Showing papers on "Benthic zone published in 2004"

Major role of marine vegetation on the oceanic carbon cycle

Abstract: . The carbon burial in vegetated sediments, ignored in past assessments of carbon burial in the ocean, was evaluated using a bottom-up approach derived from upscaling a compilation of published individual estimates of carbon burial in vegetated habitats (seagrass meadows, salt marshes and mangrove forests) to the global level and a top-down approach derived from considerations of global sediment balance and a compilation of the organic carbon content of vegeatated sediments. Up-scaling of individual burial estimates values yielded a total carbon burial in vegetated habitats of 111 Tmol C y-1. The total burial in unvegetated sediments was estimated to be 126 Tg C y-1, resulting in a bottom-up estimate of total burial in the ocean of about 244 Tg C y-1, two-fold higher than estimates of oceanic carbon burial that presently enter global carbon budgets. The organic carbon concentrations in vegetated marine sediments exceeds by 2 to 10-fold those in shelf/deltaic sediments. Top-down recalculation of ocean sediment budgets to account for these, previously neglected, organic-rich sediments, yields a top-down carbon burial estimate of 216 Tg C y-1, with vegetated coastal habitats contributing about 50%. Even though vegetated carbon burial contributes about half of the total carbon burial in the ocean, burial represents a small fraction of the net production of these ecosystems, estimated at about 3388 Tg C y-1, suggesting that bulk of the benthic net ecosystem production must support excess respiration in other compartments, such as unvegetated sediments and the coastal pelagic compartment. The total excess organic carbon available to be exported to the ocean is estimated at between 1126 to 3534 Tg C y-1, the bulk of which must be respired in the open ocean. Widespread loss of vegetated coastal habitats must have reduced carbon burial in the ocean by about 30 Tg C y-1, identifying the destruction of these ecosystems as an important loss of CO2 sink capacity in the biosphere.

Ten years of induced ocean warming causes comprehensive changes in marine benthic communities

Abstract: One of the most commonly predicted effects of global ocean warming on marine communities is a poleward shift in the distributional boundaries of species with an associated replacement of cold-water species by warm-water species. However, these types of predictions are imprecise and based largely on broad correlations in uncontrolled studies that examine changes in the distribution or abundances of species in relation to seawater temperature. Our study used an 18-year sampling program in intertidal and subtidal habitats and before-after, control-impact analyses. We show that a 3.58C rise in seawater temper- ature, induced by the thermal outfall of a power-generating station, over 10 years along 2 km of rocky coastline in California resulted in significant community-wide changes in 150 species of algae and invertebrates relative to adjacent control areas experiencing natural temperatures. Contrary to predictions based on current biogeographic models, there was no trend toward warmer-water species with southern geographic affinities replacing colder- water species with northern affinities. Instead, the communities were greatly altered in apparently cascading responses to changes in abundance of several key taxa, particularly habitat-forming subtidal kelps and intertidal foliose red algae. Many temperature-sensitive algae decreased greatly in abundance, whereas many invertebrate grazers increased. The responses of these benthic communities to ocean warming were mostly unpredicted and strongly coupled to direct effects of temperature on key taxa and indirect effects operating through ecological interactions.

Resilience to large‐scale disturbance in coral and fish assemblages on the great barrier reef

Abstract: Recognition of the complex spatial and temporal variability of abundance and diversity found in many populations has led to a greater focus on the roles of heterogeneity, stochasticity, and disturbance in the structure and persistence of communities. This focus is directly relevant to coral reef communities that are characterized by very high species diversity in a spatially heterogeneous environment, display stochastic variability in community structure at small spatial and temporal scales, and are subject to major disturbances. We monitored coral and fish assemblages over 14 years on fixed sites spread over 80 km of the southern Great Barrier Reef (GBR), Australia, and found evidence of large-scale resilience and predictable recovery of these assemblages. Sometime between November 1987 and October 1989, live coral cover on the shallow northeast flanks of some reefs in the southern GBR decreased from >80% to <10%, probably as a result of storm damage. We compared the fish and benthic communities present ...

