The effects of diatoms on copepod reproduction: a review

Diatoms are small eukaryotic plants with over 10,000 known species, constituting one of the major components of the phytoplankton in freshwater and marine environments. Traditionally, they have been regarded as beneficial to the growth and survival of marine organisms, and to the transfer of organic material through the marine food chain to top consumers and important fisheries. From 1993 onwards, however, evidence has accumulated that has progressively challenged the classic view that diatoms are good and harmless food items for copepods, the dominant constituent of the zooplankton, which sustain the production and growth of larval fish. Laboratory results in recent years have shown that some diatoms potentially reduce copepod egg viability up to 100%; at times, egg production rates are adversely affected as well. Thus, while diatoms may provide a source of energy for copepod larval growth. they often reduce fecundity or hatching Success or both. These results constitute the paradox of diatom-copepod interactions in the pelagic food web. This biological model is new and has no equivalent in marine plant-herbivore systems, since most of the known negative plant-animal interactions have been related to repellent or poisoning processes, but never to reproductive failure. This paper reviews the literature on the inhibitory effects of diatoms on the reproductive biology of copepods and focuses on the present status and problems regarding diatom-copepod interactions.