Population ecology of the marine insect Halocladius variabilis (Diptera: Chironomidae) in the rocky intertidal zone of Nova Scotia, Canada

摘要

ABSTRACT: We studied the population ecology and productivity of the little-known marine insect Halocladius variabilis (Chironomidae) from the exposed rocky intertidal zone on the Atlantic coast of Nova Scotia, Canada. Larvae of H. variabilis are host-specific symbionts of the brown alga Elachista fucicola, which in turn is an abundant epiphyte on the dominant intertidal fucoid Ascophyllum nodosum. At our primary study site at Drum Head, A. nodosum frond density (mean ± SE) was 546 ± 46 fronds m–2 for fronds 20 cm long. Density of E. fucicola on A. nodosum was highly variable seasonally, with median densities of 20000 m–2 in July. Mean number of H. variabilis larvae E. fucicola thallus–1 varied from 0.8 ± 0.1 in November to 3.9 ± 0.3 in mid-July. Median density of larvae frond–1 of A. nodosum ranged from 0 in November to 246 in July. The latter number represents a median density of 59500 larvae m–2, making H. variabilis one of the most abundant marine insects known. Based on distributions of larval size, H. variabilis appears to be univoltine or possibly bivoltine. H. variabilis larvae were largest (6.48 ± 0.17 mm long) in May and smallest in late August (~2 mm), suggesting a mid-summer period of adult egg-laying. Larval production was conservatively estimated at 130 g m–2 yr–1, making this also the most productive chironomid known from any habitat. The high population density and production suggest that H. variabilis is an important, but overlooked, component of marine rocky shores of the northwestern Atlantic.