Distribution, Habitat, and Behavior of Rockfishes, Sebastes spp., in Nearshore Waters of Southeastern Alaska: Observations From a Remotely Operated Vehicle

We examined distribution, habitat, and behavior of rockfishes, Sebastes spp., with a remotely operated vehicle (ROV) in coastal waters <90m deep of southeastern Alaska from 1998 to 2000. We identified black, S. melanops, canary, S. pinniger, China, S. nebulosus, copper, S. caurinus, dusky, S. ciliatus, harlequin, S. variegatus, Puget Sound, S. emphaeus, quillback, S. maliger, redstripe, S. proriger, rosethorn, S. helvomaculatus, silvergray, S. brevispinis, tiger, S. nigrocinctus, yelloweye, S. ruberrimus, and yellowtail, S. flavidus, rockfish. Quillback and dusky rockfish were the most widely distributed species, China and harlequin rockfish were the least widely distributed species. Species richness was greater at sites on or near the outer coast than at sites in more inside, sheltered waters. Most (>75%) observations of rockfish were over complex bottoms of boulder and rock or in vertical bedrock wall habitats. Few rockfish were observed over soft bottoms with no relief. Median depth of observation was 30m for black, copper, dusky, and yellowtail rockfish and >30m for all other species. Median temperature of observation ranged from 6.1°C for harlequin rockfish to 9.4°C for black rockfish. Size of fish was positively correlated (p 0.036) with depth for dusky, quillback, and yelloweye rockfish. Species often observed alone were China (67%), copper (46%), quillback (46%), and rosethorn (43%) rockfish. Most (70%) observations of harlequin, Puget Sound, silvergray, tiger, and yelloweye rockfish were in mixed species assemblages. When first observed, the behavior of most rockfish species was swimming or hovering. Notable exceptions were China, harlequin, rosethorn, and tiger rockfish; 33–57% were resting on bottom or in a hole or crevice.     

Limited realized dispersal and introgressive hybridization influence genetic structure and conservation strategies for brown rockfish, <Emphasis Type="Italic">Sebastes auriculatus</Emphasis>

Understanding patterns of connectivity among marine fish populations with demersal adults and pelagic larvae is critical for effective conservation of west coast rockfishes. The brown rockfish (Sebastes auriculatus) occurs in nearshore habitat and is common from northern Baja California, Mexico to northern California, rare off the outer coast of Oregon and Washington and again common in the inland waters of Puget Sound, Washington. Here we examine patterns of microsatellite DNA diversity from throughout the species’ range as an indirect measure of long-term trends in larval dispersal. Genetic divergence was large and highly significant over all populations (F _ST=0.056, P<0.0001), and was significantly correlated with geographic distance when considering coastal populations. The best estimates of mean coastal dispersal distance were on the order of 10 km or less per generation. Diversity was relatively low in the Puget Sound, suggesting that Puget Sound rockfish populations experienced a post-glacial founder effect followed by genetic isolation and low effective population size. Puget Sound individuals appeared to have recent mixed ancestry as a result of introgression with S. maliger and S. caurinus. Genetic isolation of Puget Sound fish provides a basis for consideration as a Distinct Population Segment (DPS) under the provisions of the Endangered Species Act. We recommend that coastal brown rockfish fisheries be managed at regional rather than coast-wide scales, and that design of marine reserve networks considers the surprisingly low realized dispersal distance of some species with high dispersal potential.     

Demersal fish assemblages in the Southern California Bight based on visual surveys in deep water

