Synchronous Mass Release of Mature Medusae from the Hydroid Halocordyle disticha (Hydrozoa, Halocordylidae) and Experimental Induction of Different Timing by Light Changes

Abstract

The timing mechanism for synchronous mass release of mature medusae of Halocordyle disticha was studied, using colonies from Shirahama, Wakayama, Japan, which were kept in a 450 I aquarium tank. In near natural conditions medusa release is correlated with sudden drop of light intensity such as occurs around sunset. Timing could be manipulated by controlling light intensity. Artificial sunset 2 hours earlier than normal caused mass release of medusae earlier than under natural conditions, whereas sunset artificially delayed 3 hours later than normal caused continuous release of medusa after the onset of darkness. The spawning of gametes of H. disticha is almost simultaneous with medusa release, and since the medusa has an ephemeral planktonic existence, synchrony of mass medusa release and also spawning of gametes may maximize fertilization success.

Constant timing of medusa release in bivalve-inhabiting hydrozoans of the genus Eugymnanthea (Hydrozoa: Leptomedusae: Eirenidae)

“…It can be expected that the release time of E. japonica would not change if the sunset time is artificially delayed or advanced through artificial lighting. This is in contrast to results obtained by Genzano & Kubota (2003) for another hydroid, Halocordyle disticha . Although our observation periods do not cover the whole reproductive season (June–November; see Kubota, 1994), it can be assumed that the release time remains constant.…”

“…In contrast, other hydrozoans such as Halocordyle disticha (Goldfuss) and Millepora species begin to release their short-lived, mature medusae at about sunset and the release is continued for several hours thereafter. The release is immediately followed by spawning in order to maximize fertilization success (Song & Cho, 1998;Genzano & Kubota, 2003). Eugymnanthea species spawn in the morning hours (Kubota, 2004;Govindarajan et al, 2005), therefore the release of medusa is not synchronized with the time of spawning of the gametes.…”

Some anthoathecate hydroids and limnopolyps (Cnidaria, Hydrozoa) from the Hawaiian archipelago

“…Gonophores are eumedusoids, sometimes remaining fixed and sometimes liberated from the hydroid (Hargitt 1900;Brinckmann-Voss 1970). When released, the free eumedusoids are short-lived (surviving a few hours at most) and liberated during evening hours (Hargitt 1900;Baker 1936;Brinckmann-Voss 1970;Calder 1988;Genzano & Kubota 2003). Hoover (1998Hoover ( , 2006 reported that colonies reach about 12 inches (30 cm) high in Hawaii, and specimens up to 22 cm high were observed during this study on a pier at the Hawaii Institute of Marine Biology on Coconut Island in Kaneohe Bay.…”

Fluctuation and diversity of Hydromedusae (Hydrozoa, Cnidaria) in a highly productive region of the Gulf of Mexico inferred from high frequency plankton sampling

“…Medusae are seasonally produced in a synchronized fashion by the benthic polyps (Boero & Bouillon, 1993), but the cues triggering medusa production (and therefore their blooms) are unknown in most species. Circannual rhythms, temperature, salinity, moon phases, dissolved oxygen, and water turbidity have all been proposed as possible cues, but have only been tested on few individual species (Brock, 1975; Genzano & Kubota, 2003; Ma & Purcell, 2005; Stefani, 1956; Werner, 1954; Werner, 1961; Nowaczyk et al, 2016; Wintzer, Meek & Moyle, 2013). Upwelling, which often correlated with high productivity, has also been linked to medusa blooms in tropical waters (Miglietta, Rossi & Collin, 2008).…”