Scavenging abyssal benthic amphipods trapped under oligotrophic central North Pacific Gyre waters

Two traps baited with fish were placed on the bottom (5720 m) of the central North Pacific Gyre. A total of 1793 lyssianassid amphipods were collected no ovigerous females and no identifiable males were caught. Five amphipod species were represented [1 undescribed species of Orchomene; 2 undescribed species of Paralicella; Eurythenes gryllus (Lichtenstein); and Cyclocaris sp.], 2 by single specimens. Amphipod samples give no evidence of size-classes. Evidence for scavenging as the amphipods' primary mode of existence is discussed. Forty-four copepods, of a single harpacticoid genus (Tisbella), were also collected.     

Helium isotopic constraints on simulated ocean circulations: implications for abyssal theories

There is ongoing controversy as to the dynamical significance of geothermal heat flow in shaping the abyssal circulation. In this paper, we gauge the impact of geothermal heating and vertical mixing parameterizations in the general circulation model OPA. The experiments are evaluated by comparing simulated mantle ³He with observations collected during the GEOSECS and WOCE programs. This tracer is particularly adapted to the validation of our numerical simulations because its injection into the ocean interior is tightly linked to geothermal processes. In agreement with previous studies, the model circulation is found very sensitive to the parameterization of the vertical mixing. The meridional overturning circulation (MOC) is globally intensified when moving from a constant mixing to a version with enhanced mixing near the ocean bottom, with the most drastic variation observed for AABW (+ 50%). Adding the geothermal heat flux mainly affects AABW circulation in the model, enhancing it all the more as the meridional circulation is slow (low vertical mixing), but proportionally less so when it is more vigorous (enhanced vertical mixing). This can be understood from the requirement of the abyssal ocean to maintain heat balance. The evaluation with mantle ³He simulations reveals that the version with low vertical mixing, with its sluggish circulation, produces unrealistically high a ³He isotopic composition. However, with a vertical mixing that is enhanced at depth, the ³He distribution falls within an acceptable range of values in the deep ocean. Finally, adding the geothermal heating to this enhanced mixing case provides a substantial improvement of the simulation of AABW in all basins but the Indian Ocean. ³He isotopic composition is then in good agreement with the observations. Taken jointly with observational estimates of the MOC intensity, these independent isotopic constraints suggest that both geothermal heating and enhanced diapycnal mixing at depth are key ingredients in the realistic simulation of abyssal circulation.     

Scavenging deep-sea amphipods: Effects of food odor on oxygen consumption and a proposed metabolic strategy

In situ respiration rates as a response to the odor of food were measured for two species of scavenging amphipods, Paralicella caperesca from 3 650 m in the western North Atlantic Ocean and Orchomene sp. B from 1 300 m in the Santa Catalina Basin off southern California (USA). In addition, complementary laboratory starvation/respiration rates for a shallow-water species, Orchomene sp. A, were determined. Initial elevated O₂ consumption rates were found for up to 8 h in all deep-sea amphipods exposed to bait odor, followed by a period of lowered respiration equivalent to rates observed in individuals not exposed to bait. Orchomene sp. A revealed a response similar to that observed in the deep-sea species. A metabolic strategy is proposed whereby scavenging amphipods efficiently utilize large episodic organic falls in the food-limited environment of the deep sea. This strategy involves (1) the ability to withstand long periods of starvation, (2) rapid response to an organic fall, (3) rapid location of the organic fall, (4) maximal rate of food consumption with maximal quantity ingested, and (5) efficient utilization of the consumed food. Each of these attributes are explored with the expected and observed mechanisms employed to achieve them.     

