Seagrass Posidonia Oceanica Research Articles

Adaptive responses along a depth and a latitudinal gradient in the endemic seagrass Posidonia oceanica.

Seagrass meadows provide important ecosystem services and are critical for the survival of the associated invertebrate community. However, they are threatened worldwide by human-driven environmental change. Understanding the seagrasses' potential for adaptation is critical to assess not only their ability to persist under future global change scenarios, but also to assess the persistence of the associated communities. Here we screened a wild population of Posidonia oceanica, an endemic long-lived seagrass in the Mediterranean Sea, for genes that may be target of environmental selection, using an outlier and a genome-wide transcriptome analysis. We identified loci where polymorphism or differential expression was associated with either a latitudinal or a bathymetric gradient, as well as with both gradients in an effort to identify loci associated with temperature and light. We found the candidate genes underlying growth and immunity to be divergent between populations adapted to different latitudes and/or depths, providing evidence for local adaptation. Furthermore, we found evidence of reduced gene flow among populations including adjacent populations. Reduced gene flow, combined with low sexual recombination, small effective population size, and long generation time of P. oceanica raises concerns for the long-term persistence of this species, especially in the face of rapid environmental change driven by human activities.

Molecular level responses to chronic versus pulse nutrient loading in the seagrass Posidonia oceanica undergoing herbivore pressure.

Seagrasses are key marine foundation species, currently declining due to the compounded action of global and regional anthropogenic stressors. Eutrophication has been associated with seagrass decline, while grazing has been traditionally considered to be a natural disturbance with a relatively low impact on seagrasses. In the recent years, this assumption has been revisited. Here, by means of a 16-month field-experiment, we investigated the molecular mechanisms driving the long-term response of Posidonia oceanica to the combination of nutrient enrichment, either as a chronic (press) or pulse disturbance, and herbivory. Changes in expression levels of 19 target genes involved in key steps of photosynthesis, nutrient assimilation, chlorophyll metabolism, oxidative-stress response and plant defense were evaluated through reverse transcription-quantitative polymerase chain reaction (RT-qPCR). High herbivore pressure affected the molecular response of P. oceanica more dramatically than did enhanced nutrient levels, altering the expression of genes involved in plant tolerance and resistance traits, such as photosynthesis and defense mechanisms. Genes involved in carbon fixation and N assimilation modulated the response of plants to high nutrient levels. Availability of resources seems to modify P. oceanica response to herbivory, where the upregulation of a nitrate transporter gene was accompanied by the decline in the expression of nitrate reductase in the leaves, suggesting a change in plant-nutrient allocation strategy. Finally, press and pulse fertilizations altered nitrate uptake and reduction-related genes in opposite ways, suggesting that taking into account the temporal regime of nutrient loading is important to assess the physiological response of seagrasses to eutrophication.

Comparative assessment of trace element accumulation and bioindication in seagrasses Posidonia oceanica, Cymodocea nodosa and Halophila stipulacea

Accumulation and bioindication of trace elements were compared in three seagrasses growing in the Mediterranean Sea: Posidonia oceanica, Cymodocea nodosa and Halophila stipulacea. The levels of the elements As, Cd, Cr, Cu, Hg, Mn, Ni, Pb and Zn were investigated in water, sediments, and roots, rhizomes and leaves of seagrasses. Results showed that seagrasses can accumulate comparable levels of trace elements, but P. oceanica and C. nodosa showed higher mean values of element accumulation. Moreover, P. oceanica and C. nodosa may accumulate high element concentrations in their leaves, whereas in H. stipulacea restricted with the bulk of trace elements in roots and rhizomes. Seagrasses reflected to a different degree the levels of several trace elements in sediments, especially P. oceanica and C. nodosa, whose use as bioindicators is recommended. The future step for an effective use of seagrasses as bioindicators of marine pollution is to set up biomonitoring networks on a large scale.