Between 1995 and 2006, manned submersible fish surveys were conducted on the sea floor throughout the Southern California Bight. A total of 401 dives (comprising 1,015 transects and 14,373 habitat patches) were made in waters between 19 and 365 m deep. All natural habitat types were included, although both soft sea floors and rocky reefs were surveyed more than any other type. A total of 717,526 fishes, representing a minimum of 137 species and 47 families, were observed. Rockfishes (genus Sebastes), with a minimum of 50 species and 647,495 individuals (90.2% of all fishes observed), dominated most of the habitats. The most abundant species, squarespot (Sebastes hopkinsi), halfbanded (Sebastes semicinctus), shortbelly (Sebastes jordani), and pygmy rockfishes (Sebastes wilsoni), are dwarf taxa that either school or aggregate. The most abundant non-rockfish species was the benthic and territorial blackeye goby (Rhinogobiops nicholsii). Both species richness and overall fish densities were highest in the shallowest sites. Most of the fishes in all habitats were small (≤20 cm TL long) and economically important species were generally uncommon. Forty-four species were found to be characteristic of the study area (occurring in at least 5% of the transects) and these species formed three faunal associations centered around depths of 62, 105, and 168 m. Based on size frequency distributions, at least 18 of the characteristic species exhibited ontogenetic movements, with young-of-the-year and older juveniles living in relatively shallow waters and larger individuals generally in deeper depths. In this study, the abundance of juvenile widow rockfish (Sebastes entomelas), and the virtual absence of adults, in southern California waters may demonstrate an ontogenetic northward movement of this species. This research implies that substantial harvesting of larger species by commercial and recreational fishers has helped alter some fish assemblages, allowing small and “weedy” species to thrive. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.

Habitat selection by recruits establishes local patterns of adult distribution in two species of damselfishes: Stegastes dorsopunicans and S. planifrons

Local patterns of adult distribution in organisms that disperse young as pelagic larvae can be determined at the time of recruitment through habitat selection or, shortly thereafter, through post-recruitment processes such as differential juvenile survivorship and interspecific competition. This study addresses the importance of habitat selection by recruits in establishing the local pattern of adult distribution in two sympatric Caribbean damselfish species, Stegastes dorsopunicans and S. planifrons. Both species inhabit shallow reefs but show little overlap in their distribution; S. dorsopunicans predominates in the reef crest and S. planifrons occurs primarily on the reef slope. Furthermore, S. dorsopunicans is associated with rocky substrate, while S. planifrons occupies live coral. The substrate cover follows a similar pattern with coral being much less common on the reef crest than on the reef slope. Monitoring recruitment every other day in reciprocal removal experiments and artificial reefs indicates that the observed pattern of local adult distribution is a product of habitat selection for both species. The presence or absence of conspecifics did not influence recruitment patterns for either species. Stegastes dorsopunicans recruited primarily to shallow, rocky areas, appearing to cue on both substratum type and depth. Stegastes planifrons recruited exclusively to coral substratum independent of depth. These results indicate that local adult patterns of distribution can be explained by habitat selection at recruitment, and that substrate type and depth may be important cues. Received: 27 May 1997 / Accepted: 4 January 1998     

Habitat characteristics of juvenile cowcod, <Emphasis Type="Italic">Sebastes levis</Emphasis> (Scorpaenidae), in Southern California

We characterized habitat requirements of juvenile cowcod, Sebastes levis, using information from surveys conducted aboard the manned research submersible Delta. We conducted 303 dive surveys on rocky banks and outcrops in water depths between 28 and 365 m in southern and central California, covering 483 km (963,940 m²) of seafloor. We counted 549,263 fishes from at least 134 species; 216 individuals were juvenile cowcod, S. levis, of 45 cm or less in total length (TL). Juvenile cowcod occupied depths between 52 and 330 m and demonstrated ontogenetic shifts in their habitat associations. Small fish (5–20 cm TL) lived primarily among cobbles or cobbles and small boulders. As fish grew, they moved into high-relief rock habitats, including boulder fields and rock ridges. Small cowcods were found with pygmy, Sebastes wilsoni, and swordspine, Sebastes ensifer, rockfishes. Larger juveniles often associated with juvenile bocaccio, Sebastes paucispinis, juvenile widow rockfish, Sebastes entomelas, and squarespot rockfish, Sebastes hopkinsi. Our study resulted in a characterization of seafloor habitats on a small spatial scale that is relevant to juvenile cowcod nursery areas, which is important when considering effective management strategies for this overfished species.     

