Seasonal changes in eelgrass functions: current velocity reduction,prevention of sediment resuspension,and control of sediment–water column nutrient flux in relation to eelgrass dynamics

We assessed seasonal changes in eelgrass (Zostera marina) functions, i.e., reduction of current velocity, buffering of sediment resuspension, and control of dissolved inorganic nitrogen flux between the sediments and the water column, using field observations and experiments in the Akkeshi-ko estuary, Hokkaido, Japan. We also analyzed the relationships between eelgrass traits and functions. The efficiency of the reduction in current velocity increased with the development of the eelgrass canopy. Sediment resuspension was inhibited from May to August, during which time the eelgrass canopy developed. Eelgrass controlled the NH₄ ⁺ concentration of sediment porewater through root nutrient uptake, affecting NH₄ ⁺ flux between the sediments and the water column. Fluctuations in eelgrass functions and coincident changes in dynamics resulted in seasonal changes in the eelgrass environment, which may in turn affect the dynamics of organisms inhabiting eelgrass beds, e.g., mysids and epiphytic algae. Moreover, the developed eelgrass canopy trapped a large amount of material during spring and summer, which was resuspended into the surrounding ecosystem in autumn when the canopy and its functions (i.e., reduction of current and sediment resuspension) diminished. These results suggest that seasonal changes in eelgrass functions also affect communities within marginal coastal ecosystems through the control of allochthonous resources. Handling editor: P. Viaroli     

Relationships between bed age,bed size,and genetic structure in Chesapeake Bay (Virginia,USA) eelgrass (<Emphasis Type="Italic">Zostera marina</Emphasis> L.)

Genetic structure and diversity can reveal the demographic and selective forces to which populations have been exposed, elucidate genetic connections among populations, and inform conservation strategies. Beds of the clonal marine angiosperm Zostera marinaL. (eelgrass) in Chesapeake Bay (Virginia, USA) display significant morphological and genetic variation; abundance has fluctuated widely in recent decades, and eelgrass conservation is a major concern, raising questions about how genetic diversity is distributed and structured within this metapopulation. This study examined the influence of bed age (<65years versus<6years) and size (>100ha versus<10ha) on morphological and genetic (allozyme) structure and diversity within Chesapeake Bay eelgrass beds. Although both morphology and genetic diversity varied significantly among individual beds (F _ST=0.198), neither varied consistently with bed age or size. The Chesapeake eelgrass beds studied were significantly inbred (mean F _IS=0.680 over all beds), with inbreeding in old, small beds significantly lower than in other bed types. Genetic and geographic distances within and among beds were uncorrelated, providing no clear evidence of isolation by distance at the scale of 10's of km. These results suggest that local environmental conditions have a greater influence on plant morphology than do bed age or size. They support the hypotheses that eelgrass beds are established by multiple founder genotypes but experience little gene flow thereafter, and that beds are maintained with little loss of genetic diversity for up to 65 years. Since phenotypic and genotypic variation is partitioned among beds of multiple ages and sizes, eelgrass conservation efforts should maximize preservation of diversity by minimizing losses of all beds.     

Restoring Eelgrass (Zostera marina L.) Habitats Using a Simple and Effective Transplanting Technique

Eelgrass beds in coastal waters of China have declined substantially over the past 30 years. In this study, a simple new transplanting technique was developed for eelgrass (Zostera marina L.) restoration. To assist in anchoring single shoots, several rhizomes of rooted shoots were bound to a small elongate stone (50–150 g) with biodegradable thread (cotton or hemp), and then the bound packet was buried at an angle in the sediments at a depth of 2–4 cm. This stone anchoring method was used to transplant eelgrass in early November 2009 and late May 2010 in Huiquan Bay, Qingdao. The method led to high success. Three month survivorship of the transplanted shoots at the two transplant sites was >95%. From April 20 to November 19, 2012, the following characteristics of the 2009 and 2010 transplanted eelgrass beds were monitored: morphological changes, shoot density, shoot height, leaf biomass, and sediment particle size. Results showed that the sexual reproduction period of the planted eelgrass was from April to August, and vegetative reproduction reached its peak in autumn. Maximum shoot height and biomass were observed in June and July. After becoming established, the transplanted eelgrass beds were statistically equal to natural eelgrass beds nearby in terms of shoot height, biomass, and seasonal variations. This indicates that the transplant technique is effective for eelgrass restoration in coastal waters.     

