Seagrass Species Research Articles

Bottom‐up and top‐down control of seagrass overgrazing by the sea urchin Tripneustes gratilla

AbstractThe lack of top‐down control on Tripneustes gratilla, a sea urchin commonly known to graze on seagrass, and the bottom‐up control of its feeding preference, led to the overgrazing of seagrass meadows of the species Thalassodendron ciliatum in Changuu Island (Zanzibar Archipelago). The impact of overgrazing on seagrasses was assessed by mapping the presence of grazed versus non‐grazed seagrass patches in the study site, while the top‐down control on T. gratilla was assessed by measuring the abundance of its fish predators. The feeding preference and distribution of T. gratilla were characterized by calculating the electivity indexes for each seagrass species and measuring sea urchin density, respectively. Approximately half of the patches of T. ciliatum were overgrazed, while predatory fishes of T. gratilla were absent from the site. The Vanderploeg and Scavia's Relativized Electivity Index indicated that T. gratilla had a feeding preference for T. ciliatum, which was also supported by higher urchin densities within T. ciliatum dominated patches. Bottom‐up control of grazing activity was observed by quantifying and analyzing morphological, nutritional, and the chemical defense traits of the seagrass in relation to feeding preference and urchin density. Feeding was positively correlated to the seagrass tissue C:P ratio (ρ = 0.9), whereas urchin density showed no correlations. The bottom‐up control of the feeding preference and agglomeration of T. gratilla in T. ciliatum meadows, together with the lack of evidence of substantial top‐down control and the long recovery time of T. ciliatum led to the overgrazing of this species at this site. Overgrazing, therefore, was shown to be the result of multiple factors ranging from the traits of the seagrass and feeding preference of T. gratilla, to the abundance of predators in this area.

DNA methylation dynamics in a coastal foundation seagrass species under abiotic stressors.

DNA methylation (DNAm) has been intensively studied in terrestrial plants in response to environmental changes, but its dynamic changes in a temporal scale remain unexplored in marine plants. The seagrass Posidonia oceanica ranks among the slowest-growing and longest-living plants on Earth, and is particularly vulnerable to sea warming and local anthropogenic pressures. Here, we analysed the dynamics of DNAm changes in plants collected from coastal areas differentially impacted by eutrophication (i.e. oligotrophic, Ol; eutrophic, Eu) and exposed to abiotic stressors (nutrients, temperature increase and their combination). Levels of global DNAm (% 5-mC) and the expression of key genes involved in DNAm were assessed after one, two and five weeks of exposure. Results revealed a clear differentiation between plants, depending on environmental stimuli, time of exposure and plants' origin. % 5-mC levels were higher during the initial stress exposure especially in Ol plants, which upregulated almost all genes involved in DNAm. Contrarily, Eu plants showed lower expression levels, which increased under chronic exposure to stressors, particularly to temperature. These findings show that DNAm is dynamic in P. oceanica during stress exposure and underlined that environmental epigenetic variations could be implicated in the regulation of acclimation and phenotypic differences depending on local conditions.

Seagrasses At The Islands Iturup And Urup Of Kuril Archipelago

The islands Iturup and Urup of Kuril Archipelago have been understudied in respect of seagrasses. The research aimed to fill this gap. In 2019 during the expedition of the Russian Geographical Society a part of the coastline has been surveyed by walking, the beached remains of seagrasses and the seagrasses growing on the littoral have been registered. The length of the routes was 95 km. The possible sources of negative anthropogenic impact have been examined. Herbarium collections of several institutions (LE, LECB, MHA, MW, MWG, SAK, Kamchatka Branch of Pacific Geographical Institute of the RAS, the Herbarium of Kronotsky Nature Reserve) have been explored. Three species of seagrasses occur at Iturup and Urup: Zostera marina L., Zostera asiatica Miki, and Phyllospadix iwatensis Makino. The last two species are of particular interest as they are threatened and distributed over a relatively small area. Unlike the habitats of the main part of their range located at the coasts of Japan and Korea, the habitats of the studied islands do not suffer from anthropogenic pressure. The discovered northern refuge is significant for the seagrasses conservation. Current global warming and increasing anthropogenic pressure on the southern habitat would increase its significance. It is especially important for Phyllospadix iwatensis as it turned out to be rather numerous at the studied islands. The other two species occur in small numbers there.