Structural complexity in relation to the habitat preferences,territoriality, and hatchery rearing of juvenile China rockfish (<Emphasis Type="Italic">Sebastes nebulosus</Emphasis>)

Conservation efforts require an understanding of the basic behavior and ecology of target species. However, limited information exists for a wide range of taxa, including declining species of rockfish (genus Sebastes). First, we observed captive juvenile China rockfish (S. nebulosus) to determine how they interact with their environment and conspecifics. Juveniles exhibited site fidelity and territoriality. These aggressive interactions occurred within the context of size-biased dominance, centered on competition for structurally complex habitat. Given the apparent importance of structure and the absence of structure in typical hatchery environments, we then asked how the absence of structure affects future behavior. When barren-reared and structure-reared juveniles were combined into a structurally complex aquarium, barren-reared fish displayed less structure use and less site fidelity than structure-reared fish. However, after 1 to 2 weeks, barren-reared fish began to use structure and showed site fidelity that eventually equaled that of structure-reared juveniles, showing that those behavioral effects of the rearing environment were not permanent. Though these short-term effects may still impact survival after hatchery release, we were unable to detect significant effects on vulnerability to a predator (lingcod, Ophiodon elongatus) in laboratory trials.     

Populations of Longidorus elongatus (Nematoda: Longidoridae) in two New Zealand soils under grazed pasture

Abstract

Information on the “needle nematode” Longidorus elongatus in New Zealand pastures has hitherto been limited. Monthly sampling of Pukepuke black sand and Manawatu fine sandy loam yielded L. elongatus populations up to 87 500 m^?2 (February) and 21 600 m^?2 (August). First stage juveniles appeared when soil temperature exceeded 15°C; females dominated populations every month and males were rare. Differences in abundance between soils may reflect the pore space available to these relatively large nematodes. Specimens survived 24 weeks storage at 5 and 15°C. While abundance tended to decline with depth, at 30–40 cm depth in Pukepuke sand, numbers increased, perhaps through the impact of groundwater levels on rooting patterns. In Pukepuke sand, plant species were associated with significantly different populations of L. elongatus, with Trifolium repens and T. subter‐raneum supporting more than Lolium perenne. More L. elongatus were found in grazed pasture with lower plant available P.     

Habitat-based submersible assessment of macro-invertebrate and groundfish assemblages at Heceta Bank, Oregon, from 1988 to 1990

Exploitation of groundfish off the U.S. Pacific coast reached maximum levels during the 1990s, resulting in severe declines in at least nine species of groundfish. From 1988 to 1990, we used the 2-man submersible Delta to make 42 dives and run replicate visual belt transects at six stations ranging from 67-360 m in depth at Heceta Bank on the outer continental shelf of Oregon. We identified four major habitats and associated benthic macroinvertebrate and groundfish assemblages: (1) shallow rock ridges and large boulders (< 100 m deep) dominated by basket stars, juvenile rockfishes, yelloweye rockfish, and lingcod; (2) mid-depth small boulder-cobbles (100-150 m) dominated by crinoids, brittle stars, rosethorn, pygmy/Puget sound, and canary rockfishes; (3) deep cobble (150-200 m) dominated by crinoids, brittle stars and various small rockfish species, and (4) deep mud slope (> 200 m) dominated by fragile urchins, sea cucumbers, shortspine thornyhead, and flatfishes. Although substantial interannual variation in groundfish abundance among seafloor types was evident in the 12 most abundant and/or commercially important fish taxa sampled, high variance resulted in statistically significant differences among years only in juvenile rockfishes. These data provide a baseline for future comparisons exploring long-term change this continental-shelf ecosystem.     

The deep-water species of Halimeda Lamouroux (Halimedaceae,Chlorophyta) from San Salvador Island,Bahamas: species composition,distribution and depth records

Caribbean species of Halimeda from the steep slopes of San Salvador Island, Bahamas, were collected along vertical transects between 25 and 255 m, on the northeast, northwest, west, southwest and south sides of the island, using the Harbor Branch Oceanographic Institution's submersible Johnson Sea Link I. The characteristics delineating species (segment and utricle size) were assessed for selected species, and the depth and western Atlantic distributions of the species reviewed. Halimeda copiosa was found to show a variation of surface utricle diameter with depth, with the deeper plants having 15% larger diameter utricles than the shallower plants. Of the seven species, one variety and one form of Halimeda studied from our submersible dive sites, H. copiosa, H. cryptica and H. gracilis grew to the greatest depths, from 120 to 150-m depths. H. lacrimosa var. globosa was found growing to 91 m, and H. tuna f. platydisca and H. discoidea to a depth of 73 m. Those of lesser depth, to 61 m, were H. goreauii, H. tuna f. tuna and H. lacrimosa var. lacrimosa. These represent substantial increases in depth distribution of the nine taxa found.     

