Microscale patchiness of plankton within a sharp pycnocline

Microscale distributions of plankton around the pycnocline were studied over a 24 h period in the southern Kattegat, using a gradient sampler which collects 20 samples over a 3 m depth interval. Moderately elevated concentrations of phyto- and zooplankton were observed at the pycnocline. Microscale variance was highest for adult copepods. Nauplii and copepodites were equally well represented by sampling with ordinary vertical 5 1 water bottles as with the horizontal 1.5 1 bottles of the gradient sampler. Adult copepods were underestimated by the vertical bottles. No vertical migration of dinoflagellates was observed over the 3 m interval covered by the gradient sampler. Microscale correlations between copepods and phytoplankton within the gradient sampler were weak. Copepodites (mainly Oithona sp.) and the dinoflagellate Prorocentrum micans showed the best correlation.