Nearshore Benthic Communities Research Articles

Subfossil Chironomid Assemblages as Indicators of Remedial Efficacy in the Historically Contaminated St. Lawrence River at Cornwall, Ontario.

Long-term data are required to quantify the impacts of historic industrial pollution and subsequent remedial action on the nearshore benthic community in the St. Lawrence River Area of Concern at Cornwall, Ontario. Specifically, high-quality temporal records are needed to understand changes in benthic invertebrate assemblages in response to multiple possible drivers including industrial pollution, environmental heterogeneity, and climate warming. We compare long-term records of subfossil chironomid assemblages and geochemical variables among sediment cores from two Cornwall sites with differing pollution histories and a minimally disturbed downstream reference site. Chironomids were functionally absent from the Cornwall sediment cores when mercury and zinc concentrations were elevated. As metal concentrations decreased in more recent sediment intervals, chironomid abundance and the relative abundance of pollution-sensitive taxa increased. Recently deposited sediment in all three sediment cores display increased relative abundance of warm-water, macrophyte-associated taxa. We conclude that these temporal changes in chironomid assemblages provide evidence for ecological recovery for both of the impacted sites, consistent with the objectives of the current management strategy. These findings advance our understanding of industrial impacts on fluvial chironomid ecology, directly inform local management strategies, and further develop the application of chironomids as bioindicators for contaminated sediments.

Distribution of terrestrial organic material in intertidal and nearshore marine sediment due to debris flow response efforts

We examined the distribution and processing of terrestrial organic material, derived from the disposal of material from a massive debris flow event following a major wildfire in a coastal California (USA) catchment in intertidal and nearshore subtidal marine sediments. Organic matter biomarkers, pyrogenic carbon and lignin phenols, were used to trace the distribution of terrestrial debris material in marine environments. In intertidal sediments located <1 km east of the debris deposition site, pyrogenic carbon values did not significantly change and lambda values, a lignin measure, decreased over time, indicating little lateral transport of the disposed material. In subtidal sediment, pyrogenic carbon and lambda values were greatest in 20 m water depths indicating transport and deposition of this material nearshore. An additional lignin measure indicative of degradation suggested terrestrial organic material degradation in subtidal sediment decreased with distance from shore. Terrestrial biomarkers demonstrated that the disposed material was not detected in the top 20 cm of intertidal sediment but was retained in subtidal sediment offshore of the disposal site. Results suggest coastal management should incorporate consideration of the effects of debris disposal activities on nearshore benthic communities and biogeochemical cycling.

Diving Behavior and Fine-Scale Kinematics of Free-Ranging Risso's Dolphins Foraging in Shallow and Deep-Water Habitats

Air-breathing marine predators must balance the conflicting demands of oxygen conservation during breath-hold and the cost of diving and locomotion to capture prey. However, it remains poorly understood how predators modulate foraging performance when feeding at different depths and in response to changes in prey distribution and type. Here, we used high-resolution multi-sensor tags attached to Risso’s dolphins (Grampus griseus) and concurrent prey surveys to quantify their foraging performance over a range of depths and prey types. Dolphins (N=33) foraged in shallow and deep habitats [seabed depths less or more than 560m, respectively] and within the deep habitat, in vertically stratified prey features occurring at several aggregation levels. Generalized linear mixed-effects models indicated that dive kinematics were driven by foraging depth rather than habitat. Bottom-phase duration and number of buzzes (attempts to capture prey) per dive increased with depth. In deep dives, dolphins were gliding for >50% of descent and adopted higher pitch angles both during descent and ascents, which was likely to reduce energetic cost of longer transits. This lower cost of transit was counteracted by the record of highest vertical swim speeds, rolling maneuvers and stroke rates at depth, together with a 4-fold increase in the inter-buzz interval, suggesting higher costs of pursuing and handling prey compared to shallow-water feeding. In spite of the increased capture effort at depth, dolphins managed to keep their estimated overall metabolic rate comparable across dive types. This indicates that adjustments in swimming modes may enable energy balance in deeper dives. If we think of the surface as a central place where divers return to breathe, our data match predictions that central place foragers should increase the number and likely quality of prey items at greater distances. These dolphins forage efficiently from near-shore benthic communities to depth-stratified scattering layers, enabling them to maximize their fitness.

