The goal of the 363th cruise of R/V Poseidon in March 2008 was to study the state of the pelagic and benthic ecosystems on the western Black Sea shelf in late winter/early spring. This data set contains data on nutrients in the water (dissolved inorganic and organic forms) and particle-bound nutrient forms on the western Black Sea shelf during March 2008. Further details can be found in the cruise report of POS363 cruise (see "Related to:").Secchi depth was measured on each station using a 20 centimeter white disk on a calibrated line. It was lowered into the water until the observer lost sight of the disk, the depth of disappearance. The distance from the water surface to the level where the disk vanishes and reappears, is the Secchi disk reading.