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Deep‐sea benthic communities are strongly controlled by the quantity and quality of organic matter sinking from the ocean surface. The interaction between benthic fauna and seafloor sediments mainly occurs through bioturbation that modifies substrate properties (e.g., geochemical profiles). The intensity of the bioturbation has long been linked with organic matter and measured as a diffusive process by considering the vertical particle reworking (endobenthic bioturbation), disregarding the seafloor horizontal mixing (epibenthic bioturbation). Here, a novel approach to quantify horizontal mixing is presented: Seafloor Bioturbation Intensity (SBI). SBI calculations were based on seafloor image datasets from eight stations that reflected different environmental conditions in the north‐western Pacific (e.g., chlorophyll a, silicate). To calculate SBI, we characterized the area occupied by all different types of traces (i.e., lebensspuren) related to epibenthic bioturbation, trace makers, and their ingested sediment thickness. Our results showed a weak negative correlation between organic matter and SBI. This relationship contrast with the traditionally held view on vertical bioturbation intensity, where a dominant positive correlation is expected. It is demonstrated that lebensspuren morphotypes contributed differently to SBI. Not all morphotypes—and, by extension, their corresponding trace makers—are equally controlled by the same environmental factors. This investigation does not dismiss the importance of organic matter content, but emphasizes the importance of other environmental variables that need to be considered when determining the long‐term relation between epibenthic fauna and bioturbation intensity. Finally, we emphasize the importance of characterizing horizontal bioturbation for approaching global biogeochemical cycles and conservational strategies. [ABSTRACT FROM AUTHOR]

Human pressures are changing ocean environments, such as a shift from fish‐ to squid‐dominated ecosystems in overfished, poorly oxygenated environments. After death, carcasses of upper ocean fauna sink to the seafloor where they provide food for demersal scavengers. It is unclear how shifts in carcass type impact abyssal scavengers. We performed baited benthic camera lander deployments in the Cabo Verde Abyssal Basin to test how a shift from fish‐ to squid‐dominated carrion could modify abyssal scavenger ecology. At the fish bait, peak scavenger abundance was greater and occurred later for the majority of observed fauna. However, removal rates of squid bait were up to 10‐fold greater, and a significantly different community composition developed, favoring faster organisms with lower chemosensory thresholds. At the fish bait, slower organisms were less disadvantaged as the bait persisted for longer periods allowing the development of a more complex community and dense amphipod aggregations. The rapid squid consumption indicates that the accumulation of this type of food fall at the seafloor may not occur, preventing scientific observations necessary to estimate the importance of squid carrion to the biological C pump and deep‐sea food webs. As such, the flux of squid carrion to the seafloor is likely greater than currently recognized in this part of the Atlantic. The differences observed between bait types indicate how future changes in upper ocean ecosystems may impact abyssal scavengers and their ecosystem functions, including controlling seafloor biomass, regulating the behavior of benthic fauna, and contributing to nutrient cycling and energy transfer. [ABSTRACT FROM AUTHOR]

A rapidly warming Arctic Ocean and associated sea‐ice decline is resulting in changing sea‐ice protist communities, affecting productivity of under‐ice, pelagic, and benthic fauna. Quantifying such effects is hampered by a lack of biomarkers suitable for tracing specific basal resources (primary producers and microorganisms) through food webs. We investigate the potential of δ13C values of essential amino acids (EAAs) (δ13CEAA values) to estimate the proportional use of diverse basal resources by organisms from the under‐ice (Apherusa glacialis), pelagic (Calanus hyperboreus) and benthic habitats (sponges, sea cucumber), and the cryo‐pelagic fish Boreogadus saida. Two approaches were used: baseline δ13CEAA values, that is, the basal resource specific δ13CEAA values, and δ13CEAA fingerprints, or mean‐centred baseline δ13CEAA values. Substantial use of sub‐ice algae Melosira arctica by all studied organisms suggests that its role within Arctic food webs is greater than previously recognized. In addition, δ13CEAA fingerprints from algae‐associated bacteria were clearly traced to the sponges, with an individually variable kelp use by sea cucumbers. Although mean‐centred δ13CEAA values in A. glacialis, C. hyperboreus, and B. saida tissues were aligned with microalgae resources, they were not fully represented by the filtered pelagic‐ and sea‐ice particulate organic matter constituting the spring diatom‐dominated algal community. Under‐ice and pelagic microalgae use could only be differentiated with baseline δ13CEAA values as similar microalgae clades occur in both habitats. We suggest that δ13CEAA fingerprints combined with microalgae baseline δ13CEAA values are an insightful tool to assess the effect of ongoing changes in Arctic basal resources on their use by organisms. [ABSTRACT FROM AUTHOR]

For decades, we monitored numbers and weights of the macrozoobenthos in a vast tidal‐flat area in the Dutch Wadden Sea. We used data collected since 1992 to estimate annual secondary production. Data on chlorophyll concentrations and primary production were available for a nearby tidal inlet, showing rapid increases in the late 1970s and gradual declines since the late 1980s. The benthos responded with a doubling of biomass around 1980 and gradual declines of summer biomass, annual production as well as seasonal biomass gain for the 1992–2019 de‐eutrophication period. In nearly all years, production of bivalves (on average 25.5 gAFDM m−2 yr−1) accounted for more than half of the total zoobenthic production (averaging 42.7 gAFDM m−2 yr−1). Production values for individual years were not correlated with chlorophyll concentrations or primary production of that year, but did show a significantly positive relationship with bivalve recruitment success in the preceding year. As recruitment was governed by predation pressure on early bivalve bottom stages, it is a top‐down process. Bottom‐up processes were expressed in the gradually declining long‐term trend of bivalve growth rates and secondary production during the de‐eutrophication period and also in a few years when bivalve numbers were so high that growth rates were reduced by food competition. In by far most years, numbers of bottom animals were too low to fully exploit the carrying capacity of the system and production increased linearly with preceding recruitment. [ABSTRACT FROM AUTHOR]

In coastal systems, planktonic and benthic silicifiers compete for the pool of dissolved silicon, a nutrient required to make their skeletons. The contribution of planktonic diatoms to the silicon cycle in coastal systems is often well characterized, while that of benthic silicifiers such as sponges has rarely been quantified. Herein, silicon fluxes and stocks are quantified for the sponge fauna in the benthic communities of the Bay of Brest (France). A total of 45 siliceous sponge species living in the Bay account for a silicon standing stock of 1215 tons, while that of diatoms is only 27 tons. The silicon reservoir accumulated as sponge skeletons in the surface sediments of the Bay rises to 1775 tons, while that of diatom skeletons is only 248 tons. These comparatively large stocks of sponge silicon were estimated to cycle two orders of magnitude slower than the diatom stocks. Sponge silicon stocks need years to decades to be renewed, while diatom turnover lasts only days. Although the sponge monitoring over the last 6 yr indicates no major changes of the sponge stocks, our results do not allow us to conclude if the silicon sponge budget of the Bay is at steady state, and potential scenarios are discussed. The findings buttress the idea that sponges and diatoms play contrasting roles in the marine silicon cycle. The budgets of these two major silicon users need to be integrated and their connections revealed, if we aim to improve our understanding of the silicon cycling in coastal ecosystems. [ABSTRACT FROM AUTHOR]

