Life history and secondary production of the amphipod Haploops nirae (Kaim-Malka, 1976) in the Bay of Concarneau (South Brittany)

Haploops nirae is a gregarious tubiculous amphipod that creates dense tube mats in two ecosystems of South Brittany (i.e. the Bay of Vilaine and the Bay of Concarneau). To assess the ecological consequences of its recent expansion, the pattern of population dynamics of H. nirae was determined from January 2010 to March 2011 at a 29 m deep station in the Bay of Concarneau with a sampling interval of ca. 3 weeks (23 sampling dates). Modal analysis of size-frequency distribution at each date was used to describe the life cycle and the population dynamics of H. nirae, and to estimate the annual secondary production using the increment summation method. We showed that H. nirae is a semelparous species exhibiting a biannual life cycle with a lifespan ranging from 24 to 28 months. The recruitment was extremely high in 2010 and occurred between January and April but most recruits arrived at the end of March. Recruits are produced by two year old individuals, which die shortly after hatching. Female densities were low in winter. Females produced only one brood during their lifetime with an average brood size of 29. H. nirae secondary production was estimated at 9.66 gDW m−2 y−1 and the production to biomass ratio (P/B¯) was 2.26 y−1. Results are compared with previous published data on other Ampeliscid amphipods. The biannual life cycle appears unusual for most of Ampeliscidae except for the genus Haploops where a biannual life cycle appears characteristic of this genus. The secondary production calculated for H. nirae was high compared to other biannual Ampeliscidae species and constituted one of the highest production values calculated for an Ampeliscid.