Plant and Meadow Structure Characterisation of Posidonia oceanica in Its Westernmost Distribution Range

Posidonia oceanica is an endemic seagrass species from the Mediterranean Sea that provides critical ecological services to coastal environments. This species is distributed from the Turkish to the Spanish coast, where its westernmost record was documented in Punta Chullera, Malaga (36°18′36.45′′ N, 5°14′54.31′′ W). Nevertheless, previous studies suggested that its distribution was even further west, although these populations were never described. In this study, we documented and characterised the only known P. oceanica population on the coast of Cadiz, in Cala Sardina (36°18′38.80′′ N, 5°15′15.13′′ W). The newly documented population of P. oceanica presented a fragmented structure, consisting of nine patches found in a rocky shallow area surrounded by the invasive algae Rugulopteryx okamurae, with a total size of 61.14 m2. Shoots had a relatively small size (21.0 ± 2.9 cm) in comparison with centrally-distributed populations. The relatively small size of the plants, alongside the observed low shoot density (437 ± 42 shoots m−2) and leaf area index (4.8 ± 0.7 m2 m−2), may indicate that this meadow could be exposed to sub-optimal environmental conditions for plant development. By contrast, the meadow showed relatively high production rates (0.03 ± 0.01 leaf day−1 shoot−1) in comparison with other Mediterranean populations. The percentage of carbon in plant leaves was 38.73 ± 1.38%, while the nitrogen and C/N were 1.38 ± 0.37% and 29.93 ± 6.57, respectively. The documentation of this meadow extends the distribution of this species to the Mediterranean coast of Cadiz, making this region the place with the highest seagrass biodiversity (four species) in the Iberian Peninsula, and potentially in Europe. This exploratory study provides a baseline to examine the potential effects of climate change, anthropogenic disturbances or the presence of invasive species.

Mapping Potential Carbon Content of Seaweed Species as Gas Regulation in Sekotong Waters, West Lombok

Seagrass is one of the ecosystems that contributes to carbon absorption through the process of photosynthesis which can be stored in the form of biomass in the leaves, rhizomes and roots. The consequences of community gold mining in Sekotong District, West Lombok, have an impact on heavy metal (Mercury/Hg) pollution. The research aims to map the potential carbon sequestration capabilities of seagrass species in Sekotong waters, West Lombok. The research method used is descriptive quantitative in which the variable studied in the study is the carbon content of seagrass species affected by mercury pollution in the waters of the village, especially at Pewaringan Sak Beach. The results showed that the average Hg and carbon content of seagrass species in seagrass beds were Station 1: (Hg: 0.31, Carbon: 63%), Station 2: (Hg: 0.45, Carbon: 50%) and Station 3: (Hg :0.35%, Carbon:55%). The conclusion is that the carbon content in seagrass species decreases with the level of mercury involvement in seagrass species. The research results are expected to be used as a source of information related to carbon absorption by seagrasses in Sekantung waters, West Lombok so that they can be taken into consideration for the management of water areas, especially the waters of Waring Sekotong, West Lombok. Further research is needed on the potential of seagrass carbon sequestration as a gas regulator to prevent climate change due to greenhouse gases.

