The workshop took place at the Institute for Marine and Antarctic Studies (IMAS) in Hobart on March 25th and 26th. Kerrie Swadling organised it, and the discussions were led by K. Swadling, A. Makhado, and P. Koubbi, who are the leaders of the PHOCIS project: Pelagic high seas ocean ecoregionalisation of the Indian subantarctic. The workshop brought together participants from various countries, including Australia, South Africa, India, Japan, and France. The total number of participants was 20.
The workshop provided a detailed overview of oceanographic and biogeographic knowledge, focusing on key initiatives and findings in the Southern Indian Ocean region and the subantarctic zone. Planktonic and micronektonic species play pivotal roles in the trophic web and are important to consider in conservation ecology. They serve as indicators of water masses or oceanographic regions and are significant prey for seabirds and marine mammals. Given that some of these predators face threats from climate change and anthropogenic activities, understanding their foraging habitats becomes imperative for effective conservation efforts.
The workshop began by discussing the importance of environmental regionalisation, highlighting efforts to define coherent physical and biochemical regions within the area.
A significant part of the workshop was dedicated to the Continuous Plankton Recorder (CPR) program. The CPR delivers a consistent and reproducible method for monitoring surface plankton diversity and abundance over large sections of the Southern Ocean and can provide genus level (or higher) community composition information. This publicly available data set allows the user to map species distributions, abundances, and temporal changes to plankton distribution, providing crucial information about zooplankton and phytoplankton communities. The program has resulted in numerous publications, contributing to our understanding of Southern Ocean ecosystems. South Africa and France will be analysing CPR samples from transects going towards the Prince Edward Islands (PEI) and French Southern and Antarctic Lands (TAAF). These transects will fill the geographic gaps left by the unsampled areas of the Southern Ocean CPR program.
Furthermore, the workshop highlighted the efforts of various countries, including Australia, South Africa, Japan, France, and India, to conduct net sampling initiatives. These initiatives aim to fill data gaps and provide insights into mesozooplankton, macrozooplankton and mesopelagic fish species presence or abundance between the Southern Ocean and the Indian Ocean. Discussions during the workshop and research presentations underscored the importance of collaborative efforts in analysing and sharing data. Participants emphasised the need for high-resolution observations and datasets to improve our understanding of ecoregionalisation, food web dynamics, and species shifting in response to climate change. In this report, recommendations are made for future research, including the establishment of data-sharing platforms and the development of standardised protocols for sampling and analyses.
During the workshop, two numerical/modelling approaches for predicting species distributions and defining ecoregions in the Southern Indian Ocean and subantarctic were discussed: habitat suitability modelling (HSM) and identification of species assemblages.
Habitat suitability modelling (HSM) focuses on individual species. It uses environmental data, such as temperature and depth, to model the distribution of each species based on its preferred habitat. These predicted distributions are then grouped together to define ecoregions. While HSM offers a detailed picture for each species, it can struggle with rare species due to limited data and can be computationally expensive for complex models with many species. The identification of species assemblages takes a different approach. Here, the focus is on identifying groups of species that frequently co-occur. Once these assemblages are defined, researchers can use habitat suitability models or network analysis to predict their spatial distribution. Finally, ecoregions are defined based on the distribution of these assemblages, effectively incorporating all species in the analysis. However, this method assumes that species within an assemblage will have similar responses to environmental conditions.
Both approaches rely on existing datasets, primarily obtained from global biodiversity portals such as GBIF (Global Biodiversity Information Facility) and OBIS (Ocean Biodiversity Information System). These datasets encompass large-scale presence-only observations collected using various sampling gears. However, this diversity of sampling methods introduces potential biases due to the gear-specific targeting strategies. To mitigate these biases and enhance the data's quality, a comprehensive pre-processing step is crucial. This pre-processing should involve using the available metadata, potentially incorporating expert judgement, to ensure the data's suitability for the intended analyses. The spatiotemporal coverage of these datasets is extensive, but their quantitative representation may be limited. Addressing these limitations will be essential for robust ecological inferences. Additionally, the analysis can incorporate finer-scale surveys or Continuous Plankton Recorder (CPR) data, which is valuable due to its standardised sampling protocols and the consideration of the abundance of species. However, abundance data may be more prone to sampling biases than presence-only data, and the scaling of abundance data across different sampling methods needs to be addressed.
A sensitivity analysis will be conducted to assess the influence of data type (presence-only vs. abundance) on the outcomes of both approaches. This analysis will involve comparing results obtained using each data type and evaluating the degree of concordance or discrepancy. The results of this analysis will inform the decision of whether to conduct separate analyses based on data type or attempt to integrate the data types in a joint analysis. Integrating presence-only and abundance data requires careful consideration of potential biases and methodological challenges. Statistical methods for integrating presence-only and abundance data need to be carefully selected and applied.
Overall, the workshop emphasised the critical role of oceanographic and biogeographic data in advancing our knowledge of Southern Ocean ecosystems and informing conservation and management strategies. It underscored the importance of international collaboration and ongoing monitoring efforts to address knowledge gaps and challenges in marine research.