Variations saisonnières des appendiculaires de la région nord Adriatique

Appendicularians from 140 hauls made in the north Adriatic area, over a period of 9 months, have been examined. A high population density, with 67 specimens per cubic meter and a low specific diversity with 10 species is described. Three species: Oikopleura dioica, O. longicauda and O. fusiformis represent more than 95% of the specimens collected. The presence of a West-East gradient in the population density is shown, along with a correlation with the influence of the Pô inflow. A study of the seasonal variations of the three main species shows that all the characteristics of the Western region are very favourable to O. dioica. This fact seems to be the clue to the qualitative and quantitative variations of the appendicularian population in this area.     

Distribution and abundance of fish larvae off the coast of West Pakistan

The material was collected during 4 different cruises on the shelf off the coast of W. Pakistan in November–December, 1964 and in March, 1967 and 1968. The hydrography as well as the zooplankton-biomass distribution are briefly described. A total of 5777 larval fish were taken in 33 positive vertical hauls by an Indian Ocean Standard Net. The number of larvae in positive hauls ranged from 2 to 1262 larvae haul^-1. The most productive area of the ichthyoplankton was the waters south of Karachi, covered during the Machera Cruise, where 828 to 1262 larvae haul^-1 were obtained. The larvae were identified to species, genera or family. Sardinella sindensis (specific identification uncertain) larvae dominated in abundance. The other abundant larvae belonged to Benthosema spp., Amentum commersonii, Vinciguerria spp. and Diaphus spp. Larval distributions and abundances are described. Aggregation and spawning of adult Sardinella (sindensis) in the waters off the coast of W. Pakistan in November/December, 1964, are discussed. Presumably, the waters south of Karachi represent good feeding grounds for s. (sindensis) larvae. Displacement volume, length and weight relationships of various larval size groups have been studied and a high rate of larval mortality (at a length of 5.0 to 8.5 mm) observed.     

A comparative survey of neuston: geographical and temporal distribution patterns

Neuston samples were collected from 149 stations during a voyage west from Fiji to the Bay of Biscay from August 1979 through November 1980. The neustonic fauna was counted and assigned to 50 species groups, chosen to represent the most numerous animals in the hauls. Analyses of neustonic concentration and population structure showed regional and temporal differences in the fauna. Permanent inhabitants of the surface waters, the euneuston, were most numerous in the open tropical waters of the Central Indian Ocean. In contrast, the temporary neuston, which was composed of juveniles, vertical migrants and the uppermost individuals from deeper populations, attained its greatest concentration in the upwelling region of the Somali Current and at inshore stations around the Indonesian archipelago and in the Gulf of Aden and Red Sea. Heavy rains adversely affected the neuston, possibly by diluting the surface waters. Both neustonic groups were sparsely represented in the cooler waters of the Mediterranean Sea and the eastern Atlantic Ocean. At night considerable immigration occurred into the neustonic zone, and the mean faunal density at dusk was 21 times greater than was found at mid-day. Surface waters were inhabited by the developmental stages of many species, and eggs and juveniles of both vertebrates and invertebrates were consistently present in the hauls.     

Preponderance of a few diatom species among the highly diverse microphytoplankton assemblages in the Bay of Bengal

The microphytoplankton assemblages were studied from water samples collected at eight discrete depths in the top 120 m at five central (open ocean) and four western (shelf/slope region) locations in the Bay of Bengal. The Bay is a low-productive warm pool regime with poor inorganic nutrient inputs to its intensely stratified surface layer despite the very large riverine influx. In addition, the prolonged cloud cover has an adverse effect on the top 25–40 m, on primary production, chlorophyll concentration and phytoplankton assemblages. Microphytoplankton were the most abundant in the northern area of the Bay. A total of 153 phytoplankton species were identified during this study. The most abundant species (at least 1,800 individual cells belonging to a given species or ≥2% of the total counts of identified specimens) during this study were: Thalassiothrix longissima, Thalassiothrix fauenfeldii, Rhizosolenia styliformis, Nitzschia angularis, Thalassionema nitzschioides, Coscinodiscus radiatus, Chaetoceros eibenii, Skeletonema costatum, Coscinodiscus concinnus and Chaetoceros coarctatus. Similarly, there were 20 moderately abundant (≥0.5 but <2%) species. Thirty-three of the least abundant species (<0.5%) occurred at one station. Diatom species, T. fauenfeldii and T. longissima were ubiquitous in the study area. The exclusive occurrence of S. costatum in the northernmost stations suggests that it proliferates only in the low-salinity regions with adequate silica from the land inputs. Abundance of pennate diatoms was higher in the open Bay compared to that of centric diatoms in the more productive northern locations and the western Bay. There appears to be a basic difference between near shore flora and offshore flora. This first analysis of phytoplankton assemblages from the offshore Bay suggests that while there is predominance of only a few species, the Bay harbors very diverse diatom communities that seem to be syntrophic, non-competitive and co-habiting in the generally low nutrient, stratified surface waters.     

