Effective monitoring of seagrasses is critical for understanding their responses to anthropogenic and climatic stressors and for informing adaptive management strategies. Traditional monitoring efforts using field-based approaches provide detailed information but are often limited in spatial and temporal coverage. Conversely, monitoring utilizing broad-scale satellite or aerial imagery can detect regional trends but may overlook fine-scale meadow dynamics. Unmanned aerial vehicles (UAVs) offer a promising middle ground, providing highresolution, cost-effective imagery that captures both spatial extent and meadow-scale patterns relevant to monitoring needs. In this study, we evaluated the utility of off-the-shelf UAVs for seagrass monitoring, assessing their ability to quantify intra-annual changes in percent vegetative cover and meadow spatial configuration (meadow extent, patch number, and areas of gain or loss). UAV and field surveys were conducted monthly at 3 seagrass meadows in North Carolina for two years. UAV imagery was classified into vegetated and non-vegetated pixels, then spatial configuration metrics were derived. Simultaneously, field surveys collected Braun-Blanquet cover abundance to validate UAV classifications and to quantify species-level composition at the meadow level. UAVs effectively detected intra-annual changes in meadow extent and patchiness and resolved site specific differences in meadow stability. However, UAV estimates of cover consistently overestimated bare and dense cover while underrepresenting mid-range vegetative abundances. Field surveys revealed species composition influenced the magnitude of monthly percent vegetative cover and spatial configuration patterns. Our findings demonstrate that UAVs can bridge gaps between broad-scale mapping and intensive site-level surveys, offering a complementary framework for monitoring when paired with field-based methods.

To effectively manage and protect ocean life and the people who depend on it, we need coordinated, comparable observations of ocean biodiversity. Seagrass cover and composition is an essential ocean variable (EOV) of the Global Ocean Observing System because seagrasses are the foundation of coastal ecosystems worldwide, and support diverse marine life and ecosystem services. We present guidelines for collecting and reporting seagrass data that fulfill specifications for the EOV, including three priority measurements to maximize compatibility among data sets: seagrass cover, species composition, and areal extent, with priority environmental variables for interpreting changes in status and condition. To promote interoperability, we present a standard format for seagrass EOV data and metadata. These guidelines will enable better monitoring and assessment of seagrass ecosystems, facilitate syntheses, inform the Kunming-Montreal Global Biodiversity Framework headline indicator "Extent of natural ecosystems," and support evidence-based conservation and sustainable development.

Seagrasses are vital foundation species that support diverse communities of organisms and shape coastal ecosystems. In North Carolina, USA, two species, Zostera marina (temperate) and Halodule wrightii (tropical), coexist at the edges of their ranges in a mixed-species transition zone affected by climate change. This study examines seasonal patterns in seagrass biomass, epiphyte biomass, and species composition across monthly collections over 1 year from Topsail Sound, NC. Generalized additive models revealed significant species-by-month interactions for aboveground, belowground, and epiphyte biomass, while temperature was a non-significant predictor. H. wrightii aboveground biomass peaked in September (16.2 ± 2.9 g m−2) and reached its minimum in March (1.61 g m−2), while Z. marina peaked in July (25.4 ± 3.1 g m−2) and declined to its minimum in October (0.68 ± 0.26 g m−2). Epiphyte biomass was influenced by month, suggesting that the contrasting growth cycles of their seagrass hosts, under similar light, nutrient, and grazer conditions, drive biomass accumulation. Maximum epiphyte biomass occurred during thermal stress periods associated with low seagrass biomass: summer for Z. marina and winter for H. wrightii. The interaction between host species and month influenced epiphyte community composition, with monthly variation explaining 35