Dormancy in freshwater zooplankton: Induction, termination and the importance of benthic-pelagic coupling

Abstract: For a short-lived organism, such as a freshwater zooplankter, the ways of coping with years of local recruitment failure are either to disperse between habitats and recolonise or to disperse in time through diapause. Diapause is common among freshwater zooplankton and is generally seen as a way to escape periods of harsh environmental conditions. The egg-bank or pool of diapausing copepodites in lake sediments resulting from the production of diapausing stages has several implications for zooplankton ecology, genetics, and evolution which we outline in this review. The presence of a benthic dormant stage also creates a coupling between the benthic habitat and the pelagic, and we argue that zooplankton phenology is a result of selective forces in both habitats. The spatial distribution of diapausing eggs appears to be governed by random resuspension dynamics coupled with higher hatching rates in shallow waters. For diapausing copepodites, however, an active choice of where and how deep to enter the sediment may affect their distribution. In a reanalysis of published data, we found a size-dependent bathymetric distribution and vertical distribution in the sediment of diapausing cyclopoid copepodites. Our review of published laboratory studies showed that predictors of seasonal change such as photoperiod and temperature were the only type of cues used for the termination of diapause. We also found a relation between generation length and the type of cue used for diapause induction: copepods mainly used seasonal cues from the abiota, rotifers mainly used cues from the biotic environment, and cladocerans used a mix of both types. We describe patterns in emergence timing and contribution to population dynamics from studies using in situ estimation of emergence, and conclude that hatching from dormant stages may qualitatively and quantitatively affect zooplankton population dynamics and seasonal succession.

Influence of bioturbation by three benthic infaunal species on microbial communities and biogeochemical processes in marine sediment

Abstract: Benthic invertebrates play a key role in the physical, chemical, and biological properties of the marine water-sediment interface. The influences of invertebrates on biogeochemical processes have mainly been attributed to their sediment reworking and bioirrigation activities. The aim of this study was to compare the influences of bioturbation activities by 3 dominant species of shallow water habitats (Cerastoderma edule, Corophium volutator, and Nereis diversicolor) on microbial communi- ties and biogeochemical processes in sediment cores. C. edule acted as a biodiffuser, mixing surface particles in the top 2 cm of the sediment. Despite this mixing activity, this species had little effect on O2 consumption, water exchange between the water column and the sediment, microbial character- istics, and release of nutrients from the sediment. In contrast, C. volutator and N. diversicolor produced burrows in the sediment that allowed transport of surface particles into biogenic structures. These 2 species doubled the solute exchange between the water column and the sediment. Such modifications of sediment structure and solute transport increased the O2 consumption and the release of nutrients from the sediment. Both C. volutator and N. diversicolor stimulated the microbial communities as indicated by higher percentages of active bacteria. Reduction of the numbers of sulphate reducing bacteria was observed when the 3 invertebrates were present and could be attrib- uted to the penetration of O2 due to animal activities. N. diversicolor had a greater influence than C. volutator on pore water chemistry, ammonium release, and active bacteria. As N. diversicolor burrowed deeper in the sediment than C. volutator, it irrigated a greater volume of sediment. The modes of sediment reworking and structure building, irrigation behaviour, and burrowing depths were factors sufficient to assign the 3 species into different functional groups.

The ups and downs of life in a benthic biofilm: migration of benthic diatoms

Abstract: Benthic diatom communities have been documented many times to exhibit a predictable pattern of migration entrained to diurnal and tidal cycles forming transient biofilms in the estuarine intertidal The highly visible nature of these biofilms means that many anecdotal descriptions of this behaviour exist, yet much still remains to be elucidated about these behaviours and what drives them There has been a resurgence in work examining the migratory patterns of benthic diatoms because of the important roles they play in the overall functioning of the ecosystem (eg primary production) It is the aim of this paper to provide a comprehensive overview of the migratory literature to date The paper will review the methodology that was historically used to examine patterns in diatom migration as well as introduce new technologies (eg remote sensing) The patterns and cues for migration are discussed, highlighting the fact that whilst a “classic” pattern of migration is often found (migration of cells to the s

Particle flux and food supply to a seamount cold-water coral community (Galicia Bank, NW Spain)

