CORAL DISEASE &
PARROTFISH PREDATION RESEARCH

Principle Investigator:

Andy Bruckner
Coral Reef Ecologist
NOAA Fisheries
Office of Habitat Conservation
Coral Reef Conservation Program
andy.bruckner@noaa.gov

Background:

The first known occurrence of a disease outbreak at the FGBNMS (presumed to be white plague) was observed in February 2005. The disease was identified on multiple colonies of Montastraea faveolata, M. franksi, Diploria strigosa and Porites asteroides at East Flower Garden Bank (EFGB; Hickerson & Schmahl 2005). Because this was the first reported outbreak of a disease and the potential for substantial coral mortality, the Coral Disease and Health Consortium (CDHC) was asked to assist in determining the extent of the outbreak, possible causes, and impacts. In partnership with the FGBNMS, the CDHC pulled together a team of researchers to conduct a rapid response to characterize the event and collect samples for laboratory analysis.

During the first CDHC mission (which was delayed until April 2005 due to weather), Andy Bruckner observed signs of recent mortality on the species reported in February 2005, as well as additional species (Colpophyllia natans and Stephanocoenia intersepta) on both East and West Flower Garden Banks.  Affected colonies exhibited focal to multifocal lesions that initiated at the margins of the colony and progressively radiated inward; white recently exposed skeleton typically formed an irregular band up to 15 cm in width, with areas first affected becoming progressively colonized by filamentous algae and cyanobacteria.  Gross signs were similar to descriptions of white plague type II (Richardson et al., 1998), although rate of spread was considerably slower (e.g., 1-2 cm/week) and a bleached margin was absent. Unlike previously reported WP II outbreaks, diseased corals were first observed during periods of lowest waters temperature. In addition, by May 2005 prevalence had declined and tagged colonies showed minimal tissue loss.

Because of the unusual nature of this outbreak (e.g., the remote location of the Flower Gardens, high coral cover, low level of anthropogenic pressure, and healthy coral and fish communities), Andy felt that this was a critical location to monitor coral diseases and other biotic factors capable of killing coral.  

Recent increases in disease prevalence have been reported in deeper locations off Florida, Puerto Rico and the USVI. These have been  characterized by 1) rapid spread among colonies, 2) elevated rates of tissue loss in areas with high coral cover, 3) the dominant reef-building coral taxa (e.g., Montastraea spp.) experiencing the greatest mortality, and 4) the largest colonies of these species most severely affected.  High coral cover and close proximity of individual colonies, along with the vulnerable life history traits of these key reef-building corals (e.g., slow growth and low rates of recruitment) suggested that a disease outbreak at the FGBNMS could have devastating long-term consequences.

Since May 2005, Andy has been evaluating the prevalence and impacts of coral disease on dominant reef building corals found at the FGBNMS.  He is using belt transects (2 m X 30 m) to characterize coral population dynamics and coral condition. Along each transect, the species composition, coral size (maximum diameter and height measured to the nearest cm), condition (percent recent dead and percent long dead visually estimated from a planar view) and source of mortality (disease, predation or overgrowth by algae or invertebrate) for colonies 10 cm in diameter or larger were assessed.   In addition, multiple colonies with recent lesions are being monitored over time to document patterns of recovery/mortality.

In February 2006, a recurrence of a white-plague like syndrome was documented. This condition was recorded on a mean of 8% of all colonies examined, with up to 25% of the corals affected in localized areas.  Fortunately, by May, 2006 very few new infections were documented and colonies tagged in February had experienced minimal levels (1-10%) of partial mortality. However, Andy noticed a substantial increase in mortality from parrotfish predation and damselfish algal lawns (e.g., ridge mortality).  In some cases, colonies several meters wide and tall have been observed with recent lesions affecting 50-75% of their surface.  The extent of predation appears to vary seasonally and spatially for unknown reasons.

Research Focus:

Effects of stoplight parrotfish (Sparisoma viride) predation on the survival of star and brain coral populations and relationships with herbivore population abundance and fish pressure

Research Summary:

In addition to continued documentation of the white-plague-like condition, a major goal of Andy's ongoing research is to characterize the role of parrotfish predation (Sparisoma viride) as a community structuring agent, with emphasis on 1) the prevalence of focused biting by S. viride, including the number of coral species affected and frequency of biting; 2) effects of predation on coral growth and morphology, including the potential for regeneration of lesions created by the fish and extent of colony mortality;  3) dynamics of S. viride populations and relationships between levels of predation and fish density, structure (e.g., harem size), behavior, and coral species composition; and 4) relationships between coral diseases and the extent of predation.