Biotic Habitat Research Articles

Hatch Dates, Growth, Survival, and Overwinter Mortality of Age‐0 Alewives in Lake Michigan: Implications for Habitat‐Specific Recruitment Success

AbstractAlewivesAlosa pseudoharengusare key components of Laurentian Great Lakes ecosystems and spawn in multiple habitat types. Exploration of alewife early life history dynamics within these different habitats should help identify important recruitment processes. During 2001‐2003, we quantified physical (temperature, transparency) and biotic (chlorophylla, zooplankton densities) habitat factors and collected age‐0 alewives (using ichthyoplankton nets and trawls) in a nearshore region of Lake Michigan and Muskegon Lake, Michigan (a drowned river mouth lake connected to Lake Michigan). We characterized alewife hatch dates, individual condition, growth, mortality, and size‐dependent overwinter survival to infer differences in habitat‐specific recruitment success. Temperature, turbidity, chlorophyll‐aconcentrations, and densities of zooplankton prey were consistently higher in Muskegon Lake than in nearshore Lake Michigan. On average, young alewives in Muskegon Lake hatched earlier, grew faster, were in better condition (based on a biphasic length‐weight relationship), and had greater survival than alewives in Lake Michigan. By the end of the growing season, young alewives in Muskegon Lake obtained a larger size than those residing in nearshore Lake Michigan, suggesting that they were more likely to survive through winter (a period of intense size‐selective mortality) and ultimately recruit to the adult population.

Effects of upland disturbance and instream restoration on hydrodynamics and ammonium uptake in headwater streams

Delivery of water, sediments, nutrients, and organic matter to stream ecosystems is strongly influenced by the catchment of the stream and can be altered greatly by upland soil and vegetation disturbance. At the Fort Benning Military Installation (near Columbus, Georgia), spatial variability in intensity of military training results in a wide range of intensities of upland disturbance in stream catchments. A set of 8 streams in catchments spanning this upland disturbance gradient was selected for investigation of the impact of disturbance intensity on hydrodynamics and nutrient uptake. The size of transient storage zones and rates of NH4+ uptake in all study streams were among the lowest reported in the literature. Upland disturbance did not appear to influence stream hydrodynamics strongly, but it caused significant decreases in instream nutrient uptake. In October 2003, coarse woody debris (CWD) was added to ½ of the study streams (spanning the disturbance gradient) in an attempt to increase hydrodynamic and structural complexity, with the goals of enhancing biotic habitat and increasing nutrient uptake rates. CWD additions had positive short-term (within 1 mo) effects on hydrodynamic complexity (water velocity decreased and transient storage zone cross-sectional area, relative size of the transient storage zone, fraction of the median travel time attributable to transient storage over a standardized length of 200 m, and the hydraulic retention factor increased) and nutrient uptake (NH4+ uptake rates increased). Our results suggest that water quality in streams with intense upland disturbances can be improved by enhancing instream biotic nutrient uptake capacity through measures such as restoring stream CWD.

Geoarchaeology and late glacial landscapes in the western lake superior region, Central North America

AbstractThe transition from full glacial to interglacial conditions along the southern margin of the Laurentide ice sheet resulted in dramatic changes in landscapes and biotic habitats. Strata and landforms resulting from the Wisconsin Episode of glaciation in the area directly west of Lake Superior indicate a context for late Pleistocene biota (including human populations) connected to ice margins, proglacial lakes, and postglacial drainage systems. Late Glacial landscape features that have the potential for revealing the presence of Paleoindian artifacts include abandoned shorelines of proglacial lakes in the Superior and Agassiz basins and interior drainages on deglaciated terrains. The linkage between Late Pleistocene human populations and Rancholabrean fauna has yet to be demonstrated in the western Lake Superior region, although isolated remains of mammoth ( Mammuthus) have been documented, as well as fluted points assigned to Clovis, Folsom, and Holcombe‐like artifact forms. Agate Basin and Hell Gap (Plano‐type) artifacts also imply the presence of human groups in Late Glacial landscapes associated with the Agassiz and Superior basins. © 2007 Wiley Periodicals, Inc.

