Seagrass meadows are declining at alarming rates globally due to both anthropogenic activities and natural threats. Seagrasses play key ecological roles in coastal ecosystems as primary producers and providers of habitat and environmental structure. Therefore, mapping seagrass beds is indispensable for the effective monitoring and management of coastal vegetated habitats. In contrast to direct sampling techniques and optical remote sensing, active hydroacoustic techniques are relatively inexpensive and efficient for the detection of seagrass. We used a single beam echosounder to detect the spatial and temporal distribution characteristics of the eelgrass Zostera marina L. in an important overwintering habitat for the whooper swan Cygnus cygnus (Swan-Lake lagoon), northern China. We also distinguished echograms of the macroalgae Chaetomorpha linum K. and outlined its threat to seagrass. We also propose a method for calculating the accuracy of interpolation analyses. Results showed that: (1) The distribution of seagrass in Swan Lake varies with seasons, with maximum distribution area in summer. The maximum distribution area of seagrass beds in Swan Lake was 199.09 ha–231.67 ha, accounting for 41.48%–48.26% of the area of Swan Lake; (2) C. linum is a growing threat for seagrass beds of Swan-lake, with distribution area as high as 129.28 ha in May 2018. The invasion and competition by C. linum against seagrass beds could be one of the reasons for the decline in seagrass beds in Swan-Lake; (3) Topo to Raster has the highest interpolation accuracy and is the most conservative among three interpolation methods. Topo to Raster was the most suitable interpolation method for the sonar detection of seagrass beds. The findings may facilitate the application of sonar technology in seagrass monitoring and provide data for the formulation of appropriate seagrass bed management and restoration strategies and policies.

It is hypothesized that pH fluctuations produced by seagrasses metabolism may confer marine calcifiers resistance to ocean acidification. Here, we tested this thesis by comparing the net population growth rate (NPGR) of a foraminifer species (Rosalina sp.) epiphytic of Mediterranean seagrass (Posidonia oceanica) to average current and projected pH scenarios under either stable conditions or diel fluctuations in pH of 0.3 units; variations similar to that experienced in their habitat. No significant differences were found in NPGRs between the fluctuating and stable pH treatments at current pH levels. NPGRs in treatments where pH fluctuated did not present significant differences to the treatment with high and stable pH conditions. In contrast, foraminifers exposed to stable low pH regimes experienced a steep decline in NPGR. These results suggest that diel pH fluctuations generated by P. oceanica photosynthetic activity could confer resistance to ocean acidification to Rosalina sp.

Previous studies on PCDD/Fs and PCBs in dugong (Dugong dugon) blubber reported unexpectedly elevated TEQ levels. This study analysed archived blubber, muscle, liver and faeces obtained from dugongs from two areas along the Queensland coast. All samples showed detectable levels of PCDDs and PCBs, while PCDFs were consistently near or below LOQ. PCDD levels in dugongs contributed to a large proportion (<95%) of sum TEQ levels in all tissues (blubber: 6.7–38 pg g−1 lw, muscle: 5.7–96 pg g−1 lw, liver: 3.3–42 pg g−1 lw, faeces: 203 pg g−1 lw). Liver/blubber tissue ratios show that PCDDs are preferentially accumulated in the liver with higher degree of chlorination. The same trend was not so obvious with PCBs, which occasionally showed higher hepatic sequestration of lower chlorinated PCBs such as PCBs 28 and 77. PCDD congeners were dominated by OCDD which is similar to the profiles from the dugongs' food source, namely sediment and seagrass.

Over the last four decades the Mexican Caribbean has experienced intensive coastal development, and change on the reef system condition has already been observed. This paper describes the reef system characteristics, at local and seascape scales, and discusses the current status and trends, considering the main research efforts from academia and Non-Governmental Organizations. To date, the coral cover of most reefs in the region is between 15 and 20%, following a slight recovery on mean coral cover over the last decade. During this same period, fleshy macroalgae and herbivorous fish biomass appear to have increased. At seascape scales, an increase of macroalgae and the loss of seagrass habitat have been observed. Considering that anthropogenic and environmental disturbances will most likely increase, the establishment of newly protected areas in the Mexican Caribbean is appropriate, but sufficient accompanying funding is required.