Unraveling the multiple bottom-up supplies of an Antarctic nearshore benthic community

Disentangling the bottom-up controls of natural ecosystems is key to understanding the capacity of local communities to resist natural and anthropogenic disturbances. Here, we used carbon and nitrogen stable isotope ratios with a Bayesian multiple source mixing model to trace diverse food sources supporting the benthic trophic network in Fildes Bay (South Shetland Island, Western Antarctic Peninsula). Individuals of 16 species of consumers and five potential food sources (e.g. inter- and subtidal macroalgae, suspended and sinking particulate organic matter, and particulate organic matter from sediment) were collected during January and February 2017. The results showed that benthic organisms of Fildes Bay assimilate a broad range of available organic matter: most of the energy channeled to upper trophic consumers comes from organic matter in the surface sediment, whereas energy moving among lower trophic consumers comes largely from macroalgae and pelagic primary food sources. Overall, our evidence indicates that the present-day nearshore benthic community of Fildes Bay relies on different primary food sources, channeling bottom-up supplies through multiple pathways, which leads to highly stable systems in the face of current scenarios of global change.

Trophic Transfer of Macroalgal Fatty Acids in Two Urchin Species: Digestion, Egestion, and Tissue Building

Sea urchins are ecosystem engineers of nearshore benthic communities because of their influence on the abundance and distribution of macroalgal species. Urchins are notoriously inefficient in assimilation of their macroalgal diets, so their fecal production can provide a nutritional subsidy to benthic consumers that cannot capture and handle large macroalgae. We studied the assimilation of macroalgal diets by urchins by analyzing the profiles of trophic biomarkers such as fatty acids (FAs). We tracked macroalgal diet assimilation in both Strongylocentrotus droebachiensis and S. purpuratus. Juvenile S. droebachiensis and adult S. purpuratus were maintained for 180 and 70 days, respectively, on one of three monoculture diets from three algal phyla: Nereocystis luetkeana, Pyropia sp., or Ulva sp. We then analyzed FA profiles of the macroalgal tissue fed to urchins as well as urchin gonad, gut, digesta, and egesta (feces) to directly evaluate trophic modification and compare nutritional quality of urchin food sources, urchin tissues, and fecal subsidies. In the S. purpuratus assay, there were significantly more total lipids in the digesta and egesta than in the algae consumed. The FA profiles of urchin tissues differed among urchin species, all diets, and tissue types. Despite these differences, we observed similar patterns in the relationships between the urchin and macroalgal tissues for both species. Egesta produced by urchins fed each of the three diets were depleted with respect to the concentration of important long chain polyunsaturated fatty acids (LCPUFAs), but did not differ significantly from the source alga consumed. Both urchin species were shown to synthesize and selectively retain both the precursor and resulting LCPUFAs involved in the synthesis of the LCPUFAs 20:4⍵6 and 20:5⍵3. S. droebachiensis and S. purpuratus exhibited consistent patterns in the respective depletion and retention of precursor FAs and resulting LCPUFAs of Pyropia and Ulva tissues, suggesting species level control of macroalgal digestion or differential tissue processing by gut microbiota. For both S. droebachiensis and S. purpuratus, macroalgal diet was a surprisingly strong driver of urchin tissue fatty acids; this indicates the potential of fatty acids for future quantitative trophic estimates of urchin assimilation of algal phyla in natural settings.

Living Shorelines Support Nearshore Benthic Communities in Upper and Lower Chesapeake Bay

