Interannual Variability In Abundance Research Articles

Model-based indices of juvenile Pacific salmon abundance highlight species-specific seasonal distributions and impacts of changes to survey design

Changes in survey implementation can bias traditional design-based indices of abundance, particularly for migratory species where local abundance can vary at short temporal scales. Spatiotemporal model-based estimators provide a flexible alternative that can better account for changes in the timing and location of surveys. Here we develop a geostatistical model, a generalized linear mixed effects model with Gaussian Markov random fields, that is sufficiently flexible to account for changes in survey design, as well as seasonal and interannual variability in abundance and spatial distribution. We then apply this model to a suite of migratory species—juvenile Pacific salmon—with survey data collected from southern British Columbia’s continental shelf over the previous 25 years. Juvenile Pacific salmon showed species-specific spatial distributions with considerable seasonal variability. While the location of species-specific hot spots varied among years, seasonal variation in distributions were greater than interannual variation. We found that a shift from standard transects and opportunistic sampling to a random stratified survey design resulted in lower estimates of abundance for four of five juvenile Pacific salmon species; however, these differences were not significant after accounting for other sampling attributes. Trends in abundance for several species shifted when models included survey and diel effects. Our approach provides a means of deriving indices of abundance for migratory species from surveys with variable effort in time and space. Ultimately such indices can be used to better understand the ecological mechanisms regulating productivity by linking distribution and abundance to environmental drivers.

Otolith-inferred patterns of marine migration frequency in Nunavik Arctic charr.

Alternative migratory tactics in salmonids reflect the large observed inter-individual variation in spatial behaviour which may range from strict freshwater residency to uninterrupted anadromy. In Salvelinus, sea migrations are performed during the ice-free period as freshwater over-wintering is thought to be obligatory due to physiological constraints. As a result, individuals can either perform a migration the next spring or remain in freshwater, as anadromy is generally considered facultative. In Arctic charr (S. alpinus), skipped migrations are known to occur but limited data are available about their frequencies within and among populations. Here, we used an otolith microchemistry approach relying on Strontium (88 Sr) to infer movements between freshwater and marine habitats, and annual oscillations in Zinc (64 Zn) to help with age identification. We determined the age-at-first-migration and the occurrence of subsequent annual migrations in two Nunavik Arctic charr populations sampled in Deception Bay (Salluit) and, river systems linked to Hopes Advance Bay (Aupaluk), northern Québec, Canada. The mode for age-at-first-migration was 4+ for both populations, although it exhibited large variation (range: 0+ to 8+). Skipped migrations constituted a rare event, as 97.7% and 95.6% of the examined Arctic charr at Salluit (n = 43, mean age = 10.3 ± 2.0 years) and Aupaluk (n = 45, mean age = 6.0 ± 1.9 years), respectively, were found to have performed uninterrupted annual migrations after initiation of the behaviour. The consistency of the annual migrations suggests that the tactic is sufficiently fitness-rewarding to be maintained under current environmental conditions. From a fisheries management perspective, these repeated migrations combined with low site fidelity may lead to large interannual variations in abundance at the local scale, which may represent a challenge for monitoring Arctic charr demographics on a river-by-river basis. This article is protected by copyright. All rights reserved.

Effects of Atlantification and changing sea‐ice dynamics on zooplankton community structure and carbon flux between 2000 and 2016 in the eastern Fram Strait

AbstractThe collection of zooplankton swimmers and sinkers in time‐series sediment traps provides unique insight into year‐round and interannual trends in zooplankton population dynamics. These samples are particularly valuable in remote and difficult to access areas such as the Arctic Ocean, where samples from the ice‐covered season are rare. In the present study, we investigated zooplankton composition based on swimmers and sinkers collected by sediment traps at water depths of 180–280, 800–1320, and 2320–2550 m, over a period of 16 yr (2000–2016) at the Long‐Term Ecological Research observatory HAUSGARTEN located in the eastern Fram Strait (79°N, 4°E). The time‐series data showed seasonal and interannual trends within the dominant zooplankton groups including copepoda, foraminifera, ostracoda, amphipoda, pteropoda, and chaetognatha. Amphipoda and copepoda dominated the abundance of swimmers while pteropoda and foraminifera were the most important sinkers. Although the seasonal occurrence of these groups was relatively consistent between years, there were notable interannual variations in abundance, suggesting the influence of various environmental conditions such as sea‐ice dynamic and lateral advection of water masses, for example, meltwater and Atlantic water. Statistical analyses revealed a correlation between the Arctic dipole climatic index and sea‐ice dynamics (i.e., ice coverage and concentration), as well as the importance of the distance from the ice edge on swimmer composition patterns and carbon export.

