Mean Bottom Temperature Research Articles

Long-term changes in the density and composition of profundal macrobenthos in Lake Biwa from 1966 to 2000

Lake Biwa, the largest lake in Japan, has been affected by eutrophication and climate warming since the 20th century. To examine the effects of these environmental changes on dominant macrobenthos species in Lake Biwa, the density and composition of these organisms were determined monthly from 1966 to 2000 at an offshore station in the lake, and analyzed in terms of various physicochemical factors. Annual mean bottom temperatures at the site generally remained stable (6.1–8.0°C) until 1985, increased from 1985 (6.5°C) to 1990 (8.3°C), and remained high thereafter (7.4–8.3°C). Branchiura sowerbyi dominated the oligochaete community in terms of density and biomass until 1985. Oligochaete density increased after 1986, dominated by B. sowerbyi, Limnodrilus spp., and Tubifex tubifex. Although the increase in macrobenthic density after 1986 was mainly explained by an increase in T. tubifex density (3811–8076 individuals m–2), total macrobenthos biomass was mainly controlled by B. sowerbyi (1.9–9.5 g m–2). Notably, the increase in T. tubifex density roughly coincided with density decreases in the benthic gobid fish Gymnogobius isaza (from 567 tons to undetectable) and the shrimp Palaemon paucidens (from 758 to 142 tons). Jesogammarus annandalei density increased from 1985, roughly coinciding with the decrease in gobid fish. These findings demonstrate the importance of biological interactions such as predation in the succession of dominant macrobenthos species in Lake Biwa.

Benthic ecosystem functioning under climate change: modelling the bioturbation potential for benthic key species in the southern North Sea.

Climate change affects the marine environment on many levels with profound consequences for numerous biological, chemical, and physical processes. Benthic bioturbation is one of the most relevant and significant processes for benthic-pelagic coupling and biogeochemical fluxes in marine sediments, such as the uptake, transport, and remineralisation of organic carbon. However, only little is known about how climate change affects the distribution and intensity of benthic bioturbation of a shallow temperate shelf sea system such as the southern North Sea. In this study, we modelled and projected changes in bioturbation potential (BPp) under a continuous global warming scenario for seven southern North Sea key bioturbators: Abra alba, Amphiura filiformis, Callianassa subterranea, Echinocardium cordatum, Goniada maculata, Nephtys hombergii, and Nucula nitidosa. Spatial changes in species bioturbation intensity are simulated for the years 2050 and 2099 based on one species distribution model per species driven by bottom temperature and salinity changes using the IPCC SRES scenario A1B. Local mean bottom temperature was projected to increase between 0.15 and 5.4 °C, while mean bottom salinity was projected to moderately decrease by 1.7. Our results show that the considered benthic species are strongly influenced by the temperature increase. Although the total BP remained rather constant in the southern North Sea, the BPp for four out of seven species was projected to increase, mainly due to a simultaneous northward range expansion, while the BPp in the core area of the southern North Sea declined for the same species. Bioturbation of the most important species, Amphiura filiformis and Echinocardium cordatum, showed no substantial change in the spatial distribution, but over time. The BPp of E. cordatum remained almost constant until 2099, while the BPp of A. filiformis decreased by 41%. The northward expansion of some species and the decline of most species in the south led to a change of relative contribution to bioturbation in the southern North Sea. These results indicate that some of the selected key bioturbators in the southern North Sea might partly compensate the decrease in bioturbation by others. But especially in the depositional areas where bioturbation plays a specifically important role for ecosystem functioning, bioturbation potential declined until 2099, which might affect the biochemical cycling in sediments of some areas of the southern North Sea.

