Species assemblages of pelagic fish embryos in the southern North Sea between 1984 and 2000

The occurrence and abundance of the pelagic eggs of southern North Sea spring-spawning fish were analysed between 1984 and 2000. Species number varied between six (1986) and 14 (1999) and was positively correlated with sea surface temperature. With one exception, dab eggs were always the most abundant and usually highly dominant. Ranking of species depended on temperature, but no significant differences in ranking between years was discernible. Although with the increase in temperature in the 1990s a change in species assemblage was evident [species belonging to the boreal-Mediterranean (Lusitanian) group became more apparent in the species assemblage] this did not lead to an increased species diversity (Shannon Index) or a change in other community parameters. It appears that the recent developments regarding spawning stock biomass of commercial North Sea fish is reflected in the declining egg abundance of the respective commercial and larger species (i.e. cod, flounder, plaice) and an increase in abundance of the eggs of small species (i.e. long rough dab, rockling) over the years. Received in revised form: 5 November 2001 Electronic Publication     

Reproduction and feeding of the mountain mullet,Agonostomus monticola,in Trinidad,West Indies

Synopsis Reproduction and feeding were studied in mountain mullet,Agonostomus monticola, in northeast Trinidad during the period January 1987 to September 1988. Macroscopic and microscopic examination of the gonads indicated a single, distinct reproductive season from June to October during the wet season. Evidence implies only one spawning event per individual during the reproductive season. Females significantly outnumbered males resulting in a sex ratio of 20.4:1. The mean size at maturity for females was 135 mm fork length (FL). Fecundity (F) is related to size by the equations F = 167.3 FL^2.7 and F = 16430.7 G + 235079 (G = gutted weight).A. monticola was found to be an omnivorous feeder. The dominant food groups found in the stomachs were insects, prawns, fruits and algae, in order of decreasing importance.     

Dynamics in space and time of four testate amoebae (Difflugia spp.) co-existing in the zooplankton of a reservoir in southern China

We studied a long time series of the dynamics in space and time of four species of Difflugia (thecamoebae) that co-exist in the pelagic plankton of Liuxihe Reservoir, an oligo-mesotrophic impoundment in southern China, during 8–9 months (“summer” form March to November), and retreat to the benthos during the rest of the year (“winter”). We discuss the reasons for the winter retreat, and suggest that predator evasion may be involved, although temperature-linked physiological effects (like the rate of gas bubble production) appear more probable. Clear diel vertical migration of Difflugia was not observed, but patchiness was common. We found no evident lake edge-effects in the spatial pattern either, but the abundances were strongly influenced by trophic conditions and increased by up to one order of magnitude in the upstream, eutrophic sections of the reservoir.     

Trace elements in the muscle,ova and seminal fluid of key clupeid representatives from the Gdansk Bay (South Baltic Sea) and Iberian Peninsula (North-East Atlantic)

BackgroundBaltic herring and European sardine are pelagic, fish of particular ecological importance, on the one hand control numbers of planktonic organisms, and on the other hand exist as food for predators on higher trophic levels. Moreover, these fish are among the main species caught for human consumption. Rare earth elements (REEs) come mainly from geogenic sources but, due to their use in technology, agriculture and medicine, the importance of anthropogenic sources is growing steadily.MethodsSamples used for the study were available on the market. Fresh materials of fish muscle, ova and seminal fluid were mineralized and elements were determined by means of inductively coupled plasma – mass spectrometry (ICP-MS).ResultsThe conducted research indicated the presence of REEs in the muscles of the Baltic herring (∑REE = 0.076 ± 0.047 mg/kg) and European sardine (∑REE = 0.191 ± 0.163 mg/kg), with a clear dominance of heavy REEs in both fish species. Trace elements (TE) in the muscles of the tested fish demonstrated a similar system of concentration (Baltic herring: Zn > As > Se > Cu > Cr > Ni > Pb > Cd; European sardine: Zn > As > Se > Cu > Ni > Cr > Pb > Cd). REEs and TEs in these fish were presence in ova and seminal fluid indicates intergenerational transfer.ConclusionChanges in the concentrations of some trace elements (As, Cu, Cd) in the muscles of herring indicate increases compared to the historical data. The availability of metals in the aquatic environment may be determined by ongoing climate changes, effected water salinity and warming increased availability of labile forms of trace metals. Decline trends in the condition of pelagic fish need to extend the research in the context of contemporary environmental threats.     

