The Importance and Seasonal Variation of Terrestrial Invertebrates as Prey for Juvenile Salmonids on the Kol River Floodplain, Kamchatka, Russian Federation

Eberle, Lorri C., M.S., Spring 2007 Biological Science The Importance and Seasonal Variation of Terrestrial Invertebrates as Prey for Juvenile Salmonids on the Kol River Floodplain, Kamchatka, Russia Committee Chair: Dr. Jack Stanford Fluxes of energy and resources from one system to another across an interface can play a major role in the structure and function of the food web of the receiving system. Floodplain spring brooks have a particularly high interface value and host high densities of juvenile fish likely seeking refuge from predators, high velocity water, and stressful temperatures. We propose that one potential reason that these systems are able to support such high densities of fish is related to prey subsidies coming from the neighboring terrestrial system (i.e. terrestrial invertebrates). We examined terrestrial invertebrate inputs into spring brooks and their use as prey by salmonids in two spring brook habitats from May- October 2006 on the Kol River flood plain in Kamchatka, Russia. Benthic and drifting invertebrates, terrestrial invertebrate inputs, terrestrial invertebrate communities and fish diet were analyzed to asses the seasonal and spatial variation in the terrestrial invertebrate subsidy. Sites were selected that are representative of two different vegetation types: early and late succession. Biomass of benthic and drifting invertebrates was low for both sites and annual average of terrestrial inputs was 22.2 ± 0.1 mg∙m-2∙day-1. Terrestrial invertebrates were most important to the diets of coho salmon with as much as 68% of their diet being terrestrial in origin, whereas on average only 13% of the Dolly Varden diet was terrestrial. Terrestrial invertebrates were most important in the fall at both sites. However, in the spring, an unlikely prey item caused a spike in the terrestrial percentage at the early succession site. The Curculionidae larva (order: Coleoptera) which live in the catkins of willows were found to be far more abundant in the species of willow that exists only in early succession. This study links terrestrial prey items to floodplain succession, and demonstrates for the first time the seasonal variation in the terrestrial invertebrate subsidy in the floodplain habitats. By highlighting the link between terrestrial and aquatic systems, the results of this study raise concerns in dealing with riparian management and salmonid production and conservation. Key words: allochthonous inputs, terrestrial invertebrates, resource subsidy, forest-stream ecotone, food webs, stream ecology, salmonids, Kamchatk