1. Behaviour of individual copepods in the laboratory when exposed to patchiness of food and varying predation risk Copepods experience a variable food environment with favourable patches interspersed with large volumes of water with too low food concentration to sustain growth and development. Critical traits in copepod behaviour are therefore the ability to detect and remain in patches of food, and at the same time avoid predation. The objectives of the project are to quantify patch responses of selected small copepods and to observe how predator presence may affect foraging behaviour. Methods include video observations in small aquaria and bottle incubations with defined patches of food. Laboratory experiments showed that copepods have the ability to find and remain in food patches and that this was beneficial for them in terms of reproduction. Predation enhanced the advantage to stay in patches since increased predation risk was associated with food search. 2. Distributions of copepods and microzooplankton in the field The vertical distribution of copepods and their prey potentially has a strong impact on predator-prey interactions in the pelagic environment. The project aims at quantifying the small-scale (metre) distributions of these organisms. Since plankton nets are unsatisfactory at this resolution, an in situ video camera designed to observe copepods has been developed. The observations with the camera are amazing, a hitherto unknown world can be revealed. Results from filming with the camera shows that copepods sometimes aggregated around the pycnocline, but rarely respond to in situ fluorescence, a crude measure of food abundance. The distribution will be a balance between the swimming capabilities of the copepods and the turbulence field. At present, models have been developed that predict the distributions, and the project is in a field testing phase. 3. Distribution of marine snow in the field and association to grazing dinoflagellates The particle dynamics during blooms of phytoplankton has received considerable attention recently. It has been shown that physics will have a profound impact on the fate of phytoplankton blooms and this project aims at clarifying the combined role of physics and biology on the decline of phytoplankton blooms. In two field studies, simple coagulation theory has been successful in predicting bloom dynamics. In the Gullmarfjord, Sweden, a spring bloom ended rapidly following a storm event and mass sedimentation of marine snow was observed by in situ video recordings. Grazing by heterotrophic dinoflagellates prevented further recovery of the diatoms. In a second field study in the Benguela upwelling region, South Africa, continuous aggregation of large diatoms was observed. No sedimentation occurred, however, and the reason was found to be colonisation and grazing on the aggregates by the dinoflagellate Noctiluca scintillans. 4. Hunger responses in copepods exposed to variable food supply Food patchiness and the necessity to avoid predators means that copepods will have highly variable access to food. The aim of this project is to study dynamics of ingestion under non-steady state food conditions. Small copepods that do not store lipids have a limited capacity to survive periods of low food and should be adapted to fast and efficient utilisation of ephemeral food patches. The experimental protocol includes traditional bottle incubations with copepods and diatoms, high abundances and small bottles are used to detect fast changes (min-hours). The results show that brief periods of starvation (1-3 h) stimulated ingestion, but only temporarily on time scales of gut filling times. In contrast, longer starvation times (6-14 h) lead to elevated ingestion rates lasting longer than gut filling time. This could indicate changes in the assimilation efficiency and experiments are planned on the topic for January 1999.