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

Lisa M Wedding,David Abrego,Thierry Work,Emily Howells,John A Burt,Gareth J Williams,Monica Moritsch,Greta Smith Aeby,Jamie M Caldwell

doi:10.1007/s00338-020-01928-4

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.

Highlights

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
While coral disease prevalence has been quantified in many regions across the Indo-Pacific (Willis et al 2004; Aeby et al 2008, 2011a, 2015; Haapkylaet al. 2009; Vargas-Angel 2009; Williams et al 2011b), we know little about the levels and types of coral disease on reefs in many other regions, including around the Arabian Peninsula (Riegl et al 2012)
No significant differences among regions were found for colony densities (Kruskal–Wallis, X2 = 0.2, df = 2, p = 0.89) or coral cover (Kruskal–Wallis, X2 = 5.3, df = 2, p = 0.07), but the number of coral genera differed significantly among regions (Kruskal–Wallis, X2 = 8.8, df = 2, p = 0.01) with sites in the Persian Gulf having the lowest number of coral genera compared to sites within the Strait of Hormuz or Oman Sea (Table 2)

Summary

Introduction

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. The Persian/Arabian Gulf (hereafter called the Persian Gulf) and Arabian Sea host fringing and patch reefs with over 25 coral genera documented (Coles 2003) These coral species, typical of Indo-Pacific fauna, represent a hardy subset of corals that are able to exist under demanding environmental conditions such as extreme temperature and salinity fluctuations (Riegl et al 2012). Its shallow depth and restricted water exchange with the wider Indian Ocean result in large seasonal fluctuations in ocean temperatures, 15 °C–36 °C (John et al 1990) and chronic hypersalinity ([ 40 ppt) (Vaughan and Al-Mansoori 2019) These extremes in temperature and salinity create stressful conditions that control the distribution and diversity of coral reef species (Bauman et al 2013). The Strait of Hormuz and Oman Sea have wider connections with the larger Indian Ocean, and so, coral reefs exist in less extreme environments with temperatures ranging from 23 to 30 °C there are regional exceptions associated with seasonal monsoons and upwelling events (Claereboudt 2019) and salinities averaging 37 ppt (Pous et al 2004)

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