MEPS 155:89-101 (1997)  -  doi:10.3354/meps155089

Planktonic oligotrich ciliates in the NW Mediterranean: growth rates and consumption by copepods

Pérez MT, Dolan JR, Fukai E

In May 1995, the planktonic ciliate community of the Ligurian Sea (NW Mediterranean) was dominated by 3 Strombidium species: a mixotroph 16 µm in length, a heterotrophic species 15 µm in length and a larger (26 µm) heterotrophic species. Growth rates of these oligotrichs and their consumption by copepods were examined in 3 shipboard experiments during the JGOFS-France DYNAPROC cruise. Growth rates were estimated by means of 24 h incubations in seawater samples filtered through a 64 µm mesh and apparent growth or disappearance rates were estimated in whole water samples and in incubated samples with copepods added. Ciliate community generation time ranged from 52 to 88 h. Copepod predation was highest on the larger heterotrophic ciliate and higher on the nano-sized heterotrophic species relative to mixotrophic nanociliate. The net growth rates of the mixotroph in 'predator-free' water ranged from 0.2 to 0.4 d-1 compared to rates of 0.9 to 1.0 d-1 in samples with copepods added. Net growth rates of heterotrophic species ranged from 0.2 to 0.5 d-1. The higher mixotrophic growth rates when copepods were present was concomitant with the disappearance of heterotrophic microciliates (2.2 to 9.0 ml cleared of heterotrophic microciliates copepod-1 h-1, estimated clearance rates). While we found that mixotrophs, relative to heterotrophs, may be less subject to copepod predation, data and models suggests that mixotrophic oligotrichs have lower maximal growth rates than similar-sized heterotrophic species.

Mixotrophy · Strombidium · Predation

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