Young death assemblages with limited time-averaging in rocky and Posidonia oceanica habitats in the Mediterranean Sea

Abstract Death assemblages (DAs) are increasingly recognized as a valuable source to reconstruct past ecological baselines, due to the accumulation of skeletal material of non-contemporaneous cohorts. We here quantify the age and time-averaging of DAs on shallow subtidal (5–25 m) rocky substrates and in meadows of Posidonia oceanica in the eastern Mediterranean. We show that such DAs are very young – median ages 9–56 years – with limited time-averaging, one to two orders of magnitude less than on even nearby soft substrates. On rocky substrates, out-of-habitat transport is likely the main cause of loss of older shells. In Posidonia oceanica meadows, the root and rhizome system creates a dense structure – the matte – that quickly entangles and buries shells and limits the potential for bioturbation. The matte is, however, a peculiar feature of Posidonia oceanica , and age and time-averaging in meadows of other seagrass species may be different. The young age of DAs in these habitats requires a careful consideration of their appropriateness as baselines. The large difference in DA age between soft substrates, subject to numerous studies, and hard and seagrass substrates, rarely inspected with geochronological techniques, implies that DA dating is important for studies aiming at using DAs as baselines.

First assessment of seagrass carbon accumulation rates in Sweden: A field study from a fjord system at the Skagerrak coast

Seagrass meadows are globally important blue carbon sinks. In northern cold-temperate regions, eelgrass (Zostera marina) is the dominant seagrass species, and although their sedimentary carbon stocks have been quantified across regions, information regarding the CO2withdrawal capacity as carbon sinks remains scarce. Here we assessed the carbon (Corg) accumulation rates (CARs) and stocks as well as the organic matter sources in five seagrass meadows in the Gullmar Fjord area on the Swedish Skagerrak coast. We found that the mean (±SD) CAR was 14 ± 3 g Corgm-2yr-1over the last ~120–140 years (corresponding to a yearly uptake of 52.4 ± 12.6 g CO2 m-2). The carbon sink capacity is in line with otherZ.marinaareas but relatively low compared to other seagrass species and regions globally. About half of the sedimentary carbon accumulation (7.1 ± 3.3 g Corgm-2yr-1) originated from macroalgae biomass, which highlights the importance of non-seagrass derived material for the carbon sink function of seagrass meadows in the area. The Corgstocks were similar among sites when comparing at a standardized depth of 50 cm (4.6–5.9 kg Corgm-2), but showed large variation when assessed for the total extent of the cores (ranging from 0.7 to 20.6 kg Corgm-2for sediment depths of 11 to at least 149 cm). The low sediment accretion rates (1.18–1.86 mm yr-1) and the relatively thick sediment deposits (with a maximum of >150 cm of sediment depth) suggests that the carbon stocks have likely been accumulated for an extended period of time, and that the documented loss of seagrass meadows in the Swedish Skagerrak region and associated erosion of the sediment could potentially have offset centuries of carbon sequestration.

Delineating seagrass species in the genera Halodule and Halophila from Tanzanian coastal waters using ITS and rbcL DNA barcoding

The seagrass species in Halodule and Halophila may for several reasons be considered as taxonomic complexes. They show close evolutionary relationships, morphological plasticity and share similar features making misidentifications likely when morphological identification is applied. In Tanzanian coastal waters, there is some uncertainty about the identity of members of Halodule, particularly the existence of Halodule wrightii and the species composition of the Halophila ovalis complex. This study used morphology as well as internal transcribed spacer (ITS1 and ITS2) and ribulose‐bisphosphate carboxylase (rbcL) DNA barcoding to identify species of Halodule and Halophila. Seagrass samples were collected during low spring tides, from Tanzania's coastal waters of Tanga, Dar es Salaam, Mtwara, Mafia Island and Unguja Island, from August 2020 to February 2022. Morphological diagnosis, phylogenetic analysis and evolutionary divergences inferred from the ITS gene supported the identification of five species, namely Halophila ovalis, H. minor and H. stipulacea, with the first two forming the H. ovalis complex; as well as Halodule uninervis and H. pinifolia. It is the first time that H. pinifolia is reported in Tanzania. This is the first study reporting the delineation of seagrass species in East African coastal waters using DNA barcoding coupled with morphology.

