scholarly journals Cryptic hydrozoan blooms pose risks to gill health in farmed North Atlantic salmon (Salmo salar)

2018 ◽  
Vol 99 (2) ◽  
pp. 539-550 ◽  
Author(s):  
Anna Kintner ◽  
Andrew S. Brierley
Keyword(s):  
Species Composition ◽  
North Atlantic ◽  
Water Clarity ◽  
Apparent Lack ◽  
Root Cause ◽  
Salmon Aquaculture ◽  
Targeted Sampling ◽  
Population Sizes ◽  
Salinity Water ◽  
Gill Pathology

Sampling at four salmon aquaculture sites along the west coast of Scotland has identified short-lived aggregations of planktonic hydrozoans (>280 individuals m−3), here termed blooms. Several such blooms were linked with increases in gill pathology and mortality in caged fish. Two types, Obelia sp. and Lizzia blondina, were found to cause blooms regularly and often concurrently. Species composition of hydrozoan populations and fluctuations in population sizes were spatially and temporally heterogeneous, with adjacent sites (within 30 km of one another and with similar oceanic exposure) experiencing no correlation between species composition and population density. Blooms appeared temperature-mediated, with all identified blooms by Obelia sp. and L. blondina taking place in water above 12 °C; however, temperature alone was not found to be predictive. Blooms were not significantly associated with change in salinity, water clarity, or photoperiod. Due to the apparent lack of broadly applicable predictors, we suggest that localized, targeted sampling and examination of planktonic hydrozoan populations is required to discern the presence or absence of a bloom. It is likely that many blooms have historically caused harm in salmon aquaculture while remaining unrecognized as the root cause.

Watershed-level sampling effort requirements for determining riverine fish species composition

2005 ◽  
Vol 62 (7) ◽  
pp. 1580-1588 ◽  
Author(s):  
Katherine L Smith ◽  
Michael L Jones
Keyword(s):  
Species Richness ◽  
Species Composition ◽  
Fish Species ◽  
Correlation Coefficients ◽  
Sampling Effort ◽  
Species Accumulation Curves ◽  
Targeted Sampling ◽  
Weak Negative Correlation ◽  
Fish Species Composition ◽  
Riverine Fish

Accurate assessments of watershed-level species composition are necessary for comparative ecological studies, ecosystem health assessments, monitoring, and aquatic conservation prioritization. Several studies have addressed sampling effort requirements for characterizing fish species composition at a section of stream, but none have examined watershed-level requirements. In the spring and summer of 2002, we extensively sampled nine Great Lakes watersheds to assess sampling-effort requirements. Sampling requirements increased with the targeted percentage of estimated species richness. Sampling 15–119 randomly selected reaches of stream, stratified by stream order, was on average sufficient to detect 80%–100% of estimated species richness. Watershed size (km2) and estimated species richness each showed a weak, negative correlation with sampling-effort requirements in our study streams, with Pearson's correlation coefficients of –5.06 and –0.590, respectively. Because of among-watershed variability in sampling effort requirements, field crews should plot species accumulation curves onsite to determine adequate inventory completion. Based on the difficulty of detecting the last 10% of species, random sampling should be conducted in conjunction with targeted sampling of rare species.

scholarly journals Cluster Analysis of North Atlantic–European Circulation Types and Links with Tropical Pacific Sea Surface Temperatures

2008 ◽  
Vol 21 (15) ◽  
pp. 3687-3703 ◽  
Author(s):  
D. R. Fereday ◽  
J. R. Knight ◽  
A. A. Scaife ◽  
C. K. Folland ◽  
A. Philipp
Keyword(s):  
Cluster Analysis ◽  
North Atlantic ◽  
El Niño ◽  
Clustering Algorithm ◽  
El Nino ◽  
Tropical Pacific ◽  
Sea Surface ◽  
Optimum Number ◽  
Apparent Lack ◽  
Circulation Types