The seasonal and interannual variability of feeding in 15 species of benthic marine suspension feeder was studied over 8 yr at Ryder Bay, Antarctica. Feeding was strongly seasonal in bryozoans, gorgonians, polychaetes, and dendrochirote holothurians. The winter non‐feeding period was longest in the holothurians and shortest in bryozoans. Bryozoans started feeding in late winter at very low chlorophyll concentrations, often when surface fast‐ice was still present. In hydroids and actinians, feeding tentacles were deployed continuously throughout the year, though hydroid feeding intensity declined slightly in late winter. Water column phytoplankton biomass was strongly seasonal with marked interannual variability in the timing and intensity of the bloom, driven principally by ice dynamics. Correlation across years between the start of feeding and the development of the bloom was poor, and in seasons when a dense spring bloom of benthic filamentous microalgae developed, the start of feeding in many benthic species was delayed. This study indicates that feeding in benthic marine suspension feeders in Antarctica is influenced by factors additional to the seasonal availability of food in the water column. [ABSTRACT FROM AUTHOR]

Benthic fauna plays an important role in mediating biogeochemical cycles in coastal areas by storing carbon (C), nitrogen (N), and phosphorus (P) in their body tissues at theoretically homeostatic rates. To maintain homeostasis, the benthic consumers need to be in balance with their resource supply or alter their stoichiometric traits in response to environmental change. However, we lack an understanding regarding the potential variation in the C : N : P content ratios of benthic consumers, especially in marine coastal areas where stoichiometric shifts in macrofauna could have strong effects on sediment carbon and nutrient cycling. By monitoring two sites over a year, we quantified the magnitude and temporal stability of benthic faunal carbon and nutrient pools in coastal soft‐sediment habitats. Our results show that benthic fauna is not strictly homeostatic, but instead expresses temporal variation in C : N : P content. These aquatic consumers undergo ontogenetic changes in diet and morphology, which alter their stoichiometric characteristics. In addition, the faunal C : N : P ratios showed strong seasonal variation at both species and community level, and our results suggest that the stoichiometric traits of benthic consumers shift in response to food sources and environmental conditions. The ability to adapt to varying stoichiometric conditions is essential in face of the growing C : N : P imbalance occurring in marine and coastal ecosystems as a consequence of anthropogenic activities. Therefore, it is critically important to identify the stoichiometric plasticity of different species, before environmental change causes a shift in benthic community composition that will alter functions on an ecosystem level. [ABSTRACT FROM AUTHOR]

Benthic animal populations inhabiting intertidal flats provide important ecosystem functions and services that may be disrupted by physical disturbances such as tropical cyclones, which are predicted to increase in frequency and intensity under future climate change. However, the spatial reach at which tropical cyclones impact macrobenthos populations in intertidal flats remains poorly understood. We examined whether a typhoon with a center that remained more than 1400 km away from the study site could trigger severe erosion of intertidal flats and adversely affect macrobenthos populations. We undertook simultaneous measurements of hydrodynamics (waves, currents), morphodynamics (erosion, accretion) and density and biomass of the macrobenthic bivalve Meretrix meretrix during the passage of this typhoon, on an intertidal flat on the Chinese coast. Our results showed that, in spite of the considerable distance from the storm center, the bed shear stress greatly exceeded the critical value for erosion, resulting in rapid erosion of approximately 10 cm and a nearly 50% reduction in both the density and the biomass of the clam species. Our findings suggest that if storms become more frequent and more intense in a future warmer climate, they may increase physical disturbances to intertidal flats and their benthic animal populations, even at great distances from storm centers. [ABSTRACT FROM AUTHOR]

Pelagic primary production is the main input of organic energy for benthic production below the photic zone. In the Baltic Sea, spring phytoplankton blooms are dominated by diatoms that sink out rapidly and export nutritionally favorable matter to benthic secondary production, while the summer blooms have more variable sedimentation rates and nutritional profile. Changes in phytoplankton species composition and bloom dynamics, as a consequence of climate change and eutrophication are reducing high quality diatoms reaching the benthic fauna, while promoting cyanobacteria. Here, we test uptake and assimilation of changing phytoplankton composition for three common benthic invertebrates, a clam, an amphipod and a polychaete under varying degrees of spring‐bloom associated diatoms (Skeletonema costatum) and summer‐bloom associated cyanobacteria (Nodularia spumigena). The phytoplankton were labeled with stable isotopes (15N and 13C, respectively) in order to trace assimilation in consumers' tissues. We found that all three macrofauna species fed on both diatoms and cyanobacteria. A linear pattern was found for all three species in assimilation of carbon and nitrogen from diatoms, with increasing assimilation associated with higher proportion of diatoms. There was no clear pattern found between proportion of cyanobacteria and assimilation of carbon and nitrogen for any of the species. This study shows that the investigated macrofaunal species display a selective feeding behavior with preference for spring‐bloom associated diatoms. Thus, changes in phytoplankton bloom composition are likely affecting benthic species composition and production. [ABSTRACT FROM AUTHOR]

Understanding marine ecosystem structure and functioning is crucial in supporting sustainable management of natural resources and monitoring the health of marine ecosystems. The current study utilized stable isotope (SI) mixing models and trophic position models to examine energy flow, trophic relationships, and benthic‐pelagic coupling between food web components. Roughly 1900 samples from different trophic levels in the food web, collected during 2001–2010 from four northern and central sub‐basins of the Baltic Sea, were analyzed for SI ratios of carbon and nitrogen. Trophic structure of the food webs among the sub‐basins was consistent, but there were differences between the proportions of energy in different trophic levels that had originated from the benthic habitat. Mysids and amphipods served as important links between the benthic and pelagic ecosystems. Much (35–65%) of their energy originated from the benthic zone but was transferred to higher trophic levels in the pelagic food web by consumption by herring (Clupea harengus). One percent to twenty‐four percent of the energy consumption of apex seal predators (Halichoerus grypus and Pusa hispida) and predatory fish (Salmo salar) was derived from benthic zone. Diets of mysids and amphipods differed, although some overlap in their dietary niches was observed. The food web in the Gulf of Finland was more influenced by the benthic subsystem than food webs in the other sub‐basins. The baseline levels of δ13C and δ15N differed between sub‐basins of the Baltic Sea, indicating differences in the input of organic matter and nutrients to each sub‐basin. [ABSTRACT FROM AUTHOR]

Florida Bay nutrient budgets have shown that the majority of existing and influent nitrogen (N) is in organic forms. Consequently, local remineralization processes have been found to regulate the supply of dissolved inorganic nitrogen (DIN). Sponges have dominated benthic animal biomass in Florida Bay and are known to influence local DIN concentrations through remineralization organic matter, yet the role of these organisms in local N budgets is largely unaddressed. We quantified the role of sponges in N cycling in Florida Bay during 2012–2013 by constructing an N budget for a sponge‐rich basin. Surveys of sponge biomass conducted in Mystery Basin found sponges at 57 of the 59 assessed stations. Sponge population maxima reached 21 individuals m−2 and biomass contributions as high as 4.4 Lsponge m−2. We estimated an average areal DIN contribution from total sponge biomass of 0.59 ± 0.28 mmol N m−2 d−1. However, calculated fluxes from the 59 stations exhibited significant spatial variability associated with changes in the size and species composition of the sponge community; peak N fluxes reached 3.5 ± 0.9 mmol N m−2 d−1 in areas with large populations of high microbial abundance sponges. The average flux from the sponge community was the largest of the estimated sources of DIN to Mystery Basin, representing roughly half of the overall N sourcing. This N satisfied more than half of the demand by primary productivity. These results indicate that sponges are important sources of inorganic N to Florida Bay environments. [ABSTRACT FROM AUTHOR]