Medusa buds on Eirene elliceana gonads (Leptomedusae,Eirenidae)

The Indo-Pacific leptomedusa Eirene elliceana (Agassiz and Mayer, 1902) is known to produce blastostyles budded from the gonads of the adult medusa. Three specimens out of 5, taken during the International Indian Ocean Expedition (IIOE) in the Bay of Bengal, showed medusa buds growing on young gonads whose sex could not be determined. The new findings are illustrated.Contribution No. 320 of the Instituto Oceanográfico da Universidade de São Paulo, S. Paulo, Brazil.     

Halistaura bruuni sp. nov. (Leptomedusae,Mitrocomidae) with notes on its distribution and ecology

A new hydromedusa collected in 1963 in the Bay of Bengal during the International Indian Ocean Expedition by the RV Anton Bruun is here described as Halistaura bruuni sp. nov. Some environmental data are given. The new species is characterized by a number of open marginal vesicles approximately equal to that of the tentacles, oval gonads on the distal half of the radial canals, and by the presence of nematocyst depots in the tentacle bulbs.Publ. No. 273 of the Instituto Oceanográfico da U. S. P.     

Spatial and temporal variability of fish assemblage in Kuwait Bay

Spatial and temporal variability of fish assemblages in Kuwait Bay was studied using the catch data acquired through monthly otter trawl sampling from June 2002 through July 2004. We compared species composition using relative species density and cluster analysis among different seasons (summer’02, summer’03, winter’03, and spring’04) and areas (center, south 1, south 2, west, north and east). Significant differences in total species, species richness (SR), diversity (H′), and fish abundance were tested among (between) different seasons and areas using analysis of variance (ANOVA) and Duncan’s test. The results showed that the catches consisted of 80 species representing 41 families with Leiognathus bindus and Plicofollis tenuispinis dominating numerically. Spatially, species composition fell into three main areas: (1) east; (2) south 1 and south 2; and (3) north, center, and west. Temporally, winter’03 and spring’04 were closely related, but we found low similarity between the two summers and even lower similarity between the summers and other seasons, indicating high intra-annual variation. L. bindus was abundant in most of the areas except south 1, south 2 and the east area. Spatial changes of abundance of the two dominant species showed a complementary trend. Where L. bindus was numerically high, P. tenuispinis was low, and vice versa. Significant lower total species number and SR were observed in south 2 than all the other areas except the east, and significant higher fish abundance occurred in the summers than during the other seasons. Overall, it was concluded that variation in fish assemblages was area dependent, while fish abundance was mainly influenced by seasonal changes.     

Where is the western limit of the tropical Indian Ocean seaweed flora? An analysis of intertidal seaweed biogeography on the east coast of South Africa

New, large-scale collections have been made of marine benthic macroalgae (seaweeds) on the east coast of South Africa, and the distributions of shallow-water species were analyzed in detail by multivariate, clustering and -diversity methods. The two northernmost sites are distinct, with a predominance of tropical species, and it is concluded that the changeover from a tropical Indian Ocean flora to a temperate South African flora occurs most rapidly in the vicinity of St. Lucia, 135 km south of the Mozambique border. It is imperative that all future biogeographical studies on the South African inshore marine biota include detailed collections north of St. Lucia. The remaining 440 km of the South African east coast (southern and central Kwazulu-Natal Province) is populated by a mixture of tropical and temperate elements, with only 2% endemism in this data set. This, thus, represents a true overlap region, with relatively equal numbers of species with affinities in the temperate Agulhas and tropical Indo–West Pacific floras, rather than a distinctive sub-tropical marine province, as the South African east coast is considered to be by most previous authors. The distinction between this overlap region and the south coast (Agulhas) region proper is not as clearly distinct. The change from a temperate to a tropical flora shows a relative increase in green algae from 15% to 25% of the species present. Criteria for the delineation of marine biogeographical regions are critically discussed, and it is concluded that the monitoring of distributions of all species, including rare species, is necessary. This is particularly relevant with regard to using these data to assess effects of potential changes in seawater temperature, including those which may be caused by global warming. Criteria for the delimitation of biogeographic entities such as "marine provinces" need to be clearly spelt out in all investigations.Communicated by O. Kinne, Oldendorf/Luhe     

