Microbial to reef scale interactions between the reef-building coral Montastraea annularis and benthic algae

Abstract

Competition between reef-building corals and benthic algae is of key importance for reef dynamics. These interactions occur on many spatial scales, ranging from chemical to regional. Using microprobes, 16S rDNA pyrosequencing and underwater surveys, we examined the interactions between the reef-building coral Montastraea annularis and four types of benthic algae. The macroalgae Dictyota bartayresiana and Halimeda opuntia, as well as a mixed consortium of turf algae, caused hypoxia on the adjacent coral tissue. Turf algae were also associated with major shifts in the bacterial communities at the interaction zones, including more pathogens and virulence genes. In contrast to turf algae, interactions with crustose coralline algae (CCA) and M. annularis did not appear to be antagonistic at any scale. These zones were not hypoxic, the microbes were not pathogen-like and the abundance of coral-CCA interactions was positively correlated with per cent coral cover. We propose a model in which fleshy algae (i.e. some species of turf and fleshy macroalgae) alter benthic competition dynamics by stimulating bacterial respiration and promoting invasion of virulent bacteria on corals. This gives fleshy algae a competitive advantage over corals when human activities, such as overfishing and eutrophication, remove controls on algal abundance. Together, these results demonstrate the intricate connections and mechanisms that structure coral reefs.

Post-bleaching coral community change on southern Maldivian reefs: is there potential for rapid recovery?

“…1f), and we speculate that this may be creating localised micro-environments that act as vectors for disease (e.g. Barott et al 2012). …”

Allelochemicals Produced by Brown Macroalgae of the Lobophora Genus Are Active against Coral Larvae and Associated Bacteria, Supporting Pathogenic Shifts to Vibrio Dominance

“…Corals also respond to positive settlement cues associated with CCA (71), which may partly originate from microbial biofilms (70,(72)(73)(74). Thus, macroalgal compounds may indirectly affect larval settlement success and survivorship by influencing microbial activity, thereby influencing oxygen concentrations (22) and biofilm composition on settlement surfaces (74), which potentially make them less appealing for settlement (69) and/or reduce survivorship by weakening larval resistance to microbial infections, ultimately causing death (70). Although this study highlights the potential for macroalgae to produce metabolites that impact larval settlement dynamics, further investigation into the concentration of allelochemicals released to macroalgal surfaces and their specific impact on larval survivorship and microbial dynamics need to be defined in order to establish a direct relationship.…”

“…The species-specific impacts of macroalgae on corals continue to be investigated; however, the primary mechanisms of damage and microbial mediation are likely a combination of direct and indirect mechanisms related to physical abrasion (18), nutrient enrichment through the release of dissolved organic material (19,20), and chemical toxicity (7,21). These mechanisms will vary on a species-by-species basis, likely mediated by algal morphology and growth characteristics as well as water flow and reef heterogeneity (22,23).…”

Evidence for water-mediated mechanisms in coral–algal interactions

“…Hypoxia, especially at night, limits coral respiration [25] and reduces the metabolism of coral symbionts [50]. Hypoxia has been measured in experimentally initiated and naturally occurring interactions between corals and turf or macroalgae [8,22,27,31,37]. Stressful pH levels are also likely to develop during the night in conjunction with hypoxia as a result of net respiration of turf or macroalgae [51].…”