We quantified abundance and biomass of the amphipod Gammarus chevreuxi Sexton from benthic cores, sampled monthly over 1 y in the upper reaches of Canal de Mira, the southern arm of the Ria de Aveiro, Portugal. Abundance and biomass showed no clear seasonal patterns but were associated with variation in salinity, dissolved oxygen, and chlorophyll a concentration. Maximum abundance and biomass occurred at relatively low temperature and high food availability, conditions that likely increased survival and/or reproduction. The population showed a semiannual, iteroparous life cycle. Mean life span was ∼6 mo, with overwintering individuals hatched in autumn showing higher longevity than individuals hatched in spring. Breeding was continuous, although juvenile recruitment peaked in early autumn, winter, and early spring. Sudden fluctuations in abundance and size structure of the population may have resulted from immigration during autumn and emigration during winter. Mean fecundity (8 embryos/brood) and intramarsupial loss (0–18%) were low compared with studies of other Gammarus species. Variation in fecundity and intramarsupial loss was mostly explained by size of incubating females. The volume of the embryos was highly variable but not significantly correlated with female size or other reproductive traits. The Hynes and the Morin– Bourassa methods yielded similar estimates of annual production (∼46 g AFDM m−2 y−1) and P/B̄ ratio (11/y).
You have requested a machine translation of selected content from our databases. This functionality is provided solely for your convenience and is in no way intended to replace human translation. Neither BioOne nor the owners and publishers of the content make, and they explicitly disclaim, any express or implied representations or warranties of any kind, including, without limitation, representations and warranties as to the functionality of the translation feature or the accuracy or completeness of the translations.
Translations are not retained in our system. Your use of this feature and the translations is subject to all use restrictions contained in the Terms and Conditions of Use of the BioOne website.
Vol. 24 • No. 1