THE EFFECTS OF VARYING SALINITY ON GROWTH AND REPRODUCTION IN THE
COLONIAL HYDROID CORDYLOPHORA.

Michael J. Nies and Nadine C. Folino-Rorem.  
Biology Department, Wheaton College, Wheaton, IL 60187.

Cordylophora, (Phylum Cnidaria, class Hydrozoa, family Clavidae) is a colonial hydroid
occurring throughout the world in Europe, Australia, and the Americas.  Cordylophora exists in
both fresh and brackish water and therefore has an amazing ability to survive in varying habitats.
Since this organism can survive such a wide range of salinity, it has become more prevalent as a
fouling organism in many bodies of water globally and has become an organism of increased
interest.  Cordylophora colonies are dioecious and also reproduce asexually via budding, thus
allowing populations to quickly colonize and proliferate in a given habitat.  This experiment
sought to determine morphological and growth changes with varying salinity for two populations
of the colonial hydroid, Cordylophora.  Freshwater hydroids from the Des Plaines River in
Illinois (salinity 0ppt), and brackish water hydroids from Exeter, New Hampshire (salinity 10ppt)
were utilized.  For each population, six trays were established, each containing twelve slides.  To
each slide, a colony of five feeding polyps (no buds or reproductive polyps were used) was
attached.  All six trays of the Des Plaines population were allowed to acclimate at 0ppt for two
days.  The Des Plaines trays were moved in increments of 2ppt from 0ppt to 10ppt over a
two-week period. Through out the experiment, one tray (of twelve slides) was left in the previous
salinity in order to measure the adaptability and survival of this population at various salinities. 
The same protocol was used for the Exeter population but colonies were transferred from 10 ppt
to 0ppt.  To measure growth and morphological changes, numbers of feeding and reproductive
polyps, and buds were recorded as well as the length of tentacles, and length and width of polyps. 
The Des Plaines colonies generally increased in tentacle length, polyp length and width, and the
number of reproductive and feeding polyps as salinity was increased.  The Exeter colonies
responded in an opposite manner.  As salinity was decreased, the number of feeding and
reproductive polyps decreased over the two-week period.  This decrease eventually lead to many
of the Exeter colonies dying at salinities below 6ppt.  The control population at 10ppt continued
to flourish.  These results suggest that growth in Cordylophora is enhanced in a more saline
environment. This may explain the possible range expansion of this organism as changes in water
quality occur due to runoff and other types of water pollution.

Keywords: hydrozoan, Cordylophora, salinity, growth, fouling