Seagrass Cover Research Articles

Effects of anthropogenic pressures on the seagrass Halophila stipulacea and its associated macrozoobenthic communities in the northern Gulf of Aqaba

Halophila stipulacea is a tropical seagrass species, native to the Red Sea, Persian Gulf, and Indian Ocean, while invasive to the Mediterranean and Caribbean Seas. The benthic fauna assemblages associated with H. stipulacea in its native habitats and the potential effects of anthropogenic stressors on these assemblages remain unknown. We compared meadow characteristics, associated fauna assemblages and trophic niche structures of H. stipulacea from an impacted and a pristine site in the northern Red Sea. Seagrass cover and biomass were higher in the impacted site, however, the associated fauna community was more abundant and diverse in the pristine site. Both meadows showed comparable trophic niches based on stable isotope analysis. This study provides first insights into the macrozoobenthos associated with H. stipulacea in its native habitat and highlights the importance of better understanding the relationship between seagrasses and their associated biota and the potential effects of urbanization on this relationship.

Seagrass meadow stability and composition influence carbon storage

ContextSeagrass ecosystems are lauded for storing organic carbon in underlying sediments, but storage is highly variable, even at relatively small spatial scales. While environmental setting and seagrass cover are known drivers of carbon storage capacity, it is unclear how other seagrass features such as species composition influence carbon storage, and whether historical vs. contemporary features are better predictors of storage.ObjectivesWe examined the influence of historical and contemporary seagrass variables on surface (0–10 cm) sediment organic carbon storage at the meadow-scale (~ 25 km2), in addition to the influence of environmental drivers. Our study area was located within a subtropical mixed-species seagrass meadow along a low-energy coastline in the northeastern Gulf of Mexico (Cedar Key, Florida, USA).MethodsWe derived historical metrics of seagrass cover and composition from 14-year seagrass monitoring datasets and measured surface sediment carbon densities and grain size, contemporary seagrass biomass and species composition, as well as environmental characteristics related to hydrology and physical disturbance (i.e., relative exposure, elevation, and distance to navigation channels). We assessed bivariate relationships between predictor variables and surface carbon densities with linear regression analyses and used path analysis to assess hypothesized relationships between a subset of predictor variables and carbon densities.ResultsWhile low relative to global values, surface carbon densities in Cedar Key seagrass meadows varied by an order of magnitude. Sediment grain size was strongly related to carbon densities, but environmental variables had only indirect effects on carbon densities. Historical seagrass cover, variability in cover, and species diversity were generally better predictors of storage than contemporary variables. Historical and contemporary species identity–specifically the presence of Thalassia testudinum–were also significant drivers of storage.ConclusionsIn Cedar Key, historically diverse and persistent seagrass meadows dominated by late-successional species contained the largest surface carbon stores. Our results highlight the importance of site history in terms of meadow stability (inversely measured as variability in cover) as well as species identity and diversity in enhancing surface carbon storage. The environmental variables we examined had comparatively weak effects on carbon densities, however, relative exposure and elevation may not be the most relevant hydrological drivers of carbon storage at the meadow scale. Together, these findings suggest that drivers of seagrass meadow carbon storage are context and scale dependent.

Hubungan Kerapatan Lamun dan Kelimpahan Teripang (Holothuroidea) di Pulau Meosmangguandi Taman Wisata Perairan Padaido-Biak

