DYNAMICS OF EXPLOITED POPULATIONS OF TISBE-BOLOTHURIAE (COPEPODA, HARPACTICOIDA) .3. REPRODUCTION, SEX-RATIO, RATE OF DEVELOPMENT AND SURVIVAL TIME

In weekly exploited populations of the harpacticoid copepod T. holothuriae Humes, effects of exploitation rate on production of eggs, embryos, nauplii and adults, as well as frequency of egg-sac formation, rate of development of embryos and nauplii and survival time of adult females were studied under conditions of surplus food supply at 22.degree. and 30.permill. salinity. Three classes of egg sacs could be distinguished: egg sacs in which all eggs developed until hatching of the nauplii, egg sacs in which only part of the eggs developed and egg sacs with eggs that did not hatch at all. The fraction of egg sacs giving rise to no adult individual is larger at all exploitation rates than the fraction of egg sacs giving no nauplius. The mean number of eggs, nauplii and adults produced per egg sac depends on the mean average population densities between exploitations. At a higher removal rate or a lower density between exploitations, more eggs, nauplii and adults are produced per egg sac than at a lower removal rate or at a higher density. There seems to be a tendency to reach and to keep constant a set point of biomass, rather than population size, the culture conditions being the controlling variable. Death rate of nauplii is lowered at the exploitation rate of 0.90 and even at this highest removal rate only half of the eggs gave rise to adult individuals. The relative frequency of eggs and egg sacs in which no embryos could be detected shows no dependency upon the removal rate or mean population density between exploitations. In isolated females, an inverse relationship was found between the frequency of egg-sac formation and the average population density between exploitations shortly after isolation. There seems to be some imprinting by the populations in which the specimens are living. Sex ratio is influenced by the removal rate or the average population density between exploitations. In isolated broods an inverse relationship between embryonic developmental rate and average population density between exploitation could be established. No influence of population density on rate of development of juvenile stages and survival time of adult females could be observed in equally isolated broods. The average weight of an individual in the adult or copepodid stage, and the average length of an adult female are inversely related to the average population density between exploitations.