Habitat and transmission – effect of tidal level and upstream host density on metacercarial load in an intertidal bivalve

Transmission of parasites may be mediated by their habitat, consisting of abiotic and biotic components. I investigated the effect of 2 important habitat components in intertidal ecosystems, tidal level (abiotic) and density of upstream hosts (biotic), on the transmission of trematode cercariae to cockle (Cerastoderma edule) hosts. A field survey showed no general trend in metacercarial loads of cockles regarding tidal level but species-dependent reactions. Parasites originating from Littorina littorea (Himasthla elongata, Renicola roscovita) showed highest infection levels in the low intertidal while parasites originating from Hydrobia ulvae (H. continua, H. interrupta) showed highest infection levels in the mid-intertidal. This reflected the density of upstream hosts at both tidal levels and positive relationships between the density of upstream hosts and metacercarial load in cockles suggested the biotic habitat component to be the dominant factor in transmission. This was confirmed by a field experiment, manipulating tidal level and the density of infected upstream snail hosts. While tidal level had no significant effect on the number of metacercariae of H. elongata acquired by cockles, the effect of upstream host density was strong. In conclusion, although tidal level usually is a very important abiotic habitat component in intertidal ecosystems leading to conspicuous zonation patterns in free-living organisms, it seems of minor importance for trematode transmission. In contrast, the biotic component upstream host density is suggested to be the dominant predictor for trematode transmission to second intermediate hosts. Assessing the relative importance of abiotic and biotic habitat components in transmission is vital for the understanding of transmission processes in the field.

Factors determining length distribution and abundance of the European eel, Anguilla anguilla, in the River Mondego (Portugal)

Summary1. The distribution and abundance of the European eel, Anguilla anguilla, were investigated in the Mondego River, a strongly modified river in central Portugal. Nine freshwater sites, located below the first impassable obstacle to eel migration, were surveyed for 2 years. The study was conducted monthly during the first year and seasonally during the second year. Fish were caught by electric fishing and, physical and biotic variables potentially influencing eel length distribution and abundance were determined at each sampling session.2. Canonical correspondence analysis (CCA) was used to explain the relationships between abiotic and biotic habitat variables, and eel length distribution. Spatial variation was strongly associated with distance from the sea, number of obstacles, river width and percentage of instream cover. Depth, river flow, water temperature and cannibalism had weaker effects on the longitudinal distribution, but contributed as explanatory variables for the model. The influence of spatial variables outweighed the importance of temporal variables as predictors in this model.3. Length distribution changed in space from a dominance of small eels (<100 mm) closer to the sea to larger eels (≥250 mm) in the upper reaches of the river. The smallest length class (eels <100 mm) was strongly associated with wider stretches where instream cover, mainly composed of aquatic submerged macrophytes, was abundant (>75% area coverage). On the contrary, larger eels (≥250 mm) preferred deeper stretches with stronger river flow and less instream cover.4. The effect of biotic interactions with conspecifics as well as with the non‐native red swamp crayfish Procambarus clarkii, in sites with poor instream cover, modified this general pattern of distribution leading to fewer eels <100 mm at some sites closer to the sea. Therefore, despite the ubiquity and plasticity shown by this species, there were clear ontogenetic variations in habitat use such that the first two canonical axes of a CCA accounted for 58.4% of the spatial variability in size structure.

