Eelgrass Beds Research Articles

Marine Phytophthora species can hamper conservation and restoration of vegetated coastal ecosystems.

Phytophthora species are potent pathogens that can devastate terrestrial plants, causing billions of dollars of damage yearly to agricultural crops and harming fragile ecosystems worldwide. Yet, virtually nothing is known about the distribution and pathogenicity of their marine relatives. This is surprising, as marine plants form vital habitats in coastal zones worldwide (i.e. mangrove forests, salt marshes, seagrass beds), and disease may be an important bottleneck for the conservation and restoration of these rapidly declining ecosystems. We are the first to report on widespread infection of Phytophthora and Halophytophthora species on a common seagrass species, Zostera marina (eelgrass), across the northern Atlantic and Mediterranean. In addition, we tested the effects of Halophytophthora sp. Zostera and Phytophthora gemini on Z. marina seed germination in a full-factorial laboratory experiment under various environmental conditions. Results suggest that Phytophthora species are widespread as we found these oomycetes in eelgrass beds in six countries across the North Atlantic and Mediterranean. Infection by Halophytophthora sp. Zostera, P. gemini, or both, strongly affected sexual reproduction by reducing seed germination sixfold. Our findings have important implications for seagrass ecology, because these putative pathogens probably negatively affect ecosystem functioning, as well as current restoration and conservation efforts.

Algicidal and growth-inhibiting bacteria associated with seagrass and macroalgae beds in Puget Sound, WA, USA

The algicidal and growth-inhibiting bacteria associated with seagrasses and macroalgae were characterized during the summer of 2012 and 2013 throughout Puget Sound, WA, USA. In 2012, Heterosigma akashiwo-killing bacteria were observed in concentrations of 2.8×106CFUg−1 wet in the outer organic layer (biofilm) on the common eelgrass (Zostera marina) in north Padilla Bay. Bacteria that inhibited the growth of Alexandrium tamarense were detected within the biofilm formed on the eelgrass canopy at Dumas Bay and North Bay at densities of ∼108CFUg−1 wet weight. Additionally, up to 4100CFUmL−1 of algicidal and growth-inhibiting bacteria affecting both A. tamarense and H. akashiwo were detected in seawater adjacent to seven different eelgrass beds. In 2013, H. akashiwo-killing bacteria were found on Z. marina and Ulva lactuca with the highest densities of ∼108CFUg−1 wet weight at Shallow Bay, Sucia Island. Bacteria that inhibited the growth of H. akashiwo and A. tamarense were also detected on Z. marina and Z. japonica at central Padilla Bay. Heterosigma akashiwo cysts were detected at a concentration of 3400cystsg−1 wet weight in the sediment from Westcott Bay (northern San Juan Island), a location where eelgrass disappeared in 2002. These findings provide new insights on the ecology of algicidal and growth-inhibiting bacteria, and suggest that seagrass and macroalgae provide an environment that may influence the abundance of harmful algae in this region. This work highlights the importance of protection and restoration of native seagrasses and macroalgae in nearshore environments, in particular those regions where shellfish restoration initiatives are in place to satisfy a growing demand for seafood.

Characterization of Ecosystem Structure within Transplanted and Natural Eelgrass (Zostera marina) Beds

Seagrass ecosystems are some of the most productive coastal habitats in the world. Eelgrass (Zostera marina) is an ecosystem engineer that provides important ecosystem functions and services. In 2010, the National Oceanic and Atmospheric Administration (NOAA) began construction of their Marine Operations Center-Pacific (MOC-P) in Yaquina Bay, Oregon; coupled with this were unavoidable habitat damages, and mitigation included the creation of a transplanted eelgrass bed. The purpose of this project was to assess the recovery of ecosystem structure and function within this transplanted bed using an ecosystem-based approach. Ecological indicators (e.g., eelgrass percent cover, faunal richness and abundance) and environmental variables (e.g., sediment and water quality parameters) were monitored over 12 months at the transplanted mitigation site and two reference sites. Each bed was observed to be unique in structure, predominately driven by physical setting. Eelgrass cover at the mitigation site remained unchanged and significantly lower than at reference sites; however, most faunal indicators within the transplanted eelgrass bed were comparable to those of existing eelgrass beds. During the first year post-transplant, the eelgrass bed within the NOAA MOC-P mitigation site remained stable and was observed to be adequately performing the functions associated with eelgrass ecosystems in the Pacific Northwest. Characterizing the transplanted bed with an ecosystem-based approach allowed us to accurately assess the site's progress toward mitigation goals and provide information important to management of the NOAA MOC-P mitigation site and future eelgrass mitigation efforts.

