Impact of UV radiation on plankton net community production: responses in Western Australian estuarine and coastal waters

Abstract

Net community production (NCP) is a relevant parameter informing on the role of plankton communities as sinks or sources of CO2 in the ocean. We assessed the effect of ultraviolet (UV) radiation on NCP in different regions along the coast of Western Australia (WA). We compared 57 NCP measurements of surface communities receiving full-spectrum natural solar radiation, to communities with natural UVB radiation excluded (NCP-UV). Very high values of incident UVB radiation were registered, especially during spring and summer (up to 75 kJ m-2 d-1). Although a strong inhibitory effect of UVB on NCP was expected due to the high UVB levels, no significant differences between NCP and NCP-UV were observed in any sampled region. However, we found a general trend of NCP inhibition by 33.4% under UVB radiation along the WA coast. While NCP of autotrophic communities tended to slightly decrease under UVB radiation, no robust pattern was observed for heterotrophic communities. Experiments measuring the response of NCP exposed to a gradient of enhanced UVB doses exhibited a UV dose-dependent inhibition of NCP in estuarine communities (i.e. higher inhibition with higher UVB doses), and a UV dose-independent inhibition in coastal communities. Our in situ data showed that the net metabolism of surface plankton communities from the coast of WA was insignificantly affected by elevated environmental UVB radiation levels.