Catherine E. de Rivera

Integration of an invasive consumer into an estuarine food web: direct and indirect effects of the New Zealand mud snail

Introduced species interact both directly and indirectly with native species. We examine interactions between the introduced New Zealand mud snail (Potamopyrgus antipodarum) and native estuarine invertebrates and predators through experiments and field studies. A widely held management concern is that when P. antipodarum, which has low nutritional value, becomes abundant, it replaces nutritious prey in fish diets. We tested two key components of this view: (1) that fish consume, but get little direct nutritional value from P. antipodarum; and (2) that P. antipodarum has an indirect negative effect on fish by reducing the energy derived from native prey. We also examined predation by the native signal crayfish, Pacifastacus leniusculus. Laboratory feeding trials showed that both crayfish and fish consume P. antipodarum, a direct effect. Crayfish consumed and successfully digested higher numbers of snails than did fish [Pacific staghorn sculpin (Leptocottus armatus), three spine stickleback (Gasterosteus aculeatus), and juvenile starry flounder (Platicthys stellatus)]. P. antipodarum occurred at low frequencies in the stomachs of wild-caught fish. More interesting were the indirect effects of this invader, which ran counter to predictions. P. antipodarum presence was associated with no change or an increase in the amount of energy derived from native prey by predators. The presence of P. antipodarum also led to increased consumption of and preference for the native amphipod Americorophium salmonis over the native isopod Gnorimosphaeroma insulare. This is an example of short-term, asymmetric, apparent competition, in which the presence of one prey species (snails) increases predation on another prey species (the amphipod).

Cold tolerance of the invasive Carcinus maenas in the east Pacific: molecular mechanisms and implications for range expansion in a changing climate

Physiological studies have long been utilized to understand the role of environmental temperature in the distribution of native organisms within marine communities. For the invasive crab Carcinus maenas, temperature has been implicated as the main predictor of establishment success across temperate regions. Therefore, we determined whether the lower temperature tolerances of this non-native crab would restrict it from spreading farther poleward from a relatively new recipient environment. Cold tolerance capacity was determined in the laboratory by holding crabs sampled from Vancouver Island, British Columbia (BC)—near the present northern limit for the northeast Pacific metapopulation to an overwintering thermal profile generated from Sitka, Alaska, USA. These crabs were physiologically capable of overwintering north of their present range boundary. The cellular response to cold stress was investigated using two functional categories of the cellular stress response. We measured cyclin D1, a cell-cycle regulator, and Hsp70, a protein chaperone, after laboratory acclimation and acute cold stress on two populations of C. maenas from the west coast of North America that have disparate thermal histories (crabs sampled from CA or BC). We found site-specific differential expression of cyclin D1 after cold acclimation and cold shock, perhaps affecting invasion capacity in this species. Determining what physiological mechanisms are in place with respect to thermal tolerance and preference can give insight into what makes an invasive organism successful and aid in predicting probable distribution of such species within a new environment.

PER CAPITA EFFECTS AND BURROW MORPHOLOGY OF A BURROWING ISOPOD (SPHAEROMA QUOIANUM) IN DIFFERENT ESTUARINE SUBSTRATA

ABSTRACT Marine wood-borers and burrowers can substantially alter habitats and human-created structures in the marine environment. While many marine borers and burrowers occur only in a few substrata, burrowing sphaeromatid isopods can damage a variety of substrata. On the Pacific coast of North America, burrowing by the non-native isopod, Sphaeroma quoianum, accelerates shoreline erosion and damages marine structures. We conducted a lab experiment to quantify the per capita burrowing effect of S. quoianum on four common estuarine substrata. After two months, isopods created longer and more voluminous burrows and removed the most material (per capita) in marsh banks and Styrofoam followed by sandstone and non-decayed wood. We also examined the burrow morphology (length, diameter, volume) of burrows of S. quoianum from those four substrata collected in the field. We observed longer and more voluminous burrows in marsh bank and Styrofoam substrata, although we only detected a significant difference in length between substrata. Based on our lab results, we estimate a population of 100 000 adult isopods burrowing for two months could remove approximately 176 liters of marsh bank, 103 1 of Styrofoam, 72 1 of sandstone, or 29 1 of non-decayed wood. While the per capita bioerosion effects are lower than some bioeroders, e.g., the shipworm Bankia setacea, the pholad Penitella penita, high densities and wide distributions of S. quoianum suggest it is a substantial bioeroder within the intertidal and shallow subtidal in temperate Coos Bay, Oregon, and perhaps the other estuaries it has invaded.

Ecological investigations to select mitigation options to reduce vehicle-caused mortality of a threatened butterfly

Whereas roads that bisect habitat are known to decrease population size through animal-vehicle collisions or interruption of key life history events, it is not always obvious how to reduce such impacts, especially for flying organisms. We needed a quick, cost-efficient and effective way to determine how best to decrease vehicle-caused mortality while maintaining habitat connectivity for the federally listed Oregon silverspot butterfly, Speyeria zerene hippolyta. Therefore, we gathered targeted ecological information that informed selection of a mitigation option prior to implementation. We sampled butterfly behavior and environmental conditions along a highway and conducted a small-scale experiment along a decommissioned road corridor used by these butterflies. Using our findings, we recommended vegetation management and helped managers eliminate options they were considering that would be ineffective such as increasing shade or wind in the road, and installing fencing or hedgerows aimed at directing flight above traffic. This quick and inexpensive approach of using ecological observations and small-scale experiments to evaluate the likely success of each available mitigation option can be used to determine effective, species-specific solutions for reducing traffic impacts on pollinators and other small, flying organisms of conservation concern.