The ecology of net-spinning caddisflies in a Newfoundland lake outlet

Genge, Peter D. (1985) The ecology of net-spinning caddisflies in a Newfoundland lake outlet. Masters thesis, Memorial University of Newfoundland.

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Abstract

The community of dominant species of net-spinning caddisflies found in the Axes Pond outlet - an oligotrophic lake-stream system near Torbay, Newfoundland was investigated. The dominant species in the system included: Cheumatopsyche pettiti, Hydropsyche betteni, Hydropsyche slossonae, Hydropsyche sparna, Neureclipsis crepuscularis and Chimarra aterrima. Zonation existed in the abundance and distribution of these species along the stream within short distances from the lake outlet. H. betteni, C. pettiti and N. crepuscularis were predominant at the immediate lake outlet while 60 meters downstream H. slossonae and H. sparna were predominant with large numbers of C. pettiti and N. crepuscularis present. Downstream from this point, C. aterrima was predominant. Biomass of net-spinning caddisfly larvae varied throughout the year and between stations. Highest values were generally reached at the immediate outlet during late spring or late fall and winter. Lowest values were observed at the sampling station furthest from the outlet during mid summer. -- It is strongly suspected that density dependent drift resulted in a developmental gradient within the densest populations at the outlet. For any one generation, the modal instar number for a species population decreased with distance below the outlet. -- Life history patterns of the net-spinning caddisflies studied at Axes Pond were not necessarily comparable with those described for the same species on the mainland. Larvae of most species of hydropsychids studied at Axes Pond were larger at a given larval instar and overwintered in earlier larval instars than the same species studied on the mainland. With the exception of H. slossonae, which had a univoltine life cycle, all species studied had univoltine and/or semivoltine life cycles. This is the first report of a semivoltine life history in net-spinning caddisflies. -- Large particles of lake-derived seston disappeared from the stream faster than smaller particles. This reduction in mean food particle size over distance downstream from the outlet corresponded with the feeding habits and zonation of the net-spinning caddisflies. In addition to differences in feeding habits it is postulated that these species may be able to exist together as a result of several other factors including temporal variation in life history and differences in habitat preference. These factors permit the existence of a complex guild of net-spinning caddisflies at a lake outlet.

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