Characterising epibenthic diversity and physical drivers in unconsolidated marine habitats of Algoa Bay, South Africa

Unconsolidated marine sediment habitats spatially make up the majority of global ocean seabed, yet benthic faunal patterns and their abiotic drivers remain poorly understood. Benthic research in Algoa Bay, on the south coast of South Africa, has largely focused on rocky reefs, while the dominant unconsolidated sediment habitats have been poorly studied. This study describes epibenthic assemblages associated with unconsolidated sediment in Algoa Bay, at between 30 and 100 m depth, and investigates the relationship between biotic patterns and physical drivers. Epibenthic abundance data were quantified from benthic imagery and tested against the long-term means and coefficients of variation of 12 abiotic factors, including depth, mean grain size and bottom temperature. Multivariate analyses revealed two statistically distinct epibenthic communities. This pattern was largely explained by depth, mean grain size, mean bottom temperature and mean current speed (cumulative variation of 52.49%). To a lesser extent, the long-term variability of bottom temperature, current speed and dissolved oxygen also influenced the community (cumulative variation of 34.44%). Visual classification of the substrates indicated that a mixed substrate type (i.e. sand and a low percentage of rock) significantly influences the benthic community. The findings suggest that a combination of depth and substrate type are largely responsible for the epibenthic assemblages observed.

Oxygen Isotope Equilibrium of the Shallow-Water Benthic Foraminifer Hanzawaia nipponica Asano in Tosa Bay, Southwest Japan

Oxygen isotopic compositions (δ18O) of benthic foraminifer tests are widely used for reconstructing paleoceanographic changes, such as global ice volumes during glacial–interglacial cycles. Although deep-sea benthic foraminifers have been well characterized and are considered reliable indicators, little attention has been paid to the geochemistry of shallow-water benthic foraminifers. In this study we evaluated δ18O in the shallow-water benthic foraminifer Hanzawaia nipponica Asano, which lives in surface sediments on continental shelves and upper slopes under the influence of two warm currents, the Kuroshio and Tsushima currents, in the East China Sea, northwest Pacific, and southwestern Japan Sea. To evaluate oxygen isotope equilibrium, we analyzed δ18O of H. nipponica and ambient seawater on the continental shelf in Tosa Bay, southwest Japan. Seawater δ18O and salinity in Tosa Bay are similar to those of surface and subsurface waters in the Kuroshio region in the Okinawa Trough and the northwest Pacific. Vertical profiles of seawater δ18O show no variation with water depth (0–200 m) in Tosa Bay. However, tests of living H. nipponica (as determined by staining with Rose Bengal) and fossil (non-stained) H. nipponica, picked from samples of the top centimeter of seafloor sediment, yielded carbonate δ18O values that clearly increase with water depth, suggesting a temperature-dependent relationship. A comparison of carbonate δ18O values in living H. nipponica and those predicted on the basis of seawater δ18O and annual mean bottom temperature shows that H. nipponica tests are in oxygen isotopic equilibrium with ambient seawater. We determined the linear equations of δ18O–temperature relationship, and the slope of −5.26 (0.19‰°C−1) for living and −4.50 (0.22‰°C−1) for the fossil H. nipponica, respectively. The carbon isotopic compositions (δ13C) of H. nipponica also closely match seawater δ13C. Thus, we propose that the carbonate δ18O and δ13C of H. nipponica are useful proxies to reconstruct shallow-water paleoenvironmental changes in the northwest Pacific and its marginal seas.

Variation of Isoprenoid GDGTs in the Stratified Marine Water Column: Implications for GDGT-Based TEX86 Paleothermometry

Isoprenoid glycerol dialkyl glycerol tetraethers (isoGDGTs) derived from archaea are lipid biomarkers that exhibit high sensitivity to changes in water temperature, leading to the widespread application of the isoGDGT-based tetraether index of 86 carbon atoms (TEX86) in surface seawater temperature (SST) reconstruction. However, there remain some uncertainties regarding the robustness of TEX86 under changing water conditions (e.g., variations in water depth, oxygen and pH). Here, we analyzed isoGDGTs in suspended particles at different depths of the East China Sea (ECS) during summer 2020, aiming to constrain the applicability of the TEX86 proxy in coastal waters. Our data showed that the isoGDGTs were mainly derived from planktonic Thaumarchaeota, as revealed by the low ratio of GDGT-0/crenarchaeol (<0.5). The vertical distribution of isoGDGT concentration depicted a downward increase from the surface to the bottom. This observation was likely shaped by Thaumarchaeota, which regulate the extent of ammonia oxidation based on the availability of ammonium. The occurrence of maximal isoGDGT concentrations in the bottom layer suggests that the isoGDGTs in sediments are mainly controlled by bottom archaeal production rather than surface archaeal production. By reanalyzing the published isoGDGT data of surface sediments in the ECS inner shelf, we found that the sedimentary TEX86 relates much better to the annual mean bottom seawater temperature (BST) than to the annual mean SST, indicating that sedimentary TEX86 is more inclined to be a proxy for the BST in the shallow ECS. In addition, the positive bias of TEX86 driven by low dissolved oxygen and low pH was observed under the pycnocline, indicating that the application of TEX86 to reconstruct seawater temperature should be carefully appraised in coastal environments with strong water column stratification.