Quantifying Littoral Vertical Habitat Structure and Fish Community Associations using Underwater Visual Census

We developed and tested a new visual census technique to quantify the importance of vertical habitat structure on the associated fish assemblages in the littoral zone of a freshwater lake. We demonstrated that the primary environmental gradient, accounting for the most variation in the species data, represented a temporal gradient of seasonal characteristics. The secondary environmental gradient was related to the vertical structure at the sampling locations, showing the importance of the vertical component of the environment on fish community structure. Characterizing the vertical component at different resolutions provided different interpretations. The primary difference was the strength of influence of woody material on community structure. Woody material had a stronger influence on community structure throughout the water column when a single vertical unit defined the fish data. The appropriateness of defining the data by either multiple vertical strata or by a single vertical one would be dependent on the objectives of the study, as neither approach was found to explain substantially more variation in the species data. The current study demonstrates that fish are closely associated with particular elements of habitat structure in the littoral zone, even in the absence of major piscivorous predators. We provide a novel study quantifying the vertical multiple habitat structures and habitat use by fish in the water column of a freshwater lake. The new vertical visual census technique can be used to more comprehensively sample the three-dimensional environment of lake littoral zones, and quantify the fish–habitat spatial relationships across a range of abiotic and biotic habitat features.

Soil, human society and the environment

Abstract Soils, forming the top layer of the Earth's crust, are a mixture of mineral particles, organic matter, water, air and living organisms. Processes between these components perform vital functions within ecosystems. The soil forms an interface between the geosphere, the biosphere, the hydrosphere and the atmosphere, and is a largely non-renewable resource. Ugolini & Warkentin show the fruitful relationships which geology and soil science have established since the birth of soil science, and how these two disciplines together could contribute to solve future problems. The dynamic soil system delivers functions and services vital for human societies and the environment. Soil is the basis for food and biomass production, and plays a central role as a habitat for biota and as a gene pool. Moreover, it stores, filters, buffers and transforms a large variety of substances, including water, inorganic and organic compounds, and is a major sink and source for greenhouse gases. Soil provides raw materials for human use. It also serves as the basis for human activities (landscape and heritage) and for our technical and socio-economic infrastructure, delivering materials for their implementation and maintenance.

Head to Head

In the absence of a reproducible validated critical-habitat delineation for Nelson's bighorn sheep (Ovis canadensis nelsoni) in the northern Santa Rosa Mountains, California, Turner et al. (2004) developed a quantitative habitat model based on biotic and a biotic habitat parameters comprised of the primary constituent elements allegedly used in the United States Fish and Wildlife Service's (USFWS) habitat model (USFWS 2000, 2001). Bighorn distribution and location (observation) data used by the USFWS in its model were 96% explained on the basis of the Turner et al. (2004) model; no validation or prediction could be made from the USFWS model (USFWS 2000, 2001). Criticisms by Ostermann et al. (2005) of the Turner et al. (2004) model emphasize a basic miscomprehension by Ostermann et al. (2005) of the differences between habitat characterization and habitat utilization. Most of the Ostermann et al. (2005) critique relates to data that were not provided to Turner et al. (2004). Failure of Ostermann et al. (2005) to fully grasp the sampling strategy used by Turner et al. (2004) relates to an incomplete comprehension of the statistical methodology employed rather than with the statistical procedures themselves. Claims by Ostermann et al. (2005) that Turner et al. (2004) made extrapolations to misdirect bighorn recovery efforts, drew inferences to other bighorn populations, alleged the northern population was normal, and equated sheep density (frequency of observation) to habitat quality are without substantiation, example, or merit. Contentions of problematic water source data are unsupported by the literature cited by Ostermann et al. (2005). The permissive attitude of resource agencies allowing management and conservation efforts to be directed by special interests largely in the absence of independent scientific scrutiny, casts a question of legitimacy over this Endangered Species Act listing, recovery strategy, and critical habitat delineation.

