Dominant Seagrass Research Articles

Fish Assemblages in Subtidal Seagrass Meadows Surrounding the West Sand, South China Sea

Both beach seine (BS) and line transect-based underwater visual census (UVC) methods were applied to investigate fish assemblages of the West Sand (Xisha Islands, South China Sea) seagrass meadows and their relationship with seagrass coverage. The West Sand seagrass meadows were divided into four survey areas, two (areas A and B) to the north and two (areas C and D) to the south. The average seagrass coverages (%) in the north were significantly higher than those in the south (p < 0.05). The dominant seagrass species is Thalassia hemprichii, contributing to over 70% substrate coverage in all four areas. A total of 843 individuals from 25 fish species belonging to 22 genera, 11 families, and ten orders were recorded, with five species obtained by both BS and UVC methods. The labrids Halichoeres trimaculatus and Stethojulis strigiventer were the only two species that dominated (index of relative importance IRI > 500) in both BS and UVC methods. Fish assemblages among the four areas were significantly different (BS, p = 0.002; UVC, p = 0.002); area A was significantly different from areas B−D (p < 0.05), which was mainly driven by the variation in H. trimaculatus density. Furthermore, fish assemblages of the four areas (abundance data) revealed by both BS (r2 = 0.8455) and UVC (r2 = 0.9354) methods showed high correlation with the seagrass coverage. The majority of the individuals (>93%) recorded by BS and UVC methods were shorter than the total length at maturity (TLm), with 80.36 and 46.13% of individuals less than half the sizes of their TLm, respectively. Our results, for the first time, proved the importance of seagrass meadows at the West Sand as fish nursery grounds. The ecological roles of seagrass habitats in South China Sea merit further investigation.

Responses of Seagrass Amphibolis antarctica Roots to Nutrient Additions Along a Salinity Gradient in Shark Bay, Western Australia

Seagrass meadows in oligotrophic environments are particularly susceptible to nutrient enrichment, yet morphological and architectural seagrass root responses in these ecosystems are poorly understood. This study aimed to investigate the response of Amphibolis antarctica, one of dominant seagrass species in Shark Bay, roots to nutrient additions along a salinity gradient in the oligotrophic ecosystem of Shark Bay, Western Australia. A fully factorial nutrient additional experiment with four treatments (Control, N, P and N+P) was conducted at each of five sites along a salinity gradient (between ~38ppt in site 1 and ~50ppt in site 5) in Shark Bay across a three-year period (2012-2015). In the laboratory, the roots morphology and architecture A. antarctica were investigated using a software (WinRhizo). Then, a two-way analysis of variance (ANOVA) was performed to investigate if there was a significant change in the morphology and architecture of the roots after the nutrient inputs and along five sites with salinity gradient. There was no significant impact of nutrient addition on the root’s morphology and architecture of A. antarctica species. However, the effect of site factor with salinity gradient was significant to all morphological aspects (total root length, root surface area and root diameter) of A. antarctica roots. These findings highlight the more ecological function of A. antarctica roots being in anchoring of the plant into the seafloor rather than to absorb nutrient from the sediment.Keywords: Nutrient addition, Oligotrophic habitats, Amphibolis antarctica, Shark Bay

Biodiversity of epiphytic periphyton in the leaves of the seagrass bed of Talawaan Bajo Estuary, North Sulawesi, Indonesia