Mean and Seasonal Circulation of the Eastern Chukchi Sea From Moored Timeseries in 2013–2014

AbstractFrom late‐summer 2013 to late‐summer 2014, a total of 20 moorings were maintained on the eastern Chukchi Sea shelf as part of five independent field programs. This provided the opportunity to analyze an extensive set of timeseries to obtain a broad view of the mean and seasonally varying hydrography and circulation over the course of the year. Year‐long mean bottom temperatures reflected the presence of the strong coastal circulation pathway, while mean bottom salinities were influenced by polynya/lead activity along the coast. The timing of the warm water appearance in spring/summer is linked to advection along the various flow pathways. The timing of the cold water appearance in fall/winter was not reflective of advection nor related to the time of freeze‐up. Near the latitude of Barrow Canyon, the cold water was accompanied by freshening. A one‐dimensional mixed‐layer model demonstrates that wind mixing, due to synoptic storms, overturns the water column resulting in the appearance of the cold water. The loitering pack ice in the region, together with warm southerly winds, melted ice and provided an intermittent source of fresh water that was mixed to depth according to the model. Farther north, the ambient stratification prohibits wind‐driven overturning, hence the cold water arrives from the south. The circulation during the warm and cold months of the year is different in both strength and pattern. Our study highlights the multitude of factors involved in setting the seasonal cycle of hydrography and circulation on the Chukchi shelf.

Temperature Variability of the Baltic Sea Since 1850 and Attribution to Atmospheric Forcing Variables

AbstractThe Baltic Sea is highly impacted by global warming and other anthropogenic changes and is one of the fastest‐warming marginal seas in the world. To detect trends in water temperature and to attribute them to atmospheric parameters, the results of two different ocean circulation models driven by reconstructed atmospheric forcing fields for the period 1850–2008 were analyzed. The model simulations were analyzed at temporal and spatial scales from seasonal to centennial and from intrabasin to basin, respectively. The strongest 150‐year trends were found in the annual mean bottom temperature of the Bornholm Deep (0.15 K/decade) and in summer mean sea surface temperature (SST) in Bothnian Bay (0.09–0.12 K/decade). A comparison of the time periods 1856–2005 and 1978–2007 revealed that the SST trends strengthened tenfold. An attribution analysis showed that most of the SST variability could be explained by the surface air temperature (i.e., sensible heat flux) and the latent heat flux. Wind parallel to the coast and cloudiness additionally explained SST variability in the coastal zone affected by the variations in upwelling and in offshore areas affected by the variations in solar radiation, respectively. In contrast, the high variability in stratification caused by freshwater and saltwater inflows does not impact the long‐term variability in the SST averaged over the Baltic Sea. The strongest SST trends since the 1980s can be explained by the superposition of global warming and a shift from the cold to the warm phase of the Atlantic Multidecadal Oscillation.

Future projections of temperature and mixing regime of European temperate lakes

Abstract. The physical response of lakes to climate warming is regionally variable and highly dependent on individual lake characteristics, making generalizations about their development difficult. To qualify the role of individual lake characteristics in their response to regionally homogeneous warming, we simulated temperature, ice cover, and mixing in four intensively studied German lakes of varying morphology and mixing regime with a one-dimensional lake model. We forced the model with an ensemble of 12 climate projections (RCP4.5) up to 2100. The lakes were projected to warm at 0.10–0.11 ∘C decade−1, which is 75 %–90 % of the projected air temperature trend. In simulations, surface temperatures increased strongly in winter and spring, but little or not at all in summer and autumn. Mean bottom temperatures were projected to increase in all lakes, with steeper trends in winter and in shallower lakes. Modelled ice thaw and summer stratification advanced by 1.5–2.2 and 1.4–1.8 days decade−1 respectively, whereas autumn turnover and winter freeze timing was less sensitive. The projected summer mixed-layer depth was unaffected by warming but sensitive to changes in water transparency. By mid-century, the frequency of ice and stratification-free winters was projected to increase by about 20 %, making ice cover rare and shifting the two deeper dimictic lakes to a predominantly monomictic regime. The polymictic lake was unlikely to become dimictic by the end of the century. A sensitivity analysis predicted that decreasing transparency would dampen the effect of warming on mean temperature but amplify its effect on stratification. However, this interaction was only predicted to occur in clear lakes, and not in the study lakes at their historical transparency. Not only lake morphology, but also mixing regime determines how heat is stored and ultimately how lakes respond to climate warming. Seasonal differences in climate warming rates are thus important and require more attention.

