Seagrass Rhizomes Research Articles

Rare earth elements in the red, brown, green algae and the seagrass from Kazachya Bay (Crimea, Black Sea)

The present study is focused on the first ever quantification of rare earth elements (REE) in four mass plants of the Black Sea coast of Crimea: the brown alga Gongolaria barbata, the green alga Ulva rigida, the red alga Ceramium ciliatum, and the seagrass Zostera noltei using inductively coupled plasma mass spectrometry. The REE contents in the macrophytes were found to be one to two orders of magnitude lower than in the sediments. In the plants, three groups of REE with similar levels have been identified. The first group included the most abundant elements Sc, Y, La and Ce; the second group consisted of Pr and Nd with the intermediate contents; and the third group contained the elements with the lowest contents: Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu. The contribution of light REE (Sc, Y, La, Ce, Pr, Nd) to the total REE content in the plants was 91–96%. The highest REE levels were found in the red alga and seagrass rhizomes. Higher translocation factors of Sc, Pr, La, Ce and Tb between seagrass rhizomes and leaves were noted. In terms of the REE content decrease, the marine plants are arranged in the following order: seagrass rhizomes > red alga > brown alga > seagrass leaves > green alga. Brown algae attached to the rocky seabed are widespread in the upper sublittoral, have a long lifespan, and accumulate relatively high amounts of REE. Therefore, they can be used as effective bioindicators of REE pollution in the marine environment.

Rare Earth Elements in the Seagrass Zostera noltei and Sediments from the Black Sea Coast of Crimea

In the present work, we assessed the contents of rare earth elements (REEs), including yttrium and scandium, in rhizomes and leaves of the widespread seagrass Zostera noltei Hornemann 1832 and in the nearby sediments from the Black Sea coast. The total REE content in the sediments was found to be much higher than in Z. noltei. The order of decrease in the major REE contents in the sediments and the seagrass rhizomes was identical, except for La and Y. La was the most abundant in the sediments, and Y in the rhizomes. The contents of all REEs in rhizomes of Z. noltei were 1.5–10 times higher than in the leaves. The highest difference in the REE contents was found for the minor elements (Sm–Lu). The translocation factors for Sc and the minor elements (excluding Tb) from the sediments to the rhizomes and from the rhizomes to the leaves turned out to be pairwise equal, which indicates the similarity of the REE translocation mechanisms. Comparing our results with the literature data, it is possible to conclude that the seagrass Z. noltei does not have an advantage in the REE accumulation over marine macroalgae. At the same time, large coastal deposits of this seagrass after storms allow us to consider it as a possible source of REEs in the future.

Wrack enhancement of post-hurricane vegetation and geomorphological recovery in a coastal dune

Coastal ecosystems such as sand dunes, mangrove forests, and salt marshes provide natural storm protection for vulnerable shorelines. At the same time, storms erode and redistribute biological materials among coastal systems via wrack. Yet how such cross-ecosystem subsidies affect post-storm recovery is not well understood. Here, we report an experimental investigation into the effect of storm wrack on eco-geomorphological recovery of a coastal embryo dune in north-eastern Florida, USA, following hurricane Irma. We contrasted replicated 100-m2 wrack-removal and unmanipulated (control) plots, measuring vegetation and geomorphological responses over 21 months. Relative to controls, grass cover was reduced 4-fold where diverse storm wrack, including seagrass rhizomes, seaweed, and wood, was removed. Wrack removal was also associated with a reduction in mean elevation, which persisted until the end of the experiment when removal plots had a 14% lower mean elevation than control plots. These results suggest that subsides of wrack re-distributed from other ecosystem types (e.g. seagrasses, macroalgae, uplands): i) enhances the growth of certain dune-building grasses; and ii) boosts the geomorphological recovery of coastal dunes. Our study also indicates that the practice of post-storm beach cleaning to remove wrack–a practice widespread outside of protected areas–may undermine the resilience of coastal dunes and their services.

