Seagrass tolerance to herbivory under increased ocean temperatures

Climate change is acknowledged as a major threat to marine ecosystems, but the effect of temperature on species interactions remains poorly understood. We quantified the effects of long-term warming on plant-herbivore interactions of a dominant seagrass, Zostera muelleri. Growth, herbivory and tolerance to damage were compared between a meadow warmed by the thermal plume from a power station for 30 years (2–3 °C above background temperatures) and three control locations. Leaf growth rates and tissue loss were spatially variable but unrelated to temperature regimes. Natural herbivory was generally low. Simulated herbivory experiments showed that the tolerance of Z. muelleri to defoliation did not differ between warm and unimpacted meadows, with damaged and undamaged plants maintaining similar growth rates irrespective of temperature. These results suggest that the ability of temperate Z. muelleri to tolerate herbivory is not strongly influenced by warming, and this species may be relatively resilient to future environmental change.     

Spatial patterns of sub-tidal seagrasses and their tissue nutrients in the Torres Strait,northern Australia: Implications for management

The distribution and nutritional profiles of sub-tidal seagrasses from the Torres Strait were surveyed and mapped across an area of 31,000 km². Benthic sediment composition, water depth, seagrass species type and nutrients were sampled at 168 points selected in a stratified representative pattern. Eleven species of seagrass were present at 56 (33.3%) of the sample points. Halophila spinulosa, Halophila ovalis, Cymodocea serrulata and Syringodium isoetifolium were the most common species and these were nutrient profiled. Sub-tidal seagrass distribution (and associated seagrass nutrient concentrations) was generally confined to northern-central and south-western regions of the survey area (<longitude 142.60), where mean water depth was relatively shallow (approximately 13 m below MSL) and where sediments were comprised primarily muddy sand to gravelly sand. Seagrass nitrogen and starch content, the most important nutrients for marine herbivores, were significantly correlated with species and with the plant component (above or below ground). For all seagrass species, the above-ground component (shoots and leaves) possessed greater nitrogen concentrations than the below-ground component (roots and rhizomes), which possessed greater starch concentrations. S. isoetifolium had the highest total nitrogen concentrations (1.40±0.05% DW). However, it also had higher fibre concentrations (38.2±0.68% DW) relative to the other four species. H. ovalis possessed the highest starch concentrations (2.76±0.12% DW) and highest digestibility (83.24±0.66% DW) as well as the lowest fibre (27.2±0.66% DW). The high relative abundance (found at 55% of the sites that had seagrass) and nutrient quality characteristics of H. ovalis make it an important source of energy to marine herbivores that forage sub-tidally in the Torres Strait. There were two regions in Torres Strait (north-central and south-western) where sub-tidal seagrass meadows were prevalent and of relatively higher nutritional value. This spatial and nutritional information can be used by local agencies to manage and to protect the ecological, economic and cultural values of the sub-tidal seagrass ecosystems and associated fisheries of the Torres Strait.     

Future seagrass beds: Can increased productivity lead to increased carbon storage?

While carbon capture and storage (CCS) is increasingly recognised as technologically possible, recent evidence from deep-sea CCS activities suggests that leakage from reservoirs may result in highly CO₂ impacted biological communities. In contrast, shallow marine waters have higher primary productivity which may partially mitigate this leakage. We used natural CO₂ seeps in shallow marine waters to assess if increased benthic primary productivity could capture and store CO₂ leakage in areas targeted for CCS. We found that the productivity of seagrass communities (in situ, using natural CO₂ seeps) and two individual species (ex situ, Cymodocea serrulata and Halophila ovalis) increased with CO₂ concentration, but only species with dense belowground biomass increased in abundance (e.g. C. serrulata). Importantly, the ratio of below:above ground biomass of seagrass communities increased fivefold, making seagrass good candidates to partially mitigate CO₂ leakage from sub-seabed reservoirs, since they form carbon sinks that can be buried for millennia.     