The reproductive biology of Hymenaster membranaceus from the Rockall Trough,North-East Atlantic Ocean,with notes on H. gennaeus

Samples of the deep-sea spinulosan asteroid Hymenaster membranaceus Wyville Thomson were collected in a timeseries of 19 bottom trawls spanning the period April 1978 to October 1981 from a 2200 m-deep station in the northern Rockall Trough. The reproductive biology of this species was studied from histological sections of the gonad, and compared with that of H. gennaeus H. L. Clark which was collected in the same hauls. At first sexual development, oogonia develop in nests surrounded by small accessory cells. Previtellogenic oocytes remain in the periphery but, at maturity, oocytes ranging up to 1 100 m fill the ovary. A variety of accessory cells pack the lumen and may be nutritive or degenerative. It appears that a small number of oocytes are spawned intermittently, but there is no evidence of overproduction and break-down of superfluous oocytes. A few large oocytes become senescent and undergo internal break-down, releasing periodic acid Schiff-positive material into the lumen. Size-frequencies of oocytes indicate that eggs may be spawned as a continuous slow release, and there is no evidence of reproductive synchrony between or within samples. On reaching maturity, males appear always to be ready to release spermatozoa. Spawning is probably stimulated by egg release during chance encounters with mature females. There is no evidence for brooding, and from the large size and yolky nature of the egg direct lecithotrophic development at or near the seabed is inferred. A limited histological study of H. gennaeus indicates that egg production is very similar, but the two species differ in the nature of the accessory cells and amorphous material filling the lumen.     

The reproductive biology of echinothuriid and cidarid sea urchins from the deep sea (Rockall Trough,North-East Atlantic Ocean)

The reproductive biology of 5 species of echinothuriid (Phormosoma placenta, Calveriosoma hystrix, Araeosoma fenestrum, Sperosoma grimaldii and Hygrosoma petersii) and 2 species of cidarid (Cidaris cidaris and Poriocidaris purpurata) sea urchins from the deep sea (Rockall Trough) has been examined from samples collected during 1973–1983. In all species the gonads lie within the interambulacrum attached to aboral gonopores and when fully developed occupy most of the test not occupied by the gut or Aristotle's lantern. In all the species, initial oocyte development takes place along the germinal epithelium embedded in nutritive tissue. In all the echinothuriids and in Poriocidaris purpurata, the oocyte grows to ca. 200 to 450 m, at which stage vitellogenesis begins. Oocyte growth continues until a maximum egg size of 1 100 to 1 500 m is attained. In the echinothuriids, two types of nutritive tissue are found. In the carly stages of gametogenesis the oocyte is surrounded by well-structured periodic acid Schiff (PAS)-positive tissue. As the oocyte grows this tissue becomes vacuolated, suggesting that there is a transfer of nutriment to the developing oocyte. In Phormosoma placenta, unspawned oocytes are phagocytosed. There is no evidence of seasonality in any of the echinothuriid species or in Poriocidaris purpurata. Extrapolation with shallow-water echinothuriids suggests that larval development is lecithotrophic, omitting any planktotrophic phase. Of the species examined, only Cidaris cidaris has a reproductive strategy which produces a known larva, although the limited samples did not permit any determination of seasonality in this deep-sea population.     

Multi-marker estimate of genetic connectivity of sole (Solea solea) in the North-East Atlantic Ocean

A thorough knowledge on the genetic connectivity of marine populations is important for fisheries management and conservation. Using a dense population sampling design and two types of neutral molecular markers (10 nuclear microsatellite loci and a mtDNA cytochrome b fragment), we inferred the genetic connectivity among the main known spawning grounds of sole (Solea solea L.) in the North-East Atlantic Ocean. The results revealed a clear genetic structure for sole in the North-East Atlantic Ocean with at least three different populations, namely the Kattegat/Skagerrak region, the North Sea and the Bay of Biscay, and with indications for a fourth population, namely the Irish/Celtic Sea. The lack of genetically meaningful differences between biological populations within the southern North Sea is likely due to a large effective population size and sufficient connection (gene flow) between populations. Nevertheless, an isolation-by-distance pattern was found based on microsatellite genotyping, while no such pattern was observed with the cytochrome b marker, indicating an historical pattern prevailing in the latter marker. Our results demonstrate the importance of a combined multi-marker approach to understand the connectivity among marine populations at region scales.     

