Kelp Habitats Research Articles

Habitat use and early winter movements by juvenile Atlantic cod in a coastal area of Newfoundland

Acoustic telemetry was used to monitor the movements and landscape scale habitat use of age 2–3 year juvenile Atlantic codGadus morhuain Newman Sound, a coastal fjord of Newfoundland, during late autumn and early winter (24 October 1999 to 22 January 2000). Substratum, bathymetric relief and depth use were studied to determine if it differed from the pattern expected given an absence of selectivity (habitat use proportional to habitat availability). Prior to winter migrations, most Atlantic cod maintained small home ranges (0·5–33·4 ha, median = 2·1 ha) although a few individuals moved more widely. No relationship between total length (LT) and home range size was detected. In Inner Newman Sound, Atlantic cod occupied depths of 10–29 m more than expected given availability, while depths of 0–9 and 40–59 m were underutilized. No significant relationship between depth andLTwas detected. Areas of medium (5–10%) or high (>10%) bathymetric relief and boulder or kelp habitats were used significantly more than expected given the availability of these habitats. Sand and eelgrass substrata were underutilized given availability, although many Atlantic cod used sandy‐bottomed areas to some degree. Flexibility in habitat use by the individuals that were studied suggested reduced predation risk relative to younger conspecifics. Winter migrations to deeper water beyond Newman Sound began in mid‐November, coinciding with the disappearance of the thermocline, and continued until 27 December. Approximately 30% of monitored individuals did not migrate and maintained their home ranges into the winter season. No significant differences inLTbetween migrating and resident groups were detected, however, the condition of migrating fish was significantly higher than in resident fish. This finding supports the theory that feeding history plays a role in the decision to undertake migration.

Species distribution and habitat exploitation of fauna associated with kelp (Laminaria Hyperborea) along the Norwegian Coast

Fauna associated with the common kelp along the Norwegian coast, Laminaria hyperborea, was sampled at four sites covering 1000 km of coastline. Exploitation of the kelp habitat by the fauna, and the ways in which habitat size and seasonal variations affect the kelp fauna community were analysed. The study focused on mobile macrofauna, of which 238 species were found on 56 kelps sampled, with an average density of almost 8000 individuals per kelp. Amphipods and gastropods were the most diverse and abundant fauna groups. The species composition was different on the lamina, stipe (with epiphytic algae) and holdfast. A similar pattern of epiphyte- and holdfast-fauna composition was found for all regions. Lowest diversity and abundance were found on the lamina, and highest diversity in the holdfast. Highest abundance was found on the stipe in summer, but there were large variations between sites and seasons, from a few individuals to more than 80 000 animals per stipe. Neither seasonal changes nor variation in habitat volume affected the number of species significantly, but abundance was significantly related to season and habitat volume. These variations were most pronounced for stipe fauna. Laminaria hyperborea offers a heterogeneous habitat exploited by a diverse and abundant invertebrate community, its abundance depending on local and regional variations in kelp size.

84 Linking environmental forcing, kelp forest habitat dynamics, and community structure in the northeast pacific

Habitat‐forming species of large brown macroalgae (e.g., kelps) often differ from associated benthic species in resource requirements, sources of disturbance, and dispersal ability. Differences in environmental drivers and demographic processes may cause these habitats to fluctuate at spatial and temporal scales that differ from the “optimal” scale that would promote maximum abundance of any particular associate species. As a result, the spatiotemporal dynamics of habitat may exert important effects on benthic community structure and composition. To quantify the spatial and temporal dynamics of giant kelp (Macrocystis pyrifera), a key habitat‐former in the NE Pacific, I analyzed a 34‐year monthly time series of estimated canopy biomass spanning ∼1500 km of coastline (7° of latitude) and digital maps of annual maximum canopy cover. Canopy biomass varied interannually at dominant periods of 4–5 y, 11–13 y and ∼20 y, and spatial scales ranging from local (∼30 km) to mesoscale (∼100–150 km) and regional (∼330 km). Temporal dynamics were strongly related to basin‐scale climate fluctuations (El Niño‐Southern Oscillation, Pacific Decadal Oscillation) and spatial patterns were correlated with coastline geomorphology. Digital canopy maps reveal that changes in biomass are associated with shifts in the spatial structure of the kelp habitat. Long‐term subtidal community monitoring data from areas with markedly different spatial and temporal scales of kelp forest habitat structure reveal a complex but important influence of habitat dynamics on the distribution of life histories within kelp‐associated communities. Future changes in the dynamics of Pacific climate fluctuations may have important implications for kelp forest community structure.

Movement patterns, home range, and habitat utilization of adult kelp bass Paralabrax clathratus in a temperate no-take marine reserve

Home range, activity patterns, site fidelity and habitat preference of the kelp bass Para- labrax clathratus were determined from 12 adult fish tracked using acoustic telemetry within a tem- perate no-take marine reserve (0.13 km 2 ). Home range sizes ranged from 33 to 11 224 m 2 , averaging 3349 ± 3328 m 2 (±SD), but did not correlate with fish size. Fish were active and occupied similar-sized activity spaces during both day and night. Kelp bass exhibited a high degree of site fidelity, remain- ing resident in core areas for up to 3 yr. Relative to the total amount of available habitat, kelp bass showed a habitat selection preference for rock boulder, rock rubble and kelp habitat. These habitats offer high vertical relief, shade and large holes for shelter, and may attract and facilitate prey capture. Average home range size was 3% of the area of the reserve. Only 1 of 12 tracked fish crossed the reserve boundary, but this accounted for less than 5% of the fish's time. Natural habitat breaks along the reserve boundary may have further limited adult kelp bass movements. The small home ranges and high site fidelity of kelp bass in this reserve indicate that the reserve is effective in protecting the resident adult stock.

