Functional consequences of Palaeozoic reef collapse

Tom C L Bridge,Michael J Mcwilliam,John M Pandolfi,Mikołaj K Zapalski,Andrew H Baird

doi:10.1038/s41598-022-05154-6

Abstract

Biogenic reefs have been hotspots of biodiversity and evolutionary novelty throughout the Phanerozoic. The largest reef systems in Earth’s history occurred in the Devonian period, but collapsed during the Late Devonian Mass Extinction. However, the consequences for the functional diversity of Palaeozoic reefs have received little attention. Here, we examine changes in the functional diversity of tabulate coral assemblages over a 35 million year period from the middle Devonian to the Carboniferous, straddling the multiphase extinction event to identify the causes and ecological consequences of the extinction for tabulate corals. By examining five key morphological traits, we show a divergent response of taxonomic and functional diversity to the mass extinction: taxonomic richness peaked during the Givetian (~ 388–383 Ma) and coincided with peak reef building, but functional diversity was only moderate because many species had very similar trait combinations. The collapse of taxonomic diversity and reef building in the late Devonian had minimal impact on functional richness of coral assemblages. However, non-random shifts towards species with larger corallites and lower colony integration suggest a shift from photosymbiotic to asymbiotic taxa associated over the study period. Our results suggest that the collapse of the huge Devonian reef systems was correlated with a breakdown of photosymbiosis and extinction of photosymbiotic tabulate coral taxa. Despite the appearance of new tabulate coral species over the next 35 million years, the extinction of taxa with photosymbiotic traits had long-lasting consequences for reef building and, by extension, shallow marine ecosystems in the Palaeozoic.

Highlights

Biogenic reefs have been hotspots of biodiversity and evolutionary novelty throughout the Phanerozoic
The seaway between Laurussia and Gondwana received westward-flowing warm waters from the South Equatorial Current[19,20,21], which facilitated dispersal of benthic organisms and resulted in homogeneous ecological communities along this shelf. These huge reef systems collapsed during the Late Devonian Mass Extinction[7,22], one of the ‘Big Five’ extinction events of the Phanerozoic, which strongly affected many groups of benthic marine invertebrates[23,24,25]
Taxonomic richness was highest in the Givetian, coinciding with the peak of reef building, but collapsed at the Givetian/Frasian boundary during the Taghanic event (Fig. 3)

Summary

Introduction

Biogenic reefs have been hotspots of biodiversity and evolutionary novelty throughout the Phanerozoic. Despite the appearance of new tabulate coral species over the 35 million years, the extinction of taxa with photosymbiotic traits had long-lasting consequences for reef building and, by extension, shallow marine ecosystems in the Palaeozoic. America and Australia, from a taxonomic perspective the best-studied reefs are those of the Ardennes (Belgium and France) and the Holy Cross Mountains (Poland) in northern E urope[15] These sites form part of a large fossil reef system extending from England to Poland that during the Devonian were located ~ 1000 km apart on the tropical southern shelf of Laurussia (Fig. 1a)[8,16,17]. The seaway between Laurussia (in the north) and Gondwana (in the south) received westward-flowing warm waters from the South Equatorial Current[19,20,21], which facilitated dispersal of benthic organisms and resulted in homogeneous ecological communities along this shelf These huge reef systems collapsed during the Late Devonian Mass Extinction These huge reef systems collapsed during the Late Devonian Mass Extinction (ca. 372 Ma)[7,22], one of the ‘Big Five’ extinction events of the Phanerozoic, which strongly affected many groups of benthic marine invertebrates[23,24,25]

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Conclusion