The Challenge of Cystoseira crinita: combined effect of temperature and radiation

Abstract

The Mediterranean Sea is a hotspot of marine species biodiversity where most of the submerged forests are dominated by fucoid species of the genus Cystoseira. Benthic assemblages subjected to a low or moderate hydrodynamics between zero and one meter deep and restricted to rocky subtracts are occasionally dominated by Cystoseira crinita, that because of the shallow habitat is particularly vulnerable and finds refuge in rock pools and in very shallow waters of sheltered coves. The most important consequences of climate change on aquatic ecosystems are probably the temperature and UV radiation increases. These rocks pools, due to the low deep and hydrodynamics may experience high temperatures and radiations that, especially considering the present climate warming framework, may impair these populations which are actually vulnerable. The main objective of this study is to determine if positive thermic anomalies may be a driver of C. crinita decline, at least in the north-western Mediterranean Sea. For this, our specific aims are: determine if the temperature and ultraviolet radiation increases affects physiological state of adults individuals and elucidate if temperature and radiation have a synergistic, cumulative or antagonistic effect on this physiological state. The experiment consisted on the application of six treatments combining two different environmental parameters, radiation (PAR and PAR + UV) and temperature (21, 24 and 28 ºC) during 30 days. At 21 and 24 ºC, in both radiations, total height and maximum quantum yields of photosynthesis, Fv/Fm, remained constant during experiment, but humid weight began to decrease after 30 days and the Fv/Fm after 12. At 28 ºC effects were differentially caused by radiation exposure, so that under PAR began to lose humid weight after day 12 and reduced its total height, but under PAR + UV began to lose humid weight after day 18. In addition, at 21 ºC under PAR + UV radiation individuals increased its apex height. These results suggest that C. crinita has efficient protective mechanisms against UV radiation and its thermic tolerance is adapted to resist a long time under the current normal summer temperatures. However, our results also show that although C. crinita is able to resist short and punctual periods at high temperatures, it is not able to resist mid-long periods at temperatures up to 28ºC (thermal anomalies). Also, the interaction between temperature and radiation has an antagonistic effect