Seagrasses and sea cucumbers have a close relationship in determining ecological functions. The purpose of this study was to investigate the relationship between seagrass density and sea cucumber abundance on Meosmangguandi Island, Biak. The research was conducted in August-September 2021 at two stations. The location was chosen purposively on the East side (Station I, conservation location) and the West side (Station II, around residential areas and fishing activities). The 5m line transect method (2.5m to the right and 2.5m to the left) is used to reach the destination. The study found 6 species of seagrass namely C. rotundata, T. hemprichii, E. acoroides, H. pinifolia, H. ovalis and Syringodium isoetifolium, and 9 species of sea cucumbers namely Actinopyga lecanora, A. miliaris, A. mauritiana, Bohadschia similis, Holothuria atra, H. coluber, H. scabra, H. albiventer, and teripang malam. Percentage of seagrass cover at Station I was 85.51% and Station II was 57.71%, with a relative density of seagrass C. rotundata 39.10% and T. hemprichii 27.09%. The relationship between the density of seagrass C. rotundata and the abundance of sea cucumbers A. lecanora 4.285 > X2 (1:0.05); T. hemprichii with A. mauritiana 6.887> X2 (1;0.05); seagrass C. rotundata with A. miliaris 4.285 > X2 (1:0.05); A. miliaris with seagrass H. pinifolia 7.048 > X2 (1:0.05); density of seagrass T. hemprichii with abundance of sea cucumber B. similis: 5.274 > X2 (1:0.05); H. atra 5 > X2 (1:0.05); and H. coluber 5.172 > X2 (1:0.05), indicating an association between seagrass density and sea cucumber abundance.

Impact of sand bund removal on seagrass ecosystems: A study of macrobenthic community structure and correlation with macrophytes cover and sediments

This study investigated the impacts of the removal of sand bund on the macrobenthos community structure, seagrass cover, and sediment particle size in Merambong Shoal, Malaysia. The reclamation project deposited sand bund in the middle of Merambong seagrass shoal, resulting in its division into northern (NS) and southern (SS) halves. Ecosystem changes were monitored over a 31-month period using the transect lines method. Bi-monthly samples were collected for assessment. The results revealed a substantial decline in macrobenthos densities compared to previous studies. However, after the removal of the sand bund, there was a significant increase in macrobenthos density, specifically Polychaeta and Malacostraca, at NS. Seagrass cover at NS was initially lower than SS but showed an increase after the complete removal of the sand blockage. Sediment particle analysis reported a higher silt percentage at NS, indicating greater sedimentation at NS, which was partially sheltered from wave actions.

DESCRIPTION AND LEVEL OF DEGRADATION OF SEA SEA BASED ECOSYSTEMS IN THE COASTAL AREA OF UWEDIKAN VILLAGE, EAST LUWUK DISTRICT, BANGGAI DISTRICT

The seagrass ecosystem is an ecosystem that is very important to support the sustainability of the biota that take shelter in it. The seagrass ecosystem is known as one of the areas that is vulnerable to damage. Various human activities, such as fishing and industrial activities can trigger this damage. This study aims to provide information regarding the description and level of degradation of the seagrass meadow ecosystem in Uwedikan Village. The method used is random sampling method. The results showed that there were 5 species of seagrass found, namely Enhalus acoroides, Thalassia hemprichii, Cymodocea Serullata, Cymodocea rotundata and Halophila ovalis. Seagrass cover averaged 40.60% at Tanjung Balean and 33.1% at the Tambatan Perahu. This is included in the moderate/less rich category. The highest seagrass cover was for Thalassia hemprichii with a total of 2,169 individuals at Tanjung Balean and 1,453 at the Boat Mooring. The relationship of water parameters, namely temperature, degree of acidity (pH) and brightness greatly affect the growth of seagrass ecosystems. In particular, the temperature at the two locations obtained different values, namely 29--30.5°C at Tanjung Balean and 30--35.3°C at the Tambatan Perahu.

Warming and grazing independently and interactively impact plant defenses and palatability

