Gametogenesis, Embryogenesis, and Fertilization Ecology of Platygyra acuta

Understanding the reproductive biology of dominant coral species in subtropical nonreefal coral communities is critical in providing important information on the processes underlying the distribution limits of coral species and communities. This is the first study that investigates the reproduction cycle, gametogenesis, and fertilization ecology of Platygyra acuta. Results indicated that P. acuta is hermaphroditic and exhibits a single annual gametogenic cycle. Oogenic and spermatogenic cycle occurs for 6-7 months and for 2 months, respectively, prior to annual mass spawning event in May to June in Hong Kong. It took 18 hours for P. acuta to complete embryonic development, develop cilia, and start to rotate. High (>70%) fertilization success can be achieved under a broad range of sperm concentrations from 104 to 107 sperms mL−1. Fertilization success remained consistently high 6 h after spawning, indicating a prolonged viability of its gametes that is much longer than that recorded for other coral species. Significantly higher percentage of fertilization success was recorded in the first of the two consecutive nights of spawning, suggesting differences in the quality of the eggs and/or sperms between days of spawning. These results serve as important baseline information for better understanding of corals in marginal communities

High tolerance to temperature and salinity change should enable scleractinian coral Platygyra acuta from marginal environments to persist under future climate change.

With projected changes in the marine environment under global climate change, the effects of single stressors on corals have been relatively well studied. However, more focus should be placed on the interactive effects of multiple stressors if their impacts upon corals are to be assessed more realistically. Elevation of sea surface temperature is projected under global climate change, and future increases in precipitation extremes related to the monsoon are also expected. Thus, the lowering of salinity could become a more common phenomenon and its impact on corals could be significant as extreme precipitation usually occurs during the coral spawning season. Here, we investigated the interactive effects of temperature [24, 27 (ambient), 30, 32°C] and salinity [33 psu (ambient), 30, 26, 22, 18, 14 psu] on larval settlement, post-settlement survival and early growth of the dominant coral Platygyra acuta from Hong Kong, a marginal environment for coral growth. The results indicate that elevated temperatures (+3°C and +5°C above ambient) did not have any significant effects on larval settlement success and post-settlement survival for up to 56 days of prolonged exposure. Such thermal tolerance was markedly higher than that reported in the literature for other coral species. Moreover, there was a positive effect of these elevated temperatures in reducing the negative effects of lowered salinity (26 psu) on settlement success. The enhanced settlement success brought about by elevated temperatures, together with the high post-settlement survival recorded up to 44 and 8 days of exposure under +3°C and +5°C ambient respectively, resulted in the overall positive effects of elevated temperatures on recruitment success. These results suggest that projected elevation in temperature over the next century should not pose any major problem for the recruitment success of P. acuta. The combined effects of higher temperatures and lowered salinity (26 psu) could even be beneficial. Therefore, corals that are currently present in marginal environments like Hong Kong, as exemplified by the dominant P. acuta, are likely to persist in a warmer and intermittently less saline, future ocean

Mean size of <i>Platygyra acuta</i> recruits.

<p>Mean (+SE) size (mm²) of <i>Platygyra acuta</i> recruits in response to different temperature and salinity treatments. Number in () under each set of data represents number of replicates. Data indicated with the same letter showed no significant difference in the recruit sizes (Two-way ANOVA, <i>P</i> > 0.05; <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0179423#pone.0179423.t001" target="_blank">Table 1C</a>).</p

Mean percentage of newly settled <i>Platygyra acuta</i> larvae and cumulative surviving settlers.

<p>Mean (+SE) percentage (%) of newly and cumulatively settled <i>Platygyra acuta</i> larvae in response to different temperature and salinity treatments (<i>n</i> = 3 replicates per treatment). Data indicated with the same letter showed no significant difference in settlement success (Two-way ANOVA, <i>P</i> > 0.05; <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0179423#pone.0179423.t001" target="_blank">Table 1A</a>).</p

Schematic representation of the experimental design to study the interactive effects of temperature and salinity change on <i>Platygyra acuta</i> larvae.

