Short-term predator avoidance behavior by invasive and native amphipods in the Great Lakes

Understanding predator avoidance behavior by prey remains an important topic in community and invasion ecology. Recently, the Ponto-Caspian amphipod Echinogammarus ischnus (Stebbing 1898) was accidentally introduced into the Great Lakes. Since its introduction, it has displaced the native amphipod, Gammarus fasciatus (Say 1818), from several locations in the lower lakes. To assess whether behavioral differences in predator avoidance might be a causal mechanism increasing the success of the invasive amphipods, two experiments were conducted examining (1) native and invasive amphipod behavioral responses to five fish species with different foraging behaviors, and (2) amphipod responses to different densities of round gobies, a hyper-abundant benthic invertivore. Echinogammarus reduced its distance moved in the presence of all fish species tested, whereas Gammarus reduced its distance moved only after exposure to round gobies, black crappies, and rainbow darters. Both amphipod species increased the time spent motionless following exposure to round gobies, but not after encountering the scent of most of the remaining fish predators. The exception was that Echinogammarus also responded to black crappie scent whereas Gammarus did not. Although both amphipod species exhibited behavioral responses to many of the fish predators, the magnitude of their responses differed only after exposure to the brown bullhead. In the bullhead trials, Echinogammarus reduced its distance traveled significantly more than Gammarus. Both amphipod species increased their avoidance response to increasing goby density, however, the pattern of avoidance behavior was different. Invasive E. ischnus exhibited a consistently strong avoidance response to round gobies over the test duration. Native G. fasciatus initially avoided goby scent, but then either ceased their avoidance response or showed a hyper-avoidance response, depending on goby density. These results suggested (1) both species of amphipods were able to differentiate and react to a variety of fish predators, (2) invasive Echinogammarus amphipods avoided a larger range of fish predators than the native Gammarus, (3) increased avoidance behavior was associated with an increased density of fish, and (4) the avoidance response patterns of invasive Echinogammarus when faced with round goby predators might lead to increased predation on native Gammarus in habitats where they co-occur.     

Community‐level effects of co‐occurring native and exotic ecosystem engineers

1. Non‐indigenous ecosystem engineers can substantially affect native biodiversity by transforming the physical structure of habitats. In the Great Lakes–St. Lawrence River system, introduced dreissenid mussels (Dreissena polymorpha and D. bugensis) and the native benthic macroalga Cladophora act as ecosystem engineers by increasing substratum complexity and providing interstitial habitat for benthic macroinvertebrates. 2. We manipulated the topography and perimeter‐to‐area ratio of patches of dreissenid mussels in a series of colonisation experiments conducted at two sites in the St. Lawrence River. Experimental substrata were variably colonised by Cladophora, prompting us to examine (i) how the topography of Dreissena patches affects benthic macroinvertebrate diversity and (ii) the extent to which the effects of Dreissena are altered by the presence of another habitat‐modifying organism (Cladophora). 3. The results of our first experiment suggested that a patchy distribution of dreissenid mussels is an important driver of benthic diversity at small spatial scales. The results of our second and third experiments suggested that a native habitat engineer, Cladophora, modifies the impact of Dreissena on benthic macroinvertebrate communities. 4. While macroalgal blooms have been linked to the large‐scale impacts of Dreissena on light and nutrient availability, Dreissena shells inhibited Cladophora growth at our experimental scale. These findings demonstrate that the interactions between habitat‐modifying species can complicate efforts to predict the community‐level effects of an invasion.     

