Denis V et al. (2013), Coverage, diversity, and functionality of a hig...

ECB-ART-42733

PLoS One 2013 Jan 01;81:e54330. doi: 10.1371/journal.pone.0054330.

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Coverage, diversity, and functionality of a high-latitude coral community (Tatsukushi, Shikoku Island, Japan).

Denis V , Mezaki T , Tanaka K , Kuo CY , De Palmas S , Keshavmurthy S , Chen CA .

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BACKGROUND: Seawater 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 FINDINGS: The 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/SIGNIFICANCE: The 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.

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Genes referenced: cope LOC100887844

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	Figure 1. Study site. a.Location of Tatsukushi at Shikoku Island (Japan). b. Local geographic features of Tatsukushi Bay with the area survey and approximate locations of transects. Color scale corresponds to bathymetry obtained by sonar exploration [25].
	Figure 2. Seawater temperatures. a.Mean, maximum, and minimum seawater temperatures at the study site (at 5 m in depth) from November 2009 to October 2011. Inset represents daily temperature variations for the same period (data from [21], [25]). b. Long-term trend in sea surface temperature anomalies (deviation of mean annual temperature from mean temperature of the preceding three decades) from 1902 to 2011 in the northern part of the seas south of Japan. Red line corresponds to the linear regression analysis showing the +1.25°C increase occurring over the last century (data from [37]).
	Figure 3. Benthic community. a.Percentage cover of major benthic categories. b. Appearance of coral community at Tatsukushi dominated by Acropora spp (at 5 m in depth).
	Figure 4. Functional composition of the coral assemblage at the study site.Based on a. the occurrence of species (the dotted line represents the functional composition of the Great Barrier Reef corals assemblage, from [28]) and b. the abundance of species. Axes represent the relative contribution of each of the 8 functional groups identified according to their roles in ecosystem processes.
	Figure 5. Relationship between the diversity and functional diversity (A and B)/redundancy (C): schematic scenarios (modified from [61] and [62]).A: Functional diversity increases at declining rates with increased species diversity, which reaches an asymptote at high diversity levels; B: high functional redundancy at low species diversity followed by a rapid increase at an intermediate species diversity, until functional diversity asymptotes at high diversity levels [49]. Photo credits: CM Hsu.

References [+] :

Bellwood, Confronting the coral reef crisis. 2004, Pubmed