Intra-specific responses of Cymodocea nodosa to macro-nutrient, irradiance and copper exposure

Excess macro-nutrients, metal contamination and light limitation are three of the most commonly encountered anthropogenic stressors affecting seagrass meadows. In this study, the effects of different combinations of nutrients (N-NO3, P-PO4), copper and irradiance were investigated in shoots of Cymodocea nodosa collected from three meadows in the N. Aegean Sea, one (Nea Karvali) impacted by anthropogenically-derived environmental stressors and two in more pristine condition (Thasos, Brasidas). In a series of laboratory experiments, shoots were exposed to varying nutrient and heavy metal concentrations, as well as varying irradiance levels, for 8days and the effective quantum yield (ΔF/Fm′) and leaf elongation were quantified. Results showed that C. nodosa increased ΔF/Fm′ under high nutrient concentrations (30μΜ N-NO3−–2μΜ P-PO43−) but significant differences were only apparent in shoots collected from the oligotrophic-less stressed meadows. Irradiance affected ΔF/Fm′ significantly in all shoots irrespective of source and PO4-P concentration, while higher values were measured under low light conditions and it was identified as the main pathway of eutrophication stress in N. Aegean Cymodocea meadows. Shoots, independently of acclimation were tolerant to copper enrichment, with only the highest copper concentrations (4.7 and 7.9μM) having significant negative effects on ΔF/Fm′. Shoots from the more pristine meadows were less affected by Cu than those from the highly stressed meadow. •High nutrient exposure increased the effective quantum yield of Cymodocea nodosa.•Low irradiance caused an increase of ΔF/Fm′ irrespective of sample's source.•Shoots were tolerant to copper enrichment.•High copper concentrations (4.7 and 7.9μM) had negative effects on ΔF/Fm′.•Shoots from the more pristine meadows were less affected by Cu.