To address for the first time the carbon budget of traditional salterns, we measured the diel, seasonal, and spatial variability of water‐air CO ₂ ‐eq fluxes (CH ₄ and CO ₂ ) and the Organic Carbon (OC) stock and burial rate in the sediment. Temperature, salinity, dissolved oxygen, pH and wind were assessed as potential environmental drivers of the fluxes. The saltern emitted CH ₄ to the atmosphere throughout the year, with no significant differences among sites or seasons. On the contrary, the saltern were a sink of CO ₂ in summer, autumn and winter, and a source of CO ₂ in spring. Water temperature was the main positively related predictor variable of CH ₄ fluxes, explaining 29% of their variance, whereas CO ₂ fluxes were significantly negatively related to the concentration of O ₂ and pH in the seawater and positively related to wind, which explained 66% of fluxes variance. The sedimentary and OC stocks and burial rates were not significantly different among the sampled ponds and averaged 11.9 ± 2.2 Mg OC ha ⁻¹ and 0.011 ± 0.004 Mg OC ha ⁻¹ yr ⁻¹ , respectively. The carbon budget of the saltern was −35.0 g CO ₂ ‐eq m ⁻² yr ⁻¹ , corresponding to −1.49 Mg CO ₂ ‐eq yr ⁻¹ for the total saltern area. This suggests that the‐salt industry may function as a carbon sink as opposed to other coastal industries such as fish and shrimp aquaculture. Future studies with additional measurements across a wider range of salterns are needed to evaluate the relevance of “white carbon.”

Seagrass restoration efforts have multiplied in the last years, with very diverse success rates, justifying the need for a better understanding of the physiological aspect of transplant operations. For the first time, biochemical parameters were used as early indicators of transplant’s health. In this study, two seagrass species were transplanted using two distinct modalities per species. Zostera marina was transplanted in bundles of five and ten shoots and Cymodocea nodosa was transplanted with original sediment in trays and as bare rhizome segments of at least three shoots. Oxidative stress, antioxidant activity, photosynthetic pigment and non-structural carbohydrate (NSC) content in leaves and rhizomes were investigated before transplant and four weeks after transplant. Results revealed some significant method-specific early biochemical responses to transplant for C. nodosa. Cymodocea nodosa shoots transplanted in segments showed radical shifts in NSC storage and chlorophyll content whereas antioxidant activity was further triggered in C. nodosa transplanted in trays. Shoot density may be an important factor to consider when selecting the best transplant method for Z. marina, but no differences were observed in the early biochemical parameters measured. The results of this short-term biochemical monitoring suggest that transplanting C. nodosa in trays could be less disruptive for the plant’s biochemistry than bare-rhizome methods. This study provides insights into biochemical responses post-transplantation and emphasizes the need for adaptable restoration strategies. Coupled with transplant survival, morphological parameters and long-term monitoring, biochemical metrics can be used as a sensitive tool to monitor short-term responses in seagrass meadows.

Marine heatwaves (MHWs) are increasing in frequency and intensity as part of climate change, yet their impact on marine angiosperms is poorly known. The present work evaluated the effects of a simulated spring-like MHW on the physiology and morphology of the seagrass Cymodocea nodosa, a temperate-warm adapted species. C. nodosa shoots were transplanted into a mesocosm facility. Water temperature was raised gradually from 20 to 28 °C, kept for 7 days at 28 °C, cooled down back to 20 °C and then maintained at 20 °C during an 8-day recovery period. The photosynthetic performance, antioxidative stress level and area/dry weight ratio of the plant’s leaves were investigated at the end of the heatwave and after the recovery period. The effective quantum yield of photosystem II increased during the heatwave and was higher in the mature parts of the leaves, allowing the plants to maintain their photosynthetic activity at the control level. Negative effects on the photosynthetic performance and leaf biomass of C. nodosa were observed during the recovery period. No significant oxidative stress was observed throughout the experiment. Although C. nodosa showed a relative tolerance to MHWs compared to other species, results show that the negative effects of a MHW may only become evident in the aftermath of the heatwave peak. In the Ria Formosa coastal lagoon, southern Portugal, C. nodosa is likely to be negatively affected by recurrent MHWs in the forecasted climate change scenarios, threatening the perennity of seagrass meadows’ ecosystems.

Glyphosate-based herbicides (GBHs) are extensively used worldwide, raising concerns about their potential effect on non-target aquatic ecosystems. This study investigated the short-term physiological effects of a commercially available GBH on the seagrass Zostera marina under controlled mesocosm conditions. Z. marina individuals were exposed to three concentrations of glyphosate (0.165, 51, and 5100 mg L⁻¹) for 4 days, and the impacts on photosynthetic performance, growth rate, photosynthetic pigments content and energy metabolism were assessed. Exposure to 5100 mg L⁻¹ of glyphosate caused rapid water acidification and complete plant mortality within 24 h. Exposure to 51 mg L⁻¹ of glyphosate significantly impaired photosynthetic efficiency and foliar growth rate. Energy availability, photosynthesis and photosynthetic pigments content were highly disrupted at both higher concentrations. Exposure to 0.165 mg L⁻¹ of glyphosate decreased the foliar chlorophyll a/b ratio. These findings show that Z. marina can potentially be threatened by the presence of GBHs even at lower concentrations and underscore the necessity for monitoring herbicide pollution in coastal waters to protect seagrass habitats and associated ecosystems. Further research is needed to assess long-term effects and the role of herbicide formulations in mediating toxicity.

Glyphosate-based herbicides (GBHs) are extensively used worldwide, raising concerns about their potential effect on non-target aquatic ecosystems. This study investigated the short-term physiological effects of a commercially available GBH on the seagrass Zostera marina under controlled mesocosm conditions. Z. marina individuals were exposed to three concentrations of glyphosate (0.165, 51, and 5100 mg L⁻¹) for 4 days, and the impacts on photosynthetic performance, growth rate, photosynthetic pigments content and energy metabolism were assessed. Exposure to 5100 mg L⁻¹ of glyphosate caused rapid water acidification and complete plant mortality within 24 hours. Exposure to 51 mg L⁻¹ of glyphosate significantly impaired photosynthetic efficiency and foliar growth rate. Energy availability, photosynthesis and photosynthetic pigments content were highly disrupted at both higher concentrations. Exposure to 0.165 mg L⁻¹ of glyphosate decreased the foliar chlorophyll a/b ratio. These findings show that Z. marina can potentially be threatened by the presence of GBHs even at lower concentrations and underscore the necessity for monitoring herbicide pollution in coastal waters to protect seagrass habitats and associated ecosystems. Further research is needed to assess long-term effects and the role of herbicide formulations in mediating toxicity.