Abstract. Ogi NLIM, Herawati EY, Risjani Y, Mahmudi M. 2021. Biodiversity of epiphytic periphyton in the leaves of the seagrass bed of Talawaan Bajo Estuary, North Sulawesi, Indonesia. Biodiversitas 22: 4857-4864. This study aimed to analyze the diversity of epiphytic periphyton on the leaves of the seagrass bed of Talawaan Bajo estuary North Sulawesi Indonesia. The study was performed in three sampling points by using the line transect method with 50x50 cm2. The sampling points were located in front of the residential area, the mangrove forest, and in budo Cape. Seagrass and periphyton communities were analyzed for species density, relative frequency, diversity, evenness, and dominance index. Water quality and heavy metal Hg were also measured. The results showed that Cymodocea rotundata was the dominant seagrass based on species density and frequency distribution. Periphyton composition on the leaf of C. rotundata consisted of Bacillariophyceae (16 genera), Cyanophyceae (3 genera), Chlorophyceae (9 genera), Dinophyceae (1 genus), and Rhodophyceae (1 genus). The water quality, such as phosphate, current, nitrate, dissolved oxygen, and Hg content in the water, contributed to changing the environmental condition of Talawaan Bajo waters. Therefore, the efforts to manage coastal resource conservation in the Talawaan Bajo estuary require more concern from the government and stakeholders of Talawaan Bajo.

Antioxidant Bioactivity of Extracts from Beach Cast Leaves of Posidonia oceanica (L.) Delile.

The marine environment is a generous source of biologically active compounds useful for human health. In 50 years, about 25,000 bioactive marine compounds have been identified, with an increase of 5% per year. Peculiar feature of algae and plants is the production of secondary metabolites, such as polyphenols, synthesized as a form of adaptation to environmental stress. Posidonia oceanica is a Mediterranean endemic and dominant seagrass and represents a biologically, ecologically and geologically important marine ecosystem. Within this study, methanolic and ethanolic extracts were generated from fresh and dried Posidonia oceanica leaves, with the aim to employ and valorize the beach cast leaves. The best yield and antioxidant activity (polyphenols content equal to 19.712 ± 0.496 mg GAE/g and DPPH IC50 of 0.090 µg/µL.) were recorded in 70% ethanol extracts (Gd-E4) obtained from leaves dried for two days at 60 °C and ground four times. HPLC analyses revealed the presence of polyphenols compounds (the most abundant of which was chicoric acid) with antioxidant and beneficial properties. Bioactive properties of the Gd-E4 extracts were evaluated in vitro using fibroblast cells line (HS-68), subjected to UV induced oxidative stress. Pre-treatment of cells with Gd-E4 extracts led to significant protection against oxidative stress and mortality associated with UV exposure, thus highlighting the beneficial properties of antioxidants compounds produced by these marine plants against photo damage, free radicals and associated negative cellular effects. Beach cast leaves selection, processing and extraction procedures, and the in vitro assay results suggested the potentiality of a sustainable approach for the biotechnological exploitation of this resource and could serve a model for other marine resources.

Low Light Availability Reduces the Subsurface Sediment Carbon Content in Halophila beccarii From the South China Sea.

Eutrophication, dredging, agricultural and urban runoffs, and epiphyte overgrowth could reduce light availability for seagrass. This may affect “blue carbon” stocks in seagrass beds. However, little research is available on the effect of light intensities on carbon sequestration capacity in seagrass beds, especially small-bodied seagrasses. The dominant seagrass Halophila beccarii, a vulnerable species on the IUCN Red List, was cultured in different light intensities to examine the response of vegetation and sediment carbon in seagrass beds. The results showed that low light significantly reduced leaf length and above-ground biomass, while carbon content in both above-ground and below-ground tissues were not affected. Low light reduced both the above-ground biomass carbon and the total biomass carbon. Interestingly, while under saturating light conditions, the subsurface and surface carbon content was similar, under low light conditions, subsurface sediment carbon was significantly lower than the surface content. The reduction of subsurface sediment carbon might be caused by less release flux of dissolved organic carbon from roots in low light. Taken together, these results indicate that reduced light intensities, to which these meadows are exposed to, will reduce carbon sequestration capacity in seagrass beds. Measures should be taken to eliminate the input of nutrients on seagrass meadows and dredging activities to maintain the “blue carbon” storage service by enhancing light penetration into seagrass.

