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Seasonal and diel variation in the rhythmicity of Idotea baltica (Pallas) and Idotea granulosa Rathke
Hørlyck, V. (1973). Seasonal and diel variation in the rhythmicity of Idotea baltica (Pallas) and Idotea granulosa Rathke. Ophelia 12(1-2): 117-127
In: Ophelia: International Journal of Marine Biology. Ophelia Publications: Helsingør. ISSN 0078-5326, more
Peer reviewed article  

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Keywords
    Idotea balthica (Pallas, 1772) [WoRMS]; Idotea granulosa Rathke, 1843 [WoRMS]; Fresh water

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  • Hørlyck, V.

Abstract
    The swimming activity of Idotea baltica and I. granulosa was investigated by means of photocells. The activity patterns of both species showed great seasonal variations. Both species showed no swimming activity in winter (I. baltica from Nov-March, and I. granulosa from Sept-March). The rest of the yr both species had one activity peak between midnight and sunrise. I. baltica was nocturnal in early spring, in summer the activity was high all 24 hrs, besides the nocturnal maximum an increased activity was evident in the afternoon till 2 hrs after SS. At the end of Sept and the beginning of Oct I. baltica was nocturnal. The same variation in the activity pattern was found for I. granulosa. Under artificial light/dark conditions both species were nocturnal. When the light/dark change was right-angled this was the dominating Zeitgeber.

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