Distribution and status of Zostera capensis in South African estuaries — A review

This review collates the available knowledge on the distribution and area covered by eelgrass Zostera capensis and shows that it has a wide distribution occurring in 62 estuaries from the Olifants Estuary on the west coast to Kosi Bay on the east coast. It has protected meristems, a strong root system and flexible leaves which enable it to grow under strong tidal conditions as well as tolerate periods of exposure and desiccation characteristic of the intertidal zone. Estuaries with the largest areas of Z. capensis are Olifants, Langebaan, Berg, Knysna, Keurbooms, Swartkops and Bushmans. Only Langebaan and Knysna have some formal protection status. Large populations were lost from KwaZulu-Natal estuaries at the time of Durban Bay harbour development in the 1950s and more recently from St Lucia. There have been a number of studies in South Africa showing the utilisation of eelgrass beds by a variety of invertebrate and fish species for habitat, shelter, foraging sites and nurseries. Fewer studies have addressed nutrient recycling and other ecosystem services such as carbon sequestration. In all estuaries the distribution of Z. capensis is highly dynamic and therefore difficult to map, assess changes over time and use as an indicator of estuary health. Cover and biomass are removed after large floods and have been shown to fluctuate in response to bait digging and disturbance by boats. This review identifies eutrophication as an emerging threat that encourages macroalgal growth, which smothers Z. capensis. Despite its wide distribution range, Z. capensis is sensitive to human impacts which have led to the species being listed as vulnerable in the Red Data List. It is encouraging that approximately 46% of all estuaries with Z. capensis have estuary management plans as these strive to protect sensitive habitats using activity zoning. Studies tracking the changes over time of the Z. capensis beds in specific estuaries are needed to understand dynamic responses. In addition there is urgency for a national assessment of the distribution and health of this keystone species in South Africa.

Nonnative Species in British Columbia Eelgrass Beds Spread via Shellfish Aquaculture and Stay for the Mild Climate

Nonnative species cause economic and ecological impacts in habitats they invade, but there is little information on how they spread and become abundant. This is especially true for nonnative species in native Zostera marina eelgrass beds in coastal British Columbia, Canada, which play a vital role in estuarine ecosystems. We tested how nonnative species richness and abundance were related to both arrival vectors and environmental factors in northeast Pacific eelgrass. Using correlation tests and generalized linear models, we examined how nonnative macroinvertebrates (benthic, epifaunal, and large mobile) and some algae species were related to arrival vectors (shipping and aquaculture) and environmental factors (climate variables, human population density, and native richness and abundance). We found 12 nonnative species, 50 % with known negative impacts within eelgrass habitats. For benthic organisms, both nonnative richness and abundance were strongly correlated with shellfish aquaculture activities, and not with shipping activity. For epifaunal nonnative richness and abundance, neither vector was significantly correlated. Climate (temperature and salinity) helped explain nonnative richness but not abundance; there was no relationship of nonnative richness or abundance to native species richness and abundance or population density. Results suggest that aquaculture activities are responsible for many primary introductions of benthic nonnative species, and that temperature and salinity tolerances are responsible for post-introduction invasion success. While aquaculture and shipping vectors are becoming increasingly regulated to prevent further international spread of nonnative species, it will be important when managing nonnatives to consider secondary spread from intraregional transport through local shellfish aquaculture and shipping.