Mapping and Quantification of the Dwarf Eelgrass Zostera noltei Using a Random Forest Algorithm on a SPOT 7 Satellite Image

The dwarf eelgrass Zostera noltei Hornemann (Z. noltei) is the most dominant seagrass in semi-enclosed coastal systems of the Atlantic coast of Morocco. The species is experiencing a worldwide decline and monitoring the extent of its meadows would be a useful approach to estimate the impacts of natural and anthropogenic stressors. Here, we aimed to map the Z. noltei meadows in the Merja Zerga coastal lagoon (Atlantic coast of Morocco) using remote sensing. We used a random forest algorithm combined with field data to classify a SPOT 7 satellite image. Despite the difficulties related to the non-synchronization of the satellite images with the high tide coefficient, our results revealed, with an accuracy of 95%, that dwarf eelgrass beds can be discriminated successfully from other habitats in the lagoon. The estimated area was 160.76 ha when considering mixed beds (Z. noltei-associated macroalgae). The use of SPOT 7 satellite images seems to be satisfactory for long-term monitoring of Z. noltei meadows in the Merja Zerga lagoon and for biomass estimation using an NDVI–biomass quantitative relationship. Nevertheless, using this method of biomass estimation for dwarf eelgrass meadows could be unsuccessful when it comes to areas where the NDVI is saturated due to the stacking of many layers.

The status of seagrass beds in the coastal county of Lamu, Kenya

Abstract Biodiversity assessments within seagrass beds were conducted in six sites in Lamu, Kenya; namely, Kiweni, Tauzi, Wange, Ntopate, Manda toto and Ngoi. The objective of the assessment was to collect baseline information of the seagrasses of Lamu County in Kenya. Our findings revealed that nine out of the twelve seagrass species found in Kenya were found in the study sites. The dominant seagrass species Thalassodendron ciliatum was found to occur in deeper subtidal areas, while the pioneering species occurred in intertidal shallower areas. Average shoot densities per site ranged from 2.4 ± 1.7 shoots m-2 of Cymodocea serrulata to 1025.9 ± 139.3 shoots m-2 of Syringodium isoetifolium in Ngoi. Canopy heights ranged from 0.1 ± 0.1 cm of Halodule ovalis in Tauzi to 16.3±1.3.5 cm of Syringodium isoetifolium in Ngoi. Although the seagrass species characteristics were much lower than that found in similar mangrove fringed seagrass beds of Gazi Bay, the majority of the fish found in these seagrass areas were invertivores which indicates that these seagrass sites form a refugia for adult fish populations with nursery grounds being located elsewhere. This study forms the first comprehensive assessment of the seagrasses of Lamu and it provides important baseline information on seagrass beds. Such biodiversity information provides important support for decision-making for coastal areas that are targeted for infrastructural development such as Lamu. Biodiversity information of such critical habitats form a critical data base for marine spatial planning and can be used to effectively guide the integration of biodiversity and coastal livelihoods in the sustainable development of Kenya’s coastal areas.

Ecological co-benefits from sea cucumber farming: Holothuria scabra increases growth rate of seagrass

Sea cucumber aquaculture is increasing in extent and importance throughout the Indo-Pacific region, supplying a luxury seafood market in Asia. In this context, the grow-out of hatchery-bred juveniles in community-farmed pens is proving to be a viable model, providing increased income security and alternative livelihood options to resource-limited communities. Here, we report a study of the impacts of such sea cucumber farming on the growth of seagrass (a favourable habitat for the animals) at a village-scale aquaculture site in southwest Madagascar. Using experiments, we found that the presence of the hatchery-bred sea cucumberHolothuria scabra(sandfish), at stocking densities of 300 g m-2(similar to the density used in the farmed pens, but relatively high for natural populations), resulted in a large (~30%), statistically significant increase in the leaf extension rate of the locally dominant seagrass speciesThalassia hemprichii. However, the other dominant seagrass species,Cymodocea serrulata, did not significantly change its leaf extension rate in the presence ofH. scabra. Since seagrass is a globally important coastal habitat, supporting high biodiversity, carbon sequestration, shoreline stability and nursery grounds for commercial and small-scale fisheries, the positive effect ofH. scabrafarming on the growth rate of at least one dominant seagrass species implies potential important ecological co-benefits. These co-benefits ofH. scabrafarming are likely to be relevant across the tropical Indo-Pacific coastlines, where this species is cultured.

