Jellyfish of the Far Eastern Seas of Russia. 3. Biomass and abundance

The biomass and abundance of large jellyfish (Cnidaria: Scyphozoa, Hydrozoa) was estimated and their seasonal and interannual dynamics was studied based on the data of trawl surveys conducted by the Pacific Research Fisheries Center (TINRO Center) in the Sea of Okhotsk, Bering Sea, Sea of Japan, and the Northwestern Pacific Ocean (NWPO) in 1991–2009. Most of the jellyfish biomass (over 95%) in the Sea of Okhotsk, Bering Sea, and NWPO was formed by Chrysaora spp., Cyanea capillata, Aequorea spp., Phacellophora camtschatica, and Aurelia limbata. The same species along with Calycopsis nematophora predominated in abundance in the Bering Sea and NWPO, while Ptychogena lactea, C. capillata, and Chrysaora spp. were most abundant in the Sea of Okhotsk. In the northwestern Sea of Japan, Aurelia aurita, C. capillata, and Aequorea spp. predominated both in abundance and biomass. Generally, the jellyfish abundance reached the highest values in the summer and fall and decreased abruptly in the winter. Meanwhile, the seasonal dynamics proved to be specific for each species and were manifested in some of them by reaching maximum values at various periods of the warm season, whereas the other (Tima sachalinensis and P. lactea) showed the reverse pattern of seasonal variations, with the highest abundance in cold months. Jellyfish biomass and abundance varied greatly from year to year, which was related to the short lifecycle and alternation between sexual and asexual generations, in which reproductive success was predetermined by various environmental factors. In the fall, year-to-year fluctuations of the relative biomass could increase by ten times. In 1991–2009, it varied from 200 to 2000 kg/km² in the northern Sea of Okhotsk, from 500 to 4200 kg/km² in the northwestern Bering Sea, and from 300 to 3700 kg/km² in the southwestern Bering Sea. Taking the jellyfish abundance estimates into account, along with the vertical distribution and the seasonal dynamics, the overall biomass of large species that occurred in trawl catches in Far Eastern seas and adjacent Pacific waters during the warm season could reach 13.0–15.0 million tons, of which up to about 6.0 million tons would be concentrated in the western Bering Sea and 5.5–6.0 million tons in the Sea of Okhotsk.     

Quantitative composition,distribution, and feeding of large jellyfish (<Emphasis Type="Italic">Scyphozoa et Hydrozoa</Emphasis>) on the West Kamchatka shelf in summer

The total biomass of jellyfish on the shelf of the eastern Sea of Okhotsk in the summer is estimated as 1672700 tons according to the results of hydroacoustic measurements and 901000 tons by the method of squares. The use of hydroacoustic technologies makes evaluation of the actual stock and range of medusae more accurate, and the further enhancement and perfection of the hydroacoustic method based on multifrequency measurements enables one to obtain more reliable estimates. A significant increase (nearly 25 times) of the total jellyfish biomass takes place in the summer period. Cyanea prevailed in biomass in the spring and Chrysaora melanaster prevailed in the summer. Some species showed considerable expressed spatial differentiation of distribution and affinity to certain environmental conditions. The studied species were almost exclusively zoophages. Their algal diet consisted mainly of diatom algae. Scyphomedusa’s diet mainly included the so-called “peaceful” zooplankton, viz., euphausiids and copepods (as a rule, over 50% the mass), at the same time carnivorous zooplankton, saggits, amphipods, and small medusae also formed a substantial share of their diet. One individual of the predominant jellyfish species consumes a total of 6.1 to 70.5 kcal during its lifecycle, which corresponds to 79.1–513.0 g of raw organic material, assuming 70% assimilability. The relatively low demand for food of this sort can be explained by the low caloric value of the jellyfish body, 96–97% of which consists of water. The distribution and composition of the jellyfish prey show that scyphomedusae exert the greatest influence on the nekton community, as they concentrate in the shelf area of the eastern part of the sea, at walleye pollock spawning sites. There the larvae of bottom invertebrates, including commercially valuable organisms, such as crab and shrimp, are also consumed. In the summer, jellyfish eat nearly 100 billion eggs and 20 billion larvae of walleye pollock, as well as 130 billion decapod (mostly crab) larvae each day, which corresponds to 0.03% of the eggs and 0.003% of the larvae of walleye pollock and 0.003% of the decapod larvae in the estimated stock.     

