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Body size is related to an extensive number of species traits and ecological processes and has therefore been suggested as an effective metric to assess community changes and ecosystem's state. However, the applicability of body size as an ecological indicator in benthic environments has been hindered by the poor knowledge of the factors influencing the size spectra of organisms. By applying biological trait analysis (BTA) and generalized linear models to a species dataset collected in the German Wadden Sea (53°41/14' N, 7°14/19' E) between 1999 and 2012, we show that the size structure of the macrobenthic community changes predictably along environmental gradients. Specifically, body size increases with increasing current-induced shear stress and sediment organic matter content. In addition, the presence of oyster-mussel reefs in one of the sampling stations enhanced the survival of species belonging to the smallest size categories in habitats with high hydrodynamic energy. This was probably due to the local sheltering effects, which together with biodeposition also increased organic matter in the sediment, likely favoring large deposit feeders as well. Our results suggest that body size can be a useful trait for estimating effects of anthropogenic stressors, such as organic enrichment or alteration of hydrodynamic regime and could therefore be effectively included in current monitoring programs of intertidal macrobenthic communities., Introduction Body size is a key trait and one of the most studied attributes of organisms in biology and ecology. Body size affects biological processes at all levels of organization, [...]

Lyngbya wollei is a toxin-producing cyanobacterium, forming mats of filaments that proliferate in rivers, lakes, and springs in North America. We determined its distribution over a 250 km stretch of the St. Lawrence River (SLR; Quebec, Canada) to elaborate predictive models of its presence and biomass based on chemical and physical characteristics. A 2008 survey revealed L. wollei was generally found downstream of the inflow of small tributaries draining farmlands. As enriched waters flowed slowly through dense submerged vegetation, dissolved inorganic nitrogen (DIN) concentration dropped but dissolved organic carbon (DOC) and total dissolved phosphorus (TDP) remained high, leading to a low DIN:TDP ratio. Models identified DOC (positive effect), TP (negative effect), and DIN:TDP (negative effect) as the most important variables explaining L. wollei distribution. The risk of L. wollei occurrence in the SLR was correctly forecasted in 72%-92% of all cases with an independent data set. Proliferation of L. wollei, a potentially heterotrophic, diazotrophic cyanobacterium, is favoured by organic enrichment and imbalance of DIN:TDP ratio. Its dominance coincided with low macrophyte biomass, yielding a simplified, less productive ecosystem. Lyngbya wollei est une cyanobacterie qui produit des toxines et forme des tapis de filaments qui proliferent dans des rivieres, lacs et sources d'Amerique du Nord. Nous avons etabli sa repartition dans un troncon de 250 km du fleuve Saint-Laurent (SLR; Quebec, Canada) afin d'elaborer des modeles predictifs de sa presence et biomasse a la lumiere de parametres chimiques et physiques. Une etude realisee en 2008 a revele que L. wollei etait generalement presente en aval de la confluence de petits tributaires qui irriguent des terres agricoles. L' ecoulement lent d' eaux enrichies a travers une vegetation submergee dense se traduisait par une diminution de la concentration d'azote inorganique dissous (DIN), alors que les concentrations de carbone organique dissous (DOC) et de phosphore total dissous (TDP) demeuraient elevees, produisant un rapport DIN :TDP faible. Selon les modeles, DOC (effet positif), TP (effet negatif) et DIN :TDP (effet negatif) sont les variables les plus importantes pour expliquer la repartition de L. wollei. La probabilite que L. wollei soit presente dans le SLR a ete predite avec exactitude dans de 72 % a 92 % des cas pour lesquels un ensemble de donnees independant etait disponible. La proliferation de L. wollei, une cyanobacterie diazotrophique potentiellement heterotrophique, est favorisee par l' enrichissement organique et un desequilibre du rapport DIN :TDP. Sa predominance coincide avec une faible biomasse de macrophytes, produisant un ecosysteme simplifie de productivite reduite. [Traduit par la Redaction], Introduction The increased occurrence of harmful algal blooms (HABs) worldwide, due mainly to human activity, has important repercussions on the aquatic ecosystems (Hallegraeff 1993; Carpenter et al. 1998) through proliferations [...]

