Pathological effects of cyanobacteria on sea fans in southeast Florida

A combined diagnostic approach for the investigation of lesions resembling aspergillosis in Caribbean sea fans (Gorgonia spp.)

Aspergillosis of gorgonian sea fans is a Caribbean-wide disease characterized by focal, annular purple pigmentation with central tissue loss. We applied a holistic diagnostic approach including histopathology and a combination of culture and direct molecular identification of fungi to evaluate these lesions with the goal of determining the diversity of associated micro-organisms and pathology. Biopsies were collected from 14 sea fans without gross lesions and 44 sea fans with lesions grossly consistent with aspergillosis in shallow fringing reefs of St. Kitts. Histologically, the tissue loss margin had exposure of the axis and amoebocyte encapsulation with abundant mixed micro-organisms. Polyp loss, gastrodermal necrosis, and coenenchymal amoebocytosis were at the lesion interface (purpled area transitioning to grossly normal tissue) with algae (n = 21), fungus-like hyphae (n = 20), ciliate protists (n = 16), cyanobacteria (n = 15), labyrinthulomycetes (n = 5), or no micro-organisms (n = 8). Slender, septate hyaline hyphae predominated over other morphological categories, but were confined to the axis with little host response other than periaxial melanization. Hyphae were absent in 6 lesioned sea fans and present in 5 control biopsies, questioning their pathogenicity and necessary role in lesion causation. From cultivation, different fungi were isolated and identified by sequencing of the nuclear ribosomal internal transcribed spacer region. In addition, 2 primer pairs were used in a nested format to increase the sensitivity for direct amplification and identification of fungi from lesions, thereby circumventing cultivation. Results suggest mixed and opportunistic infections in sea fans with these lesions, requiring longitudinal or experimental studies to better determine the pathogenesis.

Pathology of multifocal purple spots, a nonspecific lesion morphology of Caribbean sea fans Gorgonia spp

Disease is contributing to the decline of coral reefs globally, but the cause and pathogenesis of most coral diseases are poorly understood. Using Gorgonia ventalina and G. flabellum as a model for coral disease diagnosis, we histologically and microbiologically examined 45 biopsies of lesions resembling Gorgonia multifocal purple spots (MFPS) with the aim of forming a comprehensive case definition based on gross and microscopic morphologic descriptions and associated etiologies. Macroscopically, all lesions were small circular areas of purple pigmentation. Gross morphologies included pigmentation only (4/45, 9%), or pigmentation with branchlet expansion and fusion (19/45, 22%), sessile masses (17/45, 38%), or hard nodules (5/45, 9%). Histological morphologic diagnoses included amoebocyte encapsulation (9/45, 20%), coenenchymal amoebocytosis (6/45, 13%), melanin (17/45, 38%), and gorgonin deposition (13/45, 29%). Sixty-four percent of instances of fungi and 86% of labyrinthulomycetes were localized to grossly normal portions of the biopsy, whereas barnacles were only within lesions, and 87% of instances of algae and 82% of cyanobacteria were within lesioned area of the biopsy. Penicillium (n = 12) was the predominant genus of fungi isolated from biopsies. Barnacles were identified as Conopea sp. using molecular techniques. The pathology and etiology underlying MFPS lesions are diverse, consistent with a highly nonspecific lesion pattern rather than a specific disease. This study demonstrates the importance of microscopic examination of tissues for accurate classification of coral diseases and lesion patterns.