Genetic effects of eelgrass restoration efforts by fishers' seeding to recover seagrass beds as an important natural capital for coastal ecosystem services

The reestablishment of seagrass vegetation is a vital part of recovering coastal marine ecosystem services. Historically the Hinase area was a famous for the fishing by coastal pound netting in eelgrass beds, but this practice was progressively displaced with oyster farming due to an enormous decline in seagrass vegetation. For several decades, the local fishers' cooperative has worked to restore eelgrass beds by a seeding method. Through these efforts, seagrass vegetation in their fishing area has increased to about half of their previous area. This study examined the effect of long-term seeding by fishers on the recovery of eelgrass beds in the Hinase area, based on analysis of eelgrass genetic structure using microsatellite markers. Specimens for the DNA analysis were collected from each of all eelgrass meadows that the fishers conducted sowing eelgrass seeds as well as from the source sites where they collected the seeds. The results found that restored beds in the study area have high genetic diversity comparable to natural ones. The multiple regression analysis revealed that a combined model of seedling intensity and geographic distance (R² = .457) better explained genetic structure across our sampling sites than models of seedling intensity (R² = .092) or geographic distance only (R² = .344). This supports that the eelgrass seeds they sowed did not disturb the genetic structure but rather supplemented natural dispersal, suggesting that the fishers' seeding did not develop nonnatural seagrass meadows but certainly contributed to the recovery of natural seagrass meadows.     

Population Genetic Analyses of Transplanted Eelgrass (Zostera marina) Beds Reveal Reduced Genetic Diversity in Southern California

Seagrass ecosystems fulfill ecologically and economically valuable functions in coastal marine environments. Unfortunately, seagrass beds are susceptible to natural and human disturbances, and their distrubution is declining worldwide. Although intentional disturbance of seagrass beds must be mitigated pursuant to U.S. law, to date mitigation of seagrass beds has not prevented a net loss of habitat. Transplantation of vegetative material from small areas of nearby beds is the primary method of seagrass mitigation. Restoration research on seagrasses has focused primarily on establishment of the plants and secondarily on the functional equivalency of the habitats. We questioned whether transplanted seagrass beds were comparable to “natural” beds in terms of genetic diversity and structure. We sampled Zostera marina L. (eel-grass) from 12 sites in the highly urbanized area of San Diego County and from pristine sites in Baja California. Using allozyme electrophoresis, we determined that genetic diversity (percentage of polymorphic loci, allele richness, expected and observed heterozygosities, and proportion of genetically unique individuals) was significantly reduced in transplanted eelgrass beds. Eelgrass from Baja California exhibited the highest genetic diversity. Based on Wright's F statistics, most of the genetic variation was distributed within rather than among sites (F_ST= 0.139), and the degree of genetic structure was only moderate at the greatest geographical scale (San Diego—Baja). Using a spatial statistical analysis (second-order analysis), we found virtually no evidence for nonrandom distribution of alleles or genotypes at scales of 3–50 m within beds. We discuss several hypotheses for reduced genetic diversity in transplanted eelgrass beds, including transplantation protocol, small size of transplantations, and reduced or failed sexual reproduction.     