Human population growth and sea-level rise are increasing the demand for protection of coastal property against shoreline erosion. Living shorelines are designed to provide shoreline protection and are constructed or reinforced using natural elements. While living shorelines are gaining popularity with homeowners, their ability to provide ecological services (e.g., habitat provision and trophic transfer) is not well understood, and information is needed to improve coastal and resource management decision-making. We examined benthic community responses to living shorelines in two case-study subestuaries of Chesapeake Bay using a before-after control-impact study design. At Windy Hill, a bulkhead was removed and replaced by three tombolos, sand fill, and native marsh vegetation. At Lynnhaven, 25 m of eroding marsh shoreline was stabilized with coir logs, sand fill, and native marsh vegetation. Communities of large (> 3 mm) infauna adjacent to living shorelines at both locations tended to increase in biomass by the end of the study period. Community compositions changed significantly following living shoreline construction at Windy Hill, reflecting a trend toward higher density and biomass of large bivalves at living shorelines compared to pre-construction. Increasing trends in density and biomass of clams and simultaneously decreasing density and decreasing trends in biomass of polychaetes suggest a transition toward stable infaunal communities at living shorelines over time, though longer-term studies are warranted.

A swath across the great divide: Kelp forests across the Samalga Pass biogeographic break

Biogeographic breaks are often described as locations where a large number of species reach their geographic range limits. Samalga Pass, in the eastern Aleutian Archipelago, is a known biogeographic break for the spatial distribution of several species of offshore-pelagic communities, including numerous species of cold-water corals, zooplankton, fish, marine mammals, and seabirds. However, it remains unclear whether Samalga Pass also serves as a biogeographic break for nearshore benthic communities. The occurrence of biogeographic breaks across multiple habitats has not often been described. In this study, we examined if the biogeographic break for offshore-pelagic communities applies to nearshore kelp forests. To examine whether Samalga Pass serves as a biogeographic break for kelp forest communities, this study compared abundance, biomass and percent bottom cover of species associated with kelp forests on either side of the pass. We observed marked differences in kelp forest community structure, with some species reaching their geographic range limits on the opposing sides of the pass. In particular, the habitat-forming kelp Nereocystis luetkeana, and the predatory sea stars Pycnopodia helianthoides and Orthasterias koehleri all occurred on the eastern side of Samalga Pass but were not observed west of the pass. In contrast, the sea star Leptasterias camtschatica dispar was observed only on the western side of the pass. We also observed differences in overall abundance and biomass of numerous associated fish, invertebrate and macroalgal species on opposing sides of the pass. We conclude that Samalga Pass is important biogeographic break for kelp forest communities in the Aleutian Archipelago and may demark the geographic range limits of several ecologically important species.

Skeletal ossicles in echinoids are unreliable chronometers: Comment on “Population dynamics of Strongylocentrotus droebachiensis in kelp forests and barren grounds in Norway” (Fagerli et al. 2015)

Sea urchins are important drivers of nearshore benthic communities. Understanding their critical life history characteristics such as age structure and mortality requires accurate and reliable estimates of growth. The green sea urchin, Strongylocentrotus droebachiensis, occurs on both sides of the northern Pacific and Atlantic oceans and can play a key role in stable state shifts from urchin barrens to kelp bed communities. A recent study of these systems in Norway used growth zones, or bands, in the skeletal ossicles (interambulacral plates) of green urchins as chronometers—estimators of age. Combined with measures of size, the age estimates were used to construct growth curves, population age structures, and estimates of site-specific mortality. However, there is much confusion surrounding the aging technique in regard to skeletal growth, ossicle selection, and misinterpretations of previous validation studies. Our comment clarifies these issues using data from the Norway study and two published validation studies. In addition, we provide criteria for assessing whether sea urchin ossicles are accurate and valid chronometers. Given the limited understanding of endogenous and exogenous causes of different types of bands, ontogenetic variation, intra- and interspecific variation, and a paucity of detailed information about their chemical composition, at least at this time, bands should not be used to determine age in sea urchins.

The impacts of climate change on Antarctic nearshore mega-epifaunal benthic assemblages in a glacial fjord on King George Island: Responses and implications