Seed size is an essential determinant of germination and survival in angiosperms. Zostera marina, one of few marine angiosperms, is a key foundation species present in temperate coastal marine ecosystems, and edge-of-range population persistence is increasingly reliant on seed production and successful seedling establishment. While environmental conditions have been linked to variability in regional patterns of seed size variation, far less is known about what influences seed size differences within a plant. Here, we genotype and measure individual seeds across parent plants to investigate the relative contributions of maternal, paternal, and offspring traits on seed size. Maternal plants varied in the size and number of seeds produced, with more heterozygous mothers producing heavier seeds. Outcrossed seeds were heavier than selfed seeds, and seeds on inflorescences with low sibling relatedness were likewise heavier. We also provide some of the first empirical evidence that seed size in natural plant populations is strongly affected by paternity. Moreover, fathers with high siring success produced significantly smaller seeds, suggesting that investment in fertilization could be condition- or stage-dependent. As such, life-history and mating system shifts, resulting from environmental stressors, may result in changes in seed size and number, with important implications for population stability and productivity.

Marine urbanization creates novel benthic habitat in coastal areas around the world. This process includes the construction of artificial reefs, energy infrastructure, and jetties. These hard structures are colonized by epibenthic communities of macroalgae and sessile invertebrates. The factors influencing the composition of epibenthic communities must be understood to build structures that incorporate epibenthic organisms into their design through anthropogenic ecosystem engineering. An epibenthic community on the Masonboro Inlet jetty at Wrightsville Beach in coastal North Carolina, USA was surveyed biweekly from May to September 2022. Both sides of the jetty (aspect), at two depths (1.0m; 5.0m below MLLW) were surveyed providing four sites (north-shallow, south-shallow, north-deep, south-deep). The orientation of each surface photographed was recorded. Physical drivers of community structure (aspect, depth, and orientation) were compared to environmental drivers (light and temperature) recorded every 15 minutes for the duration of the sampling period. Overall, the effect of depth on community composition was greater than the effect of orientation, which was greater than the effect of aspect. Community appeared to better correlate with light than with temperature, though after accounting for structural effects and sample date, additional effects of light and temperature were minimal. Algal abundance was greater at shallow sites and on horizontal surfaces while invertebrate abundance was greater at deep sites and on vertical surfaces. We propose that these patterns and drivers of community composition observed have functional implications at the ecosystem level which may be considered during planning and design of new marine structures.

North Carolina is located in a biogeographic transition zone where temperate and tropical seagrass species, Zostera marina and Halodule wrightii, form seasonal monospecific and mixed meadows. Climate change is altering the relative abundance of Z. marina and H. wrightii which may impact critical nursery habitat for the ecologically and economically important blue crab. This study aimed to determine the impact that shifting seagrass composition may have on habitat utilization by juvenile blue crabs. Five study sites were established in Topsail Sound and Chadwick Bay, North Carolina. Blue crabs were sampled monthly from April to November 2021–2022 in patches dominated by H. wrightii, Z. marina, mixed seagrass assemblages, and unvegetated habitats. Overall higher densities of juvenile blue crabs were found in seagrass meadows compared to unvegetated habitats, regardless of species, highlighting the overall importance of seagrass as one of several critical nursery habitats for blue crabs even at a biogeographical boundary for both seagrass species. When comparing between seagrass species, no differences were found in the Spring and greater densities of juvenile blue crabs were found in H. wrightii patches starting in the Summer for both years. Mixed meadows were an important intermediate habitat during transition periods in seagrass dominance. Juvenile blue crab size class varied significantly across some months and habitats, likely reflecting summer recruitment events. While the continued loss of Z. marina from NC shallow coastal habitats may negatively impact numerous ecosystem services, habitat provision for early juvenile blue crabs may be retained in areas where H. wrightii remains.

