Benthic Hydroids Research Articles

Benthic hydroids (Cnidaria: Hydrozoa) from Svalbard waters—biodiversity and distribution

The aim of the present study was to update the existing knowledge of benthic hydroids from Svalbard waters. The material for the study was collected at several locations in the Svalbard region. The list of hydropolyps from the investigated area includes about 100 species. A total of 42 taxa was noted in the present study, 18 of which were reported for the first time in this area. One species is likely new to science. The analyses address the zoogeographical status of the species and the diversity of microhabitats. Arctic-boreal species were the main component of the hydroid assemblage, and eight types of substrata were colonized by the hydroids. Their highest biodiversity occurred on algae and bryozoans. Biological studies and faunal records used to monitor the Arctic region are of increasing importance in light of climate change and its influence on benthic community structure.

Vibrio harveyi Associated with Aglaophenia octodonta (Hydrozoa, Cnidaria)

A previously unknown association between a luminous bacterium, Vibrio harveyi, and a benthic hydrozoan, Aglaophenia octodonta, is described. Aglaophenia hydrocladia showed a clear fluorescence in the folds along the hydrocaulus and at the base of the hydrotheca, suggesting the presence of luminous bacteria. This hypothesis was confirmed by isolation of luminous bacteria from Aglaophenia homogenates. Phenotypic characterization of bacterial isolates was performed by several morphological, biochemical, and cultural tests, completed with 16S rDNA sequence analysis. All the isolates were referred to a single species: V. harveyi. The association between V. harveyi and A. octodonta has epidemiological as well as ecological significance. Therefore, A. octodonta may function as habitat "islands" providing a unique set of environmental conditions for luminous bacteria colonization, quite different from those already recorded from the plankton for other Vibrio species.

The problem of seasonality of benthic hydroids in temperate waters

A wealth of data are available on the seasonal variation of plankton communities, but few studies take into consideration the circannual cycles of benthic organisms. In fact, the macrobenthos is generally considered as composed by slow-growing organisms showing variations mainly in relation to substrate competition. On the contrary, hydroids are an important group of macrobenthos that, in temperate but also in tropical waters, undergo sharp seasonal cycles. For example, on the Portofino Promontory (Ligurian Sea), about half of the recorded species thrive in winter and 30% in the summer, the rest being constant in presence. Here, we revise the available data about the environmental factors switching the passage from quiescent to active phases. The available data suggest that a mosaic of physical factors, biotic interactions, and internal clues triggers the hydroid cyclic behaviour.

Benthic hydroids associated with volcanic structures from Bransfield Strait (Antarctica) collected by the Spanish Antarctic expedition GEBRAP96

During the Spanish Antarctic expedition GEBRAP96 a survey to study the benthic fauna associated with deep volcanic structures in the Bransfield Strait was carried out. Amongst the benthic samples, a small collection of hydroids was gathered. A total of 10 species, most of them Leptothecata, was recorded; only two species of anthoathecates were present. Kirchenpaueriidae and Sertulariidae were the dominant families, and Symplectoscyphus and Oswaldella the predominant genera. Oswaldella niobae sp. nov. is described and figured. Since samples were taken at great depth, the lowest limit of the bathymetrical distribution for several species is distinctly increased. None of the samples showed signs of hydrothermal phenomena and the species of hydroids present were typical representatives of the Antarctic benthic hydroid fauna.

Benthic hydroids from the south of Livingston Island (South Shetland Islands, Antarctica) collected by the Spanish Antarctic expedition Bentart 94

Twenty-five species of benthic hydroids were collected during the Spanish Antarctic expedition Bentart 94 from the south of Livingston Island (Antarctica). All species are considered regarding autecology and geographical distribution. The systematic position amongst allied species is discussed when considered necessary. Antarctoscyphus asymmetricus and Symplectoscyphus nesioticus are reported for the second and the third time, respectively.