Dominansi Spesies Tumbuhan Lamun di Perairan Pantai Sejuk Kabupaten Lombok Utara

Seagrass is a monocotyle plant from the Angiosperms class, which has an important role for marine biota. Seagrass can be said to be a source of life for marine life because it can be a source of food, shelter, and breeding for marine animals. In Pantai Sejuk Waters, North Lombok Regency, there are several species of seagrass that lie along the coast and in shallow sea waters. This study aims to determine the dominance of seagrass in Sejuk Beach Waters, North Lombok Regency. This type of research is a descriptive exploratory research. Sampling using purposive sampling method, by making 3 stations in which there are 3 transects and 4 plots on each transect. Based on the results of the study, 4 species of seagrass were obtained in Sejuk Beach Waters, North Lombok Regency, namely: Cymodocea rotundata as many as 1993 species, Enhalus acoroides with 35 species, Syringodium isoetifolium as many as 2065 species, and Halophila minor as many as 61 species. From the data on the number of species found, it is known that the dominant seagrass with a dominance index value of 0.497 is the Syringodium isoetifolium species. Subsequently, the Cymodocea rotundata species with a dominance index value of 0.479, followed by Halophila minor with a dominance index value of 0.0146, and Enhalus acoroides with a dominance index value of 0.0084.

In situ Responses of the Eelgrass Zostera marina L. to Water Depth and Light Availability in the Context of Increasing Coastal Water Turbidity: Implications for Conservation and Restoration.

Accelerating losses of seagrass meadows has led to efforts to restore these highly productive and beneficial ecosystems globally. Depth and light availability are critical determinants of seagrass restoration success. Eelgrass (Zostera marina L.) is the dominant seagrass species in the temperate northern hemisphere, but its global distribution has reduced dramatically. The main aims of this study were to determine: (1) the depth limit for Z. marina survival in Ailian Bay, north China, and (2) how light availability affects the growth and recruitment of Z. marina as a basis for identifying a suitable depth range for successful restoration. To achieve these aims, Z. marina shoots were transplanted from a nearby donor site, Swan Lake, to an experimental site, Ailian Bay, and the temporal responses of Z. marina shoots to light availability at water depths ranging from 1 to 8 m were investigated using in situ suspended cultures. Four suspended shoot transplantation experiments were conducted in 4 years. The results showed that the transplanted Z. marina shoots could survive and branch during an annual growth cycle, permanently underwater, at a depth ≤3 m. Due to the local turbidity of the waters in Ailian Bay, a depth of 4 m led to sufficient light deprivation (reduced to 6.48–10.08% of surface irradiance) to negatively affect seagrass shoot density and clonal reproduction. In addition, reproductive shoot density also tended to decline with water depth and light deprivation. Our results indicated that Z. marina population recruitment, through sexual and asexual (clonal growth) reproduction, were negatively affected by increasing water depth and light deprivation. These findings may provide a suitable depth range for the successful restoration of Z. marina in local coastal waters. They may also be applied to the management and restoration of Z. marina globally.

Century-long records reveal shifting challenges to seagrass recovery.

