Life histories of two hyperbenthic mysids (Mysidacea: Mysidae) in an open estuary

Mysidae are widely distributed in aquatic ecosystems and form a large proportion of the hyperbenthic biomass in estuaries. The seasonality, spatial distribution and reproductive biology of the two hyperbenthic mysid species, <i>Tenagomysis chiltoni</i> and <i>Tenagomysis novaezealandiae</i>, were studied in an open estuary. Sampling was conducted bi-monthly at night between February 2008 and April 2009. These two mysid species are spatially segregated along a salinity gradient, with <i>T. chiltoni</i> upstream and <i>T. novaezealandiae</i> downstream in the estuary. The life cycle and breeding dynamics of <i>T. chiltoni</i> (bivoltine life cycle) and <i>T. novaezealandiae</i> (multivoltine life cycle) were similar to those described in intermittently closed estuaries, but their breeding period (December to April) was relatively shorter and densities were lower. Life-stage specific segregation in summer in both mysid species likely provided favourable conditions for maximum growth rates, short maturation times, and sheltering, enhancing reproductive success of both mysid species.