We examined the impacts of climate change on Antarctic nearshore marine benthic communities on the West Antarctic Peninsula, one of the most rapidly warming regions on earth. We surveyed the epibenthic megafaunal assemblages of Marian Cove, a representative fjord on King George Island. We collected specimens by SCUBA diving at varying distances from the retreating glacier front during the 2013/2014 austral summer. Based on presence/absence data from the collected taxa, we determined species richness (S), taxonomic distinctness (TD) and functional diversity (FD) and further analyzed differences in assemblages in relation to environmental characteristics. Faunal assemblages in the inner cove (ice-proximal zone) were compositionally distinct from those in the outer cove. Species number and FD were also lower in the inner cove and tended to increase toward the outer cove. Nonetheless, TD values were similar among sites, indicating that all sites were distinct taxonomically. This may be because glacier retreat affected organisms of lower taxonomic levels the most. Multivariate and univariate analyses demonstrated that these differences were significantly related to distance from the glacier, substrate grain size, and organic content. The high correlation (R=0.909, P<0.01) of assemblages with distance from the glacier front suggests that physical disturbance by ice is a major process shaping benthic communities. Thus, we provide evidence that glacier retreat and its consequent processes impact the structure and function of communities. With their spatial pattern significantly associated with environmental suites, nearshore megabenthic communities respond sensitively and measurably to climate-induced impacts, suggesting their utility as long-term biomonitors. As a small but confined glacial cove with very distinct environmental gradients related to climate-induced processes, Marian Cove could serve as a model ecosystem for assessing climate impacts on Antarctic nearshore benthic communities.

Habitat coupling in a large lake system: delivery of an energy subsidy by an offshore planktivore to the nearshore zone of Lake Superior

Summary We hypothesised that the autumn spawning migration of Lake Superior cisco (Coregonus artedi) provides a resource subsidy, in the form of energy‐rich cisco eggs, from the offshore pelagic to the nearshore benthic community over winter, when alternate prey production is likely to be low. We tested this hypothesis using fish and macroinvertebrate surveys, fish population demographics, diet and stable isotope analyses, and bioenergetics modelling. The benthic, congeneric lake whitefish (C. clupeaformis) was a clear beneficiary of cisco spawning. Cisco eggs represented 16% of lake whitefish annual consumption in terms of biomass, but 34% of energy (because of their high energy density: &gt;10 kJ g wet mass−1). Stable isotope analyses were consistent with these results and suggest that other nearshore fish species may also rely on cisco eggs. The lipid content of lake whitefish liver almost doubled from 26 to 49% between November and March, while that of muscle increased from 14 to 26% over the same period, suggesting lake whitefish were building, rather than depleting, lipid reserves during winter. In the other Laurentian Great Lakes, where cisco populations remain very low and rehabilitation efforts are underway, the offshore‐to‐nearshore ecological link apparent in Lake Superior has been replaced by non‐native planktivorous species. These non‐native species spawn in spring have smaller eggs and shorter incubation periods. The rehabilitation of cisco in these systems should reinstate the onshore subsidy as it has in Lake Superior.

Relationships among round gobies, Dreissena mussels, and benthic algae in the south nearshore of Lake Ontario

Round goby (Neogobius melanostomus) populations are established in all the Great Lakes, subsequent to the success of the Dreissena mussel invasion. Additionally, localized resurgence of the nuisance alga, Cladophora glomerata, also has been reported across several of the Great Lakes post-Dreissena. We examined the relationship among round goby size and population density and Dreissena mussel metrics and Cladophora biomass in three regions of the nearshore environment of U.S. waters of Lake Ontario during summer 2008. We also estimated the size of the round goby population in these regions. Correlations between round goby population metrics and Dreissena mussel metrics suggest a low potential for lakewide control of mussel populations by round gobies. In August but not June, fish density was positively correlated with Dreissena density, biomass, and size, suggesting round gobies did not depress mussel numbers, but may selectively remove some smaller mussel size classes. Round goby length was positively correlated with Cladophora biomass, which probably is best explained as a sampling artifact. Seasonal changes in the round goby population density with depth were suggestive of an offshore migration in late summer. Fish were generally smaller but equally abundant, moving west-to-east along the nearshore environment of the lake. We estimated that the nearshore population size of round gobies was 0.7billion fish, equivalent to 2.2 fish/m2. This translated into approximately 1287tonnes of round gobies or about 40kg/ha. Coupled with the broad diet selection of this invasive fish, results suggest that round gobies will have a substantial impact on the structure of the nearshore benthic community.