Global losses over the 20th century placed seagrass ecosystems among the most threatened ecosystems in the world, with eutrophication, and associated deterioration of the submarine light environment identified as the main driver. Growing appreciation of the ecological and societal benefits of healthy seagrass meadows has stimulated efforts to protect and restore them, largely focused on reducing nutrient input to coastal waters. Here we analyze a unique data set spanning 135years on eelgrass (Zostera marina), the dominant seagrass of the northern hemisphere. We show that meadows in the Western Baltic Sea exhibited major declines relative to historic (1890-1910) reference due to the wasting disease in the 1930s followed by eutrophication peaking in the 1980s, but have only shown modest improvement despite major eutrophication mitigation, halving nitrogen input since the 1980s. Across the past century, we identified generally shallower colonization depths of eelgrass for a given submarine light penetration and, hence, increased apparent light requirements. This suggests that eelgrass recovery is limited by additional stressors. Our study indicates that bottom trawling and intense recent warming (0.5°C per decade, 1985-2018), which impact on deeper and shallower meadows, respectively, suppress eelgrass from fully recovering from eutrophication. Warming is most severe in shallow turbid waters, while clear-water areas offer eelgrass refugia from warming in deeper, cooler waters; but trawling can prevent eelgrass from reaching these refugia. Efforts to reduce nutrient input and thereby improve water clarity have been instrumental in avoiding a catastrophic loss of eelgrass ecosystems. However, local-scale future management must, in addition, reduce bottom trawling to facilitate eelgrass reaching deeper, cooler refugia, and increase resilience toward realized and further warming. Warming needs to be limited by meeting global climate change mitigation goals.

Driving factors of biogeographical variation in seagrass herbivory

Despite the crucial role of herbivory in shaping community assembly, our understanding on biogeographical patterns of herbivory on seagrasses is limited compared to that on terrestrial plants. In particular, the drivers of such patterns remain largely unexplored. Here, we used a comparative-experimental approach in Cymodocea nodosa meadows, across all possible climate types within the seagrass distribution, 2000 km and 13° of latitude in two ocean basins, to investigate biogeographical variation in seagrass herbivory intensity and their drivers during July 2014. Particularly, the density and richness of herbivores and their food resources, seagrass size, carbon and nitrogen content, as well as latitude, sea surface temperature, salinity, chlorophyll, and sediment grain size, were tested as potential drivers. We found that shallow meadows can be subjected to intense herbivory, with variation in herbivory largely explained by fish density, seagrass size, and annual sea temperature range. The herbivorous fish density was the most important determinant of such variation, with the dominant seagrass consumer, the fish Sarpa salpa, absent at meadows from regions with low herbivory. In temperate regions where herbivorous fish are present, annual temperature ranges drive an intense summer herbivory, which is likely mediated not only by increased herbivore metabolic demands at higher temperatures, but also by higher fish densities. Invertebrate grazing (mainly by sea urchins, isopods, amphipods, and/or gastropods) was the dominant leaf herbivory in some temperate meadows, with grazing variation mainly influenced by seagrass shoot size. At the subtropical region (under reduced annual temperature range), lower shoot densities and seagrass nitrogen contents contributed to explain the almost null herbivory. We evidenced the combined influence of drivers acting at geographic (region) and local (meadow) scales, the understanding of which is critical for a clear prediction of variation in seagrass herbivory intensity across biogeographical regions.

The dominant seagrass herbivore Sarpa salpa shifts its shoaling and feeding strategies as they grow

The relative benefits of group foraging change as animals grow. Metabolic requirements, competitive abilities and predation risk are often allometric and influenced by group size. How individuals optimise costs and benefits as they grow can strongly influence consumption patterns. The shoaling fish Sarpa salpa is the principal herbivore of temperate Posidonia oceanica seagrass meadows. We used in-situ observations to describe how ontogeny influenced S. salpa individual feeding behaviour, shoaling behaviour and group foraging strategies, and its potential consequences to seagrass meadows. Shoaling was strongly influenced by body length: shoals were highly length-assorted and there was a clear positive relationship between body length and shoal size. Foraging strategies changed dramatically with shoal size. Small shoals foraged simultaneously and scattered over large areas. In contrast, larger shoals (made of larger individuals) employed a potentially cooperative strategy where individuals fed rotationally and focused in smaller areas for longer times (spot feeding). Thus, as individuals grew, they increased their potential impact as well, not merely because they consumed more, but because they formed larger shoals capable of considerably concentrating their grazing within the landscape. Our results indicate that ontogenetic shifts in group foraging strategies can have large ecosystem-wide consequences when the species is an important ecosystem modifier.

