Colony morphological features is among the best predictor of the scleractinian coral’s function in reef ecosystems. However, morphological traits are categorical and to convert this information into a quantitative value as well as estimate their influence on ecosystem process remain a challenge. Here, we propose a trait-based approach to quantify morphological diversity and assess the structural complexity of the habitat provided by corals. We used a previously published dataset that is related to a bleaching event that affected the coral reef off Tikus Island in Indonesia in 1983. We found clear signs of recovery of the coral assemblage’s complexity toward pre El Niño conditions five years after the event. Independent of the change observed in species richness, this return in structural complexity was accompanied by a global decrease in species number associated with each particular morphological entity (Functional Redundancy) and an increase in the number of single-species entities (Functional Vulnerability). Together with species loss, we show an overall functional erosion of the coral assemblage and suggest that the role of the coral reef habitat could be strongly imperiled under repeated or synergistic disturbances. This approach offers an opportunity for a better understanding of coral responses to natural and anthropogenic disturbances.

The zooxanthellate scleractinian coral, Alveopora japonica Eguchi, 1968, inhabits high-latitude waters from southern Taiwan to mainland Japan. This species may have benefited from recent increase in seawater temperature, and it has been hypothesized that a shift from kelp forest to coral dominance may be occurring at some locations at the edge of its distribution. Here, we examined the coral diversity and composition of the benthic community associated with extensive A. japonica stands from Biyangdo, northeast of Jeju Island (33.41°N), South Korea. Coral recruit density was further examined by estimating the number of juvenile corals in photographs taken directly from the benthos. The depauperate coral assemblage (five species in total) was dominated by A. japonica, which contributed to 64.0% ( SE 1.4%) of the benthic cover. Together with local reports documenting recent development of A. japonica populations, the exceptionally high density of recruits, 7590 (SE 660) recruits per m 2 , suggests a population that could be increasing. Additional data are needed to correlate the trend observed in this population with rising seawater temperature. However, this “weedy” and opportunistic coral species may be colonizing the region more aggressively than expected by chance, possibly to the detriment of the original ecosystem dominated by macroalgae. Overall, this work constitutes an important baseline against which future changes recorded in the temperate benthic communities can be assessed.

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.