Corals in the Arabian Gulf, the most thermally tolerant in the world, are not immune to extreme heat events associated with global warming that are impacting coral reefs elsewhere in the world. Using reef-based temperature loggers and mathematical models, researchers at NYU Abu Dhabi showed that coral in the Gulf become more vulnerable to bleaching events when weak summer winds don’t cool the water surface, according to research published in the journal Frontiers in Marine Science.
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 theorize 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 color and is an easy food supply thanks to photosynthesis, which gives the corals 90% of their energy, allowing them to grow and reproduce.
Burt and Paparella collected and analyzed data from three major coral habitats located in the Abu Dhabi waters of the southern Gulf: Saadiyat Island, where NYUAD is located, 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 meter 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 1970’s, 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 (EAD), 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. The results of that study were recently published in the journal Coral Reefs. “With our collaborators at EAD we continue to monitor these reefs to look for signs of long-term recovery,” said Burt. The NYUAD-EAD team are currently in the field conducting their third set of reef surveys since the 2017 bleaching event.
Coral reefs in the region are incredibly biologically valuable as they are the most biodiverse ecosystem in arid nations that occupy the area. They also represent an important economic resource for coastal populations by serving as foraging and nursery grounds for a wide variety of commercially important fish species. Many of the most important coral reefs in Abu Dhabi are guarded within marine protected areas established by EAD. “The success of conservation efforts depends crucially on understanding how the environment works. NYUAD’s expertise on environmental mathematical modelling will be a tremendous asset for planning, managing, and assessing environmental actions,” said Paparella.
The researchers are now exploring the role that wind-driven cooling may play on coral reefs in the Red Sea, north-western Australia, and other areas.