Long: Influence of water masses on the summer structure of the seabird community in the northeastern Chukchi Sea.

We used data collected during a variety of research cruises in the northeastern Chukchi Sea and contributed to the Distributed Biological Observatory to explore the influence of the seasonal change in water masses on the development of the seabird community during the summer. Surveys that included seabird observations and hydrographic sampling were conducted from Alaska’s northwestern coast to ~220 km offshore during 2008–2018. Species composition varied geographically, shifting from a nearshore community that included short-tailed shearwaters, loons, and seaducks to an offshore community dominated by crested auklets. Crested auklets were remarkably consistent in their occupation of Hanna Shoal among years and remained in the area throughout the summer. Short-tailed shearwaters exhibited the greatest seasonal and interannual variation in abundance and distribution of the 35 species recorded. They were concentrated south of 71°N and within 50 km of shore in August and tended to spread throughout the region in September. Surface-feeding species like gulls, fulmars, and phalaropes were 1–2 orders of magnitude less abundant and had wider distributions than birds that feed by diving. Including information about hydrography improved the fit of models of seabird density. Seabirds, especially those that breed in the Bering Sea, generally were more abundant in areas dominated by moderate-salinity Bering Sea Water than nearshore in low-salinity Alaska Coastal Water. The distribution of seabirds across the northeastern Chukchi Sea reflected the heterogeneity of oceanic habitats and prey availability over the shallow shelf. Our results will inform efforts to develop ecosystem models that incorporate oceanographic conditions to predict ongoing consequences of climate change.

Inter-annual variability in breeding census data across species and regions

There is an intense interest in long-term trends of species abundance that may reflect, for example, climate change or conservation actions. Less well studied are patterns in the magnitude of inter-annual variability in abundance across large spatial scales. We collated abundance time-series for 133 nesting sites across the globe of the seven sea turtle species. Inter-annual variability in nest numbers was lowest in loggerhead turtles (Caretta caretta), Kemp’s ridley (Lepidochelys kempii) and flatback turtle (Natator depressus) and highest in green turtles (Chelonia mydas), likely reflecting their lower trophic position compared to other species and hence tighter coupling of food availability to environmental conditions each year. The annual number of nests in green turtles could vary by 60-fold between successive years. We identified regional patterns in the magnitude of inter-annual variability in green turtle nest numbers, variability being highest for nesting beaches around Australia and lowest in the western Indian Ocean and equatorial Atlantic. These regional patterns are likely linked to corresponding patterns of environmental variability with, for example, areas subjected environmental extremes as part of the El Nino Southern Oscillation (ENSO) showing high inter-annual variability in nest numbers.

Seasonal and inter-annual variability in abundance of the main tropical tunas in the EEZ of Côte d’Ivoire (2000-2019)

The seasonal and inter-annual variability in abundance of the main “local tropical tuna resources” in the EEZ of Côte d'Ivoire was analysed with catch and effort data from French and Spanish purse seiners over the period 2000–2019. A seasonal spatio-temporal model developed by Thorson et al. (2020a) was used to estimate abundance indices for the main tropical tunas by commercial category (<10 kg and> = 10 kg, which correspond roughly to maturity stage: immature and mature respectively), and fishing mode (free school sets and FAD sets). Furthermore, we decomposed the abundance time series into intrinsic mode functions using the CEEMDAN algorithm. The decomposition procedure made it possible to filter out the noise in the signal and extract the seasonal and inter-annual components of the abundance indices. A generalized additive model (GAM) was applied to the abundance indices to reveal the influences of environmental factors on species abundance and spatio-temporal distribution. Biological interpretations of the seasonal and inter-annual variability in tropical tuna abundance were made and the possible effects of environmental variables on this abundance discussed. Our results suggest that there are two main fishing seasons in the EEZ of Côte d'Ivoire. It was also found that mature yellowfin tunas are abundant between the first and second quarter of the year while the best season for skipjack occurs between the third and fourth quarter. In addition, we observed a considerable change over time in the seasonal and inter-annual variability of tropical tunas in this area.

