Notes on the morphology,ecology and life cycles of Fukaurahydra anthoformis and Hataia parva (Hydrozoa,Athecata)

Fukaurahydra anthoformis and Hataia parva are solitary athecate hydroids occurring in northern Japan. New information on the external morphology, nematocysts, ecology, and life cycles of these species is presented. It is noteworthy that H. parva bears stenoteles, which are generally not found among the families of Filifera. Neither species produces free medusae. The eggs are fertilized in the female gonophores, from which unciliated larvae are released. These larvae do not swim and soon attach to a substrate. After attachment the larvae become covered by a sheath to form cysts. The cysts rest on a substrate without any outer change for several months. As the water temperature drops in autumn to early winter the cysts begin to hatch, forming tiny polyps after the larva creeps out from the chitinous sheath. Cyst formation proves to be common also in other solitary hydroids, most of which are inhabitants of cool or cold waters.     

Abundance and distribution of hydroids in a mangrove ecosystem at Twin Cays,Belize, Central America

Qualitative and quantitative collecting was undertaken in 1987 to determine the species composition, abundance, and distribution of hydroids in a mangrove system at Twin Cays, Belize. Of 49 species identified, the 5 most frequent were Ventromma halecioides, Nemalecium sp., Clytia hemisphaerica, Dynamena crisioides and Halopteris diaphana. Line-transect census data and qualitative observations showed that the hydroid fauna was sparse in sheltered, still-water areas of the mangal, but relatively abundant and diverse in areas exposed to waves and/or tidal currents. Species composition and relative abundance varied with depth at stations in exposed locations and in tidal creeks and channels. Although Turritopsoides brehmeri is known only from Twin Cays at present, it seems improbable that any of the species is restricted to mangrove ecosystems.     

Potential antifouling strategies for marine finfish aquaculture: the effects of physical and chemical treatments on the settlement and survival of the hydroid Ectopleura larynx

The hydroid Ectopleura larynx is a common fouling organism on aquaculture nets. To contribute to the development of novel cleaning methods, laboratory and field studies determined the effects of heat (30, 40, 50 and 60°C for immersion times of 1 and 3 s) and acetic acid (0.2 and 2.0% for immersion times of 1, 3 and 10 s, 1 and 5 min) on the settlement of actinulae and the survival of juvenile and adult E. larynx. Laboratory studies showed that, regardless of immersion time, a temperature of 50°C was effective in preventing the settlement of actinulae and the survival of juveniles, while ≤12% of adult hydroids could survive. A temperature of 60°C killed all adult hydroids. For an acetic acid concentration of 0.2%, an immersion time of 1 min substantially reduced the settlement of actinulae and the survival of juvenile and adult hydroids, and none of the juvenile and adult hydroids survived after 5 min. For an acetic acid concentration of 2.0%, all immersion times were effective and reduced the mean settlement of actinulae and the survival of juvenile and adult hydroids to ≤10%. Field studies with fouled net panels exposed to selected heat or acetic acid treatments showed small reductions in mean wet weight and net aperture occlusion of the net panels 2 and 5 days after treatment. Visual inspections of the net panels showed that hydranths of the hydroids were shed, but the dead stolons of the hydroids remained on the treated net panels. Novel cleaning methods and devices may utilise these results to effectively kill E. larynx on aquaculture nets, while further studies are needed to determine the necessity of removing the dead hydroids before further biofouling accumulates on thenets.     

Colony Structure and Seasonal Differences in Light and Nitrogen Modify the Impact of Sessile Epifauna on the Giant Kelp Macrocystis pyrifera (L.) C Agardh

The presence of the stoloniferous hydroid Obelia geniculata (L.) had no effect on the pigment concentration or nitrogen status of underlying blade tissue of the giant kelp Macrocystis pyrifera (L.) C. Agardh. The sheet-like colonies of the bryozoan Membranipora membranacea (L.) markedly reduced the pigment concentration of colonized blade tissue, but only during winter. Reductions in pigment concentration are most likely a result of damage to underlying tissue due to some factor related to the presence of bryozoan colonies on blade surfaces. Blade tissue colonized by M. membranacea also had higher δ¹⁵N signatures than surrounding bryozoan-free tissue, possibly indicating the provision of nitrogen to M. pyrifera by bryozoan colonies. Results show that seasonal changes in nitrogen and colony size can strongly modify the effect of epifauna on macroalgae they colonize. Unlike bryozoans, hydroid colonies provided no barrier to nitrogen uptake by colonized M. pyrifera tissue and enhanced ammonium uptake was observed for tissue colonized by O. geniculata during nitrogen limitation. Epifauna with stoloniferous growth forms such as hydroids are more likely to have benign or even mutualistic relationships with macroalgae they colonize than the sheet-like colonies of bryozoans.     