Seasonal resource selection by blue suckers Cycleptus elongatus

Telemetry data were used to quantify seasonal resource selection and rank‐preferred habitat types for blue suckers Cycleptus elongatus in the middle Missouri River and its tributaries, Iowa, Nebraska, South Dakota, U.S.A. Habitat diversity required by C. elongatus to complete its annual life‐history cycle was evident by interseasonal variation in habitat selection. Tributaries and unchannelized portions of the middle Missouri River system were selected during the inferred spawning season (spring), habitats along shorelines in the channelized middle Missouri River were selected for postspawning (summer) and areas of reduced current were generally selected for the period preceding spawning (autumn). This study provides insight into mature C. elongatus behaviour throughout its annual life cycle. Furthermore, these results document the interseasonal variability in habitat selection of C. elongatus and highlight the need for development of habitat selection models for other imperilled fish species in aquatic systems affected by anthropogenic developments.     

Predictors of the distribution and abundance of a tube sponge and its resident goby

Microhabitat specialists offer tractable systems for studying the role of habitat in determining species’ distribution and abundance patterns. While factors underlying the distribution patterns of these specialists have been studied for decades, few papers have considered factors influencing both the microhabitat and the inhabitant. On the Belizean barrier reef, the obligate sponge-dwelling goby Elacatinus lori inhabits the yellow tube sponge Aplysina fistularis. We used field data and multivariate analyses to simultaneously consider factors influencing sponge and goby distributions. Sponges were non-randomly distributed across the reef with density peaking at a depth of 10–20 m. Sponge morphology also varied with depth: sponges tended to be larger and have fewer tubes with increasing depth. Knowing these patterns of sponge distribution and morphology, we considered how they influenced the distribution of two categories of gobies: residents (≥18 mm SL) and settlers (<18 mm SL). Maximum tube length, number of sponge tubes, and depth were significant predictors of resident distribution. Residents were most abundant in large sponges with multiple tubes, and were virtually absent from sponges shallower than 10 m. Similarly, maximum tube length and number of sponge tubes were significant predictors of settler distribution, with settlers most abundant in large sponges with multiple tubes. The presence or absence of residents in a sponge was not a significant predictor of settler distribution. These results provide us with a clear understanding of where sponges and gobies are found on the reef and support the hypothesis that microhabitat characteristics are good predictors of fish abundance for species that are tightly linked to microhabitat.     

Modelling patterns of coexistence of three congeneric headwater fishes

1. Mechanisms driving patterns of occurrence and co-occurrence among North American freshwater fishes are poorly understood. In particular, the influence of biotic interactions on coexistence among stream reaches and their effects on regional species distribution patterns is not well understood for congeneric headwater fishes.
2. Occupancy models provide a useful framework for examining patterns of co-occurrence while also accounting for imperfect detection. Occupancy models may be extended to test for evidence that a dominant species influences the occurrence of a subordinate species and thus evaluate support for the hypothesis that species interactions drive patterns of coexistence.
3. We examined patterns of occurrence and co-occurrence at the stream-reach scale among three species of darters (Percidae: Etheostomatinae) that occupy headwater streams within a Gulf Coastal Plain drainage in the south-eastern U.S.A. We assessed species occurrences at 97 sites in first- to third-order streams on one occasion each and used data from four sub-reaches sampled with equal effort at each site to estimate species-specific detection probabilities. Following sampling, a suite of habitat variables was collected at three equidistant points along each of the three transects established within a sub-reach. Coarse (stream-segment, catchment, network) scale variables were also incorporated using geospatial data. Single-species and two-species occupancy models were used to examine patterns of occupancy and coexistence.
4. The occupancy of each species was influenced by distinct habitat variables. Goldstripe darters (Etheostoma parvipinne) were constrained by a stream size gradient, groundwater input appeared to influence the occurrence of Yazoo darters (Etheostoma raneyi), and local habitat heterogeneity (e.g. variation in depth and current velocity) appeared to influence the occupancy of redspot darters (Etheostoma artesiae).
5. We found no evidence that the presence of one species influenced the occurrence of another within a stream-reach based on two-species occupancy models. Rather, species co-occurrences were best explained as independent occurrences within a stream-reach according to species-specific habitat associations.
6. Occupancy modelling may provide a suitable framework for evaluating the influence of biotic interactions among congeneric stream fishes along species-specific habitat gradients at the stream reach scale. Our study offers insight into how habitat variation can influence coexistence of potential competitors across a large river system.