Identification of the natural product 2,3,4,5-tetrabromo-1-methylpyrrole in Pacific biota, passive samplers and seagrass from Queensland, Australia

Halogenated natural products (HNPs) are frequently detected in marine organisms. High HNP concentrations have previously been found in marine mammals from the Great Barrier Reef, Australia, including in the blubber of herbivorous dugongs (Dugong dugon). To identify the source of HNPs we initially focused on the analysis of Australian seagrass (Halophila ovalis) which serves as the principal food source for dugongs. GC/MS analysis of the seagrass indicated the presence of several organobromine compounds. One compound was identified as 2,3,4,5-tetrabromo-1-methylpyrrole (TBMP) by synthesis. Subsequent analysis of semipermeable membrane devices demonstrated that the photo-sensitive TBMP is widespread in the Great Barrier Reef (Queensland, Australia). The detection of larger TBMP concentrations in fish fillets from Chile and traces in mussels from New Zealand indicated that this potential HNP may be distributed throughout the Southern Pacific Ocean.     

Bioremediation and fodder potentials of two Sargassum spp. in coastal waters of Shenzhen,South China

In this study, the bioremediation potentials of two seaweeds (Sargassum hemiphyllum and S. henslowianum) against pollution in a coastal mariculture area of Shenzhen, South China, were investigated by comparing the growth, nutrient bioaccumulation capacity of plants from the seaweed bed (control site) with plants from the fish farm. Results indicated that both species are potential candidates for bioremediation in the fish farm areas in terms of their high growth rates and high bioaccumulation capacities on inorganic nutrients. Both Sargassum spp. contain high levels of crude protein (11.7–14.0%) and crude fat (2.2–2.7%), suggesting high nutritional values. The S. hemiphyllum may serve as a good aquaculture fodder with high nutritional compositions and low heavy metal contents. However, heavy metals (Cr, Pb and Cd) of S. henslowianum exceed the maximum allowable concentrations as aquatic feed, which restricts its fodder application. In general, the results of this study may contribute to the marine pollution bioremediation in the coastal areas of South China, especially in mariculture zones.     

Germination and establishment of the invasive cordgrass Spartina densiflora in acidic and metal polluted sediments of the Tinto River

Heavy metal pollution is common in rivers in the vicinity of mining areas. In these polluted environments, the survival of alien species with a high tolerance to metals may be favored. The Tinto River (Southwest Iberian Peninsula) is an excellent natural laboratory for the study of plants’ responses to acidic and metal polluted sediments. This work analyzes the tolerance of the alien species Spartina densiflora to low pH and high metal loads in the Tinto River. The main aim of this study was to determine if this alien species can invade landward along the banks of the Tinto River. S. densiflora seeds were able to germinate in heavy metal polluted aerobic sediments even at pH 2. However, these conditions decreased S. densiflora final germination, altered germination dynamics, decreased aerial and subterranean growth rates, and prevented its establishment.     

Contrasting recovery of shallow and deep water seagrass communities following climate associated losses in tropical north Queensland,Australia

Tropical seagrass decline and recovery from severe storm impacts was assessed via quarterly measurements of seagrass biomass, species composition and experimental investigations of recovery in north Queensland. Shallow and deep seagrass meadows suffered major declines. Significant recovery in the two years following loss only occurred at deeper sites. Halophila spp. in deep water areas had a high capacity for recovery through the availability of seed banks. In contrast, the shallow species did not recover quickly from experimental disturbance, had poor seed reserves and relied on asexual propagation. The potential for shallow species to recover rapidly from widespread losses was limited as seed banks were limited or non-existent. Understanding inter- and intra-specific differences in seagrass recovery and how this interacts with location is critical to predict the consequences of climate events to tropical seagrasses. This is especially important as more frequent severe storms are predicted as a consequence of climate change.     

Courage under fire: Seagrass persistence adjacent to a highly urbanised city–state

Due to increasing development Southeast Asia’s coastlines are undergoing massive changes, but the associated impacts on marine habitats are poorly known. Singapore, a densely populated island city–state, is a quintessential example of coastal modification that has resulted in the (hitherto undocumented) loss of seagrass. We reconstructed the historic extent and diversity of local seagrass meadows through herbarium records and backwards extrapolation from contemporary seagrass locations. We also determined the current status of seagrass meadows using long-term monitoring data and identified the main threats to their presence in Singapore. Results show that, even though ∼45% of seagrass has been lost during the last five decades, species diversity remains stable. The main cause of seagrass loss was, and continues to be, land reclamation. We conclude that strict controls on terrestrial runoff and pollution have made it possible for seagrass to persist adjacent to this highly urbanised city–state.     

