Production and consumption of biological particles in temperate tidal estuaries

The question is reviewed whether a balance exists between production and consumption of biological particles in temperate tidal estuaries and what the relationships are between the magnitude of production and consumption processes and system carbon metabolism. The production terms considered are primary production by phytoplankton, microphytobenthos, macroalgae and vascular plants and the chemoautotrophic production, mainly by nitrifying bacteria. The consumption terms are generalized by considering pelagic and benthic mineralization, but major consumer compartments, heterotrophic bacteria, zooplankton, meiobenthos, and macrobenthos are considered in detail. The proposition that estuaries are heterotrophic systems, and become more so when nutrient inputs are higher, is confirmed, and a general equation relating respiration to production is proposed as log R = 0.081 + 1.02 log P (R and P in gC m(-2) yr(-1)). This equation suggests that the amount of heterotrophy is a constant fraction of production. Annual pelagic primary production values lower than 160 gC m(-2) yr(-1) in nutrient- rich or heterotrophic systems are the result of light limitation. The overall recycling efficiency is constant, between 0.7 and 0.8, and is thus independent of system characteristics. Organic loading, rather than inorganic nitrogen loading, ultimately appears to control the primary production in estuarine systems. It is difficult to predict and compare phytoplankton primary production in different estuaries because it is not always clear whether gross or net primary production has been measured. Annual production in some estuaries is probably nitrogen-limited. When phytoplankton is light-limited, annual gross primary production can reasonably be predicted from biomass, incident irradiance and light availability in the water column (photic depth). It appears that interannual variations in annual production are mainly due to (the timing of) different climatological conditions, such as the amount of rainfall and sunshine. Phytoplankton biomass is lower in macrotidal estuaries than in microtidal estuaries. Despite the fact that phytoplankton primary production is controlled by nutrients or light, phytoplankton biomass seems to be determined by the biomass of suspension feeders. Primary production by nitrifying bacteria can be important in estuaries with a heavy organic load. The main suspension feeders in macrotidal estuaries belong to the macrobenthos. The feeding relations between macrobenthos and the production and sedimentation of organic matter in the water are therefore emphasized. For macrobenthic suspension feeders, it is argued that the system-wide biomass and secondary production are limited by the planktonic primary production of the system, whereas the local biomass is highly dependent on hydrodynamic conditions. Macrobenthic deposit feeders take a share of the sedimenting organic matter that depends on the quality and quantity of the organic carbon arriving at the sediment/water interface. Surface deposit feeders directly take up a considerable fraction of the freshly deposited organic matter. Deep deposit feeding is limited by adverse chemical conditions al high organic loading; microbiota take the largest share under these conditions. At low and intermediate loading levels, deep-deposit feeding animals are responsible for a relatively large share of the macrobenthos. [KEYWORDS: Copepod eurytemora-affinis; long-island sound; particulate organic-matter; mesohaline chesapeake bay; coastal marine-sediments; eelgrass zostera-marina; st-lawrence-estuary; mytilus-edulis-l; macrobenthic community structure; bacterial sulfate reduction]