Habitat preference of three-spined stickleback juveniles in experimental conditions and in wild eelgrass

Long-term population dynamics of three-spined stickleback Gasterosteus aculeatus in the White Sea during the 20th century has patterns similar to that of eelgrass Zostera marina. In this study we address possible mechanisms of such association through analysis of spatial distribution of juvenile stickleback in the wild and their substrate preferences in experimental conditions. Samples from different habitats (Z. marina, Fucus spp.) in 13 localities of Kandalaksha Bay have shown that the juvenile sticklebacks occurred mainly in the eelgrass beds. Their density was significantly lower in fucoids. In the experiments, carried out in August 2008–2009, the juveniles were offered the following types of substrates: brown macroalgae (dense and scarce), eelgrass and control (no substrate). In the experiments sticklebacks also showed a tendency to prefer eelgrass to fucoids, even if the density of the latter was higher. This may explain their higher densities associated with eelgrass in the wild.

Nitrogen Uptake and Internal Recycling in Zostera marina Exposed to Oyster Farming: Eelgrass Potential as a Natural Biofilter

Oyster farming in estuaries and coastal lagoons frequently overlaps with the distribution of seagrass meadows, yet there are few studies on how this aquaculture practice affects seagrass physiology. We compared in situ nitrogen uptake and the productivity of Zostera marina shoots growing near off-bottom longlines and at a site not affected by oyster farming in San Quintin Bay, a coastal lagoon in Baja California, Mexico. We used benthic chambers to measure leaf NH4 + uptake capacities by pulse labeling with 15NH4 + and plant photosynthesis and respiration. The internal 15N resorption/recycling was measured in shoots 2 weeks after incubations. The natural isotopic composition of eelgrass tissues and vegetative descriptors were also examined. Plants growing at the oyster farming site showed a higher leaf NH4 + uptake rate (33.1 mmol NH4 + m−2 day−1) relative to those not exposed to oyster cultures (25.6 mmol NH4 + m−2 day−1). We calculated that an eelgrass meadow of 15–16 ha (which represents only about 3–4 % of the subtidal eelgrass meadow cover in the western arm of the lagoon) can potentially incorporate the total amount of NH4 + excreted by oysters (∼5.2 × 106 mmol NH4 + day−1). This highlights the potential of eelgrass to act as a natural biofilter for the NH4 + produced by oyster farming. Shoots exposed to oysters were more efficient in re-utilizing the internal 15N into the growth of new leaf tissues or to translocate it to belowground tissues. Photosynthetic rates were greater in shoots exposed to oysters, which is consistent with higher NH4 + uptake and less negative δ13C values. Vegetative production (shoot size, leaf growth) was also higher in these shoots. Aboveground/belowground biomass ratio was lower in eelgrass beds not directly influenced by oyster farms, likely related to the higher investment in belowground biomass to incorporate sedimentary nutrients.

Comparative analysis of different survey methods for monitoring fish assemblages in coastal habitats.

Coastal ecosystems are among the most productive yet increasingly threatened marine ecosystems worldwide. Particularly vegetated habitats, such as eelgrass (Zostera marina) beds, play important roles in providing key spawning, nursery and foraging habitats for a wide range of fauna. To properly assess changes in coastal ecosystems and manage these critical habitats, it is essential to develop sound monitoring programs for foundation species and associated assemblages. Several survey methods exist, thus understanding how different methods perform is important for survey selection. We compared two common methods for surveying macrofaunal assemblages: beach seine netting and underwater visual census (UVC). We also tested whether assemblages in shallow nearshore habitats commonly sampled by beach seines are similar to those of nearby eelgrass beds often sampled by UVC. Among five estuaries along the Southern Gulf of St. Lawrence, Canada, our results suggest that the two survey methods yield comparable results for species richness, diversity and evenness, yet beach seines yield significantly higher abundance and different species composition. However, sampling nearshore assemblages does not represent those in eelgrass beds despite considerable overlap and close proximity. These results have important implications for how and where macrofaunal assemblages are monitored in coastal ecosystems. Ideally, multiple survey methods and locations should be combined to complement each other in assessing the entire assemblage and full range of changes in coastal ecosystems, thereby better informing coastal zone management.

