Assessment of the Photosynthetic Response of Posidonia oceanica (Linneaus) Delile, 1813 along a Depth Gradient in the Northern Tyrrhenian Sea (Latium, Italy)

Giulia Caporale,Marco Marcelli,Alice Madonia,Marina Penna,Simone Bonamano

doi:10.3390/geosciences11050202

Abstract

Posidonia oceanica (L.) Delile meadows are recognized to be one of the most productive ecosystems of the Mediterranean basin. Due to the impacts of human activities in coastal areas, seagrasses are experiencing a critical decline. In this context, the understanding of the dynamics of production and photosynthesis in response to the environmental factors is essential to address efficient conservation strategies that limit this trend and to assess the ecological status of marine ecosystems. Pulse Amplitude Modulated (PAM) fluorometry has been widely implemented to assess seagrass health and productivity. Here we analyzed the photosynthetic dynamics of P. oceanica according to its bathymetric distribution and daily light availability along a depth gradient to be used as baseline for monitoring purposes on the health status of the seagrass meadows in the Northern Tyrrhenian Sea. Moreover, to investigate the effects of the environmental factors on the health status of P. oceanica within the study area through a multidisciplinary approach, the models contained in the Civitavecchia Coastal Environmental Monitoring System were used. In this study, significant photo-physiological changes have been observed among the investigated meadows. Moreover, the integration of physiological and hydrodynamic information allowed the description of how P. oceanica modulates its photosynthetic capacity at different environmental conditions.

Highlights

Seagrasses are among the most productive marine ecosystems, sequestering and storing a significant amount of blue carbon in their rich organic sediments and in their living and non-living biomass
The results show that the station POS-1m is characterized by the highest values of WA (0.05 ± 0.21 Kg s−1m−2) with a maximum PET of 2.59%, identifying a high hydrodynamic condition, considerably variable during the simulated year
Our results show that Junior-Pulse Amplitude Modulated (PAM) fluorometer can detect photo-physiological changes and diurnal variations of photosynthetic activity of P.oceanica

Summary

Introduction

Seagrasses are among the most productive marine ecosystems, sequestering and storing a significant amount of blue carbon in their rich organic sediments and in their living and non-living biomass. Seagrass ecosystems have been widely recognized as good bioindicators of coastal ecosystems status [2], due to their wide distribution along the Mediterranean coasts [3], their high susceptibility to changing environmental conditions [4], their sensibility to direct and indirect anthropogenic pressures [5] and, the large amount of knowledge of the biology and ecology of this species [6]. Within the Marine Strategy Framework Directive MFSD 2008/56/EC [11], the evaluation of the ecological integrity of meadows is fundamental for the assessment of the Good Environmental Status (GES) of benthic habitats within Descriptor 1 “Biodiversity”

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Discussion

Conclusion