Castle Lake Projects
Seasonal and spatial patterns of secondary benthic production in a sub-alpine lake
Aquatic invertebrate secondary production plays an important role in ecosystem food webs by contributing energy to lake and terrestrial consumers. The objective of this study was to expand the knowledge of benthic contributions to the landscape in a subalpine ecosystem with a traditional emphasis on pelagic studies. To determine seasonal and spatial patterns in aquatic energy contributions to aquatic and terrestrial consumers, benthic and emergent invertebrate densities were measured in Castle Lake during the ice free months from May-October 2008 and 2009. Specifically, our goals were to
- determine spatial and temporal benthic secondary production dynamics
- estimate benthic emergence-to-production ratios to provide insight to potential aquatic subsidies to terrestrial consumers.
Benthic invertebrate densities and diversity were highest in sub-littoral habitats. Benthic secondary production was estimated using the size-frequency method. Annual benthic secondary production was highest for Odonata and lowest for Ephemeroptera, with 36.85 g/m²y¹ and 0.63 g/m²y¹, respectively. Secondary production varied seasonally and by depth and whole-lake benthic secondary production was estimated at 22.68 g/m²y¹. The dominant emergent invertebrate, Chironomidae, reached peak densities (45/m2) in the eulittoral and sub-littoral depths from late spring to mid-summer. Emergent Ephemeroptera and Odonata were both most abundant at eulittoral depths, with Ephemeroptera densities peaking (0.8/m2) in late summer and Odonata densities peaking (1.4/m2) in late spring. Ephemeroptera had the highest emergence-to-production ratio during all seasons, with a high of 47.5 % emergence from the lake from late summer to early fall. Odonata had 20.4 % emergence from late spring to midsummer, and dropped to < 1 % emergence from late summer to early fall. Chironomidae had 5.1-6.7 % emergence from late spring to late summer and 1 % emergence from late summer to early fall in eulittoral depths. Chironomidae emergence was 1 % or less during all seasons in sublittoral and profundal depths. This suggests that while there were abundant benthic invertebrates in Castle Lake, aquatic invertebrates did not enter the terrestrial landscape at their maximum potential possibly due to consumption by stocked fish, or to natural mortality.