149 Distribution and Invasion of Bangia Atropurpurea (Rhodophyta) in the Laurentian Great Lakes

Müller et al. (1998) noted that freshwater collections of the genus Bangia formed a distinct group separate from marine entities in gene sequence analyses. Recently, the species epithet B. atropurpurea has been resurrected to represent this freshwater lineage. This taxon is one of many invasive species within the Laurentian Great Lakes. B. atropurpurea was first observed in Lake Erie in 1964 and by 1982 was observed in all of the Great lakes except Lake Superior. The present study was initiated to examine the further spread of B. atropurpurea and determine the origin of these populations. Hence, a survey of all the Great Lakes was conducted in 1995 (86 sites) and again in 2002 (104 sites). Bangia was observed at 43 sites in 1995 and 39 sites in 2002. For the first time, this alga has been observed to be present in the St. Lawrence River (1995), Georgian Bay on Lake Huron (2002) and Lake Simcoe (eastern shore, 2002) and hence this alga appears to be spreading into new locations. Cluster analyses of morphological data reveal three distinct groupings that do not separate according to location or lake basin. Preliminary analyses of ITS 1 and 2 sequences show differences among samples within Lake Ontario and among all Lakes; however, collections from Lake Simcoe are very similar in sequence. We are continuing to examine the relationship of Great Lakes populations with freshwater collections from Europe.     

Lake Superior: an invasion coldspot?

Lake Superior receives a disproportionate number of ballast water discharges from transoceanic ships operating on the Laurentian Great Lakes. Although this provides dispersal opportunities for nonindigenous species (NIS), relatively few NIS were initially discovered in this lake prior to being recorded elsewhere in the basin. A lack of NIS records from this lake may be an artefact of sampling bias. We tested this hypothesis by sampling benthos and plankton from littoral and deepwater habitats around the perimeter of Lake Superior during June and August 2001. Using morphological analysis techniques, we identified a total of 230 invertebrate taxa representing planktonic, benthic and nektonic lifestyles. Five species with invasion histories in the lower Great Lakes, the bivalves Sphaerium corneum, Pisidium amnicum and P. moitessierianum, gastropod Potamopyrgus antipodarum and amphipod Echinogammarus ischnus, were identified for the first time in Lake Superior. In addition, records of expanded distributions within this lake are presented for the amphipod Gammarus fasciatus and oligochaetes Ripistes parasita and Vejdovskyella intermedia. Recently introduced NIS in Lake Superior were found near international ports, implicating shipping as the vector of their introduction. Intrinsic physical-chemical aspects of Lake Superior may account for the scarcity of NIS in this lake as compared to the lower Great Lakes.     

Salinity tolerance of Great Lakes invaders

1. The Laurentian Great Lakes are among the most invaded freshwater ecosystems in the world. Historically, the major vector for the introduction of non‐indigenous species (NIS) has been the release of contaminated ballast water via transoceanic ships. Despite regulations implemented in 1993, requiring vessels carrying fresh ballast water to exchange this water with saline ocean water, new reports of invasions have continued. 2. NIS often have a wide environmental tolerance allowing them to adapt to and invade a variety of habitats. It has been hypothesized that NIS with broad salinity tolerance may be able to survive ballast water exchange (BWE) and continue to pose an invasion risk to the Great Lakes. 3. We tested the short‐term salinity tolerance of eight recent invaders to the Great Lakes, specifically three cladocera (Bosmina coregoni, Bythotrephes longimanus, Cercopagis pengoi), two molluscs (Dreissena polymorpha, Dreissena rostriformis bugensis), and one species each of the families Gammaridae, Mysidae and Gobidae (Echinogammarus ischnus, Hemimysis anomala, Neogobius melanostomus) to determine if they could have survived salinities associated with BWE. 4. Overall, short‐term exposure to highly saline water dramatically reduced survival of all species. Two different methods of BWE tested, simultaneous and sequential, were equally effective in reducing survival. Species that survived the longest in highly saline water either possess behavioural characteristics that reduce exposure to adverse environments (valve closure; both Dreissena species) or are reported to have some degree of salinity tolerance in their native region (Echinogammarus). Given that exposure in our trials lasted a maximum of 48 h, and that species in ballast tanks would typically be exposed to saline water for c. 5 days, it appears that BWE is an effective method to reduce the survival of these NIS. These results provide impetus for tightening policy and monitoring of BWE, in particular for ships entering the Great Lakes from freshwater ports.     