Variable responses of native eelgrass Zostera marina to a non-indigenous bivalve Musculista senhousia

The transport and establishment of non-indigenous species in coastal marine environments are increasing worldwide, yet few studies have experimentally addressed the interactions between potentially dominant non-native species and native organisms. We studied the effects of the introduced mussel Musculista senhousia on leaf and rhizome growth and shoot density of eelgrass Zostera marina in San Diego Bay, California. We added M. senhousia over a natural range in biomass (0–1200 g dry mass/m²) to eelgrass in transplanted and established beds. The effects of the non-indigenous mussel varied from facilitation to interference depending on time, the abundance of M. senhousia, and the response variable considered. Consistent results were that mussel additions linearly inhibited eelgrass rhizome elongation rates. With 800 g dry mass/m² of M. senhousia, eelgrass rhizomes grew 40% less than controls in two eelgrass transplantations and in one established eelgrass bed. These results indicate that M. senhousia, could both impair the success of transplantations of eelgrass, which spread vegetatively by rhizomes, and the spread of established Z. marina beds to areas inhabited by M. senhousia. Although effects on leaf growth were not always significant, in August in both eelgrass transplantations and established meadows leaf growth was fertilized by mussels, and showed a saturation-type relationship to sediment ammonium concentrations. Ammonium concentrations and sediment organic content were linear functions of mussel biomass. We found only small, non-consistent effects of M. senhousia on shoot density of eelgrass over 6-month periods. In established eelgrass beds, but not in transplanted eelgrass patches (≈0.8 m in diameter), added mussels suffered large declines. Hence, eelgrass is likely to be affected by M. senhousia primarily where Z. marina beds are patchy and sparse. Our study has management and conservation implications for eelgrass because many beds are already seriously degraded and limited in southern California where the mussel is very abundant. Received: 31 May 1997 / Accepted: 4 September 1997     

关中-天水经济区生态系统服务权衡与协同关系

陆地表层植被作为生态系统主体,具有调节气候、水文调节、净化水质、保持水土等生态系统服务。理解生态系统服务权衡与协同的表现类型、形成机理、尺度依存和区域差异,对于制定区域发展与生态保护"双赢"的政策措施具有重要意义。以关天经济区为主要研究对象,利用相关模型,计算关天经济区生态系统NPP,固碳释氧,水文调节,水土保持,粮食生产等生态系统服务价值,利用ESCI和ESSI两个指数研究其生态系统服务价值时空变化,利用相关系数和空间制图的方法研究它们之间的相互权衡协同关系。结果表明:从时间角度分析,各项生态服务价值都呈现逐渐增加的趋势;从空间角度分析,2000年和2010年存在相似的空间分布格局,从北向南,NPP和固碳释氧的价值逐渐增大,水土保持价值变化量的大小也呈现不断增加的趋势,北部变化量小,南部变化量大,水文调节价值从西向东增大,从北向南增大,粮食生产价值量最小的是西安市市区,粮食生产价值量最大的是西安市的郊区和郊县及咸阳市。2000年到2010年间,调节型生态系统服务与供给型生态系统服务之间存在着此消彼长的权衡关系;各个区县的总生态服务价值指数从北向南、从西向东是不断增大的。     

Ecological diversity of the Eastern Mediterranean region of Turkey and its conservation

The Taurus Mountain range separates the central Anatolian steppe and the Eastern Mediterranean Region. The Amanos Mountains lie to the east, playing a significant role in forming this region which is strongly influenced by the Mediterranean Sea. Between the Taurus Mountains and the sea, there is a diversity of terrestrial, limnic and marine ecosystems. These contain a number of differing biotopes such as grassland above the timberline, evergreen and deciduous forests, scrubland, river beds, lagoons, coastal saltmarshes, coastal woodlands and sand dunes. Due to intensive land use, the ecological diversity is threatened, and so governmental and scientific bodies have combined resources to implement conservation measures. This paper emphasizes the importance of these conservation activities and discusses realistic proposals for conservation in the region.     

