Experimental assessment of cumulative temperature and UV-B radiation effects on Mediterranean plankton metabolism

Lara S Garcia-Corral,Carlos M Duarte,Juan Martinez-Ayala,Susana Agusti

doi:10.3389/fmars.2015.00048

Abstract

The Mediterranean Sea is a vulnerable region for climate change, warming at higher rates compare to the global ocean. Warming leads to increased stratification of the water column and enhanced the oligotrophic nature of the Mediterranean Sea. The oligotrophic waters are already highly transparent, however, exposure of Mediterranean plankton to ultraviolet radiation (UV-B and UV-A) may increase further if the waters become more oligotrophic, thereby, allowing a deeper UV radiation penetration and likely enhancing impacts to biota. Here we experimentally elucidate the cumulative effects of warming and natural UV-B radiation on the net community production (NCP) of plankton communities. We conducted five experiments at monthly intervals, from June to October 2013, and evaluated the responses of NCP to ambient UV-B radiation and warming (+3oC), alone and in combination, in a coastal area of the northwest Mediterranean Sea. UV-B radiation and warming lead to reduced net community production and resulted in a heterotrophic (NCP<0) metabolic balance. Both UV-B radiation and temperature, showed a significant individual effect in NCP across treatments and time. However, their joint effect showed to be synergistic as the interaction between them (UV x Temp) was statistically significant in most of the experiments performed. Our results showed that both drivers, would affect the gas exchange of CO2-O2 from and to the atmosphere and the role of plankton communities in the Mediterranean carbon cycle

Highlights

The Mediterranean Sea is highly vulnerable to climate change (Turley, 1999; Giorgi, 2006; Herrmann et al, 2014), because of the long water residence time and warm waters derived from its semi-enclosed nature and the high evaporation rates (Bethoux et al, 1999)
Sampled surface seawater temperature varied from 22.1◦C in June to a maximum of 27.3◦C in August, decreasing through
The results showed a clear negative trend in net community production (NCP) with warming and incident UV-B

Summary

Introduction

The Mediterranean Sea is highly vulnerable to climate change (Turley, 1999; Giorgi, 2006; Herrmann et al, 2014), because of the long water residence time and warm waters derived from its semi-enclosed nature (only a narrow connection with the Atlantic Ocean and an artificial connection with the Read Sea) and the high evaporation rates (Bethoux et al, 1999). Warming leads to increased stratification and decreased primary production, enhancing the oligotrophic nature of the Mediterranean Sea (Estrada, 1996). Llabrés et al (2010) reported that lethal UV doses required to decrease the picocyanobacteria populations by half, can penetrated down to 26 m in the Mediterranean Sea. Exposure of Mediterranean plankton to UV-B and UV-A may increase further if the waters become more oligotrophic, thereby allowing a deeper UV radiation penetration, likely enhancing impacts to biota. We experimentally assess the cumulative effects of warming and natural UV-B radiation on the NCP of plankton communities from the oligotrophic coastal waters of the NW Mediterranean Sea. We do so, by conducting experiments where at monthly intervals, from the late spring to the early fall, the responses to different levels of ambient temperature and natural incident UV-B radiation, alone and in combination, were evaluated

Materials and Methods

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Discussion