Estimating Blue Carbon Stock: Mangrove and Seagrass Biomass Assessment in Tunda Island, Serang, Banten, Indonesia

Tunda Island is one of the islands at the northern tip of Banten Province, with natural and well-maintained seagrass and mangrove ecosystems. Even though its location is close to an urban area, the use of aquatic resources such as fishing and cultivation is small compared to other islands. However, developing issues such as sand mining plans will undoubtedly impact the surrounding coastal ecosystems, such as mangroves and seagrass in Tunda Island. Related to their role in reducing the impact of climate change, these two ecosystems need to be protected because coastal ecosystems are ten times more effective at sequestering carbon dioxide per area than boreal, temperate, or tropical forests. Therefore, this study aimed to determine the potential of seagrass and mangrove biomass for blue carbon storage on Tunda Island as baseline data for managing small islands that are still natural. Calculation of the area of mangrove and seagrass ecosystems on Tunda Island was obtained by classifying high-resolution imagery from Unmanned Aerial Vehicle (UAV) Drones. The potential for blue carbon storage was calculated using the allometric equation on seagrass (percent cover and density) and mangroves (DBH and wood density). The results showed that Tunda Island had six species of seagrass, which were dominated by Thalassia hemprichii, and six species of mangrove, which Rhizopora apiculata dominated. Based on the results of the UAV Drone image classification, the mangrove and seagrass ecosystem area was 14 and 398 ha. After that, it can be calculated that the potential value of blue carbon stores in Tunda Island is 160,38 tons C, with the most significant carbon stock being 60% in the mangrove ecosystem biomass and 40% in seagrass biomass. These results mean that blue carbon stock in Tunda Island has a small value compared with Indonesia's average mangrove and seagrass carbon data.

Ecological condition of seagrass meadow in Lembeh Island, Bitung Regency, North Sulawesi, Indonesia

The condition of seagrass meadows is required information for conducting comprehensive management plans in coastal areas. This study provides information on the ecological condition of the seagrass ecosystem in Lembeh Island, based on seagrass species richness and coverage, macroalgal coverage, epiphyte coverage, and water transparency. We collected the data by performing 24 line transects at eight stations across the island. The seagrass ecosystem condition was determined using the Seagrass Ecological Quality Index (SEQI, range 0-1). We recorded eight seagrass species in the study site, with coverage of 48.88 ± 12.35% (mean ± SE). Enhalus acoroides and Thalassia hemprichii were the most common species in the sampling stations. The coverage of macroalgal and epiphyte was substantially low, indicated by values of 1.64 ± 0.41% and 12.64 ± 3.57%, respectively. Our analysis showed that most of the seagrass meadows in Lembeh Island are in poor condition (SEQI mean: 0.48 ± 0.03), especially in the locations inside Lembeh Strait. Moderate conditions were only found outside Lembeh Strait, such as in Pancuran, Limangu, and Pasir Panjang (SEQI values: 0.60, 0.58, and 0.56, respectively). We suggest a long-term seagrass monitoring program to evaluate the trend of condition, a restoration program, and improve water environment quality.

Seagrass diversity and dugong observation in North Minahasa Regency, North Sulawesi

Dugong is a marine mammal that only eats seagrass. Feeding tracks of dugongs in the seagrass beds indicate their presence. The dugong population is currently experiencing a decline due to habitat destruction and other anthropogenic factors. This study aimed to determine the seagrass diversity and their relationship to the presence of dugongs. The research was conducted in villages of Bahoi, Tarabitan, Bulutui, and Gangga I Island using the seagrass-watch method. Analysis of the data used was the percentage of seagrass cover, density of seagrass species, and indicators of the presence of seagrass, which was carried out by interviewing fishermen and surveying their feeding tracks. The results showed that the waters in the North Minahasa Regency had seven seagrass types. The average percentage of seagrass cover was 61.73% and the density of seagrass species was 766.88 shoots/m2. Feeding tracks observed in three locations, in Bahoi, Tarabitan, and Bulutui villages. The most tracks of feeding tracks were in Bahoi Village, with the type of seagrass that dominated being eaten by dugongs was Halodule pinifolia. Based on the results obtained, it concluded that certain types of seagrass are related to the location of the emergence of dugongs in the North Minahasa Regency.

