Phytoplankton Production and Seasonal Biomass Variation of Seagrass, Ruppia maritima L., in a Tropical Mexican Lagoon with an Ephemeral Inlet

Abstract

Plankton metabolism andRuppia maritima biomass were measured seasonally during 1982–83 in El Verde Lagoon, a small coastal lagoon with an ephemeral inlet on the Pacific Coast of Mexico. Total net aquatic primary production was 521 g C m−2 y−1. The water column was slightly heterotrophic, with an annual P/R ratio of 0.89. Our analysis indicates that tropical and subtropical coastal lagoons with restricted or seasonal inlets have generally higher net aquatic primary productivity levels than lagoons with permanently open inlets. We hypothesize that this is due to retention of nutrients and plankton stocks during the dry season. The seasonal pattern of water column metabolism was related to rainfall and riverflow, with higher values generally occurring during the wet season. Net production and respiration were about three times lower during the 1982 dry season as compared to the 1983 dry season which received considerable rains due to abnormal climatic conditions. The biomass ofR. maritima ranged from zero to 620 g dry wt m−2. Growth occurred only during the dry season and there were two distinct biomass peaks representing two separate crops. The second crop was heavily epiphytized with nitrogen-fixing algae. There was an apparent succession in dominance of water column productivity over the year, withRuppia dominating during the dry season and phytoplankton more important during the wet season.