Causes of Coral Mortality

Like the herbivory scenario, much of what reef ecologists believe about coral mortality is influenced by the experience at Discovery Bay. The devastation of A. cervicornis from Hurricane Allen and collateral mortality from pomacen-trids and corallivorous invertebrates (Porter et al. 1981; Woodley et al. 1981; Knowlton et al. 1981; Knowlton, Lang, and Keller 1990) was followed by some damage from Hurricane Gilbert in 1988 (Woodley 1989; Hughes 1994). In 1989 Hurricane Hugo damaged reefs in the U.S. Virgin Islands (Edmunds and Witman 1991; Hubbard et al. 1991; Rogers, McLain, and Tobias 1991; Bythell, Bythell, and Gladfelter 1993; Aronson, Ebersole, and Sebens 1994). These studies and other ecological and geological work (e.g., Ball, Shinn, and Stockman 1967; Perkins and Enos 1968; Stoddart 1974; Rogers, Suchanek, and Pecora 1982; Mah and Stearn 1986; Fenner 1991; Kobluk and Lysenko 1992; Blair, Mcintosh, and Mostkoff 1994; Blanchon 1997; Blanchon, Jones, and Kalbfleisch 1997) led to the prevailing opinion that hurricanes are a primary cause of present and past coral mortality in the Caribbean.

Hurricanes have been important at some localities, but they do not explain recent patterns of coral mortality in much of the region. Damage from hurricanes is patchy on many spatial scales (Hubbard et al. 1991; Rogers 1993b; Steneck 1994). Some areas of the Caribbean, such as Trinidad, Costa Rica, and Panama, receive virtually no hurricanes, while others, including Jamaica, are struck frequently (Neumann et al. 1987; Woodley 1992; Tremel, Colgan, and Keevican 1997). Coral populations often suffer more extensive damage from chronic disturbances (Rogers 1993b). In Belize, for example, the deeper, A. cervicornis-dominated spur-and-groove zone lost cover beginning in the 1980s, as described previously. Hurricane Greta is known to have damaged the fore reef in 1978 (Rutzler and Macintyre 1982;Kjerfve and Dinnel 1983); however, Hurricane Greta was not responsible for the mass destruction of A. cervicornis populations in the 1980s. White-band disease (WBD) was the principal cause of A. cervicornis mortality.

WBD is a presumed bacterial infection that is specific to Acropora spp. (Antonius 1981; Gladfelter 1982; Peters 1993). Cases of WBD are recognizable as segments of bare skeleton, sometimes bordered by narrow bands of disintegrating, necrotic coral tissue, on otherwise healthy-looking, brown Acropora branches. The "bands" of disease spread along the branches, generally from base to tip, and eventually kill entire colonies. The etiology of WBD and the causes of outbreaks are poorly understood, and recent reports suggest that there are several varieties ofthe disease with different symptoms (Peters 1993,1997; Antonius 1995;Peters and McCarty 1996; Santavy and Peters 1997; Richardson 1998).

Despite the difference in appearance upon careful examination, WBD in Caribbean Acropora spp. has often been mistaken for coral bleaching, which has received considerably more attention in the literature. Dramatic bleaching events at times of elevated sea temperature and ultraviolet radiation have caused mass mortalities of corals in the Indo-Pacific, although bleaching-related mortality has until recently been more limited in the Caribbean (Jaap 1979; Brown 1987, 1997; Ogden and Wicklund 1988; Glynn 1990b, 1993; Williams and Bunkley-Williams 1990; D'Elia, Buddemeier, and Smith 1991; Glynn and Colgan 1992; Lang et al. 1992; Fitt et al. 1993; Shick, Lesser, and Jokiel 1996; Aronson et al. 2000). An important reason for the current interest in bleaching is that global warming may increase its frequency and extent (Smith and Buddemeier 1992; Glynn 1996).

Acropora spp. will bleach under thermal stress (Cortés 1994). Other sources of Acropora mortality include predation by corallivores (Knowlton et al. 1981; Knowlton, Lang, and Keller 1990; Tunnicliffe 1983), nutrient loading (Weiss and Goddard 1977; Lewis 1984; Bell and Tomascik 1994), sedimentation (Rogers 1990; Cortés 1994), and, in Florida and the Bahamas, cold water stress (Davis 1982; Porter, Battey, and Smith 1982; Roberts et al. 1982; Burns 1985). Although quantitative data are generally lacking, it is becoming apparent that WBD epizootics have been the primary cause of the recent mortality of A. cer-vicornis and A. palmata over wide areas of the Caribbean (Rogers 1985; Wells 1988; Sheppard 1993; table 9.2).

Stands of A. cervicornis killed by WBD generally collapse due to weakening of the skeletons by bioerosion, and the result is large fields of A. cervicornis rubble. A. palmata is more robust, and stands of this species remain in growth position for longer periods after they have been killed, as has been observed in Anguilla, Belize, the Florida Keys, St. Croix, and elsewhere. Dead stands of A. palmata are then leveled by storms (Bythell et al. 1989; Hubbard et al. 1991). Hurricane damage has clearly been a more localized cause of Acropora mortality over the past few decades (table 9.3).

Compared with Acropora spp., the mortality of massive corals has been more variable. Colonies of M. annularis complex have been affected by hurricanes, bleaching, and disease (Rützler, Santavy, and Antonius 1983; Porter et al. 1989; Edmunds 1991; Edmunds and Witman 1991; Fitt et al. 1993; Meesters and Bak 1993; Kuta and Richardson 1996), but large stands of M. annularis can still be observed throughout the region (e.g., Shinn et al. 1989; Precht 1993; Curran et al. 1994; Edmunds and Bruno 1996; Burke et al. 1998; McClanahan and Muthiga 1998).