Putatively adaptive genetic variation in the giant California sea cucumber (Parastichopus californicus) as revealed by environmental association analysis of restriction-site associated DNA sequencing data.

Understanding the spatial scale of local adaptation and the factors associated with adaptive diversity are important objectives for ecology and evolutionary biology, and have significant implications for effective conservation and management of wild populations and natural resources. In this study, we used an environmental association analysis to identify important bioclimatic variables correlated with putatively adaptive genetic variation in a benthic marine invertebrate-the giant California sea cucumber (Parastichopus californicus)-spanning coastal British Columbia and southeastern Alaska. We used a redundancy analysis (RDA) with 3,699 single nucleotide polymorphisms (SNPs) obtained using RAD sequencing to detect candidate markers associated with 11 bioclimatic variables, including sea bottom and surface conditions, across two spatial scales (entire study area and within subregions). At the broadest scale, RDA revealed 59 candidate SNPs, 86% of which were associated with mean bottom temperature. Similar patterns were identified when population structure was accounted for. Additive polygenic scores, which provide a measure of the cumulative signal across all candidate SNPs, were strongly correlated with mean bottom temperature, consistent with spatially varying selection across a thermal gradient. At a finer scale, 23 candidate SNPs were detected, primarily associated with surface salinity (26%) and bottom current velocity (17%). Our findings suggest that environmental variables may play a role as drivers of spatially varying selection for P.californicus. These results provide context for future studies to evaluate the genetic basis of local adaptation in P.californicus and help inform the relevant scales and environmental variables for in situ field studies of putative adaptive variation in marine invertebrates.

Quantifying the influence of cold water intrusions in a shallow, coastal system across contrasting years: Green Bay, Lake Michigan

Abstract We present water column thermal structure for two climatically different years: 2012, which experienced abnormally warm spring and summer air temperatures preceded by a relatively low ice winter and 2013, which experienced cooler than average spring and average summer air temperatures and preceded by average ice conditions. Mean bottom water temperatures for the season and during cold water intrusions were significantly warmer in 2012 than 2013 leading to a significantly reduced stratified season in 2012. Cold water intrusions were driven into southern Green Bay by southerly winds while intrusions were terminated when winds switched to persistent northerly winds. 2012 observed a significant increase in northerly winds relative to 2013, decreasing cold water intrusion presence and duration but winds did not fully explain the difference in thermal conditions for southern Green Bay. These cold bottom waters drive stratification in polymictic southern Green Bay while dimictic waters were found to have significantly warmer bottom temperatures during 2012 and a deeper mixed layer. Our observations suggest that relatively shallow (

Thermal and Physical Investigations into Lake Deepening Processes on Spillway Lake, Ngozumpa Glacier, Nepal

This paper investigates physical processes in the four sub-basins of Ngozumpa glacier’s terminal Spillway Lake for the period 2012–2014 in order to characterize lake deepening and mass transfer processes. Quantifying the growth and deepening of this terminal lake is important given its close vicinity to Sherpa villages down-valley. To this end, the following are examined: annual, daily and hourly temperature variations in the water column, vertical turbidity variations and water level changes and map lake floor sediment properties and lake floor structure using open water side-scan sonar transects. Roughness and hardness maps from sonar returns reveal lake floor substrates ranging from mud, to rocky debris and, in places, bare ice. Heat conduction equations using annual lake bottom temperatures and sediment properties are used to calculate bottom ice melt rates (lake floor deepening) for 0.01 to 1-m debris thicknesses. In areas of rapid deepening, where low mean bottom temperatures prevail, thin debris cover or bare ice is present. This finding is consistent with previously reported localized regions of lake deepening and is useful in predicting future deepening.