Expansion of tubenose gobies <Emphasis Type="Italic">Proterorhinus semilunaris</Emphasis> into western Lake Erie and potential effects on native species

The Eurasian freshwater tubenose goby Proterorhinus semilunaris (formerly Proterorhinus marmoratus) invaded the Laurentian Great Lakes in the 1990s, presumably via ballast water from transoceanic cargo ships. Tubenose gobies spread throughout Lake St. Clair, its tributaries, and the Detroit River system, and also are present in the Duluth-Superior harbor of Lake Superior. Using seines and bottom trawls, we collected 113 tubenose gobies between July 2007 and August 2009 at several locations in western Lake Erie. The number and range of sizes of specimens collected suggest that that tubenose gobies have become established and self-sustaining in the western basin of Lake Erie. Tubenose gobies reached maximum densities in sheltered areas with abundant macrophyte growth, which also is their common habitat in native northern Black Sea populations. The diet of tubenose gobies was almost exclusively invertebrates, suggesting dietary overlap with other benthic fishes, such as darters (Etheostoma spp. and Percina sp.), madtoms (Noturus spp.), and sculpins (Cottus spp.). A single mitochondrial DNA haplotype was identified, which is the most common haplotype found in the original colonization area in the Lake St. Clair region, suggesting a founder effect. Tubenose gobies, like round gobies Neogobius melanostomus, have early life stages that drift owing to vertical migration, which probably allowed them to spread from areas of colonization. The Lake St. Clair-Lake Erie corridor appears to have served as an avenue for them to spread to the western basin of Lake Erie, and abundance of shallow macrophyte-rich habitats may be a key factor facilitating their further expansion within Lake Erie and the remainder of the Laurentian Great Lakes.     

The relationship between fecundity and adult body weight in Homeotherms

Summary Bythotrephes cederstroemii Schoedler, a predatory freshwater zooplankter (Crustacea: Cladocera), was first found in the Laurentian Great Lakes in December 1984. The first individuals were from Lake Huron, followed in 1985 with records from Lakes Erie and Ontario. By late August, 1986 the species had spread to southern Lake Michigan (43°N). Bythotrephes has not previously been reported from North America, but has been restricted to a northern and central Palearctic distribution. Its dramatic and widespread rise in abundance in Lake Michigan was greatest in offshore regions. Bythotrephes appears to be invading aggressively, but avoiding habitats presently occupied by glacio-marine relict species that became established in deep oligotrophic North American lakes after the Wisconsin glaciation. Because it is a voracious predator its invasion may lead to alterations in the native zooplankton fauna of the Great Lakes. It offers the chance to study how invading plankton species join an existing community. Judging from its persistence and success in deep European lakes, Bythotrephes may now become a permanent member of zooplankton communities in the Nearctic.     

Changing Abundance of Hexagenia Mayfly Nymphs in Western Lake Erie of the Laurentian Great Lakes: Impediments to Assessment of Lake Recovery?

After an absence of 40 years, mayfly nymphs of the genus Hexagenia were found in sediments of western Lake Erie of the Laurentian Great Lakes in 1993 and, by 1997, were abundant enough to meet a mayfly‐density management goal (ca. 350 nymphs m^—2) based on pollution‐abatement programs. We sampled nymphs in western Lake Erie and Lake St. Clair, located upstream of western Lake Erie, to determine the importance of seasonal abundance and life‐history characteristics of nymphs (e.g., emergence and recruitment) on density estimates relative to the mayfly‐density management goal. Two types of density patterns were observed: (1) densities were relatively high in spring and gradually decreased through late summer (observed in Lake Erie and Lake St. Clair in 1997 and Lake St. Clair in 1999) and (2) densities were relatively high in spring, gradually decreased to mid summer, abruptly decreased in mid summer, and then increased between summer and late fall (Lake Erie and Lake St. Clair in 1998 and Lake Erie in 1999). Length‐frequency distributions of nymphs and observations of adults indicate that the primary cause for the two density patterns was attributed to failed (first pattern) and successful (second pattern) reproduction and emergence of nymphs into adults in mid summer. Gradual declines in densities were attributed to mortality of nymphs. Our results indicate that caution should be used when evaluating progress of pollution‐abatement programs based on mayfly densities because recruitment success is variable both between and within years. Additionally, the interpretation of progress toward management goals, relative to the restoration of Hexagenia populations in the Great Lakes and possibly other water bodies throughout the world, is influenced by the number of years in which consequtive collections are made.     

