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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - POSEIDoN (Atlantidae: Predators at the Ocean SurfacE as InDicators of chaNge.)

Teaser

Summary

Anthropogenic release of CO2 into the atmosphere is causing ocean acidification (OA) and ocean warming (OW) at a rate unprecedented during the last 66 million years. Planktonic organisms are amongst the most vulnerable to these changes, living close to the atmosphere/ocean boundary where CO2 dissolves into the ocean and direct warming occurs. As a vital component of all open ocean food chains and an essential food source for commercially fished species, understanding the effects of ocean changes upon plankton is crucial if we are to plan for the future.

The central aim of this study was to assess the atlantid heteropods, a group of planktonic snails, for their use as bio-indicators of ocean changes in a past, present and future framework. These snails build a shell of aragonite, a form of calcium carbonate that is extremely sensitive to OA, being more difficult to grow and maintain as pH decreases. To meet this aim, the project had three main objectives. 1) Assess species boundaries. Responses to ocean changes are likely to be species-specific, so we need to understand diversity within the atlantids. 2) Determine environmental tolerances in the present by modeling geographical distributions (e.g. temperature tolerance) and carrying out experiments (e.g. responses to changing pH). 3) Evaluate the effects of ocean changes in the past and the future. Using the fossil record we can assess how past ocean changes affected the diversity and distribution of atlantid species. Using Species Distribution Models (SDMs) we can also forecast changes in distribution for predicted future environmental scenarios.

Through integrated analysis of shell morphology, molecular phylogeny and geographic distribution patterns of atlantids, we found >35% more diversity than previously thought. Our results identified 37 hypothetical species (clades), while there are only 24 atlantid species currently described. One of these species, Atlanta vanderspoeli, was described as part of this project. Geographical distributions were updated, and used to determine species-specific environmental tolerances to physical ocean parameters. For example, distributions of Atlanta ariejansseni indicate a temperature tolerance of 7.9â€“20.1Â°C, whereas the closely related Atlanta inflata has a broader temperature tolerance of 7.1â€“31.1Â°C. A fossil calibration of our atlantid phylogeny suggests that great diversification has occurred over the last ~25 Ma, potentially in response to environmental changes. These results demonstrate that confident species identification is crucial for OA experiments. If species containing multiple cryptic clades (where they cannot be identified from each other) are used, species/clade specific responses to experimental conditions could produce misleading experimental results.

During the Atlantic Meridional Transect 2017 (AMT27) expedition, eight atlantid species were kept under laboratory conditions. Analysis of one growth rate experiment and one OA experiment, both on the most southerly distributed atlantid species, A. ariejansseni indicate a negative response to decreasing ocean pH, but a positive response to increased food availability. Together, our results show that atlantids would be excellent indicators of many different ocean parameters.

Fossil analysis of two sediment cores collected offshore of the Balearic Islands (Mediterranean Sea) demonstrates that variation in abundance and diversity of atlantids over the last 15-20 ka (since the LGM) reflects known changes in ocean temperature as indicated by commonly used proxies (planktonic foraminifera abundance, diversity and oxygen isotope ratios). This suggests that atlantids could be used as palaeo-temperature indicators. Initial modelling of future atlantid biogeography shows that distributions change considerably with predicted future conditions, often showing a reduction in potential habitat.

The results of this study demonstrate that the atlantid heteropods would be excellent

Work performed

DNA barcoding of 391 specimens was carried out to produce 179 new CO1, 297 new 28S, 278 new 18S sequences of atlantids and the genus Carinaria. These data were used to produce single and combined gene phylogenies, and a fossil calibrated phylogeny. The results show hidden diversity within the atlantids and rapid diversification over the last ~25 Ma. This part of the project has been written up as a manuscript and submitted to the journal Nature Scientific Reports. Once published, the data will be available to scientists working on plankton metabarcoding (e.g. MetaZooGene platform).

Morphometric shell analysis was carried out to clarify species boundaries within the Atlanta brunnea species group and led to the description of a new species, Atlanta vanderspoeli. This part of the project has been published as an article by the journal ZooKeys.

A variety of growth rate and OA experiments were carried out on eight atlantid species during a two-month research expedition (AMT27) in the Atlantic Ocean. Specimens from the two main experiments have been analysed using fluorescence microscopy and microcomputed tomography (micro-CT), to measure the linear shell extension, thickness and volume of the shell grown. The expression of different genes was also analysed. Results indicate a negative response to decreasing ocean pH in the southern Atlantic Ocean. It was also found that high food availability could lead to increased calcification. This part of the project is being prepared as a manuscript and will be submitted to Nature Communications within the next month.

Two sediment cores from the Mediterranean Sea were analysed for their plankton fossil content (planktonic foraminifera, pteropods and atlantids). The abundance and diversity of atlantid species varied through the cores in relation to climate proxies (abundance and diversity of other plankton, oxygen isotope ratios), suggesting a link to ocean changes, particularly ocean temperature.

The geographical distribution of each species was updated from the molecular results and used to extract environmental tolerance data from the BIO-oracle database. The results indicate species-specific tolerances for most parameters. Initial Species Distribution Modelling (SDM) was carried out using these data. Results indicate a decrease in the future habitat suitable for each species. These data still require analysis. It is anticipated that a manuscript will be prepared and submitted to the journal Global Change Biology within a year.

Final results

This project has pushed the boundaries in this field, producing many â€˜firstsâ€™ and making considerable advancements beyond the state of the art. This project has produce the first 28S and 18S gene sequences, the first comprehensive molecular phylogeny and the first time-calibrated phylogeny of atlantids. This study has carried out the first laboratory studies, and OA studies on atlantids, developing techniques for future experimental research (e.g. using fluorescent indicator). Through this project we have been able to address the wider questions of how OA has already, and will continue to affect atlantids, and we are now confident that atlantids are valuable indicators of a range of ocean parameters.