TABLE 9.2. Reports of White-Band Disease as the Primary Cause or an Important Cause of Acropora Mortality on Caribbean Reefs over the Past Few Decades"

Location (habitat) Species Affected Time Period Source

Anguilla

Bahamas

Andros Barrier Reef

(fr) A. New Providence Island

(fr) A. San Salvador Island

cervicornis palmatac cervicornis cervicornis palmatac cervicornis palmata cervicornis

Lee Stocking Island, Exumas

Belize

Central Shelf Lagoon

British Virgin Islands (rc/fr)

Cayman Islands Grand Cayman (fr)

Colombia

cervicornis palmata cervicornis cervicornis palmatac

A. cervicornis

A. cervicornis

A. palmata A. cervicornis

A. palmata

A. cervicornisd

Acropora ssp.b

A. palmatab,d A. cervicornisb,d

1980s—90s Sheppard et al. 1995

1980s S. Cove, personal communication

1980s S. Cove, personal communication

1980s S. Cove, personal communication

1980s S. Cove, personal communication

1980s S. Cove, personal communication

1980s S. Cove, personal communication

1980s Shinn 1989

1980s Shinn 1989; Curran et al. 1994

A. cervicornisP 1980s-90s J. C. Lang, personal communication

1980s-90s Precht, unpublished observation

1980s-90s Precht, unpublished observation

1980s-90s Precht, unpublished observation

1980s-90s Precht, unpublished observation

1980s-90s Aronson and Precht, unpublished observation

1980s Precht, unpublished observation

1986-90 Aronson and Precht 1997

1980s-90s Precht, unpublished observation

1980s-90s Precht, unpublished observation

1980s-90s Bythell and Sheppard 1993

1980s

Woodley et al. 1997

1970s-90s Garzón-Ferreira and Kielman 1994

1970s—90s Zea et al. 1998 1970s—90s Zea et al. 1998

(Continued on next page)

TABLE 9.2. (continued)

Location (habitat)

Species Affected Time Period

Source

Cuba

Dominican Republic (fr)

A. palmatac 1980s-90s P.M. Alcolado, personal comm unication

A. cervicornisf 1980s-90s P.M. Alcolado, personal communication

A. cervicornis" 1980s-90s M. Vega, personal communication

Florida Reef Tract

Biscayne National Park (2 reefs), Northern Keys (1 reef), and Looe Key (1 reef)

Northern Keys (4 reefs) (fr)

Jamaica

Discovery Bay (fr)

Netherlands Antilles (rc/fr) (fr)

Panama

San Blas Islands (pr)

Trinidad and Tobago Tobago (rc/fr)

U.S. Virgin Islands St. Croix: Buck Island (rc/fr) (fr) St. John (rc/fr)

A. palmatad

A. cervicornis

A. cervicornisd

A. palmatac A. cervicornis

A. palmatad A. cervicornisd

1980s Porter and Meier 1992;

Porter et al. 1993

1980s Jaap, Halas and Muller 1988;

Shinn, et al. 1989

1980-88 Knowlton, Lang, and Keller 1990; Tunnicliffe 1983

1970s-80s Bak and Criens 1981 1970s-80s Bak and Criens 1981;

van Duyl 1982, 1985; Wells 1988

1990s Bruckner et al. 1997

1990s Bruckner and Bruckner 1997

Acropora spp.b 1970s-80s Ogden and Ogden 1994 A. palmata 1980s Laydoo 1984

A. palmata A. cervicornis

A. palmatad

1976-85 Gladfelter 1982; Bythell et al. 1989 1976-85 Bythell et al. 1989

1980s-90s Rogers 2000

a Habitat abbreviations: rc, reef crest; fr, fore reef; pr, patch reef; l, lagoon; g, reef habitats in general. No superscript, WBD as principal cause of widespread mortality. See Rogers (1985) and Wells (1988) for earlier reports of the presence of WBD around the Caribbean. b WBD as probable cause of widespread mortality. cWBD as cause of some mortality. d WBD associated with other sources of coral mortality.

TABLE 9.3. Reports of Hurricane Damage as the Primary Cause or an Important Cause of Acropora Mortality on Caribbean Reefs over the Past Few Decades."

Location (habitat) Species Affected Year (Storm) Source

Belize

Tumeffe Islands

(fr) A. cervicornis

Barrier Reef leeward of Turneffe Islands

Peter Douglas Cay

Carrie Bow Cay (rc)

Cayman Islands Grand Cayman (rc/fr)

Colombia San Andrés (l/pr)

Florida Reef Tract

Biscayne National Park

A. palmata A. cervicornis

A. cervicornisc

A. palmata

A. cervicornisc

A. palmatac

A. palmatab? A. cervicornisc?

1961 (Hattie) 1961 (Hattie)

1961 (Hattie) 1961 (Hattie)

1961 (Hattie)

1978 (Greta)

1978 (Greta)

1988 (Gilbert)

1988 (Joan) 1961 (Hattie)

Stoddart 1963 Stoddart 1963

Stoddart 1963 Stoddart 1963

Stoddart 1963

Highsmith et al. 1980;

Kjerfve and Dinnel 1983 Highsmith et al. 1980; Kjerfve and Dinnel 1983

Blanchon et al. 1997

Zea et al. 1998 Zea et al. 1998

Florida Reef Tract

Biscayne National Park

(pr)

A. palmatac

1992 (Andrew)

Rogers 1994; Lirman and

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