Detecting Trends in Abundance and Distribution of Seagrasses in Lake Worth Lagoon, Palm Beach County, Florida

Over the past 15 years, seagrass community stability has varied in estuaries throughout Florida. This study sought to model potential patterns of physiochemical parameters and community composition that may correlate with the fluctuation of seagrass populations in Lake Worth Lagoon (LWL), Palm Beach County, FL over time (2007–2019). Seven transects and 4 polygon areas throughout the LWL were established and stratified along a north—south gradient. Sites were sampled annually (May–August) for water quality, seagrass and macroalgal abundance, and community composition. Models developed to explain macrophyte abundance and composition were assessed using Akaike Information Criterion. Interaction between year and site best explained seagrass abundance and community composition in transect and polygon sites. Transect data revealed that seagrass and macroalgae declined after 2012 and continued until barely detected after 2016. This die off was not consistent for all transects and there was site variability in annual dissolved oxygen, nitrate, phosphate, and salinity levels. Polygon sites exhibited a shift in community composition after 2013, initially dominated by seagrass species Syringodium filiforme and Halodule wrightii before transitioning in 2012–2013 to Halophila decipiens and Caulerpa spp. Central lagoon sites transitioned to communities devoid of nearly all vegetative species. The loss of seagrass and the change in community composition could be explained by a transient dry period in 2012 and a subsequent inflow of freshwater. These events (sudden drought followed by an increase in freshwater) likely compounded the stress on the system between 2011–2014, leading to a drastic change in seagrass community.

Keanekaragaman Lamun di Perairan Pantai Ketapang Lombok Barat

Research on the diversity index, uniformity, and dominance of seagrass in Ketapang waters was carried out in November 2021. The method used in this study was a direct field experiment using a quadrant transect measuring 50x50 cm. The results showed that there were four types of seagrasses, namely Enhalus acoroides, Thalassia hemprichii, Cymodocea rotundata, and Halophila ovalis. Seagrass species C. rotundata is the type found at each observation station, so it can be said that this species can live well in the characteristics of Ketapang waters. The average diversity index, uniformity, and dominance of seagrass species in Ketapang waters were dominated by C. rotundata and E. acoroides.

Remote sensing in seagrass ecology: coupled dynamics between migratory herbivorous birds and intertidal meadows observed by satellite during four decades

AbstractTaking into account trophic relationships in seagrass meadows is crucial to explain and predict seagrass temporal trajectories, as well as for implementing and evaluating seagrass conservation policies. However, this type of interaction has been rarely investigated over the long term and at the scale of the whole seagrass habitat. In this work, reciprocal links between an intertidal seagrass species, Zostera noltei, and a herbivorous bird feeding on this seagrass species, the migratory goose Branta bernicla bernicla, were investigated using an original combination of long‐term Earth Observation (EO) and bird census data. Seagrass Essential Biodiversity Variables (EBVs) such as seagrass abundance and phenology were measured from 1985 to 2020 using high‐resolution satellite remote sensing over Bourgneuf Bay (France), and cross‐analysed with in situ measurements of bird population size during the goose wintering season. Our results showed a mutual relationship between seagrass and Brent geese over the four last decades, suggesting that the relationship between the two species extends beyond a simple grass—herbivore consumptive effect. We provided evidence of two types of interactions: (i) a bottom‐up control where the late‐summer seagrass abundance drives the wintering population of herbivorous geese and (ii) an indirect top‐down effect of Brent goose on seagrass habitat, where seagrass development is positively influenced by the bird population during the previous wintering season. Such a mutualistic relationship has strong implications for biodiversity conservation because protecting one species is beneficial to the other one, as demonstrated here by the positive trajectories observed from 1985 to 2020 in both seagrass and bird populations. Importantly, we also demonstrated here that exploring the synergy between EO and in situ bird data can benefit seagrass ecology and ecosystem management.

