Siphonophore Species Research Articles

Epipelagic siphonophore assemblages associated with water masses along a transect between Chile and Easter Island (eastern South Pacific Ocean)

We analyze for the first time the spatial distribution of siphonophores in relation to water masses along a 3750 km oceanic transect between the Chilean coast and Easter Island (27o S), a sector scarcely known of eastern South Pacific Ocean. Thirty-one siphonophore species were identified; Sulculeolaria turgida and Vogtia glabra were recorded for the first time in this sector. The most abundant species were Muggiaea atlantica (29.2%), Eudoxoides spiralis (24.5%), and Lensia subtilis (13.1%). Two different siphonophore assemblages east and west of 76o W, associated respectively with Subantarctic Water and Subtropical Water masses, can be used as water mass indicators. The former included the three most abundant species, whereas the latter showed greater species richness. The current study provides basic knowledge on spatial distribution of siphonophores, which is important to develop future research focused in understanding the ecological role and biological processes driven by planktonic organisms in the Southeastern Pacific Ocean.

Calycophorae (Siphonophora) in the open waters of the central and southern Adriatic Sea during spring 2002

Twenty species of calycophoran siphonophores were identified from the central and south Adriatic Sea in spring 2002. Highest abundance and species diversity were noted at the deepest stations in the south Adriatic. Highest total abundance was found in the upper 100 m. The dominant species above 100 m were Lensia subtilis, Eudoxoides spiralis and Sphaeronectes gracilis, none of which showed diel migration. The first two species correlated significantly with the vertical abundance of microzooplankton, and the last with that of copepods. The most abundant species in the 100-400 m layer was Lensia meteori, whereas Lensia conoidea and Chlausophyes ovata were most abundant below 400 m.

In situ observations on benthic siphonophores (Physonectae: Rhodaliidae) and descriptions of three new species from Indonesia and South Africa

Three new species of siphonophores (Rhodaliidae), a little known, uniquely benthic, family of Physonectae (Hydrozoa, Cnidaria), are described from specimens observed and collected at depths between 120 and 360 m off Indonesia and South Africa by the submersible JAGO. Special reference is made to in situ observations and video close‐ups that revealed detailed information on locomotory, fishing and feeding behaviour.

Epipelagic siphonophores off the east coast of South Africa

This work represents the first systematic analysis of the common Siphonophora from the Agulhas Current (South-West Indian Ocean). A total of 56 species of siphonophores was collected from a series of three largely epipelagic cruises between Algoa Bay and the Tugela River along the east coast of South Africa. Although no readily identifiable Cystonectae were observed, four families and nine species of Physonectae were collected. Calycophorae were the most common and abundant siphonophores, and five families and 47 species were recorded. Details of locations where each species was collected are given, but descriptions and illustrations are provided only for taxa that represent new records for the region.

Effects of the Leeuwin Current on the Distribution of Carnivorous Macrozooplankton in the Shelf Waters off Southern Western Australia

Plankton samples were collected using 500-μm nets in the surface waters (up to a depth of 70m) of the continental shelf in three regions (Albany, Bremer Bay and Esperance) off southern Western Australia in July 1992 (winter) and January 1993 (summer). The carnivorous zooplankton of these samples were characterized by low species richness and high variability in abundance. Abundances of most of the major taxa collected differed significantly between seasons and many also differed between regions. Siphonophores and chaetognaths dominated the carnivorous plankton, with lower abundances of hydromedusae and raptorial copepods. The most abundant siphonophores wereChelophyes appendiculataandEudoxoides spiralisin summer and winter, respectively. The most abundant chaetognaths wereSagitta minimain summer, withPterosagitta dracoandSagitta enflatadominant during winter. Overall, the numbers of species of both siphonophores and chaetognaths were highest during winter. At this time, there was also a trend for decreasing numbers of species in an easterly direction between Albany and Esperance, which was probably due to the presence of subtropical species entrained within the warm Leeuwin Current, which was flowing east along the continental shelf during winter. During summer, when the current was not present in this region, there was an even spread of fewer species along the coast.

Abundance of gelatinous carnivores in the nekton community of the Antarctic Polar Frontal Zone in summer 1994

The species composition, abundance, vertical distribution, biovolume and carbon content of gelatinous nekton in the Antarctic Polar Frontal Zone are described from a series of RMT25 hauls collected from a series of 200 m depth layers between 0 and 1000 m. In total, 13 species of medusa, 6 species of siphonophore, 3 species of ctenophore and 1 species of salp and nemertean were identified. On average gelatinous organisms contributed 69.3% to the biovolume and 30.3% to the carbon content of the samples, although the ranges were high (0 to 98.9% and 0 to 62.6% respectively). The most important contributor to the biovolume and carbon content was the scyphomedusan Periphylla periphylla. Some specific associations and restricted vertical distributions were related to trophic interactions among ostracods, amphipods and cnidarians. Observations made near South Georgia showed that medusae and ctenophores were preyed upon by albatrosses and notothenioid fish respectively. The results support the premise that gelatinous organisms are a major and, at times, are the main component of the oceanic macroplankton/nekton community in the Southern Ocean.

