Heloise Chenelot

Lacuna vincta (Mollusca, Neotaenioglossa) herbivory on juvenile and adult Nereocystis luetkeana (Heterokontophyta, Laminariales)

Herbivory can be an important factor structuring coastal algal communities. Herbivores may preferentially graze particular algal species or tissue types. Mesograzers, despite their small size, can critically weaken kelp thalli and impact entire kelp beds. We propose that when kelp beds are composed of several kelp cohorts, mesograzers will selectively choose to inhabit younger plants and grazing activities will have a greater impact on younger plants. This study investigated the effects of grazing by the littorinid gastropod, Lacuna vincta, on different age classes of the bull kelp, Nereocystis luetkeana by (1) testing food preference of L. vincta on juvenile, first-year adult, and second-year adult Nereocystis blades in the laboratory, (2) determining substrate (blades of different ages) preference of L. vincta in the laboratory, and by (3) estimating in-situ herbivore abundances and densities on juvenile and adult Nereocystis. Results demonstrated that grazing by L. vincta produced greater damage on juvenile than older Nereocystis tissues. Although L. vincta did not select juvenile versus older kelps as substrate in the laboratory, in situ surveys showed that differences existed between age classes with higher L. vincta densities on juvenile than adult kelp. We conclude that at a local scale, L. vincta can be an important structuring factor in Nereocystis populations due to its high density and grazing ability.

Spatial and Temporal Distribution of Echinoderms in Rocky Nearshore Areas of Alaska

Among near shore invertebrates, echinoderms play an important role in the structure (specifically in food web structure) and function of rocky intertidal and shallow subtidal communities because of their high densities, biomass, and versatile ecological functions. Alaska has a variety of near shore echinoderm species, but little is known about their spatial and temporal distribution. Rocky habitats were surveyed following Natural Geography in Shore Areas (NaGISA) protocols in three areas of the Gulf of Alaska (Prince William Sound, Kachemak Bay, and Kodiak Island) in 2003 and 2004. Within each area, two to three sites were destructively sampled. The abundance of echinoderms within five 25×25cm quadrats was recorded in the high, mid, and low intertidal heights and 1m, 5m, and 10m depths. We attempted to detect interannual variability in the distribution of echinoderms and to evaluate whether distribution was different along horizontal scales between regions 100’s of kilometers apart and, within each region, between sites 10’s of kilometers apart. We also looked at tidal height as a factor of variation and tried to determine if any vertical patterns were consistently observed over time and over regional and local areas. The diversity and abundance of echinoderms were greatly variable between our two sampling events and over all spatial scales. No clear patterns were identified over time and over (regional and local) horizontal gradients. However, different echinoderm groups showed distinctive distribution patterns over the vertical immersion gradient, with asteroids and holothuroids being more abundant in the intertidal and shallow subtidal zone and ophiuroids being more abundant at deeper depths.

Ptychodactis aleutiensis, a new species of ptychodactiarian sea anemone (Cnidaria: Anthozoa: Actiniaria) from the Aleutian Islands, Alaska

Abstract We describe a new species of ptychodactiarian sea anemone, Ptychodactis aleutiensis, and redefine the family Ptychodactiidae and the previously monotypic genus Ptychodactis to accommodate P. aleutiensis sp. nov. Individuals of the new species were photographed and collected at depths of less than 20 m off the Aleutian Islands, Alaska. Many were found detached, adrift in the water. The species differs from the only other member in its genus, Ptychodactis patula, in having more tentacles, tentacles only at the margin, frilled structures associated with only two siphonoglyphs, infertile primary mesenteries, oral stomata, holotrichous nematocysts of two size classes in the tentacles, actinopharynx, and mesenterial filaments, and by the morphology of the holotrichs and spirocysts. It is the fourth species of ptychodactiarian described; Ptychodactis is the only genus of suborder Ptychodacteae with more than one species.

Variation in Low Intertidal Communities: Submerged vs. Emerged

Organisms living in the low rocky intertidal must cope with changing conditions of submersion and emersion on a regular basis. Some mobile organisms engage in small-scale migrations, using the tidal current for passive transport or for aid in active transport while foraging for food and escaping predation. As such, it is expected that at any given intertidal depth, mobile assemblages will vary based on whether they are submerged or emerged. This study used NaGISA (Natural Geography In Shore Areas) sampling protocols at the 1m below MLLW level to examine variation in rocky intertidal mobile faunal assemblages in response to tidal immersion in Prince William Sound, Alaska. Two NaGISA survey transects were conducted at the same tidal stratum: once at high (submerged) and once at low tide (emerged). Caprellids were the only taxon to show a consistent trend of higher abundance at submersion. Amphipods, isopods and nemerteans showed different trends in abundance between sites, while crabs and errant polychaetes were more abundant during emersion. These differences could be due to water cover, species-specific movement, different species engaging in different migration patterns during the tidal cycle, patchy distribution of particular faunal species, taxon and functional group composition of the algal community, as well as the sampling technique using SCUBA at high tide versus intertidal sampling at low tide.