Eelgrass (Zostera marina) restoration on the west coast of Sweden using seeds

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 546:31-45 (2016) - DOI: https://doi.org/10.3354/meps11615 Eelgrass (Zostera marina) restoration on the west coast of Sweden using seeds Eduardo Infantes*, Louise Eriander, Per-Olav Moksnes Department of Marine Sciences, University of Gothenburg, Box 461, Göteborg 405 30, Sweden. *Corresponding author: eduardo.infantes@gu.se ABSTRACT: Along the northwest coast of Sweden, over 50% of Zostera marina L. (eelgrass) meadows have vanished since the 1980s. With the improvement of conditions, there is a growing interest to restore lost habitats, but methods are lacking for restoration of eelgrass beds at high latitudes where long winters create special challenges. We assessed if seed planting could be used for large-scale restoration, with the aim to identify the major causes of seed and seedling loss and to determine which planting method best increases restoration success. In the laboratory, we identified optimal conditions for long-term seed storage and demonstrated that eelgrass seeds can be successfully stored for 8 mo before being planted in the spring. However, field studies did not find an increased seedling establishment in seeds planted in the spring of 2013 compared to those planted in the fall of 2012. Field results suggest that the main causes for the seed loss were seed predation from crabs, seed transport by currents and bioturbation by lugworms, while the main processes affecting shoot development were light availability and physical disturbance. Covering the seeds with a layer of sand increased seedling establishment 2 to 6 times compared to uncovered seeds, probably through the reduction of seed predation and seed transport, and could potentially be developed as a method to reduce losses during restoration. In addition, positive feedback mechanisms (i.e. sediment resuspension and drifting macroalgae mats) may also prevent natural recovery and restoration success. However, high seed loss (on average 98.6%) and high shoot mortality pose a challenge that need to be addressed before restoration using seeds can be recommended for large-scale restoration. KEY WORDS: Zostera marina · Seagrass · Coastal restoration · Seed planting · Seed predation · Seed storage · Feedback Full text in pdf format PreviousNextCite this article as: Infantes E, Eriander L, Moksnes PO (2016) Eelgrass (Zostera marina) restoration on the west coast of Sweden using seeds. Mar Ecol Prog Ser 546:31-45. https://doi.org/10.3354/meps11615 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 546. Online publication date: March 21, 2016 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2016 Inter-Research.

Using Acoustics to Determine Eelgrass Bed Distribution and to Assess the Seasonal Variation of Ecosystem Service.

Eelgrass beds are an important source of primary production in coastal ecosystems. Understanding seasonal variation in the abundance and distribution of eelgrass is important for conservation, and the objectives of this study were to 1) monitor seasonal variation in eelgrass beds using an acoustic monitoring method (Quantitative echo sounder) and 2) broadly quantify the carbon circulation function. We obtained acoustic data of eelgrass beds in coastal areas north and east of Ikunojima Island. Surveys were conducted nine times over the 3-year period from 2011 to 2013 in order to monitor seasonal variation. Acoustic data were obtained and used to estimate the spatial distribution of eelgrass by geostatistical methods. To determine supporting services, we determined carbon sink and carbon fixation by eelgrass beds using data from the National Research Institute of Fisheries and Environment of Inland Sea (2011). The height and distribution of eelgrass beds were at a maximum in May and at a minimum in November of each year. Distribution trends were different between the north and east areas. Supporting services showed the same patterns throughout the year. The area of distribution was considered to be coincident with the life history of eelgrass. Distribution differed by area and changed yearly due to the effects of bottom characteristics and wind direction. Quantifying the supporting services of eelgrass beds was shown to be useful for managing the conservation of coastal ecosystems.

Plant characteristics associated with widespread variation in eelgrass wasting disease.

