Life‐history and production of the amphipod Gammarus pulex in a Dorset chalk stream

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Abstract
SUMMARY. The seasonal variation in population density of Gammarus pulex was studied in a Dorset chalk stream. The numbers increased markedly in June and July and reached a maximum of c. 10000m−2 in September whilst the most rapid decline in density occurred in October‐November and reached a minimum of 820 m−2 in February. The animals occurred in greater densities in habitats containing Ranunculus or Callitriche than in those devoid of vegetation. The population structure was determined monthly and was split into juveniles (length −2 in September and a minimum of 1.4 g dry wt m−2 in March. Production was calculated by two methods giving values of 12.9 g dry wt m−2 year−1 and 12.8 g dry wt m−2 year−1.