The ecological impacts of multiple stressors are hard to predict but important to understand. When multiple stressors influence foundation species, the effects can cascade throughout the ecosystem. Gulf of Mexico seagrass ecosystems are currently experiencing a suite of novel stressors, including warmer water temperatures and increased herbivory due to tropicalization and conservation efforts. We investigated the impact of warming temperatures and grazing history on plant performance, morphology, and palatability by integrating a mesocosm study using the seagrass Thalassia testudinum with feeding trials using the sea urchin Lytechinus variegatus. Warming temperatures negatively impacted T. testudinum tolerance traits, reducing belowground biomass by 34%, productivity by 74%, shoot density by 10%, and number of leaves per plant by 24%, and negatively impacted resistance traits through 13% lower toughness of young leaves and a trend for reduced leaf carbon:nitrogen. Lytechinus variegatus individuals preferred to consume plants grown under heated conditions, which supports findings of enhanced palatability. Simulated turtle grazing impacted more plant traits than grazing by other herbivores, potentially diminishing plant resilience to future disturbances through reduced rhizome non‐structural carbohydrate concentrations and increasing palatability through reduced fiber content and 23% lower leaf carbon:phosphorus. Simulated turtle, simulated parrotfish, and urchin grazing reduced leaf carbon:nitrogen by 11%, also potentially increasing nutritive value. Interactions between warming temperatures and grazers on plant traits were additive for 16 out of 19 response variables. However, the stressors non‐additively impacted the number of leaves per plant, fiber content, and epiphyte load. We suggest that the impacts of grazers on leaf turnover rate and leaf age may vary based on water temperature, potentially driving these interactions. Overall, increased temperatures and grazing pressure will likely reduce seagrass resilience, structure, and biomass, potentially impacting feedback systems and producing negative consequences for seagrass cover, associated species, and ecosystem services.

Seagrass cover reduction in Zanzibar from 2006 to 2019

Seagrass meadows are abundant in Zanzibar, Tanzania and provide essential ecosystem services, yet they have been less researched or protected than other marine ecosystems. Evidence suggests that anthropogenic impacts, such as seaweed farming, small-scale fishing, and tourism, are their greatest threats. Using geographic information systems (GIS) to estimate seagrass cover, this study conducted Spearman’s rank correlation analyses to estimate correlations between the scale of seaweed farming, fishing, and tourism or the implementation of marine protected area (MPA) management plans, and the change in percent of seagrass cover from 2006 to 2019. On average, seagrass cover decreased by 10.98 % over this period. The scale of tourism was negatively correlated with seagrass cover (rs (9) = -0.64, p = 0.044). No other variables were correlated with declines, though seaweed farming had a weak protective effect on seagrass cover (rs(9) = 0.28, p = 0.426). To improve the management of seagrass meadows, plans must identify seagrasses as critical ecosystems, expand seagrass restoration projects, and address harmful practices in the tourism industry.

Mapping of seagrass ecosystem on Bontosua Island, Pangkep District, South Sulawesi, Indonesia

Abstract. Rosalina D, Jamil K, Arafat Y, Amalia R, Leilani A. 2023. Mapping of seagrass ecosystem on Bontosua Island, Pangkep District, South Sulawesi, Indonesia. Biodiversitas 24: 2023-2030. Bontosua Island is one of the islands in South Sulawesi, Indonesia, that has a seagrass ecosystem. The purpose of this study was to assess the density, cover, area, and condition of seagrass on Bontosua Island. The data collection involved the use of a quadratic transect method in the field and the Lyzenga method for remote sensing. The identification of seagrass areas was made using Landsat 8 OLI/TIRS satellite. Six seagrass species were identified, namely Cymodocea rotundata, Thalassia hemprichii, Halodule uninervis, Halodule pinifolia, Syringodium isoetifolium and Halophila sp. The results showed that C. rotundata had the highest density value of 89 Ind/m² and was categorized as rather dense, while C. rotundata also had the highest percentage cover of 58%, and Halophila sp. had the lowest percentage cover of 2%. The distribution area of seagrass beds on Bontosua Island was approximately 28.26 ha, out of a total area of 92 ha, of which approximately 6 ha was land. Observations on the condition of seagrass beds showed that 16.65 ha was healthy, 6.3 ha was unhealthy, while 5.31 ha was poor.

Diversity, carbon stock and associated biota of seagrass beds in Central Tapanuli District, North Sumatra, Indonesia

