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CARBON BUDGET FOR A SUB-TROPICAL SEAGRASS DOMINATED COASTAL LAGOON: HOW IMPORTANT ARE SEAGRASSES TO TOTAL ECOSYSTEM NET PRIMARY PRODUCTION?
Citation:
Kaldy, J E., C. P. Onuf, P M. Eldridge, AND L. A. Cifuentes. CARBON BUDGET FOR A SUB-TROPICAL SEAGRASS DOMINATED COASTAL LAGOON: HOW IMPORTANT ARE SEAGRASSES TO TOTAL ECOSYSTEM NET PRIMARY PRODUCTION? ESTUARIES. Estuarine Research Federation, Port Republic, MD, 25(4A):528-539, (2002).
Description:
Seagrasses dominate macrophyte biomass in many estuaries. Historically, it has been assumed that because of the large standing stock seagrasses also dominate primary production. We tested this assumption by developing 3 carbon budgets to examine the contribution of autotrophic components to the total ecosystem net primary production (TENPP) of Lower Laguna Madre (LLM), TX. The first budget coupled average photosynthetic parameters with average daily irradiance to calculate daily production. The second budget used average photosynthetic parameters and hourly in situ irradiance to estimate productivity. The third budgeting technique integrated temperature adjusted photosynthetic parameters (using Q10 = 2) and hourly in situ irradiance to estimate productivity. For each budget TENPP was calculated by integrating production from each autotroph based on the producers' areal distribution within the entire LLM. All budgets indicated that macroalgae account for 33-42% of TENPP and seagrasses consistently accounted for about 33-38% of TENPP. The contribution by phytoplankton was consistently about 15-20% and the contribution from the benthic microalgae varied between 8 and 36% of TENPP. Additionally, the water column over the seagrass beds was net heterotrophic and consequently was a carbon sink consuming between 5 and 22% of TENPP. Total ecosystem net primary production ranged between 5.41 x 1010 and 2.53 x 1011 gC y-1, depending on which budget was used. The simplest, most idealized budget predicted the highest TENPP, while the more realistic budgets predicted lower values. Annual production rates estimated using Budget 3 for H. wrightii and T. testudinum compare well with field data. We conclude that macro and microalgae contribute 50-60% of TENPP and that seagrass may be more important as three-dimensional habitat (i.e. structure) than as a source of organic carbon in LLM. TENPP estimates are dependent on the calculation method, which also influences the percent contribution from the components.