Abstract: In a European effort (Atlantic Coral Ecosystem Study (ACES project)) to determine the key conditions for the occurrence of cold-water corals on the NW Atlantic margin, a coral community on a seamount off NW Spain (Galicia Bank) was studied Cold-water corals (Lophelia pertusa, Madrepora oculata) grow at a depth of ~800 m as isolated patches amidst small ripples and larger waves of foraminiferal sand A 17 mo deployment of a near-bottom sediment trap revealed a large seasonal and annual variability in the flux of phytodetritus and carbon The daily carbon flux in the first 5 mo of 2000 was on average 37 mgC m -2 , and in the first 5 mo of 2001 17 mgC m -2 Quantities of faecal pellets and swimmers (copepods, amphipods) were also highly variable A comparison between the daily carbon flux and the sediment carbon oxidation rate calculated from in situ com- munity oxygen consumption (SCOC), ie 17 versus 7 mgC m -2 d -1 respectively, indicated that a sur- plus of carbon is not oxidised by the sediment community We argue that the strong tidal currents (max 30 cm s -1 ) and the mobile sediment lead to winnowing of the sediment and to near-bed trans- port of the organic material The low biomass of the benthic community and the domination of filter- feeders support our arguments By means of analyses of stable isotopes (δ 15 N, δ 13 C) we attempted to find potential food items of the cold-water corals among the particles collected in the sediment trap The difference between the δ 15 N signatures of coral tissue (95‰) and phytodetritus (22‰) was >1 trophic level, indicating that sinking algae are not the sole food source The δ 15 N signatures of swimmers caught in the trap, ~10‰, were on the other hand in the same range as those of the corals A mixed diet of animals and algae could be one explanation for the observed δ 15 N of corals The δ 13 C value of the coral tissue, -2055‰, excludes a food source consisting of bacteria supported by methane seepage, as suggested by earlier studies

High mortality during settlement is a population bottleneck for a tropical surgeonfish

Abstract: Replenishment of benthic marine populations typically involves “settlement” from pelagic larval to benthic juvenile habitats. Mortality during this transition has been unknown because of the difficulty of measuring propagule supply in open water. For three weeks, we compared the nocturnal passage of presettlement fishes across the barrier reef encircling Moorea Island (French Polynesia) with the abundance of benthic recruits in the back-reef lagoon on the following morning. During this time, >40,000 presettlement unicornfish, Naso unicornis entered our study area of ∼1 km2 with half arriving on just two nights. Using coupled Beverton-Holt functions to describe the decay of each cohort, we were able to predict the daily abundance of recruits and their final age structure from the presettlement inputs. The best model estimated that ∼61% of the potential settlers were lost between their nocturnal arrival and the following morning, independent of cohort size. Postsettlement mortality was density dependent, varying between 9% and 20% per day. We attribute all mortality to predation and suggest that high risk associated with settlement has shaped colonization strategies. Because fishing targets the survivors of this population bottleneck, aquarium fisheries may be more sustainable when sourced from pelagic juveniles.

Small-scale spatial and temporal variability in coastal benthic O2 dynamics: Effects of fauna activity

Abstract: 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 22 h 21 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 O 2 consumption rate with large implications for estimated benthic mineralization rates.

Trophodynamic linkage between river runoff and coastal fishery yield elucidated by stable isotope data in the Gulf of Lions (NW Mediterranean)

Abstract: The link between climate-driven river runoff and sole fishery yields observed in the Gulf of Lions (NW Mediterranean) was analysed using carbon- and nitrogen stable isotopes along the flatfish food webs. Off the Rhone River, the main terrestrial (river POM) and marine (seawater POM) sources of carbon differed in δ13C (–26.11‰ and −22.36‰, respectively). Surface sediment and suspended POM in plume water exhibited low δ13C (–24.38‰ and −24.70‰, respectively) that differed more from the seawater POM than from river POM, demonstrating the dominance of terrestrial material in those carbon pools. Benthic invertebrates showed a wide range in δ15N (mean 4.30‰ to 9.77‰) and δ13C (mean −23.81‰ to −18.47‰), suggesting different trophic levels, diets and organic sources. Among the macroinvertebrates, the surface (mean δ13C −23.71‰) and subsurface (mean δ13C −23.81‰) deposit-feeding polychaetes were particularly 13C depleted, indicating that their carbon was mainly derived from terrestrial material. In flatfish, δ15N (mean 9.42 to 10.93‰) and δ13C (mean −19.95‰ to −17.69‰) varied among species, indicating differences in food source and terrestrial POM use. A significant negative correlation was observed between the percentage by weight of polychaetes in the diet and the δ13C of flatfish white muscle. Solea solea (the main polychaete feeder) had the lowest mean δ13C, Arnoglossus laterna and Buglossidium luteum (crustacean, mollusc and polychaete feeders) had intermediate values, and Solea impar (mollusc feeder) and Citharus linguatula (crustacean and fish feeder) exhibited the highest δ13C. Two different benthic food webs were thus identified off the Rhone River, one based on marine planktonic carbon and the other on the terrestrial POM carried by the river. Deposit-feeding polychaetes were responsible for the main transfer of terrestrial POM to upper trophic levels, linking sole population dynamics to river runoff fluctuations.

