MEPS 343:123-130 (2007)  -  DOI: https://doi.org/10.3354/meps06937

ABSTRACT: It has been hypothesized that excess nitrogen (N) contributes to coral reef decline by exacerbating the impact of disease. We tested the relationship between N concentration and the prevalence and severity of aspergillosis of the sea fan coral Gorgonia ventalina at 9 reefs along the Florida Keys Reef Tract. Quarterly water quality data, averaged over 1 and 4 yr prior to a disease survey, were used to examine whether aspergillosis dynamics reflected short- or long-term N concentrations. A positive relationship was detected between prevalence of aspergillosis and long-term total nitrogen (TN) concentration; in contrast, disease severity was positively related to the ratio between dissolved inorganic nitrogen and total phosphate (DIN:TP) over both short- and long-terms. These results may reflect the differential influence of N on the host and pathogen. We also tested whether N isotope analysis (δ¹⁵N) of sea fan coral tissue and skeleton could be used to assess the relative exposure to anthropogenic N inputs and its impact on disease. There was no relationship between δ¹⁵N and aspergillosis (either prevalence or severity). Furthermore, there was no relationship between δ¹⁵N and environmental concentrations of N. It is possible that the source of N (e.g. anthropogenic) does not affect the dynamics of sea fan aspergillosis, or that the δ¹⁵N signatures were suppressed by agricultural effluents and other N sources, thus confounding our analyses with disease.

KEY WORDS: Sea fan coral · Gorgonia ventalina · Water quality · Aspergillosis · Disease · Nitrogen · δ¹⁵N