Diseases, Harmful Algae Blooms (HABs) and Their Effects on Gulf Coral Populations and Communities


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Diseases, Harmful Algae Blooms (HABs) and Their Effects on Gulf Coral Populations and Communities

Gulf coral populations exist in a harsh environment, which only allows a small subset of the typical Indo-Pacific fauna and flora to persist and/or form viable populations (Sheppard and Sheppard 1991; Sheppard et al. 1992; Samimi-Namin and van Ofwegen 2009; Chaps. 11 and 12 ). Environmental factors have been identified as the major killers of corals and these factors regulate population dynamics and coral reef community structure (Chaps. 2, 5, 10 and 16 ). Among these, extreme temperature variability, salinity variability and turbidity (as a result of coastal construction, Chap. 16 ) have been isolated as prime killers.

However, a host of biological agents are also capable of wreaking havoc on Gulf coral populations. In the Gulf, several of the major invertebrate nemeses of corals that exist in the Indian Ocean are absent. The crown-of-thorns starfish (COTS) Acanthaster planci has only ever been reported in two individuals from a single locality in Iran (Price and Rezai 1996 ) , although this may be changing as COTS appear to be spreading from the Gulf of Oman into the Gulf, with new records from the Musandam Peninsula near the Straits of Hormuz ( Mendonça et al. 2010 ) . Furthermore, the coralivorous snail Drupella cornus, that can form equally devastation outbreaks, does not occur and the local Coralliophila spp. have not yet been reported to cause signifi cant impacts on corals by predation as they do, for example, in the Caribbean.

Other biological agents do however take a significant toll on Gulf coral populations. In particular, coral diseases are one of the most destructive agents responsible for recent losses of coral. The Gulf harbors a unique disease, Arabian Yellow Band (AYB) that has a different dynamics from diseases with similar names observed elsewhere.

Three other diseases have also been described (Riegl 2002 ; Benzoni et al. 2010 ; Samimi-Namin et al. 2010 ) , and several uncharacterized syndromes are also known. While some diseases have been observed to be unusually common and have unusual dynamics (Riegl 2002 ) , the 2010 bleaching event in the SE Gulf appears to have triggered locally significant outbreaks of a white syndrome that has taken a signifi cant toll on UAE coral populations, similar to such phenomena in the Caribbean and Pacific (Bruno et al. 2007 ; Brandt and McManus 2009 ; Eakin et al. 2010 ; Bruckner and Hill 2009 ).

Highly destructible biological agents are Harmful Algae Blooms (HABs, or also called Red Tides) that have caused significant mortality lately both inside the Gulf (Samimi- Namin et al. 2010 ) and the Arabian Sea (Bauman et al. 2010 ; Foster et al. 2011 ) . HABs have been occurring in all parts of the Gulf but appear to become more frequent, more lethal and more widespread, which is causing concern for reefs (Sheppard et al. 2010 ; Chap. 16 ).

This chapter describes the known coral diseases from the Gulf (Fig. 7.1 ) and explores their dynamics using simple mathematical models of the SIR (susceptible-infectedrecovered) type (Anderson and May 1979 ; Mena-Lorca and Hethcote 1992 ) . We explore the role of coral diseases in regulating populations of reef building corals and why some diseases are more frequent and persistent than others. Based on the outcomes of the models, we are able to speculate why, with increased ocean warming due to climate change (Sheppard and Loughland 2002 ) diseases have become more frequent and may become important agents that determine future Gulf coral populations structure and community dynamics much like the role of environmental stresses on reefs in the past. This chapter also discusses Harmful Algae Blooms and their importance in coral mortality dynamics in the Gulf.

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