Abstract Observed atmospheric circulation over the North Atlantic–European (NAE) region is examined using cluster analysis. A clustering algorithm incorporating a “simulated annealing” methodology is employed to improve on solutions found by the conventional k-means technique. Clustering is applied to daily mean sea level pressure (MSLP) fields to derive a set of circulation types for six 2-month seasons. A measure of the quality of this clustering is defined to reflect the average similarity of the fields in a cluster to each other. It is shown that a range of classifications can be produced for which this measure is almost identical but which partition the days quite differently. This lack of a unique set of circulation types suggests that distinct weather regimes in NAE circulation do not exist or are very weak. It is also shown that the stability of the clustering solution to removal of data is not maximized by a suitable choice of the number of clusters. Indeed, there does not appear to be any robust way of choosing an optimum number of circulation types. Despite the apparent lack of preferred circulation types, cluster analysis can usefully be applied to generate a set of patterns that fully characterize the different circulation types appearing in each season. These patterns can then be used to analyze NAE climate variability. Ten clusters per season are chosen to ensure that a range of distinct circulation types that span the variability is produced. Using this classification, the effect of forcing of NAE circulation by tropical Pacific sea surface temperature (SST) anomalies is analyzed. This shows a significant influence of SST in this region on certain circulation types in almost all seasons. A tendency for a negative correlation between El Niño and an anomaly pattern resembling the positive winter North Atlantic Oscillation (NAO) emerges in a number of seasons. A notable exception is November–December, which shows the opposite relationship, with positive NAO-like patterns correlated with El Niño.

scholarly journals Short term changes in zooplankton community during the summer-autumn transition in the open NW Mediterranean Sea: species composition, abundance and diversity

2008 ◽  
Vol 5 (6) ◽  
pp. 1765-1782 ◽  
Author(s):  
V. Raybaud ◽  
P. Nival ◽  
L. Mousseau ◽  
A. Gubanova ◽  
D. Altukhov ◽  
...  
Keyword(s):  
Species Richness ◽  
Species Composition ◽  
Zooplankton Community ◽  
Mesh Size ◽  
Temporal Variations ◽  
Water Masses ◽  
Short Term ◽  
Low Salinity ◽  
Low Salinity Water ◽  
Salinity Water

Abstract. Short term changes in zooplankton community were investigated at a fixed station in offshore waters of the Ligurian Sea (DYNAPROC 2 cruise, September–October 2004). Mesozooplankton were sampled with vertical WP-II hauls (200 μm mesh-size) and large mesozooplankton, macrozooplankton and micronekton with a BIONESS multinet sampler (500 μm mesh-size). Temporal variations of total biomass, species composition and abundance of major taxa were studied. Intrusions of low salinity water masses were observed two times during the cruise. The first one, which was the most intense, was associated with changes in zooplankton community composition. Among copepods, the abundance of Calocalanus, Euchaeta, Heterorhabdus, Mesocalanus, Nannocalanus, Neocalanus, Pleuromammaand also calanoid copepodites increased markedly. Among non-copepod taxa, only small ostracods abundance increased. After this low salinity event, abundance of all taxa nearly returned to their initial values. The influence of salinity on each zooplankton taxon was confirmed by a statistical analysis (Perry's method). The Shannon diversity index, Pielou evenness and species richness were used to describe temporal variations of large copepod (>500 μm) diversity. The Shannon index and Pielou evenness decreased at the beginning of the low salinity water intrusions, but not species richness. We suggest that low salinity water masses contained its own zooplankton community and passed through the sampling area, thus causing a replacement of the zooplankton population.

scholarly journals Assemblages of drosophilids (Diptera, Drosophilidae) in mangrove forests: community ecology and species diversity

2010 ◽  
Vol 100 (2) ◽  
pp. 133-140 ◽  
Author(s):  
Hermes J. Schmitz ◽  
Paulo R. P. Hofmann ◽  
Vera L. S. Valente
Keyword(s):  
Species Richness ◽  
Species Composition ◽  
Species Abundance ◽  
Mangrove Forests ◽  
Species Abundance Distribution ◽  
Conservation Areas ◽  
Apparent Lack ◽  
Breeding Sites ◽  
Richness Estimators ◽  
Harsh Conditions