Distribution of circular single‐stranded DNA viruses associated with benthic amphipods of genus Diporeia in the Laurentian Great Lakes

相似文献   

Use of ecological indicators to assess the quality of Great Lakes coastal wetlands

Over 2000 coastal wetland complexes have been identified in the Laurentian Great Lakes watershed, each providing critical habitat for numerous aquatic and terrestrial species. Research has shown there is a direct link between anthropogenic activities (urbanization and agricultural development) and deterioration in wetland health in terms of water quality and biotic integrity. In this study, we evaluate coastal marshes throughout the Great Lakes basin using a suite of published ecological indices developed specifically for coastal wetlands of the Great Lakes (Water Quality Index (WQI), Wetland Macrophyte Index (WMI), and the Wetland Fish Index (WFI_Basin)). We surveyed 181 wetlands, including 19 in Lake Superior (11%), 11 in Lake Michigan (6%), 13 in Lake Huron (7%), 92 in Georgian Bay and the North Channel (51%), 18 in Lake Erie (10%), and 28 in Lake Ontario (15%), over a 13 year period (1995–2008). Water quality parameters were measured at every site, while paired fyke nets were used to assess the fish community (132 sites) and macrophytes were surveyed and identified to species (174 sites); all of this information was used to calculate the associated index scores. One-way ANOVA results showed that there were significant differences in wetland quality among lakes. According to the WQI, we found that over 50% of marshes in Lakes Michigan, Erie, and Ontario were in degraded condition, while over 70% of marshes in Lakes Superior, Huron, and Georgian Bay were minimally impacted. Georgian Bay had the highest proportion of wetlands in very good and excellent condition and least number of wetlands in a degraded state. The WMI and WFI showed similar results. This is the largest bi-national database of coastal wetlands and the first study to provide a snapshot of the quality of coastal habitats within the Great Lakes basin. We recommend this information be used to guide conservation and restoration efforts within the Laurentian Great Lakes.     

EPIPHYTES ON CLADOPHORA GLOMERATA IN THE GREAT LAKES AND ST. LAWRENCE SEAWAY WITH PARTICULAR REFERENCE TO THE RED ALGA CHROODACTYLON RAMOSUM (= ASTEROCYTIS SMARGDINA)1

The range of Cladophora glomerata² along the east and north shorelines of the Great Lakes and St. Lawrence Seaway extends form just east of Montreal to Thunder Bay on Lake Superior. However, it does not occur at sites sampled in Georgian Bay, the North Channel or eastern Lake Superior. The dominant epiphytes on Cladophora throughout this range are the blue-green algae, particularly Lyngbya diguetii, L. epiphytica and Chamaesiphon incrustans, which account for 53 to 90% of the cell density. The diatoms Cocconeis pediculus and Rhoicosphenia curvata contribute to much of the remaining density. The red alga Chroodactylon ramosum is a minor component of Cladophora epiphyton but is widespread in Lakes Ontario, Erie and Huron. Filament morphology, cell diameters and lengths of Chroodactylon are quite similar to those of marine forms. In addition, this alga has been reported to be quite tolerant of a wide range of salinities. Chroodactylon has been found in 33 freshwater sites throughout North America and 30 of these are from the Great Lakes or its drainage basin. Therefore, it appears possible that Chroodactylon, like Bangia atropurpurea, has originated in the Great Lakes by a migration from the Atlantic Ocean.     