Modelling climate change effects on benthos: Distributional shifts in the North Sea from 2001 to 2099

In the marine realm, climate change can affect a variety of physico-chemical properties with wide-ranging biological effects, but the knowledge of how climate change affects benthic distributions is limited and mainly restricted to coastal environments. To project the response of benthic species of a shelf sea (North Sea) to the expected climate change, the distributions of 75 marine benthic species were modelled and the spatial changes in distribution were projected for 2099 based on modelled bottom temperature and salinity changes using the IPCC scenario A1B. Mean bottom temperature was projected to increase between 0.15 and 5.4 °C, while mean bottom salinity was projected to moderately increase by 1.7. The spatial changes in species distribution were modelled with Maxent and the direction and extent of these changes were assessed. The results showed a latitudinal northward shift for 64% of the species (maximum 109 km; brittle star Ophiothrix fragilis) and a southward shift for 36% (maximum 101 km; hermit crab Pagurus prideaux and the associated cloak anemone Adamsia carciniopados; 105 km). The relatively low rates of distributional shifts compared to fish or plankton species were probably influenced by the regional topography. The environmental gradients in the central North Sea along the 50 m depth contour might act as a ‘barrier’, possibly resulting in a compression of distribution range and hampering further shifts to the north. For 49 species this resulted in a habitat loss up to 100%, while only 11 species could benefit from the warming in terms of habitat gain. Particularly the benthic communities of the southern North Sea, where the strongest temperature increase was projected, would be strongly affected by the distributional changes, since key species showed northward shifts and high rates of habitat loss, with potential ramifications for the functioning of the ecosystem.

Simulating and understanding effects of water level fluctuations on thermal regimes in Miyun Reservoir

ABSTRACTWater temperature dynamics in a reservoir are affected by its bathymetry, climatic conditions and hydrological processes. Miyun Reservoir in China is a large and deep reservoir that experienced a large water level decline in 1999–2004 due to low rainfall and relatively high water supply to Beijing. To study changes of stratification characteristics in Miyun Reservoir from 1998 to 2011, the one-dimensional year-round lake model MINLAKE2010 was modified by adding a new selective withdraw module and a reservoir hydrological model. Simulation results under three scenarios demonstrated that the new MINLAKE2012 model accurately predicted daily water levels and temperature dynamics during the water level fluctuation period. The water level decline led to 7.6 and 3.8°C increases in the maximum and mean bottom temperatures and about 29 days reduction in the stratification days. These simulation results provide an insight into the thermal evolution of Miyun Reservoir during the planned future water filling process.Editor D. Koutsoyiannis Associate editor M. Acreman

Native fish community structure and Indo-Pacific lionfish Pterois volitans densities along a depth-temperature gradient in Onslow Bay, North Carolina, USA

We quantified native fish densities along a depth-temperature gradient within a tem- perate-tropical marine transition zone (North Carolina continental shelf) to examine the role of depth and temperature in structuring these communities. We also examined the distribution of in- vasive lionfish (Pterois volitans, P. miles) to evaluate a laboratory-derived thermal minimum for lion- fish. We collected year-round continuous bottom water temperature data from 2000 to 2010 and sur- veyed lionfish (2004 to 2010), conspicuous fishes (2006 to 2010) and cryptic smaller-bodied fishes (2007 to 2010) at depths from 5 to 46 m using SCUBA. Bottom water temperatures were constant across the depth gradient during summer and increased from inshore to offshore during winter. The conspicuous fish community was structured by 3 depth zones, 5-14, 15-37 and 38-46 m, that corre- sponded with winter mean temperatures of 13.9, 17.9 and 20.9°C, respectively. The cryptic fish community was structured by 4 depth zones, 5-15, 18-24, 27-38.5 and 39.5-46 m, with correspon- ding winter mean bottom temperatures of 13.8, 15.6, 18.7 and 20.9°C. In contrast, summer tempera- tures were not important in structuring either the conspicuous or the cryptic fish community. Thus, fish communities in the spring/summer appear to be structured by the pattern of bottom water tem- perature experienced the previous winter, supporting previous studies that indicate winter mini- mum temperature is important for determining fish distribution and abundance in temperate marine ecosystems. In addition, the deeper fish communities were dominated by tropical species. Lionfish, a tropical species, was found in the highest densities from 38 to 46 m and present in loca- tions with a winter mean of 15.3°C and higher. Increasing temperatures could favor a potential ex- pansion of invasive lionfish and native tropical species into the nearshore waters on the North Car- olina shelf, resulting in unforeseen community structure and trophic disruptions.

