Understanding patterns of connectivity among populations of marine organisms is essential for the development of realistic, spatially explicit models of population dynamics. Two approaches, empirical genetic patterns and oceanographic dispersal modelling, have been used to estimate levels of evolutionary connectivity among marine populations but rarely have their potentially complementary insights been combined. Here, a spatially realistic Lagrangian model of larval dispersal and a theoretical genetic model are integrated with the most extensive study of gene flow in a Caribbean marine organism. The 871 genets collected from 26 sites spread over the wider Caribbean subsampled 45.8% of the 1900 potential unique genets in the model. At a coarse scale, significant consensus between modelled estimates of genetic structure and empirical genetic data for populations of the reef-building coral Montastraea annularis is observed. However, modelled and empirical data differ in their estimates of connectivity among northern Mesoamerican reefs indicating that processes other than dispersal may dominate here. Further, the geographic location and porosity of the previously described east-west barrier to gene flow in the Caribbean is refined. A multi-prong approach, integrating genetic data and spatially realistic models of larval dispersal and genetic projection, provides complementary insights into the processes underpinning population connectivity in marine invertebrates on evolutionary timescales.

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In recent decades, a rise in coral mortality, attributed to increased frequency of massbleaching events, increased prevalence of disease, and more frequent and severe hurricanes, has contributed to a rapid proliferation of macroalgae across many Caribbean reefs. As a consequence, the frequency of coral-algal interactions has risen. Here, we document the effects of 2 dominant Caribbean macroalgae, Dictyota spp. and Lobophora variegata, and a mixed algal community on the fecundity of a massive coral. Montastraea annularis is a dominant Caribbean reef-building coral characterised by a low recruitment rate. To investigate the effects of macroalgae on coral fecundity, algal contact was experimentally manipulated around the perimeter of M. annularis patches. Fecundity was measured as the diameter of eggs (ES), the number of eggs per gonad (E#) and the number of gonads per polyp (G#). Algal contact was shown to significantly reduce the diameter of eggs at both the coral-algal boundary and at the centre of coral patches. The presence of Dictyota spp. or a mixed algal community was shown to have more detrimental effects on ES than the presence of L. variegata. Removal of algal contact immediately prior to gametogenesis increased the reproductive output of polyps directly adjacent to the cleared areas, with an increase in ES, E# and G#. Our results imply that algal competitors can reduce the fecundity of M. annularis through mechanical and/or allelochemical damage of polyps directly adjacent to the algae and by causing the reallocation of energy within the coral patch from reproduction to defence and repair. KEY WORDS: Fecundity · Competition · Coral · Macroalgae · Energy allocation Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 367: [143][144][145][146][147][148][149][150][151][152] 2008 macroalgal blooms are mostly a consequence of coral mortality, rather than the prime cause (McCook et al. 2001, Diaz-Pulido & McCook 2002. Algal recruits are hypothesised to rapidly pre-empt coral settlement space and may settle directly onto stressed or dead coral tissue, rather than overgrowing healthy coral tissue (McCook et al. 2001, Diaz-Pulido & McCook 2002, 2004, although direct overgrowth of healthy coral tissue has been observed (Hughes et al. 2007). Macroalgae have been shown to inhibit coral recruitment (Kuffner et al. 2006), and coral-algal interactions can result in reduced coral growth rates and increased tissue mortality (Lirman 2001, River & Edmunds 2001, Jompa & McCook 2002, Nugues & Bak 2006, Box & Mumby 2007. Furthermore, the presence of algae around coral colonies has also been documented to reduce the fecundity of the entire coral colony (Tanner 1995, Hughes et al. 2007). While mortality of coral tissue is likely due to the mechanical and/or allelochemical effects of direct contact with the algal fronds (River & Edmunds 2001, Jompa & McCook 2003, a reduction in growth rate or colony fecundity suggests a possible diversion of energy away from reproduction o...

Summary1. Long-lived sedentary organisms with a massive morphology are often assumed to utilize a storage effect whereby the persistence of a small group of adults can maintain the population when sexual recruitment fails. However, employing storage effects could prove catastrophic if, under changing climatic conditions, the time period between favourable conditions becomes so prolonged that the population cannot be sustained solely be sexual recruitment. When a species has multiple reproductive options, a rapidly changing environment may favour alternative asexual means of propagation. 2. Here, we revisit the importance of asexual dispersal in a massive coral subject to severe climate-induced disturbance. Montastraea annularis is a major framework-builder of Caribbean coral reefs but its survival is threatened by the increasing cover of macroalgae that prevents settlement of coral larvae. 3. To estimate levels of asexual recruitment within populations of M. annularis , samples from three sites in Honduras were genotyped using four, polymorphic microsatellite loci. 4. A total of 114 unique genets were identified with 8% consisting of two or more colonies and an exceptionally large genet at the third site comprising 14 colonies. 5. At least 70% of multicolony genets observed were formed by physical breakage, consistent with storm damage. 6. Our results reveal that long-lived massive corals can propagate using asexual methods even though sexual strategies predominate.