We aimed to show how the predicted pH decrease in the ocean would alter the toxicity, bioconcentration and dietary transfer of trace metal copper on seagrass ecosystems, on a short-term basis. Seagrass Zostera noltei was exposed to two pH levels (8.36 and 8.03) and three copper levels (nominal concentrations, <3, 30 and 300 μg Cu L⁻¹) in a factorial design during 21 days, while Gammarus locusta amphipods were continuously fed with the treated seagrass leaves. We found that the toxicity and bioconcentration of copper in seagrasses were not affected by pH, yet complex copper-pH interactions were observed in the seagrass photosynthesis. We demostrated that seagrasses can act as a copper source in the food web via direct consumption by herbivores. Future research need to investigate the interactive effects on a long-term basis, and to include biochemical and molecular endpoints to provide additional insights to the complex phisiological interactions observed.

Desalination has the potential to provide an important source of potable water to growing coastal populations but it also produces highly saline brines with chemical additives, posing a possible threat to benthic marine communities. The effects of brine (0%, 50%, 100%) were compared to seawater treatments with the same salinity (37, 46, 54 psu) for seagrass (Posidonia australis) in mesocosms over 2 weeks. There were significant differences between brine and salinity treatments for photosynthesis, water relations and growth. Germinating seedlings of P. australis were also tested in brine treatments (0%, 25%, 50%, 100%) over 7 weeks followed by 2.5 weeks recovery in seawater. Growth was severely inhibited only in 100% brine. These experiments demonstrated that brine increased the speed and symptoms of stress in adult plants compared to treatments with the same salinity, whereas seedlings tolerated far longer brine exposure, and so could potentially contribute to seagrass recovery through recruitment.

Seagrass meadows are recognized as critical and among the most vulnerable habitats on the planet. As a worldwide concern, there is an urgent need to develop techniques to restore and preserve these vital coastal ecosystems due to their alarming decline rate. To effectively preserve and restore seagrasses, more research is required on the germination ecology of seeds. The seagrass Zostera japonica Asch. & Graebn is an endangered species in its native range, the Northwestern Pacific Coast. The present study investigated the germination and seedling establishment in Z. japonica seeds (collected from northern China) under different temperature and salinity conditions to explore suitable seed germination and establishment conditions, as well as the seedling formation process. Results showed that salinity had a more significant influence on seed germination rate. Germination rate decreased with an increase in salinity, and seeds did not germinate when salinity was higher than 40 psu. Temperature was more likely to influence germination speed, which increased with an increase in temperature, with high germination rates and the most rapid germination speed observed at 30 °C. Therefore, the optimal culture conditions were 10 psu salinity at 30 °C for germination and 10–20 psu salinity at 20 °C for seedling establishment, with a seed germination rate of 45.6% after 6 days of germination culture and a seedling establishment rate of 14.3% after 6 days of seedling culture, respectively. A new seedling raising method with low salinity (5 psu) germination and high salinity (20 psu) seedling establishment was proposed and a flow chart of seedling formation of Z. japonica was created. The results provide insight into the seed germination and seedling establishment in Z. japonica, and will facilitate future large-scale seedling culture and field restoration activities for this seagrass species.

During mining activities historically developed at Sierra Minera (Cartagena-La Unión, Spain), high amounts of trace elements were discharged to the Mar Menor coastal lagoon mainly through El Beal Wadi. The objective of this study is to establish the role played by the Cymodocea nodosa in the coastal marine dynamics of trace elements at the mouth of the wadi. To this end, the content of nine trace elements (As, Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn) in different marine environmental compartments (i.e. marine and coastal sediments, C. nodosa tissues collected from live seagrass and C. nodosa beach cast litter) at two different locations were determined by inductively coupled plasma atomic emission spectrometry. The results showed that the seagrass C. nodosa could mobilise part of the elements present in marine sediments and water, thereby causing their re-accumulation in the coastal sediments through the C. nodosa beach cast litter.

The present study quantifies the levels of five trace elements (TEs) Zn, Cu, Ni, Pb, and Cd in the leaves and rhizomes of Cymodocea nodosa as well as the surficial sediments from three semi-enclosed coastal areas in Tunisia, in the south Mediterranean Sea. Samples were taken from the Bizerte and Ghar El Melh lagoons and from marina Cap Monastir. The TE ranking was found to be Zn > Cu > Pb > Ni > Cd in sediments and Zn > Cu = Ni = Pb = Cd in C. nodosa leaves and rhizomes. Except for Ni, levels of Zn, Cu, Pb, and Cd significantly differed between the sites. Translocation factors (TFs) were > 1 for all trace elements proving the high capacity of C. nodosa to accumulate TEs in its above-ground tissues. Results show that marina Cap Monastir’s meadow exhibits higher TFs than the Bizerte and Ghar El Melh lagoons. This can be due to the presence of the non-indigenous species Halophila stipulacea. The present study highlights the need for further investigation on the effect of interspecific interaction on TE uptake by seagrasses.