Not only corals: seagrass bleaching in the eastern Mediterranean

Abstract

In the Mediterranean Sea, climate change is affecting key species like the seagrass Posidonia oceanica. Discoloration of P. oceanica leaves still attached to the shoots (bleaching hereafter) has been recently observed in warm locations, but whether this phenomenon is an adaptative strategy or a symptom of stress remained unknown. This study assessed the temporal evolution of P. oceanica bleaching in Konnos Bay (Cyprus) and its potential of recovery from summer to autumn 2024, along a bathymetric gradient and from a morphological and physiological perspective. The bleached area, chlorophyll and carotenoid contents were used as response variables, and temperature was considered as a potential driver. P. oceanica bleaching occurred along the entire bathymetric gradient, albeit delayed in time at deeper depths. Leaves' chlorophyll and carotenoid contents showed a mirror-like pattern in time compared to the bleached leaf area at all depths. Correlative analyses demonstrated that the maximum daily temperature was positively related to the bleached area and negatively related to photopigment contents. However, an important result was highlighted by the increase of the total leaf area with high values of temperature, suggesting that the productivity of the plant can be compensated after the loss of leaf area due to bleaching. Values of bleached leaf area decreased in time with the decrease in temperature at all depths, indicating a high potential of recovery of the meadow. Results of this study provide novel information on an understudied phenomenon that occurs in P. oceanica.

Keywords: Carotenoids; Chlorophyll; Leaf area; Mediterranean Sea; Posidonia oceanica; Transparent leaf; Warm-edge location.