Seagrasses are ecosystem engineers of essential marine habitat. Their populations are rapidly declining worldwide. One potential cause of seagrass population declines is wasting disease, which is caused by opportunistic pathogens in the genus Labyrinthula. While infection with these pathogens is common in seagrasses, theory suggests that disease only occurs when environmental stressors cause immunosuppression of the host. Recent evidence suggests that host factors may also contribute to disease caused by opportunistic pathogens. In order to quantify patterns of disease, identify risk factors, and investigate responses to infection, we surveyed shoot density, shoot length, epiphyte load, production of plant defenses (phenols), and wasting disease prevalence in eelgrass Zostera marina across 11 sites in the central Salish Sea (Washington state, USA), a region where both wasting disease and eelgrass declines have been documented. Wasting disease was diagnosed by the presence of necrotic lesions, and Labyrinthula cells were identified with histology. Disease prevalence among sites varied from 6 to 79%. The probability of a shoot being diseased was higher in longer shoots, in patches of higher shoot density, and in shoots with higher levels of biofouling from epiphytes. Phenolic concentration was higher in diseased leaves. We hypothesize that this results from the induction of phenols during infection. Additional research is needed to evaluate whether phenols are an adaptive defense against Labyrinthula infection. The high site-level variation in disease prevalence emphasizes the potential for wasting disease to be causing some of the observed decline in eelgrass beds.

Dynamics of recruitment and establishment of the invasive seaweed Codium fragile within an eelgrass habitat.

Knowledge of the potential distribution (i.e. abundance and spatial extent) of an invasive species is important to estimating its potential impacts on recipient communities. Most previous studies have focused on the potential spatial extent of invasive species populations at regional scales, but little is known on how species successfully recruit and establish at more local scales. In this study, we examined how recruitment of the green alga Codium fragile ssp. fragile (hereafter Codium) can vary spatially and the environmental factors associated with Codium establishment in eelgrass (Zostera marina) beds. Standardized recruitment blocks (65 blocks in a 720 × 240 m2 grid) were used to monitor the number of Codium recruits, juveniles and adults over 2 years. Environmental factors (depth, relative water flow, light and temperature) and attributes of the surrounding macrophyte assemblage (eelgrass density, eelgrass length, Codium biomass) were also measured. Recruitment occurred on all blocks or nearby artificial structures (i.e. buoys) and mainly originated from button stages (i.e. female gametes or utricles). Contrary to other studies, the abundance of Codium (recruits, juveniles and adults) was best predicted by the density of the native canopy-forming species, Z. marina, which highlights a positive interaction between native and non-native canopy-forming species. Seasonal variation in recruitment was observed; it was lower during the summer. Recruitment did not show any distinct spatial pattern (e.g. gradient or patch), but the same spatial pattern of recruitment was observed every sampling date, suggesting that there are “hotspots” for recruitment. In general, the total number of Codium fronds observed on a block at the end of the experiment was positively correlated with the cumulative number of recruits. However, recruitment occurred on some blocks but recruits never grew, suggesting that some environmental factors limit Codium distribution and abundance in eelgrass beds. Overall, the assessment of Codium recruitment over 2 years showed that the colonization of suitable locations by Codium within seagrass beds may take several years and that some factors may not only limit, but also inhibit Codium expansion within eelgrass beds.

Recovery of the eelgrass Zostera marina following intense Manila clam Ruditapes philippinarum harvesting disturbance in China: The role and fate of seedlings

Manila clam Ruditapes philippinarum (Adams & Reeve 1850) harvesting has been observed to damage the eelgrass Zostera marina L. meadow in Moon Lake, Shandong Peninsula, China. An annual eelgrass bed was found bordering the perennial meadow. We monitored the morphology, growth and survival of Z. marina in both annual (AB, disturbed site) and perennial beds (PB, reference site) in Moon Lake from December 2012 to January 2014. Nearly all eelgrass shoots in AB were removed or buried in sediments due to clam harvesting, which occurred during low tides in the winter and early spring of 2012–13. Seedlings were observed in February 2013 right after the end of the clamming season. They were less abundant but exhibited higher survival rates in AB than in PB. In June, the newly established seedlings in the AB formed numerous patches, indicating that the disturbed site recovered via seedling recruitment. However, these annual plants could not survive the winter of 2013–14 as perennials did, including those free from clamming disturbance in experimental enclosures. The annual Z. marina bed had smaller plant size and much lower biomass, density and potential seed production than the perennial stand. The recovery of the disturbed bed probably mainly depended on seeds recruited from the nearby perennial bed where the potential seed production was much higher.