Seasonal and interannual variability in abundance and population development of Calanus finmarchicus at the western entrance to the Barents Sea, 1995–2019

Data on copepodid abundance and stage composition of Calanus finmarchicus was collected with seasonal resolution (5–6 times a year) from four stations along an oceanographic transect across the western Barents Sea Opening over 25 years (1995–2019). The stations were located in the Norwegian Coastal Current (NCC), inflowing Atlantic water (two stations), and near the Arctic polar front south of Bear Island. Mean copepodite abundance in the water column for the four stations increased from a level around 1000–10,000 individuals m−2 in winter to 30,000–100,000 individuals m−2 in summer (maximum 670,000 m−2). The overwintering (G0) population was dominated by copepodite stage 5 (CV) (40–70%) but with a relatively high fraction also of stage CIV (25–35%) in January. During winter, there was a progressive development of CVs into adult males and females, with mean abundances from 1500 to 4000 adult females m−2 in April and May for the stations in the NCC and Atlantic water. Young copepodids of the new spring generation (G1) appeared with relatively high abundances in April at the NCC station and in May at the Atlantic water stations. The data showed a gradient of later development from south to north, reflected both in the maturation of the overwintering generation and in the development of the spring generation. Back-calculations based on temperature-dependent development time suggested peak spawning around late April to mid-May for the Atlantic water stations, and a month or so earlier (in March) for the NCC station, during an early phase of the spring phytoplankton growth. The spring generation developed as a distinct cohort but with large interannual variability in numbers. In Atlantic water, the composition of the copepodid developmental stages in August resembled the situation in June, although it was slightly more advanced. This is interpreted to reflect development of a second generation (G2) spawned upstream sometime in June or early July. The June data suggests that only a small fraction of the G1 cohort develops into adults that spawn and form the G2. There was a tendency of increased summer abundance of C. finmarchicus in the inflow region of the southwestern Barents Sea after about 2005. This may be related to the wind regime with more eastward wind-stress at the Barents Sea opening in recent ‘high Calanus’ years compared to ‘low Calanus’ years in the early 2000s.

Temporal shifts in the abundance and preferred habitats of yellowfin and bigeye tuna larvae in the Gulf of Mexico

The influence of environmental conditions on the relative abundance of Thunnus albacares (yellowfin tuna) and Thunnus obesus (bigeye tuna) were investigated to determine the extent of the early life stage suitable habitat of these species in the Gulf of Mexico (GoM). Thunnus albacares and T. obesus larvae were commonly found (31–50% frequency of occurrence per year) in the northern GoM (26–28°N, 91–96°W), and a significant intra- and inter-annual variability in abundance of T. albacares and T. obesus was observed with higher abundance recorded in July surveys (1.3 larvae 1000 m−3 for both species) and during the Summer 2009 (1.9 and 1.7 larvae 1000 m−3, respectively). Generalized additive models (GAMs) indicated that larvae of T. albacares and T. obesus were more common and at higher abundance in water masses with moderate to high salinity (28–36), high temperature (29 °C), positive sea surface height. Species-specific environmental preferences determined with GAMs were then combined with summer environmental data over eight years (2007 to 2015) to predict the spatial coverage of suitable habitat of both species in regions beyond the 100-m isobath. Habitat suitability predictions indicated that the location and extent of highly suitable habitat of T. albacares and T. obesus larvae varied across years with the highest areal coverage in 2015 (70%) and 2010 (73%), respectively. Both T. albacares and T. obesus larvae were more commonly observed and at higher abundance off the continental slope and at margins of the Loop Current and associated warm-core eddies in the northern GoM. Because changes in environmental conditions influenced the spatio-temporal distribution of T. albacares and T. obesus larvae, habitat suitability models are valuable tools for identifying critical areas of the GoM inhabited by tuna larvae and this information can also be used to assess potential impacts of natural and anthropogenic disturbances on the recruitment and population dynamics of tunas.