Major changes in fecundity and the effect on population egg production for three species of north-west Atlantic flatfishes

Temporal and spatial variability in fecundity was investigated for three species of north-west Atlantic flatfishes: American plaice Hippoglossoides platessoides , yellowtail flounder Limanda ferruginea and witch flounder Glyptocephalus cynoglossus . Significant log₁₀ linear relationships existed between fecundity and total length ( L _T) for all three species and for all combinations of area (NAFO regulatory areas) and year. Fecundity differed between areas for yellowtail flounder and witch flounder and changed significantly for all three species since the last reported fecundity studies in the region 30–40 years ago. Three populations experienced decreases in fecundity (3LNO American plaice and yellowtail flounder, 3Ps witch flounder), one experienced an increase (3NO witch flounder) and one did not change (3L witch flounder). Significant yearly variability in fecundity at length and relative fecundity existed for all three species within the 6 year sampling period (1993–1998). Estimates of population egg production based on new and historic fecundity data revealed that using the old, invariant fecundity and L _T relationship resulted in overestimation of total annual egg production by up to 24% for 3LNO American plaice and as high as 41% for 3LNO yellowtail flounder. These results clearly demonstrate the variable nature of fecundity for flatfishes in Newfoundland waters and suggest that the use of an invariant fecundity and L _T relationship may result in inaccurate estimates of stock reproductive potential.     

Isomorphic polymorphism in the Platanaceae and Altingioideae and the problem of their relationship

Isomorphic polymorphism is demonstrated by modern and fossil members of the Platanaceae and Hamamelidaceae (subfamily Altingioideae) and is considered as evidence of structural parallelism in the evolution of the Platanaceae and Altingioideae. The supposed relationship between Platanaceae and Altingioideae is discussed from a paleobotanical perspective.     

The mechanism of retention of pelagic tomcod,Microgadus tomcod,larvae and juveniles in the well-mixed part of the St. Lawrence Estuary

Synopsis We tested the hypothesis that the mechanism of retention of tomcod, Microgadus tomcod, larvae and juveniles in the well-mixed part of the St. Lawrence Estuary is similar to that of sympatric smelt, Osmerus mordax, larvae who actively migrate to the surface during flood tides and to the bottom during ebb tides so as to minimize net downstream displacement. The vertical distribution of tomcod larvae and juveniles was documented during two 98-h sampling series at 2 anchor stations in June and July, 1986. An hourly index of the center of mass of fish in the water column calculated to take into account daytime net avoidance in surface waters suggested that tomcod remained deep in the water column and that their accumulation at the head of the estuary was the result of passive upstream transport by net residual circulation rather than active tidal migrations. For both series, depth of fish was inversely related to density of the water suggesting that the buoyancy of fish influenced their vertical distribution. Tomcod larvae and juveniles were advected by tidal currents. In June, larger larvae were found at low slack water indicating that they were located upstream of smaller larvae. In July, larger juveniles were located downstream of smaller juveniles, the difference in mean length between low and high slack water attaining 20 mm. Ontogenetic buoyancy changes may be responsible for these differences in the vertical distribution of tomcod. Comparisons of the early life-history stages of tomcod and smelt retained in the same area under the same hydrodynamical conditions indicate that more than one mechanism permits retention in a well-mixed estuary and that the observed species-specific patterns of vertical distribution are not simply interpretable as adaptations to retention.     

Diversity and distribution of single-stranded DNA phages in the North Atlantic Ocean

Knowledge of marine phages is highly biased toward double-stranded DNA (dsDNA) phages; however, recent metagenomic surveys have also identified single-stranded DNA (ssDNA) phages in the oceans. Here, we describe two complete ssDNA phage genomes that were reconstructed from a viral metagenome from 80 m depth at the Bermuda Atlantic Time-series Study (BATS) site in the northwestern Sargasso Sea and examine their spatial and temporal distributions. Both genomes (SARssφ1 and SARssφ2) exhibited similarity to known phages of the Microviridae family in terms of size, GC content, genome organization and protein sequence. PCR amplification of the replication initiation protein (Rep) gene revealed narrow and distinct depth distributions for the newly described ssDNA phages within the upper 200 m of the water column at the BATS site. Comparison of Rep gene sequences obtained from the BATS site over time revealed changes in the diversity of ssDNA phages over monthly time scales, although some nearly identical sequences were recovered from samples collected 4 years apart. Examination of ssDNA phage diversity along transects through the North Atlantic Ocean revealed a positive correlation between genetic distance and geographic distance between sampling sites. Together, the data suggest fundamental differences between the distribution of these ssDNA phages and the distribution of known marine dsDNA phages, possibly because of differences in host range, host distribution, virion stability, or viral evolution mechanisms and rates. Future work needs to elucidate the host ranges for oceanic ssDNA phages and determine their ecological roles in the marine ecosystem.     