150 Phylogenetic Systematics and Phenology of the Hawaiian Endemic Freshwater Red Alga, Batrachospermum Spermatiophorum

Müller et al. (1998) noted that freshwater collections of the genus Bangia formed a distinct group separate from marine entities in gene sequence analyses. Recently, the species epithet B. atropurpurea has been resurrected to represent this freshwater lineage. This taxon is one of many invasive species within the Laurentian Great Lakes. B. atropurpurea was first observed in Lake Erie in 1964 and by 1982 was observed in all of the Great lakes except Lake Superior. The present study was initiated to examine the further spread of B. atropurpurea and determine the origin of these populations. Hence, a survey of all the Great Lakes was conducted in 1995 (86 sites) and again in 2002 (104 sites). Bangia was observed at 43 sites in 1995 and 39 sites in 2002. For the first time, this alga has been observed to be present in the St. Lawrence River (1995), Georgian Bay on Lake Huron (2002) and Lake Simcoe (eastern shore, 2002) and hence this alga appears to be spreading into new locations. Cluster analyses of morphological data reveal three distinct groupings that do not separate according to location or lake basin. Preliminary analyses of ITS 1 and 2 sequences show differences among samples within Lake Ontario and among all Lakes; however, collections from Lake Simcoe are very similar in sequence. We are continuing to examine the relationship of Great Lakes populations with freshwater collections from Europe.     

Population structure of an introduced species (Dreissena polymorpha) along a wave-swept disturbance gradient

The zebra mussel Dreissena polymorpha was introduced to North America during the mid-1980s, and is now a dominant member of many benthic communities in the lower Great Lakes. In this study, I explored the abundance, biomass, size structure and settlement of Dreissena inhabiting rocks along a wave-swept disturbance gradient near Middle Sister Island in western Lake Erie. Ten rocks were collected from quadrats at six sites along each of three transect lines oriented perpendicular to shore. Occurrence, abundance and biomass of Dreissena on smaller, movable rocks were positively associated with rock distance from shore (lake depth) and with rock area; rocks at nearshore sites supported little, if any, Dreissena, whereas those at offshore sites were heavily colonized. Mussel size distributions also differed in relation to shore distance. Large mussels (19 mm) were underrepresented or absent on rocks collected at nearshore sites, but were overrepresented at offshore locations (37 m). Settlement of larval mussels on settling pads was positively correlated with distance offshore and with time of exposure, though settlement was substantial even at a nearshore (10 m) location. Area-adjusted mussel dry mass increased more rapidly with distance offshore on large than on small rocks. Large rocks also required more force to displace and were significantly less likely to be disturbed when transplanted at the study site. Results from this study indicate that occurrence, abundance and size structure of Dreissena in nearshore waters of Lake Erie correspond with the frequency of habitat disturbance, though other factors including food limitation and larval supply may also contribute to these patterns. These patterns complement studies that established the significance of physical disturbance in other aquatic systems.     

Lake morphometry determines Dreissena invasion dynamics

Predicting the ecosystem effects of invasive species and the best control strategies requires understanding population dynamics and population regulation. Invasive bivalves zebra and quagga mussels (Dreissena spp.) are considered the most aggressive invaders in freshwaters and have become major drivers of ecosystem processes in the Laurentian Great Lakes. Combining all lake-wide studies of Dreissena spp. conducted in the Great Lakes, we found that invasion dynamics are largely governed by lake morphometry. Where both species are present, quagga mussels generally become dominant in 8–13 years. Thereafter, zebra mussels remain common in shallow lakes and embayments and lake-wide Dreissena density may remain similar, while in deep lakes quagga led to a near-complete displacement of zebra mussels and an ensuing dramatic increase in overall dreissenid density. In deep lakes, overall Dreissena biomass peaked later and achieved?~?threefold higher levels than in shallow lakes. Comparison with 21 waterbodies in North America and Europe colonized by both dreissenids confirmed that patterns of invasion dynamics found in the Great Lakes are very consistent with other waterbodies, and thus can be generalized to other lakes. Our biophysical model predicted that the long-term reduction in primary producers by mussel grazing may be fourfold less in deep compared to shallow lakes due to thermal stratification and a smaller proportion of the epilimnion in contact with the bottom. While this impact remains greatest in shallow areas, we show that when lakes are vertically well-mixed, dreissenid grazing impact may be greatest offshore, revealing a potentially strong offshore carbon and phosphorus sink.