Consequences of hypoxia on estuarine ecosystem function: energy diversion from consumers to microbes

Abstract: As in other eutrophied estuaries and coastal embayments, persistent hypoxia now routinely develops during summer in the mesohaline portion of the Neuse River estuary (North Carolina, USA). In response to interannual differences in hydrography, summer 1997 exhibited much more intense and widespread hypoxia than summer 1998, permitting inferences about impacts of hypoxia on food web dynamics by comparing system changes across these two summers. The trophic structure of the Neuse estuary now resembles the generic pattern for a degraded temperate estuary with (1) intense planktonic algal blooms and similarly high production of free-living bacteria, (2) trivial levels of abundance of rooted aquatic plants and benthic macroalgae, (3) depleted apex predators, and (4) functional extinction of the historically dominant benthic grazer, eastern oysters. Detailed carbon-flow models, based on comprehensive field data, demonstrated large differences between the two summers in trophic transfers and system dynamics. Largely because of greater mortality of benthic invertebrates from more intense hypoxia, total biomass of heterotrophs declined over summer by 51% in 1997 as compared to only 17% in 1998. Because net primary production increased over summer and herbivory in this system is predominantly benthic, the fraction of primary production consumed by herbivores declined over summer by 35% in 1997 and 29% in 1998. Influx of juvenile fishes and their rapid growth in the estuarine nursery over summer led to increases in energy demand by demersal fishes of 380% and 507% in the successive summers. Thus, hypoxia-enhanced diversion of energy flows into microbial pathways away from consumers and mass mortality of benthic invertebrates from bottom hypoxia occurred at the season of greatest demand by predatory fishes and crabs using the estuary as nursery. Average residence time of carbon in the ecosystem declined by 51% in 1997 and 29% in 1998. Total system throughput declined over summer 1997 while increasing in 1998, indicating the reduced capacity of the system to transfer carbon to higher trophic levels in the more hypoxic summer. Late-summer trophic pathways were characterized by greater numbers of cycles, but flows became increasingly dominated by microbial loops rather than transfers to consumers. Ecosystem trophic efficiency was only ;4%, lower than other estuaries similarly analyzed. System properties indicative of resil- iency of system function including development capacity, ascendancy, and flow diversity declined over summer 1997, while increasing or declining less in 1998. Thus, intensification of hypoxia caused dramatic reduction in the ecosystem's ability to transfer energy to higher trophic levels and rendered the ecosystem potentially less resilient to other stressors.

Species interaction strength: testing model predictions along an upwelling gradient

Abstract: A recent model predicts that species interactions in benthic marine communities vary predictably with upwelling regimes. To test this model, we studied the Pisaster–Mytilus interaction at 14 rocky intertidal sites distributed among three oceanographic regions along a 1300-km stretch of the U.S. West Coast. Regions included an intermittent-upwelling region (northern), a persistent-upwelling region (central), and a region of weak and infrequent upwelling (southern). We quantified predation rates by the sea star Pisaster ochraceus on its main prey Mytilus californianus by transplanting mussels into the sea star's low-zone foraging range and comparing the rate of mussel loss in +Pisaster plots to those in −Pisaster plots. To evaluate the relation between predation rates and key ecological processes and conditions, we quantified phytoplankton concentration and rates of mussel recruitment, mussel growth, mussel abundance, and sea star abundance. Predictions of the model are expressed as responses of predator an...

Temporal variation of light availability in coastal benthic habitats: Effects of clouds, turbidity, and tides

Abstract: 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.

The role of notothenioid fish in the food web of the Ross Sea shelf waters: a review

