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between chlorophyll concentration and excess viscosity for chlorophyll concentrations higher and lower than 55 mg Chl-a l_1, respectively. On May 25, accompanying a sharp decrease in Chl-a concentration, excess viscosity was negatively related to chlorophyll concentration. Finally, in post-bloom conditions (June 20), chlorophyll concentration and excess viscosity appeared independently distributed. These observations are specified by the values of Kendall rank correlation coefficients (Fig. 4) estimated at each date between the two distributions. No significant correlation was observed in pre- and post-bloom conditions, while significant positive and negative correlations were observed during the spring bloom before and after the formation of foam, respectively (Fig. 4).

Microscale spatial structure

The results of spatial autocorrelation analysis showed that none of the investigated patterns were uniform nor random (Table 4), indicating the existence of structural complexity in 2D microscale patterns of chlorophyll a concentration and seawater viscosity. Except on June 20, consistent spatial patterns were found for chlorophyll and excess

Fig. 3 Scatterplots of seawater excess viscosity g (%) as a function of chlorophyll a concentration (mg l_1), showing the two different regimes observed over the course of our survey. The sampling conducted on 26 September has been used as a separate reference sample, characteristic of non-bloom conditions. Scatterplots of seawater excess viscosity g (%) as a function of chlorophyll a concentration (mg l—1), showing the two different regimes observed over the course of our survey

Fig. 3 Scatterplots of seawater excess viscosity g (%) as a function of chlorophyll a concentration (mg l_1), showing the two different regimes observed over the course of our survey. The sampling conducted on 26 September has been used as a separate reference sample, characteristic of non-bloom conditions. Scatterplots of seawater excess viscosity g (%) as a function of chlorophyll a concentration (mg l—1), showing the two different regimes observed over the course of our survey viscosity. More specifically, pre- and post-bloom conditions were mainly characterised by three types of aggregative distributions (Table 4). In contrast, the spatial patterns observed during the bloom were either aggregative (i.e. dominated by the presence of a few extreme peaks) or characterised by a variety of transitions from high to low values, the latter being only observed during the formation of foam. Patch sizes were finally estimated from correlograms constructed for each parameter at each date to determine spatial autocorrelation as a function of increasing distance between samples. Because the distance intervals were based on the distance intervals between the centre points of samples, patch sizes were expressed in terms of the distance interval in which the autocorrelation value changed sign (positive to negative autocorrelation or vice versa). Patch sizes for chlorophyll concentration and excess viscosity were between 5 and 10 cm in pre- and post-bloom conditions (Table 4). Larger patch sizes were found for chlorophyll concentration and excess seawater viscosity in bloom conditions. During the formation of foam viscous patches were larger than chlorophyll patches (Table 4).

Discussion

Microscale spatial patterns and Phaeocystis globosa bloom dynamics

Chlorophyll, viscosity and foam formation. The shift from significant positive correlations to significant

Phaeocystis Globosa

Fig. 3 continued negative correlations before and after the foam formation is congruent with a recent mechanistic explanation (Seuront et al. 2006), suggesting that the disruption of the mucilaginous colonial matrix by turbulent mixing in the surf zone leads: (i) to the formation of foam and to the transformation of colonial cells into flagellated ones (Peperzak 2002), (ii) to a decrease in chlorophyll a concentration (Fig. 5) as a significant proportion of cells are entrained within the foam during the emulsion process (Seuront et al. 2006), and finally (iii) to the decoupling between the viscous (i.e. colonial polymeric materials) and nonviscous (flagellated cells) contribution of P. globosa to bulk-phase seawater properties in intertidal (Fig. 5a, b) and inshore (Fig. 5c, d) water masses, located respectively 20 m and 2 nautical miles from the shoreline. However, the relationship observed between chlorophyll concentration and excess viscosity on May 10 through our microscale sampling strategy (Fig. 3) indicates that the aforementioned decoupling process could be more complex than initially thought. As the negative correlation occurs for the chlorophyll a concentrations higher than 55 mg l_ , the high-density chlorophyll patches, likely to be the largest and/or the oldest ones, may be more fragile and thus the first ones to be destroyed by turbulent mixing. This hypothesis is consistent with the strong decrease in variability and the changes in the distribution patterns observed in both chlorophyll and excess viscosity spatial patterns between April 20 and May 10 (see Tables 3 and 4, Fig. 5a, b).

The mechanistic explanation proposed above for the dynamics of chlorophyll a concentration and seawater excess viscosity is also consistent with recent work conducted on the dynamics of transparent exopolymeric particles (TEP) produced by Phae-ocystis globosa (Mari et al. 2005). Two phases for the dynamics of TEP were then identified: (i) a production phase during the growth phase of P. globosa where TEP and chlorophyll a concentration were

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