Community interactions and zoogeography of the Indian Ocean Candaciidae (Copepoda: Calanoida)

Eighteen species of Candaciidae have been identified from collections made at 339 stations in the Indian Ocean. Most species are zonally distributed; however, on the eastern and western sides of the Indian Ocean, species ranges are extended north or south by boundary currents. Factor analysis was used to cluster phenotypically similar species based on 130 characters taken from the maxilla (a feeding appendage), the first swimming foot, and the fifth foot (a secondary sexual structure). Four morphological clusters were extracted. Clusterings based on separate factor analyses limited to characters from feeding or from sexually adapted appendages are in substantial agreement with the clusters based on composite morphology. Two geographically recurrent groups of species were also identified, one from equatorial waters, one from the central gyre. Each recurrent group is composed of species exceptionally different in body size and belonging to different morphological clusters. Niches of the species are compared using Hutchinson's multidimensional hypervolume as a model. An attempt is made to describe the niche of each species in terms of environmental variables measured at stations where the species was abundant. Environmental variables (dimensions) included in this study are space, time, temperature, food, oxygen and salinity. Mean niche adaptations of most of the species are separable from congeners along at least one niche dimension. It is proposed that community relationships among the Candaciidae developed to prevent both gamete loss and to avoid trophic competition. It is postulated that newly evolving species underwent contemporaneous displacement of both secondary sexual and trophic characters as a condition for sympatry, or diverged in their physiological adaptations to escape sympatric interference.Contribution No. 3686 of the Woods Hole Oceanographic Institution. This research was supported by NSF Grants GB 27405 and GA 43126 and is based on a doctoral dissertation submitted to the Curriculum in Marine Sciences of the University of North Carolina at Chapel Hill.     

Relation between respiration,excretion (ammonia and inorganic phosphorus) and activity of amylase and trypsin in different species of pelagic copepods from an Indian Ocean equatorial area

The relationship between respiration, nitrogen and phosphorus excretion and specific activity of amylase and trypsin was investigated from shipboard experiments with several species of copepods from the equatorial divergence area of the Indian Ocean, in June 1978. Statistical analysis of O:N ratios in 6 of the most common species revealed three main groups: a group displaying low O:N (Pontella fera, Candacia pachydactyla); a group with high O:N (Undinula darwini, Euchaeta marina, Temora discaudata); and a species displaying an intermediate O:N ratio: Scolecithrix bradyi. O:P and N:P did not differ significantly between species. There was a direct relationship between average O:N and the ratios of specific activity of the digestive enzymes amylase and trypsin. Species displaying low O:N and/or A:T ratios such as P. fera, C. pachydactyla and Oncaea venusta probably metabolize proteins more efficiently than they do plant carbohydrates (high nitrogen excretion and low amylase activity). Species displaying high O:N and A:T ratios, such as U. darwini, E. marina and T. dicaudata (low nitrogen excretion and high amylase activity) were assumed to use carbohydrates (starch) and proteins with equal efficiency. S. bradyi showed a large range of variations in trypsin activity and low amylase activity, resulting in a low average A:T ratio, but its O:N ratio was intermediate. Variations in O:N and O:P ratios were related to differences in the nutritional strategy of the different species, based on literature data concerning the anatomy of their mouth parts and their selectivity for animal material in mixed-food experiments.     

