Comparison of laboratory rates of predation of five species of marine fish larvae by three planktonic invertebrates: effects of larval size on vulnerability

Rates of predation by the invertebrates Aurelia aurita, Thysanoessa raschi and Euchaeta norvegica on larval stages of cod (Gadus morhua L.), flunder (Platichthys flesus L.), plaice (Pleuronectes platessa L.), herring (Clupea harengus L.), and turbot (Scophthalmus maximus L.) were determined. Experiments were conducted in late winter and early spring 1982 with predators collected in Loch Etive, Scotland and prey obtained from several locations in Great Britain. Early stages of the smallest species, cod, flounder and turbot, tended to be most vulnerable to all three predators, while the early stages of the larger species, plaice and herring, and older stages of all species, were less vulnerable. For all stages and species of larvae, predation rates by the three predators were most closely related to larval length and escape swimming speed. Larval length itself was closely correlated to indices of larval escape ability. Low predation rates on large larvae by E. norvegica could be due to handling difficulties, whereas for A. aurita and T. raschi these low rates were due to escape abilities of the larger larvae. Prey movement is an important stimulus eliciting predation in E. norvegica but not in A. aurita or T. raschi.     

Growth and breeding of meso- and bathypelagic organisms of the Rockall Trough,northeastern Atlantic Ocean and evidence of seasonality

Seasonality of growth and reproduction of a variety of epimeso-and bathypelagic organisms living in the Rockall Trough is examined in samples collected between 1973 and 1978. Rates of growth change seasonally. Epipelagic and shallow-living mesopelagic migrators tend to grow most rapidly in the spring and summer while deeper-living mesopelagic migrators tend to accelerate their growth in the summer and autumn when seasonal water temperatures at these depths are at their seasonal maxima. Mesopelagic migrators all breed seasonally. Rates of growth of bathypelagic non-migrating species could not be determined through analyses of body length/frequency histograms because of the continuous (aseasonal) breeding and recruitment of juveniles to the adult populations. An exception was the mysid crustacean Boreomysis microps that had a seasonal period of spring recruitment of juveniles to the population. Several of the mesopelagic crustaceans and fish have extended periods of approximately linear growth in body length. There is no evidence that organisms living in the mesopelagic or bathypelagic environments have rates of growth that are markedly slower than those of congeners in shallower environments.     

Community structure of the benthos in Scottish sea-lochs. I. Introduction and species diversity

The diversity of the macrobenthos was measured, using the rarefaction method of Sanders (1968), from bottom samples from Loch Etive, Loch Creran and the Firth of Lorne (Scottish west coast). Each sample (representing 1.6 m² of bottom area) was accumulated as a series of separate hauls taken consecutively in a systematic pattern with a van Veen grab. Two habitats were considered: soft mud and muddy sand. Within-habitat comparison of species diversity clearly indicates that diversity is lower in Loch Etive than in Loch Creran or the Firth of Lorne. The reasons for this are probably connected with the relatively high freshwater runoff into Loch Etive, possibly limiting the survival of planktonic larval stages of the benthos. The values of species diversity measured for the soft-mud areas in Loch Creran and the Firth of Lorne are thought to be representative for this habitat along the west coast of the British Isles. They agree well with the diversity predicted by Sanders for such a boreal inshore area, where a maritime climate prevails, on the basis of his time-stability hypothesis and the results of his sampling elsewhere.     

Mitochondrial and nuclear rRNA based copepod phylogeny with emphasis on the Euchaetidae (Calanoida)