North Carolina (NC) is in a biogeographic transition zone where climate change is altering the relative abundances (e.g., areal extent, percent cover, biomass) of Zostera marina and Halodule wrightii. Warmer water temperatures are driving losses in Z. marina, leading to increased meadow patchiness. Although water temperatures are rising in NC, heat-tolerant H. wrightii is not filling in bare patches, which may result from abiotic stressors. This study investigated H. wrightii cold tolerance across different populations by quantifying the effects of cold stress on biomass and photosynthetic efficiency during a 3-week laboratory experiment and a 3-month observational study. H. wrightii shoots for the experiment were collected from NC, Mississippi (MS), and Florida (FL) and exposed to 23 °C, 10 °C, and 5 °C. Seagrass was also collected from FL, MS, and at 3 sites in NC during November–January of 2022–2023. Post experiment, there was a significant increase in the belowground biomass in the NC 10 °C treatment but no difference between populations in photosynthetic efficiency. Field metrics displayed population-specific differences, with the northernmost sites having the highest shoot density and belowground biomass per unit area. These findings suggest that H. wrightii at its biogeographic limit may allocate more carbon into belowground material than populations at the central part of the species range in response to thermal stress as a means of winter torpor, which may explain the lack of patch expansion in NC. Cold tolerance in tropical species like H. wrightii may therefore be essential to examine as a limiting factor for the tropicalization of temperate seagrass meadows.

Genetic diversity can modulate a population’s response to a changing environment and plays a critical role in its ecological function. While multiple processes act to maintain genetic diversity, sexual recruitment remains the primary driving force. At its southern edge-of-range, warming sea surface temperatures have resulted in shifts to a mixed-annual life-history strategy in the eelgrass (Zostera marina). Given that mating systems are intimately linked to standing levels of genetic variation, understanding the scope of sexual recruitment illuminates the processes that shape genetic diversity. To that end, developing seeds on flowering Z. marina shoots were genotyped from three meadows in Topsail, North Carolina. In all meadows, levels of multiple mating were high, with shoots pollinated by an average of 8 sires (range: 3 – 16). The number of fertilized seeds (i.e., reproductive success) varied significantly across sires (range: 1 – 25) and was positively correlated with both individual heterozygosity and self-fertilization. Outcrossing rates were high (approx. 70%) and varied across spathes. The reliance on sexual recruitment was also evident among sampled shoots, as no clones were detected and kinship among shoots was low. Given the role that genetic diversity plays in enhancing resistance to and resilience from ecological disturbance, disentangling the links between life-history, sexual reproduction and genetic structure will aid in informing the management and conservation of this key foundation species.

Estuarine seagrasses, submerged flowering plants found in tidally influenced coastal systems, deliver numerous essential ecosystem functions. These important foundation species provide habitat and nursery grounds, sequester carbon, and stabilize shallow coastal sediments. Despite their importance to coastal systems, seagrass meadows are threatened worldwide, with their known global areal extent declining by 5,602 km2 since 1880. Losses are attributed to both natural and anthropogenic sources, including direct impacts of climate change via sea-level rise, increasing water temperatures, greater storm frequency, and changes in salinity regimes. In addition, estuarine seagrasses are found in highly utilized coastal areas where climate stressors interact with non-climate impacts such as modified watersheds, increased nutrient and sediment inputs, coastal acidification, and direct impacts from coastal development or dredging. As a result, estuarine seagrasses are changing phenology and growth patterns, shifting geographic distributions, and invasive species are outcompeting native seagrasses. In response, there has been an increased effort to monitor and protect seagrasses at a global scale and to include seagrasses in management actions that will help mitigate climate and anthropogenic stressors. While climate change will be a continued challenge to seagrass survival and resiliency, efforts in rehabilitation, revegetation, and restoration of seagrass meadows continue with increasing signs of success. However, achieving seagrass recovery and stability in many systems will not be accomplished over the short term. It will require a long-term concerted mix of scientific investigations, governmental regulations and directives, management applications, regular monitoring programs, public participation and education, and periodic reassessment of the goals, methods, and their application to achieve success.

