Coral bleaching in Arabian Gulf modulated by shamal winds, say NYUAD researchers

Coral bleaching in Arabian Gulf modulated by shamal winds, say NYUAD researchers

ABU DHABI, 29th April, 2019 (WAM) -- Corals in the Arabian Gulf are not immune to extreme heat events associated with global warming that are impacting coral reefs elsewhere in the world, researchers at New York University Abu Dhabi have revealed.

Using reef-based temperature loggers and mathematical models, research published in the journal Frontiers in Marine Science, showed that coral in the Gulf - the most thermally tolerant in the world - has become more vulnerable to bleaching events when weak summer winds do not cool the water's surface.

Without these winds, which are known as shamal (northerly) winds, the Gulf’s shallow waters can reach temperatures considered lethal to coral for extended periods in summer, according to the study’s authors, NYUAD Associate Professor of Biology John Burt, and NYUAD Associate Professor of Mathematics Francesco Paparella.

As global warming trends continue, they theorise that Gulf coral reefs may continue to be at risk of bleaching if climate change affects the Indian Ocean monsoon, which underpins the summer shamal winds in this region. Corals turn white or bleach when they become stressed by heat or pollution and expel a marine alga called zooxanthellae, which live inside their tissues. This alga provides the corals with their colour and is an easy food supply thanks to photosynthesis, which gives the corals 90 percent of their energy, allowing them to grow and reproduce.

Burt and Paparella collected and analysed data from three major coral habitats located in the Abu Dhabi waters of the southern Gulf - Saadiyat Island, Ras Ghanada, and Dhabiya reefs. All three sites were located at similar depths and distances from shore. These sites are among the most abundant coral communities in the southern Gulf.

Their mathematical model, which describes the energy flowing through the water column, was able to reproduce the observed data and unveiled that during the summer months Shamal winds can achieve in excess of 300 watt every square metre of evaporative cooling - a cooling power rivalling that of most air conditioning systems.

Coral bleaching events continue to occur with increasing frequency and severity both globally and within the Gulf as the world’s seas warm, pushing corals beyond the thermal thresholds to which they have evolved. In the Gulf, there has been an overall warming trend since the 1970s, with some areas warming at rates three times the global average.

"Coral bleaching events have been occurring with increasing frequency in the Arabian Gulf in recent decades," said Burt, "and the summer of 2017 was among the most catastrophic on record."

In collaboration with the Environment Agency Abu Dhabi, Burt and his team showed that nearly three-quarters of coral across the southern Gulf was lost to bleaching-related mortality and a subsequent disease outbreak between summer 2017 and spring 2018.