Patterns of Connectivity and Isolation in Marine Populations

<p>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.</p>

Patterns of Connectivity and Isolation in Marine Populations

<p>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.</p>

Coral settlement and recruitment responses to reef fish foraging and trait diversity

The process of coral recruitment is crucial to the healthy functioning of coral reef ecosystems, as well as recovery following disturbances. Fishes are key modulators of this process by feeding on algae and other benthic taxa that compete with corals for benthic space. However, foraging strategies within reef fish assemblages are highly diverse and the effect of foraging diversity on coral recruitment success remains poorly understood. Here, we test how the foraging traits of reef fishes affect coral settlement and juvenile success at Lizard Island, Great Barrier Reef. Using a multi-model inference approach incorporating six metrics of fish assemblage foraging diversity (foraging rates, trait richness, trait evenness, trait divergence, herbivore abundance, and benthic invertivore abundance), we found that herbivore abundance had positive effects on both coral settlement and recruitment success. However, foraging trait diversity had a negative effect on coral settlement but not on recruitment. Coral settlement was higher at sites with less trait diverse fish assemblages, specifically in trait divergence and richness. Moreover, these two trait diversity metrics were stronger predictors of coral settlement success compared to herbivore abundance. Our findings provide evidence that impacts mediated by fish foraging on coral juveniles can potentially be harmful during settlement, but the space-clearing effect overall remains advantageous. We show here that the variation of fish biodiversity across reefs can be a partial driver to spatially uneven patterns of coral recruitment and reef recovery.

Settlement of larvae from four families of corals in response to a crustose coralline alga and its biochemical morphogens

Healthy benthic substrates that induce coral larvae to settle are necessary for coral recovery. Yet, the biochemical cues required to induce coral settlement have not been identified for many taxa. Here we tested the ability of the crustose coralline alga (CCA) Porolithon onkodes to induce attachment and metamorphosis, collectively termed settlement, of larvae from 15 ecologically important coral species from the families Acroporidae, Merulinidae, Poritidae, and Diploastreidae. Live CCA fragments, ethanol extracts, and hot aqueous extracts of P. onkodes induced settlement (> 10%) for 11, 7, and 6 coral species, respectively. Live CCA fragments were the most effective inducer, achieving over 50% settlement for nine species. The strongest settlement responses were observed in Acropora spp.; the only non-acroporid species that settled over 50% were Diploastrea heliopora, Goniastrea retiformis, and Dipsastraea pallida. Larval settlement was reduced in treatments with chemical extracts compared with live CCA, although high settlement (> 50%) was reported for six acroporid species in response to ethanol extracts of CCA. All experimental treatments failed (< 10%) to induce settlement in Montipora aequituberculata, Mycedium elephantotus, and Porites cylindrica. Individual species responded heterogeneously to all treatments, suggesting that none of the cues represent a universal settlement inducer. These results challenge the commonly-held notion that CCA ubiquitously induces coral settlement, and emphasize the critical need to assess additional cues to identify natural settlement inducers for a broad range of coral taxa.