Search

A genetic identification method (DNA barcoding) was used to compare the commu- nity compositions of planktonic fish eggs and larvae within a coastal embayment, testing the hypothesis that the composition of the planktonic larval fish community proportionately reflects the composition of the planktonic fish egg community (excluding species with non-planktonic eggs). By genetically identifying 843 individual eggs, we preserved the quantitative aspects of tra- ditional community analysis. The studied embayment has restricted hydrodynamic connectivity to other coastal waters. A circulation model containing simulated particles estimated average egg movement of approximately 1 km between times of spawning and sample collection, indicating locally spawned eggs were likely to be retained within the survey area. Thirteen of 14 collected egg taxa (88% of egg specimens) could be genetically identified to species level, with the 14th taxon identified to genus level. This novel approach revealed a high degree of spatial heterogene- ity in fish egg compositions within the embayment. Species that dominated the egg community (Eugerres plumieri, Cynoscion nebulosus, Centropomus undecimalis, and Prionotus spp.) were not particularly abundant amongst the 276 larvae identified, and the most abundant larval species (Achirus lineatus and Cynoscion arenarius) only comprised a minor proportion of the identified eggs. Overall, there was no correlation between the percent compositions of the egg and larval communities (r = −0.07, n = 15, p = 0.81). The clear disparities observed between the species com- positions of the egg and larvae highlight the need for directly identifying eggs when studying habitat connectivity or performing stock assessment with egg production model-based methods.

Corals are known to contain a diverse microbiota; however, few studies have explicitly addressed the spatial variability of bacterial communities across individual, healthy coral colonies. This study applied culture-based and culture-independent methods to examine the spatial hetero- geneity in bacterial communities in the mucus of 3 healthy Montastraea annularis colonies from Looe Key Reef, Florida Keys. Automated ribosomal intergenic spacer analysis (ARISA) results showed significant variability (up to 61% dissimilarity) in the composition of the total bacterial community at different locations only centimeters apart on individual coral colonies. Abundances of culturable Vib- rio spp. determined by TCBS plating were highly variable across individual coral colonies, differing by up to 100-fold between different locations on the same colony. ARISA profiles indicated that intra- colony variation rivaled intercolony differences in the composition of the culturable Vibrio commu- nity (i.e. types of culturable Vibrio spp. and their relative abundances). The high degree of spatial heterogeneity in coral-associated bacteria observed across individual colonies has implications for coral microbiology studies and coral restoration projects.

Coral reefs are suffering a long-term global decline, yet the causes remain contentious. The role of poor water quality in this decline is particularly unclear, with most previous studies providing only weak correlations between elevated nutrient levels and coral mortality. Here we experimentally show that routinely measured components of water quality (nitrate, phosphate, ammonia) do not cause substantial coral mortality. In contrast, dissolved organic carbon (DOC), which is rarely measured on reefs, does. Elevated DOC levels also accelerate the growth rate of microbes living in the corals’ surface mucopolysaccharide layer by an order of magnitude, suggesting that mortality occurs due to a disruption of the balance between the coral and its associated microbiota. We propose a model by which elevated DOC levels cause Caribbean reefs to shift further from coral to macroalgal dominance. Increasing DOC levels on coral reefs should be recognized as a threat and routinely monitored.

The coral holobiont includes the coral, zooxanthellae, fungi, endolithic algae, and >30 species of Bacteria. Using culture-independent techniques, we now show that Archaea are also abundant and widespread on corals. Sequence analyses of Archaea on 3 species of Caribbean corals revealed that coral-associated Archaea are novel, diverse, and include representatives from both the Crenarchaeota and Euryarchaeota. Unlike zooxanthellae and Bacteria, the Archaea do not appear to form species-specific associations with reef-building corals. Fluorescent in situ hybridizations with peptide nucleic acid (PNA) probes showed that Archaea were present at >107 cells cm-2 on Porites astreoides, comprising nearly half of the prokaryotic community. This study and one by Kellogg (Mar Ecol Prog Ser 273:81-88) show that Archaea are abundant, diverse, and potentially important components of the coral holobiont.