Habitat characteristics and odonate diversity in mountain ponds of central Italy

1. In central Italy mountain ponds represent an important habitat for the conservation of dragonflies; however, human disturbance of these fragile environments is threatening the stability of their biodiversity. 2. Thirty-one ponds, ranging in altitude from 1014 to 2004 m, were qualitatively sampled for odonate larvae twice during 1998. On each occasion a range of physical, chemical and biotic habitat variables were also measured. 3. The mountain ponds sampled had fewer species of Odonata than lowland ponds, and there was a large presence of pioneer species. 4. Multiple regression analysis showed that the number of odonate species was positively affected by the amount of macrophyte coverage of the pond surface and negatively affected by increasing ammonium concentration. 5. A Canonical Correspondence Analysis revealed that species number decreased with altitude, chlorophyll a and phosphorus concentrations. The presence/absence of each odonate species was weakly related to the habitat variables. 6. The intensive use of ponds for livestock watering results in damage to the peripheral vegetation, which tends to cause high turbidity and lower macrophyte coverage of the pond water. The inevitable outcome in these situations is a reduction of the odonate diversity.

Paleoclimatic Environments of the Formation of Upper Vendian Rocks on the Belomorian-Kuloi Plateau, Southeastern White Sea Region

Reconstruction of Vendian climatic conditions on the East European Craton is of principle importance for elucidation of the Ediacarian biota habitat. However, paleogeographic reconstructions for this time are largely based on fragmentary and controversial paleomagnetic data. The degree of rock maturity deduced from lithochemical indicators allowed us to identify two stages of Late Vendian sedimentation on the Belomorian-Kuloi Plateau. The first (Lyamitsa-Verkhov) stage was characterized by the delivery of immature clastic material to the basin from a provenance with arid climate. The second (Erga-Padun) stage was marked by the input of relatively mature aluminosilicate clastics from a provenance with mild humid climate. The sedimentation stages approximately coincide with replacement of the shallow-water marine environment by the fluvioalluvial environment marked by steady and intense perennial river drainage from a highland in the northeast. In the Late Vendian (since 555 Ma ago), the northeastern area of the East European Craton was influenced by humid climate.

Controls on Surficial Materials Distribution in a Rock-Framed, Glaciated, Tidally Dominated Estuary: Cobscook Bay, Maine

Surficial materials were mapped on the bottom of Cobscook Bay, ME, through aerial photography of intertidal habitats, side-scan sonar, and seismic reflection profiling of subtidal regions. Like many other estuaries in northern New England, this rocky, macrotidal estuary has only slight riverine input and contains an abundance of till and fine-grained glacial-marine sediment. Contrary to conceptual models of estuarine sediment and habitat distribution, grain size does not become finer and habitats lower in energy in a landward direction within the estuary. The irregular shoreline shape, imparted by bedrock, forms a series of narrow constrictions separating broad bays. More than 70% of the bottom of the estuary is floored by gravel and rock; mud deposits are located in shallow-water coves throughout the Bay and in two large deposits in the Central Bay. Here, circulation models predict two large gyres form because water cannot pass through a bedrock constriction quickly enough. Natural gas is present in sufficient quantities in the sediment column to facilitate sediment mass movements near the mud deposits. Almost 60% of the intertidal zone is composed of mudflats that are uniformly distributed within and along the outside margin of the Bay, with increasing abundance of bedrock in a landward direction. Small beaches occur wherever coarse-grained glacial sediment erodes from bluffs. These observations depart from existing conceptual models of estuarine sediment distribution based on coastal plain estuaries and suggest that better understanding of biotic habitat or contaminant distribution in rocky glaciated estuaries will require more localized models. These estuaries appear more complex than coastal plain estuaries because of the unique outcrop pattern of bedrock and glacial deposits in each bay.

Habitat Influence on Fish Community Assemblage in an Agricultural Landscape in Four East Central Indiana Streams

ABSTRACT The objective of this study was to relate the quality of the fish community with habitat using the Index of Biotic Integrity (IBI) and Qualitative Habitat Evaluation Index (QHEI) in four agriculturally influenced streams in east central, Indiana. A total of 48 species was collected from 42 sites. IBI scores ranged from 14 to 48, and QHEI scores ranged from 29 to 83. There was a significant positive correlation between IBI and QHEI scores. Furthermore, we found significant positive correlations between IBI scores and four individual QHEI metrics (channel morphology, substrate, poollglide and riffletrun quality, and in-stream cover). Habitat influenced the fish assemblages with channelization and substrate being the primary structuring factors. The land use in this area is 70% agriculture, which has heavily influenced lotic character through anthropogenic practices.