Evidence for thermally mediated settlement in lobster larvae (Homarus americanus)

We examined the potential for bottom temperatures ≤12 °C to inhibit successful recruitment of planktonic lobster postlarvae to the benthos. In laboratory trials, postlarvae held at 11 °C exhibited higher mortality, slower development, and reduced size increase at molt relative to postlarvae held at 13 °C. We sampled at field sites within Machias Bay, Maine (mean bottom temperature 12.39 °C, 46.1 degree-days ≥12 °C) and at the mouth of the bay (mean bottom temperature 11.57 °C, 5.1 degree-days ≥12 °C), where temperature was influenced by the cold Eastern Maine Coastal Current (EMCC). We found significantly higher settlement at the warm inshore site but, the abundance of competent planktonic postlarvae was not significantly different between sites, indicating a disconnect between postlarval abundance and settlement. Regional sampling of newly settled lobsters revealed a pattern of higher settlement at inshore sites extending across a broader coastal region impacted by the EMCC. Our results suggest that small differences in water temperature may shape settlement patterns through either behavioral avoidance of colder settlement sites or elevated postsettlement mortality of postlarvae settling at colder sites.

Lake- and channel-bottom temperatures in the Mackenzie Delta, Northwest Territories1This article is one of a series of papers published in this CJES Special Issue on the theme of Fundamental and applied research on permafrost in Canada.2Polar Continental Shelf Project Contribution 03511.

Temperature loggers were placed in 17 lakes and 13 channels throughout the Mackenzie Delta to determine the annual mean bottom temperature ([Formula: see text]) and its spatial and temporal variation for June 2009 – June 2010. The lakes were classified as perched or connected, depending on the duration of their connection to the channel hydrologic system. Average [Formula: see text] values for nine perched lakes, five channels, and eight connected lakes distributed throughout the Mackenzie Delta were 5.5, 4.6, and 3.4 °C, respectively. The range of [Formula: see text] among all instrumented water bodies in the Delta was 4.0 °C. Over the year, bottom temperatures ranged from >20 °C in midsummer to –5 °C in midwinter, with relative stability between freeze-up in mid-October and breakup at the beginning of June. Channel, perched, and connected lake [Formula: see text], and mean annual near-surface ground temperatures of –4 °C in alluvial sedge wetlands and –2.25 °C in forest, were used to estimate that about 60% of Delta lakes and nearly the entire channel network maintain through-taliks.

Phase Shift in an Estuarine Finfish Community Associated with Warming Temperatures

AbstractFinfish abundance indices, produced from seasonal trawl survey data collected in Long Island Sound, were examined for changes in community composition related to the dynamics of water temperature from 1984 to 2008. In general, seasonal mean catch of species identified a priori as cold adapted significantly decreased while warm‐adapted and subtropical species significantly increased over the time series. Bottom water temperature also significantly increased. As a group, annual abundance of cold‐adapted species exhibited significant negative correlation with mean bottom water temperatures while warm‐adapted species, but not subtropical species, exhibited significant positive correlation. Multivariate analyses identified a shift in community structure producing two primary year‐groupings. Spring groupings were clearly delineated as 1984–1998 (cold period) and 1999–2008 (warm period). Autumn groupings were temporally discontinuous in the 1990s with group membership shifting between cold and warm periods, although the distal ends of the time series were clearly divided. These patterns aligned with deviations from the 1984 to 2008 mean bottom water temperature, indicating that this estuary is experiencing a relatively rapid shift consistent with a response to climate warming. The more distinct delineation of community structure in spring suggests that the lack of advantageous spring conditions was a more important factor in the decline of cold‐adapted species than increasingly stressful conditions in autumn.Received August 30, 2011; accepted April 7, 2012