Abstract: The Ross Sea, a large, high-latitude (72–78°S) embayment of the Antarctic continental shelf, averages 500 m deep, with troughs to 1,200 m and the shelf break at 700 m. It is covered by pack ice for 9 months of the year. The fish fauna of about 80 species includes primarily 4 families and 53 species of the endemic perciform suborder Notothenioidei. This review focuses on the diet and role in the food web of notothenioids and top-level bird and mammal predators, and also includes new information on the diets of artedidraconids and bathydraconids. Although principally a benthic group, notothenioids have diversified to form an adaptive radiation that includes pelagic and semipelagic species. In the southern Ross Sea, notothenioids dominate the fish fauna at levels of abundance and biomass >90% and are, therefore, inordinately important in the food web. Antarctic krill (Euphausia superba) and mesopelagic fishes are virtually absent from the shelf waters of the Ross Sea. Of the four notothenioid families, nototheniids show the most ecological and dietary diversification, with pelagic, cryopelagic, epibenthic and benthic species. Neutrally buoyant Pleuragramma antarcticum constitutes >90% of both the abundance and biomass of the midwater fish fauna. Most benthic nototheniids are opportunistic and feed on seasonally or locally abundant zooplanktonic prey. Artedidraconids are benthic sit-and-wait predators. Larger bathydraconids are benthic predators on fish while smaller species feed mainly on benthic crustaceans. Channichthyids are less dependent on the bottom for food than other notothenioids. Some species combine benthic and pelagic life styles; others are predominantly pelagic and all consume euphausiids and/or fish. South polar skuas, Antarctic petrels, Adelie and emperor penguins, Weddell seals and minke and killer whales are the higher vertebrate components of the food web, and all prey on notothenioids to some extent. Based on the frequency of occurrence of prey items in the stomachs of fish, bird and mammal predators, P. antarcticum and ice krill E. crystallorophias are the key species in the food web of the Ross Sea. P. antarcticum is a component of the diet of at least 11 species of nototheniid, bathydraconid and channichthyid fish and, at frequencies of occurrence from 71 to 100%, is especially important for Dissostichus mawsoni, Gvozdarus svetovidovi and some channichthyids. At least 16 species of notothenioids serve as prey for bird and mammal predators, but P. antarcticum is the most important and is a major component of the diet of south polar skua, Adelie and emperor penguins and Weddell seals, at frequencies of occurrence from 26 to 100%. E. crystallorophias is consumed by some nototheniid and channichthyid fish and can be of importance in the diet of emperor and Adelie penguins, although in the latter case, this is dependent on location and time of year. Unlike the linear phytoplankton→E. superba→consumers of the E. superba food chain hypothesized for much of the Southern Ocean, the food web of the Ross Sea shelf is non-linear, with complex prey-predator interactions. Notothenioid fish play a key role: as predators, they occupy most of the trophic niches available in the ecosystem, relying on benthic, zooplanktonic and nektonic organisms; as prey, they are important food resources for each other and for most top predators living and foraging on the shelf. They also constitute the major link between lower (invertebrates) and higher (birds and mammals) levels of the food web. This is especially true for P. antarcticum. Along with E. crystallorophias, its ecological role in the Ross Sea is equivalent to that of myctophids and E. superba elsewhere in the Southern Ocean.

Soft-bottom macrobenthic faunal associations and factors affecting species distributions in an Arctic glacial fjord (Kongsfjord, Spitsbergen)

Abstract: The Kongsfjord (west Spitsbergen) hosts the most active glacier on the island. Therefore the glacial impact on the marine ecosystem is very pronounced and easily recognisable. The study examines the influence of the steep glacier-derived environmental gradients on dominant macrofaunal species distributions and faunal associations in the fjord. The macrobenthic fauna was sampled by van Veen grab at 30 stations situated throughout the fjord (at depths 38–380 m). Two major communities were recognised. An inner basin receives the outflows from three glaciers and is occupied by a Glacial Bay Community dominated by small, surface detritus-feeders, with Chone paucibranchiata and a set of thyasirid and nuculanid bivalves (Thyasira dunbari, Yoldiella solidula, Y. lenticula) as characteristic species. An outer basin of the fjord is characterised by a common set of dominant species, including Heteromastus filiformis, Maldane sarsi, Levinsenia gracilis, Lumbrineris sp. and Leitoscoloplos sp. Three associations may be distinguished within the Outer Basin Community. Association TRANS is of transitional character, with Nuculoma tenuis and Terebellides stroemi. Association CENTR is the most typical for the community. It is dominated by tube-dwelling Prionospio sp., Clymenura polaris, Galathowenia oculata and Spiochaetopterus typicus. Association ENTR contains shelf benthos elements, e.g. Ophiura robusta and Lepeta caeca. An opportunistic eurytopic Chaetozone group is present throughout the fjord and its density and dominance increase with proximity to the glaciers. Dominant species distribution is discussed in relation to environmental factors, of which sediment stability, inorganic particle concentration, sedimentation rate and amount of organic matter in sediments are considered to be most important in structuring the communities.