Report cards that are designed to monitor environmental trends have the potential to provide a powerful communication tool because they are easy to understand and accessible to the general public, scientists, managers and policy makers. Given this functionality, they are increasingly popular in marine ecosystem reporting. We describe a report card method for seagrass that incorporates spatial and temporal variability in three metrics—meadow area, species and biomass—developed using long-term (greater than 10 years) monitoring data. This framework summarises large amounts of spatially and temporally complex data to give a numeric score that provides reliable comparisons of seagrass condition in both persistent and naturally variable meadows. We provide an example of how this is applied to seagrass meadows in an industrial port in the Great Barrier Reef World Heritage Area of north-eastern Australia.

Background and aims: Long distance dispersal (LDD) contributes to the replenishment and recovery of tropical seagrass habitats exposed to disturbance, such as cyclones and infrastructure development. However, our current knowledge regarding the physical attributes of seagrass fragments that influence LDD predominantly stems from temperate species and regions. The goal of this paper is to measure seagrass fragment density and viability in two tropical species, assessing various factors influencing their distribution. Methods: We measured the density and viability of floating seagrass fragments for two tropical seagrass species (Zostera muelleri and Halodule uninervis) in two coastal seagrass meadows in the central Great Barrier Reef World Heritage Area, Australia. We assessed the effect of wind speed, wind direction, seagrass growing/senescent season, seagrass meadow density, meadow location and dugong foraging intensity on fragment density. We also measured seagrass fragment structure and fragment viability; i.e., potential to establish into a new plant. Key results: We found that seagrass meadow density, season, wind direction and wind speed influenced total fragment density, while season and wind speed influenced the density of viable fragments. Dugong foraging intensity did not influence fragment density. Our results indicate that wave action from winds combined with high seagrass meadow density increases seagrass fragment creation, and that more fragments are produced during the growing than the senescent season. Seagrass fragments classified as viable for Z. muelleri and H. uninervis had significantly more shoots and leaves than non-viable fragments. We collected 0.63 (+/- 0.08 SE) floating viable fragments 100 m 2 in the growing season, and 0.13 (+/- 0.03 SE) viable fragments 100 m 2 in the senescent season. Over a third (38%) of all fragments collected were viable. Conclusion: There is likely to be a large number of viable seagrass fragments available for long distance dispersal. This study's outputs can inform dispersal and connectivity models that are used to direct seagrass ecosystem management and conservation strategies.

Ascidians are sessile marine invertebrates found all over the world in a variety of natural and artificial habitats. The objective of this study was to provide the first inventory of ascidian diversity and abundance in North Carolina (NC) seagrass meadows. Eight sites along the NC coast were surveyed in May and June 2021 and at each site, 20 quadrats were deployed. All ascidian species within the quadrats were counted and identified based on morphological characterization and sequencing of the barcoding gene. Seagrass percent cover, biomass, and shoot density were also quantified. Ascidians were found in six sites and four species were recorded: the solitary species Molgula manhattensis, Styela plicata, and Bostrichobranchus sp., and the colonial Didemnum lutarium. Colonial specimens were generally attached to hard substrate, while solitary species were often found attached to seagrass rhizomes and leaves. S. plicata and M. manhattensis haplotype diversity were equivalent to previous descriptions from individuals collected on artificial substrates and other locations. Ascidian abundance was positively correlated with seagrass biomass but not with seagrass percent cover. A fifth species, the solitary Styela canopus, appeared in a site revisited in October 2021. Temperate ascidians are known to have seasonal cycles, thus further research should include monthly surveys to assess ascidian diversity and abundance over time.

Seed size can have an impact on angiosperm reproductive fitness. Ecological theory predicts plants that will produce larger seeds in stressful environments to increase the chances of seedling survival and numerous small seeds in favourable conditions to increase the number of recruits. We measured seed morphology of the seagrass Heterozostera nigricaulis from four populations under differing environmental conditions in South East Australia. Seed size and mass among sites showed consistent differences over four flowering seasons. Seeds from exposed, ephemeral meadows (Blairgowrie, Edwards Point) were 19%–53% heavier than those from larger, stable meadows at more sheltered sites (Swan Bay, Point Henry). Overall, heavier seeds from exposed sites performed better in germination experiments and persisted (remained viable) longer compared to small seeds from sheltered sites. Seeds from sheltered sites showed contrasting levels of seed performance. Small seeds from Swan Bay had the lowest germination but the proportion of viable seeds after 12 months were much higher (41%) than similar sized seeds from Point Henry (0%). There are clear life history benefits of large seeds that facilitate seed persistence and germination at exposed sites; however, the performance of smaller seeds varied between sites and may be a function of other site-specific advantages.