Toxigenic effects of two benthic diatoms upon grazing activity of the sea urchin: morphological, metabolomic and de novo transcriptomic analysis

Diatoms are unicellular algae playing a key role as photosynthetic organisms in the world’s ocean food webs. The chemical ecology of planktonic diatoms is well documented, but few studies have reported on the effects of benthic diatoms on their consumers, also due to difficulties in the collection, quantification and massive culturing of benthic species. Here for the first time we investigate the effects of feeding on two abundantly occurring benthic diatoms, Nanofrustulum shiloi and Cylindrotheca closterium, isolated from the leaves of the seagrass Posidonia oceanica, on the sea urchin Paracentrotus lividus. Adult P. lividus were fed for one month on diets of either one of the two diatoms and on the green alga Ulva rigida, used as a feeding control. By combining morphological, metabolomic and de novo transcriptomic approaches, we demonstrate toxigenic effect on embryos generated by females fed with these benthic diatoms. Furthermore, chemical analysis reveal the presence of polyunsaturated aldehydes only for N. shiloi, and a high production of other oxylipins (cytotoxic compounds on their grazers and on cancer cell lines) for both diatoms, including some additional peaks not correlated to the canonic oxylipins commonly observed in planktonic diatoms. These findings open new perspectives in the study of diatom secondary metabolites influencing their grazers.

Modelling the cross-shore beach profiles of sandy beaches with Posidonia oceanica using artificial neural networks: Murcia (Spain) as study case

This paper presents a model of the cross-shore beach profile taking into account the presence of the seagrass Posidonia oceanica whose ultimate objective is to reduce the volume of sand used in beach nourishment. The methodology describes the training, validation, testing and application of models of artificial neural networks (ANN) for computing the cross-shore beach profile of sandy beaches in the province of Murcia (Spain). Eighty ANN models were generated by modifying both the input variables and the number of neurons in the hidden layer. The input variables consist of wave and sediment data and data concerning the Posidonia oceanica. To select and evaluate the performance of the optimal model, the following parameters were used: R2, absolute error, mean absolute percentage error and percentage relative error. The results show a mean absolute error of 0.22 m (0.21 m in training and 0.28 m in test), representing an improvement of 85.1% compared to models that do not use the Posidonia oceanica and 69.8% against those that consider it. Although the ANN was developed for beaches with P.oceanica, it could be used in areas with other seagrass able to reduce wave energy and consolidate the sand such as Syringodium filiforme, Thaalassia testudinum, Laminaria hyperborea, Halodule wrightii and Zostera marina.

Seagrass Posidonia oceanica (L.) Delile as a marine biomarker: a metabolomic and toxicological analysis

AbstractA human‐made environmental disaster due to the shipwrecked of Costa Concordia cruise vessel on the Tuscan Island of Giglio (Italy) coast and the possible pollutants release has been feared, so requiring the activation of removal operations and the monitoring of the marine environment. In the present study, the seagrass Posidonia oceanica (L.) Delile was used as a bioindicator for the impact of the Costa Concordia accident on the marine and coastal habitat. Different P. oceanica samples were collected in the shipwrecked site under different light conditions. Using high‐performance thin‐layer chromatography, metabolic analysis of the samples was carried out in order to highlight possible changes in the secondary metabolism due to the permanent shading and the presence of pollutant traces. Moreover, sample mutagenicity, as a consequence of the possible absorption of environmental toxicants leaked by the wreck, was assessed by the Ames test. The results highlighted the permanence of the Concordia‐induced alteration in the plant secondary metabolites. However, absorption of chemical pollutants and carcinogens was not reported; this point was confirmed by the lack of mutagenic effects found for the samples tested. Our results clearly evidence that the environmental impact of Costa Concordia wreck and removal operations on P. oceanica was mainly due to the lack of light in the marine habitat. Present methodological approach, which combines metabolomic and genetic ecotoxicological analysis, could represent a suitable strategy to evaluate the impact of human disasters on the ecosystem and to monitor the environmental changes.