Nearshore benthic community structure at the Bounty and Antipodes Islands, Subantarctic New Zealand

Management decisions aimed at protecting biodiversity ideally should be based on biological information, but for remote and logistically difficult sites, such as are found at high latitudes, these data may be lacking. During March 2009, surveys were completed of the nearshore rocky reef communities around the Bounty and Antipodes Islands, in New Zealand’s subantarctic region. Previously considered to support the same habitat types (which used physical variables as surrogates for biological communities), analysis of photoquadrats taken at both island groups showed that the rocky reef communities were significantly different, both in terms of their species composition and in terms of their potential ecological function. While Antipodes Island supported fairly typical subantarctic shallow subtidal marine communities dominated by nongeniculate coralline algae, the rocky reefs at the Bounty Islands were dominated by filter- and suspension-feeding invertebrates, in particular encrusting sponges, barnacles and mussels. The mobile invertebrate fauna associated with these communities were also significantly different between the two island groups. Contrasting geology, oceanographic conditions and nutrient input from seabird and pinniped colonies may all contribute to the observed nearshore community structures at the Bounty and Antipodes Islands. Our research provides a baseline for assessing change in the subantarctic region and highlights the importance of using biological community data where available, to inform conservation management decisions.

Kelp distribution in the northwest Atlantic Ocean under a changing climate

Warming of the planet has accelerated in recent years and is predicted to continue over the next century. Environmental consequences include increasing water temperatures, and evidence of ecological responses to current warming in marine coastal ecosystems is found in poleward shifts in the geographic range of species as well as changes in the composition of nearshore benthic communities. Most evidence has, however, been obtained from intertidal studies, but similar shifts should be occurring for subtidal communities as well, especially for the ecologically important kelp species that provide both food and shelter to a multitude of organisms. Kelp may be particularly vulnerable to climate change due to their cold-water affinities and limited dispersal ability. A major biogeographic transition occurs along northwest Atlantic shores of Canada between subarctic and boreal zones where major shifts can be seen in the composition of kelp assemblages of Alaria esculenta, Laminaria digitata, Saccharina longicruris and Saccharina latissima. Here we review the historic and recent distribution and abundance of these species and find no evidence of changes in the past century. However, sparse coverage of data, inconsistent methodology and a lack of adequate time series prevent us from concluding that no changes have occurred, especially with respect to natural variation and anthropogenic alteration. These shortcomings illustrate the need for identifying sentinel species and sites for studies dedicated to the specific questions of climate-induced changes in kelp abundance and distribution. We suggest that a combination of traditional and modern tools (e.g., benthic surveys and climate model forecasting, respectively) offers the best path forward.

Novel methodology for in situ carbon dioxide enrichment of benthic ecosystems

Future climate change will likely represent a major stress to shallow aquatic and coastal marine communities around the world. Most climate change research, particularly in regards to increased pCO2 and ocean acidification, relies on ex situ mesocosm experimentation, isolating target organisms from their environment. Such mesocosms allow for greater experimental control of some variables, but can often cause unrealistic changes in a variety of environmental factors, leading to “bottle effects.” Here we present an in situ technique of altering dissolved pCO2within nearshore benthic communities (e.g., macrophytes, algae, and/or corals) using submerged clear, open‐top chambers. Our technique utilizes a flow‐through design that replicates natural water flow conditions and minimizes caging effects. The clear, open‐top design additionally ensures that adequate light reaches the benthic community. Our results show that CO2 concentrations and pH can be successfully manipulated for long durations within the open‐top chambers, continuously replicating forecasts for the year 2100. Enriched chambers displayed an average 0.46 unit reduction in pH as compared with ambient chambers over a 6‐month period. Additionally, CO2 and HCO3− concentrations were all significantly higher within the enriched chambers. We discuss the advantages and disadvantages of this technique in comparison to other ex situ mesocosm designs used for climate change research.