Macro- and megaplanktonic cnidarians collected in the eastern part of the Weddell Gyre during summer 1979

The species composition, abundance and spatial distribution of macroplanktonic cnidarians in the eastern part of the Weddell Gyre are described from a series of nekton samples collected over three depth ranges between 0 and 2000 m. On average, cnidarians contributed 52·6% to the biovolume of these samples, although the range was high (5·0–93·1%). In total 23 species of siphonophores and 20 species of medusae were identified; a number that is very high in comparison with previous studies. There was a high diversity at bathypelagic depths, with 38 species being collected below 1000 m. The most abundant siphonophores were Dimophyes arctica (up to 45 nectophores per 104 m3) and Heteropyramis crystallina (up to 22 nectophores per 104 m3). The most abundant medusa was Pantachogon haeckeli (up to 30 specimens per 104 m3). Medusae were most abundant at mesopelagic depths, reaching 46 specimens per 104 m3 in the 500–1000 m depth range. Smaller calycophoran siphonophores were concentrated in the top 500 m of the water column, with total numbers averaging 107 per 104 m3. The number of larger calycophorans in-creased with depth, being most abundant in the 1000–2000 m depth range. Although many species had a widespread geographical distribution within the sampling area, the hydrographical conditions appeared to be affecting the distribution of some.

Vertical distribution and abundance of mesoplanktonic medusae and siphonophores from the Weddell Sea, Antarctica

The composition, abundance and vertical distribution of mesoplanktonic cnidarians collected along a transect across the Weddell Sea have been analysed. The transect was characterized by a thermocline, approximately between 200 and 100 m, which deepened significantly towards the shelf edges. In total, 10 species of medusae and 18 species of siphonophores were identified. The most abundant medusae were Pantachogon scotti (up to 11,671 specimens/1,000 m3) and Arctapodema ampla (up to 960 specimens/1000 m3). The most abundant siphonophores were Muggiaea bargmannae (up to 1,172 nectophores/1,000 m3) and Dimophyes arctica (up to 230 nectophores/1,000 m3). Five assemblages of planktonic cnidarians were distinguished: (a) epipelagic species located in and above the thermocline; (b) epi- and upper mesopelagic species located in, above and just below the thermocline; (c) epi- and mesopelagic species located in and below the thermocline; (d) mesopelagic species; (e) lower mesopelagic species. Differences in the depth distribution of the various species gave rise to a clear partitioning of the mesoplanktonic cnidarian population throughout the water column. This vertical partitioning was related to the existence of a thermocline, the structure of the water column and the vertical distribution of prey.

Mesoscale coupling between planktonic cnidarian distribution and water masses during a temporal transition between active upwelling and abatement in the northern Benguela system

The composition and spatio-temporal distribution of planktonic cnidarians in the northern Benguela system are described from plankton samples collected on four cruises between December 1981 and March 1982. The sampling period was characterized by initially active coastal upwelling, followed by abatement of upwelling. In all, 20 species of medusae and 24 species of siphonophores were identified. The most abundant medusae were Chrysaora hysoscella, Aequorea aequorea and Liriope tetraphylla, and the most abundant siphonophores were Muggiaea atlantica, Abylopsis tetragona and Bassia bassensis. Three assemblages of planktonic cnidarians were differentiated. The first was associated with coastal upwelling and consisted of the medusae Proboscidactyla menoni, Aglauropsis edwardsii and juvenile C. hysoscella, along with the siphonophore M. atlantica. The second assemblage was associated with oceanic water and the component species were indicative of the offshore influence of the Benguela system; L. tetraphylla and...

A new species of Halistemma (Siphonophora: Physonectae: Agalmidae) collected by submersible

A new species of physonect siphonophore, Halistemma transliratum sp. nov., is described from two specimens collected at mesopelagic depths in Bahamian waters by the submersibles ‘Johnson-Sea-Link’ I and II, and comparisons are made with the established species of that genus.