Species, including seagrasses, at their range limits are uniquely vulnerable to climate change. In the western Atlantic Ocean, the biogeographic transition zone between temperate and tropical ecosystems is recognized as one of several global hotspots where poleward-flowing western boundary currents are forecast to warm faster than the global average. In this region seagrass ecosystem services are primarily supplied by two species, Zostera marina, a temperate seagrass at its southern range limit and Halodule wrightii, a tropical seagrass at its northern limit. Water temperatures in the study location in Back Sound, North Carolina, USA have gradually increased the length of the stressful summer season for Z. marina (beginning after 3 consecutive days of daily mean water temperatures >23°C, ending after 3 consecutive days <25°C) from 84 days in 1962 to 156 days in 2019. The occurrence of extreme water temperatures also increased resulting in temperatures ≥30°C occurring more frequently in the last decade (2009-2019) than the previous 10 years. Biomass and aerial imagery collected periodically from 1981-2019 indicate that Z. marina biomass remained stable until 2008 but declined to 30-year low levels by 2019. Meadow area estimated from imagery collected during peak Z. marina biomass did not show a significant trend over time; however, lowest meadow area during the time series was recorded in 2019. Despite summer warming, H. wrightii biomass remained steady between 1979-2019 but did not replace Z. marina as the dominant species in the cooler months. We hypothesize that persistence of temperate Z. marina populations under stressful water temperatures is positively influenced by water clarity, life history, and meadow stability, due in part to the consistent presence of tropical H. wrightii maintaining meadow biomass and area. However, temperate species in edge-of-range tropicalized meadows, are still limited by physiological thresholds, and when these limits are exceeded, related declines in meadow biomass and area may not be fully replaced by tropical species immediately. Therefore, while tropicalization of seagrass meadows may result in greater resilience to abiotic stressors in the short-term, declines in biomass and area during the process of tropicalization may have significant impacts on meadow function.

Seagrass meadows are some of the most productive marine plant ecosystems in the world, yet their loss continues on a global scale. Zostera marina , an ecologically important foundation species, reproduces both sexually and asexually, yielding different levels of genetic diversity throughout its range, which in turn can influence resistance to, and resilience from, environmental disturbances. Understanding the genetic structure and diversity of these populations, and how they fluctuate over space and time, will aid in the conservation and management of seagrasses in an environment where the effects of climate change are likely to be chronic. Using microsatellite data, we examined spatiotemporal genetic structure and genetic diversity of Z. marina over a 10 yr period at 2 sites in North Carolina (USA), the southern limit of its geographic range in the Western Atlantic. Both meadows were genetically diverse, with very little spatial genetic structure existing within and between sites, and relative temporal stability between decadal time points. Within-site kin structure was more pronounced in the earlier years, and allelic richness increased over time at both sites, suggesting an increase in sexual reproduction, potentially in response to thermal stress. Despite the genetic similarities between sites, life history strategies showed phenotypic plasticity, and several metrics of genetic diversity were associated with meadow health. These findings point to the adaptive potential of Z. marina and provide promising insight into how the species will perform as the effects of climate change continue to amplify over the next century.