Angiosperms (seagrass) within the EU water framework directive: a UK perspective

Taxonomic composition, the presence of disturbance-sensitive species and abundance are attributes for monitoring the status of marine angiosperms; a biological quality element required for assessment of environmental condition under the Water Framework Directive (WFD). Their relevance for defining the ecological status of UK water bodies and the establishment of reference conditions for these attributes are described. Founded on quantitative measurements of these attributes, a set of metrics has been developed for monitoring and assessment of the only truly marine angiosperms, seagrass. The proposed metrics are presented and tested against a variety of littoral and sublittoral UK seagrass beds. In combination they express the cumulative response of marine angiosperms to different levels of anthropogenic disturbance.     

Physiological Responses of Five Seagrass Species to Trace Metals

Trace metal run-off associated with urban and industrial development poses potential threats to seagrasses in adjacent coastal ecosystems. Seagrass from the largest urban (Moreton Bay) and industrial (Port Curtis) coastal regions in Queensland, Australia were assessed for metal concentrations of iron (Fe), aluminium (Al), zinc (Zn), chromium (Cr) and copper (Cu). Trace metal concentrations in seagrass (Zostera capricorni) leaf and root-rhizome tissue had the following overall trend: [Fe] > [Al] > [Zn] > [Cr] > [Cu]. Rainfall events and anthropogenic disturbances appeared to influence metal concentrations in seagrasses with the exception of Al, which does not appear to bioaccumulate. In laboratory experiments, five seagrass species (Halophila ovalis, H. spinulosa, Halodule uninervis, Z. capricorni, Cymodocea serrulata) were incubated with iron (1 mg Fe l⁻¹) and copper (1 mg Cu l⁻¹) and responses assessed by changes in PSII photochemical efficiency (Fv/Fm), free amino acid content and leaf/root-rhizome metal accumulation. Iron addition experiments only affected Halophila spp, while copper additions affected other seagrass species as well. Trace metal contamination of seagrasses could have ramifications for associated trophic assemblages through metal transfer and seagrass loss. The use of photosystem II photochemical efficiency as well as amino acid concentrations and composition proved to be useful sublethal indicators of trace metal toxicity in seagrasses.     

Growth and survival of Halimione portulacoides stem cuttings in heavy metal contaminated soils

The halophytic shrub Halimione portulacoides demonstrates a high tolerance to heavy metal contamination and a capacity for accumulating metals within its tissues. On the Iberian Peninsula, this species has colonized habitats with high levels of metal pollution. The aim of this study is to analyze the response of H. portulacoides stem cuttings to this pollution. Growth, photosynthesis and metal uptake were examined in H. portulacoides through an experiment in which stem cuttings were replanted in metal-contaminated soil. This condition decreased growth and lowered both photosynthetic rate and stomatal conductance. Reduced photosynthetic performance was largely due to the reduced concentration of photosynthetic pigments. Despite these responses, there was some important evidence suggesting the phytoremediatory potential of Halimione stem cuttings. The results of our study indicate that this salt-marsh shrub may represent a biotool of value in the restoration of polluted areas.     

Levels of Cd,Cu, Pb and V in marine sediments in the vicinity of the Single Buoy Moorings (SBM3) at Mina Al Fahal in the Sultanate of Oman

Recently in the Sultanate of Oman, there has been a rapid surge of coastal developments. These developments cause metal contamination, which may affect the habitats and communities at and near the coastal region. As a result, a study was conducted to assess the level of metal contamination and its impact on the marine sediments in the vicinity of the Single Buoy Moorings 3 (SBM3) at Mina Al Fahal in the Sultanate of Oman. Marine subtidal sediment samples were collected from six different stations of the SBM3 for the period ranging from June 2009 to April 2010. These samples were then analyzed for their level and distribution of the heavy metals of cadmium (Cd), copper (Cu), lead (Pb) and vanadium (V). Overall, low concentrations of all four heavy metals were measured from the marine sediments, indicating that the marine at SBM3 is of good quality.     

Monitoring seagrass beds around a sewage sludge outfall in South Australia

Digested sludge from the Port Adelaide Sewage Treatment Works has been discharged to Gulf St. Vincent, a marine embayment in South Australia, since 1978. The outfall is sited in seagrass meadows dominated by Posidonia spp. and Amphibolis spp. By 1982 the discharge had affected an area of approximately 1900 ha, 365 ha of which were completely denuded of these seagrasses. A monitoring programme conducted over summers 1983–1985, inclusive, was based on the above-ground biomass (standing crop) of Posidonia at fourteen sites around the outfall. All sites were surveyed in the first two summers and eight sites were surveyed in the third. The results indicate that there was no ongoing reduction in the standing crop of Posidonia at any of the sites. These data also suggested that excessive growth of epiphytes on the leaves of Posidonia was a likely cause of the observed impact on the seagrass beds.     