秦岭生态系统服务协同与权衡的时空异质性

秦岭是我国重要的生态功能区,探究秦岭生态系统服务权衡与协同关系对区域的生态保护和高质量发展意义重大。本研究基于遥感、气象、土壤质地等数据,在分析2000、2010和2020年土地利用时空变化的基础上,采用CASA、InVEST和RUSLE模型计算秦岭地区植被固碳量、产水量、生境质量和土壤保持量,并探讨空间异质性特征及生态系统服务关系。结果表明: 2000—2020年,研究区耕地、草地面积持续减少,林地和建设用地面积增长,水域和未利用地变化不明显。研究区固碳量东高西低,呈增长趋势;产水量持续减少,呈现南坡高、北坡低的格局;生境质量稳定增长;土壤保持量先增后减。不同地类的生态系统服务各有差异,同一地类的各个生态系统服务也各不相同。全域尺度下固碳与土壤保持、生境质量与土壤保持、固碳与生境质量皆呈协同关系,固碳与产水、土壤保持与产水、生境质量与产水为权衡关系,但不同条件下服务量间的关系存在明显差异。研究结果有助于降低权衡风险,使总体效益最大化,可为促进生态高质量发展、实现自然资源管理与人类福祉的双赢提供参考依据。     

Does the recruitment of a non‐native mussel in native eelgrass habitat explain their disjunct adult distributions?

We studied variability in the abundance of small individuals of an invasive mussel (Musculista senhousia) across the depth distribution of a native marine angiosperm, eelgrass (Zostera marina). Adult mussels and eelgrass have a disjunct local distribution, each limiting the other in complex ways. To assess whether eelgrass also influenced the distribution of juvenile mussels, we sampled inside and outside eelgrass beds in one site in Mission Bay and two in San Diego Bay, California, USA. We sampled mussels in size classes 0.26–0.50 mm, 0.51–1.00 mm, 1.10–2.00 mm and > 2.00 mm from September 1997 to April 1999. We also monitored gonad development in larger mussels and in situ growth of mussels ≤ 2 mm tagged with the chemical marker calcein. Spatial and temporal variations in mussel abundances were high but seasonal patterns were roughly similar at San Diego Bay sites; very few mussels were found in Mission Bay. Mussels with full gonads were found year‐round in San Diego Bay, as were mussels in the smallest size class (with a large peak in fall and a smaller secondary one in spring), suggesting that many of the smallest mussels represent recruitment. The observation that most, although not all, tagged mussels increased in size provides further support for recruitment. Some of the highest numbers of mussels in the smallest size class were found inside eelgrass beds, indicating that eelgrass does not restrict and may actually enhance the distribution of very small mussels. The disjunct distribution of adult mussels and eelgrass thus is apparently established primarily postrecruitment. M. senhousia is capable of year‐round reproduction, recruitment and growth, and thus is poised to preempt space from eelgrass following any disturbance that results in eelgrass declines, such as habitat fragmentation, eutrophication, or disease.     

The ecology of eelgrass, Zostera marina (L.), fish communities. I. Structural analysis

Fish populations utilizing eelgrass, Zostera marina (L.), beds in two different estuarine areas near Beaufort, North Carolina were analysed and compared to determine aspects of their community structure. The fish community of the eelgrass beds was characterized by low diversity and high standing crops of biomass and energy, both of which showed seasonal variation. Wide temperature fluctuations related to the overall shallowness of the beds probably regulated the diversity of fishes utilizing the beds. This community was dominated by pinfish, Lagodon rhombiodes (L.), which comprised 45% and 67% of the fish biomass in the Phillips Island and Bogue Sound beds, respectively.Changes in total body caloric content were probably related to developmental stages and changes in diet. Adult fish often had significantly higher weight-specific caloric contents than juvenile fish. Monthly or seasonal variations in caloric content of the organic matter of pinfish had little influence on the caloric content within the various sizes of pinfish.There was a significant correlation between fish biomass, temperature, and Zostera biomass. Fish biomass was highest when temperature and grass biomass were at a maximum. In general, water depth over the beds had little effect on the standing crop of fish within the bed, but cooler waters which occurred at night, darkness, or both, had a large effect.     

