No abstract

During a study on population dynamics of copepods in the southern North Sea some semiin-situ experiments were performed on predation by adult copepods on CO-occurring nauplii. In a period with a strong decline in naupliar abundance, experimental naupliar mortality by cannibalism amounted to 35% of the standing stock per day. Simultaneous observations on chlorophyll a and &atom concentrations in situ and on egg production by adult females suggested poor food conditions for adults. There appeared to be a tendency for increased predatory behaviour in the absence of other food, indicating the possible importance of cannibalism as a factor in naupliar mortality. Microscopic observations and a series of experiments on laboratory cultured Temora longicornis revealed adult female predation on stages N I through N V. Rates of capture declined with ascending developmental prey stage. Prey-specific predation rates increased continuously with prey density, but were significantly depressed m the presence of alternative algal food. Estimates of naupliar mortality in situ due only to cannibalism, based on experimentally determined predation rates, explained 5 to over 100 % of the estimated total naupliar mortality. It is suggested that cannibalism may act as a major factor in naupliar mortality and may contribute significantly to a rapid fall in naupliar densities in periods of algal food shortage.