EDITORIAL article Front. Mar. Sci., 01 December 2022Sec. Marine Ecosystem Ecology Volume 9 - 2022 | https://doi.org/10.3389/fmars.2022.1091366

Major storms can alter coastal ecosystems in several direct and indirect ways including habitat destruction, stormwater-related water quality degradation, and organism mortality. From 2010–2020, ten tropical cyclones impacted coastal North Carolina, providing an opportunity to explore ecosystem responses across multiple storms. Using monthly trawl and contemporaneous seagrass surveys conducted in Back Sound, NC, we evaluated how cyclones may affect the nursery role of shallow-water biogenic habitats by examining seagrass-associated fish responses within a temperate-subtropical estuary. We employed a general before-after-control-impact approach using trawls conducted prior (before) and subsequent (after) to storm arrival and years either without (control) or with (impact) storms. We examined whether effects were apparent over short (within ~three weeks of impact) and seasonal (May-October) timescales, as well as if the magnitude of storm-related shifts varied as a function of storm intensity. Our findings suggest that the ability of these shallow-water habitats to support juvenile fishes was not dramatically altered by hurricanes. The resilience exhibited by fishes was likely underpinned by the relative persistence of the seagrass habitat, which appeared principally undamaged by storms based upon review of available–albeit limited seagrass surveys. Increasing cyclone intensity, however, was correlated with greater declines in catch and may potentially underlie the emigration and return rate of fish after cyclones. Whether estuarine fishes will continue to be resilient to acute storm impacts despite chronic environmental degradation and predicted increases major tropical cyclone frequency and intensity remains a pressing question.

Angiosperms have co-evolved with animals over thousands of years leading to an array of mutualistic relationships. Passage of plant seeds through animal intestines leads to an important mutualism providing the animal with food and the plant with seed dispersal and enhanced germination. This phenomenon is well studied in terrestrial angiosperms, but there is less research in aquatic environments. We studied the effect of gut passage in marine mega-herbivores (green sea turtles and dugongs) on seed germination for a common Australian seagrass, Zostera muelleri. We collected fecal samples likely to contain seeds, as well as seagrass seeds from plants at two coastal seagrass meadows in the central Great Barrier Reef World Heritage Area, Australia. Seeds collected from feces and plants were subjected to germination trials across different temperature treatments: low (19 degrees C), medium (26 degrees C), and high (32 degrees C). We found excreted seeds had a significantly greater germination probability (two to four times greater) and germinated significantly faster (18-61% faster) than seeds from the plant. Excreted seeds which had not germinated at the end of the experiment were significantly less likely to be viable compared with seeds taken from the plant. Seeds released from the plant have a slow germination and low germination probability compared with excreted seeds, but retain a high percentage of seed viability. Our study is the first record of marine mega-herbivores enhancing germination of Z. muelleri seeds. By transporting seeds to new locations and enhancing germination, these animals are important in seagrass resilience and connectivity among metapopulations.

We examined the spatial structure (distribution, density) and function (viability) of the seagrass sediment seed bank, the storage of viable propagules (e.g. seeds, tubers, diaspores) in the sediment over time,in the northern Great Barrier Reef World Heritage Area in Cairns, Queensland, following a large-scale decline in seagrass area. A spatially explicit seagrass seed bank analysis was paired with a long-term annual assessment of seagrass distribution to assess seed bank spatial patterns and their relationship with the recovery and presence of seagrass, and water depth. Four years post-decline, the seed bank contained Zostera muelleri, Halodule uninervis, Halophila ovalis and Cymodocea serrulata seeds. Seed banks reflected adjacent meadow community composition; however, the density of seeds for all recorded species was significantly lower than analogous seagrass populations, indicating a reduction in the capacity for recovery from the seed bank. A spatial structure existed in both the total (viable + non-viable) and viable seed bank, and distance between seed clusters ranged from 50-550 m depending on species and seed type. Observed patterns in clustering may be explained by variation in water depth and the past distribution of seagrass in these meadows. These results demonstrate that the distribution of seagrass seeds within the seed bank, which directly influences the natural recovery of seagrass communities, is not uniform across species and may result in patchy recovery of the meadows. Therefore, the resilience provided by the seed bank in seagrass communities should not be viewed as a static level of insurance for the entire meadow, but rather as dynamic and species-specific, with variability over both space and time.