Catchment urbanisation and increased benthic algal biomass in streams: linking mechanisms to management

Abstract: 1. Urbanisation is an important cause of eutrophication in waters draining urban areas. We determined whether benthic algal biomass in small streams draining urban areas was explained primarily by small-scale factors (benthic light, substratum type and nutrient concentrations) within a stream, or by catchment-scale variables that incorporate the interacting multiple impacts of urbanisation (i.e. variables that describe urban density and the intensity of drainage or septic tank systems). 2. Benthic algal biomass was assessed as chlorophyll a density (chl a) in 16 streams spanning a rural-urban gradient, with both a wide range of urban density and of piped stormwater infrastructure intensity on the eastern fringe of metropolitan Melbourne, Australia. The gradient of urban density among streams was broadly correlated with catchment imperviousness, drainage connection (proportion of impervious areas connected to streams by stormwater pipes), altitude, longitude and median phosphorus concentration. Catchment area, septic tank density, median nitrogen concentration, benthic light (photosynthetically active radiation) and substratum type were not strongly correlated with the urban gradient. 3. Variation in benthic light and substratum type within streams explained a relatively small amount of variation in log chl a (3-11 and 1-13%, respectively) compared with between-site variation (39-54%). 4. Median chl a was positively correlated with catchment urbanisation, with a large proportion of variance explained jointly (as determined by hierarchical partitioning) by those variables correlated with urban density. Independent of this correlation, the contributions of drainage connection and altitude to the explained variance in chl a were significant. 5. The direct connection of impervious surfaces to streams by stormwater pipes is hypothesised as the main determinant of algal biomass in these streams through its effect on the supply of phosphorus, possibly in interaction with stormwater-related impacts on grazing fauna. Management of benthic algal biomass in streams of urbanised catchments is likely to be most effective through the application of stormwater management approaches that reduce drainage connection.

Depth coenoclines and environmental considerations of western pacific larger foraminifera

Abstract: Symbiont-bearing benthic foraminifera are restricted to the euphotic zone of tropical and warm-temperate seas Species distribution is correlated with depth, and the continuous alteration of community structures represents a coenocline Since depth is a composite environmental gradient, the coenocline of larger foraminifera is not stable but alters with changes in primary limiting factors: temperature, light, water movement, substrate, and nutrients Temperature determines geographic distribution and affects the depth distribution of larger foraminifera by the development of a shallow thermocline that truncates the distribution of shallower species and excludes species adapted to the deepest euphotic zone Within these constraints, light is the most important primary factor because larger foraminifera are at least partly dependent upon photosynthesis by their algal endosymbionts for growth and calcification The microalgae show distinct intervals along the light gradient and the foraminiferal host develops various strategies for regulating light intensity First, well-structured environments in shallow waters allow shelter against irradiation by protecting in shadow areas Second, wall and test structures enable regulation of light penetration A range of mechanisms allows species to resist the highest energies in the breaker zone of the reef edge and crest, where foraminifera attach to inorganic or organic hard substrates Concentrations of dissolved and particulate organic matter in the water column, as well as sediments or other inorganic particles, influence depth distributions by changing water transparency and, therefore, photosynthesis Permanent or episodic elevations of concentrations therefore compress the coenocline upward Species adapted to hard substrates must compete for the reduced space, while species living in the deepest euphotic zone are at a disadvantage because they are insufficiently motile to surmount large depth differences Changing light transparencies due to nutrient input and different hydrodynamic conditions alter relations between the light coenocline and water depth Thus, paleodepth interpretations based on larger foraminiferal assemblages should be based not only on foraminiferal taxa and ecology, but also on environmental evidence for climate, terrigeneous influence, water transparency, and hydrodynamic conditions based on sedimentology, geochemistry, and associated fossil biota

