Aspects of the ecology and physiology of a marine chironomid larva, Paraclunio alaskensis Coquillett
Date
1980
Authors
Parkinson, Dorothy Anne
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Abstract
The ecological and physiological adaptations of P. alaskensis larvae to the intertidal habitat have been assessed by examining the effects on larvae of environmental factors normally considered to limit the distribution of organisms -spatially and temporally in the midlittoral zone.
Desiccation factors play an important role in limiting P. alaskensis larvae because, as shown by experimentation, larvae, when placed in concentrated seawater and in air, are susceptible to evaporation of water through the cuticle. Therefore, larvae must locate in moist areas.
Salinity changes, often thought to be the key barrier to the calonization of the intertidal habitat by insects, do not limit larval distribution. The hemolymph consists of 246 mM Na⁺, 126 mM Cl⁻, 14 mM Mg⁺⁺ and 530 mOsm osmotic pressure. The composition and ratio of ions changed very little (ΔPᵢ/ΔPₒ = O) when larvae were acclimated to freshwater. Larvae regulate both hypo- and hyperosmotically. Water regulation curves indicate that, in salinities expected in the intertidal zone, the volume of the body is well regulated.
A permeable cuticle does not allow larvae to regulate the hemolymph concentration of ions and _water as efficiently in high salinities as do larvae of species having an impermeable cuticle. A drinking rate was demonstrated. The respiration rate in seawater at 15°C was determined to be 0.032 µl 0₂/mg per hour.
Larvae supercool to -11°C and, therefore, are well adapted to potential freezing temperatures in the intertidal habitat. The necessity of a suitable substrate has been demonstrated. The ecology of this species and particularly the adaptations of the life cycle to seasonal changes in the environment have been discussed.