Long-term impacts of rising sea temperature and sea level on shallow water coral communities over a ~40 year period

Effects of combined rising sea temperature and increasing sea level on coral reefs, both factors associated with global warming, have rarely been addressed. In this ~40 y study of shallow reefs in the eastern Indian Ocean, we show that a rising relative sea level, currently estimated at ~11 mm y−1, has not only promoted coral cover but also has potential to limit damaging effects of thermally-induced bleaching. In 2010 the region experienced the most severe bleaching on record with corals subject to sea temperatures of >31 °C for 7 weeks. While the reef flats studied have a common aspect and are dominated by a similar suite of coral species, there was considerable spatial variation in their bleaching response which corresponded with reef-flat depth. Greatest loss of coral cover and community structure disruption occurred on the shallowest reef flats. Damage was less severe on the deepest reef flat where corals were subject to less aerial exposure, rapid flushing and longer submergence in turbid waters. Recovery of the most damaged sites took only ~8 y. While future trajectories of these resilient reefs will depend on sea-level anomalies, and frequency of extreme bleaching the positive role of rising sea level should not be under-estimated

Coral recruitment and recovery after the 2004 Tsunami around the Phi Phi Islands (Krabi Province) and Phuket, Andaman Sea, Thailand

International audienceThe 2004 tsunami left a discontinuous pattern of destruction in the reefs along Andaman Sea coast of Thailand. Here, a comparative assessment of coral recruitment was carried out to assess differences in recovery between damaged and undamaged sites in near-shore fringing reefs 1 and 3 years after the tsunami. Settlement plates showed high frequencies of coral spat after 4 months (<17 spat tile) in both, damaged and undamaged locations. Field surveys carried out 3 years after the tsunami on natural substrate confirmed that tsunami damage did not suppress recruitment in damaged sites relative to no impacted controls. New and stable settlement space along with unabated larval supply supported post-tsunami recruit densities up to 7.2 myear. Mean recruit densities were found at the level of post-storm situations with rapid recovery success, suggesting that the duration of disturbance, degree of sorting and, hence, stability of coral rubble is a key determinant of recruitment success. Low regeneration success of some species e.g. branching acroporids and rebounding tourism industry at sites like Patong and partly around the Phi Phi Islands (dense carpets of filamentous algae) led to the assumption of selectivity and eventually to an alternation of the coral community even though live coral cover might be recovered soon

Coral community composition and reef development at the Similan Islands, Andaman Sea, in response to strong environmental variations

The Similan Islands, a Thai archipelago in the Andaman Sea located near the shelf break, are subjected to frequent (up to several events per hour) and abrupt changes in physicochemical conditions, particularly during the dry season (NE monsoon, January through April) and to an intense monsoon season with strong surface wave action (May to October). The exposed west slopes of the islands feature more coral species, but lack a carbonate reef framework. By contrast, the sheltered east sides show a complex reef framework dominated by massive Porites. Our results suggest that the sudden changes in temperature, pH and nutrients (drops of up to 10°C and 0.6 U and increases of up to 9.4 μmol NOx l−1, respectively) due to pulsed upwelling events may rival the importance of surface waves and storms in shaping coral distribution and reef development

Decadal environmental ‘memory’ in a reef coral?

West sides of the coral Coelastrea aspera, which had achieved thermo-tolerance after previous experience of high solar irradiance in the field, were rotated through 180o on a reef flat in Phuket, Thailand (7o50´N, 98o25.5´E), in 2000 in a manipulation experiment and secured in this position. In 2010, elevated sea temperatures caused extreme bleaching in these corals, with former west sides of colonies (now facing east) retaining four times higher symbiont densities than the east sides of control colonies, which had not been rotated and which had been subject to a lower irradiance environment than west sides throughout their lifetime. The reduced bleaching susceptibility of the former west sides in 2010, compared to handling controls, suggests that the rotated corals had retained a ‘memory’ of their previous high irradiance history despite living under lower irradiance for 10 years. Such long-term retention of an environmental ‘memory’ raises important questions about the acclimatisation potential of reef corals in a changing climate and the mechanisms by which it is achieved