LIFE-HISTORY AND PRODUCTION OF THE AMPHIPOD BYBLIS-JAPONICUS DAHL (GAMMARIDEA, AMPELISCIDAE) IN A WARM TEMPERATE ZONE HABITAT, SHIJIKI BAY,JAPAN

The life history and production of the infaunal tube-dwelling amphipod Byblis japonicus (Dahl) were studied from Shijiki Bay, Japan. The spe cies produces three generations per year: a spring generation with thr ee cohorts recruited from April to June; a summer generation with two cohorts recruited in July and August; and an autumn-winter generation with three cohorts recruited from October to January. The spring cohor ts exhibit rapid growth, early maturity, small brood size and small bo dy size. The converse set of life history traits characterizes the aut umn-winter cohorts. The summer cohorts have characteristics of both th e spring and autumn-winter cohorts. The first cohort is similar in tra its to spring cohorts. The second cohort also has traits similar to sp ring cohorts until it first reaches maturity. This second cohort then overwinters, grows slowly and reproduces again at old age with large b rood size and large body size as autumn-winter cohorts. Life span is 2 .5 to 3.5 months for the spring and the first summer cohorts with heav y mortality at the end of a short life span. It is 7 to 8 months for t he second summer and autumn-winter cohorts with a constant and low mor tality rate. Secondary production calculated as the sum of growth incr ements was 7.53 g dry weight . m(-2) . yr(-1) with an annual ratio of production to mean biomass (PIE) of 10.83. The high temperature of the water in Shijiki Bay may be responsible for this ratio, which is by f ar the highest reported for ampeliscid amphipods.