Morphological and Anatomical Differences among Three Seagrass Species in a High-energy Coastal Area Typically Dominated by Surfgrass in a Rocky Coastal Area of Shandong Peninsula, China

Surfgrass Phyllospadix iwatensis is the dominant seagrass species in the coastal area of Mashanli, which lies at the east end of Shandong Peninsula, China. To our surprise, some Zostera marina and Zostera caespitosa patches have been recently found adjoining the surfgrass meadows. How the two Zostera species adapt to the high-energy habitats where Phyllospadix spp. thrive, and what kind of differences there are in the morphology and anatomy among the three species are unknown. To understand their adaptation strategies to the environment, we observed their morphological feature and anatomical structure of the three seagrass species by optical microscope. The results showed that much narrower leaves were observed in P. iwatensis, much higher plant density was observed in Z. caespitosa and Z. marina and much lower plant height was observed in Z. marina, which might have contributed to their adaptation in the environment. While for the supporting tissues (the epidermis, mesophyll cells, and vascular bundles for leaves, as well as the epidermis, exodermis and stele for rhizomes), the number of mesophyll cells in the leaves and the proportion of the other tissues in the cross sections in the leaves and rhizomes were significantly different among species. The results suggested that the three species adapt to the high-energy environment through different strategies.

Home for Marine Species: Seagrass Leaves as Vital Spawning Grounds and Food Source

Seagrass beds provide nursery habitats for marine species. Seagrass leaves, in particular, are used as spawning grounds and food source for fishes and invertebrates, but direct evidence of spawning in seagrass leaves is rare. It is also very challenging to identify eggs through morphological analysis, since the eggs of many marine species appear similar. To accurately identify the eggs on the leaves of the dominant seagrass species in the South China Sea, and evaluate seasonal contribution of seagrass leaves as food source, DNA barcoding and stable isotope technique were conducted. Interestingly, Monetaria annulus was found to spawn on the leaf sheath of Thalassia hemprichii in Li'an gang, Hainan Island. This selection of oviposition site might increase embryo survival compared to the other parts of the seagrass leaves. Meanwhile, the eggs of Stethojulis trilineata were deposited on the entire leaf of Halophila ovalis in Liusha Bay, Guangdong Province. The small fingernail-shaped leaves of H. ovalis might be beneficial for S. trilineata to lay eggs as they are closer to the sediment surface than other seagrass leaves. Based on the stable carbon and nitrogen isotope analyses, the primary food source of M. annulus in summer and in winter were particulate organic matter and seagrass, respectively. The results suggest that seagrass leaf is not only important for fish and invertebrates as a spawning site, but also as a food source. The findings of the present study may support the urgent requirement of the conservation of seagrass beds for sustaining the productivity of marine fisheries.

Seagrass bed status: Case study of Panjang Island, Banten Bay

Seagrass community status was measured using a vegetation analysis method at three observation stations in Panjang Island, Banten Bay. Each station was transected by three lines that divided these stations into plots measuring 50 × 50 cm to record the seagrasses species found, number of seagrass shoots, and coverage. In addition, measurements of water quality parameters, including temperature, salinity, pH, brightness, and sediment grains at each station, sediment grain. A Pearson’s correlation test was conducted to determine the correlation between sediment and seagrass density. The measurement of water quality in Panjang Island indicates optimal conditions for seagrass growth, with sediment mixed with clay and sand rubble. The seagrasses found were Enhalus acoroides, Cymodocea serrulata, Syringodium isoetifolium, Halodule uninervis, and Halophila ovalis. The seagrass community in Panjang Island has good coverage (60.16 %) and high density levels (235.03 ind/m2). S. isoetifolium was the dominant seagrass with an importance value (IV) of 119.90. The correlation test showed that mud and clay sediments correlated with the density of E. acoroides.