Clarifying the effects of environmental factors and fishing on abundance variability of Pacific saury (Cololabis saira) in the western North Pacific Ocean during 1982–2018

AbstractPacific saury (Cololabis saira) has a 2‐year life span and age‐1 fish migrates from the central and western North Pacific to Japanese waters from summer to winter. To understand interannual abundance variability of Pacific saury in the North Pacific, we examined the extended Japanese standardized catch per unit effort (esCPUE) with generalized linear models (GLMs) during 1982–2018. Explanatory variables included proxies of total and non‐traditional fishing effort (Ettl and Ent) and environmental factors. Each environmental variable was averaged for years t ‐1 and t, corresponding to esCPUE in year t, as esCPUE represented two‐year classes. Ettl and Ent were averaged for years t ‐ 2 and t‐1, assuming fishing of year t affects biomass in year t + 1. We compared four GLMs with different explanatory variables: (a) environmental factors only, (b) fishing effort (without interactions) only, (c) environmental factors and fishing effort (without interactions) and (d) environmental factors and fishing effort (with interactions, i.e., time‐varying effects). Explanatory variables of the best GLM in terms of AICc included the following: Ent with different effects between 1982–2015 and 2016–2018, sea surface water temperature (SST) of the Kuroshio Recirculation Area (KRA) in winter, North Pacific Gyre Oscillation (NPGO) in winter, Southern Oscillation Index in winter, and the biomass of Japanese sardine. The NPGO, a proxy of zooplankton abundance, and KRA‐SST may affect the early growth and survival rates of Pacific saury. We hypothesized the abundance variability of Pacific saury was driven by environmental factors and fishing, the latter of which more adversely affected since 2016.

Pseudodiaptomus marinus Sato, 1913 in the Black Sea: morphology, genetic analysis, and variability in seasonal and interannual abundance.

Calanoid copepod Peudodiaptomus marinus Sato, 1913 was first recorded in Sevastopol Bay in the northern Black Sea in September 2016. We performed regular observations of this new invasive species between October 2016 and December 2018. We conducted bi-weekly plankton sampling at three stations located within or adjacent to Sevastopol Bay. This is the first paper to combine (i) a detailed morphological study, (ii) molecular genetic analysis, and (iii) an investigation of P. marinus seasonal dynamics and interannual abundance variability in the coastal Black Sea. Our morphological research showed similarities between Pseudodiaptomus specimens and existing P. marinus illustrations and descriptions. Our morphological analysis results were confirmed using molecular genetic studies. Based on the genetic variability of ITS2 and cytb, we found that all investigated specimens from Sevastopol Bay belonged to P. marinus. Investigations of P. marinus seasonal and interannual abundance variability showed the same seasonal patterns throughout the studied period, with a higher seasonal abundance from October to November and one pronounced density peak in autumn. The highest abundances (2,000 ind m–3 at the mouth of the bay and more than 5,000 ind m–3at its centre) were recorded in November 2018. In the samples, we found adults of both sexes, including ovigerous females, copepodites I–V, and nauplii, suggesting that the species reproduce in Sevastopol Bay. Our research indicated that P. marinus is a new non-indigenous species (NIS) in the Black Sea, and we will discuss a possible vector of its introduction into this basin.

