The impact of predation by perch on the size-structure of Chironomus larvae - the role of vertical distribution of the prey in the bottom sediments, and habitat complexity

• Published in: Hydrobiologia 1997-01, Vol.342-343, p.207-213
• Main Author: Kornijow, R
• Format: Article
• Language: English
• Subjects: Aquatic ecosystems; Bottom sediments; Chironomidae; Chironomus; Diptera; Fish; Freshwater; Insects; Lakes; Larvae; Pisces; Predation; Prey; Vertical distribution; Water depth
• ISSN: 0018-8158; 1573-5117
• DOI: 10.1023/A:1017067621668

The study was performed in June-August 1993, in eighteenenclosures (1 × 2 m) built in a fertile, small (area2.5 ha) and shallow (max. depth 1.7 m) lake, Little Mere(north-western England). Three densities of Nuphar lutealeaves were manipulated in enclosures to 10%, 50% and90%coverage of the water surface. Perch (total length ca. 15 cm)wasstocked in half of the enclosures in a density 3 fishm^sup -2^. Thevertical distribution of Chironomus f.l. plumosuslarvae (classified in the size classes: 0-5, 5-10, 10-15,15-20and >20 mm) in the bottom sediment showed a clear pattern,withbigger larvae burrowing to the greatest depth. Densities ofalllarval size classes except 0-5 mm were negatively affectedboth byplant density and by perch in three sediment layers considered(0-2, 2-5 and 5-10 cm). The larvae formerly at the surfacedidnot move deeper in the sediments to avoid fish predation. Thesizedistribution of the larvae, with the prevalence of the 15-20and10-15 mm larvae, found in the guts of perch was the mostsimilarto that in the upper sediments at low and medium plantdensities,and to that in the intermediate, 2-5 cm, sediment layer athighplant density. The effect of the interaction between plantdensityand fish was significant for all the larvae except those of10-15and 15-20 mm. Although the results of the experiment showedsize-selective feeding by perch, the direct overall effect ofthefish on the size-structure of the larvae was limited byverticaldistribution of the prey in the bottom sediment. In addition,itwas modified by nymphaeids, which, at high density, alteredfoodconditions and acted as a refuge for Chironomus larvaebothdirectly (providing shelter) and indirectly (providing fishwiththe additional, epiphytic prey).[PUBLICATION ABSTRACT]