Nematocysts of the invasive hydroid Cordylophora caspia (Cnidaria: Hydrozoa).

Although there is significant genetic diversity among populations of the hydroid Cordylophora caspia, the species has not been split into multiple species or subspecies, in part because its members also show great physiological and morphological plasticity. This plasticity makes new taxonomic units hard to define or identify and obscures the connection between historically used names and the genetically defined clades. We explore variation in nematocysts, a character system not previously assessed in Cordylophora but which has demonstrated phylogenetic signal in other cnidarian taxa. We measured more than 5000 capsules from 112 individuals belonging to 14 populations, including representatives of the major genetic lineages. We found no correlation between the size range of capsules and either clade or salinity. Thus, for C. caspia, nematocysts are neither phenotypically plastic with respect to salinity nor taxonomically informative. Nematocyst size and density in particular tissues may be correlated to other environmental factors (such as prey type, size, and abundance in the location of each population) and may aid in distinguishing more distantly related species.

Genetic analysis across different spatial scales reveals multiple dispersal mechanisms for the invasive hydrozoan Cordylophora in the Great Lakes.

Discerning patterns of post-establishment spread by invasive species is critically important for the design of effective management strategies and the development of appropriate theoretical models predicting spatial expansion of introduced populations. The globally invasive colonial hydrozoan Cordylophora produces propagules both sexually and vegetatively and is associated with multiple potential dispersal mechanisms, making it a promising system to investigate complex patterns of population structure generated throughout the course of rapid range expansion. Here, we explore genetic patterns associated with the spread of this taxon within the North American Great Lakes basin. We collected intensively from eight harbours in the Chicago area in order to conduct detailed investigation of local population expansion. In addition, we collected from Lakes Michigan, Erie, and Ontario, as well as Lake Cayuga in the Finger Lakes of upstate New York in order to assess genetic structure on a regional scale. Based on data from eight highly polymorphic microsatellite loci we examined the spatial extent of clonal genotypes, assessed levels of neutral genetic diversity, and explored patterns of migration and dispersal at multiple spatial scales through assessment of population level genetic differentiation (pairwise F(ST) and factorial correspondence analysis), Bayesian inference of population structure, and assignment tests on individual genotypes. Results of these analyses indicate that Cordylophora populations in this region spread predominantly through sexually produced propagules, and that while limited natural larval dispersal can drive expansion locally, regional expansion likely relies on anthropogenic dispersal vectors.

Microsatellite loci for the invasive colonial hydrozoan Cordylophora caspia.

Cordylophora caspia, a colonial hydrozoan native to the Ponto-Caspian region, has become a common invader of both fresh and brackish water ecosystems of North America and Europe. We describe 11 polymorphic microsatellite loci for this species. Preliminary analyses indicate that population substructure may contribute to departures from Hardy-Weinberg equilibrium. In addition, new loci failed to consistently amplify Cordylophora samples known to be genetically distant from those utilized in this study, indicating the presence of cryptic diversity within the taxon.

Controlling biofouling caused by the colonial hydroid Cordylophora caspia.

The euryhaline hydroid, Cordylophora caspia, causes fouling problems in Europe and the United States. Researchers propose that this hydroid is becoming more prevalent in freshwater habitats as evidenced in Morris, IL where it was found clogging intake pipes and screens at a power plant, Midwest Generation's Collins Station. Our objective was to determine ways to curtail growth or kill C. caspia. Hydroid colonies in the laboratory were exposed to thermal treatments of 35, 36.1, 37.7, and 40.5 degrees C ranging from 1 to 8h. Hydroids did not survive at the two highest temperatures. Colonies exposed to lower temperatures exhibited varying degrees of survival relative to temperature and exposure time and demonstrated regeneration. In addition, experiments using chlorine were conducted using concentrations ranging from 0.2 to 5.0 mgl(-1). Chlorine experiments using exposure times of 105 min and three 20 min exposures in a 24h period did not kill colonies but were effective in curtailing growth. Thermal treatments are preferred because they are effective and result in less environmental impact in receiving waters than chemicals.