Seasonal cycles of activity and inactivity in some hydroids from Virginia and South Carolina, U.S.A.

Abstract

Hydroids investigated in estuaries of Virginia and South Carolina, USA, were characteristically seasonal in occurrence. Of 20 species studied in Virginia, 14 were active only during warmer months and 6 only during colder months of the year. Seven of the 18 species examined in South Carolina were active all year, whereas 9 were active only in warmer months and 2 only during colder months. Reflecting the differing temperature regimes of the two study areas, warm-water species were active for a longer period of time in South Carolina than in Virginia; cold-water species were active longer in Virginia than in South Carolina. Warm-water species commenced activity in late winter or spring at higher temperatures than those coinciding with hydranth regression in autumn or early winter. Activity in cold-water species began at lower temperatures than those observed at regression in spring. Correlations were apparent in the seasonality, water temperature tolerances, and latitudinal distribution of most species. Field observations and laboratory experiments demonstrated that a number of species survived unfavourable periods as dormant coenosarc in stems and stolons. With the return of favourable conditions, new growth began and hydranths were regenerated from dormant tissue. Water temperature is considered the prime factor influencing the seasonal activity–inactivity cycles of hydroids in the two study areas.

Hydroids (Cnidaria, Hydrozoa) of the intertidal zone of Governador and Paquetá islands, Guanabara Bay, Rio de Janeiro, Brazil

“…This small number of species contrasts with that recorded on panels in the São Sebastião Channel, state of São Paulo, where MIGOTTO et al (2001) collected 22 species. This number corresponds to about 1 / 3 of the species recorded in the natural environment (VANNUCCI, 1956;SILVEIRA & MIGOTTO, 1984;MARQUES, 1993;MIGOTTO, 1996), as previously observed by other researchers in different parts of the world (MILLARD, 1959;CALDER, 1990).…”

“…If this hypothesis is valid, the species may effectively inhibit competing organisms. But one must also consider the possibility of not finding some species during their seasonal ''resting periods '' (CALDER, 1990), considering that the collections were made only from August 2004 through January 2005.…”

“…These substrates were investigated because, according to NISHIHIRA (1969), some larvae select the locale where they will settle. Though many authors consider that most hydroids are generalists (CALDER, 1991a), some species of campanulariids and sertulariids are only found as epiphytes. Many epizootic hydractiniids will settle only on a specific species (CALDER, 1991b;.…”

Temporal variation in richness and composition of recruits in a diverse cnidarian assemblage of subtropical Brazil

“…It is also common to see some hydroids that develop into relatively large and robust colonies, which can then resist settlement and overgrowth by other sessile invertebrates, such as sponges, tunicates, and bryozoans (Migotto et al, 2001). Seasonal variation in abundance of hydroids has been associated with activity-quiescence cycles (Bavestrello et al, 2006), recruitment (Migotto et al, 2001), and reproduction (Gili and Hughes, 1995), and fluctuations often follow sudden changes in sea surface temperature (Calder, 1990;Migotto et al, 2001). Most studies on cnidarian seasonality have focused on one or few common species (Bavestrello et al, 2006;Calder, 1990;Migotto et al, 2001), while temporal variation in assemblage structure, including richness and relative commonness and rarity in time and space has not been amply reported.…”

Occurrence and biogeography of hydroids (Cnidaria: Hydrozoa) from deep-water coral habitats off the southeastern United States

“…Seasonal changes in water temperature control reproductive timing in shallow-water coastal hydroids of the mid-SEUS (Calder, 1990), but temperature variability on the SEUS deep-water coral habitats is not well known. Alternatively, reproductive timing may track variation in other environmental factors, such as food supply.…”