Acoustic survey of a jellyfish-dominated ecosystem (Mljet Island,Croatia)

Acoustic techniques have been proposed as a new tool to assess jellyfish populations. However, the presence of mixed echoes from jellyfish and other organisms that share their distribution often prevent accurate estimates of their abundance and distribution being obtained. The isolated population of Aurelia inhabiting the Veliko Jezero (Big Lake-BL) of Mljet Island, in the South Adriatic Sea, offered a good opportunity to employ acoustic techniques to assess an entire jellyfish population. During October 2–5, 2006, combined video and acoustic methods were used in BL to determine the vertical distribution of medusae. Two synoptic acoustic surveys were performed during the day and night. In the daylight echograms, medusae were clearly discernible from the acoustic data, and their presence verified by video camera images, as forming a layer of varying density at and below the thermocline (15–30 m). The depth of the jellyfish layer also coincided with the depth of maximum dissolved oxygen concentration. The echointegration of these daylight data enabled quantification the Aurelia population, at a frequency of 120 kHz. In the night echograms, the acoustic signals of Aurelia were at least partially masked by pelagic and demersal fish, which disaggregated from schools and formed a layer associated with a strong thermocline at 15 m. An average target strength (TS) of −76.4 dB was obtained in situ corresponding to a mean length of 10.8 cm and a mean wet weight of 134 g measured from sampled medusae. These results were combined with echo-integration values to provide an estimate of 4,238,602 individuals and a biomass of 568 tons of Aurelia in BL. This study provided a synoptic view of Mljet Lake and illustrated the potential of acoustic surveys of jellyfish populations to contribute to ecosystems studies. Guest editors: K. A. Pitt & J. E. Purcell Jellyfish Blooms: Causes, Consequences, and Recent Advances     

The distribution and abundance of scyphomedusae (Scyphozoa) of the family Ulmaridae in the pelagic zone of the Sea of Okhotsk and the Sea of Japan

The distribution and abundance of jellyfish of the family Ulmaridae was studied based on the data of trawl surveys conducted in the Sea of Okhotsk (1998–2006) and the Sea of Japan (2003) in the fall. The jellyfish Aurelia aurita mainly inhabits the waters of the Sea of Japan, while in the Sea of Okhotsk small quantities of this species were recorded in southern areas, and solitary individuals, off North Sakhalin. Aurelia limbata tends to shelf waters of the Sea of Okhotsk, being less abundant in the southern deepwater area and in the Sea of Japan. Phacellophora camtschatica, in contrast, aggregates mostly over deep basins, whereas in shallow areas a significant quantity of this species was found only off West Kamchatka. In the northern Sea of Okhotsk, the species A. limbata dominated in biomass and abundance among Ulmaridae. During the studied period, its biomass varied from 27 to 803 kg/km² and its abundance varied from 69 to 1706 ind/km². In the southern Sea of Okhotsk, as a rule, P. camtschatica prevailed (1–16 kg/km² and 6–46 ind/km²). In the Sea of Japan, the most abundant species was A. aurita (29 kg/km² and 104 ind/km²). The jellyfish size structure in catches is presented.     

Predation potential of the jellyfish Drymonema larsoni Bayha & Dawson (Scyphozoa: Drymonematidae) on the moon jellyfish Aurelia sp. in the northern Gulf of Mexico

The jellyfish Drymonema larsoni bloomed in the northern Gulf of Mexico in the Fall of 2000 and fed voraciously on the moon jellyfish Aurelia sp., especially where they were concentrated in frontal convergence. We evaluated the predation potential of D. larsoni on Aurelia sp. medusa using laboratory and field data. Our data set represents the most complete study to date on the new scyphozoan family Drymonematidae and indicates that D. larsoni may be one of the most effective predators on other jellyfish recorded to date. On average, each D. larsoni medusa contained 2.7 Aurelia sp. prey, but as many as 34. In addition, 94% of moon jellyfish unassociated with D. larsoni showed scarring from previous contact with D. larsoni tentacles. Digestion times for D. larsoni feeding on individual Aurelia sp. ranged from 2 to 3 h and averaged 2.7 h. Potential clearance rates for predation on Aurelia sp. were extremely high (320–1043.5 m³ d⁻¹) and indicate that D. larsoni is potentially an important predator on Aurelia sp. blooms where the species co-occur. When the two species co-occur in numbers, predation by D. larsoni medusae could reduce moon jellyfish blooms, possibly alleviating predation pressure on lower trophic levels utilized by Aurelia sp., such as copepods and the early life history stages of ecologically and economically important fish and invertebrate species.     