Simulated Green Turtle Grazing Reduces Seagrass Productivity and Alters Benthic Community Structure While Triggering Further Disturbance by Feeding Stingrays

While green turtles (Chelonia mydas) were once abundant throughout the Caribbean, over-exploitation has dramatically reduced their numbers. We conducted a 168-day simulated grazing experiment to determine how loss of this once-abundant mega-herbivore could have affected the productivity and community composition of Thalassia testudinum-dominated seagrass beds in Bocas del Toro, Panama. Simulated grazing reduced both percent cover and productivity of T. testudinum. High runoff and local pollution from industrial farming may limit light availability and reduce seagrass photosynthetic performance to replace biomass lost to simulated grazing. Other seagrass species and algae failed to colonize space opened by reductions in T. testudinum percent cover. Many plots subjected to simulated grazing were also bioturbated by stingrays. Relevance of these findings to balancing sea turtle and seagrass conservation efforts are discussed.

KEANEKARAGAMAN, KERAPATAN DAN PENUTUPAN JENIS LAMUN DI PANTAI KASTELA, TERNATE SELATAN, MALUKU UTARA

Kastela coastal waters are one of the tourist attractions in the coastal area of ​​Ternate city where seagrass is found. Information related to diversity, density and, the diverse cover is still lacking and has not been supported by previous scientific research, especially in the area of ​​Kastela Beach. Therefore, this study was conducted to determine the diversity, density and, cover of seagrass species on the Kastela coast, South Ternate. Seagrass diversity in Kastela Beach includes 6 types of seagrass, namely: Halodule pinifolia, Halophila ovalis, Thalassia hemprichii, Cymodocea rotundata, Syringodium isoetifolium and, Enhalus acoroides. Based on the Shannon-Wienner index, the diversity of seagrass on the beach is classified as moderate with a value of 1.42 (station 1), 1.46 (station 2), 1.29 (station 3). Seagrass species Thalassia hemprichii has the highest density among seagrass species found on Kastela Beach with a density value of 580.27 individuals/m². At station 1, 358.27 individuals/m². At station 2, and station 3 it was dominated by Halodule pinifolia species as many as 326.53 individuals/m². For total seagrass closure at each station, especially station 1 and station 2, it was classified as rich or healthy (>60 %), where the value of station 1 was 124.16%/m², and station 2 was 95.2%/ m². Station 3 is classified as less healthy or less rich with a value of 59.79%/m².

Microplastic accumulation in Halophila ovalis beds in the Swan-Canning Estuary, Western Australia

Small ephemeral seagrass (Halophila ovalis) beds in the Swan-Canning Estuary, Western Australia, were sampled to determine if microplastics attach to seagrass blades and accumulate in higher concentrations in seagrass sediment compared to bare sediment. Three microplastics were observed attached to sampled seagrass blades (n = 108). Microplastics had a mean concentration in seagrass sediments of 1000 ± 100.37se particles kg−1 and in bare sediment of 972 ± 92.19se particles kg−1. ATR FTIR further verified 64.2 % of subsample particles as plastic (n = 28). This is the first known study to identify microplastics within the leaf canopy of H. ovalis however we could not support our hypothesis that this seagrass species acts as a sink for microplastic particles in sediments, as seen in studies on other seagrass species. The ability for seagrass habitats to trap and accumulate microplastics in sediments is likely influenced by species morphology, seagrass canopy density and life history.

