A novel symbiosis between scleractinians and hydroids (Zanclea spp.) was recently discovered using taxonomic approaches for hydroid species identification. In this study, we address the question whether this is a species-specific symbiosis or a cosmopolitan association between Zanclea and its coral hosts. Three molecular markers, including mitochondrial 16S and nuclear 28S ribosomal genes, and internal transcribed spacer (ITS), were utilized to examine the existence of Zanclea species from 14 Acropora species and 4 other Acroporidae genera including 142 coral samples collected from reefs in Kenting and the Penghu Islands, Taiwan, Togian Island, Indonesia, and Osprey Reef and Orpheus Island on the Great Barrier Reef, Australia. Molecular phylogenetic analyses of the 16S and 28S genes showed that Acropora-associated Zanclea was monophyletic, but the genus Zanclea was not. Analysis of the ITS, and 16S and 28S genes showed either identical or extremely low genetic diversity (with mean pairwise distances of 0.009 and 0.006 base substitutions per site for the 16S and 28S genes, respectively) among Zanclea spp. collected from diverse Acropora hosts in different geographic locations, suggesting that a cosmopolitan and probably genus-specific association occurs between Zanclea hydroids and their coral hosts.

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The scale and intensity of marine cage culture have increased in the Asian-Pacific region, particularly in oligotrophic waters where coral reef organisms flourish. In this study, the influence of marine cage culture on subtropical coral communities in turbid waters was evaluated by measuring environmental parameters and benthic community compositions at Magongwan in the Penghu Islands, Taiwan. A canonical discriminant analysis of environmental parameters revealed that elevated levels of ammonium, nitrite, and chlorophyll a (chl a) released from the cages were the main pollution indicators that, in addition to sedimentation and turbidity, distinguished Impact Zone 1 (cage-culture zone) from the other 2 zones -Impact Zone 2 (800 m away from the cages) and the reference zone -in these turbid waters. Results of the canonical correlation analysis indicated that the coverage extents of macroalgae, sponges, and zoanthids were strongly correlated with levels of ammonium, nitrite, phosphate, chl a, and dissolved oxygen. Coral communities in Impact Zone 1 were mostly composed of stress-tolerant massive and submassive corals, but were lacking branching Acropora corals. In contrast, coral communities in the other zones, with high habitat complexity and species richness, were dominated by coral species with diverse morphologies, including branching Acropora coral communities. These results suggest that marine cage culture has been causing chronic nutrient enrichment in the surrounding waters at Magongwan, which may have resulted in a deterioration of suitable habitats for coral reef organisms. Nevertheless, intermediate levels of nutrients and particulate organic matter relative to the other zones might have been caused by the adjacent cage culture, resulting in the high coral coverage and diversity in the Impact Zone 2 in particular.

Seasonal variation in temperature fluctuations may provide corals and their algal symbionts varying abilities to acclimate to changing temperatures. We hypothesized that different temperature ranges between seasons may promote temperature-tolerance of corals, which would increase stability of a bacterial community following thermal stress. Acropora muricata coral colonies were collected in summer and winter (water temperatures were 23.4–30.2 and 12.1–23.1 °C, respectively) from the Penghu Archipelago in Taiwan, then exposed to 6 temperature treatments (10–33 °C). Changes in coral-associated bacteria were determined after 12, 24, and 48 h. Based on 16S rRNA gene amplicons and Illumina sequencing, bacterial communities differed between seasons and treatments altered the dominant bacteria. Cold stress caused slower shifts in the bacterial community in winter than in summer, whereas a more rapid shift occurred under heat stress in both seasons. Results supported our hypothesis that bacterial community composition of corals in winter are more stable in cold temperatures but changed rapidly in hot temperatures, with opposite results for the bacterial communities in summer. We infer that the thermal tolerance ranges of coral-associated bacteria, with a stable community composition, are associated with their short-term (3 mo) seawater thermal history. Therefore, seasonal acclimation may increase tolerance of coral-associated bacteria to temperature fluctuations.

The distribution and the structure of benthic assemblages vary with latitude. However, few studies have described benthic communities along large latitudinal gradients, and patterns of variation are not fully understood. Taiwan, lying between 21.90°N and 25.30°N, is located at the center of the Philippine-Japan arc and lies at the northern margin of coral reef development. A wide range of habitats is distributed along this latitudinal gradient, from extensive fringing coral reefs at the southern coast to non-reefal communities at the north. In this study, we examined the structure of benthic communities around Taiwan, by comparing its assemblages in four regions, analyzing the effects of the latitudinal gradient, and highlighting regional characteristics. A total of 25 sites, 125 transects, and 2,625 photographs were used to analyze the benthic communities. Scleractinian corals present an obvious gradient of increasing diversity from north to south, whereas macro-algae diversity is higher on the north-eastern coast. At the country scale, Taiwanese coral communities were dominated by turf algae (49%). At the regional scale, we observed an important heterogeneity that may be caused by local disturbances and habitat degradation that smooths out regional differences. In this context, our observations highlight the importance of managing local stressors responsible for reef degradation. Overall, this study provides an important baseline upon which future changes in benthic assemblages around Taiwan can be assessed.