Localized outbreaks of coral disease on Arabian reefs are linked to extreme temperatures and environmental stressors

Abstract

The Arabian Peninsula borders the hottest reefs in the world, and corals living in these extreme environments can provide insight into the effects of warming on coral health and disease. Here, we examined coral reef health at 17 sites across three regions along the northeastern Arabian Peninsula (Persian Gulf, Strait of Hormuz and Oman Sea) representing a gradient of environmental conditions. The Persian Gulf has extreme seasonal fluctuations in temperature and chronic hypersalinity, whereas the other two regions experience more moderate conditions. Field surveys identified 13 coral diseases including tissue loss diseases of unknown etiology (white syndromes) in Porites, Platygyra, Dipsastraea, Cyphastrea, Acropora and Goniopora; growth anomalies in Porites, Platygyra and Dipsastraea; black band disease in Platygyra, Dipsastraea, Acropora, Echinopora and Pavona; bleached patches in Porites and Goniopora and a disease unique to this region, yellow-banded tissue loss in Porites. The most widespread diseases were Platygyra growth anomalies (52.9% of all surveys), Acropora white syndrome (47.1%) and Porites bleached patches (35.3%). We found a number of diseases not yet reported in this region and found differential disease susceptibility among coral taxa. Disease prevalence was higher on reefs within the Persian Gulf (avg. 2.05%) as compared to reefs within the Strait of Hormuz (0.46%) or Oman Sea (0.25%). A high number of localized disease outbreaks (8 of 17 sites) were found, especially within the Persian Gulf (5 of 8 sites). Across all regions, the majority of variation in disease prevalence (82.2%) was associated with the extreme temperature range experienced by these corals combined with measures of organic pollution and proximity to shore. Thermal stress is known to drive a number of coral diseases, and thus, this region provides a platform to study disease at the edge of corals' thermal range.

A comparative baseline of coral disease across the central Red Sea

“…There were differences in disease prevalence among coral genera with Acropora, Favites/Dipsastraea and Millepora having a higher disease prevalence than expected based on their abundance in the field. This is consistent with other regions of the world where disease susceptibility differs across families or genera [40,55,64,71,72]. Our study differed from other regions, in that, over half of the coral genera within transects had signs of disease (16 out of 30 coral genera).…”

“…at three sites. Porites bleached patches have been reported from the Persian Gulf and Oman Sea [64], New Caledonia [53], and the GBR [65]. This study now extends this disease to the Red Sea (biogeographic range extension).…”

Annual outbreaks of coral disease coincide with extreme seasonal warming

“…Relatively high prevalence was also recorded in Siderastrea (14%, n = 7) and Favites (33%, n = 3), but these estimates are based on only a few individual colonies present within the survey area (Table S3). The community-wide prevalence of whitesyndrome did not differ between Saadiyat and Sir Bu Nair reefs (generalised linear model, z = 0.85, p = 0.40), and although we were only able to survey the Bu Nair sites in August 2015, very similar levels of white syndrome were recorded at the same sites in August 2016 (Aeby et al 2020).…”

“…1 of 14 tagged and resurveyed colonies at Saadiyat; see Howells et al 2016b). Other tissue loss diseases also impact corals in the southern Gulf, including Porites yellow-banded tissue loss and black band disease (this study; Riegl 2002;Aeby et al 2020). Whole and partial mortality of coral colonies in the southern Gulf from annual disease and frequent bleaching events (1996,1998,2002,2007,2010,2011,2012,2017) has resulted in widespread losses of coral cover and a shrinking of remaining colonies, with negative implications for reef accretion and self-recruitment from sexual reproduction (Bauman et al 2013b;Riegl and Purkis 2015;Riegl et al 2017;Burt et al 2019).…”

“…Black band disease was also only observed at Saadiyat below 0.5% prevalence, and other signs of compromised health (scars from Drupella snails, unknown scars, pigmentation responses, cyanobacteria, and algae interactions) were typically below 0.5% prevalence at either Saadiyat or Sir Bu Nair. Spatial patterns and drivers of coral health and disease at our study reefs and the wider Arabian coastline (southern Persian Gulf to the northern Oman Sea) are described in Aeby et al (2020).…”