Distribution,quantitative composition,and feeding of jellyfish in the Western Bering Sea in summer and fall

Materials from six complex trawl surveys conducted by the TINRO-Center in the upper epipelagic zone of the Western Bering Sea during the summer-fall seasons from 2002 through 2006 were used as the basis of this paper. The overall biomass (and abundance) of jellyfish increased from 0.6–0.8 million t (1.1–1.8 billion individuals) in the summer up to 0.9–1.7 million t (4.4–4.8 billion individuals) in fall. Scyphomedusa Chrysaora melanaster and the Hydromedusa Aequorea forskalea made up the major part of the jellyfish biomass (67–97%). Their distribution varied significantly. A. forskalea aggregated mainly in the deepwater part of the Bering Sea. Ch. melanaster was widely dispersed across the entire area of the investigations and formed the most considerable aggregations in the Anadyr-Navarin area. In the fall of 2006 the diet of jellyfish generally consisted of plankton organisms (copepods, euphausiids, amphipods, pteropods, chaetognaths, ostracods, and larval decapods). However, Ch. melanaster had a greater portion of fish and larval squid in its diet.     

Cnidaria from the Croker passage (Antarctic Peninsula) with a special focus on Siphonophorae

Studies of “gelatinous” zooplankton are rather rare, and little is known about the biology and ecology of Antarctic Cnidaria, especially for siphonophores. More investigations are necessary for complementing the current information on the “gelatinous” zooplankton inhabiting this important but little know biogeographical region, especially because siphonophores very likely play a significant role in the Antarctic food chains. The species composition, abundance and vertical distribution of planktonic cnidarians in the Croker Passage were evaluated using the data obtained from three expeditions. Zooplankton were sampled with a double plankton net between 0 and 1,200 m water depth in both summer and winter seasons. In total, ten species of siphonophores and four species of medusae were identified. Siphonophore assemblages were dominated by Dimophyes arctica, Pyrostephos vanhoeffeni, and Diphyes dispar. D. arctica and D. dispar occurred in greatest numbers in summer, mainly in the upper mesopelagic zone. P. vanhoeffeni, a cryophilic species, occurred most abundantly in winter (in the lower mesopelagic zone), when they probably reproduce. Restricted circulation from the Bellingshausen Sea over the continental shelf into Croker Passage may exclude the deeper-living oceanic fauna from the area of investigation, as indicated by the low abundances of Crystallophyes amygdalina, Muggiaea sp., and Heteropyramis spp. Four species of medusae were identified. The highest abundance was noted for Solmundella bitentaculata and Arctapodema sp. These occurred most abundantly in the middle (January) and end (April) of summer.     

Causal analysis of the diversity of medusae in East China Sea

Based on the maritime data collected from 23°30′–33°00′ N and 118°30′–128°00′ E of the East China Sea (ECS) in four seasons during 1997–2000, the dynamics of medusae diversity and their causes were analyzed. A total of 103 medusae species were identified, and these species mainly distributed in the southern and northern offshore areas of the ECS. Species diversity index (H′) of medusae was higher in the south than those in the north, higher in summer and winter than in spring and autumn, and higher in offshore than in the nearshore areas. The species number was closely correlated with H′ value, whereas the abundance of species had no significant relationship with the diversity index. The lower H′ value of the nearshore in spring and autumn resulted from the aggregation of Muggiaea atlantica in the south nearshore and Diphyes chamissonis in the north nearshore. In addition, water temperature, followed by salinity, is the main environmental factor influencing the distribution of species diversity. The H′ value was related to the water temperature at the 10 m layer in winter and spring, and it was associated with the surface water temperature in summer and with the 10 m-salinity-layer in autumn. In spring and summer, the isoline distribution of H′ value reflected the direction of the Taiwan Warm Current and the variation of the water masses in the ECS. In winter, the isoline of the H′ value indicated the incursion of Kuroshio current. In conclusion, the H′ isoline is an good indicator for water masses in ECS. __________ Translated from Biodiversity Science, 2006, 14(6): 508–516 [译自:生物多样性]     