Comparative study of sympatric populations of two hyperiid amphipods,Primno johnsoni and P. evansi,from the eastern North Atlantic Ocean

Hyperiid amphipods are common components of oceanic plankton communities, and yet information is lacking on the ecology and biology of the majority of species. This study compares sympatric populations of two phrosinids, Primno johnsoni Bowman and P. evansi Sheader, using material collected on R.R.S. Discovery Cruises 121 and 140 in the eastern North Atlantic Ocean. The two species were essentially very similar in terms of their vertical distribution and diurnal migration, and in the timing and sequence of reproductive events (onset of maturity, ovary/oocyte development, marsupial development). Mature female and male size ranges were comparable for the two species, males maturing at a small body size, with little subsequent growth, and females producing a succession of 5 (P. evansi) or 6 (P. johnsoni) broods maximum. The species differed significantly in egg size and in total egg output. These dissimilarities were accentuated by differences in the patterns of female mortality in the two species, such that actual egg output per female was 1.8 times greater (2.4 times in terms of total egg volume) in P. johnsoni than in P. evansi. These differences were reflected in the relative size of populations in the field. Although both species are capable of consuming a wide range of planktonic prey, it is assumed that gelatinous species are important, especially as hosts for the parasitoid juvenile stages, and it is suggested that host-specificity might act to separate the niches.     

The near-bottom shrimp faunas (Decapoda: Natantia) at two abyssal sites in the Northeast Atlantic Ocean

Bottom and near-bottom decapod shrimp communities from two northeast Atlantic abyssal sites (ca. 4 040 and 5 440m) were examined in 1984 and 1985. In both cases, an increase in abundance was observed in the bottom 90 m of the water column, with the largest numbers of shrimps occurring closest to the sediment surface (10 to 25 m off the bottom). The benthopelagic communities were composed of species drawn from both pelagic and benthic habitats rather than being specific and discrete. Hymenodora glacialis was the dominant species at the shallower site but it was absent from the near-bottom samples at the deeper one. H. acanthitelsonis, however, occurred at both sites. Several new depth records have been established, and there are two recordings of species previously unknown to the eastern Atlantic basin. Vertical migration and differences in modes of reproduction are discussed.     

Effects of recreational diving on early colonization stages of an artificial reef in North-East Atlantic

Increasing interest for recreational SCUBA diving worldwide is raising the concern about its potential effects on marine ecosystems. Available literature is still much focused either on impacts on coral reefs of tropical regions or on diver’s behaviour underwater. In this study we analysed, through photo-quadrats, the benthic community composition in a section of a decommissioned Portuguese navy ship that was sunk for touristic purposes. The ship broke down and became separated in two sections enabling a Control versus Impact sampling design, as one section is less attractive for diving. Gorgonians (mainly belonging to the species Leptogorgia sarmentosa and Eunicella verrucosa) were the taxa more negatively affected in the dived ship section, with smaller coverage and size. More resilient species such as the acorn barnacle Amphibalanus amphitrite were positively correlated with the Impact samples. In the case of the study area, according to the available data, 70% or more of the total amount of dives are now on the sunken ships. From these results, lessons can be taken to apply on natural reefs and related management plans.     

Hyperiid amphipods from the zooplankton community of the North Pacific central gyre

The hyperiid amphipods have been examined from an extensive series of depthstratified bongo net tows taken at 28°N; 155°W in the North Pacific central gyre, an open-ocean ecosystem. Seventy-nine samples from 6 depth ranges produced 14, 581 individuals belonging to 13 families, 42 genera, and 83 species. Data on depth distributions, rank orders of abundance, sex ratios, and vertical migration are presented. Most of these species are shown to be reproductively active in the gyre, and there appears to be no seasonality to their reproductive behavior. No species endemic to the gyre are yet known.     

