Search for: All records

As climate change drives health declines of tropical reef species, diseases are further eroding ecosystem function and habitat resilience. Coral disease impacts many areas around the world, removing some foundation species to recorded low levels and thwarting worldwide efforts to restore reefs. What we know about coral disease processes remains insufficient to overcome many current challenges in reef conservation, yet cumulative research and management practices are revealing new disease agents (including bacteria, viruses, and eukaryotes), genetic host disease resistance factors, and innovative methods to prevent and mitigate epizootic events (probiotics, antibiotics, and disease resistance breeding programs). The recent outbreak of stony coral tissue loss disease across the Caribbean has reenergized and mobilized the research community to think bigger and do more. This review therefore focuses largely on novel emerging insights into the causes and mechanisms of coral disease and their applications to coral restoration and conservation. 

Abstract Cryptic species (evolutionarily distinct lineages that do not align with morphologically defined species) are being increasingly discovered but are poorly integrated into ecological theory. In particular, we still lack a useful understanding of if and how cryptic species differ in ways that affect community recovery from disturbances and responses to anthropogenic stressors, such as the removal of consumers and pollution from nutrients. On coral reefs, nutrient pollution increases the growth of macroalgae that displace corals. Reductions in herbivorous fishes reduce the suppression of macroalgae, while reductions in coralivorous fishes reduce predation on corals. An unresolved question is if and how cryptic coral species respond differently to these impacts, thereby differing in their ability to influence coral community dynamics and maintain coral dominance. Therefore, we assessed how the response of crypticPocilloporaspecies over a period of three years following a simulated disturbance from a cyclone depended on the experimental reduction of fish consumer pressure and nutrient addition. After three years, five morphologically cryptic, but genetically distinct,Pocilloporaspecies recruited to the reef. However, recruitment was dominated by two species:Pocillopora tuahiniensis(46%) andPocillopora meandrina(43%). Under ambient conditions, recruitment ofP. tuahiniensisandP. meandrinawas similar, but experimentally reducing consumer pressure increased recruitment ofP. tuahiniensisby up to 73% and reduced recruitment ofP. meandrinaby up to 49%. In both species, nutrient enrichment increased recruitment and colony growth rates equally, but colonies ofP. tuahiniensisgrew faster and were up to 25% larger after three years than those ofP. meandrina,and growth was unaffected by reduced consumer pressure. Predation by excavating corallivorous fish was higher forP. meandrinathan forP. tuahiniensis, especially under nutrient enrichment. In contrast, polyp extension (an indicator of elevated heterotrophic feeding as well as susceptibility and attractiveness to corallivores) was lower forP. meandrinathan forP. tuahiniensis, especially under low to medium consumer pressure. Overall, we uncovered ecological differences in the response of morphologically cryptic foundation species to two pervasive stressors on coral reefs. Our results demonstrate how cryptic species respond differently to key anthropogenic stressors, which may contribute to response diversity that can support ecological resilience or increase extinction risk. 

Abstract Perturbations in natural systems generally are the combination of multiple interactions among individual stressors. However, methods to interpret the effects of interacting stressors remain challenging and are biased to identifying synergies which are prioritized in conservation. Therefore we conducted a multiple stressor experiment (no stress, single, double, triple) on the coralPocillopora meandrinato evaluate how its microbiome changes compositionally with increasing levels of perturbation. We found that effects of nutrient enrichment, simulated predation, and increased temperature are antagonistic, rather than synergistic or additive, for a variety of microbial community diversity measures. Importantly, high temperature and scarring alone had the greatest effect on changing microbial community composition and diversity. Using differential abundance analysis, we found that the main effects of stressors increased the abundance of opportunistic taxa, and two-way interactions among stressors acted antagonistically on this increase, while three-way interactions acted synergistically. These data suggest that: (1) multiple statistical analyses should be conducted for a complete assessment of microbial community dynamics, (2) for some statistical metrics multiple stressors do not necessarily increase the disruption of microbiomes over single stressors in this coral species, and (3) the observed stressor-induced community dysbiosis is characterized by a proliferation of opportunists rather than a depletion of a proposed coral symbiont of the genusEndozoicomonas.