Using seagrasses to identify local and large-scale trends of metals in the Mediterranean Sea

Trajectories of trace element accumulation in seagrass (Posidonia oceanica) over a decade reveal the footprint of fish farming

To evaluate the effect of trace element (TE) release from fish farms on seagrass Posidonia oceanica, we compared TE concentrations (As, Cd, Co, Cu, Mn, Mo, Ni, Pb, V, Zn) in shoots near fish cages (Station 'Cage') with those away from them (Station 'Control') in two fish farm facilities (Site 1 and Site 2, North Aegean Sea, Greece). We assessed the present (i.e., 2021, year of sampling) and past (reconstructed period 2012-2020) accumulation of TEs using the living compartments (leaf blades, sheaths, rhizomes, roots, epiphytes) and the dead sheaths, respectively. We also assessed possible seagrass degradation by reconstructing past rhizome production. P. oceanica rhizome production at the 'Cage' stations was up to 50% lower than at the 'Control' stations. Most TE concentrations were higher at 'Cage' stations, but the differences often depended on the seagrass living compartment. Significant differentiation between 'Cage' and 'Control' stations was observed based on the TE concentrations of the dead sheaths during 2012-2020. The contamination level at the 'Cage' stations was mostly moderate in Site 1 and low in Site 2, during the reconstructed period, while an increasing contamination trend was found for certain potential phytotoxic TEs (As, Cu, Cd, Mo, V). Our results emphasize the need for the aquaculture industry to work towards a more ecologically aware approach.

The efficiency of trace element uptake by seagrass Cymodocea serrulata in Rabigh lagoon, Red Sea

The search for solutions to environmental pollution has been on the increase, with many questions recently as to which marine organisms can bioaccumulate trace elements in the marine ecosystem. Cadmium, Cr, Cu, Fe, Mn, Ni, Pb, and Zn concentrations in sediment, seawater, and seagrass compartments (root, rhizome, and leaf blade) were determined at Rabigh lagoon, Red Sea. This is to provide an insight into the potential of Cymodocea serrulata to bioaccumulate trace elements and as a good candidate to biomonitor these elements in a natural aquatic ecosystem. Results revealed significant variations in trace element concentrations across the three compartments of C. serrulata and the sites, with site S8 located in the most closed part of the lagoon recording the highest concentrations for all the trace elements. The translocation factor (TF_rhizome/root = 1.00) of trace elements was higher in the root compartment. This implies that the root compartment is a better bioindicator of trace elements and has more potential to be utilized for biomonitoring. A significant positive correlation (p < 0.01) was established between the trace element concentrations in sediment, seawater, and the three compartments of C. serrulata except for Mn concentration in the compartments. The seagrass C. serrulata can be used for biomonitoring of trace elements in marine ecosystems as our results provide information on its capacity to bioaccumulate these elements. This is one of the key characteristics of a typical bioindicator of aquatic pollutants.

Increasing nutrient inputs over the last 500 years in an Italian low-impacted seagrass meadow

Posidonia oceanica is a seagrass endemic to the Mediterranean and it has been widely used as a bioindicator. We studied the layers of a 500-year-old matte using a multiproxy approach (δ¹³C, δ¹⁵N, ¹⁴C and C and N concentrations in seagrass debris) in order to evaluate the potential of P. oceanica as a long-term environmental indicator of N pollution and CO₂ emissions. From 1581 to 1800, accumulation rate was ca. 0.35 cm year^-1, while in the last 100 years it has amounted to ca. 0.51 cm year^-1. We observed increasing δ¹⁵N values with height in the vertical matte profile, indicating an increase in anthropogenic organic N inputs over time. In contrast, no clear trend in the δ¹³C values was observed. This study reconstructs the long-term impact of human activities on a seagrass meadow located off the Italian coast, yielding long-term background information that can help managers to implement efficient plans.

Heavy metal accumulation and ecological risk on four seagrass species in South China

Zn, Pb, Cr, Cu, Ni, Cd concentration and ecological risk were studied in three bays to evaluate the heavy metal (HM) contamination of seagrasses. Seasonal HM accumulation varied according to locations, seagrass species and tissues. Halophila beccarii had much higher HM concentrations except for Cr in Zhelin Bay, however, bioconcentration factors (BCF) of Cu, Ni, Pb, Zn were higher in Liusha than Zhelin Bay. Cr was much enriched in Thalassia hemperichii and Enhalus acoroides than Halophila beccarii and Halophila ovalis. Cr, Cu, Ni, Pb were easy to accumulate in belowground tissues in Halophila ovalis. In contrast, almost all HM were more enriched in aboveground tissues in other species. Generally, BCF exceeding 1 and high metal pollution index suggested HM had potential ecological risk on seagrasses. The results provide the reference for managing and protecting seagrass ecosystem in South China, and are significant to expand the global seagrass detection network.