Bacterial flora from echinoderm guts and associated sediment in the abyssal Vema Fault

Individuals of the asteroid Solaster sp. and the holothurian Pseudostichopus villosus (Theel) were collected from deep-sea bottom of the Vema fault in the mid-Atlantic ridge during the BIOVEMA cruise (November, 1977) of the R.V. Jean Charcot. Heterotrophic aerobic bacteria of the guts were isolated, identified and compared with bacterial isolates from surface sediment of the same area. Bacterial population structures displayed a predominance of Gram-negative rods in the echinoderm guts and a predominance of Gram-positive bacteria (particularly cocci) in the surface sediment. Investigation of the metabolic potentialities of the isolates suggested that the microflora of echinoderms, and in particular of the Asteroidea, have more specialized orientations in the catabolism of organic compounds. Single-linkage cluster analysis of all the isolates (130 strains) based on 139 phenotypic features revealed that out of 15 identified clusters, only one included both enteric and sediment isolates. The bacteria in this cluster were similar to the genus Micrococcus.     

Electrophoretic and biometric variability in the abyssal grenadier Coryphaenoides armatus of the western North Atlantic,eastern South Pacific and eastern North Pacific Oceans

Specimens of the abyssal grenadier Coryphaenoides armatus (Hector, 1875), from the western North Atlantic and eastern North Pacific Oceans were compared electrophoretically at 27 presumptive gene loci. At 6 of the 7 polymorphic loci there were only minor differences in allelic frequencies but a nearly fixed difference was found at one locus, phosphogluconate dehydrogenase. Eastern North Pacific grenadiers typically have a narrower interorbital space, a shorter dorsal interspace, more soft rays in the 1st dorsal fin (9–10 versus 8–9) and more pelvic fin rays (21–23 versus 18–21) than grenadiers from the western North Atlantic (as well as grenadiers from the eastern South Pacific, which were included in the biometric analysis). There is an apparent disjunction in the distribution of C. armatus in the eastern Pacific at the Gulf of Panamá which coincides with the change of morphology. It is suggested that North Pacific grenadiers comprise a subspecies, C. armatus variabilis Günther, 1878, which is morphologically distinct from the subspecies C. armatus armatus (Hector, 1875) of the other areas.     

Herbivory and detritivory among gammaridean amphipods from a Florida seagrass community

The gammaridean amphipods Cymadusa compta (Smith), Gammarus mucronatus Say, Melita nitida Smith and Grandidierella bonnieroides Stephensen from a seagrass community in the Indian River estuary of Florida (USA) fed variously upon large drift algae, small algae epiphytic on seagrasses and seagrass leaf debris and detritus. Consumption was measured in the laboratory using an index (CI) equivalent to mg ingested mg^-1 amphipod day^-1. Observations revealed that the amphipods fed by macrophagy, an attack upon large algae and seagrass debris, and by microphagy, small particle detritus feeding and scraping of plant surfaces for diatoms and other epiphytic algae. C. compta was a macrophagous feeder with a generalized diet of algae and seagrass debris, preferring epiphytic algae and drift algae at mean rates of 1.10 and 0.87 CI, respectively. Gammarus mucronatus fed upon epiphytes and seagrass debris equally at mean rates of 0.90 and 0.97 CI, respectively. The diet of M. nitida condisted primarily of epiphytes, consumed at an average rate of 1.05 CI. Grandidierella bonnieroides fed in a specialized microphagous manner, grooming plant surfaces for small particle detritus and diatoms at an approximate CI rate of 1.45. Assimilation of plants ingested, as reflected by carbon-14 uptake, varied similarly among the 4 amphipods. Epiphytic algae appeared to be most useful as food, providing means of 41 to 75% carbon-14 uptake as ingesta. Drift algae and seagrass debris were of less value, with means varying between 11 and 24 % of carbon-14 uptake by the amphipods. The data show a pattern of feeding which resembles resource partitioning of food both by size and kind. Other evidence, however, including population limitation by predators and an apparent overabundance of food, indicate that resource partitioning as seen may be an artifact, and one which has no co-evolutionary basis among the present species.Contribution No. 102 of Harbor Branch Foundation, Inc.     