Species of Oswaldella Stechow, 1919 (Cnidaria, Hydrozoa) from recent antarctic expeditions with R. V. 'Polarstern', with the description of eight new species

Twelve species of the genus Oswaldella Stechow have been studied, eight of which are new to science [Oswaldella delicata sp. nov., O. encarnae sp. nov., O. garciacarrascosai sp. nov., O. gracilis sp. nov., O. grandis sp. nov., O. incognita sp. nov., O. obscura sp. nov. and O. rigida sp. nov.], originating from the Weddell Sea and collected by several antarctic expeditions with R.V. Polarstem. Each is described and figured, its systematic position is considered and current data concerning its autecology and geographical distribution are given. Finally, a comparative table is presented including the principal features of all known species of the genus.     

The growth patterns of some hydroids that are obligate epiphytes of seagrass leaves

The growth patterns of the hydroids Campanularia asymmetrica, Sertularia perpusilla and Algaophenia harpago on the Mediterranean seagrass Posidonia oceanica, and of Laomedea angulata on the temperate seagrass Zostera marina, were examined. The seagrass leaves grow from a basal meristem and have a short life which presents problems for these long-lived obligate epiphytes. Downward growth onto younger leaf tissue, shown by S. perpusilla and C. asymmetrica, reduces the risk of interspecific competition with other epiphytes, and places the hydroids on substrates that survive longer than older distal leaf tissue, close to short young leaves which they can colonize by stolon transfer. S. perpusilla was found only on the basal areas of leaves, possibly because of the progressive degeneration of their most apical tissue. C. asymmetrica showed no such degeneration and was found over most of the length of the leaves. The hydrorhizae of most small A. harpago and L. angulata grew both upward and downward along the leaves. Both species were most abundant on the apical halves of older leaves. This distal distribution is considered to be advantageous for these large branched hydroids which are suited for capturing planktonic prey, and to enhance their probability of colonizing neighbouring plants. Its disadvantages include the reduced probability of maintaining the hydroids on the same plant and an increased risk of being eaten by seagrass grazers.     

Physiological and metabolic aspects of experimental heterochrony in colonial hydroids

Hydractiniid hydroids display a range of morphological variation from sheet-like to runner-like forms, thus exemplifying the patterns of heterochrony found in many colonial animals. Experimental studies of clonal replicates of a Podocoryne carnea colony demonstrate a relationship between these heterochronic traits and physiological and metabolic factors. While colonies exposed to dilute solutions of 2, 4-dinitrophenol (an uncoupler of oxidative phosphorylation) for 4 hours per day show a strong dose-response relationship between within-colony gastrovascular flow rate and the timing of morphological development, colonies exposed for 20 hours per day fail to show this relationship. Spectrofluorometric measures of redox state suggest that the degree of “loose-coupling” of oxidative phosphorylation is proportional to the exposure time. Thus colonies exposed for 20 hours have significantly diminished ATP production relative to colonies exposed for 4 hours. Two underlying factors may be responsible for the breakdown of the dose-response relationship between flow rate and development: (1) colonies exposed to a high dose of uncoupler for 20 hours per day allocate a larger-than-normal share of their total energy budget into maintaining the minimal flow rate required physiologically, and (2) colonies' redox state has a direct effect on the timing of morphological development. The latter effect is particularly intriguing, given the extensive literature relating “metabolic activity” to development. In general, these results suggest a relationship between energy allocation, metabolism, and development in these hydroids, and these interrelationships may be central to the evolutionary process of heterochrony.     

Protection of the hermit crab Pagurus pollicaris say from predators by hydroid-colonized shells

Only one study has shown that a hydroid-colonized gastropod shell was a deterrent to predation on hermit crabs. In the present study, the hydroid-colonized shell protected the hermit crab Paguruspollicaris Say from the shell-crushing stone crab Menippe mercenaria (Say) and the non-shell-crushing octopus Octopus joubini Robson. The shell-crushing calico crab Hepatus epheliticus (Johansson) was not deterred, however, by a hydroid-colonized shell.     

Regression and replacement of hydranths in thecate hydroids,and the structure of hydrothecae

In 1953 the author described a regression and replacement cycle of hydranths in Laomedea flexuosa and proposed that this is a common feature of thecate hydroids. Here examples are presented of replacement of hydranths in species from 5 families of thecates, but it has not been demonstrated that this is as common as had been thought. More continuous studies are needed. A brief consideration is given to the origin of hydrothecae and their development.