Effect of broadband chirp signal on the sonic behavior of the /kwa/ fishes inhabiting Posidonia oceanica seagrass meadow

Early experiment to study acoustics of Posidonia oceanica seagrasses (USTICA99) transmitted acoustic chirp signals (0.2-16 kHz, 15.8 s) every minute during 3 days over a meadow. Receiving hydrophones recorded vocalizations from unknown fish inhabitants, which sound like /kwa/. Here, we address the impact of our measurements on this fish population. The authors’ ears analyzed the recordings to identify all fish vocalizations and attempt to recognize /kwa/ individuals based on timbre. A comparative analysis of the /kwa/ sound production within time intervals between and during chirp transmission was made to understand if and how the sonic behavior is affected. As in few similar studies for other anthropogenic noise sources on a limited number of species, there was an observable effect. The major part of the vocalization patterns that were identified within the chirp time interval started near the onset of the frequency sweep, which first spans the range of /kwa/ sound production (0.4-2 kHz). The number of single vocalizations per unit time during that period was close to that during the no-chirp time interval while during higher swept frequencies was markedly smaller. This suggests the fish detection range may extend toward ultrasound to avoid dolphin predators. Quantitative results will be presented.

Ultrasonic Transmission Behavior in Posidonia oceanica Rhizomes

The roots and rhizomes of seagrass can form a complicated multi-phase layer within sediments. Gas channels in the rhizomes, known as aerenchyma, give rise to a complicated acoustic response. A model for acoustic propagation through such rhizomes would be beneficial for acoustic remote sensing communities. Ex situ measurements of the ultrasonic sound speed through the dense woody structure of the rhizomes of the seagrass Posidonia oceanica are presented. Ultrasonic (1–5 MHz) time-of-flight measurements were made with the rhizomes segments aligned both lengthwise and crosswise to the propagation direction of the acoustic pulse. The acoustic behaviors of plants collected from different locations in the Mediterranean are compared to each other and to the behaviors of the associated leaf blade tissues. Two measurements were also made of rhizomes before and after degassing the aerenchyma, to quantify the effects of entrained gasses on acoustic behavior. [Work supported by ONR and ONR Global.]

ALEX index enables detection of alien macroalgae invasions across habitats within a marine protected area

A modified version of the ALien Biotic IndEX (ALEX) has been recently proposed to evaluate biological invasions in macroalgal assemblages. ALEX was applied in a Marine Protected Area where a recreational-fishing port is present testing the following hypotheses: ALEX increases with the distance from the port, it changes between the two directions off the port and it changes among three different habitats: Cystoseira beds, algal turf and dead matte of the seagrass Posidonia oceanica. A total of 78 native macroalgal taxa and 4 introduced species were found, the Chlorophyta Caulerpa cylindracea and the Rhodophyta Apoglossum gregarium, Acrothamnion preissii and Womersleyella setacea. All study sites were in high quality status highlighting that the assemblages investigated were at an early stage of NIS invasion. However, ALEX detected different values among conditions and habitats within the MPA, suggesting a local dynamics of NIS spread and different resistance to invasion of the investigated habitats.

Comparative analysis of trace element accumulation in seagrasses Posidonia oceanica and Cymodocea nodosa: Biomonitoring applications and legislative issues

This study aimed to compare the bioaccumulation patterns and translocation of trace elements (As, Cd, Cr, Cu, Hg, Ni, Pb and Zn) from the environment in the seagrasses Posidonia oceanica and Cymodocea nodosa. Results showed that P. oceanica has a higher capacity of accumulation. P. oceanica and C. nodosa accumulate mainly in roots and leaves, the main organs acting as potential bioindicators. No significant correlation was found between water and both seagrasses. In turn, P. oceanica and C. nodosa were correlated, to a different extent, with As, Cd, Cu, Ni and Zn in sediments. This study showed also that current European regulations do not provide an exhaustive set of legal concentration limits of trace elements in marine water and sediments. Seagrasses P. oceanica and C. nodosa can act as effective bioindicators of trace elements only if quality limits are set for the most toxic elements present in marine ecosystems.