Quantifying the relative importance of stock level, river temperature and discharge on the abundance of juvenile Atlantic salmon (Salmo salar)

AbstractFisheries scientists need to understand the relationships between river temperature, discharge and production of juvenile salmonids to inform evidence‐based management and regulation of rivers and to understand the potential effects of climate change. These relationships can be determined by characterising interannual variability in abundance and environmental conditions from long‐term monitoring data and assessing their inter‐relationships. Two major challenges are (1) the requirement to separate the relative effects of stock level and environment which both affect interannual variability in abundance and (2) obtaining long‐term environmental time‐series that do not suffer from temporal biases. This study built on recent advances in hydrological, river‐temperature and juvenile salmonid modelling to investigate the influence of temperature and discharge on interannual variability in Atlantic salmon (Salmo salar) fry (age: 0 years) and parr (age: 1 year) production. The study used a unique long‐term dataset (&gt;50 years) with detailed age‐differentiated census data collected for multiple life‐stages. The study shows that most of the interannual variability in recruitment was explained by stock level. Discharge had a comparatively small effect on fry recruitment, but a greater effect than artificial stocking. Discharge had no discernible effect on parr recruitment. Temperature had no effect on recruitment of either life‐stage. This study suggests that salmon are well adapted to current environmental variability in natural upland rivers in Scotland, but reductions in discharge during spawning and emergence could negatively affect fry recruitment with consequences for regulation of river flows. The study highlights the importance of high‐quality census data for accurately determining the effects of environmental variability on recruitment.

Interannual variations in abundance and distribution of Chattonella cysts, and the relationship to population dynamics of vegetative cells in the Yatsushiro Sea, Japan

The fish-killing raphidophytes Chattonella spp. have a resting cyst stage. To investigate the abundance and distribution of Chattonella cysts and determine their relationship to the population dynamics of vegetative cells, we conducted field observations from 2002 to 2017 in the Yatsushiro Sea, a semi-enclosed embayment in Japan, and analyzed the data including environmental conditions. Analysis of sediment sampled in the spring (mid-April to early June), shows that cysts are relatively abundant in the northern to middle area, where initial vegetative cells and large blooms are frequently detected. The maximum density of cysts was 616 cysts cm–3 in the northern area in 2016. Mean cyst abundance in the spring varied interannually, ranging from 5 to 138 cysts cm–3. A significant positive correlation between mean cyst abundance in the spring and maximum density of vegetative cells the preceding summer was seen, but no significant correlation was observed the following summer. The first detected date of vegetative cells (FDD) each year, which is likely related to cyst abundance and environmental conditions influencing cyst germination and/or growth characteristics of vegetative cells, also varied interannually from mid-April to early June. Regression analyses showed that FDD tended to be early when cyst abundance and bottom-water temperature were high. However, no significant correlation was observed between mean cyst abundance and bloom timing (the period from FDD to the occurrence date of the bloom), and bloom duration the following summer, as was the maximum density of vegetative cells. Instead, the timing and duration of blooms were correlated significantly with meteorological factors (e.g., solar radiation) for a month after FDD. The results suggest that cyst abundance reflecting the bloom magnitude of the preceding summer contributes to the timing of the appearance of vegetative cells in the year, but that bloom occurrence is likely to be controlled by the growth dynamics of vegetative cells through environmental conditions rather than by cyst abundance. The three distinct peaks in Chattonella cysts and vegetative cells from 2002 to 2017 correspond to the timings just after the El Niño. Large-scale atmospheric variability and its global teleconnection are possibly linked to long-term population dynamics of Chattonella in the area through local meteorological conditions and their life cycle.

Spatial and temporal dynamics of Pacific capelin Mallotus catervarius in the Gulf of Alaska: implications for ecosystem-based fisheries management

Pacific capelin Mallotus catervarius are planktivorous small pelagic fish that serve an intermediate trophic role in marine food webs. Due to the lack of a directed fishery or monitoring of capelin in the Northeast Pacific, limited information is available on their distribution and abundance, and how spatio-temporal fluctuations in capelin density affect their availability as prey. To provide information on life history, spatial patterns, and population dynamics of capelin in the Gulf of Alaska (GOA), we modeled distributions of spawning habitat and larval dispersal, and synthesized spatially indexed data from multiple independent sources from 1996 to 2016. Potential capelin spawning areas were broadly distributed across the GOA. Models of larval drift show the GOA’s advective circulation patterns disperse capelin larvae over the continental shelf and upper slope, indicating potential connections between spawning areas and observed offshore distributions that are influenced by the location and timing of spawning. Spatial overlap in composite distributions of larval and age-1+ fish was used to identify core areas where capelin consistently occur and concentrate. Capelin primarily occupy shelf waters near the Kodiak Archipelago, and are patchily distributed across the GOA shelf and inshore waters. Interannual variations in abundance along with spatio-temporal differences in density indicate that the availability of capelin to predators and monitoring surveys is highly variable in the GOA. We demonstrate that the limitations of individual data series can be compensated for by integrating multiple data sources to monitor fluctuations in distributions and abundance trends of an ecologically important species across a large marine ecosystem.