Introduction,dispersal and potential impacts of the green crab Carcinus maenas in San Francisco Bay,California

The North Atlantic portunid crab Carcinus maenas (Linnaeus, 1758) has invaded the North Pacific Ocean following more than two centuries of global dispersal due to human activities. C. maenas was first collected in San Francisco Bay, California, in 1989–1990, where its distribution and prey selectivity were investigated in 1992–1994. It has become abundant in shallow, warm lagoons (which as favorable and retentive microhabitats may have served as invasion incubators) and spread throughout the north, central and south bays. It may have arrived in ballast water, on fouled ships, amongst algae with imported live bait or lobsters, or by intentional release; genetic comparisons of the Bay population with possible source populations may aid in defining the transport mechanism. C. maenas' eurytopic nature, its high breeding potential, and its diet and feeding behavior suggest the potential for extensive ecosystem alterations through predator-prey interactions, competition, disturbance, and indirect effects. Although both negative economic impacts through reduction or disruption of fisheries and positive impacts of providing bait and human-food fisheries have been documented in a few regions, the potential economic impacts in San Francisco Bay remain largely unknown.     

PCR-based detection of mtDNA haplotypes of native and invading mussels on the northeastern Pacific coast: latitudinal pattern of invasion

Frequencies of mitochondrial haplotypes characteristic of native Mytilus trossulus and introduced M. galloprovincialis were determined in populations along the west coast of North America from San Diego, California, to the Aleutian Islands, Alaska. We also identified the haplotypes of mussels cultured from larvae arriving in Coos Bay, Oregon, during 1988–1990 from sites in Japan in the seawater ballast of ocean-going ships. All mussels from ballast-water samples were M. galloprovincialis. We found that sampled populations north of San Francisco Bay, including Coos Bay, were entirely composed of mussels with the M. trossulus haplotype, while haplotypes of both species were present in all sites in and south of San Francisco Bay. The presence of M. trossulus in southern sites is contrary to evidence from allozyme studies, and we suggest that mtDNA introgression from M. trossulus to M. galloprovincialis may explain this discordance. This study demonstrates that, despite continued transport and release, M. galloprovincialis has not become established in northern sites. Failure to invade the north coast of North America may reflect environmental unsuitability for M. galloprovincialis. However, invasion success may be probabilistic, and the continuing release of M. galloprovincialis larvae may foreshadow a future successful invasion.     

Benthic macrofaunal compositional variations in the northern Bering Sea

Point sampling of soft-sediment macrofauna provided a regional-scale analysis of species composition, diversity, and demographic distributions in the northern Bering Sea (61°0??C65°30??N Lat) in spring 2006. Taxonomic differences distinguished subregions north and south of St. Lawrence Island (P?<?0.1%). High compositional variability occurred within and between sites, with higher variability among northern sites. One to two species dominated most assemblages, with moderately common or rare species. Ampeliscid amphipods characterized the north, and bivalves the south. Bivalves (Macoma calcarea Gmelin, Nuculana radiata Krause, Ennucula tenuis Montagu) were commonly widespread, in varied abundances and sizes. Overall, the extensive soft-sediment habitat supports a varied fauna composition with location, in species dominance, abundance, and size-class. This spatially heterogeneous regional structure is important in assessing ecosystem performance related to secondary production, biogeochemistry, bioturbation, top predator feeding strategy, recruitment, and in measuring change.     

Patterns and selectivity in the feeding of certain mesopelagic fishes

Stomach contents were analysed from the 7 most numerous species of mesopelagic fish caught in a series of 11 hauls over a 24 h period at 230 to 266 m depth in the eastern North Atlantic Ocean. The numerical abundance of organisms per filled stomach and the frequency of occurrence of empty stomachs were used to indicate feeding periodicity. The ecological significance of the feeding periodicity was considered by examining it in connection with an investigation of the day-night vertical distribution of zooplankton and micronekton to 2000 m at the same station. Additional dietary evidence on the 7 species considered was also obtained from the vertical series. Feeding selectivity was examined by comparing the composition of the zooplankton population, sampled separately but simultaneously with the micronekton, with that from the overall stomach contents of the species examined. Feeding periodicity was demonstrated for 6 species, of which 3 were found to be feeding selectively: Valenciennellus tripunctulatus on calanoid copepods, Argyropelecus aculeatus on ostracods, and Lampanyctus cuprarius on amphipods and possibly euphausiids. The limited data available on the other 3 species suggested that they were either random feeders (A. hemigymnus and Lobianchia dofleini) or perhaps selecting against a particular group (Notolychnus valdiviae). No indication of feeding periodicity or selectivity was found for Chauliodus danae. The overall pattern of results confirmed the supposed close correlation between vertical migration and feeding in mesopelagic fish.     