Environmental influence on the bottom and near-bottom megafauna communities of the Dogger Bank: a long-term survey

This paper deals with climate-driven changes of the species composition of the bottom and near-bottom megafauna of the Dogger Bank (central North Sea), which was sampled each summer with a 2-m beam trawl on a yearly basis since 1991. The station grid consists of 37 stations, covering an area of approximately 17.000 km². A selection of commoner species is analysed and correlated with temperature data gained during the research period. Temperatures are derived from our own measurements, combined with CTD data from the International Council for the Exploration of the Sea. The results show a decrease in biodiversity and a clear regime shift around the beginning of the 21st century, combined with rising mean bottom temperatures. In addition, details are given about the Dogger Bank hydrography and the climate sensitivity and abundance of the main species caught with the beam trawl. Our long-term study reveals the changes in the community structure of the megafauna of the Dogger Bank over a period of almost two decades. It suggests a link between changes in species composition/abundance and changes in the environment, especially the marine climate.

Tanaidacea (Crustacea, Peracarida) of the North-east Atlantic: the Agathotanaidae of the AFEN, BIOFAR and BIOICE projects, with a description of a new species of Paragathotanais Lang

The tanaidacean fauna of the Iceland-Faroes-Shetlands sector of the North-east Atlantic was studied using material from the BIOFAR, BIOICE and AFEN surveys. Seven agathotanaid species were recorded from the genera Agathotanais, Paragathotanais and Paranarthrura, a total comparable to those from a similar bathymetric range in the Rockall-Biscay area and the Gulf of Mexico. A new species of Paragathotanais is described. All records of this family were from benthic stations with a mean bottom temperature of >= 2 degrees C, with none from the 'cold-water' region north of the Iceland-Shetlands ridge complex. An analysis of North-east Atlantic agathotanaid sex-ratios shows that these are not highly skewed in favour of females and are consistent with the status of the males as relatively non-dimorphic and long-lived entities.

Reanalysis of long-term surveys on the ecology and biology of mud skate (Rhinoraja taranetzi Dolganov, 1985) in the northwestern Pacific (1993-2002)

Summary Based on data sampled in 1992–2002, the occurrence, spatial distribution, bathymetry, bottom temperatures preferences, size composition, feeding, and some features of reproductive biology of mud skate Rhinoraja taranetzi in the Pacific waters off the northern Kuril Islands and southeastern Kamchatka are considered. Throughout the year, the mud skate was most abundant in the central part of the study area, from the coast of Onekotan Island to the southern tip of Kamchatka peninsula. The proportion of this species in bottom trawl catches in different seasons has changed slightly. However, maximum catch occurred in September–December. In April–May mud skates occupied shallower depths (mean 230–270 m), moving deeper in the summer period (mean 340–390 m). In December–March the skate occurred at lower bottom temperatures (mean 0.8–1.6°C) whereas the rest of the year it inhabited warmer waters with mean bottom temperatures of 2.5–3.1°C. Throughout the year decreasing body weight with depth was observed, indicating that adult and juvenile mud skates inhabit different depths. Total length of mud skates in catches ranged from 17 to 70 cm with a mean of 51.71 cm. Relation between total length (TL, cm) and body weight (W, g) was: W = 0.0029TL3.1614 (r2 = 0.978). Males were more abundant among small skates ( 30 cm) comprising about 70% in 60–70 cm length class. Female mud skates were longer and heavier than males (mean length 56.9 vs 51.2 cm and mean weight 1206 vs 807 g, respectively). This species is considered to be benthophagous, consuming mostly amphipods (34.9% by weight), polychaete worms (27.6%), decapod crustaceans (12.7%), and fishery discards (13.9%). Small skates (20–40 cm) fed mostly on amphipods (85.4%); medium-sized (40–60 cm) ate amphipods (40.2%), polychaetes (29.1%) and decapods (19.3%); the largest individuals (>60 cm) consumed fishery offal (27.9%) and less amphipods (26.6%) and polychaetes (27.7%). Preliminary data on the maturation of the species in the western Bering Sea showed that males and females become mature at lengths above 61 cm TL.