Estimating global "blue carbon" emissions from conversion and degradation of vegetated coastal ecosystems

Recent attention has focused on the high rates of annual carbon sequestration in vegetated coastal ecosystems-marshes, mangroves, and seagrasses-that may be lost with habitat destruction ('conversion'). Relatively unappreciated, however, is that conversion of these coastal ecosystems also impacts very large pools of previously-sequestered carbon. Residing mostly in sediments, this 'blue carbon' can be released to the atmosphere when these ecosystems are converted or degraded. Here we provide the first global estimates of this impact and evaluate its economic implications. Combining the best available data on global area, land-use conversion rates, and near-surface carbon stocks in each of the three ecosystems, using an uncertainty-propagation approach, we estimate that 0.15-1.02 Pg (billion tons) of carbon dioxide are being released annually, several times higher than previous estimates that account only for lost sequestration. These emissions are equivalent to 3-19% of those from deforestation globally, and result in economic damages of $US 6-42 billion annually. The largest sources of uncertainty in these estimates stems from limited certitude in global area and rates of land-use conversion, but research is also needed on the fates of ecosystem carbon upon conversion. Currently, carbon emissions from the conversion of vegetated coastal ecosystems are not included in emissions accounting or carbon market protocols, but this analysis suggests they may be disproportionally important to both. Although the relevant science supporting these initial estimates will need to be refined in coming years, it is clear that policies encouraging the sustainable management of coastal ecosystems could significantly reduce carbon emissions from the land-use sector, in addition to sustaining the well-recognized ecosystem services of coastal habitats.     

The scientific research on rhodolith beds: A review through bibliometric network analysis

Rhodolith beds are benthic biogenic calcareous habitats formed by the aggregation of unattached, non-geniculate coralline algae. They have a worldwide distribution and, due to their 3D structural complexity and functioning, they provide several ecosystem services (i.e., provisioning and regulating). Recently, their importance and vulnerability have been internationally recognized by international policy and scientific research, and more attention has been drawn to their investigation and conservation. In this study, we conducted a systematic review integrated with a bibliometric analysis of the academic literature related to rhodolith beds. The analysis was based on published literature data over the period 1965–2022, and allowed the generation of maps based on network data displaying the relationships among countries, researchers, keywords, and scientific journals. A total of 853 publications were identified, revealing that scientific research on rhodolith beds is still relatively limited if compared to other coastal vegetated habitats (e.g., seagrass beds, kelp forests), although it has increased over time. Results showed that the scientific documents were published by 77 countries, 2255 researchers, and 279 journals. USA led the research production in this field with 159 documents and 4802 citations, and Amado-Filho was the most productive author with 36 documents and 1126 citations. The co-occurrence network map of keywords showed that the main research fields linked to rhodolith beds are geology, paleontology, algal taxonomy, community ecology, conservation, and physiology. The results also highlighted that most focus on the subject is recently shifting from geological and paleontological aspects to molecular taxonomic, conservation, and ecophysiological ones, while studies on the current topics of ecosystem services and carbon sequestration are still very limited.     

白洋淀流域生态系统服务评估及其调控

政策制定者在制定土地利用相关政策时需要权衡各方面的利益关系,协调资源保护和经济发展之间的关系.由于缺乏有效的评价与权衡办法,目前对这方面研究还较少.采用InVEST模型,评价了白洋淀流域7种服务功能指标,分析了其空间分布特征.通过情景(政策情景与保护情景)分析,较好的反映了农业直接经济收入与服务功能之间的关系.结果表明:生物多样性、水源涵养、土壤保持和固碳重要区域主要分布在流域西部、北部和流域中部山区;水质保护和授粉重要区域主要分布于流域东部、南部和中部平原区.政策情景下,产水量第二,农业产出有所下降,固碳能力较保护模式差,N/P输出最少.保护情景下产水量最大,农田产出价值不变,氮磷保持与政策情景差不多,但固碳效果最好.通过权衡不同情景下服务功能得失,筛选既不损害流域居民实际经济收入,又能使得水文服务功能得到提高的管理模式.研究表明InVEST模型可以很好的用于对自然资本评估和空间化特征分析,通过建立不同情景,评价结果可以用于权衡不同管理策略下服务功能得失,是一种评价和预测自然资本变化的有效方法,对政策制定和策略筛选具有重要的指导意义.     