The Nearshore Benthic Community of Kasatochi Island, One Year after the 2008 Volcanic Eruption

A description is presented of the nearshore benthic community of Kasatochi Island 10–12 months after a catastrophic volcanic eruption in 2008. The eruption extended the coastline of the island approximately 400 m offshore, mainly along the south, southeast, and southwest shores, to roughly the 20 m isobath. Existing canopy kelp of Eualaria (Alaria) fistulosa, as well as limited understory algal species and associated fauna (e.g., urchin barrens) on the hard substratum were apparently buried following the eruption. Samples and observations revealed the substrate around the island in 2009 was comprised almost entirely of medium and coarse sands with a depauperate benthic community, dominated by opportunistic pontogeneiid amphipods. Comparisons of habitat and biological communities with other nearby Aleutian Islands, as well as with the Icelandic volcanic island of Surtsey, confirm dramatic reductions in flora and fauna consistent with an early stage of recovery from a large-scale disturbance event.

Predicting habitat use and trophic interactions of Eurasian ruffe, round gobies, and zebra mussels in nearshore areas of the Great Lakes

The Laurentian Great Lakes have been subject to numerous introductions of nonindigenous species, including two recent benthic fish invaders, Eurasian ruffe (Gymnocephalus cernuus) and round gobies (Neogobius melanostomus), as well as the benthic bivalve, zebra mussel (Dreissena polymorpha). These three exotic species, or “exotic triad,” may impact nearshore benthic communities due to their locally high abundances and expanding distributions. Laboratory experiments were conducted to determine (1) whether ruffe and gobies may compete for habitat and invertebrate food in benthic environments, and (2) if zebra mussels can alter those competitive relationships by serving as an alternate food source for gobies. In laboratory mesocosms, both gobies and ruffe preferred cobble and macrophyte areas to open sand either when alone or in sympatry. In a 9-week goby–ruffe competition experiment simulating an invasion scenario with a limited food base, gobies grew faster than did ruffe, suggesting that gobies may be competitively superior at low resource levels. When zebra mussels were added in a short-term experiment, the presence or absence of mussels did not affect goby or ruffe growth, as few zebra mussels were consumed. This finding, along with other laboratory evidence, suggests that gobies may prefer soft-bodied invertebrate prey over zebra mussels. Studies of interactions among the “exotic triad”, combined with continued surveillance, may help Great Lakes fisheries managers to predict future population sizes and distributions of these invasive fish, evaluate their impacts on native food webs, and direct possible control measures to appropriate species.

The nearshore phosphorus shunt: a consequence of ecosystem engineering by dreissenids in the Laurentian Great Lakes

Dreissenid mussels have been exceptionally successful invaders in North American lakes and rivers, especially in the lower Laurentian Great Lakes. As benthic filter feeders capable of attaching to hard substrates, the magnitudes of their biomass and filtering activity in nearshore waters are without precedent. The dreissenid colonization has implications for the removal and fate of materials filtered from the water by the mussels and for the longer-term development of the nearshore benthic community and lake ecosystem. A conceptual model, the nearshore shunt, seeks to describe a fundamental redirection of nutrient and energy flow consequent to dreissenid establishment. The model explains some emergent problems in the Great Lakes, such as reemergence of Cladophora in some coastal zones while offshore P concentrations remain low, and highlights areas in need of more research. The source of particulate nutrient inputs to dreissenids and the fate of materials exported from the benthic community are critical to understanding the role of dreissenids in the lakes and assessing the applicability of current models for managing nutrients and fisheries. The nearshore shunt would require even more stringent P management for lakes strongly impacted by dreissenids to maintain nearshore water quality.

Alongshore and temporal variability in chlorophyll a concentration in Chilean nearshore waters