Features of the spatial structure of the macro- and meiobenthos community of the lagoon ecosystem of Kislaya Bay head (Gulf of Kandalaksha, White sea)

The spatial and species structure of meio- and macrobenthos communities of the Kislaya Bay (Gulf of Kandalaksha, White Sea) lagoon ecosystem was analysed. A total of 32 species of benthic organisms (including 11 species of invertebrate larvae) and 9 species of seagrasses and algae were found. Eumeiobenthos groups were identified to the level of large taxa (nematodes, harpacticoids, ostracods, turbellaria). The highest total biomass of macrobenthos organisms was mainly observed in the lower horizon of the littoral zone and at the exit from the lagoon (high biomass of Mytilus edulis populations). For meiobenthos biomass was the highest in the middle and upper littoral horizons and in the bayhead. This may indicate a complementary distribution of meio- and macrobenthos: the role of meiofauna grew where macrobenthos development was somewhat inhibited. An analysis of the similarity of meio- and macrobenthos of different habitats revealed differences in the species structure of communities between the three littoral horizons – upper, middle, and lower. Communities of the lower and middle horizons of the littoral zone exhibited a greater similarity of the species structure than communities of the upper horizon. The differences in the structural characteristics of the community lengthwise – with increasing water salinity, are less pronounced (especially when compared with the corresponding structural changes in meio- and macrobenthos in the Chyornaya River estuary). This is probably due to the milder salinity conditions in the lagoon versus the Chyornaya River estuary, lower impact of this factor on the distribution of aquatic organisms and, accordingly, smaller change in the species structure of the community lengthwise – from the bayhead towards the sea.

Seagrasses of West Africa: New Discoveries, Distribution Limits and Prospects for Management

The onset of a major seagrass initiative in West Africa enabled important seagrass discoveries in several countries, in one of the least documented seagrass regions in the world. Four seagrass species occur in western Africa, Cymodocea nodosa, Halodule wrightii, Ruppia maritima and Zostera noltei. An area of about 62,108 ha of seagrasses was documented in the studied region comprising seven countries: Mauritania, Senegal, The Gambia, Guinea Bissau, Guinea, Sierra Leone and Cabo Verde. Extensive meadows of Zostera noltei were recorded for the first time at Saloum Delta, Senegal, which represents the new southernmost distribution limit of this species. This paper also describes the seagrass morphology for some study areas and explores the main stressors to seagrasses as well as conservation initiatives to protect these newly documented meadows in West Africa. The produced information and maps serve as a starting point for researchers and managers to monitor temporal and spatial changes in the meadows’ extent, health and condition as an efficient management tool.

Mapping the structure of mixed seagrass meadows in the Mexican Caribbean

The physical and ecological importance of seagrass meadows in coastal processes is widely recognized, and the development of tools facilitating characterization of their structure and distribution is important for improving our understanding of these processes. Mixed (multi-specific) meadows in a Mexican Caribbean reef lagoon were mapped employing a multiparameter approach, using PlanetScope remote sensing images, and supervised classification based on parameters related to the structure of the seagrasses meadows, including the cover percentages of seagrass/algae/sediment, algae thalli and seagrass shoot densities, canopy heights and estimated leaf area index (LAI). The cover, seagrass and algae densities, and seagrass canopy heights were obtained using ground truth sampling, while the LAI was estimated using data obtained from long-term monitoring programs. The maps do not show the differentiation of seagrass species, but ground truthing contemplated characterization of the density of Thalassia testudinum, Syringodium filiforme and Halodule wrightii and their respective LAIs. S. filiforme was the dominant species in terms of shoot density, and T. testudinum was dominant in terms of LAI. In the multiparameter-based map four classes were defined, based on the cover and structural characteristics, and its overall accuracy was very high (~90%). Maps based on sediment cover and LAI alone also had 4 classes, but they were less accurate than the multiparameter-based map (~70% and ~80%, respectively). The multiparameter-based seagrass map provided spatially-explicit data on the abundance and structure of seagrasses, useful for future monitoring of the changes in the meadows, and also for studies of that require data of large-scale meadow structure, such as inventories of associated biota, blue carbon storage, or modelling of the local hydrodynamics.