Diagnostics Involved in the Certification of Aquacultured Corals for Restoration
The University of Florida Tropical Aquaculture Laboratory and The Florida Aquarium are developing health assessment and disease diagnostic protocols for issuance of a federal certificate of health for aquaculture propagated corals for reintroduction to restoration sites. Studies focus on defining fundamentals of coral health appraisal including visual inspection, water quality testing, biosecurity review, and histology. Additional diagnostics, e.g., microbiology, will be employed when clinical signs of disease are evident. Many coral diseases are recognized by patterns of visible tissue change (such as tissue loss, growth anomaly, or color change).
While studies on diseases in wild populations of corals are increasing, information on captive diseases is scarce. By surveying American Zoo and Aquarium Association member institutions, we are identifying common disease syndromes in captive coral collections such as bleaching, rapid tissue necrosis, and "brown jelly."
Histology provides another means to assess coral tissue health. There are several different methodologies under investigation by the National Oceanic and Atmospheric Administration's Coral Disease and Health Consortium. We have chosen the agar embedded technique. Samples for histology are fixed in formalin or Z-fix® and filtered seawater solution, and then are embedded in agar using a vacuum oven. Following decalcification, routine methods are used to prepare histology slides. Sets of normals for all ten species in our current propagation project are being developed.
The use of microbiological testing for coral health assessments is more problematic. Many marine bacteria that may be present may not grow well on standard media and those that do grow may not be primary pathogens. Despite these uncertainties, microbiological tests were employed on two occasions in an attempt to determine the usefulness of employing microbiological techniques for health assessment purposes. In the first, fragments of Montastrea faveolata and Porites asteroides with regressing tissue margins were sampled for bacteria. Tissues from "healthy" and "diseased" sections, based on visual inspection, were sampled. Tissue was ground in a sterile mortar and pestle and serially diluted using sterile, filtered seawater. Dilution aliquots were plated on Tryptic Soy Agar with 5% sheep's blood and incubated at 30°C. Staphylococcus xylosus was isolated from healthy and diseased tissue from the Montastrea fragment and Brevundimonas diminuta was isolated from diseased Porites. The second sampling event occurred after a system malfunction. Water temperature reached 92°F and several coral fragments began to die. Diploria strigosa and Dichocoenia stokesi fragments were most susceptible and were chosen for microbiological evaluation. Vibrio vulnificus and V. alginolyticus were isolated from healthy and diseased tissues on the Diploria fragment. Healthy Diploria strigosa also yielded Mannheimia haemolytica. Brevundimonas was isolated from diseased Dichocoenia and healthy Diploria. Additional bacteria isolated from healthy D. stokesi included Pseudomonas putida, Aeromonas hydrophila, and Chryseobacterium, while diseased tissue from this species was associated with Vibrio vulnificus. Despite bacterial isolation, elevated water temperature alone may have been the primary cause of death of the fragments.
Although a considerable amount of work remains for the development of a health certificate, achieving this goal will accelerate coral restoration efforts.