Effects of habitat complexity on benthic assemblages in a variable environment

Abstract: SUMMARY 1. Habitat complexity is thought to exert a significant influence on ecological communities, but its operation under variable natural conditions is not well understood, particularly in freshwater. To elucidate the role of habitat complexity, in particular the fractal structure of surface irregularity, in a stream system, field colonisation experiments were conducted at three times of year (summer, winter and spring) using natural substrates with different levels of fractal dimension in a small coastal mountain stream of southern Japan. 2. In the winter experiment, comparison was also made between the standard (control) treatment and the resource-preconditioning treatment whereby experimental plates were conditioned in the natural stream environment to allow the accumulation of potential food resources (algae and detritus) for 1 month prior to the experiment. 3. Species abundance patterns observed at different times of year showed little systematic variation with levels of habitat complexity but largely followed the patterns expected from, or lying in between, the Random Assortment model and the random fraction model. 4. Taxon richness and density increased with habitat complexity in all seasons except for density in spring. Different taxa showed different patterns of change with habitat complexity, which also varied with seasons. Biomass of invertebrates showed no systematic trend with an increase in habitat complexity. 5. Chlorophyll-a concentrations tended to be lower in more complex habitats, particularly in summer. In contrast, fine particulate organic matter (FPOM) tended to increase with habitat complexity. However, the relationship between these potential food resources and invertebrate assemblages remain unclear. 6. While there were no significant differences in taxon richness and biomass of invertebrates between the resource-preconditioning and the control treatment, density was higher in the former than in the latter. The abundance of relatively large, surface-dwelling animals showed more marked temporal variation over the entire period of colonisation in the resource-preconditioning treatment than in the control treatment. 7. Body size of invertebrates tended to decline with fractal complexity, indicating that crevice sizes could affect habitat use by benthic animals of different sizes. In addition, body size was larger in the resource-preconditioning treatment than in the control treatment, suggesting that body size in invertebrate assemblages was controlled by a mixture of factors. Thus, the present study demonstrates that habitat structure affects benthic invertebrate assemblages in a complex manner.

Degradation and mineralization of coral mucus in reef environments

Abstract: With in situ and laboratory chamber incubations we demonstrate that coral mucus, an important component of particulate organic matter in reef ecosystems, is a valuable substrate for microbial communities in the water column and sandy sediments of coral reefs. The addition of coral mucus to the water of benthic chambers placed on lagoon sands in the coral cay Heron Island, Aus- tralia, resulted in a rapid and significant increase in both O2 consumption and DIC production in the chambers. The permeable coral sands permitted the transport of mucus into the sediment with inter- facial water flows, resulting in the mucus being mainly (> 90%) degraded in the sediment and not in the water column of the chambers. A low ratio of 0.48 (in situ) to 0.64 (laboratory) for O2 consump- tion/DIC production after the addition of coral mucus, and high sulfate reduction rates (SRR) in natural sediments which were exposed to coral mucus, suggest a large contribution of anaerobic processes to the degradation of coral mucus. Oxygen penetrated less than 5 mm deep into these sediments. The microbial reaction to mucus addition was rapid, with a calculated in situ C turnover rate ranging from 7 to 18% h -1 . The degradation of coral mucus showed a dependency on the permeability of the carbonate sediments, with faster degradation and remineralization in coarse sands. This indicates the importance of permeable reef sediments for the trapping and degradation of organic matter. We suggest that coral mucus may have a function as a carrier of energy to the benthic microbial consumers.

Biological and chemical consequences of the 1997-1998 El nino in the Chilean coastal upwelling system: a synthesis

Abstract: The coastal upwelling ecosystem of the Humboldt Current System off Peru and Chile exhibits strong interannual variability due to changes in the oceanographic conditions related to the El Nino (EN) Southern Oscillation. It is generally believed that major changes occur in the community structure and biological production of this system as a consequence of El Nino-La Nina periods. This paper presents a summary of the information available on the physical, chemical, and biological responses of the Chilean upwelling zone resulting from the strong 1997–1998 EN event. Oceanographic changes for the whole region included the intrusion of oceanic, low-nutrient, warmer, and more oxygenated waters into the coastal areas, with positive sea-surface temperature anomalies lasting until the winter of 1998. Off northern Chile, small-sized phytoplankton prevailed and chlorophyll-a fluctuated widely during most of the EN event, although inshore levels were consistently high. Zooplankton assemblages shifted to smaller species during the warm phase; the total biomass, however, did not change. Primary production rates and the vertical flux of carbon were not greatly affected. The total anchovy catch for 1997 held stable, reaching up to 1 million tons. In 1998, the catch decreased to 400,000 tons before recovering to 1.2 million tons in 1999 and 2000. Off central/southern Chile, the ‘normal’ seasonal regime (spring/summer benthic hypoxia) was replaced by oxygenation near the bottom and lower carbon input as a result of the EN event. Macrofaunal biomass increased significantly in the inshore sediments during the warm phase, then diminished in the following spring/summer period. The decreased macrofaunal biomass was associated with the disappearance of filamentous bacterial mats and increased benthic bioturbation. The overall productive capacity of the Chilean upwelling systems seems to have recovered rapidly after the EN decline, suggesting weaker ecological impacts than those observed in the seasons after the 1972–1973 and 1982–1983 events.