Succession and growth limitation of phytoplankton in the Gulf of Bothnia (Baltic Sea)

A one year field study of four stations in the Gulf of Bothnia during 1991 showed that the biomass was ca. two times, and primary productivity ca. four times, lower in the north (Bothnian Bay) than in the south (Bothnian Sea) during the summer. Nutrient addition experiments indicated phosphorus limitation of phytoplankton in the Bothanian Bay and the coastal areas in the northern Bothnian Sea, but nitrogen limitation in the open Bothanian Sea. A positive correlation between the phosphate concentration and the production/biomass ratio of phytoplankton was demonstrated, which partly explained the differences in the specific growth rate of the phytoplankton during the summer. Differences in photosynthetic active radiation between the stations also showed a covariation with the primary productivity. The relative importance of nutrient or light limitation for photosynthetic carbon fixation could not, however, the conclusively determined from this study. Marked differences in phytoplankton species composition from north to south were also observed. The number of dominating species was higher in the Bothnian Sea than in the Bothnian Bay. The distribution of some species could be explained as due to nutrient availability (e.g. Nodularia spumigena, Aphanizomenon sp.), while salinity probably limits the distribution of some limnic as well as marine species. The potentially toxic phytoplankton N. spumigena, Dinophysis acuminata and Chrysochromulina spp. were common in the Bothnian Sea but not in the Bothnian Bay. The pico- and nanoplankton biomass during late summer was higher than previously reported due to a revised carbon/volume ratio.     

The spatial ecology of juvenile loggerhead turtles (Caretta caretta) in the Indian Ocean sheds light on the “lost years” mystery

While our understanding of the early oceanic developmental stage of sea turtles has improved markedly over recent decades, the spatial context for this life history stage remains unknown for Indian Ocean loggerhead turtle populations. To address this gap in our knowledge, 18 juvenile loggerheads were satellite tracked from Reunion Island (21.2°S, 55.3°E) between 2007 and 2011. Nine turtles swam north toward Oman (20.5°N, 58.8°E), where one of the world’s largest rookeries of loggerheads is located. Three individuals traveled south toward South Africa and Madagascar, countries that also host loggerhead nesting grounds. Fourteen of the transmitters relayed diving profiles. A dichotomy between diurnal and nocturnal diving behavior was observed with a larger number of shorter dives occurring during the day. Diving behavior also differed according to movement behavior as individuals spent more time in subsurface waters (between 10 and 20 m) during transit phases. The study provides an understanding of the oceanic movement behavior of juvenile loggerheads in the Indian Ocean that suggests the existence of an atypical trans-equatorial developmental cycle for the species at the ocean basin scale in the Indian Ocean. These results address a significant gap in the understanding of loggerhead oceanic movements and may help with the conservation of the species.     

Neue kriechede ctenophoren der gattung Coeloplana aus Madagaskar

Three new species of creeping ctenophores of the genus Coeloplana were found as ectocommensals on the octocoral Sarcophyton spec. in the Indian Ocean, near Madagascar, at water depths down to 45 m. The species are described as Coeloplana wuennenbergi, Coeloplana lineolata and Coeloplana punctata. Some observations on the biology and behaviour of these species were made in the field and under laboratory conditions. The new Coeloplaae differ from other Coeloplanae in colouration, colourmarks, position, and number of the aboral papillae, and in specific host-preference. The systematic significance of most characteristics, thus far described of Coeloplanae, are discussed and summarized in Table 1.     

Floating kelps in Patagonian Fjords: an important vehicle for rafting invertebrates and its relevance for biogeography

Floating macroalgae are common dispersal vehicles for associated benthic invertebrates. In order to investigate the importance of kelp rafts for species dispersal in the Patagonian Fjord Region (PFR), the abundance and distribution pattern of floating kelps (Macrocystis pyrifera, Durvillaea antarctica) and of the invertebrate fauna associated with M. pyrifera were evaluated during austral spring of 2002–2005, 2008 and 2010. In the southernmost Magellan Region (MR), benthic M. pyrifera were additionally sampled to compare the community structures in both conditions. Floating kelps were abundant throughout the entire PFR, harbouring a diverse and abundant invertebrate fauna. The density of floating kelps increased towards the south. In the MR, a loss of species was observed between benthic and floating condition (e.g. decapods, echinoderms, several peracarid species), but a high diversity of organisms from all major phyla were observed on rafts. Throughout the PFR, the predominant rafting species belonged to the peracarids, molluscs and annelids, but the community composition differed between floating samples from the northern and southern zones of the PFR. Relative abundances of peracarids were higher in northern zones, whereas molluscs and annelids dominated in the southern areas. Species of the peracarid genera Peramphithoe, Gondogeneia, Bircenna and Limnoria were shared between all areas. The results suggest that kelp rafts not only contribute to local population connectivity in the PFR, but could also be an important dispersal vehicle for rafting species along the PFR in north–south direction, crossing the biogeographic boundary around Taitao Peninsula. Furthermore, the MR appears to be an important stepping stone for species dispersal via kelp rafting in the subantarctic region.     

