Coverage, Diversity, and Functionality of a High-Latitude Coral Community (Tatsukushi, Shikoku Island, Japan)

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.

The Real Bounty: Marine Biodiversity in the Pitcairn Islands

“…The coral cover was comparable to several other significant high latitude reefs [54]–[55]. Consequently, Ducie should be considered a high priority conservation site given its current lack of local human impacts and the potential to be more resilient to climate change [56].…”

Typhoon damage on a shallow mesophotic reef in Okinawa, Japan

“…To assess potential changes in the functionality of the coral community after the typhoon coral taxa were classified into functional groups according to the shapes of the colonies following Denis et al (2013). Each OTU was assigned to one or more of eight functional groups: massive, encrusting, foliose, columnar, plate-like, bushy, arborescent, and unattached (Table S1).…”

The Future of Coral Reefs Subject to Rapid Climate Change: Lessons from Natural Extreme Environments

“…Species temporal turnover can be high depending on larval supply and recruitment from lower latitudes and fluctuations in environmental conditions. Whilst coral cover (Harriott et al, 1994;Thomson and Frisch, 2010;Denis et al, 2013) and even coral growth rates can be high (e.g., Ross et al, 2015), reef accretion and development are nevertheless often limited, with corals sometimes only forming living veneers on rocky substrate and references therein). Furthermore, future reef accretion could become increasingly challenged with the percent changes in arag predicted to be greater at high-latitude reefs relative to their tropical counterparts .…”