Linking global change and deep-sea macrobenthos diversity – bathyal Atelostomata as a model taxon.

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The deep-sea is the Earth’s largest ecosystem, and due to its sheer size and inaccessibility, our knowledge on global deep-sea biota and its controlling mechanisms is still ambiguous. While chemosynthetic ecosystems are progressively understood, the bathyal to abyssal plains and the hadal deep-sea trenches remain widely unexplored. Due to the scarce geologic record of deep-sea sediments onshore and the lack of continuous geological/palaeontological records of any group of higher deep-sea Metazoa, our knowledge on deep-sea palaeobiogeography and macrofauna evolution is even more rudimentary. A survey to extract remains of deep-sea macrobenthos from Lower Cretaceous to Upper Miocene sediments deposited at deep bathyal palaeo-waterdepths below 2000 m in ODP/DSDP/IODP core samples yielded astonishing results: Echinodermata (holothurians, brittle stars, sea stars, crinoids), today common in the deep-sea, are absent, while only spines of irregular echinoids (Holasteroida, Spatangoida: Atelostomata) occur frequently. Because the spines are morphologically highly variable, the assessment of spine morphospace, its changes in time and the spine accumulation rate bears the potential to map diversity and biomass changes in the deep-sea in response to global change. In particular, global warming results in decreasing export productivity due to lower primary productivity especially in open oceanic settings, why the eastern tropical Pacific serves as a model area to clarify two hypotheses. i) Atelostomate spine diversity correlates inversely with Cenozoic warm periods, supporting the productivity-diversity relation and ii) atelostomate spine abundance is expression of biomass and export productivity, showing lower values in warm phases. Atelostomate spines from selected intervals of the rapidly changing Cenozoic world with massive sea surface and bottom water temperature changes and were considered (Mid-Miocene cooling, Mid-Miocene climatic optimum, late Oligocene warming; Oi-2c glaciation and aftermath, Upper Oligocene; Oi-2b glaciation and aftermath). Spine characters (e.g. shaft morphology, arrangement and frequency of thorns, shape/number of pores, shape of tips etc.) are included in a data matrix and statistically processed. Variations in spine diversity are considered to express changing biodiversity, and decreasing diversity and biomass is expected during warming periods. A principal component analyses of the spine assemblages from the intervals above aid the recognition of morphospace disparity between the time-specific intervals and diversity changes. This give additionally clues on gradual (evolution?) or abrupt (extinction and speciation/immigration?) faunal changes between the deep-sea Atleostomata and the relation of faunal turnovers/changes to fluctuating export productivity into the dee-sea during global change.