Phylogenetic relationships within the copepod family Euchaetidae and between representatives of three copepod orders (Calanoida, Harpacticoida, and Poecilostomatoida) were investigated using partial nucleotide sequences of the mitochondrial 16S rRNA and the nuclear 28S rRNA genes. DNA isolation, polymerase chain reaction, cloning, and DNA sequencing techniques were customized for these crustaceans. Our results support the monophyly of each copepod order, but in contrast to traditional morphology-based phylogenies of copepod orders, the Poecilostomatoida are basal to the Calanoida and Harpacticoida on our DNA-based phylogenetic tree. Phylogenetic trees generated by maximum parsimony, neighbor-joining, and maximum-likelihood analyses support the classification of the genera Euchaeta and Paraeuchaeta in the family Euchaetidae; results, however, suggest that Euchaetaacuta Giesbrecht is more closely related to species of the genus Paraeuchaeta than to those of Euchaeta, although limited taxon sampling may be partially responsible for this result. Phylogenetic mapping using the most parsimonious 16S tree suggests that the morphological synapomorphies distinguishing the genus Euchaeta evolved independently twice during the history of the Euchaetidae. Further, phylogenetic mapping suggests that the most recent common ancestor of the Euchaetidae and the Aetideidae was a deep-living, vertically migrating copepod, and that a bathypelagic, vertically migrating lifestyle characteristic of Paraeuchaeta is an ancestral trait of the family Euchaetidae which was lost apomorphically by Euchaeta. The application of a molecular clock suggests that the sibling species Euchaeta rimana Bradford and Euchaeta marina (Prestandrea) diverged due to the emergence of the Panamanian land bridge. Received: 9 October 1997 / Accepted: 5 August 1998     

Growth,mortality and shell morphology of cultivated mussel (Mytilus edulis) stocks cross-planted between two Scottish sea lochs

One-year-old rope-grown blue mussels (Mytilus edulis L.) were held in experimental lantern nets and cross-transplanted between two sea lochs (Lochs Etive and Leven) on the west coast of Scotland. Growth and mortality were monitored from May 1991 to May 1992, as well as shell morphology in native and transplanted mussels. There were highly significant differences (P0.001) in growth rates between lochs; both native and transplanted mussels performed better in all shell and tissue growth-parameters in Loch Etive than in Loch Leven. Stock also had a significant (P0.05) influence on shell length and live weight, but its contribution to total variance was considerable only in the latter case. Wet and ash-free dry meat weights were governed mainly by site and to some extent by site x stock interaction. Mortality rates were quite low (6 to 7% yr^-1) and did not show any significant variation either between sites or stocks. There were significant morphological differences (ratios of shell length, height and width) between the Loch Etive and Loch Leven populations (P0.001) which persisted for one year after transfer. Stock appeared to be the main factor affecting shell morphology, as opposed to site. Linear regressions of shell height and width on length were significantly different between the native stocks, but became indistinguishable from those of the recipient populations one year after reciprocal transfer. This did not, however, conceal the effect of stock origin on dimensional ratios. It is concluded that site differences related to environmental factors, notably chlorophyll a levels and currents, and also possible stress caused by high levels of Zn and Cu, are major determinants of growth, which are of main interest to aquaculture, while morphological differences most probably result from genotypic variation.     

Biology of euphausiids in the subarctic waters north of Iceland

The seasonal abundance, maturity, spawning, and population dynamics of Thysanoessa inermis (Krøyer, 1846), T. longicaudata (Krøyer, 1846), and Meganyctiphanes norvegica (M. Sars, 1857) were studied in the subarctic waters north of Iceland from February 1993 to February 1994. The material was sampled at approximately monthly intervals along a transect of eight stations extending from 66°16′ to 68°00′N at 18°50′W. Information on temperature and chlorophyll a concentrations is also presented. Spring warming of the water began in March to April and maximum temperatures were recorded in August (3.8?°C). The spring bloom of the phytoplankton started in late March and highest chlorophyll a concentrations were measured during middle to late April (7.0?mg chlorophyll a m^?3). T. inermis was the dominant species in the samples, constituting 77% of juvenile, male and female euphausiids present. The greatest abundance of juvenile, male and female T. inermis and M. norvegica was observed during autumn and winter, with lower abundance in spring and summer. T. longicaudata showed only limited changes in seasonal abundance. Male T. inermis had spermatophores in their ejaculatory ducts from February to May, while mature females had spermatophores attached during April and May. T. longicaudata males bore spermatophores from February to July, whereas females only bore spermatophores in April and May. M. norvegica males had spermatophores from February to April, while the single female with spermatophores was caught in February. Euphausiid eggs were first recorded during the latter part of April; the highest numbers of eggs were observed in the samples taken in late May. Maximum numbers of nauplii of both Thysanoessa spp. and M. norvegica were recorded in late May. The main spawning of the euphausiids coincided with the phytoplankton spring bloom. Most male T. inermis took part in breeding at 1 yr of age while most females appeared not to mature until 2 yr of age. T. inermis has a life span of just over 2 yr, T. longicaudata appears to live just over 1 yr. Limited data did not allow the life span of M. norvegica to be determined.     