A molecular biogeographic analysis of the relationship between North American melanoploid grasshoppers and their Eurasian and South American relatives

The Melanoplinae constitute one of the two largest subfamilies of Acrididae. Distributed mainly throughout the New World and parts of Eurasia, this group of grasshoppers includes over 100 genera and 800 species. Over the past five decades there has been considerable speculation on the origins of North and South American taxa. The most favored hypothesis proposes an ancient division of Laurasian taxa accompanying the separation of North America and Eurasia, with subsequent radiations within those continents, followed by a recent incursion of Nearctic melanoplines into the southern hemisphere with the establishment of the Isthmus of Panama. This research tests that scenario by phylogenetic analysis using as characters portions of five mitochondrial gene sequences, totaling 2285 bp. Three tree-building methods, maximum-parsimony, neighbor-joining, and maximum-likelihood, strongly support the different view that melanopline grasshoppers originated somewhere in the Americas and spread to the Old World. The feasibility of these findings is discussed within a geological context.     

Diversity and distribution of foliose Bangiales (Rhodophyta) in West Greenland: a link between the North Atlantic and North Pacific

Greenland is a continental island in the northern part of the North Atlantic where the foliose Bangiales flora is poorly known. It is an important area for the study of algal biogeography because of the region’s glacial history, in which Greenland has been alternately exposed to or isolated from the North Pacific via the Bering Strait. A molecular study using 3′ rbcL + 5′ rbcL–S sequences was undertaken to assess the diversity of foliose Bangiales on the west coast of Greenland and rbcL sequences were used to study the Greenland flora in a larger phylogenetic and floristic context. New and historic collections document seven species in four genera from the west coast of Greenland. All species had a close link to North Pacific species, being either conspecific with them or North Atlantic–North Pacific vicariant counterparts.     

Reproductive strategy of the snapping shrimp Alpheus armillatus H. Milne-Edwards, 1837 in the South Atlantic: fecundity,egg features,and reproductive output

Summary

The family Alpheidae, composed by shrimps of relatively small size, popularly known as snapping shrimps, is the one of the most diverse decapod groups. These shrimps are found worldwide and occur in tropical and subtropical waters, from the intertidal zone to great depths. We investigated reproductive aspects of Alpheus armillatus, in order to gather information on egg production, aiming to enhance knowledge of its reproductive strategies in a population in an intertidal area of the South Atlantic. Ovigerous females were collected under rocks, in May and July 2006 (dry season) and in November 2006 and March 2007 (rainy season). Egg production and reproductive output were analyzed and compared seasonally and during the period of embryonic development. Females measured on average 11.28 mm CL, with a mean of 763 eggs and 0.10 mm3 egg volume. The egg volume of this population was smaller than previous estimates for other species of snapping shrimps, but the mean egg number was higher. The volume of eggs doubled during the incubation period, but despite this increase, no significant loss of eggs was observed. Alpheus armillatus invests on average about 12% of body weight in reproduction. The proportional investment in egg production is significantly higher in the rainy season when compared with the dry season (17.9% vs 4.8%), correlated with higher temperatures and increased food availability at this time. Our results corroborated the hypothesis of a pattern of egg production influenced by environmental conditions and intraspecific variability among the family Alpheidae, as a function of the biogeographic region.     