Abstract. Maulita M, Nugraha E, Suharti R, Tanjung NW, Sayuti M, Mulyono M, Mantani S, Setiarto RHB. 2023. Diversity, carbon stock and associated biota of seagrass beds in Central Tapanuli District, North Sumatra, Indonesia. Biodiversitas 24: 2080-2087. Various human activities emit carbon dioxide which drives global warming and climate change. Seagrass ecosystems can absorb and store enormous quantities of carbon, hence reducing carbon emissions. This research aimed to assess the diversity, vegetation cover, carbon stock and associated biota of seagrass beds in Central Tapanuli District, North Sumatra, Indonesia. Purposive sampling method was employed with data collection used the line transect quadrant method. Carbon stock was measured using the loss of ignition method. There were four species of seagrass in the studied area, namely Enhalus acoroides (L.f.) Royle, Thalassia hemprichii (Ehrenb. ex Solms) Asch., Cymodocea rotundata Asch. & Schweinf. and Halodule uninervis (Forssk.) Boiss. with a density ranging from 23-164 stands/m2. Seagrass cover ranged from 3.87%-34.37%. Associated biota (fish and crustaceans) at each observation station were Siganus javus Linnaeus 1766, Siganus canaliculatus Park 1797, Siganus vermiculatus Valenciennes 1835, Colomesus psittacus Bloch & Schneider 1801, Epinephelus fuscoguttatus Forsskål 1775, Terapon jarbua Forsskål 1775, Ambassis dussumieri Cuvier 1828, Cryptocentrus leptocephalus Bleeker 1876, Leiognathus robustus Sparks & Dunlap 2004, Portunus armatus A.Milne-Edwards 1861, Rhinolambrus pelagicus Rüppell 1830 and Hippolyte obliquimanus Dana 1852. The total carbon stock of the top substrate (leaves) was 12.8 tons, while carbon bottom substrate (rhizomes and roots) was 12.9 tons, resulting in a total carbon stock of 25.7 tons. The analysis of water quality parameters indicated that the studied area had suitable environmental conditions for seagrass growth. The results of this study add new information regarding seagrass ecology of the western region of Indonesia, especially Sumatra.

Evaluation feasibility and ecological gap in marine conservation area of Southeast Sulawesi Province

Aquatic Tourism Park (ATP) of the Southeast Sulawesi Province has significant contribution to achieve the total targeted of 30 million of Marine Protected Areas (MPA) in Indonesia. The conservation area is located in 3 coastal districts of Konawe, South Konawe, and Kendari City Districts. The time-consuming process of legalizing the conservation area has driven the need to re-evaluate the ecological conditions from 2012 to 2020. The objective of this study is to this aims to determine the status, gaps and ecological feasibility of conservation areas in the Southeast Sulawesi region. One of the noticeable gaps is the change of ecological conditions in the reservation area. The gap could be identified by comparing ecological conditions before and after the area was reserved for a conservation area. Ecosystem suitability was measured by using ecological criteria, such as number of protected fish species, mangrove density, seagrass coverage, coral coverage, and naturalness. The score of suitability assessment was 31, which showed that the reserved location was suitable for a Marine Conservation Area. However, gap analysis results showed 10% decline in coral coverage and 17% decrease in seagrass coverage, while mangrove density decreased as much as 102 trees/ha during that period. Evaluation on the ecosystem condition was conducted by applying suitability analysis of the modified E-KKP3K dan Sambah et al. (2020) methods, resulting a status of suitable or conservation area allocation (score 31). Criteria used were chosen based on its contribution in facilitating important ecological processes and as ecosystem buffer system in the area. This study will give the implementation on MPA management optimalisation and it can be contributed on fisheries management.Keywords:Conservation areaFeasibility areaGapSoutheast Sulawesi

Capturing twenty years of change in ecosystem services provided by coastal Massachusetts habitats

Accounting for ecosystem services across expansive and diverse landscapes presents unique challenges to managers tasked with navigating and synthesizing the social-ecological dynamics of varied stakeholder interests and ecological functions. One approach to this challenge is through expert based matrices that provide valuations for specific service-habitat combinations. In this study, we combine a literature review with local expert input to build an ecosystem service capacity matrix for the Massachusetts Bays National Estuary Partnership (MassBays). We then apply this matrix to a custom conglomerate land cover data set and a habitat connectivity analysis to assess the spatial and temporal dynamics in select ecosystem services of coastal habitats across MassBays from 1996 to 2016. In 1996, saltmarsh was the primary provider of coastal ecosystem services, representing roughly 60% of the total service capacity. More specifically, high elevation saltmarsh was top-ranked, followed by tidal flats, seagrass, low elevation saltmarsh and unclassified saltmarsh. This distribution of service provisioning varied considerably among the five regions of MassBays, reflecting the unique habitat mixes and local expert valuations of each. Although saltmarsh dominated the overall production of services, seagrass and tidal flats drove 97% of the service changes that occurred from one year to the next. From 1996 to 2016, MassBays lost 50% of its seagrass cover and gained 20% more tidal flats, resulting in a 5% overall loss in ecosystem services. Again, this varied among the five regions, with Cape Cod losing as much as 12% of a given service while the Upper North Shore gained 4% in services overall. We bootstrapped the analysis to provide a range of probable outcomes. We also mapped the changes in service production for each of the sixty-eight embayments. This analysis will aid local managers in accounting for ecosystem services as they develop management plans for their represented stakeholders.