Assessing methods for restoring seagrass (Zostera muelleri) in Australia’s subtropical waters

Zostera muelleri, the dominant seagrass species along the eastern coastline of Australia, has declined due to anthropogenic stressors, including reduced water clarity. Water quality has improved in recent years, but restoration efforts are hampered by limited knowledge of transplantation methods. To support future restoration efforts, we tested multiple techniques for transplanting mature seagrass shoots: (1) sediment cores with intact seagrass plants (plug); (2) individual shoots anchored on frames (frame); (3) frame methods combined with subsurface mats to exclude bioturbating animals (mat+frame); (4) above-ground cages to exclude grazing fish (cage+frame); and (5) combined treatment of above-ground cages and subsurface mats (cage+mat+frame). Transplant success over 10 months showed considerable variability among locations. At one site, seagrass persisted in all treatments, with highest growth in the mat+frame treatment. At two locations, uncaged shoots were lost within 6–35 days of transplanting, presumably due to grazing by fish. In treatments with cages, growth was again highest in the mat+frame treatment. At the fourth location, all seagrass was lost due to physical stress. Thus, we conclude that transplantation success is highest using the mat+frame technique, but overall success depends on careful assessment of biotic and abiotic stressors at the chosen locations.

Disturbance size and frequency mediate the coexistence of benthic spatial competitors.

Disturbance plays a key role in structuring community dynamics and is central to conservation and natural resource management. However, ecologists continue to debate the importance of disturbance for species coexistence and biodiversity. Such disagreements may arise in part because few studies have examined variation across multiple dimensions of disturbance (e.g., size, frequency) and how the effects of disturbance may depend on species attributes (e.g., competitiveness, dispersal ability). In light of this gap in understanding and accelerating changes to disturbance regimes worldwide, we used spatial population models to explore how disturbance size and frequency interact with species attributes to affect coexistence between seagrass (Zostera marina) and colonial burrowing shrimp (Neotrypaea californiensis) that compete for benthic space in estuaries throughout the west coast of North America. By simulating population dynamics under a range of ecologically relevant disturbance regimes, we discovered that intermediate disturbance (approximately 9-23% of landscape area per year) to short-dispersing, competitively dominant seagrass can foster long-term stable coexistence with broad-dispersing, competitively inferior burrowing shrimp via the spatial storage effect. When holding the total extent of disturbance constant, the individual size and annual frequency of disturbance altered landscape spatial patterns and mediated the dominance and evenness of competitors. Many small disturbances favored short-dispersing seagrass by hastening recolonization, whereas fewer large disturbances benefited rapidly colonizing burrowing shrimp by creating temporary refugia from competition. As a result, large, infrequent disturbances generally improved the strength and stability of coexistence relative to small, frequent disturbances. Regardless of disturbance size or frequency, the dispersal ability of the superior competitor (seagrass), the competitive ability of the inferior competitor (burrowing shrimp), and the reproduction and survival of both species strongly influenced population abundances and coexistence. Our results show that disturbance size and frequency can promote or constrain coexistence by altering the duration of time over which inferior competitors can escape competitive exclusion, particularly when colonization depends on the spatial pattern of disturbance due to dispersal traits. For coastal managers and conservation practitioners, our findings indicate that reducing particularly large disturbances may help conserve globally imperiled seagrass meadows and control burrowing shrimp colonies that can threaten the viability of oyster aquaculture.