     

Suppression of microzooplankton by zebra mussels: importance of mussel size

1. The zebra mussel (Dreissena polymorpha) is amongst the most recent species to invade the Great Lakes. We explored the suppressive capabilities of mussels 6–22-mm in size on Lake St Clair microzooplankton (< 240)μm) in laboratory experiments. 2. Absolute suppression of rotifers and Dreissena veliger larvae was proportional to mussel shell length for individuals larger than 10 mm; larger zooplankton, mainly copepod nauplii and Cladocera, were not affected. Mussel clearance rates on rotifers generally exceeded those on veligers, although rates for both increased with increasing mussel size. Rotifer-based clearance rates of large (22 mm) mussels approached published values for phytoplankton food. 3. Most zooplankton taxa, particularly rotifers, declined significantly in western Lake Erie during the late 1980s concomitant with the establishment and population growth of zebra mussels in the basin. Densities of some taxa subsequently increased, although rotifers and copepod nauplii densities remained suppressed through 1993. Available evidence indicates that direct suppression by Dreissena coupled with food limitation provides the most parsimonious explanation for these patterns.     

Moitessier's pea clam Pisidium moitessierianum (Bivalvia,Sphaeriidae): a cryptogenic mollusc in the Great Lakes

Pisidium moitessierianum Paladilhe, 1866, a small pea clam native to Europe, was identified for the first time from the lower Great Lakes basin based on an examination of historical collections of Pisidium performed by V. Sterki in 1894 and 1903 and new material collected during 1997 and 1998. During recent surveys, P. moitessierianum individuals were found in the St. Clair River delta, Lake St. Clair and western Lake Erie, but were not detected in the Detroit River or western Lake Ontario. Pisidium moitessierianum was collected on sand, silty sand and mud substrata from water depths ranging between 0.6 and 5.4 m. Populations occurred at an average density of 51 ind. m^–2 and included juveniles and adults. All individuals were less than 2.0 mm in length. We examined the structure of the umbos and hinge, surface sculpture and shape of the shell, and the anatomy of gills, mantle and nephridia in populations from the lower Great Lakes and Ukrainian inland basins (Dnieper River and Lake Beloye). The results indicated that the Great Lakes' pea clams match European specimens of P. moitessierianum in these conchological and anatomical characteristics. As with other nonindigenous sphaeriids in the Great Lakes, P. moitessierianum was likely introduced through shipping activities into the Great Lakes, possibly as early as the 1890s.     

NUTRIENT LIMITATION OF BENTHIC ALGAE IN LAKE MICHIGAN: THE ROLE OF SILICA1

In the Laurentian Great Lakes, phytoplankton growth and biomass are secondarily limited by silica (Si), as a result of phosphorus (P) enrichment. Even modest levels of P enrichment can induce secondary Silimitation, which, in turn, promotes a shift from the native diatom phytoplankton flora to chlorophyte and cyanobacteria species. However, very little is known about the nutritional status of benthic populations and their response to nutrient enrichment. Two experiments were performed in the littoral zone of Lake Michigan where nutrients were delivered to in situ benthic algal (episammic and epilithic) assemblages using nutrient‐diffusing substrata. In order to test the hypothesis that benthic algae in Lake Michigan are Si limited, a 2 × 3 factorial experiment was used to deliver all combinations of Si, N, and P to resident assemblages growing on artificial substrata composed of natural (Si rich) versus calcium carbonate (Si poor) sand. A second experiment utilized a serial enrichment to evaluate the role of Si in mediating changes in taxonomic composition. These findings indicate that benthic algae in Lake Michigan exhibit signs of secondary Si limitation, and that their response to enrichment is similar to the phytoplankton. Moreover, natural sand substrata may provide a source of Si to resident benthic algae.     