Detecting trends in seagrass cover through aerial imagery interpretation: Historical dynamics of a Posidonia oceanica meadow subjected to anthropogenic disturbance

Over the last century, P. oceanica meadows have undergone significant regression along Mediterranean coasts due to anthropogenic disturbances. Using an integrated approach based on historical aerial photography interpretation in GIS environment and Bayesian modelling, we mapped the upper limits of a P. oceanica meadow and identified the most influential disturbance factors acting along the coast of Giglio Island, where several local human-mediated impacts have historically co-occurred from 1968 to 2013. Model selection based on the DIC criterion suggested that the presence of the impacts is suitable for describing the seagrass coverage variation. Similarities in P. oceanica cover within 13 investigated zones were highlighted when considering the most relevant impacts, such as harbour expansion, mining, and anchoring. The detected adverse effects indicate the need for implementing management actions focusing on the present and past sources of impact to reduce their effect on P. oceanica beds actively.

Carbon Stored on Seagrass Beds in Gili Maringkik, Lombok, Indonesia

Seagrass beds are an important vegetation for reducing the impact of global warming besides the function of forest and mangroves vegetation. The research aims to find the composition of seagrass species, density, seagrass coverage, seagrass standing biomass, seagrass standing carbon and substrate carbon. The research was conducted in Gili Maringkik, Lombok, Indonesia. The research included observation of species composition and the sample was collected from 0.5 ×0.5 m plot area. Total plot area was 25 on five lanes with the space between plots 25 m and between lanes 100 m. The researcher found that there were eight seagrass species (two families, six genera): Cymodocea rotundata, Cymodocea serrulata, Enhalus acoroides, Halodule pinifolia, Halophila minor, Halophila spinulosa, Syringodium isoetifolium and Thalassia hemprichii. Cymodocea rotundata (506.40±187.809 stand.m-2) was the species of highest density and while the species of Thalassia hemprichii (36.52±30.004 %) was the species of highest coverage. Total of seagrass standing biomass in Gili Maringkik was 1081.85 g.DW.m-2 with the carbon stock of seagrass beds was 483.86 g.C.m-2 and substrate carbon content was 0.09%–0.49%. the total carbon stock of seagrass beds in Gili Maringkik has 153.96 ton.C (4.84 ton.C.Ha-1).

Short Communication: Diversity, biomass, and carbon stock of seagrass community in three coastal waters of Minahasa Peninsula, North Sulawesi, Indonesia

Abstract. Wagey BT, Paruntu C, Lasabuda R, Kambey A. 2023. Short Communication: Diversity, biomass, and carbon stock of seagrass community in three coastal waters of Minahasa Peninsula, North Sulawesi, Indonesia. Biodiversitas 24: 1793-1798. Seagrasses are well-known for their ecological and economic importance. However, just like any other ecosystem, seagrass meadows around the world are threatened by anthropogenic activities. This paper aimed to analyze the seagrass abundance (expressed as shoot density), richness, diversity, biomass, and carbon stocks in three locations in the Minahasa Peninsula of North Sulawesi, Indonesia. Transect survey techniques were conducted in Bajo, Bolsel and Bunaken. The study recorded 8 species across the three locations with Bolsel having the highest number of species (7), followed by Bajo (6) and Bunaken (4). Seagrass species differed significantly in terms of shoot density across the sampling locations in which denser shoots were observed for the eelgrass (Enhalus acoroides) at Bolsel while the other two species (Thalassia hemprichii and Cymodocea rotundata) were least abundant at the Bunaken site. Seagrass cover did not vary significantly between sites. With the exception of Bunaken, above-ground and below-ground biomasses, as well as carbon stock, did not differ among locations. The lower species diversity as well as above-ground biomass and carbon stocks in Bunaken were likely due to grazing by herbivores (e.g., fish and sea urchins) and tourism activities (e.g., boat traffic, diving, snorkeling). Grazing effects and human tourism activities should be included in future investigations to monitor the dynamics of seagrass biomass and carbon stocks in the area. This study provides baseline information that can be used to better manage the seagrass ecosystems, not only in the Minahasa Peninsula but in Indonesian waters and even beyond.

