High-resolution observations on fine-scale spatial and temporal heterogeneity of phytoplankton communities using FlowCAM

摘要

To understand the fine-scale spatio-temporal phytoplankton dynamics with reference to the environmental properties of the water column, high-frequency samplings every 4 h, at 0.5-2 m depth intervals using a submersible pump was conducted in Tateyama Bay, Japan, for 24 h from 12 h of 12 May to 08 h of 13 May 2017. The FlowCAM, which is an automatic device, was used to identify, count and size the phytoplankton. As a result, the phytoplankton distribution significantly varied within a few meters and a short timescale (several hours) of a day. For example, Thalassiosira sp. and Prorocentrum minimum were detected at all sampling depths and times rather evenly, but the water-column total abundance of Dactyliosolen fragilissimus and Scrippsiella trochoidea significantly decreased after the 2nd set of the samplings. Species-specific vertical distributions were various but related to the condition (strength and depth) of the thermocline at each sampling time. These phytoplankton species-specific distributions and variations in the composition reflect the eco-physiological characteristics and size structure of phytoplankton and the short-term hydrodynamic events. The high value of chlorophyll-a in the bottom layers was not only from the phytoplankton but also from the fluorescence of the aggregate particles.