Evolution and diversity of two cisco forms in an outlet of glacial Lake Algonquin

The diversity of Laurentian Great Lakes ciscoes (Coregonus artedi, sensu lato) arose via repeated local adaptive divergence including deepwater ciscoes that are now extirpated or threatened. The nigripinnis form, or Blackfin Cisco, is extirpated from the Great Lakes and remains only in Lake Nipigon. Putative nigripinnis populations were recently discovered in sympatry with artedi in a historical drainage system of glacial Lake Algonquin, the precursor of lakes Michigan and Huron. Given the apparent convergence on Great Lakes form, we labeled this form blackfin. Here, we test the hypothesis that nigripinnis may have colonized this area from the Great Lakes as a distinct lineage. It would then represent a relict occurrence of the historical diversity of Great Lakes ciscoes. Alternatively, blackfin could have evolved in situ in several lakes. We captured more than 600 individuals in the benthic or pelagic habitat in 14 lakes in or near Algonquin Provincial Park (Ontario, Canada). Fish were compared based on habitat, morphology, and genetic variation at 6,676 SNPs. Contrary to our expectations, both cisco and blackfin belonged to an Atlantic lineage that colonized the area from the east, not from the Great Lakes. Sympatric cisco and blackfin were closely related while fish from different lakes were genetically differentiated, strongly suggesting the repeated in situ origin of each form. Across lakes, there was a continuum of ecological, morphological, and genetic differentiation that could be associated with alternative resources and lake characteristics. This study uncovers a new component of cisco diversity in inland lakes of Canada that evolved independently from ciscoes of the Laurentian Great lakes. The diversity of cisco revealed in this study and across their Canadian range presents a challenge for designating conservation units at the intraspecific level within the framework of the Committee on the Status of Endangered Wildlife in Canada (COSEWIC).     

Thirty-Year Time Series of PCB Concentrations in a Small Invertivorous Fish (<Emphasis Type="Italic">Notropis Hudsonius</Emphasis>): An Examination of Post-1990 Trajectory Shifts in the Lower Great Lakes

The production and use of polychlorinated biphenyls (PCBs) have been restricted in North America since the 1970s; yet, PCBs are still detected in all components of the Great Lakes ecosystems. Our objective was to determine how total PCB (PCB_T) concentrations in spottail shiner (Notropis hudsonius) changed over the period 1975–2007 in the lower Great Lakes. Trends were best described by three basic models: (1) piecewise models where concentrations followed a decreasing trend before the break point (T) and an increasing trend post-T (Lake St. Clair, eastern Lake Erie, and upper Niagara River); (2) piecewise models where concentrations decreased both pre- and post-T but where the rate of decline post-T was less than that pre-T (western Lake Erie and Niagara River’s Tonawanda Channel); and (3) linear models where concentrations declined at a constant rate across the entire temporal range (lower Niagara River and western Lake Ontario). Piecewise models best described the trends in shallow areas that are susceptible to full water-column mixing whereas constant-slope models best described trends in deeper areas. For piecewise models, T typically occurred during the years 1988–1992. Two events coincided with this timing: (1) a sustained shift towards warming summer temperatures and (2) the proliferation of dreissenid mussels (Dreissena spp.). The weight-of-evidence suggests that the dreissenid invasions were a more likely driving factor behind the observed trends.     

Trends in body condition of native piscivores following invasion of Lakes Erie and Ontario by the round goby

相似文献