Abstract: Benthic fluxes of chlorophyll a (Chl a) and particulate organic carbon (POC) and nitrogen (PON) were quantified on Tallon reef, a strongly tide‐dominated (spring range > 8 m) reef located in the Kimberley region of northwestern Australia, over a 2‐week period. Extensive hydrodynamic observations were used to construct a reef‐scale mass balance to estimate material exchange between the reef and ocean over individual tidal cycles. Additionally, a one‐dimensional control volume approach was used to estimate fluxes of Chl a in waters traversing the reef platform. Particulate material was delivered to the reef platform in a pulse during flood tide, and benthic uptake of Chl a declined to negligible values toward the end of ebb tide. On the scale of tidal cycles, a net uptake of Chl a was observed on the reef platform (on average 1.3 mg Chl a m−2 d−1), which was lower than previous studies of many reef communities. Fluxes showed variability depending on the magnitude of individual tidal cycles, which was likely related to volumes of oceanic Chl a inputs. Tallon reef was a net source of detrital POC and PON to the surrounding coastal ocean, with average POC exports ∼ 3% of the reef's benthic gross primary production. Seasonal measurements of water quality reported here are among the first records for the coastal Kimberley, and suggest that reefs in the west Kimberley may experience naturally elevated levels of phytoplankton and particulate nutrients, especially during the wet season. [ABSTRACT FROM AUTHOR]

Abstract: Sponges are conspicuous and abundant within the benthic fauna on Caribbean reefs. The ability of these organisms to efficiently capture carbon from particulate sources is well known and the importance of dissolved organic carbon (DOC) uptake has been recognized for several species. We surveyed DOC ingestion by seven sponge species common to Florida Keys reefs using nondisruptive sampling methods on undisturbed individuals. Three of the seven species exhibited significant DOC removal ranging from 13% to 24% of ambient concentrations. The tested species that removed DOC host large microbial consortia within their tissues, while the converse was observed for those that did not. This divergent behavior may suggest an important role for sponge associated microbes in the utilization of DOC by these species. The feeding behaviors of individuals of Xestospongia muta were then monitored over time to investigate its respiratory consumption of particulate and DOC. The uptake rates of dissolved oxygen (DO) and organic carbon by two undisturbed individuals revealed that DOC represented 96% of removed C, and that the tested individuals removed approximately equal quantities of C and DO. This demonstrates that X. muta largely satisfies its respiration demands through DOC consumption, and that DOC likely represents the dominant C source for biomass production and cell overturn in this species. These results further illustrate the metabolic importance of DOC to sponges, and suggest that these organisms are an important pathway for remineralizing organic matter on Caribbean reefs. [ABSTRACT FROM AUTHOR]

In the high Arctic, recruitment of hard-bottom benthic organisms has been studied at single locations, but little is known about how it varies spatially or temporally, or how it is influenced by abiotic factors. In this study, settlement plates were simultaneously deployed at five locations in three Svalbard (Norway) fjords at depths ranging from 7 m to 215 m. Recruitment was significantly different among fjords and among locations within a fjord. Recruits at each site co-occurred randomly even though interspecific overgrowth was observed. This finding provides further evidence that there is not necessarily a relationship between non-random co-occurrence and interspecific competition, such as is traditionally assumed for other isolated, island-like habitats. We found significantly lower recruitment in an Arctic-influenced fjord than in more Atlantic-influenced fjords. The abundance and richness of recruits was significantly lower in fall-winter than in spring-summer, but the spirorbid Circeis armoricana recruited in high abundance in fall-winter. Both the abundance and taxonomic richness of recruits declined exponentially with depth, with the hydroid Stegopoma plicatile dominating at 215 m in an Atlantic-influenced fjord. The most abundant recruiting taxa ( C. armoricana, Semibalanus balanoides, Harmeria scutulata, Celleporella hyalina) can be described as pioneer (early-succession) species. Crustose coralline algae, a slow-growing superior competitor, also recruited at one location. Recruitment in Svalbard is highly variable, both spatially and temporally, and our results show the influence of local factors such as adult species composition. [ABSTRACT FROM AUTHOR]

Community ecology has broadened considerably with the recognition that it is not only at the species-level data where biological patterns and their determinants should be studied. Rather, also functional and phylogenetic data should be examined, as they may provide important information for both basic ecology and applied fields such as conservation and bioassessment. We thus explored the distance decay of taxonomic, functional, and phylogenetic community compositions along spatial and environmental gradients within a boreal lake metacommunity. We used distance-based methods (i.e., Mantel test, Mantel correlograms and db-RDA) to examine different facets (i.e., taxonomic, functional, and phylogenetic) and components (i.e., total, turnover and nestedness-resultant) in relation to spatial and environmental variables. We found that the species compositions of lake benthic invertebrate communities varied mostly along environmental gradients, but were also weakly related to spatial distances between lakes. We also showed that functional and phylogenetic compositions were solely related to environmental variation across the lakes, but these relationships were generally weak. Our exploration of different facets and components of beta diversity added to the knowledge of lake invertebrate communities by adding functional and phylogenetic views, which has rarely been done in studies of aquatic metacommunities. Such information is also important in valuing lakes for conservation and bioassessment because it is not only at the species-level data where ecological patterns and underlying mechanisms should be explored. [ABSTRACT FROM AUTHOR]

The trend of increasing dissolved organic carbon (DOC) in surface waters motivated us to gain a mechanistic understanding of DOC exchange at the sediment water interface in lakes. We quantified seasonal DOC and solute fluxes under different redox conditions, in a small drinking water reservoir using sediment core incubations. Processes governing benthic DOC exchange were microbial production of DOC and interaction with mineral surfaces. Mobilization of DOC in anoxic sediments seemed to be closely linked to reductive dissolution of ferric minerals as shown by the strong positive correlation ( r2 = 0.99) between DOC and Fe fluxes. Oxidized surface sediments were an efficient DOC trap where DOC was bound to ferric minerals. Redox conditions appeared to be the primary regulator of the DOC exchange, resulting in sedimentary uptake of DOC (−1.8 mmol m−2 d−1) only under oxic conditions. DOC production was regulated by temperature, leading to higher DOC fluxes (up to 2.4 mmol m−2 d−1) in summer. The sediment was a net sink of DOC (−0.2 tonnes yr−1) but this was small compared with the annual DOC load (15 tonnes yr−1) of the reservoir. However, the benthic DOC flux was about 10-20% of the dissolved carbon flux at the sediment-water interface, making it a significant process in the lake internal carbon cycle. Climate change is supposed to promote reducing conditions at the bottom of lakes, which might increase benthic DOC production in the future. [ABSTRACT FROM AUTHOR]

Food web productivity in lakes can be limited by dissolved organic carbon (DOC), which reduces fish production by limiting the abundance of their zoobenthic prey. We demonstrate that in a set of 10 small, north temperate lakes spanning a wide DOC gradient, these negative effects of high DOC concentrations on zoobenthos production are driven primarily by availability of warm, well-oxygenated habitat, rather than by light limitation of benthic primary production as previously proposed. There was no significant effect of benthic primary production on zoobenthos production after controlling for oxygen, even though stable isotope analysis indicated that zoobenthos do use this resource. Mean whole-lake zoobenthos production was lower in high-DOC lakes with reduced availability of oxygenated habitat, as was fish biomass. These insights improve understanding of lake food webs and inform management in the face of spatial variability and ongoing temporal change in lake DOC concentrations. [ABSTRACT FROM AUTHOR]