A Systematic Review of How Multiple Stressors From an Extreme Event Drove Ecosystem-Wide Loss of Resilience in an Iconic Seagrass Community

A central question in contemporary ecology is how climate change will alter ecosystem structure and function across scales of space and time. Climate change has been shown to alter ecological patterns from individuals to ecosystems, often with negative implications for ecosystem functions and services. Furthermore, as climate change fuels more frequent and severe extreme climate events (ECEs) like marine heatwaves (MHWs), such acute events become increasingly important drivers of rapid ecosystem change. However, our understanding of ECE impacts is hampered by limited collection of broad scale in situ data where such events occur. In 2011, a MHW known as the Ningaloo Nino bathed the west coast of Australia in waters up to 4°C warmer than normal summer temperatures for almost 2 months over 1000s of kilometres of coastline. We revisit published and unpublished data on the effects of the Ningaloo Nino in the seagrass ecosystem of Shark Bay, Western Australia (24.6 – 26.6o S), at the transition zone between temperate and tropical seagrasses. Therein we focus on resilience, including resistance to and recovery from disturbance across local, regional and ecosystem-wide spatial scales and over the past 8 yearsThermal effects on temperate seagrass health were severe and exacerbated by simultaneous reduced light conditions associated with sediment inputs from record floods in the south-eastern embayment and from increased detrital loads and sediment destabilisation. Initial extensive defoliation of Amphibolis antarctica, the dominant seagrass, was followed by rhizome death that occurred in 60-80% of the bay’s meadows, equating to decline of over 1000 km2 of meadows. This loss, driven by direct abiotic forcing, has persisted, while indirect biotic effects (e.g. dominant seagrass loss) have allowed colonisation of some areas by small fast-growing tropical species (e.g. Halodule uninervis). Those biotic effects also impacted multiple consumer populations including turtles and dugongs, with implications for species dynamics, food web structure, and ecosystem recovery. We show multiple stressors can combine to evoke extreme ecological responses by pushing ecosystems beyond their tolerance. Finally, both direct abiotic and indirect biotic effects need to be explicitly considered when attempting to understand and predict how ECEs will alter marine ecosystem dynamics.

Biomonitoring environmental status in semi-enclosed coastal ecosystems using Zostera noltei meadows

Semi enclosed waters, such as estuaries and lagoons, are vulnerable ecosystems that are experiencing persistent trace element (TE) contamination. Seagrasses have been reported worldwide as valuable bioindicator species for coastal contamination monitoring purpose. This is, to our knowledge, the first time the TE contamination of semi-enclosed ecosystems has been monitored along the full latitudinal gradient of the Moroccan Atlantic coast. In these ecosystems, the dominant seagrass species is Zostera noltei. 23 TEs (Fe, Al, Cr, Mn, Co, Ni, V, Cu, Zn, Sr, Li, As, Ag, Cd, Sn, Sb, Mo, Ba, Ti, Pb, U, Bi and Hg) and four major elements (Na, Mg, K, Ca) were measured in sediments and seagrass leaf samples were collected upstream and downstream of five semi-enclosed areas. They contrasted in both climatic conditions and levels of environmental contamination. The Trace Element Pollution Index (TEPI) and the Trace Element Spatial Variation Index (TESVI) were calculated from chemical element concentrations in the samples. Of the five semi-enclosed areas, Sidi Moussa lagoon’s sediments were the most contaminated (TEPI = 1.18). The TESVI differed highly between chemical elements among the five water bodies for sediments and seagrass leaves, the highest spatial variability being for Ag (TESVI = 72.01 and 21.05 respectively). For Z. noltei leaves, a latitudinal gradient of TE accumulation was recorded. A high bioconcentration factor (BCF > 1) for Cd, Mo, Sb, Ag, Zn and U indicated that the sediments were efficiently uptaken by the seagrass. Significant correlations (p < 0.05) between levels of Cd, Ag, Fe, Al, Ba, Hg, Mn and Zn in sediments and in Z. noltei leaves indicated similar contamination occurrences in both environmental matrices and their bioavailability for seagrasses. Overall, leaf TE bioconcentration among and within the study sites resulted from differences in element bioavailability and environmental conditions (climatic context, hydrological conditions and human impact). Ultimately, Z. noltei is a useful bioindicator of Cd, Mo, Sb, Ag, Zn, U, Al, Fe, Mn, Ba and Hg contamination in sediments.