Abstract
Coral bleaching can be induced by many different stressors, however, the most common cause of mass bleaching in the field is high sea temperatures (SST). Here, we describe an unusual bleaching event that followed very calm sea conditions combined with higher than average sea surface temperatures (SST). Patterns of mortality differed from typical thermal bleaching in four ways: 1) mortality was very rapid; 2) the suite of species most affected was different; 3) tissue mortality in Acropora spp. was often restricted to the center of the colony; 4) the event occurred early in the summer. The two weeks prior to the event included 8 days where the average wind speed was less than 3 ms -1. In addition, SSTs in the weeks preceding this event were 1.0-1.5°C higher than the mean for the last 30 years. We hypothesize that the lack of water movement induced by low wind speeds combined with high SST to cause colonies anoxic stress resulting in this unusual bleaching event.
Highlights
Coral bleaching is a generalized response that can be induced by many different stressors[1,2,3]
We identify a number of characteristic features of this doldrums bleaching that allow it to be distinguished from thermal bleaching in the field
Mean daily sea surface temperatures (SSTs) in the month preceding the second survey were 1.0–1.5°C higher than the mean for the previous 30 years (Table 3). This bleaching event was different to typical thermal bleaching in a number of important ways
Summary
Coral bleaching is a generalized response that can be induced by many different stressors[1,2,3]. Whilst the most common cause of large scale bleaching on coral reefs is unusually high sea surface temperatures (SSTs)[4,5], prolonged periods of calm weather, known as the doldrums, have been associated with mass bleaching events in the Caribbean[6,7] and the Indo-Pacific[8,9,10]. Temporal patterns are apparent with most high temperature induced mass bleaching events generally occurring towards the end of the summer months[18,19]. Any change in this predictable bleaching ecology suggests an alternative cause (i.e., not thermal stress) for a given bleaching event
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