     

Recent change in spatial distribution of the European flat oyster (Ostrea edulis) inferred from field data and empirical models of living oysters and empty shells

Marine coastal areas are increasingly affected by human activities resulting in changes in species and habitat distributions. Understanding these patterns and its causes and consequences is important for conservation and restoration of such changing habitats. One habitat that has been heavily affected by human use are the North Sea oyster beds which once were abundant but have lost large parts of its coastal distribution due to overexploitation. Based on data of living and dead assemblages of Ostrea edulis collected using video transects, we used an ensemble modeling technique to model and predict current and recent distribution of O. edulis along the Swedish west coast where its distribution is, in relative terms, still rather unaffected. We could detect a recent change in the distribution of O. edulis along the coast which to a large extent could be attributed to a change in depth distribution, suggesting that the population of O. edulis have a slightly shallower distribution today than in the past. Although a potential mismatch between living and dead assemblages, caused by a complex combination of biological and environmental conditions, needs to be considered in the interpretations drawn, it may be a way around the lack of suitable background data in management decisions. This provides important information for management and conservation of the native oyster beds. Furthermore, this study illustrates a method for identifying recent changes in species distribution using dead assemblages of bivalves.     

Is there a link between the type of habitat and the patterns of abundance of holothurians in shallow rocky reefs?

The presence of a mosaic of habitats, largely determined by sea urchin grazing, across shallow rocky reefs may potentially influence in differences in the distribution patterns of invertebrates. The aim of this paper was to assess, using a correlative approach, whether the type of habitat influences the abundance patterns of holothurians in the eastern Atlantic. We hypothesized that abundances of large (> 10 cm) holothurians varied among four types of habitat (3 vegetated habitats with low abundances of the sea urchin D. antillarum vs. ‘barrens’ with hyperabundances of sea urchins), and that these differences were consistent at a hierarchy of spatial scales, including two islands and several replicated sites within each type of habitat and island. Three species of large holothurians were found, accounting for a total of 300 specimens. We found remarkable differences in abundances of holothurians between the ‘barrens’ and the three vegetated habitats. This pattern was strongest for the numerically dominant species, Holothuria sanctorii. Total abundances of holothurians were between 5 and 46 times more abundant in ‘barrens’ compared with the vegetated habitats. Inter-habitat differences were species-specific with some inconsistent patterns from one island to the other. The total abundances of holothurians tended to increase with the abundance of sea urchins within ‘barrens’. Our study suggests that there may be a link, at least for the dominant species Holothuria sanctorii, between the distribution and abundances of large holothurians and the habitat across shallow-waters of the eastern Atlantic.     

Diversification of body shape in Sebastes rockfishes of the north‐east Pacific

Body shape variation is integrally related to many aspects of fish ecology, including locomotion and foraging, and can indicate the functional diversity of fish assemblages. Few studies have thoroughly characterized body shape in a diverse marine fish clade, or investigated both temporal and spatial patterns of variation in body shape disparity. Here, I use digital photographs to measure geometric body shape in 66 species of north‐east Pacific rockfish (Sebastes spp.), including a correction for error introduced by arching of specimens. Different components of interspecific shape variation show associations with fish size, depth habitat, trophic niche and phylogenetic relationships. Overall, the accumulation of body shape disparity appears to have been near‐constant over time, and shows little variation across the latitudinal range of rockfish.     