Seasonal change of multifrequency backscatter in three Baltic Sea habitats

This study investigated the seasonality of acoustic backscatter intensities, exploring three habitats in the southwestern Baltic Sea: 1) a mussel-covered reef, 2) coarse sand and gravel, and 3) seagrass meadows. Backscatter information of different, partly calibrated frequencies (200, 400, 550, and 700 kHz) was collected in three seasons (May, August, and October). The acoustic data were supported by point samples and video profiles for grain size and benthic community analysis. Angular response curves helped to quantify the seasonal backscatter response of the different frequencies. The multifrequency and multiseasonal backscatter maps distinguish the three habitats and reveal variable seasonal differences in acoustic backscatter, but not all changes in the benthic community can be recognized in the acoustic data. 1) The high-backscatter response of the mussel-covered reef shows little seasonal differences and was frequency independent. 2) The ecologically valuable coarse sand and gravel areas show small-scale seasonal alterations in the sediment composition and morphology, mainly caused by changes in local hydrodynamics. Higher frequencies were found best suited to identify coarse sand and gravel. 3) Seagrass meadows seasonality is dominated by growth of seagrass blades, increasing the backscatter response compared to bare sand. The use of multiple frequencies is beneficial as the low frequency is sensitive to changes in the shallow subsurface and benthic features such as seagrass rhizomes, while the higher frequency highlights changes related to coarser sediment.

Resolving Chemical Gradients Around Seagrass Roots—A Review of Available Methods

Steep geochemical gradients surround roots and rhizomes of seagrass and protect the plants against the harsh conditions in anoxic sediment, while enabling nutrient uptake. Imbalance of these gradients, due to e.g., low plant performance and/or changing sediment biogeochemical conditions, can lead to plant stress and large-scale seagrass meadow die-off. Therefore, measuring and mapping the dynamic gradients around seagrass roots and rhizomes is needed to better understand plant responses to human impact and environmental changes. Historically, electrochemical microsensors enabled the first measurements of important chemical species like O2, pH or H2S with high sensitivity and spatial resolution giving important insights to the seagrass rhizosphere microenvironment; however, such measurements only provide information in one dimension at a time. In recent years, the use of reversible optical sensors (in the form of planar optodes or nanoparticles) and accumulative gel sampling methods like Diffusive Gradients in Thin films (DGT) have extended the array of analytes and allowed 2-D mapping of chemical gradients in the seagrass rhizosphere. Here, we review and discuss such microscale methods from a practical angle, discuss their application in seagrass research, and point toward novel experimental approaches to study the (bio)geochemistry around seagrass roots and rhizomes using a combination of available techniques, both in the lab andin situ.

Recolonization Dynamics of Warm Affinity Halophila nipponica in a Temperate Seagrass Meadow With Zostera marina

Because Halophila nipponica has only recently been reported in the temperate coastal waters of the northwestern Pacific, the recolonization dynamics of this species have not yet been investigated in temperate seagrass meadows. H. nipponica typically occurs in monoculture or in mixed meadows with Zostera marina, the most abundant seagrass species in this region. In this study, small gaps (0.5 × 0.5 m) were created in a mixed seagrass meadow of H. nipponica and Z. marina at Namhae Island on the southern coast of Korea to compare recolonization dynamics of the two species. Eight gaps were created by carefully removing all seagrass tissues to minimize sediment loss in September 2010. Four gaps were marked using only a steel stake at each corner (un-bordered gaps), while the margins of the other four gaps were blocked to a sediment depth of approximately 20 cm using stainless steel blades to prevent penetration of seagrass rhizomes (bordered gaps) to examine the relative contribution of sexual and asexual reproduction to recolonization. Shoot densities of Z. marina and H. nipponica were measured in the gaps and in natural reference plots to estimate recolonization rates. In the bordered gaps, a few Z. marina seedlings and H. nipponica fragments were observed during winter, but no shoots of either species survived to the end of experiment. In the un-bordered gaps, the density of H. nipponica increased rapidly, with approximately 60% recovery after 2 months and reaching 85% after 10 months through only asexual reproduction via clonal growth. By contrast, recolonization of Z. marina was much slower than that of H. nipponica, with only approximately 25% recovery after 10 months through vegetative growth and recruitment of a few seedlings. Asexual reproduction was the principle reproductive mechanism for the recolonization of both Z. marina and H. nipponica at the study site. According to our results, gaps created naturally in mixed seagrass meadows by high water temperatures or catastrophic events such as typhoons may be primarily recolonized by H. nipponica rather than Z. marina, leading to a change in the seagrass ecosystem structure in the northwestern Pacific under ongoing climate change.