We used equatorial glacier-fed streams as a model system to investigate the relationships between flow fluctuation and benthic fauna at different temporal scales. Water level was measured at 30 min intervals over 29 months (942 d) and benthic macroinvertebrates were sampled 14 times over the study period. We performed wavelet analyses on water-level time series to identify temporal scales at which significant flow variation occurs, and calculated three indices: intensity, frequency and temporal clustering of the diurnal flow variation for periods from 2 d to 50 d. We determined the effect of temporal scaling (length of the periods considered) on relationships between benthic community dissimilarity (using Sørensen index) and differences in flow indices among the 14 sampling dates. Temporal scaling affected flow-variation frequency and temporal clustering and their subsequent relationships with benthic community dissimilarity. A time scale of 15 d before benthic sampling was relevant to the assessment of flow-biota relationships. Community dissimilarity significantly increased with increasing difference in flow-fluctuation intensity. This dissimilarity was associated with a decrease in the density of dominant taxa and a taxa turnover along the temporal gradient in flow-fluctuation intensity. Although flow fluctuations are frequent and highly predictable in equatorial glacier-fed streams, macroinvertebrate communities exhibited a temporal variability in taxon assemblage, which was linked to the intensity of flow fluctuation. We explain these patterns by downstream displacement during high flow events and upstream displacement during low flow periods, thereby highlighting the need of considering temporal scaling effects on benthic fauna to understand the ecological dynamics of lotic systems. [ABSTRACT FROM AUTHOR]

Benthic metabolism, nutrient fluxes, and denitrification were measured in Caulerpa taxifolia communities that had recently invaded (between 2003 and 2008) bare sediments following the loss of Zostera capricorni (prior to 2003), and in adjacent Z. capricorni communities and bare sediments, to determine the likely changes in ecosystem function following C. taxifolia colonization. Areas colonized by C. taxifolia had higher gross primary production (GPP), net primary production (NPP), and dark benthic N2 effluxes than adjacent bare sediments, but lower dark benthic Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed. effluxes. C. taxifolia invasion of bare sediments had a beneficial role in removing excess nitrogen from the system through enhanced denitrification. In contrast, areas occupied by C. taxifolia had similar GPP and NPP relative to Z. capricorni beds and similar benthic N2 and Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed. effluxes. Thus, C. taxifolia appears to play a comparable role to Z. capricorni in terms of some ecosystem functions, although the degree of similarity is likely to be affected by the relative densities of the two macrophytes. However, replacement of Z. capricorni communities by C. taxifolia appears to significantly alter the quantity and quality (higher ratio) of benthic dissolved organic carbon and dissolved organic nitrogen fluxes. [ABSTRACT FROM AUTHOR]

Physiological mechanisms of bleaching were studied on larger benthic foraminifera (LBF) hosting endosymbiotic diatoms. Amphistegina radiata, Heterostegina depressa, and Calcarina hispida were exposed to increasing temperatures in static temperature experiments (23°C to 33°C, 6 d). Photosynthetic activity (Fv :Fm, measured with a pulse-amplitude modulated fluorometer), chlorophyll a (a proxy for symbiont biomass), and motility (a proxy for overall fitness of the foraminifera) were reduced in specimens at 32°C to 33°C, and cytoplasm color changes associated with bleaching were observed. A 30-d flow-through experiment at three temperatures (26°C to 31°C) and three levels of inorganic nitrate concentration (0.5 to 1.4 µmol L-1) confirmed negative effects of temperature at 31°C for A. radiata (including growth) and H. depressa. Another Calcarina species, Calcarina mayorii, was not affected. This suggests that temperature effects are species-specific. However, elevated nutrient concentrations did not affect any of the parameters measured. Temperatures . 30°C stress the foram-diatom endosymbiosis in some LBF species, which may lead to subsequent bleaching of the host. Given that a 2-3°C increase led to rapid bleaching of most species, we propose that, similar to corals, these species are threatened by sea-surface temperature increase predicted for tropical reef waters in the near future. [ABSTRACT FROM AUTHOR]

A compilation of more than 30 studies shows that adult Antarctic krill (Euphausia superba) may frequent benthic habitats year-round, in shelf as well as oceanic waters and throughout their circumpolar range. Net and acoustic data from the Scotia Sea show that in summer 2-20% of the population reside at depths between 200 and 2000 m, and that large aggregations can form above the seabed. Local differences in the vertical distribution of krill indicate that reduced feeding success in surface waters, either due to predator encounter or food shortage, might initiate such deep migrations and results in benthic feeding. Fatty acid and microscopic analyses of stomach content confirm two different foraging habitats for Antarctic krill: the upper ocean, where fresh phytoplankton is the main food source, and deeper water or the seabed, where detritus and copepods are consumed. Krill caught in upper waters retain signals of benthic feeding, suggesting frequent and dynamic exchange between surface and seabed. Krill contained up to 260 nmol iron per stomach when returning from seabed feeding. About 5% of this iron is labile, i.e., potentially available to phytoplankton. Due to their large biomass, frequent benthic feeding, and acidic digestion of particulate iron, krill might facilitate an input of new iron to Southern Ocean surface waters. Deep migrations and foraging at the seabed are significant parts of krill ecology, and the vertical fluxes involved in this behavior are important for the coupling of benthic and pelagic food webs and their elemental repositories. [ABSTRACT FROM AUTHOR]

The Håkon Mosby Mud Volcano is a highly active methane seep hosting different chemosynthetic communities such as thiotrophic bacterial mats and siboglinid tubeworm assemblages. This study focuses on in situ measurements of methane fluxes to and from these different habitats, in comparison to benthic methane and oxygen consumption rates. By quantifying in situ oxygen, methane, and sulfide fluxes in different habitats, a spatial budget covering areas of 10-1000-m diameter was established. The range of dissolved methane efflux (770-2 mmol m-2 d-1) from the center to the outer rim was associated with a decrease in temperature gradients from 46° Cm-1 to < 1°C m-1, indicating that spatial variations in fluid flow control the distribution of benthic habitats and activities. Accordingly, total oxygen uptake (TOU) varied between the different habitats by one order of magnitude from 15 mmol m-2 d-1 to 161 mmol m-2 d-1. High fluid flow rates appeared to suppress benthic activities by limiting the availability of electron acceptors. Accordingly, the highest TOU was associated with the lowest fluid flow and methane efflux. This was most likely due to the aerobic oxidation of methane, which may be more relevant as a sink for methane as previously considered in submarine ecosystems. [ABSTRACT FROM AUTHOR]

To quantify and explore the role of temperature on population outbreaks of a nonindigenous bryozoan (Membranipora membranacea) in kelp beds in the western North Atlantic (Nova Scotia, Canada), we constructed an individual-based model using field-derived estimates for temperature-dependent colony settlement and growth. Using temperature as the single input variable, the model successfully simulated the timing of onset of settlement, colony abundance, colony size, and coverage on kelps. We used the model to examine the relative effect on the population of varying temperature by -2°C to +2°C each day. The timing of onset of settlement varied by 18 d °C-1 with changes in temperature from January to August. Variations in temperature had nonlinear effects on the population, with an increase in daily temperature of 1°C and 2°C causing the cover of colonies on kelps to increase by factors of 9 and 62, respectively. Changes in winter and spring temperature had the most pronounced effects on the timing and abundance of colonies, while changes in summer temperature had the most pronounced effect on colony size and coverage on kelp blades. Outbreaks of this species will increase in frequency and intensity if temperatures warm as a result of climate change, causing defoliation of kelp beds and, thus, facilitating the invasion of other nonindigenous benthic species. [ABSTRACT FROM AUTHOR]