Phytoplankton and particulate organic matter constitute the primary food source for adult filter-feeders, as well as for larval stages of many benthic and pelagic organisms. The structure and dynamics of nearshore benthic communities may be associated with variation in nearshore primary production. However, we know little about the scales of variability in phytoplankton in nearshore waters along open coasts, or about their causes. To characterize spatial and temporal patterns of chl a concentration, we conducted 2.5 yr of daily, shore-based monitoring at 3 sites separated by 10s of km within an upwelling region in central Chile. We found that: (1) peaks in chl a concentration were typ- ically short-lived, persisting no longer than 4 d, (2) blooms occurred in spring to early summer months at all sites, but also during autumn months at 1 site (Las Cruces), and (3) the intensity and frequency of blooms were consistently different among sites; highest concentrations were at Las Cruces, lower at El Quisco, and the lowest at Quintay. Analyses of wind data and surface temperature, and inspection of Advanced Very High Resolution Radiometer (AVHRR) satellite images, suggested that among-site dif- ferences were due, at least in part, to alongshore variation in upwelling intensity and the formation of warm-water pockets or upwelling shadows in sections of the coast, such as Las Cruces. In contrast to the spatial pattern described offshore and over larger spatial scales, chl a concentrations were signifi- cantly lower at the coldest site, Quintay, located at the core of an upwelling center (Pta. Curaumilla), than at the warmer site of Las Cruces, which lies downstream from upwelling. Day-to-day variation in chl a levels during spring at Las Cruces seems related to the alongshore intrusion of waters upwelled upstream. Overall, the pattern observed at our 3 sites, together with previous studies at other up- welling systems, suggests that sections of the coast around 15 to 20 km downstream (equatorward) from upwelling centers could exhibit consistently higher phytoplankton concentrations than sites lo- cated in front of upwelling centers, generating a source-sink type of geographic pattern of nearshore nutrients and phytoplankton along the coast.

No longer the pristine confines of the world ocean: a survey of exotic marine species in the southwestern Atlantic

We conducted a comprehensive survey of existing knowledge about exotic marine organisms introduced to the southwestern Atlantic Ocean, including coastal and shelf areas of Uruguay and Argentina. This domain is equivalent to the so-called Patagonian Shelf Large Marine Ecosystem, and corresponds to two biogeographic provinces: warmtemperate (Argentine Province) and cold temperate (Magellanic Province). The search included species that can be confidently categorized as introduced (31) and cryptogenic species (46). We present a comprehensive picture of recorded introductions (the first for this region) and some prominent ecological consequences. Most coastal ecosystems between the La Plata River estuary and central Patagonia have already been modified, or are expected to be so in the short term. Five recent, human-mediated biological invasions have already had a significant ecological impact. A barnacle (Balanus glandula) belt has developed on all rocky shores where none was present 30 years ago, a macro-fouler (Limnoperna fortunei) and a reef-builder (Ficopomatus enigmaticus) have strongly modified estuarine ecosystems, Pacific oyster (Crassostrea gigas) reefs are expanding in shallow bays at a fast rate, and kelp (Undaria pinnatifida) is rapidly modifying nearshore benthic communities along the coasts of central Patagonia. At this point, it is uncertain how many of the cordgrasses (Spartina spp.) found in coastal salt marshes correspond to exotic forms. Only exposed sandy beaches appear to be free from the pervasive ecological impact of invasion by exotic species. Poor knowledge of the regional biota makes it difficult to track invasions.

Impact of Bleached Kraft Pulp Mill Effluent on the Nearshore Benthic Community of Jackfish Bay, Lake Superior

Abstract We assessed the impact of bleached kraft pulp mill effluent on benthic invertebrate community structure in the shallow (1 m) nearshore waters of Jackfish Bay, Lake Superior. Duplicate benthic samples were collected from 0.5 m2 quadrats at twenty-three stations along two shorelines of Jackfish Bay up to 1800 m from the point of effluent discharge, and from a reference station located within the Jackfish Bay study area. Detrended correspondence analysis (DCA) revealed a gradient of stations on both shorelines which was strongly correlated with distance from effluent outfall and hence exposure to the effluent plume. Within this gradient were two distinct clusters of stations. The first cluster contained all but one station on both shores &amp;lt;300 m from the outfall; these stations receive constant exposure to the effluent and were dominated (&amp;gt;90%) by tubificids (Limnodrilus hoffmeisteri, Tubifex tubifex, T. ignotus and Spirosperma ferox) and the naidid Chaetogaster diaphanus. The second cluster contained all stations on both shores &amp;gt;300 m from the outfall; community structure at these stations was generally comparable to that at the reference site and was characterized by several species of Chironomidae, C. diaphanus and Nais barbata, and low numbers of several insect taxa. The results of this study show that benthic community structure in nearshore environments can be significantly impacted by pulp mill effluent and should be considered in monitoring assessments. At Jackfish Bay, such impacts appear to be restricted primarily to within the first 500 m of effluent discharge.