Brazilian fauna of drosophilids has been researched in various ecosystems, but those in mangrove forests remain overlooked in Brazil and elsewhere. The present study attempts to characterise the assemblages of drosophilids of this environment, based on 28 collections taken in three mangrove areas in Santa Catarina Island, southern Brazil. The three mangroves surveyed were different in their surroundings, which varied from highly urbanised areas to conservation areas with natural vegetation. Overall, 69 species were collected, and no remarkable difference was detected in species composition and abundances or in the richness, evenness and heterogeneity between sites. The species abundance distribution observed fitted to a theoretical lognormal distribution in the three mangroves. The species richness scored and the performance of the species richness estimators showed an unexpectedly high diversity, considering the very low floristic diversity and the harsh conditions of the environment. Regarding species composition and abundances, the drosophilid mangrove assemblages were shown to be more similar to those found in open environments, with a marked dominance of exotic species. Finally, considering the apparent lack of feeding and breeding sites, we suggest that mangrove forests are acting as sink habitats for the drosophilids populations.

scholarly journals SPECIES COMPOSITION AND RELATIVE POPULATION SIZE OF FISHES IN THE OSTER RIVER (THE DESNA RIVER BASIN): 50 YEARS ANALYSIS

2021 ◽  
Vol 26 (1(48)) ◽  
pp. 73-88
Author(s):  
S. V. Mezhzherin ◽  
S. V. Kokodii ◽  
D. S. Lutsenko ◽  
А. О. Tsyba
Keyword(s):  
Species Composition ◽  
Population Size ◽  
Absolute Number ◽  
River Systems ◽  
Relative Population ◽  
Population Sizes ◽  
Invasion Species ◽  
Chondrostoma Nasus ◽  
Leuciscus Idus ◽  
Current Species

Inroduction. Changes in the species composition and population size of freshwater fihes are determined by deformations of the habitat in Ukraine and are characterized by a pronounced negative dynamics. Deformation of ichthyofauna is caused by extinction of a number of aboriginal fihes and emergence of alien species.Aim. To establish the current species composition and relative population size of fih species in the Oster River and the dynamics of these characteristics over a 50-yearlong period in the context of negative transformations of the ichthyofauna of the rivers of Ukraine.Results. Comparative study of the species composition and relative population size of fih species in the fih catches by small-river fihing gear in the Oster river was conducted during the period since 1971-72 till 2019. During this time considerable changes in species composition took place. The following species disappeared from the catches: Leuciscus leuciscus, Leuciscus idus, Chondrostoma nasus, Carassius carassius, Blicca bojerkna and Neogobius flviatilis, they were replaced by three invasion species (Percottus glenni, Pseudorasbora parva, Proterorhinus marmoratus). The changes in the dominant species took place, thus, in the Oster ichthyocene the species with the short life cycle started to prevail, the share of invasion species increased from 1.4 to 37%, and the share of initial marine fih among them is very low. The comparison with the river systems of the Stugna and the Lower Dnipro represents the fact that the mentioned negative tendencies are common for the whole Dnipro system, however the situation in the Lower Dnipro must be considered less critical than in the Oster and the Stugna rivers. The fact that the catches of industrial fih decreased more than 10 times in the Desna river during this period of time gives the reason to consider that the dramatic reduction of the absolute number of their populations occurred in the Oster river as well. That is why even relatively safe species (Abramis brama, Rutilus ritilus, Scardinius erythrophthalmus, Esox lucius, Perca flviatilis, Alburnus alburnus, Squalius cephalus) are in critical situation in this transformed river system.Сonclusions. In the ichthyocene of the Oster River over a 50-year period there have been signifiant changes in species composition, relative and absolute population numbers associated with the extinction and reduction of population sizes of rheophilic species and fih that are adapted to life in the flodplain. The modern Oster River is dominated by invasive and short-cycle species. The obtained tendencies in the dynamics of the ichthyofauna of the Oster River are similar to the nature of changes in other river systems of Ukraine, although they occur at a faster pace, which is characteristic of the smallest plain rivers.