Sedimentation of organic detritus in Lochs Etive and Creran,Argyll, Scotland

The rates of sedimentation of organic detritus were measured at 3 stations in two Scottish sea lochs, Loch Etive and Loch Creran, using sedimentation jars exposed at various depths. Details are given of the seasonal and depth distribution of sedimenting material, and its composition for a 1-year period. Differences in the pattern of sedimenting material collected at different depths and in the seasonal patterns of sedimentation at the different stations suggested that, in each case there were differences in the relative importance of detritus from various sources. At all stations, phytoplankton production made a relatively small contribution to the total detritus collected, either directly as dead cells, or indirectly as the faeces of zooplankton organisms. Near the head of Loch Etive there were contributions by filamentous algae and Enteromorpha sp., but a major source of detritus was terrestrial debris, mainly carried into the loch in the waters of the River Etive. In the lower basin of Loch Etive, terrestrial detritus also contributed to the total sedimenting near the surface, but at greater depths much of the material collected in the sedimentation jars probably resulted from short-term resuspension and re-deposition of bottom material, reflecting a net transport of fine sediment from the shallower to the deeper areas of the loch. Secondarily resuspended material was also a major source of material collected in the jars exposed in Loch Creran.     

Deep-sea bottom-living fishes at two repeat stations at 2 200 and 2 900 m in the Rockall Trough,northeastern Atlantic Ocean

Repeated sampling of deep-sea bottom-living fishes was conducted at two stations in the Rockall Trough at depths of 2 200 and 2 900 m. The 2 200 m station (M) was sampled 16 times by an Agassiz trawl between April 1978 and April 1985 and yielded 473 fish belonging to 17 species. The 2 900 m permanent station (PS) yielded 781 fish belonging to 11 species from 9 Agassiz trawls, 2 small box otter trawls, 4 semi-balloon otter trawls and 7 epibenthic sledges between March 1975 and April 1985. Macrourid fishes were numerically dominant at both stations with Coryphaenoides guentheri and Coryphaenoides (Nematonurus) armatus being the most abundant species at M and PS, respectively. In terms of biomass the morid, Antimora rostrata, was dominant at M but C. (N.) armatus was dominant at PS. The only species that showed clear evidence of a seasonal reproductive cycle was C. guentheri. Many species showed no indication of reproducing in the Rockall Trough. The diets of almost all the species are described and considered in relation to the food resources exploited. Investigations on the pelagic and benthic invertebrate faunas at these stations should reveal the extent to which the bottom-living fishes exploit the available resources.     

Brood size and chemical composition of Pareuchaeta norvegica (Crustacea: Copepoda) in Loch Etive,Scotland

Brood size and chemical composition (carbon, nitrogen, and ash) of Pareuchaeta norvegica in Loch Etive, Scotland have been determined. From 23 to 37 eggs were found in each egg mass (mean=30 eggs). The eggs are oval; the mean size of the longer axis is 438 m. Variation in egg mass (as dry weight) is related to increase in dry weight of the maternal body. an increase of 1 mg in maternal body dry weight produces an increase of 0.03 mg dry weight in the egg mass. Carbon content increases with increasing body dry weight both in pre-spawning and spent females, but nitrogen content decreases with increasing body weight. Thus, the carbon:nitrogen ratio increases with increasing body dry weight. The carbon content of an egg mass ranges from 61.4 to 65.3%, and nitrogen content from 9.6 to 13.2% of the total dry weight. Some examples of partitioning of chemical components of the maternal body into the egg mass are also described.     

