Over the past few decades, coral reef communities have been subjected
to increasingly stressful conditions from a variety of natural and
anthropogenic impacts (e.g. bleaching events, local habitat degradation,
over-fishing, high sedimentation and pollutant input), which have
resulted in significant losses of hard coral cover. Of particular
concern is the increasing role of diseases in the current deterioration
of these communities. Although now we know that the coral disease
problem has a World wide distribution, the Caribbean continues to
be a “disease hot spot” and today, diseases stands out
as one, if not the most important factor in the deterioration of many
Caribbean coral reefs (Harvell et al. 1999, Weil et al. 2002, Weil
2004). The following are the major characteristics of the coral reef
disease problem in the region: (1) high number of different diseases/syndromes
and wide geographic and local distribution, (2) wide host ranges (up
to 42 species for white plague), (3) chronic epizootics affecting
common and important species (i.e. aspergillosis, yellow blotch syndrome
and dark spots syndrome), and frequent epizootics (white plague, patchy
necrosis, yellow blotch) that last few months but produce significant
tissue loss in some of the most important reef-building species (Montastraea, Colpophyllia, Diploria, Siderastrea,
etc) (Weil, 2002, 2004). Many coral syndromes represent new types
of pathologies, or recurrent, more virulent old forms. Even though
reef-related diseases have been studied and described since the early
1970’s, knowledge of their pathology (identification
of the pathogen), etiology (description of macroscopic
symptoms), and epizootiology (determination of local
and geographic distributions of pathogens and hosts, rates of incidence,
reservoirs and vectors, and local, geographic and temporal variability,
etc.) is still limited.
The goals and objectives of this part of the project are:
Localities: Nine coral reef systems distributed from the coast line to the insular shelf edge were selected for the study. Three fringing reefs are located near the coast, three fringing reefs are located in the mid shelf area (1.5-2.5 km from the coast line) and two deep (20 m) spur-and-grove bank reefs and one hard bottom coral community are located at the edge of the insular platform (5 miles offshore).
Prevalence and incidence: The CARICOMP band transect protocol is being used to estimate the prevalence and incidence of diseases in each locality. Each reef has sixteen 20 m long permanent transects that are being used for the community characterization and monitoring. In the fringing reefs, there are four transect in each of four depth intervals. Every coral, octocoral, sponge and crustose algae (Neogoniolithon accretum) colony is checked for disease signs, bleaching, predation or if it is healthy-looking along a 2 x 10 m wide band (one meter on each side of the tape) in each permanent transect. The proportion of colonies in each category is calculated for each transect as the pooled occurrence of each condition in all coral (octocoral, crustose algae, etc.) colonies affected, normalized against the total number of coral colonies (or octocoral colonies) for each transect. Then, the average proportion (standard deviation and standard error) of colonies affected by each syndrome for each depth interval and each reef locality within each species (prevalence) a and for the communities (incidence) is calculated from the pooled transects in each geographic locality. After checking for the test requirements, ANOVAS are then used to compare prevalence/incidence across depth within reefs, across species and across reefs, and repeated measures Analysis of Variance is used to compare across temporal scales for surveys over the same transects. Percentage data is transformed with the arcsine function.>
Impact: Disease impact will be measured at the level of population/species as the total amount of tissue loss per colony per unit time, and at the level of the communities as total loss of live coral tissue per unit time and changes in the community structure and diversity. Disease colonies are tagged along the permanent transect bands and the rest of the reefs, the disease edge marked with nails and the colonies photographed and mapped and, monitored every month. Many colonies have been tagged during two disease outbreaks in the area. Loss of tissue is measured every week during the outbreaks and every month afterwards. Colonies are photographed every time a measurement is made.
Fulfillment of Koch’s postulates for white band disease: Samples from disease tissues in different species will be collected and bacteria cultures prepared for re-innoculations. Branches of Acropora cervicorniswith signs of white band disease will be collected and samples from the disease area will be plated to isolate Vibrio – like bacteria that will then be grown in pure culture. In a controlled re-inoculation experiment, bacteria samples embedded in a small piece gauze will be attached (tie-wraps) to healthy looking branches and observe daily to check which one (s) produce the disease signs.
Identification of pathogens: Samples from corals with yellow blotch, dark spots and dark bands, patchy necrosis and white band will be taken for microbiological studies and sequencing to try to isolate and identify the putative agents producing these syndromes. Same will be done with new syndromes identified in the field.
Vectors and reservoirs: We know practically nothing about the vectors and reservoirs for most coral diseases. Therefore, gut samples will be taken from common coral predators such as the fire worm (Hermodice carunculata), snails (Coralliophyllia abbreviata and C. caribbaea), other snails that roam over coral heads, parrot fish and damselfish. Microbiological analyses will be conducted to isolate potential pathogenic bacteria and their identity will be corroborated with sequencing.
Disease Incidence: is the proportion (%) of infected (by all diseases or by a single disease) colonies of all coral or octocoral species (community level). All infected colonies (all diseases) over total number of colonies of all species (diseased + healthy).
Disease Prevalence : is the proportion (%) of infected (by a single disease) colonies of the same species in the community. All infected colonies (single disease) over total number of colonies in the population/species (diseased + healthy).
Disease impact: The impact of diseases could be measured in different ways: (1) the average proportion (the relative proportion of live coral surface loss in %) of tissue loss per colony/species, (2) the total area (cm² or m²) of live tissue loss in the population or community, (3) the total number of dead colonies within a population (reduction in abundance), (4) changes in community structure and/or biodiversity (number of species loss), and (5) the reduction in reproductive output (fecundity).
Rate of diseases advance : is the average rate of tissue loss (cm²/day) per colony or species or the average rate of linear advance (cm/day) (tissue loss) per colony/species
Recovery: Is the average gain in new healthy tissue (cm/month) due to the linear modular growth of the colony.
Seasonal variability : Comparison of the variability in incidence, prevalence, rate of advance (tissue loss) and recovery between summer and winter months.
Spatial variability : Comparison of the variability in incidence, prevalence, rate of advance (tissue loss) and recovery across depth intervals and reefs.
Taxonomic variability : comparison of the variation in incidence, prevalence, rate of advance (tissue loss) and recovery among the different coral and octocoral species.
