Quantifying the effect of seagrass productivity on growth and survival of foraminifera Marginopora vertebralis

Large benthic foraminifera (LBF) contribute significantly to sediments on coral reefs and sandy cays. Like most calcifying organisms, LBF are vulnerable to ocean acidification (OA). Some species such as Marginopora... [ view full abstract ]

Large benthic foraminifera (LBF) contribute significantly to sediments on coral reefs and sandy cays. Like most calcifying organisms, LBF are vulnerable to ocean acidification (OA). Some species such as Marginopora vertebralis live predominantly within seagrass meadows or on algae as epiphytes. Seagrass habitats provide refuge from OA as the photosynthetic uptake of dissolved inorganic carbon of seagrass can increase pH and carbonate saturation. This study aims to determine whether a seagrass habitat can function as a refuge under OA (increased pCO2) conditions by quantifying the effects of seagrass productivity on growth and calcification of M. vertebralis. In a 5 week experiment, M. vertebralis growth, survival, and photochemistry (using PAM fluorometry) were investigated for 4 different habitat treatments (glass tank, sand only, seagrass and sand, and artificial grass and sand). Initial results from the first 4 weeks showed greater M. vertebralis mortality (≥20%) in treatments without seagrass Cymodocea rotundata than in treatments containing the seagrass (11.8%). Short-term incubations (≤ 24 hours) under controlled laboratory conditions investigated differences in productivity and calcification of M. vertebralis with and without C. rotundata. As a literature search presented inconsistent results on pCO2 effects on LBF, a range of pCO2 concentrations (300-3000µatm) were tested to determine under which condition M. vertebralis becomes adversely affected. Incubations were then repeated using seagrass treatments to determine whether the seagrass counteracted the negative effect of increasing pCO2. These preliminary results indicate that there may be some benefit to living amongst seagrass, although calcification and productivity may or may not be affected significantly by this relationship. Pending data and analysis from short and long-term experiments will be presented to determine whether such organisms may have mechanisms to persist under OA scenarios. This will allow us to refine estimates and indicate whether community structures will change as drastically as predicted.