TRACE METAL CYCLES IN SEAGRASS COMMUNITIES

Abstract

Processes which make essential trace metals, as well as other nutrients, readily available may account for the distribution of and patterns of succession in seagrass meadows. Complete inventories of Fe, Mn, Zn, and Cu were compared for the five species of Texas seagrasses from study areas in Redfish Bay and Northern Laguna Madre. Seasonal fluctuations in an area were minimal, while major areal differences between plants in Laguna Madre and Redfish Bay were detected. The seagrasses from Laguna Madre contained more Mn and less Fe (Halodule leaf avg. Fe/Mn ratio = 0.37, avg. Mn = 250 ppm) than Redfish Bay plants (Halodule leaf avg. Fe/Mn ratio = 4.0, avg. Mn = 90 ppm), although sediments from Laguna Madre had 50% lower concentrations of leachable (i.e. “available”) Fe and Mn than Redfish Bay sediments. Measurements showed that seagrass detritus remained high in the 4 trace metals; thus unless the detritus is recycled at its source of production, large amounts of metals will be removed from the ecosystem. We suggest that recycling of detritus and gradual release of nutrients into the water column in the closed Laguna Madre system may be more advantageous to seagrass growth than increased levels of trace metals in the sediments of a more open system such as Redfish Bay.