Non - structural carbohydrate reserves of eelgrass Zostera marind

The high minimum light requirement of eelgrass Zosfera marina L. suggests that this species has difficulty in maintaining a positive carbon balance except under high fight conditions. The carbon balance of Z. marina can be studied by following seasonal changes in non&ructural carbohydrate (NSC) reserves, however, little is known about the seasonal variation in NSC reserves in seagrasses or the influence of shading on NSC reserve content and distribution. Seasonal changes in eelgrass NSC reserves were measured in a shallow coastal lagoon, Chfncoteague Bay, Maryland/Virgima, USA, near the southern edge of this species’ distributional range. Concentrations of sugar varied seasonally in leaves, rhizomes and roots, with maxhnum concentrations occurring in the rhizomes. In contrast, starch concentrations did not vary with the season, but were highest in the roots. Seasonal peaks in rhizome NSC reserves parallel the spring and fall bimodal growth patterns observed for Z. marina in the region. Total NSC reserves change from an estimated 52 to 73 g mJ in June to 4 to 18 g rns2 in January, or a decrease of 75 to 92 %. Experimental shading for 3 wk in the spring reduced (p c 0.001) sugar but not starch concentrations in leaves (48%), rhizomes (40%) and roots (51%). ln addition, shading reduced (p e 0.05) leaf biomass (34 %), root and rhizome biomass (23 %) and density (27 Yo). Potential NSC reserve storage during shading was reduced by an estimated 86%. Spring appears to be an important time for both growth and storage of NSC reserves in 2. marina, and the NSC reserves are generally depleted throughout the remainder of the year. Turbidity during thts springtime ‘window of opportunity may jeopardize subsequent snrvival as a result of inadequate NSC reserves to maintain a positive carbon balance during the rest of the year.