Hydrozoan biology: the view from a workshop

Abstract

The Hydrozoan Society was founded in 1985 with the aim of promoting all aspects of the study of hydrozoans, from taxonomy, ecology and physiology to molecular biology. Instead of holding meetings with a formal agenda of talks and lectures, the Society has carried out its objectives by organizing workshops, which encourage internal work groups and new collaboration. Conference sessions and round tables are nevertheless an important activity of the Society and are where the most recent research in the field of hydrozoan biology is presented. The 6th Workshop of the Hydrozoan Society was held in June 2007 at Plymouth in collaboration with the Marine Biological Association of the United Kingdom. It followed the same philosophy as before and as usual the working atmosphere was very open and enthusiastic, making it easy for young scientists to collaborate with more experienced researchers. This propitious environment has always been a key factor in the Society’s activities (Boero, 2007) and it has distilled into one of its best legacies. The Society does not have an official consolidated structure, since it is the work of researchers during and between the workshops that gives it direction and consistency. In addition, although the structure is not very rigid, this actually promotes collaboration and the participation of specialists in joint projects and other activities. Like previous meetings, the Plymouth Workshop hosted a wide range of themes related to the biology of hydrozoans (Mills et al., 2000). The diversity of the work presented, however, was even broader than hitherto. The scientific community has evolved to such an extent that, although basic research on taxonomy and ecology continues hydrozoans also offer a resource increasingly used for studies related to genetics and molecular biology. Papers from this meeting report a bright spectrum of discoveries but do not pretend to include all strands of contemporary research. Many of the authors work at only one remove from live material in the field. Indeed, the Society’s meetings are held within sight of the sea (and where freshwater forms such as hydra are rare). A group of papers on ecology and distribution is full of surprises. The exploration of new habitats, such as the mid-water ecosystems, has led not only to the discovery of new species but also to an understanding of the functions of mid-water habitats and of new aspects of the biology and ecology of their pelagic fauna (Lindsay et al., 2008). The capture of large amounts of phytoplankton and its digestion confirm the omnivorous and also herbivorous feeding of hydroids and hence their significant role in transferring energy from pelagic to benthic ecosystems (Gili et al., 2008). Detailed studies even of highly surveyed areas, such as the Mediterranean, provide unexpected observations concerning unknown species and their life cycles, which demonstrate that even in the best-known areas there is still much to discover (Gravili et al., 2008). This has been the case in the rediscovery of Protohydra leuckarti near Plymouth (Kilvington et al., 2008). The study of colonization processes in species with a patchy distribution has also given unforeseen results, such as asexual reproduction processes not being those which favour aggregation, whereas patchiness in some species is explained by the poor dispersion capacity of larvae with a sexual origin (Marfenin & Belorustseva, 2008). In epiphytic hydrozoan communities, the pattern of biodiversity is related to microhabitat characteristics associated with the algal host’s morphology, on a scale very different from that of environmental processes such as the physical drivers of glacial activities in Arctic communities (Ronowicz et al., 2008). A study of the morphological characteristics of different ecological strategies such as phalanx and guerilla phenotypes in Hydractinia suggests that the traditional view of guerilla growth as an adaptive strategy is no longer correct, and that in several species guerilla-like growth is better seen as poor adaptation (Ferrell, 2008). In populations of tropical hydroids, studies of seasonal variation show that seasonal trends are linked to rainfall and hence to abundant food availability (Di Camillo et al., 2008). Environmental differences in temperature and salinity influence the timing of asexual budding in a hydromedusa (Proboscidactyla) (Kawamura & Kubota, 2008). In bivalve-inhabiting hydroids, the liberation of medusae occurs regularly, and although they are all released at sunset this is not related to a decrease in light intensity (Kubota, 2008a). Hydrozoans which form large colonies, such as the genus Eudendrium, host rich epibiontic organisms that show a highly heterogeneous distribution over the colony as well as some unexpected seasonal patterns (Bavestrello et al., 2008). One of the most complex tasks in the taxonomic study of a phylum such as the Cnidaria is not only to reorganize existing information and situate species correctly according to their