Distribution and diversity of tunicates utilizing eelgrass as substrate in the western North Atlantic between 39° and 47° north latitude (New Jersey to Newfoundland)

Seagrass meadows are ecologically important habitats that are declining globally at an accelerating rate due to natural and anthropogenic stressors. Their decline is a serious concern as this habitat provides many ecosystem services. Eelgrass (Zostera marina) is the dominant seagrass species in the western North Atlantic. It has recently been established that invasive tunicate species possibly threaten the health of eelgrass beds. Colonization of eelgrass leaves by tunicates can inhibit eelgrass growth and may cause shoot mortality. To document the distribution and diversity of tunicate species that attach to eelgrass in the western North Atlantic, we surveyed twenty-one eelgrass sites from New Jersey to Newfoundland. Eight species of tunicates were found to be colonizing eelgrass, of which 6 are considered invasive. Botrylloides violaceus and Botryllus schlosseri were most commonly attached to eelgrass, with B. schlosseri having the largest latitudinal range of any species. Tunicate faunas attached to eelgrass were less diverse north of Gloucester, Massachusetts, where individual survey sites exhibited two species at most and only 4 of the 8 species observed in this study. Percent tunicate cover on eelgrass tended to fall within the 1–25 range, with occasional coverage up to >75–100. Density of eelgrass was highly variable among sites, ranging from <1 to 820 shoots/m 2 . The solitary tunicate Ciona intestinalis was only found on eelgrass at the highest latitude sampled, in Newfoundland, where it is a new invader. The tunicates observed in this study, both solitary and colonial, are viable when attached to eelgrass and pose a potential threat to overgrow and weaken seagrass shoots and reduce the sustainability of seagrass meadows.

Characterization of Zostera marina meadows in the Artabro Gulf (NW Iberian Peninsula).

Characterization of Zostera marina meadows in the Artabro Gulf (NW Iberian Peninsula).

가막만과 여자만의 잘피밭에 서식하는 농어(Lateolabrax japonicus) 유어의 성장 및 환경과의 관계

This study aims to reveal the relationship between growth of young sea bass and environmental variables in two adjacent eelgrass beds. Fishes were collected from Gamak Bay (GB) and Yeoja Bay (YB) on the southern coast of Korea from February 2006 to February 2007 using a dragnet (15 m in length and 3 m in width). During the study period, a total of 367 individuals of young sea bass Lateolabrax japonicus were collected from GB (171 inds.) and YB (196 inds.). Significant differences were observed in the occurrence periods and growth patterns of young sea bass, as well as in environmental variables between GB and YB. Young sea bass were collected from April to December in GB, but from April to July in YB. These differences may be associated with differences in eelgrass density, leaf width, and zooplankton density between GB and YB.

Variation in abundance and species composition of fishes in eelgrass (Zostera marina) bed and around Geomundo

The purpose of this study is to compare the ichthyofauna between the eelgrass bed waters located in the open sea and the nearby sea free of eelgrass, and this study collected a total of 26 species. Comparing the fish collected on the eelgrass bed (St.2) of Geomun–do coast with the fish collected on the coastal waters (St.1) void of the nearby eelgrass bed, the fish collected from the eelgrass bed included 19 species, 413 individual with 16,110.6g in weight while the fish collected from the coastal waters void of the eelgrass bed included 19 species, 290 individuals with 12,961.5g in weight. Accordingly, it was found that the population size and biomass of the fish collected from the eelgrass bed were higher than the coastal waters void of the eelgrass. This study could identify that diversity, richness, evenness index except dominance were also much higher even in the result of cluster analysis.

