Lake Typology from Identity of Profundal Chironomidae Larvae

(Considerably Simplified)

Necessary conditions:

• Dimictic or warm monomictic lake with maximum summer temperatures in the hypolimnion of 15 C or less
• (plus one note about indicators in warmer hypolimnions).
• Identified dipteran larvae that have been collected from fine sediments retrieved from the profundal zone, but not necessarily from the deepest part of the lake.

Ultra-oligotrophic

Heterotrissocladius

• description:  small larvae (6 - 9 mm long in 4th instar); white with translucent purplish, grey or green patterns in life; thorax slightly thickened and abdomen tapers slightly, posterior prolegs longer than wide and slightly tapered; no blood gills on 11th segment, head capsule with a larger and a semi-detached, smaller eyespot on each side.
• larval habit: wandering through upper 1 - 2 cm of sediment without maintaining open tubes; surface- and sub-surface deposit-feeders

associated environment:  northern, high-latitude (50^o-plus) or high-altitude lakes with very low productivity

Oligotrophic

"Tanytarsus" (actual genera: Micropsectra, Tanytarsus, Lauterbornia, etc.)

• description:  medium to small larvae (6 -  8 mm long in 4th instar), body nearly cylindrical with thorax as narrow as abdomen and abdomen not tapering, posterior prolegs shorter than wide; in life with translucent pink, pale red, or orange, often with green patterns due to subcutaneous fat bodies; very long antennae extending forward parallel to body; two small, separate, equal-sized eyespots on each side of head capsule.
• larval habit:  build cohesive silt tubes on the sediment surface that may be from 1.5 to 5 or 6 times as long as the larva; often remain hidden in tubes when sampled and preserved; collect small food particles from sediment surface.
• associated environment:  minimum  oxygen concentrations within 2 mm of the sediment surface of no less than 50 % saturation in late summer.

Mesotrophic

Sergentia and Stictochironomus (and sometimes Phaenopsectra)

• description:  medium to large larvae (9 - 12 mm long in 4th instar); bright red in life; thorax slightly thickened and abdomen tapers slightly, posterior prolegs longer than wide and slightly tapered; no blood gills on 11th segment; two small, separate, equal-sized eyespots on each side of head capsule
• larval habit:  in temporary tubes, or wandering through upper 2 - 4 cm of sediment without maintaining open tubes; sub-surface deposit-feeders
• associated environment:  minimum  oxygen concentrations within 2 mm of the sediment surface of no less than 15 % saturation in late summer.

Intermediate Condition

Eutrophic

Chironomus of the C. anthracinus-type

• description:  large larvae (11 - 14 mm long in 4th instar); bright red in life; overall shape like Phaenopsectra but with two pairs of long, ventral blood gills on 11th segment and none on the preceding segment.
• larval habit:  maintain open, U-shaped tubes in the sediment; filter-feeders using mucus nets across the tube lumen, or foraging on surficial sediments around tube mouths; extend tubes up to 10 mm above the sediments as "chimneys" when oxygen gets low near the mud surface.
• associated environment:  minimum  oxygen concentrations within 2 mm of the sediment surface of 0 % saturation for up to 3 weeks in late summer

Intermediate Condition

Hyper-eutrophic

profundal zone temperatures no warmer than 12 C

Chironomus plumosus-type

description: very large larvae (18 - 22 mm in fourth instar), otherwise like C. anthracinus-type larvae except they have short, postero-lateral gills on segment 10.

larval habit: like other Chironomus but do not make chimneys or feed as much on the sediment surface

associated environment:  profundal zone is anoxic for up to 2 months in late summer

or

Chaoborus

description: medium larvae (10 - 14 mm in fourth instar); transparent and clear in life, white when preserved; head laterally compressed; thorax distinctly wider than strongly tapered abdomen; ventral-caudal fan of long, fine bristles; pairs of silvery gas bladders in thorax and posterior abdomen.

larval habit: fourth instars remain in or near profundal sediments during the day, rise into epilimnion at night to prey on zooplankton.

associated environment:  0 % oxygen lasts several months, and profundal temperatures rise above 12 C.

Dystrophic

Zalutschia

• description: larvae are pale, yellowish-brown, about 9 - 10 mm long in the last instar; shape and eyespots like Heterotrissocladius.
• larval habit:  wander freely through the upper 1 - 4 cm of mud without maintaining tubes, surface- and subsurface deposit-feeders
• associated conditions:  water stained dark brown by dissolved humic materials, productivity and benthos densities low; sediments sandy, gelatinous-organic, or covered with coarse detritus.

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Maintained by Sam Mozley, s_mozley@ncsu.edu

Last modified November 18, 1999.