<p>Schematic representation of the experimental design to study the interactive effects of temperature and salinity change on <i>Platygyra acuta</i> larvae.</p

Mean percentage of surviving settlers of <i>Platygyra acuta</i>.

<p>Mean (+SE) percentage (%) of surviving settlers of <i>Platygyra acuta</i> in response to different temperature and salinity treatments (<i>n</i> = 3 replicates per treatment). * denotes those results of pairwise comparisons that showed significant difference (<i>P</i> < 0.05) between ambient salinity and lowered salinity treatments under the fixed factor of temperature. Data indicated with the same letter showed no significant difference in percentage of post-settlement survival (Mixed ANOVA, <i>P</i> > 0.05; <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0179423#pone.0179423.t001" target="_blank">Table 1B</a>).</p

Results of Two-way (A and C) and Mixed (B) ANOVA showing the effects of different factors and their interaction on (A) cumulative settlement, (B) post-settlement survival of recruits and (C) size changes of the recruits.

<p>Results of Two-way (A and C) and Mixed (B) ANOVA showing the effects of different factors and their interaction on (A) cumulative settlement, (B) post-settlement survival of recruits and (C) size changes of the recruits.</p

Exploring coral microbiome assemblages in the South China Sea

Coral reefs are significant ecosystems. The ecological success of coral reefs relies on not only coral-algal symbiosis but also coral-microbial partnership. However, microbiome assemblages in the South China Sea corals remain largely unexplored. Here, we compared the microbiome assemblages of reef-building corals Galaxea (G. fascicularis) and Montipora (M. venosa, M. peltiformis, M. monasteriata) collected from five different locations in the South China Sea using massively-parallel sequencing of 16S rRNA gene and multivariate analysis. The results indicated that microbiome assemblages for each coral species were unique regardless of location and were different from the corresponding seawater. Host type appeared to drive the coral microbiome assemblages rather than location and seawater. Network analysis was employed to explore coral microbiome co-occurrence patterns, which revealed 61 and 80 co-occurring microbial species assembling the Galaxea and Montipora microbiomes, respectively. Most of these co-occurring microbial species were commonly found in corals and were inferred to play potential roles in host nutrient metabolism; carbon, nitrogen, sulfur cycles; host detoxification; and climate change. These findings suggest that the co-occurring microbial species explored might be essential to maintain the critical coral-microbial partnership. The present study provides new insights into coral microbiome assemblages in the South China Sea

Pharmaceutical Residues in Edible Oysters along the Coasts of the East and South China Seas and Associated Health Risks to Humans and Wildlife

The investigation of pharmaceuticals as emerging contaminants in marine biota has been insufficient. In this study, we examined the presence of 51 pharmaceuticals in edible oysters along the coasts of the East and South China Seas. Only nine pharmaceuticals were detected. The mean concentrations of all measured pharmaceuticals in oysters per site ranged from 0.804 to 15.1 ng g–1 of dry weight, with antihistamines being the most common. Brompheniramine and promethazine were identified in biota samples for the first time. Although no significant health risks to humans were identified through consumption of oysters, 100–1000 times higher health risks were observed for wildlife like water birds, seasnails, and starfishes. Specifically, sea snails that primarily feed on oysters were found to be at risk of exposure to ciprofloxacin, brompheniramine, and promethazine. These high risks could be attributed to the monotonous diet habits and relatively limited food sources of these organisms. Furthermore, taking chirality into consideration, chlorpheniramine in the oysters was enriched by the S-enantiomer, with a relative potency 1.1–1.3 times higher when chlorpheniramine was considered as a racemate. Overall, this study highlights the prevalence of antihistamines in seafood and underscores the importance of studying enantioselectivities of pharmaceuticals in health risk assessments