Spatial and Temporal Patterns in the Occurrence of Peritrich Ciliates as Epibionts on Calanoid Copepods in the Chesapeake Bay, USA

Abstract

We investigated temporal and spatial patterns of distribution in two peritrich ciliates (i.e. Zoothamnium intermedium and Epistylis sp.) living as epibionts on calanoid copepods (i.e. Acartia tonsa and Eurytemora affinis) in Chesapeake Bay. Net tow samples collected along the main axis of the Bay were analyzed to estimate the occurrence of epibionts on copepods and to explore relationships among infestation prevalence, host abundance, and environmental variables. Zoothamnium intermedium and Epistylis sp. colonized populations of A. tonsa during spring and summer months, while only Z. intermedium colonized E. affinis during spring. Occurrence of epibionts on copepods showed high interannual variation, marked seasonality, and geographic heterogeneity. Extensive statistical analyses rejected simple scenarios of interactions between epibiosis, environmental variables, and host density, suggesting a more complex dynamics for the system. Analyses of epibiont colonies and zooids per host area (i.e. the sum of width and length of the body including antennae and swimming legs calculated assuming a cylindrical shape) were also performed. Overall, epibiont infestation prevalence (i.e. colonies/host area) and load (i.e. zooids/host area) were higher on copepodites than on adults for both host species, suggesting a preferential attachment to juveniles, or a higher predation pressure on adult stages. Infestation density and loads of both epibiont species were higher on the cephalothorax and abdomen of A. tonsa and E. affinis in comparison to the antennae and swimming legs, suggesting that ciliates can more easily colonize less active parts of the host.

Attachment of the peritrich epibiont Zoothamnium intermedium Precht, 1935 (Ciliophora, Peritrichia) to artificial substrates in a natural environment

“…Filters were omitted from the preparation and cover slips were run throughout the procedure and mounted on glass slides. Protargol slides were observed using light microscopy, and morphological characteristics such as organization of the oral apparatus were observed for each Zoothamnium colony and compared to the described morphology of Z. intermedium attached to copepods (Utz and Coats, 2005).…”

“…Identification of Z. ntermedium was confirmed by staining infested copepods randomly selected from the samples (~5 copepods/ sample). The Protargol staining technique (Zagon and Small, 1970) was run following the procedure described in Utz and Coats (2005), and diagnostic characteristics of Z. intermedium were observed using light microscopy. Infestation prevalence (percentage of copepods carrying epibionts) was calculated for adults and copepodites of both host species.…”

“…Previous studies (Utz and Coats, 2005) showed that Z. intermedium colonizes only these two species of copepods in the field, even when they are not the most abundant species in the zooplanktonic community. Laboratory studies also demonstrated that telotrochs of Z. intermedium failed to colonize non-living substrates, living only about 9 hours after being released from the colony without having a suitable host (Utz, 2003).…”

Growth of the peritrich epibiont Zoothamnium intermedium Precht, 1935 (Ciliophora, Peritrichia) estimated from laboratory experiments

“…These Petri dishes were incubated for 3 days before the beginning of the experiment to allow bacterial growth. As food for the copepods, the diatom Thalassiosira weisflogii (Grunow, 1880), cultured as described in Utz and Coats (2005), was added at a final concentration of 1 x 103 cells.mL ) with three replicates per treatment and one infested host per replicate. Experimental chambers were kept in an incubator at 20 °C with photoperiod of 14:10 light:dark hours.…”

“…Copepods were transferred to 4 -L beakers (3 cultures for each species) containing 2 L of < 0.45 μm filtered seawater with salinity adjusted for 15 psu. Cultures of clean copepods (without epibionts) and of copepods carrying Z. intermedium were maintained following the methods described in Utz and Coats (2005). The cultures were maintained in the laboratory for at least two weeks before starting the experiments.…”