Benthic hydroids (Cnidaria, Hydrozoa) from off Bouvet Island (Antarctic Ocean)

Twenty-seven species of benthic hydroids have been found in a small collection from off Bouvet Island (Antarctic Ocean). The material was obtained during the XXI/2 German Antarctic expedition with R.V. Polarstern 2003–2004. Of the 27 species collected, 21 were unknown from those waters. Consequently, the number of known species of benthic hydroids from the area has risen to 32, representing a high diversity location for this group in the Southern Ocean considering the sampling effort made. All species, including those previously known from Bouvet waters, are considered with respect to geographical distribution.

Mixoscyphus antarcticus gen. nov., sp. nov. (Cnidaria, Hydrozoa, Sertulariidae), the first truly endemic genus of Antarctic benthic hydroids

A genus and species of Antarctic benthic hydroids new to science, Mixoscyphus antarcticus gen. nov., sp. nov., is described and figured. Its systematic position amongst allied genera of the family Sertulariidae is discussed. The studied material originates from the South Shetland Islands area (West Antarctica), which was collected by several Spanish and US Antarctic expeditions. Mixoscyphus gen. nov. currently represents the only complete endemic genus of Antarctic benthic hydrozoans. A discussion of other genera of benthic hydroids that are largely endemic to the Antarctic is also provided.

How rich is the deep-sea Antarctic benthic hydroid fauna?

The bathymetric distribution of the 155 known species of Antarctic benthic hydroids has been studied with the aim of determining bathymetric groups and estimating the richness of the deep-sea Antarctic benthic hydroid fauna. Six bathymetric groups could be recognized on the basis of vertical zonation patterns. Most species have wide bathymetric ranges, but must nevertheless be considered shelf species. Although 62 species of benthic hydroids have been found in the Antarctic deep-sea, only 10 are strict inhabitants of that area. An inverse relative dominance between anthoathecate and leptothecate hydroids has been observed, with the former being more frequent in shallow waters.

The hydroid and early medusa stages of Mitrocoma cellularia (Hydrozoa, Mitrocomidae)

The leptomedusa, Mitrocoma cellularia, ranges from the Bering Sea to southern California and may be found year-round in the surface waters of Monterey Bay, California. These jellies are relatively long-lived, making them ideal hydromedusae for display at public aquaria. While M. cellularia are commonly found in Monterey Bay, it is not always possible to collect them due to foul weather and patchy distribution. To maintain a constant and reliable source of these medusae, a laboratory cultivation protocol was developed and implemented. The described life cycle of M. cellularia remained incomplete, lacking information regarding the benthic hydroid colony and early medusa. This paper reports descriptions for the hydroid colony and early medusa stages of M. cellularia based on specimens grown at the Monterey Bay Aquarium, California, and provides a brief description of the rearing methods used.

Bydrozoa (Cnidaria) of Iceland collected by the BIOICE programme

Abstract This study summarises the findings of benthic hydrozoans (Cnidaria, Hydrozoa, including Hydroidea and Siphonophora) collected around Iceland during the BIOICE programme. The vertical distribution of the encountered species is examined. Species diversity is highest in the upper 200 m and then decreases with increasing depth. Two new species were found: Eudendrium islandicum and Cladocarpus paraformosus. The following 15 species are new records for Iceland; Amphinema biscayana, Hydractinia borealis (polyp), Gymnogonos crassicaulis, Acaulis primarhis, Acryptolaria conferta, Campamilina panicula, Modeeria rotunda (polyp), Lovenella producta, Cladocarpus paraventricosus, Abietinaria pulchra, Abietinaria thuiarioides, Diphasia margareta, Sertularia similis, Kirchenpaueria bonnevieae, and Stephalia corona. The gonophores of Garveia biscayana Browne, 1907 and Stegopoma plicatile (M. Sars, 1863) are described for the first time. Both species produce free medusae. Garveia biscayana is transferred from the family Bougainviltidae to the Pandeidae as Amphinema biscayana comb. nov. Campanularia groenlandica Levinsen, 1893 is here recognised as a valid species and removed from synonymy with Campanularia volubilis.