First Field-Based Evidence That the Seagrass-Lucinid Mutualism Can Mitigate Sulfide Stress in Seagrasses

Seagrass meadows form vital ecological components of coastal zones worldwide, but are rapidly declining. Large-scale seagrass diebacks have been related to accumulation of toxic sulfide in the sediment, a phenomenon predicted to occur more frequently in the near future due to ongoing global warming and increasing organic loading of coastal systems worldwide. Recently, a facultative mutualism between seagrasses and lucinid bivalves with endosymbiotic sulfide-consuming gill bacteria was discovered that may prevent toxic sulfide accumulation in seagrass sediments. Yet, direct field-based evidence for the importance of this mutualism in alleviating sulfide stress in seagrasses is currently lacking, as well as how its role may change when sediment sulfide levels increase due to environmental change. Here, we investigated the sulfide detoxification function of this seagrass-lucinid mutualism and its resilience to organic-loading induced sulfide stress in a temperate lagoon system (Thau lagoon, France), using a correlative field survey and a full factorial field experiment. The field survey revealed a strong positive correlation between seagrass above-ground biomass and lucinid densities, and pore water sulfide concentrations close to zero at all sites. Furthermore, the field experiment revealed that addition of organic matter (starch mixed with sucrose) increased sedimentary sulfide intrusion into seagrass (Zostera noltei) leaves (a proxy for sulfide stress), while experimentally enhanced lucinid densities reduced sulfide intrusion, regardless of addition of organic matter. Moreover, addition of organic matter reduced seagrass rhizome biomass and increased pore water sulfide levels, lucinid tissue sulfur content, lucinid condition (expressed as flesh/shell dry weight ratio), and total lucinid biomass, while enhancement of lucinid densities reduced lucinid condition. These results provide the first field-based evidence that lucinid bivalves and their sulfide-oxidizing gill symbionts mitigate sulfide stress in seagrasses, and suggests that the dependence of seagrass on this seagrass-lucinid mutualism will increase under conditions of enhanced sediment sulfide production, as predicted for the near future. Therefore, we suggest that awareness of the ecological importance of the seagrass-lucinid mutualism may be instrumental for designing new measures for improving long-term restoration success and seagrass resilience to global change.

First record of the seagrass-boring shipworm Zachsia sp. (Bivalve: Teredinidae) in natural and transplanted Enhalus acoroides (Hydrocharitaceae) rhizomes in tropical Southwest Pacific

Seagrass ecosystems are under threat worldwide. Seagrass transplantation is one restoration approach which is has been tried with uneven success. While transplantation methods and oceanographic parameters have been investigated in attempts to understand the factors affecting transplant survival rate and seagrass transplantation success, little attention has been paid to the possible impact of pests. We observed borer molluscs in a seagrass Enhalus acoroides both from natural bed and transplant area. This is thought to be the first record from Indonesian waters of these bivalve molluscs of the genus Zachsia, family Teredinidae, the only mollusc genus known to bore into seagrass rhizomes. In a further eleven E. acoroides shoots (average length 10.5cm) we found between one and four calcareous burrows 2mm to 5mm in diameter inside the rhizome. Further research is required to determine the species present and its distribution in Indonesian waters as well as the true ecological impact of Zachsia sp. on seagrasses.

Fossil Sirenia of the West Atlantic and Caribbean region. XII. Stegosiren macei, gen. et sp. nov.

