Development of the “plankton emergence trap/chamber (PET Chamber)”, a new sampling device to collect in situ germinating cells from cysts of microalgae in surface sediments of coastal waters

A simple device was developed to collect germinating cells from settled cysts of microalgae on the sea bottom. This new device – the plankton emergence trap chamber (PET Chamber) – made of a clear acrylic plastic, consists of a top cylinder and a base plate attached to a bottom cylinder. After plugging the bottom cylinder with sediment collected from in situ sea bottom and filling the top cylinder with filtered seawater, the PET Chamber attached to a platform specially made for submerging the chambers is placed on the seafloor. An adequate area of the lateral side of the top cylinder is opened and covered by a plankton net (10 μm mesh) to allow a water exchange between the inside and outside the cylinder. Thus, the PET Chamber can replicate in situ environments, such as temperature, irradiance and dissolved oxygen. Using the PET Chamber, we have succeeded in collecting germinating cells and estimating the germination flux (cells m−2 day−1) of two dinoflagellates, Alexandrium catenella and Scrippsiella spp., in Ago Bay, Japan. Mircoscopic observations on the samples collected from July to October 2003 revealed fluxes of 124–2022 and 622–3732 cells m−2 day−1 in A. catenella and Scrippsiella spp., respectively. The data indicate that the new device can detect variations in the number of germinating cells of dinoflagellates. Its sampling ability, coupled with simplicity in deployment and retrieval procedures, can allow one to monitor the in situ emergence from/on the surface sediments of various organisms, that possess resting stages during their life histories, in various coastal waters.