Strong seasonality in phytoplankton cell lysis in the NW Mediterranean littoral

The seasonality of phytoplankton cell lysis rates in the NW Mediterranean coastal waters was examined based on measurements of the dissolved esterase activity between 1995 and 1998 in the Blanes Bay (NE Spain). The temporal variability of phytoplankton biomass and gross primary production (GPP) were characterized by a late winter bloom dominated by diatoms and high GPP in summer despite the low phytoplankton biomass in this season. The phytoplankton lysis rates were found to be strongly seasonal, being highest in summer (mean +/- SE = 0.41 +/- 0.049 d(-1)) when values as high as 1.47 d(-1) were attained. However, during the rest of the year, phytoplankton lysis rates remained low, particularly in winter (0.061 +/- 0.005 d(-1)). There was a strong (R-2 = 0.71, P < 0.00001) positive relationship between monthly average lysis rates and water temperature. In addition, monthly average lysis rates followed gross primary production with a maximum correlation (r = 0.65, P < 0.05) at a lag time of 1-2 months, similar to the time span from bloom initiation to bloom collapse. These results identify phytoplankton cell lysis as an important route of phytoplankton carbon flow in Blanes Bay.