 3) Determine the levels of A. cincta larval movement and settlement from an isolated source; and 4) Asses the effect of the larval abundance on settlement rates. This thesis includes laboratory studies; population genetic studies; and field surveys within New Zealand and in the Wakatobi National Park, Indonesia. Eight novel polymorphic microsatellite loci were developed for A. cincta and five of these loci were used to investigate population connectivity across seven populations within the Cook Strait region, including four marine reserves. In the population genetics study, in contrast to what was expected, I recorded low, but significant genetic differentiation between most population pairs within the Cook Strait region, over a minimum and maximum spatial scale of 55 to 300 km, including several of the MRs. In a large-scale field settlement survey on the Kapiti coast combined with the use of microsatellite markers I investigated A. cincta larval movement and settlement and found that most larvae settle within 5 km, although some larvae might travel up to 50 km. Finally, the coral settlement studies in the Wakatobi National Park revealed lower coral settlement rates at sites with low adult coral cover, suggesting an effect of the the amount of local available larvae on coral settlement rates. While it has been suggested that marine populations are demographically open, with larvae connecting populations separated over large spatial scales, this thesis shows that populations might not be as open as previously considered and localized dispersal and self-recruitment processes might be a frequent feature in marine populations. This thesis provides valuable information to managers about marine reserve networks and the importance of adequate environmental protection to ensure future viable populations.