Coypu (<Emphasis Type="Italic">Myocastor coypus</Emphasis>) in a Mediterranean remnant wetland: a pilot study of a yearly cycle with management implications

Following an apparent increase of local population density of coypu (Myocastor coypus) in a Mediterranean remnant wetland, we developed a pilot study aimed to evaluate a specific control program. Inside the study area, we performed three transects per month from August 2008 to July 2009, grouping data in bimonthly periods. The water level in the study area showed a maximum in December–January, significantly decreasing from late spring to summer and significantly increasing from late summer to winter. Sampled individuals mainly occurred in Phragmites reed beds and in rush beds (dominance of Carex sp., Juncus sp. Bolboschoenus sp.). The index of mean relative density of coypu individuals ranged between 1.40 (February–March) and 5.72 (October–November) with an evident increase in late summer–autumn. During this period, mean density of runways was higher in reed beds than in rush beds, with differences tending to significance. In summer, the network of channels in reed beds, locally used for fishery farm, may maintain a water level suitable for the coypu. These results (preference for reed beds and increase of coypu density in late summer–autumn) should be considered when coypu populations are under control program, at least in the Mediterranean region where there is a scarcity of available data.     

Numerical increases and distributional shifts of Chrysaora quinquecirrha (Desor) and Aurelia aurita (Linné) (Cnidaria: Scyphozoa) in the northern Gulf of Mexico

Fisheries resource trawl survey data from the National Marine Fisheries Service from a 11–13-year period to 1997 were examined to quantify numerical and distributional changes of two species of northern Gulf of Mexico scyphomedusae: the Atlantic sea nettle, Chrysaora quinquecirrha (Desor), and the moon jelly, Aurelia aurita (Linné). Trawl surveys were grouped into 10 statistical regions from Mobile Bay, Alabama to the southern extent of Texas, and extended seaward to the shelf break. Records of summertime C. quinquecirrha medusa populations show both an overall numerical increase and a distributional expansion away from shore in the down-stream productivity field of two major river system outflows: Mobile Bay and the Mississippi-Atchafalaya Rivers. In addition, there is a significant overlap between summer C. quinquecirrha and lower water column hypoxia on the Louisiana shelf. In trawl surveys from the fall, A. aurita medusae showed significant trends of numerical increase in over half of the regions analyzed. For both species, there were statistical regions of no significant change, but there were no regions that showed significant decrease in number or distribution. The relationships between natural and human-induced (e.g. coastal eutrophication, fishing activity and hard substrate supplementation) ecosystem modifications are very complex in the Gulf of Mexico, and the potential impact of increased jellyfish populations in one of North America's most valuable fishing grounds is a most critical issue. Several hypotheses are developed and discussed to guide future research efforts in the Gulf of Mexico.     

Brittle star fauna (Echinodermata: Ophiuroidea) of the arctic northwestern Barents sea: composition,abundance, biomass and spatial distribution

 Epibenthic brittle star assemblages were investigated on the northwestern Barents Sea shelf between 81° and 77°N in July 1991. At 9 drift stations in water depths between 80 and 360 m, series of 35–71 photographs, each depicting about 1 m² of the seabed, were taken along transects of about 150- to 300-m length to assess abundances and spatial distribution patterns of adult brittle stars (disc diameter ≥1 mm). Biomass values were derived by combining abundances with size-weight relationships and size frequencies established using specimens from trawl catches. Six brittle star species were identified on the seabed images. Ophiocten sericeum was the most abundant species on shallow shelf banks (≤100 m). Up to 2,800 individuals were counted on a single photograph; median abundances per station ranged from 32 to 524 ind.m^-2 and biomass from 0.3 to 5.0 g ash-free dry weight (AFDW) m^-2. The spatial distribution along the transects (i.e. on the 100-m scale) was, however, extremely patchy. Disc diameters of O. sericeum ranged between 1.6 mm and 15.4 mm. In deeper shelf habitats (>150 m), O. sericeum was rare or absent, and Ophiacantha bidentata dominated the brittle star fauna with median densities and biomasses of 2–49 ind.m^-2 and 0.07–1.9 g AFDW m^-2, respectively. Its disc diameters ranged from 2.9 to 14.4 mm. The other species (Ophiura sarsi, Ophiopholis aculeata, Ophioscolex glacialis, Ophiopleura borealis) occurred in distinctly lower numbers. Our findings provide further evidence that brittle stars dominate epibenthic communities on Arctic shelves and locally reach very high abundances. Dense beds of Ophiocten sericeum seem to be a general phenomenon on high-Arctic shallow shelf banks. Received: 30 March 1995/Accepted: 30 June 1995     