Conducting animal censuses amongst abrupt topography; a GIS‐based alternative to Distance

Management often bases decisions on estimates of animal density and population size. Aerial sampling is expensive whilst current ground methods, noticeably Distance sampling, assume a single detection function for each habitat and that visibility in a given habitat type declines in a smooth, increasing manner with distance from the observer. If the visibility within a habitat varies widely or is suddenly cut off, as amongst abrupt topography, these assumptions are invalidated. We present an affordable, accessible and accurate method for conducting repeated annual censuses on large herbivores in such terrain. We used a GIS habitat‐based approach. Monthly, over a two year period, we conducted repeated road transects in Ithala Game Reserve, South Africa, using GPS to record the geographic position of each sighting. These records (n = 8742) were then imported into a GIS and overlaid onto an existing habitat‐type GIS layer. With the sampled area thus defined as an irregular polygon in the GIS encompassing all records, we calculated densities of each herbivore species by habitat type and extrapolated total population size estimates. Estimates of maximum population size for wildebeest and zebra correlated (±15%) with management's estimates based on aerial surveys, walked transects and experience. White rhino are individually counted in the reserve and our estimates (year 1: 52; year 2: 57) matched these known numbers (year 1: 50; year 2: 53). Our method also yielded realistic numbers for impala, but unrealistic numbers for kudu and warthog. Our GIS‐based census technique produced realistic maximum population estimates for abundant grazing and mixed‐feeder mesoherbivores and for scarce, but highly visible, megaherbivores, but not for cryptic species. With the increasing availability of GIS data, the technique is recommended to those working in abrupt terrain frustrated by the inability of current ground census techniques, principally Distance sampling, to produce realistic population estimates.     

The Spatial Segregation of Zooplankton Communities with Reference to Land Use and Macrophytes in Shallow Lake Wielkowiejskie (Poland)

The spatial distribution of zooplankton in relation to two types of land‐use (forested and pastoral‐arable) of a lake's surroundings and to various habitats (helophytes, elodeids, nymphaeids and open water) was examined along 16 parallel transects on a macrophyte‐dominated lake (area – 13.3 ha; mean depth – 1.4 m). The type of habitat was the main determinant of zooplankton community structure. Dissected‐leaved elodeids harboured the richest and most abundant community with typically littoral (e.g., Colurella uncinata) and pelagic species (e.g., Keratella cochlearis). Two species (Polyarthra major and P. vulgaris) selectively chose the open water and one (Lecane quadridentata) the Typha stand. No spatial differentiation in zooplankton abundance was recorded between the two types of the catchment area. One possible explanation may be the shallowness and small area of this lake which may support full mixing and no difference in physical‐chemical gradients. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Winter and summer upwelling modes and their biological importance in the California Current Ecosystem

Analysis of monthly coastal upwelling intensities revealed two seasonal and biologically relevant upwelling ‘modes’ in the California Current Ecosystem (CCE). The first mode reflected upwelling during the summer months and was characterized by low‐frequency (multidecadal) processes, including significant (P<0.01) linear trends at some latitudes. In contrast, the second mode reflected wintertime upwelling and was defined by higher‐frequency variability associated with the North Pacific High and El Niño Southern Oscillation events. These modes were compared with multidecadal time series of splitnose rockfish (Sebastes diploproa) otolith growth, yelloweye rockfish (S. ruberrimus) otolith growth, Chinook salmon (Oncorhynchus tshawytscha) scale growth, and indices of Cassin's auklet (Ptychoramphus aleuticus) and common murre (Uria aalge) reproduction in the central‐northern CCE. In redundancy and correlation analyses, salmon growth and Cassin's auklet fledgling success associated with the summer upwelling mode while all other time series associated with the winter upwelling mode, indicating that CCE biology was differentially sensitive to these seasonal upwelling patterns. Thus, upwelling occurred in unrelated seasonal modes with contrasting trends, atmospheric forcing mechanisms, and impacts on the biology of the CCE, underscoring the importance of seasonality when evaluating ecosystem response to climate variability and change.     