Exchange Dynamics Reveal Significant Accumulation of Dimethylated Sulfur by Mediterranean Benthic Communities

One fifth of Mediterranean waters can be classified as shelf – much higher than the global average. Consequently, the shelf / coastal zone plays a proportionally greater biogeochemical role than in the major oceans, including the support of a wide range of range of endemic or culturally important species and ecosystems. However, despite their known importance in regulating ecosystem function and the marine sulphur cycle, our understanding of the dynamics of dimethylated sulphur compounds such as dimethylsulphide (DMS) and dimethylsulphoniopropionate (DMSP) in Mediterranean benthic habitats is limited. Here, a community-level approach was adopted to quantify DMS and DMSP dynamics in Mediterranean ecosystems including seagrass (Posidonia oceanica) meadows, coralligene (an algal carbonate reef found along the Mediterranean shelf) and macroalgal stands. It was found that P. oceanica and coralligene are likely to act as significant benthic stocks of DMSP in the coastal / shelf environment. ‘Hotspots’ of water column DMS and DMSP processing were observed where net benthic production was high (e.g. P. oceanica meadows), demonstrating that benthic communities are able to modify DMS biogeochemistry in the overlying water column. High variability between, and within, habitat types illustrates the importance of ecosystem structure and light availability in determining benthic DMS and DMSP accumulation, and highlights a previously under-appreciated complexity in benthic dimethylated sulphur dynamics.

Fungal root symbionts of the seagrass Posidonia oceanica in the central Adriatic Sea revealed by microscopy, culturing and 454-pyrosequencing

Fungal root symbionts of the seagrass Posidonia oceanica in the central Adriatic Sea revealed by microscopy, culturing and 454-pyrosequencing

Experimental evidence of warming-induced flowering in the Mediterranean seagrass Posidonia oceanica

Sexual reproduction in predominantly clonal marine plants increases recombination favoring adaptation and enhancing species resilience to environmental change. Recent studies of the seagrass Posidonia oceanica suggest that flowering intensity and frequency are correlated with warming events associated with global climate change, but these studies have been observational without direct experimental support. We used controlled experiments to test if warming can effectively trigger flowering in P. oceanica. A six-week heat wave was simulated under laboratory mesocosm conditions. Heating negatively impacted leaf growth rates, but by the end of the experiment most of the heated plants flowered, while controls plants did not. Heated and control plants were not genetically distinct and flowering intensity was significantly correlated with allelic richness and heterozygosity. This is an unprecedented finding, showing that the response of seagrasses to warming will be more plastic, more complex and potentially more resilient than previously imagined.

Effects of in situ CO2 enrichment on epibiont settlement on artificial substrata within a Posidonia oceanica meadow

Alterations to colonization or early post-settlement stages may cause the reorganization of communities under future ocean acidification conditions. Yet, this hypothesis has been little tested by in situ pH manipulation. A Free Ocean Carbon Dioxide Enrichment (FOCE) system was used to lower pH by a ~0.3unit offset within a partially enclosed portion (1.7m3) of a Posidonia oceanica seagrass meadow (11m depth) between 21 June and 3 November 2014. Epibiont colonization and early post settlement stages were assessed within the FOCE setup, as part of the larger community-level study, to better understand the outcome for a multispecies assemblage and the ecological processes that result in reported community shifts under altered carbonate chemistry. Two types of artificial collectors (tiles and scourers) were placed within three treatments: a pH-manipulated enclosure, an un-manipulated control enclosure, and an open plot in the ambient meadow. Tiles and scourers were collected after one to four months. Additionally, to see whether the outcome differed for communities in a later successional stage, previously settled scourer-collectors were also placed in the same three treatments. Enclosures acted to reduce settlement and migrant colonization. Scourers deployed for one to four months within the open-plot contained a community assemblage that could be distinguished from the assemblages within the enclosures. However, a comparison of enclosure assemblages on tiles showed evidence of a pH effect. There was lowered coverage of crustose coralline algae and fewer calcareous tube-forming polychaetes (Spirorbis sp. and Spirobranchus sp.) on tiles placed in the pH-manipulated enclosure compared to the un-manipulated enclosure. For assemblages in scourer collectors, shared and common taxa, in all treatments, were invertebrate polychaetes Psamathe fusca, Sphaerosyllis sp., Chrysopetalum sp., arthropods Harpacticoida, and Amphipoda, and the juvenile bivalve Lyonsia sp. Similar organism composition and abundance, as well as taxonomic richness and evenness, were found in scourers from both enclosures. Pre-settled scourers contained greater numbers of individuals and more calcified members, but the assemblage, as well as the growth rate of a juvenile bivalve Lyonsia sp., appeared unaffected by a two-month exposure to lowered pH and calcium carbonate saturation state. Results from this case study support the hypothesis that early stages of specific calcifiers (crustose coralline algae and calcareous tube-forming polychaetes) are sensitive to near future ocean acidification conditions yet suggest that negative effects on sessile micro-invertebrate assemblages will be minimal.