ABSTRACTStegosiren macei, a new genus and species of halitheriine dugongid from the mid-Oligocene of South Carolina, U.S.A. (Ashley and Chandler Bridge formations, late Rupelian–late Chattian), represents a stage of halitheriine evolution more derived than that of the Old World early Oligocene Eosiren imenti and Halitherium schinzii, but slightly less derived than the West Atlantic late Oligocene Metaxytherium albifontanum. It is more comparable in stage of evolution to its early Oligocene contemporaries Caribosiren turneri and Priscosiren atlantica and may be a sister taxon of these two. It is distinguished autapomorphically from all other sirenians by a notably broadened frontal roof and a thickened anterior tip of the frontal, which formed a butt joint with the premaxilla. Analogous (independently evolved) joints in several other sirenians (principally dugongines) are correlated with enlarged upper tusks thought to be used for excavating seagrass rhizomes. This suggests that large tusks also may have been present (although not preserved) in Stegosiren, which is only the second halitheriine in which such a feature has been observed. Stegosiren macei brings to at least seven the number of potentially sympatric sirenian species lineages known from the West Atlantic-Caribbean Oligocene (six or more from South Carolina alone). This extraordinary sirenian diversity, unmatched elsewhere in the world, poses problems for ecomorphology and feeding-niche partitioning.

HEPATOPROTECTIVE EFFECT OF 50% ETHANOL EXTRACT OF SEAGRASS RHIZOME (CYMODOCEA ROTUNDATA) AGAINST LIVER TISSUES IN PARACETAMOL-INDUCED RATS

Objective: This study aimed to determine the hepatoprotective effect of 50% ethanol extract of seagrass rhizome in terms of serum glutamicoxaloacetic transaminase (SGOT) and serum glutamic pyruvic transaminase (SGPT) activities in paracetamol-induced rat plasma.Methods: This study included 28 male, white rats randomly divided into seven groups. Groups I and II represented the normal control and controlgroups, respectively, administered with 280 mg/kg BW of rhizome extract. Group III represented the negative control group induced by a suspensionof paracetamol (2g/kg BW). Group IV represented a positive control group administered with Hepa-Q® at a dosage of 150 mg/kg BW. Groups V, VI,and VII were administered with seagrass rhizome extract at doses of 140, 280, and 560 mg/kg BW, respectively, before paracetamol induction. Thetest material was orally administered for 17 days. On days 12–17, the rats were induced with paracetamol through the same route. On day 18, bloodsampling was performed followed by SGOT and SGPT plasma measurements.Results: Our results revealed that seagrass rhizome extracts could significantly decrease SGPT and SGOT levels in paracetamol-induced rats (p<0.05)compared with those in the negative control group.Conclusion: Thus, seagrass rhizome extracts possess the potential for development as a hepatoprotective agent.

The occurrence of boring bivalve (Genus: Zachsia), in a tropical seagrass meadow in Gaya Island (Sabah, Malaysia) and its possible ecological implications


 Shipworms (family Teredinidae) are specialized bivalves that bore into the submerged wooden structures and mangrove trees, except genus Zachsia which is associated with seagrass rhizome. However, only one species has been described, located in Russian, Korean and Japanese waters and associated only with genera Phyllospadix and Zostera. Potentially wider distributions and even new species within this group have not been reported from another bioregion. Given the potential impacts on seagrass health, it is important to ascertain if the distribution of Zachsia extends across other climatic regions and seagrass species. In response, a study was conducted in a seagrass meadow at Gaya Island (Sabah, Malaysia). A total of 900 seagrass shoots were randomly excavated from a mixed seagrass bed of Enhalus acoroides, Cymodocea rotundata and C. serrulata. It was found that Zachsia sp. was present within the rhizomes of E. acoroides and C. rotundata, with an occupancy of around 12% occupancy (n=100) and 1% (n=400), respectively. A post-mortem examination indicated that the bivalve appeared to have ingested most of the rhizome’s internal tissues, leaving behind a calcareous hollow tube. Furthermore, this apparent infestation appeared to significantly reduce shoot growth by around 70% from 0.738±0.036 to 0.220±0.038 cm day-1. This finding may be significant, as it suggests, for the first time, that the rhizome parasitism is another possible vector in controlling seagrass growth and mortality. Further investigations are required to determine if this boring bivalve is indeed a new species, its distribution in other tropical areas and its role in the ecosystem.

