Dataset: Phytoplankton abundance in seawater samples collected from Project "DaVINCi" incubations in the Gulf of Naples, Italy from April to May 2022

Samples were fixed with 1% Lugol's. The quantitative analysis is carried out using an inverted microscope after the settling of a variable volume of sample (Utermhöl, 1958). The settled volumes vary in relation to the number of cells present in the sample, which is estimated on the basis of the chlorophyll a concentration or of the depth of the Secchi Disk. The counting is carried out on various proportions of the sedimentation chamber (transects, random fields or the entire chamber), depending on the characteristics of the sample.

The abundance of phytoplankton cells present in the sample is calculated by applying the following general formula:

C = N × factor × 1000/v

where C = concentration of phytoplankton expressed as cells per liter (cells L-1);
N = number of cells counted;
v = volume of settled sample (milliliters (mL));
factor = ratio between the total area of the chamber and the explored area.

Instruments: Samples from incubation bottle treatments were collected after gently mixing bottles and dispensing 250 mLs into a dark glass bottle containing 1% Lugol's solution and stored in the dark at 4 degrees Celsius.