The effect of the presence of sulfide on the survival of benthic organisms under hypoxia was tested using a meta-analysis of published experimental results evaluating the effects of the presence of hydrogen sulfide on the median survival time of benthic macrofauna under hypoxia. The meta-analysis confirmed that survival times under hypoxia are reduced by an average of 30% in marine benthic communities exposed to hydrogen sulfide. The effect of sulfide on survival was higher for egg forms than for juvenile or adult stages. The aggravation of the negative effects of spreading hypoxia in the presence of sulfide suggests that the threats derived from hypoxia to marine biodiversity are greater than anticipated on the basis of the direct effects of low oxygen concentration alone. [ABSTRACT FROM AUTHOR]

Widespread seagrass and sponge mortality and increased water column turbidity caused by phytoplankton blooms and suspended sediments occurred throughout Florida Bay from 1987 to the mid 1990s. This disturbance led to the hypothesis that Florida Bay was shifting from dependence on benthic production to dependence driven primarily by water-column production. We tested this hypothesis by (1) evaluating the current trophic structure of Florida Bay and then (2) comparing it to a reference site in Biscayne Bay populated by dense seagrass beds with no recent history of large-scale seagrass mortality. Additionally, we (3) compared the current trophic structure of Florida Bay to a prior trophic structure recorded in historical specimens collected before the onset of the environmental disturbance. No evidence was found to support the occurrence of a large-scale shift from a seagrass-dominated to a plankton-dominated system. The δ13C and δ34S signatures of macroinvertebrates and fishes collected from sites in Florida Bay expressed the strong dominance of benthic production and were similar to values obtained from the Biscayne Bay reference site. Highly mobile apex predators that effectively integrate the signatures of their prey over longer temporal and larger spatial scales had δ13C signatures that ranged from -13‰ to -11‰ and δ34S signatures that ranged from +2‰ to +6‰, indicating that the food web of the bay is currently dominated by strong benthic-pelagic coupling. A comparison between Florida Bay's historic communities (preserved fish from 1956-1966) and its contemporary communities also supports the conclusion that the fundamental character of the bay remains relatively unchanged. [ABSTRACT FROM AUTHOR]

We used mesocosms equipped with two-dimensional (2D) pore water samplers (24 rows x 24 columns, 9-mm spatial resolution) to resolve and quantify some of the complex spatial patterns in diagenetic reactions produced by irrigated biogenic structures. The mesocosms were filled with an organic-, iron-, and phosphorus-rich sediment, and chironomids and oligochaetes were added in high densities to three of six mesocosms; the other three mesocosms served as controls. In the mesocosms without macrozoobenthos, a classic redox zonation developed. In the mesocosms with macrozoobenthos, profiles of redox-sensitive dissolved species were less steep in the vicinity of the sediment--water interface, and more irregular throughout the sediment, than in the mesocosms without macrozoobenthos. Furthermore, pore water P concentrations were decreased overall and showed much more small-scale 2D heterogeneity in the mesocosms with macrozoobenthos than in the controls. A comparison of the calculated heterogeneity indices of pore water P concentrations (the ratio of horizontal to vertical flux components) of this laboratory study with in situ-determined indices of previous studies indicates that the presence of macrozoobenthos is the major factor causing heterogeneity. A conceptual model of the effects of macrozoobenthos on biogeochemistry along with pore water and sediment analysis showed a close coupling of P cycling with iron and sulfur cycling. This led to the conclusion that pore water P concentrations and heterogeneity were mainly redox-controlled by association of P with iron oxyhydroxides precipitating along oxidized burrow walls, and not a consequence of mineralization processes occurring in organic-rich "hot spots" of increased P turnover. Decreased P release rates accompanied addition of macrozoobenthos and indicated that redox control of P release by iron oxyhydroxide precipitation and dissolution was of major importance. [ABSTRACT FROM AUTHOR]

The benthic communities of streams contain invertebrates of a wide range of body size and from many taxa. Owing mainly to methodological problems, however, the contribution of smaller and more obscure metazoans to community structure and dynamics, including production, is poorly known compared with that of larger size fractions and, particularly, insects and macrocrustaceans. Based on a monthly survey of a first-order, acidic English stream, we used the size-frequency method to estimate annual production of the whole metazoan benthos (down to organisms retained on a 42-µm mesh and being as taxonomically inclusive as possible). Mean total secondary production (5.22 g dry weight m-2 yr-1) was low, presumably mainly due to the stream's acidity. About 15% (0.76 g m-2 yr-1) of this total production, however, was contributed by the permanent meiofauna (species always small enough to pass through a 500-µm mesh, and mainly made up of ostracods and copepods but also including rotifers, microturbellarians, and others). By estimating separately production from the macrofaunal and meiofaunal net fractions (500/xm and 42-500 µm, respectively), we found that about 51% of total production could be accounted for by the permanent and temporary meiofauna together, the latter being defined as organisms that potentially grow into the macrofaunal size class and here consisting primarily of oligochaetes, chironomids, and plecopterans. This study points to the potentially substantial underestimation of production arising from the problems of assessing the meiofauna, including the former use of coarse-meshed (e.g., 500 µm) sampling devices, the requirement for live sorting of many soft-bodied taxa, and other difficulties of counting and identifying less well known groups. [ABSTRACT FROM AUTHOR]

We analyzed the contributions of clouds, turbidity, and tides to variations in irradiance and predicted benthic primary productivity on a coastal coral reef over a period of 2 yr (2001-2002). At 1.5 m below lowest astronomical tide (3.8-m tidal range), attenuation by suspended solids (turbidity) accounted for 74-79% of the total annual variation in irradiance, clouds for 14-17%, and tides for 7-10%. With increasing depth, the contribution from turbidity to irradiance variation increased asymptotically toward 95%. Fourier (spectral) analyses indicated that the benthic irradiance regime followed strong 8-week periodicities and weaker 2-4-week periodicities. The 8-week cycle was driven primarily by turbidity and secondarily by clouds and matches the periodicity of the intraseasonal Madden-Julian atmospheric oscillation. The weaker 3-4-week irradiance cycle was driven by turbidity; the 2-week cycle was driven by tides and, to a lesser extent, clouds. Comparisons of the benthic irradiance pattern with predictions of physiologically optimal irradiance levels (parameter Ek) for the coral Turbinaria mesenterina suggested that corals at the site alternate between states of potential light limitation and light stress, with a 2-8-week periodicity caused mainly by variations in turbidity. The effect of external sources of light reduction, such as episodic runoff events, on the energetics of benthic primary producers is likely to vary critically with the timing of such events. [ABSTRACT FROM AUTHOR]

Using a multicomponent inverse model, we quantified the rates of organic matter (OM) remineralization and the relative importance of major terminal electron acceptors [Fe(III)-(oxy)hydroxides and SO2-4] in salt marsh sediments with varying degrees of bioturbation and vegetation at Skidaway Island, Georgia. The model determined the rates of OM diagenesis by seeking simultaneous agreement between measured and model-calculated depth-concentration profiles of multiple major redox species while using the biological transport parameters determined from direct field observations. The OM degradation rates are found to be greater and penetrate deeper in sediments with vegetation or bioturbation than in sediments with limited macrobenthic components, in which organic matter degradation is restricted to the immediate vicinity of water-sediment interface. The results also confirmed previous observations that Fe(III)-(oxy)hydroxides are much more important than sulfate as terminal electron acceptors in the heavily bioturbated station and provided the numerical values to the depth-dependent relative importance. Solid-phase Fe is recycled as a terminal electron acceptor ≥30 times in the bioturbated station, because biological mixing repeatedly moves reduced Fe(II) back into the aerobic environment, where it is reoxidized to form Fe(III)-(oxy)hydroxides and is reused as a terminal electron acceptor. Vegetation appears to have little influence on net solute transport, but it stimulates microbial activities and significantly enhances the remineralization of OM at depths. [ABSTRACT FROM AUTHOR]