Die verbreitung der kaltwasser- und der warmwasserfauna der Appendicularien im nördlichen Nordatlantischen Ozean im Spätwinter und Spätsommer 1958

The Appendicularia caught in vertical hauls during the cruises of R.V. “Anton Dohrn” and R.V. “Gauß” in the northern North Atlantic Ocean, in late winter and late summer of the International Geophysical Year (I.G.Y.), 1958, were investigated. In addition, material caught during spring, 1955 by R.V. “Anton Dohrn” was used (Figs. 1 and 2; Tables 1 and 2). Seasonal differences are revealed in the appendicularian fauna in the open ocean between 40° and 65° northern latitude. Among the species caught (Table 2) in 1955, northwest of the Hebrides, Pelagopleura australis Bückmann 1923 (Fig. 3) is of special interest. This species has hitherto only been found in antarctic and southern waters; it is, however, possible that Sinistroffia scripsii Tokioka 1957 is a synonym. In the same place, a new form of Fritillaria venusta Lohmann was found, which is described as F. venusta f. replicata n.f. (Fig. 4). The hitherto known form should be named F. venusta f. bicornis. In Figs. 5 to 7, the species dominating in single catches are indicated by symbols. A borderline between the areas of cold-water and warm-water forms can be drawn. This line is located farther to the North in late summer than in late winter. In the eastern part of the area investigated, the difference amounts to 5° latitude. Warm-water species prevail over cold-water species or appear in equal numbers in both seasons in places where water with temperatures above 11°C is found within the upper 100 m (Figs. 8 and 9). It is, however, known that Oikopleura dioica thrives also at temperatures of 10°C and below; this was also found in the spring of 1955. Cold-water species exhibited higher frequencies as well as abundances, in the late summer than in the late winter of 1958. This fact is chiefly due to an increase in individual numbers of the most important boreal species, Oikopleura labradoriensis, but also of the arctic O. vanhoeffeni and the boreal Fritillaria borealis typica. Relative to O. labradoriensis, the population of F. borealis typica decreases in late summer. During spring 1955, both species exceeded the 1958 values by far. This is considered to be the result of annual, rather than seasonal, differences. The composition of the warm water fauna (Tables 4 and 5) reveals considerable seasonal differences. In late winter, O. longicauda is the most abundant species; it prevails in almost all warm-water catches. In late summer, it is outweighed by O. dioica and O. fusiformis in the total catch, by O. dioica in many single catches in the whole warm-water area, by O. fusiformis in its north eastern part in a few very rich catches, together with Fritillaria pellucida. For size comparison of the individnals, standard trunk length could not be used because of the generally bad state of preservation. In Oikopleura, the lengths of the left stomach lobe were measured instead. It is, however, to be taken into account that the regression of body length to the stomach length (left side) is different at different stages of maturity. In ripening and ripe individuals, body length increases at a higher rate because of growths in length of the gonads. The regressions were calculated for 3 maturity stages (A, B, C; Figs. 10, 12 and 14) of O. labradoriensis and O. vanhoeffeni. In O. longicauda, the specimens were distinctly smaller during late summer, and the proportion of juveniles (stage A) was much higher (Fig. 11). Possibly, this is caused by a reproduction rate still reduced during late winter, but increasing later in the year. O. labradoriensis shows similar, though less pronounced, differences in the proportion of maturity stages, and no significant differences in size composition (Fig. 13). The 1955 material contains a much higher proportion of mature individuals than either cruise of 1958. Similar conditions as in O. longicauda cannot, therefore, be assumed to be involved in regard to O. labradoriensis, at least not at present. There were more mature O. vanhoeffeni individuals present in spring 1955, but they were much smaller than during late summer 1958. No explanation for this observation can, at present, be offered.