Nutrient subsidies from nekton in salt marsh intertidal creeks

Abstract

Motile organisms are thought to play a role in biogeochemical cycles in tidal systems, but few studies have addressed links between animal activities and dissolved nutrients. Our observations and experiments indicated that movements, feeding, and excretion by fishes and shrimps resulted in subsidies of NH4+ and PO43- to intertidal salt marsh creeks. During low tide, isolated pools inhabited by nekton became biogeochemical hotspots with up to fivefold increases in water column nutrient concentrations. In field experiments, simultaneous measurements in artificial pools and an adjacent natural intertidal pool demonstrated that nekton were sources of NHz 4 during day and night, contributing 17-109% of the net increase in NH4+ and 3-18% of the PO3{ 4 in the natural intertidal pool. Nekton residing in intertidal pools generated the equivalent of 5% of the total NH4+ imported to the creek. At night, nekton in pools contributed the equivalent of 12% of the NH4+ and 4% of the PO43- imported from the subtidal channel. As the tide flooded the intertidal creek, nutrient enriched pool water was pulsed up the creek and into the intertidal basin. Tidally controlled patterns of nekton movements and feeding result in retention and reintroduction of nutrients to the upper reaches of intertidal creek basins. Accordingly, nekton contribute to the recycling of nutrients through a positive feedback loop that may enhance primary production and invertebrate prey within salt marsh creek basins. We conclude that nekton can be important and underappreciated contributors of dissolved nutrients in tidal systems. © 2013, by the Association for the Sciences of Limnology and Oceanography, Inc.