Spatial ecology of a small desert shrub on adjacent geological substrates

Summary 1 Spatial pattern analyses were used to generate hypotheses about the processes that shape the structure of a plant community in the Mojave Desert of North America, with a focus on the semi‐shrub Ambrosia dumosa. We analysed spatial distributions and sizes of this species relative to other semi‐shrubs, shrubs and annuals, and the relationships between spatial patterns and abiotic and biotic habitat characteristics. 2 The analyses were based on maps of sample plots placed along a transect spanning two adjacent geological substrates: aeolian sand and gravelly, sandy to loamy alluvium. Of these two substrates, sand supported higher total biomasses of Ambrosia and of all woody perennials, while alluvium supported on average higher biomasses of winter annuals. 3 Annuals and seedlings of Ambrosia were much more strongly aggregated with Ambrosia canopies on sand than on alluvium, suggesting that these small plants were more strongly facilitated by Ambrosia on sand than on alluvium. 4 Ambrosia semi‐shrubs were spatially segregated on sand but aggregated on alluvium, and the degree of segregation on sand increased with the total above‐ground biomass of Ambrosia per unit area, indicating that negative interactions between Ambrosia plants were stronger in more productive habitats. Canopy sizes of Ambrosia in all mapped plots increased with distance to the nearest conspecific neighbour, which suggests that neighbour interactions negatively affected plant sizes. 5 Ambrosia plants on sand were spatially aggregated with Acamptopappus sphaerocephalus semi‐shrubs, suggesting that at least one of these species may benefit from the association. Ambrosia plants were spatially segregated from Larrea tridentata shrubs on both substrates, possibly due to negative effects of Larrea roots on Ambrosia roots reported in previous studies. 6 Subtle differences in substrate characteristics were correlated with strong differences in the spatial distribution of Ambrosia plants relative to their neighbours, which suggests that edaphic conditions may affect the spatial structure of the community by modifying complex positive and negative interactions between neighbouring plants.

Relations between Biotic Integrity and Physical Habitat in the Embarras River Basin, Illinois

ABSTRACT This study investigated the relationship between a habitat quality index and stream fish assessment indices used to evaluate stream quality in an agricultural setting. Fish data and stream habitat quality data were collected from 13 sampling localities within the Embarras River basin. Habitat quality was measured using a stream habitat assessment procedure, a qualitative index comprised of 15 metrics. Stream quality was determined by fish species richness and an index of biotic integrity (IBI). Multiple regression analysis identified pool quality, bank vegetation, and width-to-depth ratio as the best estimators of IBI. These variables were used in creating a model for predicting IBI. This model demonstrates the potential for predicting the biotic integrity of a stream fish community from commonly collected, and often readily available, habitat data. Thus, models which use habitat information may be an important management tool which will allow for the rapid prediction of the biotic integrity of a stream, and thus permit intensive management practices to be focused on critical sites within a stream basin.

Surface albedo in Ny-Ålesund, Svalbard: variability and trends during 1981–1997

Since 1981, hourly values of albedo have been measured routinely at Norwegian Polar Institute's research station in Ny-Ålesund, Svalbard. We have undertaken statistical analysis of the time series 1981–1997 to investigate potential long-term variability and trends in the albedo data set. The following questions have been raised and answered by regression analysis: (i) Has the time of beginning of snow melt changed? (ii) Have melt rates changed? (iii) Has the time of snow arrival in fall changed? (iv) Has the period without snow cover changed? The period without snow on the ground is studied because of its importance for tundra characteristics as a habitat for biota, e.g. length of the growth season. Our data show that albedo varies seasonally, with large variations in spring and autumn and much smaller variations in winter and summer. The variability is reasonably constant within each season. Density estimates of the albedo data suggest that the dates with highest likelihood for (i) start of snow melt and (ii) start of snow formation are 5th of June and 17th of September, respectively. Highest probability for the length of snow-free season is 94 days. None of the tests indicated any significant trends (or indications of climate change) in the 17-year record of albedo, that means that the four questions above were all answered by “no.” Correlation with the North Atlantic Oscillation (NAO) index is also investigated. No correlation between the NAO index and albedo nor temperature or precipitation was found. Even so, because of the short duration that our data set spans, we cannot rule out that such a correlation exists on decadal time scales.