Benthic amphipods (Crustacea: Malacostraca) in Icelandic waters: diversity in relation to faunal patterns from shallow to intermediate deep Arctic and North Atlantic Oceans

Patterns in diversity, species replacement and species composition of gammaridean amphipods (Crustacea: Malacostraca) were studied in two areas on different sides of the Greenland–Iceland–Faeroe Ridge. One was sited south of the Ridge in the North Atlantic Ocean off southern Iceland and the other north of the Ridge in the Arctic Ocean (subarctic and arctic waters of the Iceland Sea) off northern Iceland. Samples were taken with a Rothlisberg–Pearcy epibenthic sled within the depth range of about 50 to 1200 m at a total of 28 stations. In all 21 150 individuals were found belonging to 156 species. Of these 102 were found in the northern area with 64 of the species restricted to this area. In all 94 species were found in the southern area with 52 of the species restricted to this area. This suggests a similar regional diversity, but a different faunal composition. The amphipods showed similar species replacement patterns with depth on both sides of the Ridge, while the diversity patterns differed between the areas. In the North Atlantic the number of species increased with depth, while in the Arctic there seemed to be no pattern at all. It is suggested that diversity patterns of amphipods on each side of the Ridge are shaped by different factors, and these may not be the same as those determining diversity patterns of other groups in the area. Salinity (as indicative of water masses) was found to be the most important environmental variable in explaining the species composition when both areas were considered, suggesting a number of contributing factors (adaptation to water masses, dispersal, etc.). Water temperature was the most important variable in explaining the variance in the species composition in the northern area, while depth was the most important variable in explaining the variance in the species composition of the southern area. Received: 9 March 1997 / Accepted: 10 December 1997     

Interception and dispersal of artificial food falls by scavenging fishes in the abyssal Northeast Atlantic: early-season observations prior to annual deposition of phytodetritus

The hypothesis that the behaviour of deep-sea scavenging fishes is influenced by seasonal input of organic matter from the ocean surface was investigated by observing responses to baits placed on the sea floor at 4800 m depth in the NE Atlantic (48°50′N; 16°30′W) during spring (April 1994). Data from the present study are compared with those from previous studies of the same location made in summer 1989. The first fishes to arrive at baits were the grenadier Coryphaenoides (Nematonurus) armatus and the eel Histiobranchus bathybius, after delays of 28 and 29 min, respectively; these results are not significantly different from those of summer 1989. Similarly, other indices of activity (staying time and swimming speed) showed no evidence of differences between years/seasons. However, the rate of radial dispersal of bait (0.009 m s⁻¹) by C. (N.) armatus was much slower than in all previous studies. A change in the size distribution of C. (N.) armatus to smaller individuals in spring 1994 was also evident. It is suggested that the fish on the abyssal plain may not comprise a steady-state population and that major episodic or seasonal migrations may occur. Received: 18 October 1996 / Accepted: 20 December 1996     

Organic content and biomass of abyssal holothuroids (Echinodermata) from the Bay of Biscay

The levels of ash, lipid, carbohydrate, protein and calories in the body walls of 3 abyssal holothuroids of the Bay of Biscay [Benthogone rosea Koehler, Paelopatides gigantea (Verrill) and Psychropotes longicauda Theel] are similar to those found in the body walls of shallow-water holothuroids. The biomass of abyssal holothuroids in terms of calories comprises an important fraction of the total biomass in the deep sea; at 2 000 m depth, the holothuroids correspond to one-sixth of the total biomass. However, the numerical and caloric densities of abyssal holothuroids are 4 orders of magnitude less than those of shallow-water holothuroids, although the sizes and caloric contents of individuals are of similar magnitude.Contribution No. 742 of Centre Océanologique de Bretagne     

Continuous Plankton Records: Seasonal cycles of phytoplankton and copepods in the North Atlantic ocean and the North Sea

Data from the Continuous Plankton Recorder survey of the North Atlantic Ocean and the North Sea are used to study geographical variations in the amplitude, duration and timing of the seasonal cycles of total phytoplankton and total copepods. It is shown that the distribution of overwintering stocks influences the distributions throughout the year. There is a relationship between the timing of the spring increase of phytoplankton and the amplitude of the seasonal variation in sea surface temperature. In the open ocean, the timing of the spring increase of phytoplankton corresponds with the spring warming of the surface waters. In the North Sea the spring increase occurs earlier, associated, perhaps, with transient periods of vertical stability, resulting in a relatively slower rate of increase. It is suggested that in the open ocean the higher rate of increase is under-exploited by copepods due to low overwintering stocks and longer generation times. Exceptionally early spring increases of phytoplankton off the west coast of Greenland and over the Norwegian shelf are probably associated with permanent haloclines. A high and late autumn peak of phytoplankton off the coast of Portugal may be associated with coastal upwelling.     

