Depth-related controls on the quantitative taxonomic composition of rhodoliths

Pyko IA, Wisshak M, Teichert S (2024)

Publication Language: English

Publication Type: Conference contribution, Abstract of lecture

Publication year: 2024

Event location: Le Castella IT

Abstract

The calcareous matrix of rhodoliths can be composed of one or more crustose coralline algal (CCA) taxa as well as a mixed assemblage of various encrusting organisms. Morphology analyses of the inner arrangement and assemblages of organisms forming rhodoliths can provide valuable information to reconstruct palaeoenvironmental and palaeoclimatic condition  (Basso et al. 1998, Aguirre et al. 2017) Descriptive studies on modern and fossil rhodoliths assume associations with water depth. Here we explore the quantitative biological composition of calcareous rhodolith matrices along a bathymetric gradient at the Arctic Svalbard archipelago. We hypothesize that (1) the composition of calcareous rhodolith matrices is taxonomically quantifiable and that (2) this quantitative composition is controlled by water depth, implying that (3) the matrix composition could be used for (palaeo-)bathymetrical reconstructions. Using a methodological combination of virtual micro-CT cross-sections with a modified point counting approach, we distinguished five different taxonomic groups: CCA, bivalves, serpulids, bryozoans, and balanids. The identified matrix component CCA is mainly represented by the species Boreolithothamnion glaciale Kjellman) Gabrielson et al. (2023) (Basionym Lithothamnion glaciale Kjellman, 1883), which is the dominant CCA species in Mosselbukta. The identified matrix component bivalves are represented by the drilling bivalve species Hiatella arctica (Linnaeus, 1767). The other taxa, serpulids (family Serpulidae), balanids (family Balanidae), and bryozoans (phylum Bryozoa) could not be identified to species level. While water depth does not influence the general taxon richness as well as the abundance of bivalves, it significantly affects the proportional matrix composition of encrusting organisms by a combination of environmental factors and biological interactions. The decrease in CCA skeletal material with increasing water depth is significantly governed by impaired irradiance conditions. Regular rhodolith movement in shallow waters fosters the proportion of CCA, while decreased movement in deeper waters spurs the proportion of heterotrophic encrusters. This results from post-mortem fouling of dead rhodolith parts followed by a recolonization with slow-growing CCA. Our results highlight new mechanisms controlling the biogenic composition of calcareous rhodolith matrices and the potential of quantitative matrix compositions for palaeogeography and -bathymetry. However, it also stresses the importance of sufficiently large sample sizes, ideally deriving from different facies types. The introduced methodological combination allows for a straightforward and non-destructive identification and quantification of rhodolith matrix components and also provides a new tool for rhodolith-focused quantitative research from a more general perspective.

Authors with CRIS profile

Ines Anna Pyko Professur für Paläontologie (Schwerpunkt Faziesanalyse) Sebastian Teichert Lehrstuhl für Paläoumwelt

Involved external institutions

Senckenberg Gesellschaft für Naturforschung DE Germany (DE)

How to cite

APA:

Pyko, I.A., Wisshak, M., & Teichert, S. (2024). Depth-related controls on the quantitative taxonomic composition of rhodoliths. Paper presentation at 13th International Symposium on Fossil Algae, Le Castella, IT.

MLA:

Pyko, Ines Anna, Max Wisshak, and Sebastian Teichert. "Depth-related controls on the quantitative taxonomic composition of rhodoliths." Presented at 13th International Symposium on Fossil Algae, Le Castella 2024.

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