We measured microbial heterotrophic activity, bacteria, and virus-like particle (VLP) abundance in homogenized, undiluted, and anoxic enclosures of sediment collected at a coastal station. The bacterial growth rate and VLP net production increased along with the respiratory activity in response to temperature. This suggests that VLPs represent a dynamic component of benthic microbial communities and that the net production of viriobenthos is regulated by the metabolic activity of bacteria. The abundance, net production, and decay rate of VLPs were significantly higher than those encountered in most pelagic systems. However, the rates were lower than the very few available potential rates (three studies) of viriobenthic activity, which all were obtained applying different slurry approaches. Our measurements support the general observation that virus abundance and production correlate with the trophic status of the environment and show that microbial activity can regulate the viriobenthic production in undiluted, homogenized marine sediments. The virus-induced bacterial mortality corresponded to ∼20% of bacterial net production and ∼2% h-1 of the total bacterial population. This is moderate compared with the results of most pelagic studies, and the associated leakage of lysates (dissolved organic carbon) only amounted to 4-8% of the produced dissolved inorganic carbon. Despite high standing stocks and relatively high turnover rates, VLP-induced bacterial lysis represented only a minor shunt in the benthic carbon cycle at the investigated site. [ABSTRACT FROM AUTHOR]

Larval supply in marine benthic invertebrates influences patterns of settlement and recruitment to adult populations. To successfully colonize newly formed or distant hydrothermal vents, which are discontinuous and ephemeral habitats, larvae of vent invertebrates must possess long-range dispersal abilities. However, a significant proportion of locally produced larvae must remain within the adult habitat to maintain the observed dense assemblages of invertebrates. I compared spatial and temporal patterns in larval availability (flux and abundance) at hydrothermal vents within and between ridge segments in the northeast Pacific ocean at Axial Seamount and Endeavour Segment on the Juan de Fuca Ridge and at Magic Mountain on Explorer Ridge. Near-bottom (within 50 cm) larval supply (individuals m-2 d-1) at five vents on Axial Seamount, measured with passively collecting traps in 2000 and 2001, varied temporally by an order of magnitude, but not spatially at scales of tens of meters to kilometers. The most abundant larval taxa were gastropods (particularly the limpet Lepetodrilus fucensis) and polychaetes. Larval abundance in the water column within the axial valley was measured with net tows by the remotely operated vehicle ROPOS at the three ridge segments: Axial Seamount (2000, 2001); Endeavour Segment (2001, 2002); Magic Mountain (2002). Abundance was greater by an order of magnitude at the Endeavour Segment than at Axial Seamount and Magic Mountain, and it did not differ between on-vent (within tens of meters) and off-vent (up to 5 km from the venting source) locations within the axial valley. The uniformly high abundance of larvae within axial valleys suggests that larval supply within a ridge segment is most likely localized, implying significant larval retention on the scale of vent fields and possibly ridge segments. [ABSTRACT FROM AUTHOR]

Stratospheric ozone depletion over Antarctica is expected to continue for the next 50 years, with increases in ecologically damaging ultraviolet radiation (UVR: 290-400 nm), specifically the ultraviolet-B (UVB: 290-320 nm) portion of the spectrum. Most of coastal Antarctica is covered with 2-3 m of annual sea ice during the occurrence of the "ozone hole." This physical barrier to UVR transmission has long been assumed to provide complete protection from the biologically damaging effects of UVR, especially for the planktonic developmental stages of the benthic invertebrate fauna. We found that short-wavelength UVB (down to 304 nm) is transmitted through the Austral spring annual ice of McMurdo Sound, and causes significant mortality and DNA damage in the embryos of the sea urchin Sterechinus neumayeri. Although mortality of sea urchin embryos has been reported for the open waters of the Antarctic, this is the first documentation of mortality and DNA damage for embryos under the annual sea ice. The degree of mortality and DNA damage was dependent on both year and depth, with higher mortality and DNA damage at 1 m depth below the ice compared to 3 m and 5 m. Greater DNA damage occurred in 2003 compared to 2002 despite the thicker annual ice (3.1 m vs. 2.5 m). Although the thickness of the annual ice was greater, the severity of the ozone hole, 230 Dobson units (DU) versus 320 DU, and the ratio of UVB to visible radiation was greater in 2003. Embryo and larval mortality from exposure to UVR under the annual ice should be considered as another abiotic factor potentially affecting the temporally episodic recruitment of invertebrates that occur in this benthic ecosystem. [ABSTRACT FROM AUTHOR]

In extreme environments, retention of nutrients within stream ecosystems contributes to the persistence of aquatic biota and continuity of ecosystem function. In the McMurdo Dry Valleys, Antarctica, many glacial meltwater streams flow for only 5-12 weeks a year and yet support extensive benthic microbial communities. We investigated NO3- uptake and denitrification in Green Creek by analyzing small-scale microbial mat dynamics in mesocosms and reach-scale nutrient cycling in two whole-stream NO3- enrichment experiments. Nitrate uptake results indicated that microbial mats were nitrogen (N)-limited, with NO3- uptake rates as high as 16 nmol N cm-2 h-1. Denitrification potentials associated with microbial mats were also as high as 16 nmol N cm-2 h-1. During two whole-stream NO3--enrichment experiments, a simultaneous pulse of NO2- was observed in the stream water. The one-dimensional solute transport model with inflow and storage was modified to simulate two storage zones: one to account for short time scale hydrologic exchange of stream water into and out of the benthic microbial mat, the other to account for longer time scale hydrologic exchange with the hyporheic zone. Simulations indicate that injected NO3- was removed both in the microbial mat and in the hyporheic zone and that as much as 20% of the NO3- that entered the microbial mat and hyporheic zone was transformed to NO2- by dissimilatory reduction. Because of the rapid hydrologic exchange in microbial mats, it is likely that denitrification is limited either by biotic assimilation, reductase limitation, or transport limitation (reduced NO2- is transported away from reducing microbes). [ABSTRACT FROM AUTHOR]

Three-dimensional modeling of lake morphometry enables the calculation of lake volume, planar surface area, and basin surface area, which are critical components of a conceptual model of how planktic and benthic habitat areas change with changing lake level. We have applied three-dimensional modeling to Foy Lake, Montana, and compared model results of changing ratios of planktic and benthic habitat areas at all possible lake levels to sediment cores recovered from the lake. The model allows us to produce semiquantitative depth reconstructions and greatly improves lake-level reconstruction of this morphometrically complex basin. The conceptual model also was modified to examine the influence of resuspension versus gravity redistribution of diatomaceous material on the sedimentary record. Comparison of the model results with both long and short sedimentary records from Foy Lake, Montana, suggests that planktic:benthic ratios may be a better predictor of mean lake depth than maximum lake depth. The model developed here is simple enough to be easily implemented, has few requirements, can be adapted to suit any lake basin, and can be augmented to examine a variety of different lake processes that affect habitat availability. [ABSTRACT FROM AUTHOR]