Two new species of prayine siphonophore (Calycophorae, Prayidae) collected by the submersibles Johnson-Sea-Link I and II

Two new species of prayine siphonophore (Calycophorae, Prayidae) collected by the submersibles <i>Johnson-Sea-Link I</i> and <i>II</i>

THE FUNCTIONS OF NEMATOCYSTS IN PREY CAPTURE BY EPIPELAGIC SIPHONOPHORES (COELENTERATA, HYDROZOA)

The nematocysts of 24 siphonophore species were examined by light and scanning electron microscopy (SEM) for differences that could relate to differences in the sizes and types of prey captured. The siphonophore species in the suborder Calycophorae had 4-30 microbasic mastigophores (0.7-18.0 µl volume), and 50-2000 smaller homotrichous anisorhizas in uncoiled nematocyst batteries. The physonect siphonophore species had 4-120 stenoteles or microbasic mastigophores (1.8-40.7 µl volume), and 150-20,500 smaller homotrichous anisorhizas in coiled nematocyst batteries. The sizes of crustacean prey (primarily copepods) captured by species in both suborders increased with increasing nematocyst size and numbers. Examination by SEM of captured, but uningested prey showed that the heavily-spined threads of these nematocysts adhered to the prey surface, and primarily entangled the prey. In contrast, the tentacles of siphonophores in the suborder Cystonectae, which includes Physalia physalis, have only isorhizas of 1.0-18.0 µl volume with and without small spines on the threads. These nematocysts penetrate the soft-bodied prey (mostly fish larvae) of these siphonophores, but apparently do not penetrate or entangle hard-bodied prey. Thus prey capture by siphonophores differs with the sizes, numbers, and types of nematocysts present in each species. The possible functions of nematocyst batteries in tentacle spreading, and luring of large zooplankton prey are discussed.

Dietary composition and diel feeding patterns of epipelagic siphonophores

Prey consumption patterns are described for 24 species of epipelagic siphonophores studied during 1977–1980 in the Gulf of California, off Southern California, in the Sargasso Sea, and in Friday Harbor, Washington. Of the species, 7 were studied by day and at night, 15 were studied only by day, and 2 were studied only at night. Each of the 3 suborders of siphonophores had a characteristic diet. Siphonophores in the suborder Cystonectae, which had large gastrozooids, fed primarily on fish larvae. Species in the suborder Physonectae, which generally had few, large gastrozooids, consumed some small copepods, but consumed mainly large copepods and a variety of large, noncopepod prey. Species in the suborder Calycophorae, which generally had many small gastrozooids, fed mainly on small copepods, and also on other small prey organisms. The maximum size of prey tended to be correlated with gastrozooid length for all the siphonophores studied. For a given siphonophore species, the number of ingested prey was greatest at localities where prey organisms were most abundant in the surrounding seawater. For siphonophore species collected both day and night, there was a tendency for more prey to be consumed at night. Behavioral observations in the laboratory indicated that of 7 siphonophore species tested, 2 fed only in the light, and another fed only in the dark.

Influence of Siphonophore Behavior upon Their Natural Diets: Evidence for Aggressive Mimicry

Collection by divers permitted determination of the natural diets of siphonophore species within II genera. Siphonophores that swim rapidly to spread their tentacles capture small prey, whereas those that swim very weakly capture much larger prey. Nematocyst batteries of two species of weak swimmers closely resemble copepods and fish larvae. Morphology, behavior, and diet suggest that these two species attract large prey by mimicking other zooplankton.

Sperm chemotaxis in the hydromedusae. I. Species-specificity and sperm behavior

Egg extracts from 32 species of marine hydromedusae, siphonophores and sessile hydroids were tested for sperm attracting activity using the sperm of all species in both homo- and heterospecific combinations. Species-specific sperm chemotaxis could be demonstrated in nearly every species tested. Of the 1,024 possible combinations, 272 could not be attempted for lack of material. Of the 752 which were carried out, only 13 heterospecific cross-reactions were found. The bulk of these involved reactions which were either weaker in the heterospecific direction or unidirectional. The sperm behavior in response to both homospecific and heterospecific egg extracts is described. In the latter case, no changes in sperm motility or direction of movement were observed. In the former case, the sperm show turning behavior which brings them closer to the source of the extract. Since most of the Hydrozoa tested share the same habitat and are reproductively active at the same time of year, it appears that species-specific sperm chemotaxis may be a significant mechanism for both ensuring fertilization in an environment which subjects the gametes to massive dilution and preventing hybridization.