日本海全海域の水産・漁獲変化 ～粒子追跡実験で表現された2017年のマアジ太平洋系群新規加入量増加イベント～

日本海全海域の水産・漁獲変化 ～粒子追跡実験で表現された2017年のマアジ太平洋系群新規加入量増加イベント～

Abiotic conditions are not sufficient to predict spatial and interannual variation in abundance of Ciona intestinalis in Nova Scotia, Canada

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 628:105-123 (2019) - DOI: https://doi.org/10.3354/meps13076 Abiotic conditions are not sufficient to predict spatial and interannual variation in abundance of Ciona intestinalis in Nova Scotia, Canada K. J. Murphy1,4,*, D. Sephton2, K. Klein3,5, C. D. Bishop1, R. C. Wyeth1 1Department of Biology, St. Francis Xavier University, 2320 Notre Dame Ave., Antigonish, NS B2G 2W5, Canada 2Fisheries and Oceans Canada, Bedford Institute of Oceanography, 1 Challenger Drive, Dartmouth, NS B2Y 4A2, Canada 3Clinical Trial and Biostatistics Unit, QIMR Berghofer Medical Research Institute, 300 Herston Road, Brisbane, QLD 4006, Australia 4Present address: Institute for Marine and Antarctic Studies, University of Tasmania, 20 Castray Esplanade, Battery Point, Hobart, TAS 7004, Australia 5Present address: Royal Automobile Club of Queensland Ltd, 2649 Logan Road, PO Box 4 Springwood, QLD 4127, Australia *Corresponding author: kimurphy@tcd.ie ABSTRACT: The vase tunicate Ciona intestinalis is an invasive sea squirt that poses several challenges for coastal marine ecosystems and human activities. Despite its widespread distribution, temporal and spatial variability in population abundances is high. We tested whether this variation could be explained by 4 abiotic variables: temperature, salinity, pH and water movement. We repeatedly measured these 4 variables and relative abundance of C. intestinalis at 11 sites along the Atlantic coastline of Nova Scotia, Canada, each month between May and October 2014 and 2015. Using nonlinear mixed-effects modelling, we found that salinity moderately explained abundance of C. intestinalis across sites in 2014, while in 2015 there were no strong associations between abundance and any measured abiotic variable. The combination of little explanatory power within years and inconsistency between years led us to conclude that none of the measured abiotic conditions was useful in predicting the abundance of C. intestinalis. This finding contrasts with previous studies in which temperature and salinity were effective at predicting the presence or absence of the species. Thus, we suggest that tolerances of these 2 factors may determine whether C. intestinalis can survive in a location, but that other factors predict the rate of population growth. Given that increased abundance exacerbates the negative effects of this invasive species, we advocate further study of alternative factors that lead to higher abundances of C. intestinalis, to help inform management decisions. KEY WORDS: Ascidian · Benthic invertebrate · Biofouling · Invasion biology · Longitudinal · Population dynamics · Tunicate · Sea squirt Full text in pdf format Supplementary material PreviousNextCite this article as: Murphy KJ, Sephton D, Klein K, Bishop CD, Wyeth RC (2019) Abiotic conditions are not sufficient to predict spatial and interannual variation in abundance of Ciona intestinalis in Nova Scotia, Canada. Mar Ecol Prog Ser 628:105-123. https://doi.org/10.3354/meps13076 Export citation Mail this link - Contents Mailing Lists - RSS Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 628. Online publication date: October 10, 2019 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2019 Inter-Research.

