Gross and Microscopic Lesions in Corals from Micronesia

Area of Science:

• Marine Biology
• Coral Pathology
• Ecology

Background:

• Coral reefs face threats from diseases impacting colony health.
• Understanding coral lesion morphology and etiology is crucial for conservation.
• Previous studies have identified various coral diseases, but comprehensive histopathological analysis is often limited.

Purpose of the Study:

• To document the gross and microscopic morphology of coral lesions across Micronesia.
• To identify the potential etiologies of observed coral diseases using histopathology.
• To investigate host responses to different coral disease agents.

Main Methods:

• Sampling of 76 coral colonies across 30 species and 18 genera on 7 Micronesian islands.
• Gross examination of lesions, categorizing them by type (tissue loss, discoloration, growth anomaly) and stage (acute, subacute, chronic).
• Histopathological analysis of tissue samples to determine microscopic findings and identify potential causative agents.

Main Results:

• Tissue loss was the most common gross lesion (41%), followed by discoloration (30%) and growth anomalies (29%).
• Histopathology revealed fungal infections in dark discoloration, zooxanthellae depletion in bleached corals, and basal body wall hyperplasia in growth anomalies.
• Specific host responses included tissue fragmentation associated with algae and necrosis associated with fungi; two new symbiotic metazoans were observed.

Conclusions:

• Histopathology is essential for accurate coral disease diagnosis, revealing multiple potential etiologies for gross lesions.
• The study expands the known range of corals affected by cell-associated microbial aggregates.
• Findings underscore the complexity of coral diseases and the need for integrated diagnostic approaches.