Abstract
The distribution of corals in Japan covers a wide range of latitudes, encompassing tropical to temperate zones. However, coral communities in temperate zones contain only a small subset of species. Among the parameters that determine the distribution of corals, temperature plays an important role. We tested the resilience to cold stress of three coral species belonging to the genus Acropora in incubation experiments. Acropora pruinosa, which is the northernmost of the three species, bleached at 13 °C, but recovered once temperatures were increased. The two other species, A. hyacinthus and A. solitaryensis, which has a more southerly range than A. pruinosa, died rapidly after bleaching at 13 °C. The physiological effects of cold bleaching on the corals included decreased rates of photosynthesis, respiration, and calcification, similar to the physiological effects observed with bleaching due to high temperature stress. Contrasting hot bleaching, no increases in antioxidant enzyme activities were observed, suggesting that reactive oxygen species play a less important role in bleaching under cold stress. These results confirmed the importance of resilience to cold stress in determining the distribution and northern limits of coral species, as cold events causing coral bleaching and high mortality occur regularly in temperate zones.
Highlights
Cold temperature stress can cause bleaching in corals, and sometimes mass mortality[9]
No visible bleaching was observed in the fragments of all three species at 18 °C or 23 °C, while severe bleaching (A. pruinosa) and mortality (A. solitaryensis and A. hyacinthus) occurred at 13 °C
On day 0, A. hyacinthus bleaching was not severe (Fig. 1b), whereas A. solitaryensis was already severely bleached by day 0
Summary
Cold temperature stress can cause bleaching in corals, and sometimes mass mortality[9]. Experiments have shown that cold temperatures lead to higher mortality rates in tropical corals than high temperatures[10]. The physiological effects of cold stress on coral hosts are less well-documented, studies have reported reduced growth and feeding rates at low temperatures[15,16]. Experiments investigating the mechanisms of cold bleaching have varied in their selection of minimum temperatures, tropical or temperate study species, and the duration of exposure to cold stress. We investigated the physiological effects of cold stress on these corals, and the mechanisms of any resulting cold bleaching, by means of laboratory experiments
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