What Happens After – Succession of an Epibenthic Hard-Bottom Community after Coral Mass Mortality in Chilean Patagonia

Juergen.Laudien [ at ] awi.de


Climate-related extremes and anthropogenic impacts cause disturbances in benthic marine ecosystems. The fjords of Chilean Patagonia host a highly diverse benthic community, including three species of cold-water corals. The dominant scleractinian Desmophyllum dianthus Esper, 1794 shapes its habitat by forming calcareous skeletons and is assumed to be an important ecosystem engineer. After a significant disturbance in 2012 in Comau Fjord (42°20´S, 72°30´W), >99.9 % of the highly abundant scleractinian D. dianthus died along 8.4 km of coastline. This study was conducted to analyze the effect of the mortality event and subsequent recovery of the benthic community. To further investigate the role of D. dianthus in the community, a coral removal experiment was conducted. Underwater pictures of the community affected by the coral die-off (starting 2014) and the experimentally disturbed community (starting 2015) were taken annually to document the species succession, and abiotic parameters were measured. Image analysis was conducted to identify the occurring benthic species and measure abundance and percentage cover. Species richness S, Shannon-Wiener diversity H’ and Pielou’s evenness J’ were calculated and statistical community analysis was applied. After the mortality event, total abundance and percentage cover increased continuously from 2014 to 2016. The scleractinian Caryophyllia huinayensis Cairns, Häussermann and Försterra, 2005 became significantly more abundant. Octocorals and hydrozoans significantly increased in percentage cover, colonizing dead coral skeletons. No taxon exhibited continuous decline in abundance or cover. Individuals of D. dianthus resettled in the benthic community, exhibiting normal growth rates and a steady rise in abundance, and this coral is expected to return to a dominant role in the community. Biodiversity indices were stable over the monitored time span and agreed with results of previous studies conducted in Comau Fjord. At coral removal sites, percentage cover increased due to expansion of encrusting bryozoans and immigration of actinians. Cover reached values comparable to control sites within one year. The changes in the benthic community in both monitoring stations may be attributed to the availability of free substrate and the relief of biotic pressure. The community showed high resilience and stability after the disappearance of the dominant species D. dianthus and no changes in biodiversity were shown. Due to the slow growth of cold-water communities, full recovery of the pre-mortality community structure is estimated to be a long process. This highlights the need for protection of this diverse ecosystem.

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Reichardt, A. M. (2017): What Happens After – Succession of an Epibenthic Hard-Bottom Community after Coral Mass Mortality in Chilean Patagonia , Master thesis, Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research and University of Bremen.

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