We tested the role of benthic infaunal functional diversity in regulating the biogeochemistry of nearshore sediments using laboratory microcosms. Single and multispecies assemblages of deposit-feeding polychaetes (Clymenella torquata, Spio setosa, and Leitoscoloplos fragilis) were used, and fluxes of oxygen and phosphate, as well as profiles of oxygen and pH in the sediment pore water, were measured. Significant differences in flux rates were found among treatments that were unrelated to polychaete abundance or biomass alone. Multispecies assemblages had lower flux rates of both oxygen and phosphate than rates calculated from the single-species treatments. Depth-integrated oxygen and pH profiles also showed significant differences between multispecies assemblages and selected single-species treatments. These differences were most likely from species-specific feeding and burrowing behavior and species-related interactions. Coefficients of variance for both oxygen and pH were highest for microcosms with no polychaetes and lowest for the assemblages, indicating a dampening effect of multispecies assemblages on pore-water heterogeneity. When oxygen flux data was incorporated into a model of oxygen dynamics in Long Island Sound, results indicated that shifts in the benthic community composition could change sediment oxygen consumption rates sufficiently to disrupt the balance between the physical supply of oxygenated water and biological oxygen demand. The results of this study confirm the importance of benthic functional biodiversity to nearshore sedimentary processes and suggest that losses of functional diversity can have significant effects on ecosystem function. [ABSTRACT FROM AUTHOR]

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 O2 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 O2 uptake rates of ∼5.3 mmol m-2 h-1 at the onset of darkness. The activity gradually diminished during the night, and the O2 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 O2 consumption revealed that the O2 uptake through the burrow walls just after sunset accounted for the major part of the total O2 uptake on a diel scale. The study demonstrates that light-driven variations in fauna activity can have great effects on the total benthic O2 consumption rate with large implications for estimated benthic mineralization rates. [ABSTRACT FROM AUTHOR]

We investigated emergence of marine benthic harpacticoid and cyclopoid copepods from subtidal sediment into the bottom water. Previous studies that used traps in the field found that copepods emerged from the sediment within 2 h of dusk. We examined emergence in 20-min sampling periods over 13 h from 1200 to 0100 h in a laboratory flume under conditions of constant flow speed. The light intensity was adjusted to field conditions every 20 min. We observed a peak in emergence during the 20-min sampling period after the onset of darkness, greatly increasing the accuracy with which the timing of emergence is known. This result will help to set the stage for studies of emergence cues. [ABSTRACT FROM AUTHOR]

The distributional patterns of benthic foraminifera provide key information for paleoclimatic, paleoecologic, and paleoceanographic studies. Yet the dispersal mechanisms that provide a crucial link between local populations and large-scale biogeographic patterns are not well documented. We experimentally demonstrate the dispersal of propagules, which include both sexually and asexually produced young (perhaps only the proloculus), though the sexually produced young appear to have a greater potential for dispersal. The propagules can rest in a cryptic state for months, constitute a substantial bank of individuals in sediments from water depths beyond the natural distribution of conspecific adults, and grow in these sediments when exposed to favorable conditions. Propagule dispersal probably provides an effective mechanism for colonization of widely separated habitats in a fashion broadly similar to other eukaryotic microbial groups and many groups of marine invertebrates. [ABSTRACT FROM AUTHOR]

Annual rates of sediment denitrification and sediment-water fluxes of oxygen and nutrients were quantified at two shallow locations, Virksund and Ulbjerg, in the Limfjorden, Denmark. The sediment was sandy and colonized mainly by bivalves with a wet weight of 2,508 g m[sup-2] at Virksund and 572 g m[sup-2] at Ulbjerg. A benthic microalgal community was present throughout the year, and for 1-2 months in the summer, floating macroalgae partly covered the sediment. Annual budgets for the sediment both including and excluding the activity of macroalgae were calculated. In the absence of macroalgae, the benthic primary production was highest at Ulbjerg, which was autotrophic on an annual basis, whereas Virksund was heterotrophic. When macroalgae were included, both sites were strongly autotrophic on an annual basis. From 13% to 58% of the NH[sup+, sub4] produced by mineralization was retained in the sediment in the absence of macroalgae, primarily because of the assimilation of NH[sup+, sub4] by the microphytobenthic community. Only 25% and 38% of the total NO[sup-, sub3] uptake at Ulbjerg and Virksund, respectively, was denitrified in the absence of macroalgae, whereas in the presence of macroalgae, 12% and 39% of the NO[sup-, sub3] uptake was denitrified at those sites. Nitrate uptake associated with benthic primary production limited denitrification through competition for NO[sup-, sub3]. The release of NH[sup+, sub4] from the sediment at Virksund was reduced more than 50%, and at Ulbjerg, release of NH[sup+, sub4] changed to uptake when the macroalgae were included in the annual budget. Nutrient uptake by macroalgae competed with all other nutrient-consuming processes, and the transient occurrence of macroalgae totally changed both the primary productivity and the nutrient budgets for the two sites. [ABSTRACT FROM AUTHOR]

O[sub2] plays a key role in early sedimentary diagenetic processes, but the effect of most macrofaunal species on the pathways and rates of supply of O[sub2] into the seabed are not well known. We investigated the effect of the ophiuroid Amphiura filiformis, one of the dominant macrobenthic species on soft bottoms in the northeast Atlantic, at depths of ∼ 15-100 m, in a laboratory environment. We determined how the presence of the ophiuroid changed the total O[sub2] uptake of macrofauna-free sediment by combining measurements from a microcosm approach and an approach that uses microelectrodes and a flushed aquarium. We suggest that natural populations of A. filiformis can account for 80% of the total flux of O[sub2] into the soft bottom. At least 67% of this portion is due to the diffusion of O[sub2] across additional sediment-water interfaces excavated by the brittle star. [ABSTRACT FROM AUTHOR]

Presents a study which examined the nocturnal vertical migration marine organisms from the seabed using an acoustic monitoring system. Migration of marine organisms in shallow coastal water; Methodology of the study; Discussion on the results of the study.

Presents a study which investigated the benthic oxygen uptake and the oxygen microdistribution in a coastal sediment of Aarhus Bay, Denmark. Measurement of oxygen uptake of marine organisms; Materials and methodology of the study; Discussion on the results of the study.

Presents a study that explored the issues concerning green urchins that were induced to spawn in a benthic boundary layer in a flow-through flume. Materials and methods; Velocity profiles; Temporal pattern of fertilization at main stream flow velocities.

We report gross primary production (GPP), community respiration (CR), and net community production (NCP) over a Posidonia oceanica meadow at 10 m in Corsica (Bay of Revellata) based on the open water O2 mass balance from a data set of hourly measurements with an array of three O2 optodes deployed from August 2006 to October 2009. The method was checked by comparison with discrete measurements of metabolic rates derived from benthic chamber incubations also based on the diel change of O2. This comparison was satisfactory and actually highlights the potential caveats of benthic incubation measurements related to O2 accumulation in small chambers leading to photorespiration and an underestimation of GPP. Our data confirmed previous P. oceanica meadows GPP and CR values, strong seasonal variations, and net autotrophy. High-resolution data revealed strong interannual variability, with a decrease of GPP by 35% and NCP by 87% during 2006-2007 characterized by a mild and less stormy winter compared with 2007-2008 and 2008-2009. P. oceanica meadows are then expected to decrease export of organic carbon to adjacent communities (decrease of NCP), since a decrease in frequency and intensity of marine storms is expected in the future in the Mediterranean Sea as a result of a northward shift of the Atlantic storm track. [ABSTRACT FROM AUTHOR]