An early Miocene dugongine (Sirenia: Dugongidae) from Panama

ABSTRACTHerein, we describe a new early Miocene dugongine from marine deposits of the Culebra Cut (Gaillard Cut) of the Panama Canal. The new taxon, Culebratherium alemani, gen. et sp. nov., represents one of the few records of late Aquitanian–early Burdigalian sirenians and the oldest sirenian from Central America. A phylogenetic analysis places Culebratherium in a clade with Dioplotherium cf. D. allisoni (Miocene of Brazil), Dioplotherium allisoni (Miocene of Baja California Sur, Mexico, and California, U.S.A.), and Dioplotherium sp. (Pliocene of Yucatan, Mexico). Similar to these taxa, Culebratherium is characterized by the presence of large incisor tusks, a premaxillary symphysis without a boss, a premaxilla-frontal suture forming a butt joint, and a moderately downturned rostrum. In addition, Culebratherium exhibits prominent occipital-cervical attachment sites for enlarged neck musculature. These features taken together are interpreted as adaptations for uprooting large, deeply buried seagrass rhizomes. Other dugongines with similar, yet convergent, dental and facial adaptations are known from earlier or coeval deposits in Puerto Rico, Florida, South Carolina, California, Baja California Sur, Brazil, and India and were constituents of sympatric paleocommunities of sirenians. Only fragmentary evidence of a second smaller and unidentifiable sirenian species is known from the Culebra Formation, but future discoveries may reveal a similar sympatric paleocommunity during the early Miocene of Panama. Finally, we used the results of the phylogenetic analysis to propose the new clade Pan-Sirenia as the most inclusive group consisting of stem and crown groups and redefine the Sirenia, Dugongidae, and Dugonginae clades.

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.]

A functional-structural model of ephemeral seagrass growth influenced by environment.

Ephemeral seagrasses that respond rapidly to environmental changes are important marine habitats. However, they are under threat due to human activity and are logistically difficult and expensive to study. This study aimed to develop a new functional-structural environmentally dependent model of ephemeral seagrass, able to integrate our understanding of ephemeral seagrass growth dynamics and assess options for potential management interventions, such as seagrass transplantation. A functional-structural plant model was developed in which growth and senescence rates are mechanistically linked to environmental variables. The model was parameterized and validated for a population of Halophila stipulacea in the Persian Gulf. There was a good match between empirical and simulated results for the number of apices, net rhizome length or net number of internodes using a 330 d simulation. Simulated data were more variable than empirical data. Simulated structural patterns of seagrass rhizome growth qualitatively matched empirical observations. This new model successfully simulates the environmentally dependent growth and senescence rates of our case-study ephemeral seagrass species. It produces numerical and visual outputs that help synthesize our understanding of how the influence of environmental variables on plant functional processes affects overall growth patterns. The model can also be used to assess the potential outcomes of management interventions like seagrass transplantation, thus providing a useful management tool. It is freely available and easily adapted for new species and locations, although validation with more species and environments is required.

Niche partitioning of intertidal seagrasses: evidence of the influence of substrate temperature.