Xenobrama microlepis,a new genus and species of bramid fish,from subantarctic waters of the South Pacific

Xenobrama microlepis gen. et sp. nov. is described on the basis of 17 adult and subadult specimens collected by surface gill nets, bottom trawl and midwater trawl from the subantarctic waters of the South Pacific Ocean. This monotypic new genus is distinguished from other bramid genera by the following characters: inner lower edges of mandible touching each other (except near symphysis); gill rakers short, thick, and stout; subpectoral region very narrow; interpelvic space flat and wide; vertebrae 49–51; and scales in longitudinal series more than 83. The new taxon is widely distributed in the high seas of the South Pacific, 38–54°S, 79–176°W, but is rather rare compared toBrama spp. in catches of drift gill nets.     

New data on the distribution and feeding habits of jellyfish in the Northwest Pacific

In June and July of 2012, the jellyfish catches in the northeastern portion of the surveyed Pacific waters off the Kuril Islands substantially exceeded those in the southwestern portion. This indicates that jellyfish disperse over the studied area predominantly from the southern Bering Sea and from the eastern coast of Kamchatka. Their strobilation probably takes place as well on the shelf and continental slope of eastern Kamchatka. The distribution of jellyfish with medium-sized bells does not show any geographic pattern; the aggregations that are formed are mixed regarding the original locality of individuals. Jellyfish occur within a broad range of surface water temperatures and their catches have declined significantly only in the southeast of the area of surveys near the Subarctic Front. As is seen from the data we compared, not only the abundance of jellyfish, but their feeding activity and, as a consequence, the amount of consumed food decreased by an order of magnitude during the cold season (in the spring 2011). However, irrespective of the season, the largest quantities of food were recorded in the largest and most numerous jellyfish (Phacellophora camtschatica, Chrysaora melanaster). The quantitative results of the studies on the diet of jellyfish may be somewhat underestimated, as fragile jellyfish bodies are easily damaged in trawl nets and evaluating the diet is possible only for intact individuals. Use of specialized catching gear in the future may help us to specify the feeding dynamics in jellyfish, as well they may provide an opportunity to observe their feeding behavior. At the same time, quantitative estimates of the daily-food intake in jellyfish can be obtained only by taking the rates of digestion and prey consumption found under laboratory conditions into account, with their subsequent verification in balance models.     

Associations of large jellyfish distributions with temperature and salinity in the Yellow Sea and East China Sea

Climate change may contribute to the increasing frequency and intensity of jellyfish blooms around the world. To test the null hypotheses that distributions did not differ among species of jellyfish or according to temperature salinity, we sampled large jellyfishes using bottom trawl surveys during 2006–2007 in the Yellow Sea (YS) and East China Sea (ECS). The total biomass of large jellyfish in the YS was low in April 2006 in cool waters, increased with warming waters, peaked in early September 2006 (22,891 ± 25,888 kg km^–2), and then decreased with cooling to minimal biomass during March 2007. During its peak early September 2006, Nemopilema nomurai was relatively eurythermal and distributed throughout the YS. Cyanea spp. occurred in warmer waters and attained maximum biomass in May 2007 in the ECS. Ulmaridae, which preferred colder temperatures, reached maximum biomass in October 2006 and occurred mainly in the central YS. Aequorea spp. usually occurred in colder waters, with maximum biomass in May 2007 mainly north of 30°N. Our analyses suggest that environmental preferences of the large jellyfish may enable prediction of jellyfish population sizes and distributions in Chinese waters, which is essential in order to address ecological problems caused by large jellyfish blooms in East Asia Waters.     