Respiration and ammonium excretion by open ocean gelatinous zooplankton1

Warm‐water species of siphonophores, medusae, ctenophores, heteropods, pseudothecosomatous pteropods, salps, and doliolids were individually collected in jars by SCUBA divers in the western North Atlantic Ocean. In situ rates of oxygen consumption and ammonium excretion were estimated by difference from control jars of seawater enclosed simultaneously. The cystonect siphonophores Rhizophysa filiformis and Bathyphysa sibogae had low respiration and excretion rates [4–7 µl O2 (mg protein‐h)−1 and 0.3–0.5 NH4+(mg protein‐h)−1], while several calycophore siphonophores, heteropods, and salps had high rates [19–192 µl O2 (mg protein‐h)−1 and 1.0–3.1 µg NH4+ (mg protein‐h)−1]. Most O: NH4+ ratios ranged from 16–38 and suggest that both protein and lipid are important metabolites in tropical and subtropical gelatinous zooplankton. Many physonect siphonophores, scyphomedusae, heteropods, and salps excreted ammonium at rates exceeding 0.3 µg‐atom NH4+‐N h−1 and may play an important role in recycling nitrogen in the upper mixed layer of oligotrophic ocean regions.

The distribution of siphonophores in a transect across the North Atlantic Ocean at 32°N

A study has been made of the distribution of siphonophores in a series of twelve oblique (0–1000 m) hauls made in a transect across the North Atlantic at 32°N, from 16°W to 60°W. A total of 66 species was identified, of which twelve were physonect siphonophores and the remainder calycophorans. In order to assess the changes in the population of the nineteen most abundant species, the species correlation coefficient matrix was calculated and six factors were extracted and rotated to simple structure. The first two factors indicated a clear east-west trend in the distributional pattern for thirteen of these siphonophore species. The coefficient of proportional similarity between stations was also calculated using the data for all of the species present. From this it was possible to divide the stations into two clear zones, namely the first three and the last eight, while the fourth station was intermediate. A comparison of these results with the TSD data for these stations showed that the fourth station was in the transitional zone between the eastern North Atlantic water and that characteristic of the Sargasso Sea, and that these two major water masses were distinguishable at all the depths where siphonophores would be expected to be found. It is concluded that there was some interrelationship between the physical features of the separate water masses and the composition of the siphonophore populations found in each. The problems involved in deciding on a sampling programme for such a study as this are also discussed.

Deep-Scattering-Layer Observations off Southern and Baja California

In coastal waters off San Diego, October 1962, large populations of a physonect siphonophore were observed from TRIESTE at the depths of an extremely strong scattering layer. Peak scattering coefficients of −50 dB were measured from a surface ship. Similar measurements in deep oceanic waters off Southern California recorded slightly deeper layers, but net hauls indicate few siphonophores were present, the best correlation being with bathypelagic fishes. Off Cape San Lucas, February 1965, visual observations from a diving saucer showed the presence of a population of lantern fishes to correspond with the depths of the main component of a scattering layer. Observations were made while the layer was at the surface, at its daytime depth, and while the layer was migrating. A deeper, weak component and a shallow, diffuse layer of scattering were correlated with two species of physonect siphonophores. It appears that these two types of organisms are the major causes of the scattering-layer phenomenon, the siphonophores being more restricted in time and space. Visual observations suggest that squid and fish schools are responsible for large acoustic reflecting features frequently recorded on echo sounders. Motion picture films documenting these observations are shown.

On the Development of Muggiaea Atlantica Cunningham

In September 1937 Muggiaea atlantica Cunningham was very abundant off Plymouth. The presence of large numbers of eudoxids in the plankton afforded an opportunity to rear the early stages of this siphonophore. The development of M. kochi (Will) was worked out by Chun (1882, 1913), and he also described the eudoxid of that species. The eudoxid of M. atlantica has, however, never been described for certain. The allocation of eudoxids collected in the plankton to their respective species is necessarily fraught with uncertainty when more than one species is present. Throughout the whole of September 1937 M. atlantica was the only species of siphonophore to be found off Plymouth, and there can be no reasonable doubt that the eudoxids described below belonged to that species and that the development of the early stages from their eggs is that of M. atlantica.For the terminology used in the description of the eudoxid I have followed Totton (1932), to whom I am grateful for helpful advice.The EudoxidThe bract (Fig. 2 a) is cone-shaped with a broad flat suture running from its apex to the base. The edges of the suture are raised into a slight flange. The right edge is continued downwards into a sweeping curve while the left edge cuts away horizontally at its lower end; the bract is thus asymmetrical. There is a slight cavity on the lower surface in which the somatocyst is centrally placed. The general form of the bract can also be seen in the different views of the whole eudoxid given in Fig. 1.

On the Occurrence of the Siphonophores Muggiœa atlantica Cunningham and Muggiæa kochi (Will) in the English Channel

In 1892 Cunningham described a new species of Siphonophore, Muggiœa atlantica, which was first noticed by him in the waters of the English Channel off Plymouth in the autumn of 1891. Since then there have been records from time to time of the occurrence of this species at Plymouth (see Plymouth Marine Fauna, 1931, p. 84), and its distribution in the English Channel and Irish Sea in 1904 was worked out by Gough (1905).