The European coastal zone: characterization and first assessment of ecosystem metabolism

Abstract: The geomorphic, oceanographic, terrestrial and anthropogenic attributes of the European coastal zone are described and published data on ecosystem function (primary production and respiration) are reviewed. Four regions are considered: the Baltic Sea, Mediterranean Sea, Black Sea and the European Atlantic coast including the North Sea. The metabolic database (194 papers) suffers from a non-homogeneous geographical coverage with no usable data for the Black Sea which was therefore excluded from this part of our study. Pelagic gross primary production in European open shelves is, by far, the most documented parameter with an estimated mean of 41 mmol C m −2 d −1 , the lowest value is reported in the Mediterranean Sea (21 mmol C m −2 d −1 ) and the highest one in the Atlantic/North Sea area (51 mmol C m −2 d −1 ). Microphytobenthic primary production, mostly measured in shallow areas, is extrapolated to the entire 0–200 m depth range. Its contribution to total primary production is low in all regions (mean: 1.5 mmol C m −2 d −1 ). Although macrophyte beds are very productive, a regional production estimate is not provided in this study because their geographical distribution along the European coastline remains unknown. Measurements of pelagic community respiration are clearly too sparse, especially below the euphotic zone, to yield an accurate picture of the fate of organic matter produced in the water column. With a mean value of 17 mmol C m −2 d −1 , benthic community respiration consumes approximately 40% of the pelagic organic matter production. Estuaries generally exhibit high metabolic rates and a large range of variation in all parameters, except microphytobenthic primary production. Finally, the problem of eutrophication in Europe is discussed and the metabolic data obtained in the framework of the Land–Ocean Interactions in the Coastal Zone (LOICZ) project are compared with available direct measurements of net ecosystem production.

Evolution and diversity of the benthic fauna of the Southern Ocean continental shelf

Abstract: The modern benthic fauna of the Antarctic continental shelf is characterized by the lack of active, skeleton-breaking (durophagous) predators such as crabs, lobsters and many fish, and the dominance in many areas of epifaunal suspension feeders. It has often been remarked that these ecological characteristics give the fauna a distinctly Palaeozoic feel, with the assumption that it may be an evolutionary relic. We now know that this is not so, and fossil evidence shows clearly that many of the taxa and life-styles that are absent now were previously present. The modern fauna has been shaped by a number of factors, important among which have been oceanographic changes and the onset of Cenozoic glaciation. Sea-water cooling, and periodic fragmentation of ranges and bathymetric shifts in distribution driven by variability in the size and extent of the continental ice cap on Milankovitch frequencies will all have caused both extinction and allopatric speciation. The modern glacial setting with relatively low terrestrial impact away from immediate coastal regions, and scouring by icebergs are the key factors influencing the ecology and population dynamics for the modern Antarctic benthos.

Temporal and Spatial Distribution of Dissolved Oxygen in the Pearl River Estuary and Adjacent Coastal Waters

Abstract: The Pearl River is one of the large rivers in the world and it discharges to the northern part of the South China Sea. There has been a concern about the deterioration of dissolved oxygen conditions in the Pearl River estuary and adjacent coastal waters. In this study, historical data on dissolved oxygen (DO) from 1980s, recent data from a summer cruise in 1999, and a 10-year time series in DO for 1990-2000 were used to examine spatial and temporal distribution of DO in the Pearl River estuary and adjacent coastal waters near Hong Kong. In the adjacent coastal waters, low oxygen waters 4 mg 1(-1) in the western part in August 1984. In July 1999, DO was 4 mg 1(-1). The 9-year time series showed that DO decreased periodically in summer, but rarely dropped to < 3 mg 1-1. There was no apparent trend of decreasing DO between 1990 and 2000. Compared to August 1984, DO decreased significantly during the summer of 1999 in the Pearl River estuary, but large scale hypoxia (< 2 mg 1-1) was not observed. The spatial distribution of low oxygen waters may be controlled by estuarine circulation because DO was significantly correlated with salinity in the summers of 1981 and 1984. Furthermore, the spatial distribution of DO in the bottom layer was parallel to the topography of the bottom, indicating the importance of benthic consumption of DO in the sediment and the subsequent flux of low DO waters from the sediment water interface resuspended by physical mixing. Relative to the high loading of nitrogen from the Pearl River, the present PO4 concentration is still low. It is possible that the lack of large areas of hypoxia in the region may be linked to phosphorus limitation as shown in the previous study. Phosphorus may also be a limiting factor for bacterial decomposition which has a strong control on total oxygen consumption in the water column and sediments. (C) 2004 Elsevier Ltd. All rights reserved.