Dana E. Williams

Coral disease outbreak at Navassa, a remote Caribbean island

In November 2004, a high prevalence of coral disease was observed at several sites around Navassa, an uninhabited Caribbean island between Haiti and Jamaica. At least fifteen mounding and foliaceous scleractinian species were affected with ‘white disease’ signs. Coral disease incidence was observed to be absent in quantitative surveys in 2002, but in 2004 average prevalence (i.e., % of colonies) of active disease ranged up to 15% and an additional 19% prevalence of colonies with patterns of recent mortality consistent with disease. Large and/or Montastraea spp. colonies were disproportionately affected and the anticipated loss of these large, reef-building colonies will impact coral community structure. One or more potential factors may influence the initiation and persistence of disease outbreak conditions at Navassa including recent hurricane disturbance, regional patterns of increasing disease impact in deep or remote Caribbean reefs, or vectoring of disease by the corallivorous worm, Hermodice carunculata.

Disease dynamics and potential mitigation among restored and wild staghorn coral, Acropora cervicornis

The threatened status (both ecologically and legally) of Caribbean staghorn coral, Acropora cervicornis, has prompted rapidly expanding efforts in culture and restocking, although tissue loss diseases continue to affect populations. In this study, disease surveillance and histopathological characterization were used to compare disease dynamics and conditions in both restored and extant wild populations. Disease had devastating effects on both wild and restored populations, but dynamics were highly variable and appeared to be site-specific with no significant differences in disease prevalence between wild versus restored sites. A subset of 20 haphazardly selected colonies at each site observed over a four-month period revealed widely varying disease incidence, although not between restored and wild sites, and a case fatality rate of 8%. A tropical storm was the only discernable environmental trigger associated with a consistent spike in incidence across all sites. Lastly, two field mitigation techniques, (1) excision of apparently healthy branch tips from a diseased colony, and (2) placement of a band of epoxy fully enclosing the diseased margin, gave equivocal results with no significant benefit detected for either treatment compared to controls. Tissue condition of associated samples was fair to very poor; unsuccessful mitigation treatment samples had severe degeneration of mesenterial filament cnidoglandular bands. Polyp mucocytes in all samples were infected with suspect rickettsia-like organisms; however, no bacterial aggregates were found. No histological differences were found between disease lesions with gross signs fitting literature descriptions of white-band disease (WBD) and rapid tissue loss (RTL). Overall, our results do not support differing disease quality, quantity, dynamics, nor health management strategies between restored and wild colonies of A. cervicornis in the Florida Keys.

Reef-scale trends in Florida Acropora spp. abundance and the effects of population enhancement

Since the listing of Acropora palmata and A. cervicornis under the US Endangered Species Act in 2006, increasing investments have been made in propagation of listed corals (primarily A. cervicornis, A. palmata to a much lesser extent) in offshore coral nurseries and outplanting cultured fragments to reef habitats. This investment is superimposed over a spatiotemporal patchwork of ongoing disturbances (especially storms, thermal bleaching, and disease) as well as the potential for natural population recovery. In 2014 and 2015, we repeated broad scale (>50 ha), low precision Acropora spp. censuses (i.e., direct observation by snorkelers documented via handheld GPS) originally conducted in appropriate reef habitats during 2005–2007 to evaluate the trajectory of local populations and the effect of population enhancement. Over the decade-long study, A. palmata showed a cumulative proportional decline of 0.4 –0.7x in colony density across all sites, despite very low levels of outplanting at some sites. A. cervicornis showed similar proportional declines at sites without outplanting. In contrast, sites that received A. cervicornis outplants showed a dramatic increase in density (over 13x). Indeed, change in A. cervicornis colony density was significantly positively correlated with cumulative numbers of outplants across sites. This study documents a substantive reef-scale benefit of Acropora spp. population enhancement in the Florida Keys, when performed at adequate levels, against a backdrop of ongoing population decline.

White rings on the threatened coral, Acropora palmata, associated with foraging activity of the honeycomb cowfish, Acanthostracion polygonius (Ostraciidae)

Monitoring of the threatened Caribbean coral, Acropora palmata, in the upper Florida Keys, USA, since 2002, has revealed annular lesions of unknown origin. On September 13, 2012, a honeycomb cowfish (Acanthostracion polygonius) was observed creating annular lesions on A. palmata colonies at Molasses Reef in the Florida Keys (Fig. 1; video in Electronic Supplemental Material). A. polygonius typically preys on tunicates, alcyonarians, sponges, small crustaceans and gastropods (Randall 1967), and is not known to be a corallivore (Cole et al. 2008). To our knowledge, this is the first report of this species creating lesions on A. palmata. Lesions created by A. polygonius are distinct from other known fish bites (Bruckner 2007). They appear as a white ring with apparently healthy, intact tissue in the center, and are approximately 2 cm in diameter (Fig. 2). The ring appearance results from partial removal of tissue from the sides of the corallites and coenosteum, leaving polyps within the ring intact. There is no apparent mechanical damage to the corallites. As healing progresses, the ring gradually becomes a ring of pale tissue until zooxanthellae are recovered. Lesions heal rapidly (less than 6 weeks) and do not contribute to significant losses of live tissue. It is uncertain whether the fish is actively feeding on the coral tissue or the lesion is a by-product of the fish’s foraging behavior. Although these lesions are rare, affecting 6 ± 4 % (mean ± SD) of colonies in the Florida Keys, their occurrence is typically clustered, affecting nearly 100 % of colonies at some sites. Of our 24 monitoring sites in Florida, colonies are consistently affected at three sites, while rings were rare to absent at the remaining sites. Through A. palmata monitoring in other locations: Curaçao (since 2006), Navassa (since 2006), British Virgin Islands (2006–2007), Puerto Rico (2007–2009), and US Virgin Islands (2007–2009), we have observed these annular lesions to have a similar patchy occurrence but lower average prevalence than in the Florida Keys.