Discerning the interacting effects of phytoplankton blooms and temperature anomalies on the relationship between algal symbionts of the genus Symbiodinium and their reef coral hosts in the Arabian Gulf

Abstract

Coral reefs are among the most threatened ecosystem worldwide, partly due to the sustained and continuing effects of global climate change. The coral from the Arabian/Persian Gulf (hereafter “the Gulf”) are exposed to several extreme environmental factors. This thesis reports on the understanding of how local climate factors modulate the tolerance of the algal symbionts to thermal stress in the Gulf. In situ measurements, remote sensing data and meteorological variables were used as tools to determine anomalies and trends of different environmental factors focusing on three regions within the southern Gulf, Delma (latitude 24.5208/longitude 52.2781), Saadiyat (lat. 24.599/long. 54.4215) and Ras Ghanada (lat. 24.8481/long. 54.6903) over the period from 1982 to 2015. A severe bleaching event affected coral communities off the coast of Abu Dhabi, UAE in August and September, 2012. In Saadiyat and Ras Ghanada reefs ~40% of the corals showed signs of bleaching whereas, only 15% of the corals were affected on Delma reef. The work presented in this thesis shows that, in spite of their proximity, there were differences in the severity of local bleaching between the sites (Ras Ghanada=34.48 °C, Saadiyat=34.55 °C, Delma= 35.05 °C). The result also suggests that phytoplankton density in Saadiyat durng 2012 bleaching event might have temporarily reduced certain nutrients, such as nitrate and phosphate, below average levels leading to a reduced availability of these essential nutrients to the corals. In the study regions, the seasonal chl-a cycle was characterised with a summer maximum and a winter minimum. The results also show that positive anomalies of dust are likely to be observed one to two months before the emergence of a phytoplankton bloom. This study shows that the combination of satellite observations and in situ measurements can help generate detailed insights into coral bleaching events. The 2010 bleaching event was accompanied by a phytoplankton anomaly that spread over a wider Gulf area. The thesis highlights the needs of integrating different observation platforms to establish an integrated monitoring water quality system in the Gulf, in particular around coral reefs.

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ORCID for Joerg Wiedenmann: orcid.org/0000-0003-2128-2943

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