Global diversity of inland water cnidarians

Global diversity of inland water cnidarians is low, containing <40 species belonging to phylogenetically distinct groups representing independent invasion events: the common and cosmopolitan hydras (12–15 species); the sporadically occurring freshwater medusae (6–16 sp.); the Cordylophorinae (2 sp.); the parasitic Polypodium (1 sp.); the medusae occurring in saline lakes (4 sp.). Freshwater cnidarians inhabit nearly all types of freshwater on all continents (except Antarctica), but only a few species have cosmopolitan distributions. Due to uncertainty in species knowledge, fine scale regions of endemicity are not yet clear. Guest editors: E. V. Balian, C. Lévêque, H. Segers & K. Martens Freshwater Animal Diversity Assessment     

Patterns in species richness,species density,and evenness in groundfish assemblages on the continental slope of the U.S. Pacific coast

For many taxa, diversity, often measured as species richness, decreases with latitude. In this report patterns of diversity (species richness, species diversity, and evenness) in groundfish assemblages were investigated in relation to depth (200–1200 m) and latitude (33–47°N) on the continental slope of the U.S. Pacific coast. The data originated from the 1999–2002 upper continental slope groundfish surveys conducted by the National Marine Fisheries Service. When the data were pooled across depths, species density and evenness were found to decline with latitude. All three diversity measures declined with depth, with the lowest overall diversity in the 600- to 900-m depth range where longspine thornyhead Sebastolobus altivelis constituted close to 70% of the catch. When latitudinal gradients were examined within four depth zones (200–300 m, 400–500 m, 600–900 m, and 1000–1200 m) more complex patterns emerged. At depth species richness and evenness were inversely correlated with latitude as longspine thornyhead dominated catches to the north. However, in shallower areas of the slope, species richness and evenness were positively correlated with latitude. Latitudinal patterns of diversity in the deeper zones and when pooled across depths were positively correlated with temperature and broadly consistent with the Ambient Energy hypothesis discussed by Willig et al. [Annu Rev Ecol System 34:273–309 (2003)].     

Stranding events provide indirect insights into the seasonality and persistence of jellyfish medusae (Cnidaria: Scyphozoa)

It is becoming increasingly evident that jellyfish (Cnidaria: Scyphozoa) play an important role within marine ecosystems, yet our knowledge of their seasonality and reproductive strategies is far from complete. Here, we explore a number of life history hypotheses for three common, yet poorly understood scyphozoan jellyfish (Rhizostoma octopus; Chrysaora hysoscella; Cyanea capillata) found throughout the Irish and Celtic Seas. Specifically, we tested whether (1) the bell diameter/wet weight of stranded medusae increased over time in a manner that suggested a single synchronised reproductive cohort; or (2) whether the range of sizes/weights remained broad throughout the stranding period suggesting the protracted release of ephyrae over many months. Stranding data were collected at five sites between 2003 and 2006 (n = 431 surveys; n = 2401 jellyfish). The relationship between bell diameter and wet weight was determined for each species (using fresh specimens collected at sea) so that estimates of wet weight could also be made for stranded individuals. For each species, the broad size and weight ranges of stranded jellyfish implied that the release of ephyrae may be protracted (albeit to different extents) in each species, with individuals of all sizes present in the water column during the summer months. For R. octopus, there was a general increase in both mean bell diameter and wet weight from January through to June which was driven by an increase in the variance and overall range of both variables during the summer. Lastly, we provide further evidence that rhizostome jellyfish may over-wintering as pelagic medusa which we hypothesise may enable them to capitalise on prey available earlier in the year. Handling editor: K. Martens     

Unique Similarity of Faunal Communities across Aquatic–Terrestrial Interfaces in a Polar Desert Ecosystem