Mid- to late-Holocene oceanographic variability on the Southeast Greenland shelf

The Holocene ◽  
2012 ◽  
Vol 23 (2) ◽  
pp. 167-178 ◽  
Author(s):  
CS Andresen ◽  
MJ Hansen ◽  
M-S Seidenkrantz ◽  
AE Jennings ◽  
MF Knudsen ◽  
...  
Keyword(s):  
North Atlantic ◽  
Late Holocene ◽  
Water Masses ◽  
Ice Age ◽  
Subpolar Gyre ◽  
North Atlantic Current ◽  
The North ◽  
East Greenland Current ◽  
Irminger Sea ◽  
Salinity Water

A reconstruction of oceanographic variability of the past 5800 years on the southeast Greenland shelf was obtained by analysing a combined marine sediment record based on two cores from the same site. Cores Fox04G/05R were retrieved from a side basin to a cross-shelf trough connecting the 900 m deep Sermilik Fjord with the Irminger Sea in the northwestern North Atlantic. The record was analysed in terms of grain size distribution, XRF and benthic and planktonic foraminiferal content and the chronology was obtained on the basis of 210Pb and 14C dating. The late-Holocene paleoceanographic variations in the record were characterised by a marked influence from the Irminger Current (IC) at the onset of the record at 5800 cal. yr BP and the regional Holocene Climatic Optimum between 5200 and 4200 cal. yr BP. After 3600 cal. yr BP Neoglacial cooling with increased influence of polar waters from the East Greenland Current (EGC) diminished the influence from the IC. Between 1500 and 700 cal. yr BP, the environment was highly dominated by cold low-salinity water masses characterised by sea ice forming locally and/or transported with an intensified EGC. At 700 cal. yr BP, concordant with the onset of the ‘Little Ice Age’, inflow of IC water masses intensified, notably during short-lived warming episodes of the North Atlantic Current most likely related to a contracted subpolar gyre. At the same time, the EGC polar water transport also intensified leading to a stratified water column on the shelf and this may have favoured entrainment of warm subsurface IC waters. Alternatively, the relatively warm rim of the eastern subpolar gyre may have promoted intense submarine melting of extended Southeast Greenland outlet glaciers at this time, producing enhanced meltwater outflow which favoured estuarine circulation processes maintaining the inflow of IC water masses.

scholarly journals Contrasting Response of the Eastern and Western North Atlantic Circulation to an Episodic Climate Event*

2011 ◽  
Vol 41 (9) ◽  
pp. 1630-1638 ◽  
Author(s):  
Ayan H. Chaudhuri ◽  
Avijit Gangopadhyay ◽  
James J. Bisagni
Keyword(s):  
North Atlantic ◽  
High Salinity ◽  
Scale Model ◽  
High Salinity Water ◽  
Low Salinity ◽  
The North ◽  
Basin Scale ◽  
Salinity Water ◽  
The North Atlantic ◽  
The North Atlantic Oscillation

Abstract Regional observational studies in the North Atlantic have noted significant hydrographical shifts in 1997–98 because of the episodic drop in the North Atlantic oscillation (NAO) during 1996. Investigation using a basin-scale model finds that, although the western North Atlantic (WNA) witnessed unusually low-salinity water by 1997, the eastern North Atlantic (ENA) simultaneously evidenced intrusions of high-salinity water at intermediate depths. This study shows that a major source of high salinity in the ENA is from the northward penetration of Mediterranean Outflow Water (MOW) that occurred concurrently with a westward shift of the subpolar front. The authors confirm that the low-salinity intrusion in the WNA is from enhanced Labrador Current flow. Results from climatological high- and low-NAO simulations suggest that the NAO-induced circulation changes that occurred in 1997–98 are a characteristic North Atlantic basin response to different forcing conditions during characteristic high- and low-NAO periods.

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