Observations on the reproduction and postlarval morphology of pourtalesiid sea urchins in the Rockall Trough area (N.E. Atlantic Ocean)

Gametogenesis was studied histologically in the deep-sea species Pourtalesia jeffreysi (Wyville Thomson), P. miranda (A. Agassiz) and Echinosigra phiale (Wyville Thomson) collected during 1973–1983 from various positions at depths of 1 040 to 2 921 m in the Rockall Trough. The gonads are small and no synchrony in terms of the stage of gametogenic development was evident in females of the latter two species collected at different times of the year, indicating nonseasonal breeding. Males appear to be ripe at all times of the year. Follicle cells were well developed around the developing oocytes. Both the size range of the yolky ripe eggs (173 to 357 m diam) and potential fecundity within the range of 1 000 to 4 000 oocytes per individual, are indicative of an abbreviated, indirect, lecithotrophic mode of development occurring in all three species. Pourtalesiid postlarvae occurred also in fine-meshed trawl hauls, and their morphology is described. It was not possible to distinguish between P. miranda and E. phiale at sizes <3 mm in length.     

Meganyctiphanes norvegica in the Kattegat

From 1979 to 1983 a population ofMeganyctiphanes norvegica was regularly found in a confined location in the northern Kattegat. The development of this pelagic population was followed over one complete year-cycle, and is discussed in light of published data on landlocked and oceanic populations. In the Kattegat,M. norvegica mature at the age of 9 to 12 months. Copulation starts in january, but fully developed spermatophores are present in males for at least 9 months. Spawning starts in April and continues until October with a marked peak in July. As only 10 to 15% of the gravid females belong to the II-group, it is concluded that recruitment is due to the I-group. Linear growth is fastest in spring and early summer, rises to a second maximum in October and stagnates during winter. The weight development shows some discontinuties caused by spawning or the accumulation of reserves towards winter. Weight decreases during winter. Growth in length and in weight runs largely parallel in both sexes, and can be closely correlated with the prevailing food supply. Diurnal vertical migration could be demonstrated. The results indicate a continuous development, which suggests the existence of an autonomous palagic population, a well suited subject for long-term investigation.     

A universal method for quantifying and comparing the residual variability of element concentrations in biological tissues using 25 elements in the mussel Mytilus edulis as a model

Heavy metal concentrations (especially Cu, Cd and Zn) have been measured in oceanic hyperiid amphipods (Themisto gaudichaudii and T. compressa) and euphausiids (Meganyctiphanes norvegica and Euphausia superba), collected in the Antarctic and Atlantic Oceans. In some cases, metal concentrations displayed size-dependencies which were allowed for in interspecific or intersite comparisons, which often showed intraspecific geographical differences not attributable to anthropogenic effects. Cadmium concentrations in Themisto species are high in comparison with those of other oceanic crustaceans and may represent significant sources of cadmium in the diets of particular seabrids.     

Unexpected new species of deep-water Hydroidomedusae from Korsfjorden,Norway

Two new species of Hydroidomedusae, Parateclaia norvegica sp.nov. and Foersteria quadrata sp.nov., are described from specimens collected in Korsfjorden, western Norway. Neither genus has previously been observed in the North-Atlantic Ocean. The closest congenerics to the new species occur in the Mediterranean, where family Teclaiidae has been considered endemic. P. norvegica and F. quadrata were only collected at sites 500 m or deeper and are possibly deep-water benthopelagic species like their congenerics elsewhere. Sampling took place for the entire year 2003 at 2- to 4-week intervals. F. quadrata, the more numerous of the new species, was absent from the water column only during the spring months, the implications of which regarding its lifecycle are discussed. Hypotheses on speciation in the Foersteria species group and family Teclaiidae are shortly discussed.     

Laboratory study of predation by Aurelia aurita on larvae of cod,flounder, plaice and herring: development and vulnerability to capture

Capture success of the medusa Aurelia aurita preying on various developmental stages of fish larvae was measured together with larval reactivity and escape speed after being stung. These experiments were conducted in the spring of 1983 with A. aurita medusae collected from Loch Etive, Scotland and laboratory-reared larvae of Gadus morhua L., Platichthys flesus L., Pleuronectes platessa L. and Clupea harengus L. Capture success of the medusae increased with medusa size, but decreased with advancing larval development. Smaller species of larvae were more vulnerable to capture. Larval reactivity to encounters with medusae increased with advancing development, and larger species of larvae were more reactive to encounters. Larval escape swimming speeds also increased with advancing larval development and size. These results indicate that earlier stages of larvae within a species and smaller species of larvae at a given stage are more vulnerable to predation by medusae since they are less reactive to encounters. Apparently they are more susceptible to the effects of neurotoxins. Predation rates on different developmental stages of herring larvae are documented and compared with rates predicted by a predation model. Predictions fell within the range of observed predation rates, but tended to overestimate rates by larger medusae feeding on larger herring larvae. This indicates the possibility of predator satiation and/or behavioural avoidance.     