North Pacific Spiny Dogfish (Squalus suckleyi) Presence in Eelgrass Habitat in the Salish Sea, Washington

Eelgrass (Zostera marina) is the dominant seagrass along the Pacific North American Coast, providing complex physical structure, high trophic productivity, and protection from predators (Phillips 1984; Simenstad 1994). Because of these multiple functions, many fish species and life stages use Eelgrass beds more than other nearshore habitat types (Dean and others 2000; Murphy and others 2000; Johnson and Thedinga 2005). Currently, there is growing evidence identifying nearshore habitats as places that may be regularly inhabitated by large-bodied fish, including sharks (Tobin and others 2014), but it is not clear how much sharks use Eelgrass habitat. In other parts of North America, several sharks have been reported inhabiting Eelgrass habitat, including Sandbar Sharks (Carcharhinus milberti) in Chesapeake Bay, Maryland and Virginia (Orth and Heck 1980), Leopard Sharks (Triakis semifasciata) in Humboldt Bay, California (Ebert and Ebert 2005), and Gray Smooth-hound Sharks (Mustelus californicus) in Bolsa Chica, Orange County, California (Espinoza and others 2011). Conversely, reports of sharks are rare in Eelgrass beds in the Salish Sea region, which is located between the southwestern tip of British Columbia and the northwestern tip of Washington (Fig. 1; Farrer 2009). In this region, North Pacific Spiny Dogfish (Squalus suckleyi Girard 1854; Ebert and others 2010), hereafter Spiny Dogfish, are currently considered an abundant upper trophic level predator (Harvey and others 2010). Although Spiny Dogfish have been documented as making local movements along the nearshore in Puget Sound, Washington (Andrews and Harvey 2013), they have not generally been reported in Eelgrass habitat. Spiny Dogfish, however, have been captured in sand and Eelgrass habitat in Samish Bay, Washington, using overnight commercial gill net sets (Farrer 2009). Here we document the use of Eelgrass habitat by Spiny Dogfish. We conducted our study in Padilla Bay National Estuarine Research Reserve, Mount Vernon, Washington. Padilla Bay sustains one of the most extensive Eelgrass beds in the inner Salish Sea region (Berry and others 2003; Fig. 1). The shallow estuary covers nearly 4500 ha, of which .3200 ha is Eelgrass of both the native Z. marina and the non-native Z. japonica (Shull 1999). Padilla Bay differs from most estuaries in the region because it has become isolated from major rivers as it has filled with sediment from the Skagit River to the south, and the Eelgrass has thrived in the absence of a major freshwater input. However, drainage from adjacent agricultural lands enters via sloughs with tidegates. Other nearby sources of freshwater are the Samish River to the north and the Skagit River via the Swinomish Channel to the south. Tides in the region are mixed semidiurnal. We sampled 3 sites along major tidal channels in contiguous Z. marina habitats that were located over mud bottoms. These sites were located in the north (Short Channel), middle (Middle Channel), and south (Bayview Channel) portions of Padilla Bay (Fig. 1). At each site, we sampled 2 adjacent locations to have replicate samples, thereby completing 6 overnight gill-net sets for each month of May, June, and July of 2004. We trawled during the day to characterize the fish assemblage in the shallows (Penaluna 2006), and we set gill nets overnight in Eelgrass locations parallel to the adjacent tidal channel to document nocturnal movements of larger fishes. Each 15-m by 2-m experimental gill net was composed of five 3-m panels, with square mesh size increments of 12, 25, 38, 50, and 68 mm, with leadand foam-core lines. We sampled when tidal elevations ranged from –1.5to –3.0-m mean lower low water. Catch per unit of effort (CPUE) was measured as number of fish per net-hour. The highest CPUEs of Spiny Dogfish captured during overnight gill-net sets were recorded in June and July (Table 1; Fig. 2). Spiny GENERAL NOTES

The effect of parameter variability in the allometric projection of leaf growth rates for eelgrass (Zostera marina L.) II: the importance of data quality control procedures in bias reduction.