Ecological typologies of large areas. An application in the Mediterranean Sea

One approach to identifying and mapping the state of marine biophysical conditions is the identification of large-scale ecological units for which conditions are similar and the strategies of management may also be similar. Because biological processes are difficult to directly record over large areas, abiotic characteristics are used as surrogate parameters. In this work, the Mediterranean Sea was classified into homogeneous spatial areas based on abiotic variables. Eight parameters were selected based on salinity, sea surface temperature, photosynthetically active radiation, sea-wave heights and depth variables. The parameters were gathered in grid points of 0.5° spatial resolution in the open sea and 0.125° in coastal areas. The typologies were obtained by data mining the eight parameters throughout the Mediterranean and combining two clustering techniques: self-organizing maps and the k-means algorithm. The result is a division of the Mediterranean Sea into seven typologies. For these typologies, the classification recognizes differences in temperature, salinity and radiation. In addition, it separates coastal from deep areas. The influence of river discharges and the entrance of water from other seas are also reflected. These results are consistent with the ecological requirements of the five studied seagrasses (Posidonia oceanica, Zostera marina, Zostera noltei, Cymodocea nodosa, Halophila stipulacea), supporting the suitability of the resulting classification and the proposed methodology. The approach thus provides a tool for the sustainable management of large marine areas and the ability to address not only present threats but also future conditions, such as climate change.

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

To manage trace metal pollution it is critical to determine how much temporal trends can be attributed to local or large-scale sources. We tracked changes in metal content in the seagrass Posidonia oceanica, along the NW Mediterranean from 2003 to 2010. While Cu, Cd and Ni showed a large inter-site variation, likely due to local factors, Fe, Mn and Pb showed little local variation and synchronous interannual variability across sites, most likely due to large-scale sources. Zn showed equal importance of local and large-scale sources of variation. Temporal trends of Ni, Zn, Cd, Cu remained almost stable. In contrast, Fe, Mn and Pb slightly increased in the last decade. These trends suggest that metals like Cu, Cd, Ni can be effectively managed at local scale. Whereas, elements like Fe, Mn and Pb have an important large-scale component that needs to be managed across the frontiers of national jurisdictions.

Ecosystem functions and economic wealth: Trajectories of change in seagrass meadows

Increasing anthropogenic pressure on coastal regions, coupled with a conflicting relationship between ecosystem health and economic growth, has resulted in a worldwide deterioration of marine ecosystems and loss of ecosystem services. The seagrass Posidonia oceanica is an emblematic example, constituting extensive and highly valuable meadows whose extent largely declined in the last decades. In this paper, more than one century of history of P. oceanica meadows has been reconstructed in a NW Mediterranean region combining models and historical information. The equivalent economic value of P. oceanica ecosystem functions was evaluated according to a donor-side approach and compared with the main economic sector of the region. A loss of more than 50% of the original surface of P. oceanica meadow extent has been documented between 1850 and around 1980, followed by stabilization in the last decades. Decline of P. oceanica has often been coupled with its replacement by the more tolerant seagrass species Cymodocea nodosa, only partially compensating for the loss of P. oceanica. The loss of the value of ecosystem functions between 1861 and 2009 was computed in 1106.8 billion emergy-euros (em€), a figure greater than the value added in the same period by tourism-related activities. Protection measures undertaken in the last decades slowed down the decline of P. oceanica meadows, while no concomitant decrease of the regional economic growth occurred. This study illustrates the tradeoffs between ecosystem conservation and economy growth, underlining the importance of long-term monitoring for environmental management and preservation of the natural capital.