Local community attitudes towards mangrove forest conservation

Local communities have preferences and expectations regarding mangrove ecosystems that are typically underrepresented in valuation studies. Therefore, this study identifies how the local community of Mahahual (Mexico) perceives the ecosystem services provided by the mangrove forest and how these preferences differ between households. A survey was designed by one of the authors and local stakeholders building on previous knowledge and experts (local environmental research centre and non-governmental organisation Takata and its experts in biology and coastal conservation, ecotourism businesses’ owners, and the mayor of the village). The survey is used to cover a wide range of ecosystem services such as carbon sequestration, recreation and cultural activities as well as improved connectivity with local seagrass beds and coral reefs. Ecosystem services were specifically chosen by biologists and ecologists of the local NGO to perfectly reflect the local mangroves ecosystem. The small land area of the village, its low population and its rapid expansion offer a unique context, aiming at preserving the natural environment while keeping in mind that the main economy is based on tourism. While mangroves are greatly appreciated for the local protective services they provide such as coastal protection, local inhabitants also care about services that have a wider impact such as biodiversity and carbon sequestration. We find that the educational background of local inhabitants plays an important role in determining the importance of local ecosystem services and that information provision can help to counterbalance this effect. We also observe that preferences for specific ecosystem services differ based on how close residents live to the mangroves and to the coast, which accentuates the different needs and ideas of the households based on their local neighbourhood.     

How subtidal were the ’subtidal beds’ ofZostera marina L. before the occurrence of the wasting disease in the early 1930's?

In the available literature about eelgrass beds in the former Zuiderzee, now western Dutch Wadden Sea, it is suggested that these stands mainly occurred in the subtidal zone. There is, however, no evidence that this suggestion is right because the relative distribution of eelgrass beds over the intertidal zone and the subtidal zone in the former Zuiderzee was never studied. A detailed mapping of eelgrass beds was carried out in 1869 and another one in 1930. The 1869 map is combined with available nautical charts by application of GIS packages and the distribution of eelgrass beds calculated. It was necessary to carry out corrections because of inaccuracies both in the eelgrass mapping and in the old nautical charts. It is concluded that in 1869 45%±4 of the eelgrass beds were present in the intertidal zone and that 55%±4 of the beds were present in the subtidal zone. In 1930 the distribution amounted to 56% in the intertidal zone versus 44% in the subtidal zone. These values illustrate that in the period prior to the wasting disease and the closure of the former Zuiderzee, eelgrass occurred in both the intertidal zone as well as in the subtidal zone.     

Residents’ valuation of ecosystem services in a Mediterranean coastal dune ecosystem: The case of the Ritoque dunes in central Chile

Coastal dunes provide a variety of cultural and ecological ecosystem services to local communities. However, most of these ecosystems are globally threatened by anthropic factors. Chile is home to important dune ecosystems such as the emblematic Ritoque coastal dunes located in the hotspot for biodiversity conservation in central Chile where there is a delicate relationship between conservation and human development interests, among local communities and authorities. Here, we performed a choice experiment study to determined willingness to implement conservation measures in the Ritoque dunes. In particular, we assessed residents’ preferences for improvements of the current state of local ecosystem services such as scenic beauty, biodiversity and archaeological sites. Residents showed preferences for improvements in Ritoque coastal dunes’ ecosystem services, and a high willingness to pay for protecting biodiversity and archeological sites, rather than for recreational infrastructure. Our study highlights the importance of place-based research that specifically addresses residents and stakeholders’ conservation priorities, which could be used to design and implement effective conservation management strategies for coastal ecosystems and coastal cities near them.     

