Disease in the Caribbean sea fan coral Gorgonia ventalina

Sea fan aspergillosis is one the best characterize coral affliction. However, several fundamental issues relating this disease remain elusive. The presence of the presumably causative agent, A. sydowii in healthy fans, or of fungal biomass associated to the corals, has never been studied before, at the microbiological or histological level. Neither have differential impacts of purpling, tissue necrosis, galls and tumors been described.;In chapter 1 we developed a sampling strategy for estimating cultivable fungal diversity in Gorgonia ventalina. The best way to estimate fungal diversity is the sampling of small tissue fragments combined with homogenization of tissue fragments. Both techniques revealed different fungi.;In chapter 2 we describe the cultivable fungal community of 203 healthy and diseased sea fans colonies. At least 37 fungal species from 15 general were isolated from sea fans. Fungal diversity and species richness was higher in healthy fans when compared to diseased one. The fact that no single fungi was exclusively associated to healthy or diseased sea fans and that A. sydowii was never isolated from diseased colonies suggest that aspergillosis might be caused by other microorganisms.;In Chapter 3 we document the main causes of sea fan mortality and compared the growth rates among small, medium and large sea fans of different healthy conditions. Detachment occurred in all sea fan size classes and health conditions, but was significantly higher in small colonies. Mortality due to disease was exclusively observed in small fans. Growth rate was independent of colony size and health condition. The interaction between colony size and health condition significantly influence the growth rate of small diseased fans. High mortality and lower growth rates among small fans may have serious repercussions at the population level because it may delay or prevent the transition of small colonies to reproductively active stages.;In chapter 4 using microwave technology we develop a histological procedure for sea fans that reduced the time of tissue fixation, dehydration, infiltration, embedding, staining and slicing from more than 3 days to 4 hours.;In chapter 5 we fail to induce disease signs after inoculating pure cultures of A. sydowii and grafting diseased tissues to healthy ones. These two results suggest that A. sydowii is not always pathogenic to sea fans, and that contact between diseased and healthy tissue is not sufficient to induce disease signs. Histological examination of healthy and diseased fans revealed the presence of fungal hyphae, demonstrating the ubiquitous nature of fungi in sea fans. However, ergosterol quantification revealed that fungal biomass was higher in healthy compared to diseased tissues. This suggest that sea fans' immune response is generalized, killing or suppressing all fungi in the affected area, whether beneficial or harmful or that infectious agent(s) (fungi, bacteria, protozoa among others) are outcompeting the other microorganisms normally found in sea fan.