Variability and profiles of lipophilic toxins in bivalves from Great Britain during five and a half years of monitoring: azaspiracids and yessotoxins

Cefas has been responsible for the delivery of official control biotoxin testing of bivalve molluscs from Great Britain for just over a decade. Liquid chromatography tandem mass spectrometric (LC–MS/MS) methodology has been used for the quantitation of lipophilic toxins (LTs) since 2011. The temporal and spatial distribution of okadaic acid group toxins and profiles in bivalves between 2011 and 2016 have been recently reported. Here we present data on the two other groups of regulated lipophilic toxins, azaspiracids (AZAs) and yessotoxins (YTXs), over the same period. The latter group has also been investigated for a potential link with Protoceratium reticulatum and Lingulodinium polyedra, both previously recognised as YTXs producing phytoplankton.On average, AZAs were quantified in 3.2% of all tested samples but notable inter-annual variation in abundance was observed. The majority of all AZA contaminated samples were found between July 2011 and August 2013 in Scotland, while only two, three-month long, AZA events were observed in 2015 and 2016 in the south-west of England. Maximum concentrations were generally reached in late summer or early autumn. Reasons for AZAs persistence during the 2011/2012 and 2012/2013 winters are discussed. Only one toxin profile was identified, represented by both AZA1 and AZA2 toxins at an approximate ratio of 2 : 1, suggesting a single microalgal species was the source of AZAs in British bivalves. Although AZA1 was always the most dominant toxin, its proportion varied between mussels, Pacific oysters and surf clams.The YTXs were the least represented group among regulated LTs. YTXs were found almost exclusively on the south-west coast of Scotland, with the exception of 2013, when the majority of contaminated samples originated from the Shetland Islands. The highest levels were recorded in the summer months and followed a spike in Protoceratium reticulatum cell densities. YTX was the most dominant toxin in shellfish, further strengthening the link to P. reticulatum as the YTX source. Neither homo-YTX, nor 45−OH homo-YTX were detected throughout the monitored period. 45−OH YTX, thought to be a shellfish metabolite associated with YTX elimination, contributed on average 26% in mussels. Although the correlation between 45−OH YTX abundance and the speed of YTX depuration could not be confirmed, we noted the half-life of YTX was more than two-times longer in queen scallops, which contained 100% YTX, than in mussels. No other bivalve species were affected by YTXs.This is the first detailed evaluation of AZAs and YTXs occurrences and their profiles in shellfish from Great Britain over a period of multiple years.

State-space analysis of power to detect regional brook trout population trends over time

Threats to aquatic biodiversity are expressed at broad spatial scales, but identifying regional trends in abundance is challenging owing to variable sampling designs and temporal and spatial variation in abundance. We compiled a regional data set of brook trout (Salvelinus fontinalis) counts across their southern range representing 326 sites from eight states between 1982 and 2014 and conducted a statistical power analysis using Bayesian state-space models to evaluate the ability to detect temporal trends by characterizing posterior distributions with three approaches. A combination of monitoring periods, number of sites and electrofishing passes, decline magnitude, and different revisit patterns were tested. Power increased with monitoring periods and decline magnitude. Trends in adults were better detected than young-of-the-year fish, which showed greater interannual variation in abundance. The addition of weather covariates to account for the temporal variation increased power only slightly. Single- and three-pass electrofishing methods were similar in power. Finally, power was higher for sampling designs with more frequent revisits over the duration of the monitoring program. Our results provide guidance for broad-scale monitoring designs for temporal trend detection.

Spatial, seasonal and inter-annual variation in abundance and carbon turnover of small copepods in Young Sound, Northeast Greenland