The potential use of fairy prions (Pachyptila turtur) as monitors of heavy metal levels in Tasmanian waters

The purpose of the present study was to examine the potential use of the fairy prion to monitor contamination in the marine food chain following ocean dumping of industrial waste in S.E. Tasmania. Factors considered that can complicate interpretation of heavy metal levels detected include age, sex, seasonal, and other ecological aspects of the indicator species chosen. Unlike some other species of seabirds, the influence of sex and season on metal levels was unimportant. Copper, zinc, cadmium, and lead were tested in the liver and muscle tissue of fairy prions. In this preliminary study, cadmium levels were found to be significantly higher statistically in fairy prions closest to a potential source of pollution compared to levels from distant locations. This trend was not found in other metals investigated. However, it is suggested that this species would provide a useful future means of monitoring heavy metal levels.     

The roles of flowering,overwinter survival and sea surface temperature in the long-term population dynamics of Zostera marina around the Isles of Scilly,UK

Interaction between biotic and abiotic drivers of dynamics is an important topic in ecology. Despite numerous short-term studies, there is a paucity of evidence about how environmental structure modifies dynamics in marine systems. We quantified Zostera marina flowering and non-flowering shoot density annually from 1996 to 2012 around the Isles of Scilly, UK, parameterizing a population dynamic model. Flowering is structured in time and space, with temperature and flowering positively associated at some locations only. We found no evidence that flower production contributes to seagrass density but ‘patchiness’ was positively associated with flowering in the previous year. With evidence of substantial overwinter survival, findings support the hypothesis that local populations are maintained largely through vegetative reproduction but sexual reproduction may contribute to colonisation of vacant habitat. This long-term study (1) tests validity of shorter-term investigations, (2) quantifies interaction between biotic and abiotic factors and (3) promotes seagrass as a model ecosystem.     

Monitoring in the Western Pacific region shows evidence of seagrass decline in line with global trends

Seagrass systems of the Western Pacific region are biodiverse habitats, providing vital services to ecosystems and humans over a vast geographic range. SeagrassNet is a worldwide monitoring program that collects data on seagrass habitats, including the ten locations across the Western Pacific reported here where change at various scales was rapidly detected. Three sites remote from human influence were stable. Seagrasses declined largely due to increased nutrient loading (4 sites) and increased sedimentation (3 sites), the two most common stressors of seagrass worldwide. Two sites experienced near-total loss from of excess sedimentation, followed by partial recovery once sedimentation was reduced. Species shifts were observed at every site with recovering sites colonized by pioneer species. Regulation of watersheds is essential if marine protected areas are to preserve seagrass meadows. Seagrasses in the Western Pacific experience stress due to human impacts despite the vastness of the ocean area and low development pressures.     

Epiphyte loads on seagrasses and microphytobenthos abundance are not reliable indicators of nutrient availability in oligotrophic coastal ecosystems

Despite marked gradients in nutrient availability that control the abundance and species composition of seagrasses in south Florida, and the importance of nutrient availability in controlling abundance and composition of epiphytes on seagrasses in other locations, we did not find that epiphyte load on the dominant seagrass, Thalassia testudinum, or that the relative contribution of algal epiphytes to the epiphyte community, was positively correlated with nutrient availability in the water column or the sediment in oligotrophic seagrass beds. Further, the abundance of microphytobenthos, as indicated by Chlorophyll-a concentration in the sediments, was not directly correlated with concentrations of nutrients in the sediments. Our results suggest that epiphyte and microphytobenthos abundance are not unambiguous indicators of nutrient availability in relatively pristine seagrass environments, and therefore would make poor candidates for indicators of the status and trends of seagrass ecosystems in relatively low-nutrient environments like the Florida Keys.     

