Effects of Coastal Acidification on the Metabolism of Eelgrass (Zostera marina) in South Bay, VA
INTRODUCTION
Ocean acidification (OA) generates high CO2 / low pH conditions, affecting an array of marine organisms. However little is known about how acidification affects coastal and estuarine ecosystems, where organisms are affected by multiple biogeochemical cycles. This study investigated how the high pCO2 / low pH conditions of coastal acidification may affect coastal seagrass meadows. These coastal plants provide valuable ecosystem services and can sequester and store as much as 10% of all oceanic organic carbon in organic-rich loams for thousands of years, slowing the rate of climate change. This carbon capture and storage (CCS) depends on two factors: rates of photosynthetic carbon assimilation and on the ability of plant tissues to resist degradation in sediments. Rates of seagrass photosynthesis are not uniform within meadows, in part because of photosynthesis itself depletes pCO2. However, it is unclear if the location of seagrasses within a meadow, and thus their exposure to pCO2, alters tissue qualities in a way that would alter their degradation rates.
METHODS
To test the hypothesis that the location or seagrasses within meadow alters their phenolic biochemistry, this study examined assessed the metabolic processes of eelgrass (Zostera marina) at 30 locations exposed to different daytime pCO2 levels within the large meadow in South Bay, VA. Average daytime pCO2 levels were significantly lower within the center of the meadow where plant densities were highest and photosynthetic processes were greatest (300 ppm), compared to the meadow’s edge (432 ppm). Plant tissue extracts were analyzed through colorimetry, RP-HPLC, and LC-MS.
RESULTS/DISCUSSION
We observed that levels of antimicrobial phenolics (caffeic and rosmarinic acid), as well as the total phenolic acid content in the leaves of eelgrass plants, were 45-70% lower along the meadow’s edges, compared to those growing within the meadow. In contrast, there were no significant differences detected in the levels of soluble sugars, soluble and crude proteins, or lignins at these locations. The loss of soluble antimicrobial phenolics along meadow edges suggests that these same plants may be the most susceptible to outbreaks of Labyrinthula, the seagrass wasting disease pathogen, and less effective at CCS.