Doctor of Philosophy (Ph.D.)
Virginia Institute of Marine Science
M. L. Brehmer
W.J. Hargis Jr.
Hydrozoans of southern Chesapeake Bay and its tributaries were studied from April 1965 until March 1968 to determine faunal diversity, seasonality and reproductive periodicities. Laboratory culture techniques were used in describing unknown or inadequately known stages in the life history of several species and as an aid in identification. A total of 55 species was identified, including 43 hydroids and 32 medusae. Of these, 22 hydroids and 15 medusae are reported in Chesapeake Bay for the first time. Two species earlier reported from the bay, Eudendrium carneum and Blackfordia virginica, were not found. Clytia paulensis and the hydroid of Proboscidactyla ornata are previously unreported in North America, and the hydroid of Amphinema dinema is recorded for the first time from the North American Atlantic coast. The southern range of Hybocodon prolifer, Obelia longissima and Opercularella pumila is extended, as is the northward range of Podocoryne minima, Clytia kincaidi and Phialucium carolinae. Both hydroids and hydromedusae show an affinity with the Carolinian Zoogeographic Province; 76% of the hydroids and 77% of the hydromedusae occur south of Cape Hatteras, while 59% of the hydroids and 35% of the hydromedusae occur north of Cape Cod. The hydroid of Dipurena strangulata and the older medusae of Bougainvillia rugosa and Lovenella gracilis are described for the first time. Partial life histories are described for four other species. The genus Calyptospadix Clarke, 1882 is placed in synonymy with Bimeria Wright, 1859.
Hydroids are shown to be characteristically seasonal in occurrence due to the annual water temperature range, which varies from approximately 2 C to 28 C. During seasons of inactivity, laboratory-tested species, Ectopleura dumortieri, Bougainvillia rugosa and Eudendrium ramosum, remained in a dormant state in the stems, stolons, or both, until favorable temperatures returned. Field observations on other hydroid species indicated a similar phenomenon. Dormant stages are resistant to unfavorable temperatures and may have important implications on hydrozoan zoogeography. In nature, the temperature at which renewed growth commenced in spring for winter-dormant species was higher than that at which regression occurred in autumn, and the converse was true for summer-dormant species. This may be an adaptive mechanism insuring favorable conditions for growth once development has begun. Of 23 hydroids whose seasonality was studied in detail, 16 were ’’summer” species and 7 were ’’winter” species. Among the hydromedusae, seasonality was typically less prolonged, with a maximum diversity in late summer and early autumn and a minimum diversity in winter. Although undescribed species or endemics to the bay were not found, two unidentified hydroids, ’’Campanulina” sp. and coast and should not be ruled out as being new species, endemics or both, until more is known about their biology.
© The Author
Calder, Dale R., "Hydrozoa of Southern Chesapeake Bay" (1968). Dissertations, Theses, and Masters Projects. Paper 1550154024.