Zostera muelleri patches in New Zealand affect the sediment carbon consumption dynamics across patch boundaries into the surrounding unvegetated sediment

Abstract

Seagrass beds are recognized for being a very efficient natural carbon sink. In the face of the climate crisis, there has been an increased interest in seagrass for its ability to reduce atmospheric carbon concentrations through biological processes. Practices that have contributed to high CO2 levels have also negatively affected seagrass distribution in the intertidal. Urbanization has indirectly caused sedimentation and eutrophication in the oceans, which has reduced light availability, causing seagrass beds to become more fragmented, changing the landscape and patch configuration. In recent studies, scientists have worked to quantify the carbon stocks associated with seagrass beds but have failed to consider how landscape attributes may contribute variability to the results. This study works to assess how the spatial complexity of seagrass patches influences the carbon dynamics, including consumption and sequestration, across the patch boundary. Carbon consumption rates were quantified in the top 15cm of sediments in Zostera muelleri patches in New Zealand using rapid organic matter assay (ROMA). Carbon storage was measured by taking sediment samples from the top 9cm and running them through Elementar’s TOC cube. Other biophysical properties, including chlorophyll a and organic matter in the sediments, were quantified in the middle, edge, outer edge, and on the outside of six patches with different perimeter-to-area ratios. The results indicate that the spatial configuration of the patch has no real bearing on the carbon dynamics. However, this research highlights the importance of the surrounding sediment, as carbon consumption and sequestration were done at similar rates in unvegetated sediment as they were in vegetated sediment. Furthermore, the rate of carbon consumption was found to have no relationship to storage rates, emphasizing the importance of measuring both factors when determining the benefits of seagrass. The results presented have real implications for seagrass conservation and restoration efforts. They suggest that seagrass has a broader impact on blue carbon stores than initially thought, as the surrounding sediment stores carbon at similar rates. While the implications of these findings are not restricted to the region and species they were found on, there is a need to expand this research to other species. Additionally, the need to conduct similar studies on patches with larger differences in their perimeter-to-area ratio has been identified to definitively state that the size of the patch has no impact on carbon dynamics.