Effects of habitat complexity on the abundance and diversity of seagrass leaf meiofauna communities in tropical Kenyan seagrass meadows

We examined the abundance and diversity of seagrass leaf meiofauna, with special emphasis on harpacticoid copepods (Crustacea), in Thalassodendron ciliatum seagrass meadows differing in structural attributes (complexity) in terms of shoot density, canopy, and epiphytic microalgae as well as environmental variables (nutrients). Higher biomass of epiphytic microalgae was observed in study sites with lower shoot density and canopy height. Further, our results showed that seagrass leaf meiofauna assemblages (including harpacticoid copepods) were positively correlated with epiphytic microalgae and water nutrients but negatively correlated to seagrass variables (seagrass cover, shoot density, and canopy height). Our study revealed that food resources were the major determinant of the abundance and diversity of seagrass leaf meiofauna assemblages in these meadows. In contrast to our expectations, meiofauna abundance was negatively associated with seagrass density and canopy height. Thus, the findings indicate that variation in seagrass habitats may, in turn, influence the distribution, community structure, and functioning of epiphytic communities. We suggest that habitat quality depends on the substrate’s longevity supporting epiphytic microalgal biomass that serves as a food source for seagrass leaf meiofauna communities.

Geographic variation in organic carbon storage by seagrass beds

AbstractSince seagrasses are efficient sinks for marine organic carbon, there is growing interest in incorporating seagrass protection and restoration into climate mitigation schemes, that is, offering credit for accumulated carbon to offset carbon dioxide emissions. However, patterns and drivers of organic carbon storage by seagrasses are not well resolved, especially at scales relevant to management decisions. Here, we quantified geographic variation in standing stocks of sedimentary organic carbon (Mg Corg ha−1) associated with seagrasses along the northern Florida Gulf Coast using field surveys and sediment cores. We measured plant biomass, organic carbon, and sediment composition in each core. Using a multivariate modeling approach, we evaluated the relative importance of ecological, physical, oceanographic, and seascape drivers, developing the first spatially explicit predictions of seagrass‐associated carbon stocks for this region. Applying model predictions to confirmed seagrass beds and potential recovery areas, we also estimated the carbon storage value of potential seagrass conservation and restoration as the resulting stock enhancement value per hectare of seagrass (Δ Mg Corg ha−1). We found that organic carbon stored by seagrass sediments varied considerably across this region, with stocks significantly increasing with seagrass cover, proximity to oyster reefs, and distance from river outlets, highlighting potential synergies for coordinated management. We also found that current seagrass beds could offer nearly double the carbon storage value of potential recovery areas, emphasizing the importance of conservation as well as restoration. Our results have important implications for management, restoration, and understanding biogeographic patterns of seagrass ecosystem services.