Ontogenetic changes in the critical swimming speed of Gadus morhua (Atlantic cod) and Myoxocephalus scorpius (shorthorn sculpin) larvae and the role of temperature

Most studies on behavioural contributions to dispersal and recruitment during early life history stages of fishes have focused on coral reef species. For cold ocean environments, high variation in seasonal temperature and development times suggest that parallel studies on active behaviour are needed for cold-water species. Thus, we examined the critical swimming speed (U_crit) of marine fish larvae from 2 contrasting species: Gadus morhua (Atlantic cod) and Myoxocephalus scorpius (shorthorn sculpin), a pelagic and bottom spawner respectively. Within-species comparisons showed that sculpin reared at 6 °C had lower initial U_crit values, but a faster U_crit increase through development compared with 3 °C conspecifics, ultimately resulting in faster critical swimming speeds at metamorphosis (10.5 vs. 9.1 cm·s^− 1). In contrast, although cod larvae reared at 10 °C were faster swimmers at first feeding than 6 °C fish, temperature differences were absent after the first week. These results show that temperature influences the trajectory of larval critical swimming speed development, but that the relationship is species-specific. Although 6 °C sculpin and cod of similar length had equivalent U_crit values, the smaller size of cod at hatch (5.3 vs. 10.8 mm for sculpin) resulted in much lower age-specific U_crit values for cod. These data have significant implications for how swimming activity of the two species might affect dispersal, particularly in the first few weeks post-hatch. Overall, our data suggest that temperature during larval development influences the swimming capacity of cold-water marine fishes, and has important ramifications for biophysical models of dispersal.     

Remembrance of things past: modelling the relationship between species' abundances in living communities and death assemblages

Accumulations of dead skeletal material are a valuable archive of past ecological conditions. However, such assemblages are not equivalent to living communities because they mix the remains of multiple generations and are altered by post-mortem processes. The abundance of a species in a death assemblage can be quantitatively modelled by successively integrating the product of an influx time series and a post-mortem loss function (a decay function with a constant half-life). In such a model, temporal mixing increases expected absolute dead abundance relative to average influx as a linear function of half-life and increases variation in absolute dead abundance values as a square-root function of half-life. Because typical abundance distributions of ecological communities are logarithmically distributed, species' differences in preservational half-life would have to be very large to substantially alter species' abundance ranks (i.e. make rare species common or vice-versa). In addition, expected dead abundances increase at a faster rate than their range of variation with increased time averaging, predicting greater consistency in the relative abundance structure of death assemblages than their parent living community.     

Ecology and Gametogenic Biology of the Genus Umbellula (Pennatulacea) in the North Atlantic Ocean

Four putative species of the seapen genus Umbellula, U. lindahli, U. thomsonii, U. durissima and U. monocephalus, are found at bathyal and abyssal depths in the Porcupine Seabight and Abyssal Plain in the NE Atlantic Ocean and at bathyal depths off the Bahamas. The most common species, U. lindahli, has a cosmopolitan distribution in the world ocean. In situ observations, from bathyal depths in the Bahamas, of the posture of U. lindahli show that the polyps are spread out to maximize particle capture from the water column. In addition, the individuals of U. lindahli from the Bahamas suggest that the tentacles are cropped by a predator, but there is no evidence of predation in the NE Atlantic specimens. Reproduction in U. lindahli is typical of that previously observed in pennatulids. Fecundity is high, although most of the oocytes present are previtellogenic with only a few developing through to maximum size at any one time. Some specimens of U. lindahli appear to be infested with a small flatworm.     

The relationship between river flow and entry to the Aberdeenshire Dee by returning adult Atlantic salmon

One hundred and nine returning adult salmon were radio-tagged in the estuary of the Aberdeenshire Dee, Scotland between February and August 1985 to 1989 and the times when 62 fish entered the river were recorded. Elapsed times between tagging and river entry were significantly greater during periods of lower than average river flows in all months where there were sufficient data to allow statistical comparison. The degree of association between river entry and particular levels of river discharge rate varied seasonally. The proportion of days associated with river entry declined at the lower end of the range of flows available to tagged fish in the summer months. Absolute levels of river discharge played a significant role in modifying the response of salmon to changing flows. During periods of lower than average seasonal flow, river entry was closely associated with days when flow had increased since the previous day. During periods of higher than average flow, river entry was not significantly associated with such periods of increased flow. The results suggest that models which relate river entry by salmon to absolute discharge rates alone are unlikely to be generally reliable.     