Coastal bays and coral cays: Multi-element study of Chelonia mydas forage in the Great Barrier Reef (2015-2017)

There is increasing interest in understanding potential impacts of complex pollutant profiles to long-lived species such as the green sea turtle (Chelonia mydas), a threatened megaherbivore resident in north Australia. Dietary ingestion may be a key exposure route for metals in these animals and marine plants can accumulate metals at higher concentrations than the surrounding environment. We investigated concentrations of 19 metals and metalloids in C. mydas forage samples collected from a group of offshore coral cays and two coastal bays over a period of 2-3 years. Although no samples exceeded sediment quality guidelines, coastal forage Co, Fe, and V concentrations were up to 2-fold higher, and offshore forage Sr concentrations were ~3-fold higher, than global seagrass means. Principal Component Analysis differentiated coastal bay from coral cay forage according to patterns consistent with underlying terrigenous-type or marine carbonate-type sediment geochemistry, such that coastal bay forage was higher in Fe, Co, Mn, Cu, and Mo (and others) but forage from coral cays was higher in Sr and U. Forage from the two coastal bays was differentiated according to temporal variation in metal profiles, which may be associated with a more episodic sediment disturbance regime in one of the bays. For all study locations, some forage metal concentrations were higher than previously reported in the global literature. Our results suggest that forage metal profiles may be influenced by the presence of some metals in insoluble forms or bound to ultra-fine sediment particles adhered to forage surfaces. Metal concentrations in Great Barrier Reef forage may be present at levels higher than expected from the global seagrass literature and appear strongly influenced by underlying sediment geochemistry.

Heavy Metal Accumulation and Anti-Oxidative Feedback as a Biomarker in Seagrass Cymodocea serrulata

The pursuit of a good candidate to biomonitor environmental pollutants has been on the increase. In this study, the concentrations of Fe, Mn, Cu, Zn, Cd, Cr, Pb and Ni in sediment, seawater and seagrass Cymodocea serrulata compartments and antioxidant enzymes activities in C. serrulata were determined. Our results revealed that bioconcentration factors for all the metals were less than 1 (BCF < 1) and concentrations in seagrass compartments were in the order root > leaf > rhizome for Fe and Mn, leaf > root > rhizome for Cu, Zn, Pb and Ni, and root > rhizome > leaf for Cd and Cr. Effect range low concentrations (ER-L) revealed that Cu, Zn, Cd, Pb and Ni concentrations were above ER-L values and Cr concentration was below ER-L values while concentrations in seawater for all the heavy metals were above the estimate average element concentrations in seawater (ECS). Significant variation (p < 0.05) was recorded for heavy metals in sediment, seawater, seagrass compartments and heavy metal concentrations across stations. Influence of heavy metals on antioxidant enzymes activities; catalase (CAT), superoxide dismutase (SOD), glutathione S-transferase (GST) and acetylcholinesterase (AChE) were recorded, and high activities of the antioxidants were recorded in station S8 corresponding to high concentrations of heavy metals in the same station. There is a need for the promotion of biomonitoring networks across the marine environment using C. serrulata and antioxidant enzymes as biomarkers of oxidative stress caused by environmental pollutants.

Assessment of trace elements pollution in sea ports of New South Wales (NSW), Australia using macrophytobenthic plant Ecklonia radiata as a bio-indicator

In this study seaweeds (Ecklonia radiata) from six major sea ports of NSW, Australia were used as a bioindicator to assess the distribution and levels of trace elements accumulation in the ports compared to the background ecosystem. Bioconcentration ratio (BCR), biota sediment accumulation factor (BSAF), enrichment factor, multivariate statistical analysis and hierarchical cluster analysis were used to identify trace elements contamination. The results illustrate BCRs of Al, Fe, Mn, Zn, Pb, Cu, As and Ba in E. radiata whereas the BASFs portray boron enrichment in all sea ports along with bioaccumulation of As in Port Jackson and Pb in Port Botany. However, trace elements variations between studied and background locations was found to be significant for Port Kembla and Newcastle. The principal component analysis result explained four principal groups with 76.25% cumulative variance. Cluster analysis was further performed to detect major groups of elements and sites to portray interconnection between the contaminants and the locations.

Seagrass Halophila stipulacea: Capacity of accumulation and biomonitoring of trace elements

This study aimed to shed further light on the capacity of the seagrass Halophila stipulacea to accumulate and biomonitor the elements As, Cd, Cr, Cu, Hg, Mn, Ni, Pb, and Zn, present in water and sediments. Results showed that the organs of H. stipulacea accumulate different levels of trace elements, whose concentrations decrease mainly in the order of roots>rhizomes>leaves. The seagrass H. stipulacea showed levels of trace elements similar to those found in other Mediterranean seagrasses, e.g. Posidonia oceanica and Cymodocea nodosa. This study showed that H. stipulacea could act as a promising bioindicator of several elements, present in sediments, including As, Cd, Cu, Mn, Ni and Zn.