Extreme concentration of marine biodiversity and exploitation of marine resources in the Coral Triangle pose challenges to biogeographers and resource managers. Comparative phylogeography provides a powerful tool to test biogeographic hypotheses evoked to explain species richness in the Coral Triangle. It can also be used to delineate management units for marine resources. After about a decade of phylogeographical studies, patterns for the Coral Triangle are emerging. Broad connectivity in some species support the notion that larvae have maintained gene flow among distant populations for long periods. Other phylogeographic patterns suggest vicariant events resulting from Pleistocene sea level fluctuations, which have, at least occasionally, resulted in speciation. Divergence dates ranging back to the Miocene suggest that changing land configurations may have precipitated an explosion of species diversification. A synthesis of the marine phylogeographic studies reveals repeated patterns that corroborate hypothesized biogeographic processes and suggest improved management schemes for marine resources.

The Coral Triangle is the global center of marine biodiversity; however, its coral reefs are critically threatened. Because of the bipartite life history of many marine species with sedentary adults and dispersive pelagic larvae, designing effective marine protected areas requires an understanding of patterns of larval dispersal and connectivity among geographically discrete populations. We used mtDNA sequence data to examine patterns of genetic connectivity in the boring giant clam (Tridacna crocea) in an effort to guide conservation efforts within the Coral Triangle. We collected an approximately 485 base pair fragment of mtDNA cytochrome c oxidase 1 (CO1) from 414 individuals at 26 sites across Indonesia. Genetic structure was strong between regions (phi(ST)=0.549, p < 0.00001) with 3 strongly supported clades: one restricted to western Sumatra, another distributed across central Indonesia, and a third limited to eastern Indonesia and Papua. Even within the single largest clade, small but significant genetic structure was documented (phi(ST)=0.069, p < 0.00001), which indicates limited gene flow within and among phylogeographic regions. Significant patterns of isolation by distance indicated an average dispersal distance of only 25-50 km, which is far below dispersal predictions of 406-708 km derived from estimates of passive dispersal over 10 days via surface currents. The strong regional genetic structure we found indicates potent limits to genetic and demographic connectivity for this species throughout the Coral Triangle and provides a regional context for conservation planning. The recovery of 3 distinct evolutionarily significant units within a well-studied taxonomic group suggests that biodiversity in this region may be significantly underestimated and that Tridacna taxa may be more endangered than currently recognized.

No abstract

The formation and persistence of modern coral reefs depends largely on organisms that host dinoflagellate algal symbionts of the genus Symbiodinium. There are important ecological and physiological differences among Symbiodinium types, and many host species are able to associate with multiple types, which may facilitate adaptation to local environmental change. Using denaturing gradient gel electrophoresis (DGGE) and sequencing of internal transcribed spacer-2 (ITS2) ribosomal DNA, we identified 11 Symbiodinium types belonging to clades A, C, and D in 250 host animals from 3 Tridacna species in eastern Indonesia. Individuals with multiple symbiont types were common: 42% of all clams had symbionts from multiple clades and 15% of all clams had multiple types from a single clade. T. crocea associated more often with clade C symbionts and less frequently with clade D symbionts. T. squamosa associated more frequently with clade D and less often with clade C symbionts. T. maxima did not preferentially associate with a particular Symbiodinium clade, but sample sizes were low. We used both satellite sea surface temperature and in situ recordings to characterize the thermal environment in the study area. Clams with clade C and D symbionts were located in areas with higher mean temperatures, while clams with clade A symbionts were in cooler areas. This is consistent with previous research indicating that clade C and D types may be more heat-tolerant than clade A. These results support the hypothesis that giant clams can associate with different symbiont types based on local environmental conditions. KEY WORDS: Symbiodinium · Tridacna spp. · Thermal tolerance · Climate change · Coral reef · IndonesiaResale or republication not permitted without written consent of the publisher

No abstract