Controversy exists about the historic shift of primary producer community structure (PPCS) in Lake Apopka, a shallow, 125-[km.sup.2] lake in central Florida, U.S.A. The controversial questions are: was a lake-wide shift from macrophyte to phytoplankton dominance triggered by a 1947 hurricane or tornadoes spawned by the hurricane within a few weeks or months, or was the shift forced by progressive cultural eutrophication over several years? In 1947, fringing wetlands (35 [km.sup.2]) were being diked and drained for agricultural purposes changing their function from nutrient sinks to nutrient point sources to the lake. We examined whether anthropogenic darkening of the water column induced the PPCS shift during a 0.6-m lake-stage rise. Darkening was defined as lake-bottom photosynthetically available radiation (PAR) [less than or equal to] 1.0% of incident PAR. We simulated darkening from changes in the light extinction coefficient ([[Kappa].sub.d]) due to water color, chlorophyll a, and rising lake stage. Simulations predicted that darkening was restricted to 80% of the lake deeper than 2.16 m, a finding consistent with persistence of shallow-water submersed macrophytes after 1947. Anthropogenic wetland draining increased water color, lake stage, and phytoplankton blooms stimulated by phosphorus enrichment, causing a progressive shift to lake-wide phytoplankton dominance over at least several years. The relationship between the 1947 hurricane and the PPCS shift was not causal, but only a temporal coincidence. Our darkening model can be applied to other systems with known bathymetry to predict submersed aquatic vegetation (SAV) coverage from SAV light requirements and water-column light attenuation. doi: 10.4319/lo.2010.55.3.1201

Early theories of species diversity proposed that communities at equilibrium are saturated with species. However, experiments in plant communities suggest that many communities are unsaturated and species richness can be increased by adding propagules of new species. We experimentally tested for community saturation and measured the effects of propagule supply on community structure in a benthic marine system. We manipulated propagule supply (arrival of individuals of numerous species) of mobile grazers in experimental mesocosms over multiple generations and, unlike previous tests, we examined the cascading effects of propagule supply on prey (macroalgae) biomass. We found little evidence for saturation, despite the absence of processes such as disturbance and predation that are thought to alleviate saturation in nature. Increasing propagule supply increased the total number of species and made rare species more abundant. Perhaps surprisingly, given the strong effect of propagule supply on species richness, supply-related changes in body size and composition suggest that competitive interactions remained important. Grazer supply also had strong cascading effects on primary production, possibly because of dietary complementarity modified by territorial behavior. Our results indicate that propagule supply can directly influence the diversity and composition of communities of mobile animals. Furthermore, the supply of consumer propagules can have strong indirect effects on prey and fundamental ecosystem properties. biodiversity | propagule limitation | saturation

A transecting microprofiler documented a pronounced small-scale variation in the benthic [O.sub.2] concentration at 1450-m water depth (Sagami Bay, Japan). Data obtained during a single deployment revealed that within a sediment area of 190 [cm.sup.2] the [O.sub.2] penetration depth varied from 2.6 mm to 17.8 mm (average; 6.6 [+ or -] 2.5 mm) and the diffusive [O.sub.2] uptake, calculated from the vertical concentration gradient within the diffusive boundary layer, ranged from 0.6 mmol [m.sup.-2] [d.sup.-1] to 3.9 mmol [m.sup.-2] [d.sup.-1] (average; 1.8 [+ or -] 0.7 mmol [m.sup.-2] [d.sup.-1,] n = 129). However, correction for microtopography and horizontal diffusion increased the average diffusive [O.sub.2] uptake by a factor of 1.26 [+ or -] 0.06. Detailed 2D calculations on the volume-specific [O.sub.2] consumption exhibited high variability. The oxic zone was characterized by a mosaic of sediment parcels with markedly different activity levels. Millimeter- to centimeter-sized 'hot spots' with [O.sub.2] consumption rates up to 10 pmol [cm.sup.-3] [s.sup.-1] were separated by parcels of low or insignificant [O.sub.2] consumption. The variation in aerobic activity must reflect an inhomogeneous distribution of electron donors and suggests that the turnover of material within the oxic zone to a large extent was confined to hot spots. The in situ benthic [O.sub.2] uptakes, measured during four cruises, reflected a seasonal signal overlying the observed small-scale variability. The annual benthic mineralization balanced -50% of the estimated pelagic production. However, the central bay is characterized by a significant downslope sediment transport, and mass balance estimates indicate 90% retention of the total organic material reaching the bottom of the central bay.

