Abstract
BackgroundMarine diseases are of increasing concern for coral reef ecosystems, but often their causes, dynamics and impacts are unknown. The current study investigated the epidemiology of Aplysina Red Band Syndrome (ARBS), a disease affecting the Caribbean sponge Aplysina cauliformis, at both the individual and population levels. The fates of marked healthy and ARBS-infected sponges were examined over the course of a year. Population-level impacts and transmission mechanisms of ARBS were investigated by monitoring two populations of A. cauliformis over a three year period using digital photography and diver-collected data, and analyzing these data with GIS techniques of spatial analysis. In this study, three commonly used spatial statistics (Ripley’s K, Getis-Ord General G, and Moran’s Index) were compared to each other and with direct measurements of individual interactions using join-counts, to determine the ideal method for investigating disease dynamics and transmission mechanisms in this system. During the study period, Hurricane Irene directly impacted these populations, providing an opportunity to assess potential storm effects on A. cauliformis and ARBS.ResultsInfection with ARBS caused increased loss of healthy sponge tissue over time and a higher likelihood of individual mortality. Hurricane Irene had a dramatic effect on A. cauliformis populations by greatly reducing sponge biomass on the reef, especially among diseased individuals. Spatial analysis showed that direct contact between A. cauliformis individuals was the likely transmission mechanism for ARBS within a population, evidenced by a significantly higher number of contact-joins between diseased sponges compared to random. Of the spatial statistics compared, the Moran’s Index best represented true connections between diseased sponges in the survey area. This study showed that spatial analysis can be a powerful tool for investigating disease dynamics and transmission in a coral reef ecosystem.
Highlights
Substantial impacts on marine populations and communities have been attributed to diseases of marine organisms [1,2]
Analysis of sizes at each time point showed that while diseased sponges were initially larger than healthy sponges (ANOVA: P = 0.02), by the final sampling time there was a trend towards diseased sponges being smaller than healthy sponges (P = 0.06)
The main loss in sponge biomass on the reefs seems to be related to periodic storm events, as Hurricane Irene caused a pronounced reduction in sponge biomass on both reefs in September 2011
Summary
Substantial impacts on marine populations and communities have been attributed to diseases of marine organisms [1,2]. ARBS has been recorded throughout the Caribbean at prevalence rates as high as 15% of the individuals within a population [9,18] This disease can result in partial or total mortality of sponges that it infects, and while it is able to spread through experimental contact, the main mechanism of transmission within a natural population remains unknown [18]. The current study investigated the epidemiology of Aplysina Red Band Syndrome (ARBS), a disease affecting the Caribbean sponge Aplysina cauliformis, at both the individual and population levels. Population-level impacts and transmission mechanisms of ARBS were investigated by monitoring two populations of A. cauliformis over a three year period using digital photography and diver-collected data, and analyzing these data with GIS techniques of spatial analysis. Hurricane Irene directly impacted these populations, providing an opportunity to assess potential storm effects on A. cauliformis and ARBS
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