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Coral Bleaching

Coral Bleaching

Coral Reef Studies

From 2005 to 2022, the main node of the ARC Centre of Excellence for Coral Reef Studies was headquartered at James Cook University in Townsville, Queensland (Australia)

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Photosymbiosis in the Palaeozoic: the origin of MCEs and Devonian bleaching


Thursday July 11, 12:00 to 13:00 hrs (AEST)

JCU Location: Building 19 (Kevin Stark Research Building) Room 106
Mikołaj K. Zapalski
Mikołaj K. Zapalski

Abstract:  Photosymbiosis is the main driver of reef development because it enhances calcification rates, thereby allowing corals to grow in oligotrophic environments. The reefal systems of the Palaeozoic were even larger than modern reefs in both their size and geographic extent, with Devonian reefs reaching latitudes up to 50°S. These reefs were dominated by extinct tabulate and rugose corals, and could not be possible without symbiosis with photosynthetic organisms. However, since algae have virtually no potential for fossilization, evidence of photosymbiosis in ancient reefs is indirect. Two potential lines of evidence for photosymbiosis are available: geochemical and anatomical. Geochemical pathway is risky and full of reefs (nomen omen), so most of evidence must rely on morphology. Recent mesophotic coral ecosystems (MCEs) are dominated by platy corals, a morphology that generally does not occur in in azooxanthellate taxa. Recently-discovered assemblages of platy tabulate corals from Holy Cross Mountains, Central Poland, from the Devonian and Gotland, Sweden (Silurian) spaning the period from 430-385 million years ago suggest that these giant ancient reef systems were powered by photosymbiosis. Sedimentological data show that both Silurian and Devonian MCEs were developing in the deeper shelf environments, while coral assemblages in shallower environments exhibited different morphologies (e.g. massive and branching) analogous to contemporary reefs. This evidences that Palaeozoic platy coral assemblages were functionally similar to recent MCEs and most probably photosymbiotic. The demise of the great Siluro-Devonian reef systems at the end of Devonian (the Frasnian-Famennian crisis) is characterised by steep decrease in coral and the lack of any shared species in pre- and post-extinction beds. Interestingly, pre-extinction corals display morphologies typical for recent zooxanthellates, while post-extinction morphologies resemble modern azooxanthellate taxa suggesting a loss of photosymbiotic corals in the Late Devonian reef crisis.  Geochemical evidence indicates that temperatures during the crisis rose above 32°C, which is likely to have caused collapse of photosymbiosis. Therefore, we conclude that thermally-induced bleaching-like event triggered the Late Devonian reef crisis, resulting in the collapse of the largest reef systems in the history of the planet.


Biography: 2010-today – Faculty of Geology, University of Warsaw, assistant professor;
2009-2010 – Institute of Paleobiology, Polish Academy of Sciences, assistant professor;
2004-2008 – Ph. D. student at the University of Warsaw and Université Lille-1
2003 – Museum of the Earth, Polish Academy of Sciences, assistant
Research interests:

My main research interest are extinct, exclusively Palaeozoic tabulate corals. My interests evolved from studies oriented more towards their taxonomy (my Ph. D. thesis was devoted mostly to taxonomy and systematics of Devonian tabulates from the Central Poland), through their diversified ecological interactions with other organisms. My key interest in this area was parasitism in the fossil record, especially in bioconstructing animals such as stromatoporoids and corals. My more recent studies concentrate on photosymbiosis in the Palaeozoic corals (these studies resulted in my habilitation). I have started with a small paper on geochemistry of coral skeleton (Proc. R. Soc. B., 2014); my research on tabulate coral photosymbiosis led me to discoveries of the oldest mesophotic coral ecosystems (first – 2017 – from the Devonian of Poland, and two years later from the Silurian of Sweden, both papers published in Coral Reefs). Together with colleagues from the Adam Mickiewicz University (AMU; Poznań, Poland) we have also shown that the Late Devonian collapse of great reef systems was probably a result of phenomenon similar to recent bleaching, and also correlated with the rise of SST. I am also interested in cryptic environments in Palaeozoic reefs. Besides, I have recently been involved in research on Devonian reefs from Morocco (Anti-Atlas), led by colleagues from AMU. We have published series of papers dealing with Devonian coral palaeoecology, criptic assemblages, sedimentology and taxonomy. Now I am trying to develop my knowledge on Recent reefs, to make my comparative studies more accurate and reliable. My visit in Townsville is sponsored by Polish National Agency for Academic Exchange, and I intend to broaden my knowledge about Recent coral reefs, especially MCEs and bleaching.


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