EGU2020-8566
https://doi.org/10.5194/egusphere-egu2020-8566
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Quaternary molluscan assemblages of cold-water coral mounds: a new perspective on deep-sea ecosystem dynamics in the western Mediterranean

Chelsea Korpanty1, Leon Hoffman2, Jürgen Titschack1, Claudia Wienberg1, and Dierk Hebbeln1
Chelsea Korpanty et al.
  • 1MARUM Center for Marine Environmental Sciences, University of Bremen, Bremen, Germany (ckorpanty@marum.de)
  • 2Marine Research Department, Senckenberg am Meer, Wilhelmshaven, Germany, 26382

Cold-water corals (CWC) act as ecosystem engineers and thus contribute to biodiversity on continental margins worldwide. CWC mounds – built over geologic time by the interplay of biological, sedimentological, and oceanographic processes – create ecological niches for a variety of macrobenthic marine taxa (e.g. molluscs, sponges, bryozoans). The growth of CWC mounds is discontinuous over time due to changes in environmental and ecological conditions, such as food supply, water temperature, and dissolved oxygen concentration. While surficial distribution patterns of living and recently-dead mound macrobenthic communities have been described, their temporal ecological relationship with coral growth and mound formation is yet largely unexplored. Therefore, this project aims to determine what effects stagnations in CWC growth (i.e. repeated periods of ecosystem “turn off”) have on the local biodiversity and community structure of other CWC mound taxa, and thus what influences CWC mound development may have on regional biodiversity and biogeography in the deep sea over geologic time. Focusing on a single taxonomic group with high preservation potential, this study 1) quantitatively assesses temporal ecological trends of coral mound molluscan assemblages (bivalves and gastropods), and 2) statistically correlates those data with coral growth and palaeoceanographic records. Preliminary results from two CWC mound gravity cores through Brittlestar Ridge I in the Alboran Sea, western Mediterranean (~13.2 – 2.9 ka) indicate that throughout both cores the molluscan assemblages are typically quantitatively dominated by sessile benthic filter-feeding bivalves, particularly Heteranomia squamula and Hiatella arctica. Although bivalves are more abundant and diverse than gastropods in both cores, these taxonomic groups yield generally similar downcore dynamics in abundance and diversity. Comparisons of total molluscan assemblages (bivalves and gastropods combined) suggest that the older assemblages – those associated with the Bølling-Allerød interstadial (13.5-12.8 ka) and Early Holocene (11.3-9.8 ka) – are more similar to one another than to younger assemblages in the cores. Rotational vector fitting analyses indicate that these older assemblages are significantly related to higher productivity and different hydrodynamics (and sediment input), which are factors that have also been linked to CWC growth in the region. Altogether, our paleoecological reconstructions so far reaffirms the connectivity of benthic communities with local oceanographic conditions and adjacent taxa. Additional ecological assessments will further refine our understanding of the relationships between CWC growth and benthic communities, and in turn the temporal drivers and dynamics of CWC mound biodiversity.

How to cite: Korpanty, C., Hoffman, L., Titschack, J., Wienberg, C., and Hebbeln, D.: Quaternary molluscan assemblages of cold-water coral mounds: a new perspective on deep-sea ecosystem dynamics in the western Mediterranean , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8566, https://doi.org/10.5194/egusphere-egu2020-8566, 2020

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Presentation version 2 – uploaded on 01 May 2020
Slight highlighting issue in a figure on two slides. No scientific content change.
  • CC1: Comment on EGU2020-8566, Stefano Dominici, 05 May 2020

    Hi Chelsea, and thanks for participating to the session with your study on molluscan diversity at a deep-sea coral mound. It's surprising to see as many species per sample at -400m as you have in the same sea at shallow depths. Your interpretation of the results is pretty streightforward: this habitat hosts a recurring assemblage, irrespective of position with respect to mound's crest, but changes in time responding to climate change. I have a question: you write about collecting off-mound sediment cores. Can you tell us what species richness you found there and if dominant species are the same?

    • AC1: @ Stefano Dominici, Chelsea Korpanty, 06 May 2020

      Hi Stefano and thanks for your question. 

      Unfortunately I did not have the opportunity to sample and investigate the off-mound core. Colleagues of mine and their former students conducted the off-mound proxy analyses (e.g. see Fink et al. 2013, Marine Geology; that citation might have been mistakenly left out of the presentation - apologies). As such, I cannot say for sure what molluscan species were or could be found in the off-mound core. According to original sediment log analyses of the cores (again Fink et al. 2013), there is only one observation of shell fragments in the off-mound core. I suspect that if there are molluscs in the off-mound core they are quite small (< a few cm) and therefore allude surficial observations of the cores. I also suspect that there may be some similar species off-mound as there are on-mound, but in far far fewer numbers and in lower diversity. Other studies have found that benthic diversity markedly decreases as you move away from cold-water coral mounds - indicating the importance of cold-water coral mounds as habitat. 

      • AC3: Reply to AC1, Leon Hoffman, 06 May 2020

        Hello, Off mound mollusk assemblages are dominated by bivalve in-faunal detritivores (such as Thyasiridae and Yoldiidae), carnivores (general Septibranchia like Cuspidariidae) and occasional filter feeder (like Semelidae - Abra spp). Gastropods are mostly carnivore mud dwellers feeding on bivalves or other gastropods. The biotope is mostly dominated by muddy silt. 98% is < 5 mm.

        Best regards, Leon Hoffman

  • CC2: Diversity and taphonomy, Emilia Jarochowska, 05 May 2020

    Hi Chelsea, cheers to an impressive study! I would like to join Stefano's question:

    how distinct are the assemblages from the benthos surrounding the mound?

    And also ask: do these mounts create  distinct taphonomic conditions? e.g. post-mortem downward transport?

    Maybe I'm not used to this type of data but what do "Feeding" and "Mobility" mean next to your diversity through time curves mean? Is it "Filter feeders" and "Motile benthos" or something like this? 

    Thanks, Emilia

    • AC2: @ Emilia Jarochowska, Chelsea Korpanty, 06 May 2020

      Thanks for your questions, Emilia. 

      In response to the first question regarding off-mound molluscan diversity - please see my response to Stefano. 

      Regarding taphonomy in the mound - no, I did not notice any taphonomic changes down-core in any of the cores, nor could I recognize any taphonomic differences among the molluscs in the three cores. I was also thinking there might be signs of down-mound transport or exposure, particularly in the shells in the lower flank core, but I did not. 

      Regarding "Feeding" and "Mobility" - These elements were left a bit vague in the presentation for simplicity's sake, so thanks for asking about them. "Feeding" encompasses the different common feeding-strategies of molluscs. In this study they include: filter feeders, deposit feeders, carnivores, spongivores, corallivores, and those that are unknown (the number of these is relatively low). "Mobility" recognizes the different common modes of attachment or movement, and recognizes epi- vs. infaunal. These include: epifaunal mobile, infaunal mobile, rock borers, and sessile (byssal attachment and cementation). The compositions of Feeding and Mobility assemblages were assessed in the same quantiative way that the taxonomic (species) assemblages were (e.g. MDS, EnvFit, ANOSIM). In general, the statistical analyses told the same story - whether it was the taxonomic, feeding traits, or mobility traits compositions being analyzed. 

Presentation version 1 – uploaded on 01 May 2020 , no comments