Seasonal coupling of a tropical mangrove forest and an estuarine water column: enhancement of aquatic primary productivity

Seasonal and spatial patterns of aquatic primary production were compared i n a tidal creek (Estero Pargo) bordered by mangroves and open waters of Ter minos Lagoon, Mexico. Comparisions were made during a 17-month period in 19 90-91 that spanned dry, rainy, and storm or 'Norte' seasons, Annual net pri mary productivity was 478 g C m(-2) yr(-1) in the lagoon and 285 g C m(-2) yr(-1) in the tidal creek. In some months, there were significant differenc es in primary production between the two sites. In both areas, the highest productivity occurred in summer at the start of the rainy season (June 1991 ), and the lowest production occurred during the dry season from February t o May. Aquatic primary production was lower during the dry season of 1991 i n comparison to 1990, possibly related to unusually low precipitation durin g 1991. Seasonal changes in water column productivity were correlated to va riations in light and precipitation. The effect of runoff from mangrove for ests was assessed by serial additions of surface water from a fringe forest to bottle incubations of lagoon water. Small additions of mangrove water s timulated primary production in lagoon waters during all seasons. The net p roductivity was extremely sensitive to aliquot volume; small amounts (0.3 a nd 1.7% of total volume) were stimulatory, increasing rates by > 50% in 7 o f 12 experiments. The greatest effect occurred in September, 1990, when pro ductivity tripled after an amendment with I mi (0.3% by volume) of mangrove water. Additions greater than 3% of total volume generally led to reductio n in net productivity probably due to the inhibitory effect of humic substa nces. In many tropical systems, tidal exchange of estuarine waters with man grove forests is likely to be important to enhancing water column productiv ity by exporting organic nutrients and other growth-enhancing substances to the estuary.