Territorial damselfish enhances multi-species co-existence of foraminifera mediated by biotic habitat structuring

The structures of benthic foraminiferal communities inside and outside the territory of the pomacentrid damselfish Stegastes nigricans on coral rocks in a moat of Sesoko Is. (26°38′N, 127°52′E) in Okinawa, Japan were compared. Inside the territory, an algal farm, i.e., a dense stand of a filamentous rhodophyte, Womersleyella setacea, was maintained throughout the year. Outside the territory, in areas subjected to intensive and continuous grazing by various grazers, the flora was composed of mat-like cyanophytes, a prostrate turf-form Padina sp., microscopically thin filaments and scattered filamentous rhodophytes. Algal biomass was greater inside the territory than outside the territory of the damselfish. These differences were reflected by the structure of the associated foraminiferal communities. We classified foraminiferal species based on their microhabitat use around algal communities into four life types: free-living type, crawling type, sedentary type, and sessile type. The abundance of foraminifera, especially the free-living type (e.g., Peneroplis pertusus and Quinqueloculina seminulum) and sedentary type ( Rosalina globularis and Cymbaloporetta squammosa), was greater inside the territory of the damselfish than outside the territory. Species richness was also higher inside the territory, mainly due to an increase in species richness of the free-living and sedentary types. These increases in abundance and species richness were caused by habitat structuring. W. setacea is a relatively tall and complicated alga with tangled rhizoids. Its dense stand inside the territory trapped a larger amount of sediment, which provided free-living foraminifera with heterogeneous and stable habitats. In addition, the dense stand of W. setacea provided sedentary-type foraminifera with a large, complex substratum, providing refuge and food inside the territory. This assumption was confirmed by the results of plate experiments showing that foraminiferal community structures were controlled by associations between foraminifera and algae. We showed that habitat-conditioning is an important process in biotic habitat-structuring and that habitat-conditioning by territorial damselfish maintains and enhances multi-species coexistence of foraminifera on coral rocks in a coral reef.

Some observations on the zooplankton and macrobenthos of the Okhuo River, Nigeria

Some abiotic and biotic habitat characteristics of the shallow Okhuo River (average depth 0.85 m) were determined and are described. Water temperature (25.80C) is slightly lower than 25.90C of air. The mean conductivity was 291.4 m Scm-1. The pH is low (5.63) as the alkalinity (8.95mg CaCO3 l-1). The low biochemical oxygen demand (2.94 mg l-1) and high dissolved oxygen (11.1mg l-1) indicate low level of organic matter in the water. Ephemeroptera and Oligochaeta are widely distributed and not inclined to habitat restrictions. Oligochaetes (8.8%), rotifers (72.60%), cladocerans (8.64%), copepods (15.52%), ostracods (3.65%), shrimps (15.9%), insects (75.3%) were sorted out and identified from the collections. Numerically rotifers (72.60% of plankton) and insects (75.3% of benthos) were dominant. The proportions of biota (Ephemeroptera, 67.2%; Chironomidae, 8.1%) interplaying with the physico-chemical characteristics are conducive to cleanliness of the Okhuo River. Key words : Zooplankton, Macroinvertebrates, Nigeria. Journal of Aquatic Sciences Vol.17(2) 2002:145-149

Allelopathy: Past Achievements and Future Approaches, Proceedings of a Symposium of the Weed Science Society of America, February 9, 2000, Toronto, Canada