The dispersal between Amazonia and Atlantic Forest during the Early Neogene revealed by the biogeography of the treefrog tribe Sphaenorhynchini (Anura,Hylidae)

The Amazonia and the Atlantic Forest, separated by the diagonal of open formations, are two ecoregions that comprise the most diverse tropical forests in the world. The Sphaenorhynchini tribe is among the few tribes of anurans that occur in both rainforests, and their historical biogeographic have never been proposed. In this study, we infer a dated phylogeny for the species of the Sphaenorhynchini and we reconstructed the biogeographic history describing the diversification chronology, and possible patterns of dispersion and vicariance, providing information about how orogeny, forest dynamics and allopatric speciation affected their evolution in South America. We provided a dated phylogeny and biogeography study for the Sphaenorhynchini tribe using mitochondrial and nuclear genes. We analyzed 41 samples to estimate the ancestral areas using biogeographical analysis based on the estimated divergence times and the current geographical ranges of the species of Sphaenorhynchini. We recovered three characteristic clades that we recognize as groups of species (S. lacteus, S. planicola, and S. platycephalus groups), with S. carneus and G. pauloalvini being the sister taxa of all other species from the tribe. We found that the diversification of the tribe lineages coincided with the main climatic and geological factors that shaped the Neotropical landscape during the Cenozoic. The most recent common ancestor of the Sphaenorhynchini species emerged in the North of the Atlantic Forest and migrated to the Amazonia in different dispersion events that occurred during the connections between these ecoregions. This is the first large‐scale study to include an almost complete calibrated phylogeny of Sphaenorhynchini, presenting important information about the evolution and diversification of the tribe. Overall, we suggest that biogeographic historical of Sphaenorhynchini have resulted from a combination of repeated range expansion and contraction cycles concurrent with climate fluctuations and dispersal events between the Atlantic Forest and Amazonia.     

Experimental selection reveals a trade-off between fecundity and lifespan in the coliphage Q?

Understanding virus evolution is key for improving ways to counteract virus-borne diseases. Results from comparative analyses have previously suggested a trade-off between fecundity and lifespan for viruses that infect the bacterium Escherichia coli (i.e. for coliphages), which, if confirmed, would define a particular constraint on the evolution of virus fecundity. Here, the occurrence of such a trade-off is investigated through a selection experiment using the coliphage Qß. Selection was applied for increased fecundity in three independent wild-type Qß populations, and the ability of the virions to remain viable outside the host was determined. The Qß life-history traits involved in the evolution of fecundity and the genetic changes associated with this evolution were also investigated. The results reveal that short-term evolution of increased fecundity in Qß was associated with decreased viability of phage virions. This trade-off apparently arose because fecundity increased at the expense of reducing the amount of resources (mainly time) invested per produced virion. Thus, the results also indicate that Qß fecundity may be enhanced through increases in the rates of adsorption to the host and progeny production. Finally, genomic sequencing of the evolved populations pinpointed sequences likely to be involved in the evolution of Qß fecundity.     

Modelled spatial distribution of marine fish and projected modifications in the North Atlantic Ocean

The objectives of this work were to examine the past, current and potential influence of global climate change on the spatial distribution of some commercially exploited fish and to evaluate a recently proposed new ecological niche model (ENM) called nonparametric probabilistic ecological niche model (NPPEN). This new technique is based on a modified version of the test called Multiple Response Permutation Procedure (MRPP) using the generalized Mahalanobis distance. The technique was applied in the extratropical regions of the North Atlantic Ocean on eight commercially exploited fish species using three environmental parameters (sea surface temperature, bathymetry and sea surface salinity). The numerical procedure and the model allowed a better characterization of the niche (sensu Hutchinson) and an improved modelling of the spatial distribution of the species. Furthermore, the technique appeared to be robust to incomplete or bimodal training sets. Despite some potential limitations related to the choice of the climatic scenarios (A2 and B2), the type of physical model (ECHAM 4) and the absence of consideration of biotic interactions, modelled changes in species distribution explained some current observed shifts in dominance that occurred in the North Atlantic sector, and particularly in the North Sea. Although projected changes suggest a poleward movement of species, our results indicate that some species may not be able to track their climatic envelope and that climate change may have a prominent influence on fish distribution during this century. The phenomenon is likely to trigger locally major changes in the dominance of species with likely implications for socio‐economical systems. In this way, ENMs might provide a new management tool against which changes in the resource might be better anticipated.