Freshwater crayfish are successful invaders in many ecosystems and as cryptic nocturnal species display a potential niche overlap with benthic nocturnal fish. In this study, we tested the effects of the invasive spinycheek crayfish (Orconectes limosus) on native young-of-the-year (YOY) and adult burbot (Lota lota) in Lake Constance. Using mesocosm experiments, we tested if shelter preferences of YOY and adult burbot and crayfish changed between single and mixed species treatments. To further study the role of crayfish as a stressor for burbot, we monitored the nocturnal behaviour of the species in mesocosms using passive integrated transponder (PIT) tag technology and subsequently determined the plasma cortisol levels in burbot after single and mixed species treatments. Spinycheek crayfish successfully repelled YOY burbot from their preferred daytime shelters into alternative, previously unselected shelters. Crayfish also affected the nocturnal behaviour of YOY burbot by eliciting avoidance behaviour and caused an increase in the plasma cortisol levels. While adult burbot did not display any changes between single and mixed species treatments, our results indicate negative effects of spinycheek crayfish on YOY burbot. We conclude that the frequently dense, invasive crayfish populations in lakes may negatively influence local benthic fish populations via their YOY cohorts. Les ecrevisses d'eau douce ont envahi avec succes de nombreux ecosystemes et, en tant qu'especes nocturnes cryptiques, elles peuvent presenter un chevauchement de niche avec les poissons benthiques nocturnes. Dans notre travail, nous evaluons les effets de l'ecrevisse americaine (Orconectes limosus) envahissante sur les jeunes de l'annee (YOY) et les adultes de la lotte (Lota Iota) indigene du lac de Constance. Des experiences en mesocosme nous ont servi a tester si les choix d'abris des lottes YOY et adultes et des ecrevisses changent dans des conditions experimentales d'isolement ou de cohabitation. Pour etudier plus en detail le role des ecrevisses comme facteurs de stress pour les lottes, nous avons suivi le comportement nocturne des especes dans les mesocosmes a l'aide d'une technologie d'etiquettes PIT (a transpondeurs integres passifs); nous avons ensuite dose les teneurs de cortisol plasmatique chez la lotte apres des conditions experimentales d'isolement et de cohabitation. Les ecrevisses americaines eliminent avec succes les YOY de leurs abris preferes de jour et les releguent dans des abris de rechange, non choisis auparavant. Les ecrevisses affectent aussi le comportement nocturne des lottes YOY en declenchant une reaction d'evitement et causent une augmentation des concentrations de cortisol plasmatique. Bien que les lottes adultes ne subissent aucun changement dans les conditions experimentales d'isolement et de cohabitation, nos resultats indiquent que les ecrevisses americaines ont des effets negatifs sur les lottes YOY. En conclusion, les populations souvent denses d'ecrevisses envahissantes dans les lacs peuvent influencer negativement les populations locales de poissons benthiques en affectant les cohortes de YOY. [Traduit par la Redaction], Introduction Crayfish are among the most commonly introduced invasive freshwater species and can have complex effects on aquatic ecosystems (Nystrom et al. 1996; Lodge et al. 2000; Bubb et al. [...]

Given the presumed importance of benthic and epibenthic estuarine habitats in Chinook salmon (Oncorhynchus tshawytscha) smolt growth and survival, resource managers would be well served by an improved understanding of how smolts use such habitats. A cabled acoustic positioning system was used to precisely track ( Etant donne l'importance presumee des habitats estuariens benthiques et epibenthiques pour la croissance et la survie des saumoneaux du saumon chinook (Oncorhynchus tshawytscha), une meilleure comprehension de l'utilisation de ces habitats par les saumoneaux serait utile aux gestionnaires des ressources. Nous avons utilise un systeme de positionnement acoustique avec cables pour suivre avec precision (resolution de [Traduit par la Redaction], Introduction Estuarine residence is a critical life history stage for most salmonids. The interface between fresh and salt water aids in the physiological changes of smoltification (Simenstad et al. 1982; [...]

Abstract: Survey indices play an important role in stock assessments as they provide information on stock trends. In certain cases, large interannual variations have been observed that are unlikely to [...]

Abstract: An in situ experiment was done in July 2004 to test and compare the influence of suspended bivalve cultures (1- and 2-year-old blue mussels (Mytilus edulis) and sea scallops [...]

In situ measurements in a shallow water sediment were performed using three different modules--a microprofiling unit, a transparent benthic chamber, and a planar optode periscope. The combined data set revealed an extremely patchy and variable benthic [O.sub.2] distribution primarily due to temporal variations in fauna activity and photosynthesis. A distinct diel pattern in the fauna activity, dominated by Hediste diversicolor, resulted in strongly elevated [O.sub.2] uptake rates of ~5.3 mmol [m.sup.2] [h.sup.-1] at the onset of darkness. The activity gradually diminished during the night, and the [O.sub.2] uptake decreased to less than half the maximum rate just before sunrise. The volume of oxic sediment around burrow structures was influenced by changing environmental conditions (benthic photosynthesis and fauna activity) but grossly exceeded that below the primary sediment surface. The volume specific respiration rate around burrows was more than seven times higher than the equivalent value at the sediment surface. A budget of the [O.sub.2] consumption revealed that the [O.sub.2] uptake through the burrow walls just after sunset accounted for the major part of the total [O.sub.2] uptake on a diel scale. The study demonstrates that light-driven variations in fauna activity can have great effects on the total benthic [O.sub.2] consumption rate with large implications for estimated benthic mineralization rates.