The most suitable time and depth to sample Cymodocea nodosa (Ucria) Ascherson meadows in the shallow coastal area. Experiences from the northern Adriatic Sea

Abstract

       The Lesser Neptune grass, Cymodocea nodosa, is the most common seagrass species in shallow sheltered to semi-exposed sites along the Mediterranean soft bottom. The MediSkew index was recently developed as an improvement of the CymSkew index, in order to assess the status of C. nodosa meadows correctly in view of the implementation of three European Directives. The index takes into account the length of the photosynthetic part of C. nodosa leaves, which increases from the less degraded meadow to the most degraded meadow. To adequately assess temporal and spatial trends in the status of C. nodosa meadows, including estimates of the effects of natural disturbances within marine protected areas, the MediSkew index was applied to new samples collected at 3 m and at 6 m of depth, during two months (in July and in September). The analyses are discussed in view of monitoring and conservation of C. nodosa meadows. According to the results of this study, the monitoring programme in the northern Adriatic Sea should be conducted in July, with the collection of samples at 3 m of depth. The presented sampling and assessing methodology proved to be timeand cost-effective for the evaluation of the status of C. nodosa meadows and of human-induced pressures.