Ecology of Acartia tonsa in Apalachicola Bay, Florida, and implications of river water diversion

Abstract

Acartia tonsa herbivory, carnivory, egg production rate, egg production efficiency, and abundance were studied within various salinity regimes in Apalachicola Bay throughout a 2 yr period. The percent of phytoplankton productivity ingested by A. tonsa ranged from 0 to 24% (median 0.4%). The diet of A. tonsa was mixed. On average, 53% of the diet was composed of phytoplankton. Per capita total ingestion rate averaged 1.1 ± 1.3 (± SD) μg C adult-1 d-1 during winter, peaked to about 6 μg C adult-1 d-1 during summer, and averaged 2.2 ± 1.8 μg C adult-1 d-1 during summer. A. tonsa ingested the equivalent of 38 ± 48% and 120 ± 93% of its body carbon during winter and summer, respectively. During summer, per capita total ingestion rate increased below 20 psu. Average egg production rate (EPR) was lower during winter (13 ± 15 eggs female-1 d-1) than during summer (28 ± 24 eggs female-1 d-1). During summer, EPR peaked between about 4 and 10 psu. During winter and summer, egg production efficiency (EPE) peaked between about 8 and 14 psu. Salinity tolerance and biochemical composition of phytoplankton ingested may have influenced EPE. Phytoplankton allocated more carbon to protein and lipid synthesis in lower salinity water. The areal extent of lower (<20 psu) salinity water decreases in Apalachicola Bay during periods when river discharge is low. Therefore, upstream water diversion during summer can be expected to reduce the areal extent of lower (<20 psu) salinity waters where ingestion rate, EPE, and EPR of A. tonsa are greatest and where A. tonsa is an important prey for Anchoa mitchilli. © Inter-Research 2007.