Prioritising Mangrove Ecosystem Services Results in Spatially Variable Management Priorities

Incorporating the values of the services that ecosystems provide into decision making is becoming increasingly common in nature conservation and resource management policies, both locally and globally. Yet with limited funds for conservation of threatened species and ecosystems there is a desire to identify priority areas where investment efficiently conserves multiple ecosystem services. We mapped four mangrove ecosystems services (coastal protection, fisheries, biodiversity, and carbon storage) across Fiji. Using a cost-effectiveness analysis, we prioritised mangrove areas for each service, where the effectiveness was a function of the benefits provided to the local communities, and the costs were associated with restricting specific uses of mangroves. We demonstrate that, although priority mangrove areas (top 20%) for each service can be managed at relatively low opportunity costs (ranging from 4.5 to 11.3% of overall opportunity costs), prioritising for a single service yields relatively low co-benefits due to limited geographical overlap with priority areas for other services. None-the-less, prioritisation of mangrove areas provides greater overlap of benefits than if sites were selected randomly for most ecosystem services. We discuss deficiencies in the mapping of ecosystems services in data poor regions and how this may impact upon the equity of managing mangroves for particular services across the urban-rural divide in developing countries. Finally we discuss how our maps may aid decision-makers to direct funding for mangrove management from various sources to localities that best meet funding objectives, as well as how this knowledge can aid in creating a national mangrove zoning scheme.     

Limited recovery following a massive seagrass decline in subarctic eastern Canada

Over the last few decades, there has been an increasing recognition for seagrasses' contribution to the functioning of nearshore ecosystems and climate change mitigation. Nevertheless, seagrass ecosystems have been deteriorating globally at an accelerating rate during recent decades. In 2017, research into the condition of eelgrass (Zostera marina) along the eastern coast of James Bay, Canada, was initiated in response to reports of eelgrass decline by the Cree First Nations of Eeyou Istchee. As part of this research, we compiled and analyzed two decades of eelgrass cover data and three decades of eelgrass monitoring data (biomass and density) to detect changes and assess possible environmental drivers. We detected a major decline in eelgrass condition between 1995 and 1999, which encompassed the entire east coast of James Bay. Surveys conducted in 2019 and 2020 indicated limited changes post-decline, for example, low eelgrass cover (<25%), low aboveground biomass, smaller shoots than before 1995, and marginally low densities persisted at most sites. Overall, the synthesized datasets show a 40% loss of eelgrass meadows with >50% cover in eastern James Bay since 1995, representing the largest scale eelgrass decline documented in eastern Canada since the massive die-off event that occurred in the 1930s along the North Atlantic coast. Using biomass data collected since 1982, but geographically limited to the sector of the coast near the regulated La Grande River, generalized additive modeling revealed eelgrass meadows are affected by local sea surface temperature, early ice breakup, and higher summer freshwater discharge. Our results caution against assuming subarctic seagrass ecosystems have avoided recent global declines or will benefit from ongoing climate warming.     

Intertidal community structure differs significantly between substrates dominated by native eelgrass (<Emphasis Type="Italic">Zostera marina</Emphasis> L.) and adjacent to the introduced oyster <Emphasis Type="Italic">Crassostrea gigas</Emphasis> (Thunberg) in British Columbia,Canada

Eelgrass beds represent important habitats for marine organisms, but are in decline in many coastal areas around the world. On Cortes Island, British Columbia, Canada, oysters coexist regionally with native eelgrass (Zostera marina L.), but eelgrass is typically absent directly seaward of oyster beds (the “below-oyster cobble zone”). We compared assemblage structure of nekton (fish and swimming macroinvertebrates) and epibenthos (macroinvertebrates and macroalgae) between eelgrass bed and below-oyster habitats. We sampled the intertidal zone on Cortes Island at low tide using two methods: quadrats to enumerate epibenthic macroinvertebrates and macroalgae, and beach seines to enumerate fish and swimming macroinvertebrates. Using multivariate analysis of similarity (ANOSIM), we found that the structure of nektonic and epibenthic assemblages associated with below-oyster cobble zones were significantly different from those in eelgrass-beds. Univariate measures showed that nektonic species richness and abundance were significantly higher in eelgrass beds than in below-oyster cobble habitat, whereas epibenthic species richness and abundance were significantly higher in below-oyster habitat. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. Handling editor: J. Trexler