The sea-skater Halobates micans: an open ocean bioindicator for cadmium distribution in Atlantic surface waters

Our knowledge of the horizontal distribution of heavy metals in the open ocean with time and space is still very incomplete. Complementary to chemical water analyses suitable biological indicator species may be used to fill this gap. The pleuston organism Halobates micans was collected from 1966 to 1987 at 151 sampling stations of the tropical and subtropical Atlantic Ocean. The cadmium data from more than 1000 individuals analysed display a chemicaloceanographic meaningful distribution in surface waters and compare favourably to primary production values. Chemical analysis of individual plankton species offer a new tool for a better understanding of geochemical cycling of heavy metals in the ocean.     

Photographic and acoustic tracking observations of the behaviour of the grenadier Coryphaenoides (Nematonurus) armatus the eel Synaphobranchus bathybius,and other abyssal demersal fish in the North Atlantic Ocean

Using an autonomous free-fall vehicle (AU-DOS), observations were made of demersal fish attracted to baits and baited acoustic transmitters at two stations in the North Atlantic Ocean. A comparison was made between Station PAP (48°50N; 16°30W), 4800 m deep on the Porcupine Abyssal Plain which is relatively eutrophic, and Station MAP (31°N; 20°W), 4900 m deep on the Madeira Abyssal Plain, which is oligotrophic. Experiments were conducted during summer, in 1989 and 1990. Four species of fish were observed at Station MAP, the grenadier, Coryphaenoides (Nematonurus) armatus, the eel, Synaphobranchus bathybius, and the ophidiids Spectrunculus grandis, and Barathrites sp. At Station PAP, C. (N.) armatus and H. (S.) bathybius were attracted to bait on all deployments and only two other individuals of different species, probably ophidiids, were seen. The mean first grenadier arrival time was 30 and 138 min at Stations PAP and MAP, respectively. Mean first eel arrival time was 29 and 151 min at Stations PAP and MAP, respectively. Estimated population densities of fish were 167 grenadiers km^-2 and 180 synaphobranchid eels km^-2 at Station PAP and 8 grenadiers km^-2 and 7 eels km^-2 at Station MAP. Only the grenadier C. (N.) armatus definitely ingested transmitters, and this species dominated fish activity around the baits. Mean time of departure of grenadiers with transmitters in their stomachs across an acoustic horizon at 1000 m range was 371 and 488 min at Stations PAP and MAP, respectively. Grenadiers had a longer mean staying time at the food source at the more oligotrophic Station MAP (364 min) than at Station PAP (141 min). This corresponds with predictions of optimal foraging theory.     

Hyperiid amphipods in the eastern part of the South Pacific gyre

Studies were made of Amphipoda Hyperiidea collected in 1987 with a pelagic trawl in the South Pacific anticyclonic gyre in the vicinity of the Nazca and Sala y Gómez ridges (17°35 to 26°01S, 80°10 to 100°50W), at depths ranging from 50 to 300 or 600 m. Forty-three hauls contained 7 198 specimens, comprised of 119 species within 43 genera. Two of the species appeared to be new for science; two others were found in the Pacific Ocean for the first time. A comparison with hyperiid collections from other tropical Pacific regions revealed great stability of oceanic faunal composion. However, the collections differed considerably in their dominant species. Furthermore, comparison of Hyperiidea from various parts within the investigated area of the South Pacific gyre also reflected differences in dominant species. The degree of these mesoscale spatial differences was comparable to that among the central regions of the northern and southern anticyclonic gyres.