Using the Presence of Seagrass Posidonia oceanica to Model the Equilibrium Profile Parameter A of Sandy Beaches in Spain

ABSTRACT Aragones, L.; Lopez, I.; Villacampa, Y., and Navarro-Gonzalez, F.J., 2017. Using the presence of seagrass Posidonia oceanica to model the equilibrium profile parameter A of sandy beaches in Spain. The study of equilibrium profile is a fundamental concept in beach morphodynamics and necessary in the design of nourishment. For this reason, it is important to introduce new modelling methodologies that are capable of analysing its behaviour. The aim of the research was to generate mathematical models for obtaining parameter A of the potential function, which describes the equilibrium beach profile on the coast of Valencia and Alicante, using only those variables that are easy to obtain. The presence of Posidonia oceanica in the study area was also taken into account, and on the basis of that, the energy reduction coefficient (Kv) was included as an independent variable in the models. To select the optimal model, the volume error, root mean-square error, mean error, and relative error percentage have ...

Preservation protocol for dimethylsulfoniopropionate and dimethylsulfoxide analysis in plant material of the Mediterranean seagrass Posidonia oceanica, and re-evaluation of dimethylsulfoniopropionate leaf content

We tested three treatments to preserve Posidonia oceanica leaves for the analysis of dimethylsulfoniopropionate (DMSP) and dimethylsulfoxide (DMSO): oven dried at 60°C for 24h, frozen at −20°C, and frozen-in-ice and kept at −20°C. The DMSP content was analyzed by proxy as dimethylsulfide (DMS) by gas chromatography after alkaline cleavage at room-temperature. The DMSP leaf content of P. oceanica in samples that were oven dried at 60°C for 24h, then stored at room temperature decreased by 87% over 80days of storage and then remained stable for about 88 additional days compared to the control. The DMSO leaf content of P. oceanica in samples that were oven dried increased nine-fold after 198days of storage following drying compared to the control. Both the DMSP and DMSO leaf content of P. oceanica remained stable for 198days compared to the control with frozen and frozen-in-ice treatments, which we both recommend as adequate protocols to preserve P. oceanica tissues for DMS(P,O) analysis. The annual average DMSP leaf content of P. oceanica at 10m in the Bay of Calvi (Corsica, France) was 205±58μmolg−1 (fresh weight) based on samples preserved frozen, two orders of magnitude higher than the value we previously reported based on samples that were oven dried. The newly determined DMSP leaf content allows ranking P. oceanica as the highest DMSP producer reported to date among marine and inter-tidal autotrophs.

Multiple environmental descriptors to assess ecological status of sensitive habitats in the area affected by the Costa Concordia shipwreck (Giglio Island, Italy)

The aim of the study was to evaluate the effectiveness of the application of multiple environmental descriptors through an asymmetrical sampling design to detect possible impacts related to the Costa Concordia event on the coastal marine environment. The Costa Concordia shipwreck occurred on a submerged rocky reef in the north-western Mediterranean Sea and the wreck was removed 2 years later. To achieve the proposed objective two main coastal ecosystems, the seagrass Posidonia oceanica and coralligenous assemblages were studied using two ecological indices, PREI and ESCA, respectively. Both indices show a lower ecological quality in the disturbed sites compared with the control ones. Differences between the disturbed and control sites observed in both studied ecosystems would seem to indicate an increase of turbidity around the shipwreck as the most plausible cause of impact. The concurrent use of different ecological indices and asymmetrical sampling designs allowed detection of differences in ecological quality of the disturbed sites compared with the controls. This approach may represent an interesting tool to be employed in impact evaluation studies.