Feeding and egg production of Oithona spp. in tropical waters of North Queensland, Australia

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Despite the acknowledged importance of small copepods of the genus Oithona in marine pelagic ecosystems, there is little information about their ecological role, potential food resources and egg production rates (EPR) in tropical environments. In the present study, feeding and EPR of adult females of two species of Oithona were determined in two different tropical marine food webs in North Queensland, Australia, during the 2011 austral autumn. Oithona attenuata was studied in the waters of the Great Barrier Reef lagoon, and Oithona dissimilis was studied in a mangrove area. Oithona spp. ingested dinoflagellates and ciliates preferentially to other prey items of the nano- and microplankton assemblage. Oithona spp. clearance rates on dinoflagellates and ciliates ranged from 3.7 to 10.4 mL female−1 day−1, and from 4.3 to 18.1 mL female−1 day−1, respectively. The daily body carbon ingested per female was <1% when feeding on dinoflagellates, and varied from 1 to 10% when feeding on ciliates. Our results suggest that Oithona spp. feed on small flagellates (5–20 µm), although the contribution of carbon to the diet was low (2.5–3.2% body carbon). Egg production and weight-specific EPR ranged from 0.22 to 3.34 eggs female−1 day−1, and 0.2–4.5% day−1 respectively. The ingestion rates measured in all the feeding experiments were too low to sustain metabolic and egg production costs, indicating that other food resources, not considered in this study, might contribute significantly to the diet of Oithona spp. in tropical environments.

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