The influence of soil temperature on rhizome depths of four intertidal seagrass species was investigated in central Queensland, Australia. We postulated that certain intertidal seagrass species are soil temperature-sensitive and vertically stratify rhizome depths. Below-ground vertical stratification of intertidal seagrass rhizome depths was analysed based upon microclimate (soil temperature) and microhabitat (soil type). Soil temperature profiles exhibited heat transfer from surface layers to depth that varied by microhabitat, with vertical stratification of rhizome depths between species. Halodule uninervis rhizomes maintain a narrow median soil temperature envelope; compensating for high surface temperatures by occupying deeper, cooler soil substrates. Halophila decipiens, Halophila ovalis and Zostera muelleri rhizomes are shallow-rooted and exposed to fluctuating temperatures, with broader median temperature envelopes. Halodule uninervis appears to be a niche specialist, with the two Halophila species considered as generalist niche usage species. The implications of niche use based upon soil temperature profiles and rhizome rooting depths are discussed in the context of species' thermal tolerances and below-ground biomass O2 demand associated with respiration and maintenance of oxic microshields. This preliminary evidence suggests that soil temperature interaction with rhizome rooting depths may be a factor that influences the distribution of intertidal seagrasses.

Invisible trophic links? Quantifying the importance of non-standard food sources for key intertidal avian predators in the Eastern Atlantic

Coastal wetlands are heterogeneous systems with multiple inputs and complex interactions within local food webs. Interpreting such complexity is limited by incomplete knowledge of trophic interactions among organisms. Although widely recognized as secondary consumers and predators of intertidal macroinvertebrates, shorebirds can also consume lower-trophic-level food sources, and frequently forage in adjacent supratidal habitats. To ascertain potential trophic links between overwintering shorebirds and alternative non-standard food sources, we collected carbon and nitrogen stable isotope data of shorebirds and benthic organisms from 4 coastal wetlands along the Eastern Atlantic: Tejo Estuary, Portugal; Sidi-Moussa, Morocco; Banc d'Arguin, Mauritania; and Bijagos Archipelago, Guinea-Bissau. Using dual-isotope Bayesian mixing models, we evaluated the relative importance of intertidal benthic macroinvertebrates and 3 other potential food sources (biofilm and seagrass rhizomes from intertidal areas, and saltpan macroinvertebrates) in the diet of wintering shorebirds. Although intertidal macroinvertebrates form the main part of most shorebird species' diet, our data revealed that supratidal saltpans can contribute to >30% of the biomass ingested by several shorebird species. Seagrass rhizomes represented >10% of the diet of several species in Banc d'Arguin and in Sidi Moussa. Little stint Calidris minuta appears to consume biofilm on all 3 wetlands where they were sampled, which is the first time biofilm consumption by shorebirds has been detected along the East Atlantic Flyway. Empirical evidence for generalized consumption of alternative food sources by intertidal avian predators show the greater complexity and food web connectivity in and of intertidal habitats, and also with the surrounding habitats.

Body shrinkage due to Arctic warming reduces red knot fitness in tropical wintering range.

Reductions in body size are increasingly being identified as a response to climate warming. Here we present evidence for a case of such body shrinkage, potentially due to malnutrition in early life. We show that an avian long-distance migrant (red knot, Calidris canutus canutus), which is experiencing globally unrivaled warming rates at its high-Arctic breeding grounds, produces smaller offspring with shorter bills during summers with early snowmelt. This has consequences half a world away at their tropical wintering grounds, where shorter-billed individuals have reduced survival rates. This is associated with these molluscivores eating fewer deeply buried bivalve prey and more shallowly buried seagrass rhizomes. We suggest that seasonal migrants can experience reduced fitness at one end of their range as a result of a changing climate at the other end.

Structurally complex sea grass obstructs the sixth sense of a specialized avian molluscivore