BackgroundEelgrass grants important ecological benefits including a nursery for waterfowl and fish species, shoreline stabilization, nutrient recycling and carbon sequestration. Upon the exacerbation of deleterious anthropogenic influences, re-establishment of eelgrass beds has mainly depended on transplantation. Productivity estimations provide valuable information for the appraisal of the restoration of ecological functions of natural populations. Assessments over early stages of transplants should preferably be nondestructive. Allometric scaling of eelgrass leaf biomass in terms of matching length provides a proxy that reduces leaf biomass and productivity estimations to simple measurements of leaf length and its elongation over a period. We examine how parameter variability impacts the accuracy of the considered proxy and the extent on what data quality and sample size influence the uncertainties of the involved allometric parameters.MethodsWe adapted a Median Absolute Deviation data quality control procedure to remove inconsistencies in the crude data. For evaluating the effect of parametric uncertainty we performed both a formal exploration and an analysis of the sensitivity of the allometric projection method to parameter changes. We used parameter estimates obtained by means of nonlinear regression from crude as well as processed data.ResultsWe obtained reference leaf growth rates by allometric projection using parameter estimates produced by the crude data, and then considered changes in fitted parameters bounded by the modulus of the vector of the linked standard errors, we found absolute deviations up to 10 % of reference values. After data quality control, the equivalent maximum deviation was under 7 % of corresponding reference rates. Therefore, the addressed allometric method is robust. Even the smaller sized samples in the quality controlled dataset produced better accuracy levels than the whole set of crude data.ConclusionsWe propose quality control of data as a highly recommended step in the overall procedure that leads to reliable allometric surrogates of eelgrass leaf growth rates. The proliferation of inconsistent replicates in the crude data points towards the importance of discarding incomplete leaves. We also recommend avoiding errors in estimating the biomass of small leaves for which precision of the used analytical scale might be an issue.

Land use and nitrogen loading in seven estuaries along the southern Gulf of St. Lawrence, Canada

Nitrogen loading from coastal watersheds is a principal factor associated with the decline in eelgrass bed health and cover in estuaries worldwide. We apply the Nitrogen Loading Model (NLM) framework developed in Waquoit Bay, Massachusetts to 7 estuaries in eastern New Brunswick. Using watershed-specific information on human population, wastewater production, atmospheric deposition, and land use in each watershed we estimate annual input of Total Dissolved Nitrogen (TDN) from point and non-point sources. We also estimate flushing time of each estuary using available hydrodynamic and bathymetric data incorporated in a tidal prism model. Finally, we validate the NLM results by testing the link between estimated nitrogen loading, flushing time and nitrogen signals in eelgrass tissue including nitrogen content and stable isotopes. Overall, total nitrogen load (kg TDN yr−1) was strongly dependent on watershed and estuary size, while loading rate per unit watershed area (yield) was linked to watershed population density. Atmospheric deposition was the largest contributor of nitrogen to all estuaries except one, where seafood processing effluent was the greatest source. Stable isotope analysis of eelgrass tissue reflected this distinction, with high δ15N values of 8–10‰ related to high wastewater loading, compared to 2–6.5‰ in the other estuaries that receive proportionally more atmospheric deposition. Tissue nitrogen content was positively related to nitrogen yields and loading rate per volume of estuary, highlighting the influence of variable watershed:estuary size ratio. Multiple regression analysis identified a significant interaction between nitrogen yield and flushing time on eelgrass tissue nitrogen content and isotopes, pointing to the mitigating effect an estuary's quick flushing time can have on the expression of nitrogen enrichment in primary producers. The compilation of new information on nitrogen loading to east Canadian estuaries is a novel contribution from a region where human influences are still at a relatively low level, and hence will add to existing information from cold temperate, mainly forested watershed-estuary environments.