A recently developed autonomous benthic lander equipped with an underwater potentiostat and a micromanipulator for in situ voltammetric depth profiling of main redox species in pore waters was deployed for 3 yr at multiple stations along the Satilla River estuary (Georgia, U.S.A.). These measurements revealed that biogeochemical processes in estuarine sediments vary seasonally and are influenced by riverine discharge. A prolonged drought decreased river discharge, altered the salinity gradient in the estuary, and profoundly affected anaerobic respiratory processes in the underlying sediments. Under normal hydrologic conditions, iron reduction was the dominant anaerobic respiratory process across the estuary, likely due to the significant supply of iron from the coastal plane and low salinity of the estuary. Under drought conditions, the salinity of the estuary increased to full seawater strength and carbon remineralization was enhanced significantly. Yet, sulfate reduction was only observed near the mouth of the estuary, whereas a substantial increase in iron reduction was distinctive upriver. Evidence indicates that the increase in iron-reducing activity during the drought resulted mainly from the deposition of mineral particles in the upper estuary when the salinity gradient increased. Altogether, this study demonstrates that the biogeochemical response of estuarine sediments to natural perturbations is rapid and that respiration processes are controlled by a combination of temperature, supply of inorganic and organic substrates, and hydrological processes. These findings also suggest that an increase in the frequency of droughts as a result of climate change may enhance the resiliency of iron-reducing bacteria in river-fed estuarine sediments. [ABSTRACT FROM AUTHOR]

Pockmarks are one of the most obvious and abundant structural features of the North Sea seabed, yet their influence on fauna is virtually unknown. We report the distribution of benthic megafaunal assemblages in and around four "pockmark complexes" in the North Sea to determine the structure of megafaunal communities inside pockmarks and whether these ubiquitous topographical features acted as refuges against trawling and other disturbances. The study focuses on the large central pockmarks in each of the pockmark complexes. These large pockmarks had depths of around 10 m and diameters of 160-235 m. Remotely operated vehicle video transects showed that megafauna increased in abundance, species richness, and diversity from outside (background seabed) toward the center of the pockmarks. The number of taxa present in the center of pockmarks was approximately double those of similar surrounding areas, and the centers had almost an order of magnitude more individuals than outside. Carbonate rocks were found in the centers of all the pockmarks and may be indicative of their formation (past methane seeps). These rocks also provide novel habitat to fauna: a complex hard substrate for colonization and shelter in an otherwise homogeneous soft sediment environment. Habitat enrichment and morphological protection are suggested to be the main reasons for the increased faunal abundance and species richness. Indeed, despite fishing data showing the area to be intensively disturbed, large slow-growing (old) and vulnerable species, such as gorgonian corals, were found in the center of the pockmarks. Pockmarks may offer important refuges from trawling activity. [ABSTRACT FROM AUTHOR]

On the basis of 16-yr satellite time series (1987-2003) of sea surface temperature (SST) and using univariate and multivariate statistical techniques, we quantified patterns of fluctuation in oceanographic conditions, as well as their spatial structure along the coasts of South Africa and Chile between 29.0° and 34.5°S. Since variations in environmental conditions over multiple timescales are driven by oceanographic-atmospheric processes modulated by coastal morphology, all of which affect in different ways coastal organisms, we hypothesized that dynamic properties of the environment contribute to characteristic patterns on rocky intertidal biomass structure across upwelling ecosystems. Although long-term mean temperatures were similar between coasts, the relative importance of annual, semiannual, intraseasonal, and high-frequency SST fluctuations differed; South Africa is more strongly pulsed over shorter timescales. Similar spatial discontinuities in thermal regimes were observed, with changes at about 32°S. Multivariate summaries of benthic community structure derived from functional group biomasses revealed striking differences between South Africa and Chile, as well as between regions north and south of 32°S within each ecosystem. Between-continent and regional-scale differences in community structure were largely unrelated to mean SST, but correlated with the different measures of temporal variance in SST. For all functional groups, as well as aggregate measures of benthic community composition, the weekly to annual SST fluctuations explained large fractions (>35%) of biological variability. Results highlight the importance of quantifying the temporal variance of regimes of hydrographic conditions since multispecies assemblages are expected to respond in different ways to the driving oceanographic processes behind these fluctuations. [ABSTRACT FROM AUTHOR]

Thousands of moribund thaliacean carcasses (Pyrosoma atlanticum) were deposited between February and March 2006 at the seafloor in the Ivory Coast area (West Africa). Remotely operated vehicle surveys were conducted in a continuous depth gradient between 20 and 1275 m along an oil pipeline. Video and still photography were used to estimate the carcass distribution, density, and size on the seabed, as well as recording the local megafauna interactions with the gelatinous material. Large patches of dead pyrosomids covered extensive areas on the continental slope, whereas minor aggregations were found on the shelf. The carcasses were in many instances trapped along the pipelines, accumulating extensively in troughs and furrows in the slope, and especially in soft sediment channels. Pyrosoma atlanticum dried samples were used to calculate the carbon content, enabling the extrapolation to the densities and sizes recorded in the video surveys. The average standing stock of organic carbon associated with the carcasses was >5 g C m-2 in the whole slope and canyon, with values as high as 22 g C m-2 in certain areas. Eight megafaunal species from three different phyla were observed 63 times directly feeding on the decomposing carcasses. The gelatinous carbon may have contributed substantially to the detrital food web including microbes at the seabed, and certainly to the diet of larger benthic organisms. The organism-level carbon measurements and documented fate of pyrosomid organic carbon is new evidence of the importance of gelatinous material in large-scale processes and elemental cycling. [ABSTRACT FROM AUTHOR]

Deep-sea fishes prey on benthic fauna and scavenge on the carcasses of surface-living animals. Few studies have addressed the relative importance of each trophic pathway. Recent documentation of inter-decadal fluctuations in macrourid densities in the abyssal Pacific, related to changing food supplies, hastens the need for information. We conducted stomach content and stable isotope analyses of two abyssal macrourids, carrion sources, and benthic prey, collected concurrently at 4100 m off California. Squid and fishes were the most frequent prey for Coryphaenoides armatus, with small crustaceans numerous in the diet of small specimens. The diet of Coryphaenoides yaquinae included more benthic prey such as crustaceans, polychaetes, and the holothuroid Protankyra brychia. Carrion was present in both species and it was 69% of the mass of food of large C. armatus. Carrion δ15N values were comparable to those in abyssal deposit feeders, but carrion was relatively enriched in 13C, giving it a unique isotopic signature compared to benthic prey sources. The highest δ13C and δ15N values were observed in benthic shrimps and large polychaetes. The two macrourids had intermediate values, with C. armatus having slightly but significantly lower δ15N relative to C. yaquinae. Results of isotope mass balance suggest that carrion was the most important prey resource for both species but to a lesser extent in C. yaquinae. These two species bypass the conventional phytodetritus-based abyssal food web for much of their nutrition. Their population dynamics may be tied more closely to fluctuations in epipelagic nekton populations through fishing effects and direct climatic forcing on top trophic levels. [ABSTRACT FROM AUTHOR]

We describe mixing on the basis of the radon distribution in Catalina Harbor, a small embayment on the southwest side of Catalina Island, California. During June 1998, there was a 2-3-m-thick warm surface layer in the inner harbor, underlain by cooler water. A radon budget for this system was constructed with the objective of evaluating boundary fluxes and developing a box model to describe mixing and transport into and within the harbor waters. Benthic inputs were evaluated with in situ benthic flux chambers. Loss via decay and gas evasion was characterized by surveys of radon concentration in the water column. Closure of the budget required another large radon source, which was assumed to be tidal pumping of seawater through beach sands. The budget indicates that inputs were primarily attributable to benthic input (55%) and tidal pumping (38%). Losses were due to evasion to the atmosphere (29%), radioactive decay (35%), and mixing to the open ocean (36%). The average upwelling velocity into surface water was 0.73 m d-1. Horizontal mixing was parameterized as an eddy diffusion, calculated to be 0.54 ± 0.19 m² s-1, which was consistent with mixing predictions on the basis of scaling arguments. [ABSTRACT FROM AUTHOR]