Non-viable seasonal settlement of larvae of the upper bathyal brittle star Ophiocten gracilis in the Rockall Trough abyssal

Re-examination of ine structure of postlarvae previously identified as the abyssal species Ophiura ljungmani (Lyman) in a time series of samples taken from 1975 to 1980 from a 2900 m deep permanent station in the southern Rockall Trough (Northeast Atlantic Ocean) has shown the majority of the large summertime peak of brittle-star postlarvae to belong to a second species. Most were incomplete and probably corpses when collected. The few intact specimens present were identical to postlarvae collected in benthic samples from the neighbouring continental slope, where a dense population of the bathyal species Ophiocten gracilis (G. O. Sars) is present from 600 to 1 200 m depth. Examination of population size-structures indicates synchronous reproduction in January/February and annual recruitment to the population. The presence both of Ophiopluteus ramosus and intact postlarvae of Ophiocten gracilis in midwater plankton samples from the vicinity of the permanent station in March/April are thought to derive either from the adjacent slope population or, less probably, from larvae transported in the North Atlantic Current from the Flemish Cap area off Newfoundland. In deep water, viability of these benthic postlarvae is low, none surviving longer than the following winter in the Rockall Trough. These observations suggest a large seasonal transfer from the slope of non-viable larvae and postlarvae as food to the abyssal benthic community.Communicated by J. Mauchline, Oban     

Diets of clupeoid,stomiatoid and salmonoid fish of the Rockall Trough,northeastern Atlantic Ocean

The trophic interactions of species of fish of the continental slopes have not been investigated previously in detail. The present study examines the diets of the clupeoid, stomiatoid and salmonoid species occurring demersally and pelagically in the Rockall Trough to the west of Scotland and Ireland. Pelagic fish were collected between the surface and about 2 500-m depth between 1973 and 1978. Demersal fish were sampled at 250-m intervals of depths between 500- and 2 900-m depth during the years 1975 and 1981. Of the 28 species caught, 18 were strictly pelagic and dominated by the stomiatoids while five were strictly demersal. The remaining five species occurred in both the pelagic and demersal environment. The commonest clupeoid was Alepocephalus bairdii, which is a dominant species within the demersal fish associations at depths of 750 to 1 250m. This species, along with the deeper-living A. agassizi, and 3 other alepocephalid species feed primarily on benthopelagic prey but also exploit the epibenthos. The stomiatoid species, such as Cyclothone microdon, C. braueri, Maurolicus muelleri and Argyropelecus hemigymnus, dominate the associations of pelagic fish in the Trough. They feed on different proportions of ostracods, copepods and amphipods. Of the salmonoids, only Argentina silus and Bathylagus euryops occurred commonly and both feed on benthopelagic fauna, the latter at much greater depths than the former. The principal factor acting to prevent direct competition between species is the modal centres of bathymetric distribution of the species. Other contributing factors are briefly discussed.     

Growth and production of Euphausiacea (Crustacea) in the Rockall Trough

The euphausiid fauna of the Rockall Trough has been sampled in time series at approximately two-monthly intervals between 1973 and 1976 between surface and depths greater than 2000 m. Length/frequency histograms have modes that are coherent for periods of at least 4 to 6 mo, indicating that populations are being sampled. Rates of growth were determined for six species. Epipelagic species have winter checks to the growth rates, but such checks are absent in the growth of Thysanopoda acutifrons, Nematobranchion boöpis and Stylocheiron maximum. Ratios of annual production: biomass were determined and are all within the previously determined range of values for epipelagic and coastal populations. Lack of a winter check to the growth rate in deep-living species enables these potentially to have overall rates of growth comparable to those of temperate, epipelagic, shelf and coastal species.     