Melting of the Arctic cryosphere affects the marine ecosystem in general and the coastal zone in particular. In Greenland, melting of the Greenland Ice Sheet has accelerated with complex but largely undocumented effects on marine carbon cycling and ecosystem structure. We studied production and population dynamics of the abundant copepods Oithona similis, Triconia borealis and Pseudocalanus spp. in Young Sound, Northeast Greenland, during the ice-free period from July to October 2014 at four stations located along a freshwater gradient from the inner fjord to the Greenland Sea. Additionally, inter-annual variation in copepod species composition in August from 2003 to 2015 was examined. Melt water resulted in strong stratification of surface water during July and August. Integrated chlorophyll a was lower at the stations nearest the glaciers and a bigger proportion of the chlorophyll was made up of small cells (< 10 μm). Small non-calanus copepod species dominated total copepod abundance especially in the freshwater impacted inner fjord and late in the ice-free period. Production of Pseudocalanus spp. was related to chlorophyll a concentration while production of O. similis was less so. Egg production and stage composition indicated that O. similis reproduce throughout the ice-free season, while reproduction of Pseudocalanus spp. was restricted to July and August. The production of small species was minor compared to Calanus spp. in July and August, but it accounted for a relatively large fraction of the total production in September and October (up to 69%). On a decadal scale only Pseudocalanus spp. showed an overall reduction in abundance, while the abundances of other genera were relatively constant. Our study suggests that increasing freshwater runoff and a longer growth season, due to later ice formation, may increase the proportion of primary production passing through the smaller copepod species.

Habitat description and interannual variation in abundance and phenology of the endangered beetle Lucanus cervus L. (Coleoptera) using citizen science monitoring

Conservation of threatened saproxylic beetles, which are often elusive, faces the problem of efficient monitoring. Lack of standard monitoring protocols has hindered the much needed assessment of temporal trends in phenology and abundance of the stag beetle, Lucanus cervus, and the development of landscape ecology studies. Our main objective was to illustrate how transects at dusk, implemented by means of citizen science projects, could provide reliable information on habitat characterization and population trends in the stag beetle. Abundance and phenology was studied in a longitudinal study during 7 years in E Spain. Habitat characterization was studied in a transversal study in N Spain. Our longitudinal study detected between-year variation in phenology (up to 4 weeks in peak activity) and abundance (twofold among maxima and minima recorded). In addition, both our longitudinal and transversal studies detected variation among sites in abundance, that was related to rainfall in the previous winter. In this sense, transects at dusk were a suitable monitoring method. Abundance variation could not be related to habitat variables. Nevertheless, we provide one of the few descriptions available of stag beetle habitat at scales of tens to hundreds of meters. Forest was the dominant vegetation in a 25 m buffer around the transects. However, open natural vegetation prevailed in a 1000 m buffer around the transects, indicating strong habitat fragmentation. We conclude that transects at dusk are easily implemented in citizen science projects and provide much needed information about temporal trends in abundance, phenology and habitat description of stag beetles.

Dynamics of an upland stream fish community over 40 years: trajectories and support for the loose equilibrium concept

Previous theoretical models and empirical studies suggested that communities can exist in a "stochastic" or "loose" equilibrium, diverging transiently but eventually returning toward earlier or average structure, in what we call here the "loose equilibrium concept" (LEC). We sampled the fish communities at 12 local stream reaches spaced broadly throughout a relatively undisturbed watershed in the Ozark Mountains of northern Arkansas, USA, in 11 surveys from 1972 to 2012 at a scale of decades, and at a subset of five of these local sites in a total of 16 surveys, allowing tests of the LEC at different spatial and temporal scales. Multivariate analyses of the dynamics of communities over the 40-year period provided support for the LEC at both "global" and "local" scales within the watershed. At the broadest spatial scale, core species numerically dominated the community, and most common species remained so across all decades. In spite of two extraordinary floods, and interannual variation in abundance of some species, the 12-site and five-site global communities and eight of 12 local communities repeatedly returned toward average positions in multivariate space. Trajectories of the global and local fish communities varied relative to model hypothetical trajectories that were based on gradual vs. saltatory changes, and prevalence of returns toward average community structure. Beta diversity among sites was variable across time, but beta partitioning consistently showed that pure spatial turnover dominated over nestedness, because many common species were consistently distributed either upstream or downstream. This study suggests that vertebrate communities in relatively undisturbed environments may display dynamics consistent with the LEC. The LEC, combined with quantification of community trajectory patterns, can help to clarify whether systems are moving about within ranges of conditions that reflect expected noise, or, conversely, have moved so far out of previous bounds, as a result of climate change or human intervention, that they are permanently changed or "novel."