The Distribution of Nearshore Fishes in Kelp and Eelgrass Communities in Prince William Sound, Alaska: Associations with Vegetation and Physical Habitat Characteristics

The nearshore (less than 20m depth) demersal fish community in Prince William Sound, Alaska, is dominated by Pacific cod, Gadus macrocephalus, pricklebacks (mostly Arctic shanny Stichaeus punctatus), gunnels (mostly crescent gunnels Pholis laeta), a variety of greenlings (Hexagrammidae) and sculpins (Cottidae). During summer, the spatial distribution of fishes, over scales of 100's of m to 10's of km, varied by habitats characterized by different vegetation types. Juvenile Pacific cod and greenlings were numerically dominant in eelgrass, Zostera marina, beds. Pricklebacks and sculpins were dominant in areas with an understory of the kelps Agarum cribrosum and Laminaria saccharina. Greenlings and sculpins were the most abundant demersal fishes in more exposed sites with a canopy of Nereocystis luetkeana and an understory of L. bongardiana. Measured habitat variables, including vegetation type, slope, vegetation biomass, and substratum type, explained a significant proportion of the variation in the presence or absence of most fishes. The relative importance of different habitat characteristics varied between taxonomic groups of fishes. Vegetation type explained a significant proportion of variation for cod, rockfishes, and ronquils. Juvenile cod were closely associated with eelgrass, while rockfish and ronquils were associated with kelps. Pricklebacks and rockfishes were more frequently observed on steeply sloped shorelines, while ronquils were more often found at sites with higher biomass of vegetation. Within A. cribrosum habitats, more greenlings and sculpins were present at sites where algal biomass was higher. Also, sculpins were more abundant in deeper water and gunnels were more abundant in shallow water within this habitat. These associations may not have been causative. However, evidence suggests that some differences between fish communities in eelgrass and Agarum beds may have been causally related to vegetation characteristics. The possible roles of different vegetation types as refugia from predators or as sources of prey are discussed.     

Food quality influences habitat selection in Daphnia

1. The vertical distribution of Daphnia in stratified lakes strongly depends on the depth profiles of temperature and food resources. However, ecological requirements for these factors are slightly different for juvenile and adult Daphnia. 2. Here, I investigated whether food quality influences the habitat selection of Daphnia pulicaria at night and whether the habitat selection of juvenile and adult D. pulicaria is different. Daphnia were allowed to choose their optimal habitat in large, stratified water columns (plankton towers, Plön) that held either the green alga Scenedesmus obliquus (high quality) in the cold hypolimnion (Hypo‐treatment) or S. obliquus in the warm epi‐ and cold hypolimnion (SCEN‐treatment) or the non‐toxic cyanobacterium Synechococcus elongatus (low quality) in the warm epilimnion and S. obliquus in the cold hypolimnion (SYN treatment). 3. When food (S. obliquus) was present only in the hypolimnion (Hypo‐treatment), juveniles and adults distributed similarly in the water column and spent most of their time in the interface between the warm and the food rich layer. 4. When food was present in the epilimnion and hypolimnion (SCEN‐ and SYN‐treatments), juvenile and adult D. pulicaria moved into the warm and now also food‐rich epilimnion, however, the magnitude of this shift depended on the food type and age class of Daphnia. Adult and juvenile D. pulicaria spent most of their time in the epilimnion when food there was of a high quality (S. obliquus; SCEN‐treatment). However, compared to the juveniles, adult Daphnia spent significantly more time in the colder hypolimnion when epilimnetic food was of a low quality (S. elongatus; SYN‐treament). 5. Therefore, habitat selection of adult D. pulicaria was affected by food quality whereas the habitat selection of juveniles was not. 6. Additional growth and reproduction experiments show that the food quality is likely to be responsible for the different habitat selection of juveniles and adults in the SYN‐treatment. 7. In conclusion, my experiments show that D. pulicaria behaviourally reacts to the quality of its food source.