Predators have evolved many different ways to detect hidden prey by using advanced sensory organs. However, in some environmental contexts sensory information may be obscured. The relation between sensory organs, obstruction and searching efficiency remains little explored. In this study we experimentally examined the ways in which a sensory system (‘remote detection’), which enables red knots, Calidris canutus, to detect hard objects buried in wet soft sediments, is obstructed by plants. At an important coastal nonbreeding site of this species, the Banc d'Arguin (Mauritania, West Africa), most of the intertidal foraging area is covered by sea grass. The structurally complex networks of belowground roots and rhizomes and aboveground sea grass may obstruct information on the presence of buried bivalves and thus affect searching efficiency. Under aviary conditions we offered red knots buried bivalves in either bare soft sediments or in sea grass patches and measured prey encounter rates. Red knots detected prey by direct touch in sea grass but remotely in bare sediment. Physical modelling of the pressure field build-up around a probing bill showed that within a layer of sea grass rhizomes, permeability is reduced to the extent that the pressure field no longer reveals the presence of an object. In bare sediment, where searching efficiency is constant, red knot intake rate levelled off with increasing prey density (described by a so-called type II functional response). In the sea grass beds, however, prey density increases with sea grass density and simultaneously decreases searching efficiency, which will at some point lead to a decrease in intake rate when prey densities increase (i.e. a type IV functional response). Clearly, prey detection mechanisms dictate that the combined effects of prey density and habitat complexity should be taken into account when predicting forager distributions and habitat preference.

Species specific effects of three morphologically different belowground seagrasses on sediment properties

Roots and rhizomes of seagrass play an important role in coastline zone by anchoring the substrate firmly which prevent resuspension and also controlling sediment biogeochemistry. The aim of this study was to compare the physical and chemical differences of sediments for 3 seagrass species, which have different root morphology between summer (February 2013) and the monsoon month (September 2013). Seven seagrass communities were studied and are: the mono stand of Halophila ovalis, Thalassia hemprichii, and Cymodocea rotundata, the mixed patches of H. ovalis with T. hemprichii, H. ovalis with C. rotundata, and T. hemprichii with C. rotundata and the mixed patches of 3 seagrass species. The roots of seagrasses were the main driver of differences in sediment properties; the branched, long root species, C. rotundata, showed an increasing redox potential by means of oxygen releasing from their roots. The unbranched, long root with dense root hair species, T. hemprichii, tended to cause more poorly sorted sediments. The carbon storage was also estimated and results showed a trend of higher organic carbon density was in the multispecific patches, the mono specific patches and bare sand, respectively. Season also influenced the sediment properties; high wave action in the monsoon stirred up the sediments, this led to lower organic carbon density and high redox potential. Our results suggest that the roots of seagrass species both increase and decrease sediment properties.

Detecting water quality improvement along the Catalan coast (Spain) using stress-specific biochemical seagrass indicators

Evaluating the efficacy of management actions to improve environmental quality is often difficult because there may be considerable lags before ecosystem management actions translate into measurable indicator responses. These delays make it difficult to justify often-expensive remedial actions to prevent eutrophication. Therefore, it is critical to identify reliable, rapid and sensitive indicators to detect degradation and environmental quality improvement. We evaluate the efficacy of a set of indicators based on the seagrass Posidonia oceanica to reliably and quickly detect ecosystem improvements using a 7-year (2003–2010) dataset of 10 stations along the Catalan coast (north-western Mediterranean Sea). In the Catalan region, environmental agencies have invested heavily on wastewater treatment, resulting in significant reductions (ca. 75%) in the BOD5 discharged to coastal waters from 2003 to 2010. These improvements were clearly reflected at the regional level (i.e. for all the stations averaged) in six biochemical seagrass indicators from our dataset. These indicators were directly related to eutrophication (nitrogen, δ15N, phosphorus and total non-structural carbohydrates content in rhizomes, δ34S and δ13C in seagrass rhizomes and N content in epiphytes). In contrast, seagrass structural indicators, related to seagrass abundance or meadow structure (density, cover) did not show any sign of overall recovery during the monitored period. These results confirm that biochemical seagrass indicators are the most sensitive to water quality improvements within management time-scales (7–10 years) for slow-growing species like P. oceanica. Given the budgetary restrictions under which most management actions operate, the availability of decision-support tools that function at appropriate time-scales is crucial to help managers validate the relative success of their remedial efforts. Our results indicate that low inertia, biochemical seagrass indicators fit this task, and can be a robust set of tools to include in monitoring programmes.