Abstract
Seasonal variations of pico- and nano-sized marine detrital particles (DAPI Yellow Particles, DYP) and their relationships with components of the microbial food web were studied from April 1993 to March 1994 in the NW Mediterranean Sea. A hierarchical flexible clustering distinguished 2 major groups of DYP: less than or equal to 10 mu m and 10-20 mu m. Average abundance and total surface area of less than or equal to 10 mu m DYP in surface waters were 21.6 +/- 3.2 x 10(6) l(-1) and 153 +/- 55 mm(2) l(-1), respectively, approximately an order of magnitude greater than abundances or total surface areas reported for larger detrital particles. Relationships of DYP, chlorophyll a and micro-organisms were investigated within and among 5 different hydrographic periods distinguished via vertical temperature gradients. Peak concentrations of less than or equal to 10 mu m DYP occurred in early autumn at the end of stratification. In contrast, DYP 10-20 mu m peaked at the beginning of the stratification period in early June. Correlation analysis revealed only weak relationships between DYP and abundance of bacteria, heterotrophic microflagellates and ciliates. However, declines in chlorophyll were generally followed by increases in DYP concentrations.