Distribution, population dynamics and estimates of production for the estuarine mysid, Rhopalophthalmus terranatalis

Abstract

The biology of the mysid shrimp Rhopalophthalmus terranatalis is described from a warm temperate estuary in southern Africa. Intensive quantitative field sampling continued over 21 months while laboratory culture provided detailed information for production estimates. Three generations are produced annually and individual females produce multiple broods. The overwintering generation has a lifespan of 9–10 months and is characterized by low population density, but individuals are relatively large with females producing large broods. The summer generation survives for 6 months. Population density is high (maximum may exceed 4000 m −3 of water) but individuals attain a smaller size and produce fewer progeny. The spring generation has characteristics which may generally be described as intermediate between the other two generations. Daily production values of 2·69, 6·93 and 13·97 mg m −3 were calculated for the overwintering, spring and summer generations, respectively. Daily P B coefficients varied between 0·020 and 0·026. The P B ratio for the overwintering generation was 5·86; for the spring generation, 3·06 and for the summer generation 4·74. The annual P B ratio for the whole population was 7·85. Comparative values using a second method of population production are provided. The biology of R. terranatalis allows for rapid recovery of the population in a region where catastrophic aperiodic fresh-water flooding occurs.