Spatial patterns of submerged macrophytes and heavy metals in the hypertrophic, contaminated, shallow reservoir Lake Qattieneh/Syria

Our investigation on macrophytes in Lake Qattieneh, a large, shallow reservoir in western Syria, is a first assessment of ecological status of this lake. We studied spatial distribution patterns of aquatic macrophyte vegetation and heavy metal concentrations to determine if they can be used as indicators of point sources of pollution. Industrial and municipal point sources at the lake shore increase nutrient load and contamination by heavy metals. Water analyses revealed high concentrations of some heavy metals at some littoral sites: Ni 88.7 μg L⁻¹, Cr 49.99 μg L⁻¹, Co 14.38 μg L⁻¹, and Cu 11.65 μg L⁻¹. Despite hypertrophic conditions and high heavy metal contamination, we recorded several submerged macrophyte species with heterogeneous spatial distribution patterns. Whereas Potamogeton pectinatus L. dominates in the eastern part of the lake, near industrial point sources, both Myriophyllum spicatum L. and Potamogeton lucens L. form extended patches in the western part of the lake. The shallow, littoral areas near villages are dominated by Ranunculus trichophyllus Chaix in Villars and Ceratophyllum demersum L. The west-east gradient in nutrient and heavy metal concentrations in waters and sediments are reflected by the spatial distribution of submersed species. While the heavy metal concentrations of the water body vary considerably in different seasons, the contents in submersed macrophytes integrate seasonal variations of longer time periods. Spatial distribution and tissue accumulation of littoral macrophyte species reflect the environmental conditions at respective sites such as heavy metal contents in water and sediment.     

Heavy metals in marine nematodes: Uptake,tissue distribution and loss of copper and zinc

The uptake and loss of copper and zinc was studied in two species of marine nematode from a non-polluted site and in one species from a polluted site. Copper and zinc concentrations were measured during and after accumulation from seawater in six different tissues of the nematodes. Most of the metal taken up was found to be associated with the cuticle and with a group of tissues including the hypodermis. The importance of the different tissues in heavy metal metabolism by the nematodes is discussed together with the possible routes of uptake of the metals into the animals.     

Metal levels in seston and marine fish flesh near industrial and metropolitan centres in South Australia.

Port Pirie is the site of the largest lead smelter in the world, depositing 250 t of zinc, and 100 t of lead annually into Spencer Gulf. Barker Inlet is adjacent to metropolitan Adelaide, and receives unknown quantities of urban and industrial discharges. Both areas are sites of major commercial and recreational fisheries, contained within delicately balanced marine wetland ecosystems, comprising large areas of mangrove and seagrass habitats. Aldrichetta forsteri and Sillago schomburgkii are major species within these fisheries and as estuarine-dependent species were chosen for this study as indicator species for the detection and monitoring of pollutant impacts in the nearshore marine ecosystems of South Australia. Seston sediment collectors were deployed at each site and analysed seasonally for the presence of cadmium, lead and copper. Flesh samples from A. forsteri and S. schomburgkii were examined seasonally for the presence of cadmium, lead and copper and the results correlated with levels found in the seston sediment at each site. Metal concentrations were also correlated with a biomarker of genotoxicity measured in the same animals (micronuclei in erythrocytes) that were reported previously. Seston levels of cadmium, lead and copper were highest at Port Pirie, followed by Barker Inlet and were lowest at Wills Creek, with cadmium undetectable at the latter site. Metals in seston varied considerably with season, with generally higher levels in winter samples. In fish flesh, metal levels followed broadly similar trends as for seston. Spearman rank correlations between metals in seston and in flesh were strongly positive. There was also a significant correlation between flesh concentrations of each metal and the frequency of micronuclei in erythrocytes. This study has shown that seston concentration of pollutant metals are high in areas of industrial activity, and that these levels are also reflected in metal content of fish flesh. Mean flesh levels of cadmium and copper did not exceed Australian health based maximum permitted levels of fish for human consumption, whereas flesh levels of lead in fish from Port Pirie and Barker Inlet exceeded these standards in each of the seasons monitored. This may represent a significant dietary source of lead in humans, especially at Port Pirie where human lead exposure from terrestrial sources is important. There may also be the potential for accumulation of metals in residents of metropolitan Adelaide whose diets are high in fish (and/or crustaceans), particularly estuarine-dependent species, such as A. forsteri and S. schomburgkii. The study also showed that a non-specific biomarker of genotoxicity (micronuclei in erythrocytes) is potentially useful as a monitoring technique in fish species to evaluate their exposure and genotoxic responses to pollutants in South Australian waters. These data represent a snapshot of the current situation in this area and may act as background levels against which future improvements or decrements in water quality may be compared.