a. Apply integrated condition, causal pathway, and ecological risk assessment to redseach design
and management decisions: Control and mitigation of diseases affecting elkhorn and staghorn
corals is impeded because the factors and their interactions (host, agent(s), environment) that determine disease occurrence in these corals are poorly understood (Richardson 1999). Very little is known about the etiology of Caribbean Acropora diseases. There is speculation that many coral diseases are the result of opportunistic or polymicrobial infections that are initiated once the coral host immunity has been compromised (Lesser et al. 2007, Work et al. 2008). Many marine bacteria are resistant to cultivation, thus inhibiting a definitive identification and the testing of pure strains as disease-causing agents in healthy corals (Ritchie et al. 2001). Though some information is
emerging about the relationship between disease and temperature induced bleaching, scientists are only beginning to explore disease relationships with other physical environmental stresses (e.g., pH, salinity); and uncovering relationships between coral disease and environmental degradation (e.g., pollutants) is at the earliest stages (Jaap & Wheaton 1975, Ostrander et al. 2000, Downs et al. 2010). Because of the complex physical, chemical, and biological interactions affecting coral health,
understanding these factors and interactions will require an investigative approach, drawing on many types of information being proposed in this Recovery Plan and elsewhere to develop
quantitative comparisons among groups and various factors. A mechanistic understanding of modes of action, susceptibility differences among species, interactions between chemical and
environmental variables (e.g., temperature, salinity, light), and tools that allow detection of exposures and effects will enable causal and risk analyses to be used for coral reef assessments (Hahn and Stegeman 1999, Downs et al. 2005b).
Practical approaches developed from the theory of epidemiology (Thursfield 2007), integrated environmental assessment, causal analysis, and risk assessment are needed to provide a quantitative basis for informed management decisions (Downs et al. 2005b, 2011, Suter 2006). These methods offer a forensics investigative approach to understanding the complexities of disease by blending pathology and epidemiology (i.e., biological assessment and causal analyses) with risk assessment (i.e., risk models that link alternative decisions to future conditions) to provide a systematic means to better identify causal factors and their path from source to impairment. Three inter-related research priorities to determine risk factors and their relative contribution to Acropora disease are:
i. Condition assessment: The first step is to choose specific health indicators (e.g., percent coral
cover, genetic diversity, lesion regeneration, physiological diagnostic markers, reproductive viability) that can be easily measured in field monitoring efforts to be able to detect change (i.e., condition assessment) (Downs et al. 2005b, Cormier and Suter 2008) in coral health at the population and individual organism levels. Surveys are conducted to establish normal levels for the relevant health indicators so changes in the coral’s condition (possibly leading to
impairment) can be detected (see Action 5: Monitor the Species and Their Environments). Similar to biological monitoring, monitoring of the chemical (e.g., water quality, toxicants) and physical (e.g., temperature, water flow, turbidity, sedimentation) nature of the environment is
Recovery Plan for Elkhorn and Staghorn Corals
performed to detect background levels and changes that might be associated with alterations in biological condition.
ii. Stressor identification and causal pathway assessment: There are numerous methods that can
be used to determine causality such as exposure-response relationships, pathology,
biochemistry, cellular physiology, and mechanistic models. Whichever method(s) is used, it must be able to identify putative causative agents, identify the links in the cause-effect chain, recognize the level of uncertainty associated with each link, and discriminate among possible causes and the relative contribution of each in inducing the observed effect. As these
relationships and interactions are explored, it is vital to also establish that the interactions are supported along a hierarchical biological chain in order to determine mechanisms of action. Possible causes of harm to coral health are inferred by evaluating how the chemical, physical, and biological environments interact to affect the health of organisms within the particular context (Wobeser 1994, Cormier 2006, Suter 2006, Thursfield 2007).
iii. Ecological risk assessment: An ecological risk assessment is a tool that can help managers
generate sound information as a basis for management action(s) toward a particular activity or problem. Relative risk factors are assigned to the potential causes of impairment, and
management alternatives, including no action, are then developed based on the risk
assessment. It is a powerful and cost-effective tool in determining the probability of a risk (or threat) to the resource (i.e., corals) by a stressor (activity or specific pollutant(s)) when funds, expertise, and time are limited. This tool does not require knowledge of the mechanism of the impairment to coral (e.g., increased disease, population decline, loss of reproductive fitness), but if the concentration of pollutant or extent of activity under question (exposure
characterization) can be shown to pose a credible threat to the biological integrity of the resource (effect characterization), it can be used as the basis for a management action.
For all three parts of this action, Initiation: Immediately. Duration: Estimate 2-5 years for initial assessment, then on-going. Cost: $500,000 to $2,000,000 per watershed per year but highly variable and dependent on management actions or need for greater certainty.
b. Develop disease recovery criterion: Information on the effects of disease on elkhorn and staghorn corals is needed to inform the development of a criterion to evaluate the abatement of this threat. Losses due to disease must be less than gains from growth and recruitment to have a positive population trajectory. Many coral disease surveys report instantaneous disease prevalence at a certain point in time, but information on both colony and population level effects of disease over time are needed to inform criterion development. Multi-seasonal and multi-year surveys of reference robust populations (extant thickets) are needed to aid determination of disease carrying capacity. Types of relevant data include seasonal prevalence and incidence of disease, amount of partial mortality at the individual colony and population level, colony growth and mortality rates, disease progression rates, and population growth and recruitment rates (see also Action 5aiii). Initiation: Immediately. Duration: 5 years. Cost: $500,000 per year.
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