Effects of UV radiation and salinity on the intertidal macroalgae Palmaria palmata and Ulva lactuca: effects on photosynthetic performance, growth and pigments

Abstract

The tolerance of Palmaria palmata and Ulva lactuca from two positions (upper and lower) of the shoreline to low salinity and Ultraviolet radiation (UVR) was assessed using chlorophyll fluorescence, relative growth rates, chlorophyll a (Chla) and carotenoid concentrations. Species differences and position on shore at collection were major factors in the ability to tolerate increases in UVR. Both species were found to have sensitivity to both UVR and low salinities, although P.palmata was more sensitive to treatment than Ulva. The ability to increase chlorophyll and carotenoid concentrations when under low salinities and Ultraviolet B (UVB) compared to normal salinity was seen in P.palmata on the lower shore. This resulted in no further reduction in relative growth rate (RGR) from other light levels which occurred when treated with normal salinity occurred, indicating antagonistic effects. However, on the upper shore the effects were additive, as with decreased Chla and carotenoids. P.palmata showed a lower (RGR)(g per day) under UVB, which was not seen under normal salinity. Ulva showed sensitivity, but increased photosynthetic efficiency of PSII and growth rates compared to P.palmata. Additive effects were also observed in lower shore Ulva under UVB and low salinity, whereby the two together caused greater decreases in growth rate. The interactive effects of light and salinity have been seen to be complex with differences within species, between locations and light treatments all governing the action observed, which have been seen to range from antagonistic to additive.