Long-term monitoring reveals biomass loss and concurrent dominance changes in coastal zooplankton community

Time series dataset from Tvärminne Storfjärden. Data includes Zooplankton biomass, physical and chemical parameters collected between 1993 and 2021.
All information about taxa is biomass in mg/m³. Biomass was calculated from standard values considering the species (if available) and sex of each individual (HELCOM monitoring guidelines, Hernroth 1985).
, , # Long-term monitoring reveals biomass loss and concurrent dominance changes in coastal zooplankton community

Dataset DOI: [10.5061/dryad.08kprr5h3](https://doi.org/10.5061/dryad.08kprr5h3)

## Description of the data and file structure

Zooplankton samples were generally collected once a month throughout the year, including the winter season. Samples (vertical net tows) were taken during the day using a 150 μm Hensen hand-net with a 0.35 m diameter from a depth of 25 m to the surface (depth of the sampling site is approx. 32 m). If the sea surface was frozen, a hole was drilled or cut into the ice. The samples were stored in 4% buffered formalin and analysed microscopically. Prior to the analysis, the samples were divided using a Folsom splitter (max 10 times which equals a 1/1024 sample) and subsamples were counted to 300 – 500 individuals of adult copepods, copepodites, cladocerans or polychaete larvae.

Temperature and salinity were measured every 10 days in the vertical profile...,