Chapter 9 Aquatic Primary Production in Coastal Lagoons

Abstract

Measurements of hourly, daily and annual rates of aquatic primary production in coastal lagoons are now numerous, but the mechanisms that regulate primary production are still difficult to assess. Short term dynamics in functioning and diversity in geomorphological configuration, hydrodynamics, nutrient supply, and autotrophic populations, as well as the usage of various methods in primary production measurements, are among some reasons. Mesotrophic to eutrophic choked lagoons with depths exceeding about two meters and light limitation at the bottom are commonly phytoplankton based. In shallower choked to restricted lagoons with high nutrient loading perennial macroalgae appear in succession with phytoplankton. Restricted to leaky lagoons harbor more macrophytes and species predominance is selected by a combination of depth, tidal flushing, and nutrient loading. Nutrient budgets for coastal lagoons are still lacking, but external inorganic nitrogen loading seems to supply 5-20% and sediment release 5-30% of primary production demand. Regenerated production is thus high and its largest fraction is maintained by nutrient recycling in the water column. In comparison to primary production yield, approximately 10-25% of carbon is accumulated in lagoon sediments. Many tropical and sub-tropical lagoons particularly those with typical dry/wet seasons are marked by seasonal shifts between autotrophic and heterotrophic metabolism Beholding exceptions, annual primary production ranges from 200 to 500 g Cm−2year−1, and is highest in tropical choked phytoplankton based lagoons and those governed by macrophytes. Global coastal lagoon primary production is estimated at 1011kg C year−1 and is similar to the contribution by upwelling areas and by a factor of four less than estuaries where primary production per unit area is similar to that in lagoons.