HABITAT-SPECIFIC RECOVERY OF SHALLOW SUBTIDAL COMMUNITIES FOLLOWING THEEXXON VALDEZOIL SPILL

We contrasted impacts of the Exxon Valdez oil spill within kelp and eelgrass communities and examined recovery of these communities over a period of up to 10 yr after the spill. Impacts were greatest in sheltered bays that were subject to heavy oiling. The effects of oiling and associated cleanup activities on nearshore subtidal communities within these bays were more evident in eelgrass than in kelp habitats. In 1990, a year after the spill, concentrations of total polycyclic aromatic hydrocarbons (TPAHs) were higher, more groups of organisms were impacted, and more groups showed a negative response to oil (i.e., lower densities at oiled vs. reference sites) in eelgrass than in kelp beds. Recovery was slower in eelgrass than in kelp habitats. About 80% of the groups impacted in eelgrass beds failed to show clear signs of recovery by 1995, six years after the spill. In contrast, most impacted groups in kelp beds recovered within two years. The stronger, more persistent impacts in eelgrass beds were probab...

Seasonal changes in subarctic sea urchin populations from different habitats

This paper documents seasonal variation in certain sea urchin (Strongylocentrotus polyacanthus) characteristics in habitats of varying environmental conditions. At Shemya Island, Alaska, three habitat types [dense kelp beds, intermediate kelp beds, and algal barrens (low to no foliose algal cover)] were monitored seasonally from September 1995 to August 1996, for live and drift foliose algae. In general, drift algal abundance was greater in areas with more attached kelp, but this varied with season. Along with drift algae, sea urchin density, test size diameter, gonad and nutrition indices, and mobility were seasonally sampled within each habitat. Densities were highest in the algal barrens and lowest in the kelp beds. Seasonally, densities varied between summer/fall, and winter/spring, with lower numbers in the winter/spring. Test size was largest in the kelp habitats when compared to the intermediate or barren sites. Test size was seasonally consistent in the kelp habitats but not in the intermediate or barren sites. Here, test size did vary depending on season (larger urchins were found in winter). The gonad index showed much seasonal variation at the kelp and intermediate kelp sites, but was relatively more stable over time in the barren habitats. Between habitats, gonad and nutrition indices were larger in areas with kelp. Urchin movement varied seasonally between habitats, with more overall movement and variation in barren habitats. These results illustrate the importance of small-scale temporal and spatial variation. Monitoring for 1 year demonstrated that certain parameters varied more in areas of higher foliose algal cover (gonad indices), while other parameters varied more in low kelp areas (test size and movement). These results suggest that studies involving urchins should consider both time of year and overall algal community composition when conducting any type of experimental or monitoring work.

Atypichthys strigatus (Pisces: Scorpididae): An opportunistic planktivore that responds to benthic disturbances and cleans other fishes

Abstract Atypichthys strigatus (Günther) were abundant on temperate reefs in New South Wales, Australia. Dietary analyses indicated that they feed primarily on plankton, but also consume benthic organisms. Initial observations suggested thai A. strigatus respond to disturbances of the substratum for the purpose of feeding. The substratum in barrens and kelp habitats was experimentally disturbed to examine the response by A. strigatus. Significantly more A. strigatus were found in disturbed areas than in undisturbed areas and their feeding rate was greater in disturbed areas. The response by A. strigatus to disturbance was the same in barrens and kelp habitats, although there was a more marked response in the barrens habitat. Atypichthys strigatus also responded to natural disturbance by large reef fishes (e.g. Achoerodus viridis: Labridae). Furthermore, A. strigatus of a broad range of sizes (25–90 mm standard length) were observed cleaning other reef fishes. The behavioural flexibility of A. strigatus probably leads to increased feeding opportunities, and hence increased foraging success, for the fish. Moreover, it raises questions about the accuracy of partitioning fish species according to one trophic group.

High turnover of inorganic carbon in kelp habitats as a cause of ?13C variability in marine food webs

In a study to assess qualitatively the importance of organic matter derived from kelp production in the Aleutian Islands of subarctic Alaka, replicated samples of autotrophic sources and primary and secondary consumer organisms were sampled for δ13C among sources, sites, (treatment) islands, and years. Unanticipated variation in the δ13C of kelps occurred among overtly similar sites at different islands. Variation in the δ13C of the surface canopy-forming kelp Alaria fistulosa was particularly extreme, ranging from-15.5 to-28.0‰ compared to the understory kelps, Laminaria spp. A. fistulosa δ13C varied by as much as 6 to 7‰ among similar sites at a given island within years, and by as much as 3 to 4‰ between years at the same sampling site. In serveral cases, δ13C variation was weakly tracked by some consumer organisms, suggesting that even detritus pathways through the food web can be localized and tightly coupled. Dynamic cycles in the concentration and δ13C of dissolved inorganic carbon (DIC) and aqueous CO2 concentration ([CO2]aq) were measured at three sites on one island. The δ13C or organic carbon fixed by A. fistulosa, calculated from diurnal DIC concentration and δ13C measurements, varied by 15‰ and varied inversely with [CO2]aq concentrations. Local DIC variability, probably resulting from high productivity and decreased turbulence in dense kelp habitats, provides a possible mechanism of variation in kelp δ13C. The short-term variability in the δ13C of organic carbon fixed by kelps indicates that sampling methodology and design must assess this potential variation in marine macrophyte δ13C before making assumptions about the transfer of δ13C-invariate organic matter to higher trophic levels. On the positive side, a predictable relationship between [CO2]aq concentration and kelp δ13C offers a potentially robust means to assess productivity effects on CO2 limination in kelps and other complex aquatic macrophyte habitats.