Population structure and fecundity of the microcopepod Oncaea bispinosa in the Red Sea—a challenge to general concepts for the scaling of fecundity

Abstract

General concepts of reproductive traits in pelagic marine copepods have been developed largely without data from the microcopepod family Oncaeidae. For a very abundant oncaeid species in the Red Sea, Oncaea bispinosa Bottger-Schnack, reproductive parameters are provided and used for testing how the copepod family Oncaeidae may fit into these concepts. Total number and vertical distribution of eggs of this species have been calculated for populations in the northernmost Red Sea and the Gulf of Aqaba during spring, based on counts of detached egg sacs retained in fine mesh net samples. Reproduction is indicated to take place in the meso- and bathypelagic zones, with maximum abundances of eggs occurring within the deep population centres of females at 250 to 450 m depth. The epipelagic population appeared to be non-reproductive. By calculating the biomass of the eggs and the females using published data on size/weight relationships, a first estimate of the reproductive potential of O. bispinosa was obtained and compared with various other oncaeid species. The presently available data for Oncaeidae in total suggest a relationship between single egg (Ec) and female (Fc) carbon weight (Ec = 0.012 × Fc0.48) that differs from corresponding regressions reported in the literature for other marine pelagic copepods. In addition, regressions are given for minimum and maximum clutch carbon related to female carbon weight. Potential egg production rates of O. bispinosa have been calculated from the observed fractions of egg-bearing females and published data on egg developmental times, as available for larger oncaeids. These production rates appear to be lower than have been observed in experimental studies for different pelagic microcopepod taxa. Remaining uncertainties in generalizing concepts for the scaling of fecundity in pelagic marine copepods are discussed, and the need for more comparable data, especially for the numerically abundant oncaeids, is emphasized.