Figure 2.

Changes in phytoplankton and particulate organic material at BB and SH in summer 1993. Daily samples were taken during two relaxations (June 24 to July 3 and September 2–11); other values were monthly samples (note the time gaps on the abscissa). All measures were determined from replicated samples collected from shore at low tide in opaque HDPE plastic bottles (250 ml for Chl-a and particulates, 1000 ml for productivity). In 1993, a nested sampling design evaluated variation in Chl-a at different spatial scales: 1–2 m, tens of meters, hundreds of meters, and tens of kilometers (i.e., site). Differences between site accounted for most of the variance (usually 80–90%; ref. 30), so only site-level data are reported. (A) Chl-a was determined using a Turner Designs 10 fluorometer after extraction in 90% HPLC acetone for 12 hr in the dark at −20°C. (B) Phytoplankton primary production was estimated using light-dark bottle methodology with [¹⁴C]bicarbonate as a tracer (43). Six-hour incubations were done under simulated in situ conditions. Phytoplankton was collected on glass fiber filters, and radioactivity was determined using liquid scintillation counting. Productivity was calculated based on appropriate seasonal daylight periods as described in ref. 43. (C and D) Particulate material was collected on glass fiber filters and analyzed using a Carlo Erba CHN analyzer. Dissolved organic carbon was estimated from frozen filtered water samples using a Shimadzu gas chromatograph. SH estimates were significantly greater than those for BB in most samples (repeated measures ANOVA; sites differed at the P < 0.00001 level or more).