Macroalgae Has No Effect on the Severity and Dynamics of Caribbean Yellow Band Disease

Abstract

By removing herbivores and promoting increases in macroalgae, overfishing is thought to indirectly cause coral disease and mortality. We performed three field manipulations to test the general hypothesis that overfishing and the subsequent alteration of coral reef trophic dynamics are a cause of coral epizootics. Specifically, we asked whether the presence of macroalgae can influence within- and among-colony spread rates of Caribbean Yellow Band Disease in Montastraea faveolata. Macroalgae were placed next to infected and healthy, adult and small coral colonies to measure effects on disease spread rate, coral growth and coral survival. Surprisingly, the addition of macroalgae did not affect disease severity or coral fitness. Our results indicate that macroalgae have no effect on the severity and dynamics of Caribbean Yellow Band Disease and that fisheries management alone will not mitigate the effects of this important epizootic.

Allelochemicals produced by Caribbean macroalgae and cyanobacteria have species-specific effects on reef coral microorganisms

“…Microbial growth can cause coral mortality through oxygen depletion, accumulation of poisons, and/or microbial predation on weakened coral polyps (Cole 1982;Segel and Ducklow 1982;Smith et al 2006). However, macroalgae may need to be in direct contact with coral tissues to result in high enough DOC and other metabolite levels to influence microbial proliferation and/or coral bleaching and subsequent tissue death (Vu et al 2009;Rasher and Hay 2010). Antibacterial and/or stimulatory effects of coral-algal contact on associated microbes likely would be exacerbated in low flow and high-temperature microclimates (Smith et al 2006;Bruno et al 2007).…”

“…Elevated microbial growth rates appear to cause coral mortality through depletion of oxygen, accumulation of poisons (e.g., hydrogen sulfide, secondary metabolites), and/or microbial predation on weakened coral polyps (Segel and Ducklow 1982;Smith et al 2006). However, high concentrations of DOC and metabolites may cause elevated and detrimental microbial growth only under certain conditions, including direct coral-algal contact, low water flow in interstitial microenvironments, and/or high temperature stress (Smith et al 2006;Bruno et al 2007;Vu et al 2009). …”

The effects of water flow and sedimentation on interactions between massive Porites and algal turf

“…Algal turf filaments may need to be in direct contact with coral tissue in order for metabolites to reach high enough levels to stimulate microbial activity, or coral tissue damage or mortality (Vu et al 2009, Rasher and Hay 2010, Rasher et al 2011.…”

Chemically rich seaweeds poison corals when not controlled by herbivores

“…In contrast, laboratory-based studies of multiple seaweed-coral pairings suggest that release of seaweed primary metabolites (i.e., sugars and carbohydrates) can indirectly mediate coral mortality through effects on coral-associated microbes (24). These laboratory-based effects have yet to be documented under field conditions, and a recent field study found no effect of nearby seaweeds on the severity and dynamics of a microbe-generated coral disease, suggesting that natural hydrodynamic conditions may limit the impacts of algal generated metabolites in the field (25). Thus, the relative frequency, intensity, and general ecological effects of seaweed allelopathy against corals remain unknown, as do the chemical nature and mechanisms of allelopathy between seaweeds and corals (e.g., the activity of primary vs. secondary metabolites and the role of direct poisons vs. indirect effects on microbes).…”