FIGURE 3 Phytoplankton pigments in the two estuaries. Surface waters along the salinity gradient in the Krka River Estuary (a, c and e) and in the Wenchang River Estuary (b, d and f). The distribution of Chl a (a and b). The inlet in (b) describes the Chl adistribution at higher salinities. The distribution of pigment markers (c and d) and their relative abundance (%) (e and f). The full names of the pigments can be found in Material and Methods.
3.2Membrane lipid remodeling
The contribution of second MGDG to cell lipids, sMGDG (%), was low for the river endmembers in the Krka River Estuary (<1%) and Wenchang River Estuary (<3%). High sMGDG concentrations (0.2-112.8 µg L-1) were detected in Wenchang River Estuary. Their concentrations in Krka River Estuary were lower, ranging from 0.2 to 3.9 µg L-1. The sMGDG (%) increased significantly at the lowest S compared to river waters, and then its contribution was decreasing with increasing S. In contrast to other detected membrane lipids (not shown), sMGDG (Figure 4), showed a statistically significant negative correlation with the increase in salinity in both estuaries analyzed. All correlations were performed for estuarine samples, while freshwater endmembers were omitted.
There was a negative correlation trend between fMGDG and sMGDG, albeit not statistically significant (Figure 4b). These results suggest a change in MGDG fatty acid composition in response to salinity stress.