Benthic bioluminescence in the bathyal North East Atlantic: luminescent responses of <Emphasis Type="Italic">Vargula norvegica</Emphasis> (Ostracoda: Myodocopida) to predation by the deep-water eel (<Emphasis Type="Italic">Synaphobranchus kaupii</Emphasis>)

Using two autonomous lander systems, one equipped with a high sensitivity intensified silicon intensifier target (ISIT) video camera and a second with a 4.1-megapixel digital stills camera, observations were made of bioluminescent emissions and fauna attracted to artificial food falls at ca. 1,000 m depth in the carbonate mound provinces of the Porcupine Seabight and Rockall Bank, North East Atlantic. On the Galway coral mound (Belgica Mound Province), seven bioluminescent events per hour were observed, whereas on an area of sediment at the base of the Kiel Mount on the Rockall Bank 133 events per hour were observed. This increase in bioluminescent activity was associated with the presence of the deep water eels Synaphobranchus kaupii, and the ostracods, Vargula norvegica. Captured ostracods luminesced readily in response to mechanical stimulation and were also observed emitting a luminous secretion. We hypothesise that V. norvegica, attracted to bait, luminesce as a defence response against the predatory activity of S. kaupii that compete for bait but also feed on the ostracods. Benthic bioluminescence in the carbonate mound provinces was not directly linked to the presence of corals.     

Diets and bathymetric distributions of the macrourid fish of the Rockall Trough,northeastern Atlantic Ocean

The Macrouridae are the most common fish caught in demersal trawls on the continental slope and rise of the Rockall Trough. They represented 41% of all fish caught, with Coryphaenoides rupestris amounting to 28% of the catch. No previous study of the trophic interaction of these fish has been made over a wide bathymetric range. Samples were obtained at 250-m intervals of depth between 400 and 2 900 m in the period 1975 to 1981. The stomachs of 5 326 fish belonging to 12 species were examined to define their diets. Eight species are primarily benthopelagic feeders while four are primarily epibenthic feeders. The bathymetric centres of distribution of the populations of the benthopelagic feeding Trachyrhynchus murrayi, Malacocephalus laevis, Coryphaenoides rupestis, C. guentheri, Nematonurus armatus, Chalinura brevibarbis, C. leptolepis and C. mediterranea are different from each other. Similar differences in bathymetric distribution occurred among the epibenthic feeding Nezumia aequalis, Coelorhynchus coelorhynchus, C. occa and Lionurus carapinus. These differences decrease competition among species that exploit similar resources.     

Bathymetric distribution of chaetognaths in the South Eastern Pacific Ocean

The bathymetric distribution of chaetognath fauna observed at planktonic stations in the South Eastern Pacific Ocean during three different expeditions, is presented quantitatively. The material from the cruises IFOP-01 (October–December, 1964) and IFOP-04 (November–December, 1965) was collected by vertical closing net, at regular intervals, from 2000 and 1000 m depth, respectively; the R.V. A. Bruun Cruise 13 data include vertical samples at usual depth intervals from 3000 m (see Table 12), Isaac-Kidd Midwater Trawl (IKMT) and surface collections. They allowed us to identify, for the first time, the meso and bathypelagic species of this region and to extend the longitudinal distribution of the epipelagic species, which had been previously limited to the coastal areas. Among the epiplanktonic species, it was shown that two, Sagitta serratodentata and S. bipunctata, do not penetrate into the Peru Coastal Current region, where the endemic S. bierri is to be found extending westwards to the west boundary of the Peru Coastal Current, and that both mesopelagic species, previously reported for the epipelagic level of this area, S. decipiens and Eukrohnia hamata, inhabit the upper mesopelagic level in the oceanic region, but also rise to the epipelagic level near the coast, where upwellings do occur. The lower mesopelagic levels (500 to 1000 m) are occupied by E. fowleri and S. macrocephala, this latter species being reported for the first time in the South Eastern Pacific Ocean. The other mesopelagic species, S. zetesios and S. bathypelagica, also found for the first time in this region, were not found in large enough numbers to obtain a correct view of their stratification. Eukrohnia bathyantarctica, described for the Southern Ocean and previously reported only in the bathypelagic levels of the Gulf of Mexico and Caribbean Sea, was found at only bathypelagic levels. The faunistic data from the R.V. A. Bruun Cruise 13, were compared with the corresponding hydrographical profiles.