Growth and Production of Eogammarus confervicolus (Amphipoda: Anisogammaridae) at a Log Storage Site and in Areas of Undisturbed Habitat within the Squamish Estuary, British Columbia

Growth and production of Eogammarus confervicolus was investigated in three contrasting habitats within the Squamish estuary: a log debris area, an embankment along the perimeter of a Carex lyngbyei marsh, and a Fucus distichus community. Eogammarus confervicolus annual production was highest in the "bank" habitat (21.38–21.65 g∙m−2∙yr−1) followed by Fucus (11.31–12.99 g∙m−2∙yr−1) and then wood debris (6.12–6.75 g∙m−2∙yr−1). P: B ratios were similar for the bivoltine wood debris and bank animals (4.67–5.15 and 5.94–6.01, respectively) but lower for the univoltine Fucus population (3.28–3.76). Growth rates were judged to be higher in bank and Fucus than in wood debris. Mortality rates were highest in wood debris. The food available for estuarine amphipods in wood debris habitats is thought to be inferior to that produced in marsh and algal communities. Despite the fact that E. confervicolus production in wood debris was much lower than in undisturbed locations, the possibility remains that such areas are still adequate food gathering areas for juvenile salmonids, if water quality conditions permit fish access to the log storage site.

The biology and energetics of Eogammarus confervicolus (Stimpson) (Amphipoda, Anisogammaridae) at the Squamish River Estuary, B.C.

Data on the biology and energetics of the gammarid amphipod Eogammarus confervicolus (Stimpson) are presented from the Squamish River estuary in southwestern British Columbia. At low tide, E. confervicolus was most abundant under cover material, especially sedge rhizomes (Carex lyngbyei) and rockweed (Fucus distichus). Maximum biomass was observed in spring under the sedge mat (16.1 g dry weight m−2) and rockweed (16.8 g dry weight m−2). The minimum sized female bearing eggs was observed to be approximately 7 mm and egg number ranged up to 75. Incubation time (10 °C, 15‰) was 17 days. In 2 years of data, mature females were most abundant in samples from October to December and July to August. Oxygen consumption rates at 5 and 10 °C were lowest in fresh water and increased with higher salinities. At 15 °C, lower salinities increased consumption rates. Net growth efficiency (K2) was calculated from growth rates on four diets used in a previous study and for respiration under prevailing environmental conditions. The following are ranked diets: Enteromorpha linza (51.2%), Pilayella littoralis (44.2%), Navicula spp. (42.7%), and Carex lyngbyei debris (22.4%). The central sector of the estuary showed the highest K2 values when averaged over diets (53.2%).

Association and Feeding Relationships Between Eogammarus confervicolus (Amphipoda, Gammaridae) and Benthic Algae on Sturgeon and Roberts Banks, Fraser River Estuary

Field and laboratory studies of the feeding and association of the gammarid amphipod Eogammarus confervicolus with algae and vascular plant debris were conducted on jetties, marshes, and sandflats at the Fraser River Estuary. Associations with Prasiola meridionalis (alga), and debris from Carex lyngbyei (vascular plant) were statistically significant. Vascular plant debris was more widespread in winter (January) compared to a summer survey (August). Laboratory growth rates and survival varied with food types, which were ranked (best to worst) as follows: Enteromorpha linza, Pylaiella littoralis, Porphyra spp., Navicula grevillei, Carex lyngbyei debris and Ulva lactuca. Assimilation efficiencies, measured with gravimetric and radioisotope techniques (14C) ranged from about 78% with P. littoralis to 62% with U. lactuca. Construction of jetties could increase the surface area for algal growth, but there would be no appreciable enhancement of primary production compared to a natural marsh/sandflat ecosystem.Key words: Crustacea, Eogammarus confervicolus, benthic algae, Fraser Estuary, intertidal distribution, feeding, ecological associations, engineering structures