Providing a framework for seagrass mapping in United States coastal ecosystems using high spatial resolution satellite imagery

Seagrasses have been widely recognized for their ecosystem services, but traditional seagrass monitoring approaches emphasizing ground and aerial observations are costly, time-consuming, and lack standardization across datasets. This study leveraged satellite imagery from Maxar's WorldView-2 and WorldView-3 high spatial resolution, commercial satellite platforms to provide a consistent classification approach for monitoring seagrass at eleven study areas across the continental United States, representing geographically, ecologically, and climatically diverse regions. A single satellite image was selected at each of the eleven study areas to correspond temporally to reference data representing seagrass coverage and was classified into four general classes: land, seagrass, no seagrass, and no data. Satellite-derived seagrass coverage was then compared to reference data using either balanced agreement, the Mann-Whitney U test, or the Kruskal-Wallis test, depending on the format of the reference data used for comparison. Balanced agreement ranged from 58% to 86%, with better agreement between reference- and satellite-indicated seagrass absence (specificity ranged from 88% to 100%) than between reference- and satellite-indicated seagrass presence (sensitivity ranged from 17% to 73%). Results of the Mann-Whitney U and Kruskal-Wallis tests demonstrated that satellite-indicated seagrass percentage cover had moderate to large correlations with reference-indicated seagrass percentage cover, indicative of moderate to strong agreement between datasets. Satellite classification performed best in areas of dense, continuous seagrass compared to areas of sparse, discontinuous seagrass and provided a suitable spatial representation of seagrass distribution within each study area. This study demonstrates that the same methods can be applied across scenes spanning varying seagrass bioregions, atmospheric conditions, and optical water types, which is a significant step toward developing a consistent, operational approach for mapping seagrass coverage at the national and global scales. Accompanying this manuscript are instructional videos describing the processing workflow, including data acquisition, data processing, and satellite image classification. These instructional videos may serve as a management tool to complement field- and aerial-based mapping efforts for monitoring seagrass ecosystems.

Seasonality of Fish Juvenile Community Structure and Diversity in a Tropical Seagrass Meadow of Watamu, Kenya

Seagrass are important marine habitats that function as nursery grounds for juvenile fish. Human activities and other natural factors have contributed to their decline, and this has compromised their role as nurseries, specifically in non-continuous patchy seagrass beds. In this study, juvenile fish abundance from tropical seagrass beds of Watamu were examined, while testing the hypothesis that seagrass cover and seasonality influenced juvenile fish abundanceand diversity. Two sampling stations were identified, Watamu Blue Lagoon (WBL) and Watamu Beach (WB), based on seagrass cover, and were sampled for a period of 10 months that included two south-east monsoon (SEM) and two north-east monsoon (NEM) seasons. Monthly samples were collected by seining within the shallow seagrass habitats of WBL and WB. A total of 31 juvenile fish families were obtained, the dominant taxa being Lutjanidae and Siganidae. Seasonal and interannual variability in juvenile abundance was observed over the two years (p<0.05); year 1 recorded higher abundance than year 2, specifically during the SEM. In year 2 a higher mean abundance was recorded during the NEM when compared to the SEM. Chlorophyll a (p<0.05) and salinity (p<0.05) were found to significantly influence juvenile fish abundance.

Flushing time variability in a short, low-inflow estuary

Flushing time, the time scale for exchange and mixing between embayed and oceanic waters in an estuary, plays an integral role in determining water quality and aquatic ecosystem health. Here, we investigated the spatiotemporal variability of flushing times throughout Morro Bay, a short, low-inflow estuary (LIE) on the California coast, using a calibrated and validated hydrodynamic model (Delft3D). Morro Bay has historically supported an extensive eelgrass (Zostera marina) habitat, which declined substantially from 139 to 5.4 ha during 2007–2017. Eelgrass decline motivated the current research into the role of changing bed roughness and oceanic drivers (i.e., tide and sea-level rise) on estuarine hydrodynamics and flushing times. We found that tidal variability exerts the strongest control on flushing times compared to other effects, i.e., bed roughness or sea-level rise. Additionally, we found that increasing sea level and decreasing bed roughness (associated with declining seagrass coverage) yielded higher rates of mixing (lower flushing times). We detected a strong correspondence between areas having shorter flushing times (e.g., near the estuary mouth) and areas occupied by resilient eelgrass populations in Morro Bay. Our findings further indicated that flushing times in short LIEs are particularly sensitive to several factors (e.g., bed roughness, sea level) that are susceptible to anthropogenic disturbance and future climate change.

Battle for the mounds: Niche competition between upside-down jellyfish and invasive seagrass.

Battle for the mounds: Niche competition between upside-down jellyfish and invasive seagrass.