Biogeographical distribution of the benthic thecate hydroids collected during the Spanish Antartida 8611 expedition and comparison between Antarctic and Magellan benthic hydroid faunas

The biogeographical distribution of the benthic hydroid species collected during the Spanish Antarctic expedition Antartida 8611 has been studied. An inventory of the Antarctic and Magellan benthic thecate hydroid faunas, along with a comparison between the two, have been also carried out. 104 and 126 species of thecate hydroids have been considered in the Antarctic and Magellan areas, respectively. 72 species (69%) of the Antarctic species and 49 (39%) of the Magellan species are endemic. 23 species are present both in the Antarctic Region and in the Magellan area, representing 22% and 18% respectively, and indicating an important relationship between both faunas.

Benthic diatoms as the major food source in the sub-Antarctic marine hydroidSilicularia rosea

Analysis of the gut contents and scanning electron microscopy examination of the benthic hydroidSilicularia rosea from intertidal communities of Potter Cove (King George Island, South Shetlands) suggest that diatoms are the principal source of food for this species. The great number of items captured daily by each polyp (a mean of 287 in January and 162 in December) and the benthic origin of these prey items suggest an adaptation to daily resuspension processes caused by tidal currents. This is an unusual trophic strategy for a benthic hydroid, which would result in an important degree of independence from the highly fluctuating planktonic food conditions in Antarctic waters.

Quantification of sexual reproduction in the marine benthic hydroid Campanularia everta

Campanularia everta is an epiphytic hydroid that may form dense populations on the macroalga Halimeda tuna. The main objects of this study were to quantify sexual reporduction and estimate sexual reproductive output of this hydroid. Sexual reproduction occurred from mid-October to mid-December 1991 along the Spanish Mediterranean coast. During this period, male and female colonies formed gonangia. Four oocytes mature in each female gonangium, and embryonic development starts probably after internal fertilization occurs. Planulae complete their development within a mucus sheath attached to the top of the gonotheca (acrocyst). Eight successive gonangia with a life-span of ≈1 wk each were formed over a 2 mo period. The fertile period was characterized by high initial production of gonangia followed by a progressive decline resulting from a decrease both in the number of fertile colonies and in the gonangia density of fertile colonies. Annual production was estimated at ≈42000 gonangia m-2, representing 83000 oocytes m-2. The high fertilization rates observed (77 to 100%) yielded a minimum production of 64000 planulae m-2. Reproduction in C. everta is characterized by: (1) a high number of larvae produced m-2; (2) formation and gradual release of larvae throughout the sexual reproduction period; (3) direct formation of planulae with no intermediate medusa stage; (4) low dispersive ability of the planula. All these mechanisms are part of a reproductive strategy designed to ensure the permanence of the population in its habitat.

Feeding cycles and prey capture in Eudendrium racemosum (Cavolini, 1785)

The natural diet and in situ feeding frequency of the hydroid Eudendrium racemosum, common in certain western Mediterranean shallow-water benthic communities, have been studied by analyzing their coelenteron contents. One hundred polyps were sampled, and their contents studied, every 2 h over three 24-h cycles. The overlying Zooplankton was simultaneously sampled in order to compare the prey with the available plankton. The maximum residence time of the prey in the coelenteron was estimated to be ≈ 5 h. Eudendrium is carnivorous, each polyp taking an estimated mean of 4.3 prey items · day −1. Thirty-nine percent of the polyps had at least one prey item at all times. Prey items had smaller dimensions than the polyp, but long thin organisms were sometimes taken. The number of captured items was strongly correlated with Zooplankton density, suggesting that E. racemosum is an opportunist with no innate diurnal or other feeding rhythm. Estimated captures of E. racemosum are of 100000 prey items · m −2· day −1 in the study area. Therefore, benthic hydroids may exert considerable effects on local plankton populations and play an important rôle in the transfer of energy from the plankton to the benthos.

Halammohydra vermiformis and H. coronata (hydrozoa), new to the fauna of the Netherlands

The freeliving benthic hydrozoans Halammohydra coronata Clausen, 1967, and H. vermiformis Swedmark & Teissier, 1957, are recorded from the estuarine area of the southwestern part of The Netherlands.