[Coral-List] Cyanobacterial mats during ICRS2020

[Fleur van Duyl]

Dear Colleagues
We would like to draw your special attention to the Session  "Rise of  cyanobacterial mats on reefs" (Theme 11: Resilience, phase shifts and novel ecosystems) during the ICRS to be held  in Bremen in 2020.
Panel: Fleur Van Duyl , Erik Meesters, Lisa Becking, Petra Visser (NIOZ, WMR, WUR, UvA, Netherlands)

Description: Benthic cyanobacterial mats increase worldwide on coral reefs. Benthic filamentous cyanobacteria are common on reefs, but the cover and density of mats has increased the last two decades with up to 30% on many present day reefs. Their presence in the past was more concealed e.g. as subgroup in algal-dominated turfs on hard bottom substrates. Nowadays you can find dense filamentous mats growing on sand, bare hard substratum, macroalgae as well as next to and on live corals. Mats appear to be dominated by common cyanobacterial species such as Lyngbya majuscule, Oscillatoria sp. Moreover, mats can be toxic and their palatability is overall low. Putative drivers of mat development are pollution (eutrophication by sewage, freshwater flooding, iron input, degrading reefs) and temperature. Calm hydrodynamic conditions might be required for the establishment of mats. The local wax and wane of mats tends to be highly variable in space and time, which casts doubt on the role of different drivers. Interesting is the not well-understood sudden disappearance of mats. Is this due to e.g. grazing by herbivores, microbial degradation, burial or dislodgement and transport? Mats are known for their fixation of nitrogen and release of bioavailable nitrogen and dissolved organic matter (OM) during day and night. Mats appear to be the strongest OM releasers of all benthic primary producers per unit surface area of reef. As a consequence of the consortium metabolism, mats can become anoxic during the night. Pelagic microbes stimulated by the OM release may further contribute to hypoxic conditions in the benthic boundary layer. Such hypoxic conditions may persevere in stagnant water under, within and above dense mats during day and night which may be harmful or deleterious to corals in the mat-coral interaction zone and interaction with other benthic reef organisms (macroalgae, sponges, crustose coralline algae). Little is known whether toxins excreted by the mats may also deter settlement of larvae and harm neighbouring benthic reef organisms. We welcome contributions on distribution, wax and wane of mats, chemical fluxes in and out of mats, toxicity, grazing and molecular ecology including metagenomics of mats and interactions between mats and other benthic organisms.

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