Abstract Critical transition zones, such as aquatic–terrestrial interfaces, have been recognized as important features in landscape ecology. Yet changes in the community structure of soil and sediment biota across aquatic–terrestrial boundaries remain relatively unstudied. We investigated the community structure of the dominant fauna, namely nematodes, rotifers and tardigrades, across lake sediment–soil transects in three basins in a species-poor, polar desert ecosystem (McMurdo Dry Valleys, Antarctica). We also examined substrate (that is, soil and sediment) properties, including moisture, salinity, carbon, nitrogen and phosphate concentration, across these transects. Differences in faunal community structure and biochemical properties were typically explained by hydrologic basin and the sediment–soil gradient, but not by transects within each basin. Bonney Basin contained the least organic carbon, chlorophyll a, nematodes and taxa, whereas there was little difference in many of these measures between Fryxell and Hoare Basins. Nematode (Scottnema lindsayae and Plectus sp.) and rotifer abundance varied along sediment–soil transects. Scottnema lindsayae, the most abundant and widely distributed soil animal in this ecosystem, increased in abundance from sediments to soils, whereas Plectus sp. and rotifer abundance, and taxa richness (that is, nematodes, rotifers and/or tardigrades), decreased; Eudorylaimus sp. and tardigrade abundance did not differ significantly along the transects. Previous studies of soil biodiversity and faunal abundance in this ecosystem have revealed a positive association between these measures and biogeochemistry, if this holds true for lake sediments, our findings suggest sediments in Lake Bonney experience lower rates of nutrient cycling than either Lakes Fryxell or Hoare. Despite differences in faunal abundances along the sediment–soil transects, taxa occurrence was surprisingly similar in soil and sediment, only S. lindsayae was restricted to soil or the lake shore. In contrast, in other ecosystems, soil community composition differs greatly from lake sediments, suggesting that the observed similarity in species occurrence in both soils and sediments may be unique to Antarctica. This finding might result from the extreme low diversity of this ecosystem, presumably limiting competition among fauna, and thus promoting broad ecological niches. Alternatively, environmental conditions in Antarctica may select for species with broad ecological niches.     

Morphological differences between,and reproductive isolation of,two populations of the jellyfish Cyanea in Long Island Sound,USA

Two populations of Cyanea, one in the Niantic River estuary and the other in the adjacent Niantic Bay portion of Long Island Sound, were studied for more than a decade. The estuary and the bay are connected by a narrow channel: this and hydrographic features constrain transport between them. Specimens from each site exhibit morphological and seasonal differences comparable to those which distinguish C. capillata from C. lamarckii in European waters. Reproducing River medusae never cooccurred with reproducing Bay medusae. Estuarine jellyfish are sometimes found in the Bay, but reproducing individuals have not been seen there. Reproductively mature Bay jellyfish occasionally appear in the River, but benthic samples show that they do not deposit planulae at this site and thus do not contribute to the next generation of medusae in the River. Such differences suggest an absence of gene flow between these two populations, indicating that the River medusae and Bay medusae might be separate species.     

Ecological and economic implications of a tropical jellyfish invader in the Gulf of Mexico

A large population of a previously unreported jellyfish occurred across the northern Gulf of Mexico (USA) from May through September of 2000. The jellyfish, identified as Phyllorhiza punctata by von Lendenfeld (1884), is not indigenous to the Gulf of Mexico or to the Atlantic Basin. Current theory states that this invasive species was introduced into the Atlantic from the Pacific Ocean through the Panama Canal about 45 years ago, and several confirmed reports indicated that a cryptic population may have existed in the northern Gulf since 1993. However, mesoscale hydrographic anomalies in spring 2000 may have directly transported the population from the Caribbean Sea where populations of P. punctata have been reported previously in Puerto Rico. We undertook a rapid-response sampling program from June through September to obtain ecological information regarding P. punctata in the highly productive northern Gulf waters. Jellyfish bell diameter increased by about 50% (from an average of 32 ± 12 to 45 ± 6 cm) as animals invaded nearshore waters during July. As the summer progressed, a net westerly distribution shift followed nearshore currents to an accumulation point near the mouth of Lake Borgne, Louisiana, in the far western Mississippi Sound. In the Lake Borgne aggregation, we estimated 5.37 × 10⁶ medusae over an area of about 150 km². All of the medusae appeared to lack the symbiotic algae that are present in all other described populations, and therefore must have depended solely on planktivory for their nutrition. Clearance rates estimated from ambient zooplankton, gut contents and published digestion times ranged from < 1 m³ d^–1 for adult copepods to over 90 m³ d^–1 for fish eggs. Based on these clearance rates, the central core of this aggregation (30 km²) was being turned over at least once per day with even higher turn-over in very concentrated `super-swarms'. Clogging of shrimp nets was the greatest economic impact, and perhaps contributed to millions of dollars in economic losses. The indirect effect of predation on eggs and larvae of commercially important finfish and shellfish remained intangible in the determination of economic effects. In 2001, P. punctata has recurred along southern Louisiana and has apparently spread into the coastal and lagoonal waters of the Florida east coast.