The number of papers published on allelopathy was low until the 1970s but has accelerated rapidly in recent years. Alleged allelopathic activity has been suggested for numerous weed and crop species; however, many studies employed preliminary bioassays (leachates or extracts in the absence of soil). The importance of substratum and of abiotic and biotic stresses (nutrients, shade, herbides, plant diseases, herbivores), plant density, habitat, and climate has been realized in recent years. Laboratory bioassay, the first step to investigate probable involvement of allelopathy, should be designed to correspond to field conditions. Studies need to focus on the effects of (1) climatic, environmental, and habitat factors on allelopathic potential; (2) abiotic and biotic soil components on fate and biological activity of allelochemicals; and (3) allelochemicals on soil nutrient dynamics, microbial ecology, and other abiotic and biotic components. Recently, attempts to find crop cultivars with a competitive allelopathic edge have been made. Interaction of professionals from different disciplines is needed to understand the complexity of the ecosystem. The following are important topics for discussion: allelopathy and the transition to sustainable agriculture; physiological and biochemical studies; using transgenes to produce allelopathic crops; microbial allelochemicals and pathogens as weed biological agents; bioassays for allelopathy (problems and solutions); pollen allelopathy; and an ecological perspective of allelopathy.

Influence of habitat on grouper abundance in the Florida Keys, U.S.A.

There was a significant inshore to offshore pattern in grouper species composition and density on Florida Keys coral reefs. Red grouper Epinephelus morio and black grouper Mycteroperca bonaci were most abundant on inshore patch reefs. Graysby Cephalopholis cruentata was most abundant on offshore reef types. Density among sites ranged from 0 to 0·43, 0 to 0·26 and 0 to 1·23 100 m−2 for red grouper, black grouper, and graysby, respectively. Grouper density exhibited no consistency among sites within similar reef types. The densities of red and black grouper were correlated significantly with either physical or biotic habitat parameters. Graysby were observed in microhabitats with whose benthic features differed significantly from the surrounding habitat. This species was observed in high‐relief areas with significantly less octocoral species and colony densities. Larger graysby were observed in areas of higher relief and less octocorals than smaller graysby. Habitat was one of several important factors influencing the distribution of groupers among coral reefs types in the Florida Keys.

Habitat-specific distribution of Pacific ocean perch ( Sebastes alutus) in Pribilof Canyon, Bering Sea

Shelf edge canyons are well-known sites of enhanced biomass due to on-shore transport and concentration of zooplankton along their axes, both of which contribute to the high densities of nekton frequently found in these canyons. Using a combination of acoustics, trawling, and in situ observations with a remotely operated vehicle (ROV), the distribution of pelagic and demersal biota within Pribilof Canyon in the Bering Sea was examined in September of 1995 and 1997. Near-bottom acoustic scattering patterns in the 38 kHz data showed high concentrations of biomass beginning around the 180 m bottom depth contour and continuing to about 220 m, which were presumed to be adult fish based on their target strength distributions. The 120 kHz data also showed very strong scattering in the water column between 150 and 175 m, which was absent from the 38 kHz data, and therefore attributed mainly to zooplankton. The dominant taxa collected in bottom trawls and mid-water plankton tows were adult rockfishes (Pacific ocean perch, Sebastes alutus) and euphausiids ( Thysanoessa spp.), respectively. In situ videos revealed dense aggregations of these rockfishes inhabiting a “forest” of attached sea whips, Halipteris willemoesi, during night deployments of the ROV, while areas with damaged sea whips had far fewer rockfish, and areas without this biotic habitat structure had no rockfish. During the day, the rockfishes were seen above the “forest”, where they were apparently feeding on dense swarms of euphausiids. It appears that these rockfish utilize this predictable and abundant food resource in the canyon during the day and are associated with the sea whip habitat at night during periods of inactivity. More research is needed on these slow-growing biotic habitats and how fishing activities in the Bering Sea and elsewhere may impact these habitats.