Abstract
BackgroundSeawater temperature is the main factor restricting shallow-water zooxanthellate coral reefs to low latitudes. As temperatures increase, coral species and perhaps reefs may move into higher-latitude waters, increasing the chances of coral reef ecosystems surviving despite global warming. However, there is a growing need to understand the structure of these high-latitude coral communities in order to analyze their future dynamics and to detect any potential changes.Methodology/Principal FindingsThe high-latitude (32.75°N) community surveyed was located at Tatsukushi, Shikoku Island, Japan. Coral cover was 60±2% and was composed of 73 scleractinian species partitioned into 7 functional groups. Although only 6% of species belonged to the ‘plate-like’ functional group, it was the major contributor to species coverage. This was explained by the dominance of plate-like species such as Acropora hyacinthus and A. solitaryensis. Comparison with historical data suggests a relatively recent colonization/development of A. hyacinthus in this region and a potential increase in coral diversity over the last century. Low coverage of macroalgae (2% of the benthic cover) contrasted with the low abundance of herbivorous fishes, but may be reasonably explained by the high density of sea urchins (12.9±3.3 individuals m−2).Conclusions/SignificanceThe structure and composition of this benthic community are relatively remarkable for a site where winter temperature can durably fall below the accepted limit for coral reef development. Despite limited functionalities and functional redundancy, the current benthic structure might provide a base upon which a reef could eventually develop, as characterized by opportunistic and pioneer frame-building species. In addition to increasing seawater temperatures, on-going management actions and sea urchin density might also explain the observed state of this community. A focus on such ‘marginal’ communities should be a priority, as they can provide important insights into how tropical corals might cope with environmental changes.
Highlights
As chances to limit global temperature increase to,2uC by the end of the century seem seriously compromised [1], tropical reef corals must demonstrate exceptional acclimatization and/or adaptation capacities in order to survive future environmental changes [2]
The Biological Institute of Kuroshio (BIK) was in charge of routine surveys for the Marine Park of Tatsukushi, and since we were working in collaboration with the BIK and collected no coral samples for this research, there was no need to obtain formal permission from the Marine Park authorities
In terms of benthic coverage, Acropora spp. were the dominant taxa (Figure 3b) with 2 species, A. hyacinthus and A. solitaryensis, being abundant. They contributed to .80% of the coral cover (Table 1)
Summary
As chances to limit global temperature increase to ,2uC by the end of the century seem seriously compromised [1], tropical reef corals (hereafter ‘corals’) must demonstrate exceptional acclimatization and/or adaptation capacities in order to survive future environmental changes [2]. Corals can tolerate water temperatures of as low as 14uC for a short period of time, but coral reef development is usually considered to be limited by temperatures of ,18uC [6]. Coral communities usually fail to form limestone reef structures at high latitudes [9] and are considered ‘marginal’ [10]. There is a growing need to understand the structure of these high-latitude coral communities in order to analyze their future dynamics and to detect any potential changes
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