Eelgrass Patches Research Articles

Distribution of sexually reproductive eelgrass (Zostera marina) seeds in microhabitats of eelgrass beds in intertidal zones

Eelgrass (Zostera marina) seedling establishment based on the sexually reproductive seed bank depends on habitat factors, and there are different microhabitats in eelgrass beds. Seedling abundance varies with microhabitat. Why is the distribution pattern of seedlings so? Is there an edge effect of eelgrass patches on seedling distribution? To clarify the distribution and variation patterns of ungerminated seeds, germinated seeds and seedlings in microhabitats, field investigations were conducted from December 2020 to April 2021. The density of the total seed bank varied with microhabitat except in March. In April, the density of germinated seed banks in the highland, low-lying area edge and low-lying area was 0.00 ± 0.00, 0.33 ± .33 and 7.44 ± 0.96 seeds.cm−3, respectively, and the density in the low-lying area was higher than that in the other microhabitats. The order of density of the seedling bank was highland < low-lying area edge < low-lying area in April. The relative proportion of germinated seeds in the low-lying area was higher than that in the highland from March to April, during which the increase rate in the seedling bank of the highland was lower than that of other microhabitats. The distribution pattern of eelgrass seeds varies with microhabitat. The change characteristics of germinated seeds or seedling banks are related to microhabitats. There are edge effects of eelgrass patches on the distribution of germinated seeds and seedlings. All these factors contribute to the formation of seedling distribution. Sowing eelgrass seeds in the edge area of a continuously distributed eelgrass bed can promote the seedling establishment rate.

Effects of Estuary-Wide Seagrass Loss on Fish Populations

Globally, habitat loss in coastal marine systems is a major driver of species decline, and estuaries are particularly susceptible to loss. Along the United States Pacific coast, monospecific eelgrass (Zostera marina) beds form the major estuarine vegetated habitat. In Morro Bay, California, eelgrass experienced an unprecedented decline of > 95%, from 139 ha in 2007 to < 6 ha by 2017. Fish populations were compared before and after the eelgrass decline using trawl surveys. Beach seines surveys were also conducted during the post-decline period to characterize species within and outside of remnant eelgrass beds. While the estuary-wide loss of eelgrass did not result in fewer fish or less biomass, it led to changes in species composition. The post-eelgrass decline period was characterized by increases in flatfish (mainly Citharichthys stigmaeus) and staghorn sculpin (Leptocottus armatus), and decreases in habitat specialists including bay pipefish (Syngnathus leptorhynchus) and shiner perch (Cymatogaster aggregata). There were similar trends inside and outside of remnant eelgrass patches. These findings support evidence across multiple ecosystems suggesting that the predominance of habitat-specialists predicts whether or not habitat loss leads to an overall decline in fish abundance. In addition, loss of critical habitats across seascapes can restrict population connectivity and lead to range contraction. For bay pipefish, the loss of eelgrass in Morro Bay is likely to create a population biogeographic divide. Currently, Morro Bay is dominated by flatfish and sculpins, and the longevity of this new ecosystem state will depend on future eelgrass recovery dynamics supported by ecosystem-based management approaches.

Large-scale eelgrass transplantation: a measure for carbon and nutrient sequestration in estuaries

The accelerated global losses of seagrass meadows makes restoration increasingly important. This restoration study was conducted in a shallow Danish estuary and describes one of the rare examples of successful large-scale eelgrass Zostera marina restoration outside North America. A simplified 3-step site selection approach was successfully applied to locate an optimal site for large-scale transplantation. It consisted of (1) qualitative assessments of vegetation using aerial photos, (2) inspection of potential sites with assessments of stressor presence and potential growth conditions and (3) transplantation tests for a final assessment of site suitability and methodology. The large-scale transplantation was initiated at the test site with the highest shoot production. After transplantation, shoot densities developed rapidly, achieving a 70-fold increase in density after about 2 yr. A rapid edge expansion (0.32 m yr-1) of the transplanted area was detected using drone-based monitoring. Both the final shoot density and edge expansion were comparable to those of natural eelgrass patches in the estuary. Eelgrass-transplanted areas accumulated more fine sediment particles and organic C, N and P than adjacent unvegetated sediment. Burial of organic C, N and P in eelgrass-transplanted sediments was 33 ± 7.5, 6.6 ± 0.9 and 3.0 ± 0.5 g m-2 yr-1, respectively (mean ± SE). In addition, inorganic C and N were assimilated by eelgrass transplants at rates of 290 ± 22 and 12 ± 1.0 g m-2 yr-1, respectively. The results highlight that important ecosystem services are already restored 2 yr after successful eelgrass restoration.

Role of eelgrass on bed‐load transport and sediment resuspension under oscillatory flow

AbstractCoastal vegetation is widely attributed to stabilize sediment. While most studies focused on how canopy causes flow reduction and thereby affects sediment dynamics, the role of roots and rhizomes on stabilizing the surface sediment has been less well studied. This study aims to quantify interactions between above‐ and belowground biomass of eelgrass (i.e., living Zostera marina plants and mimics) with surface sediment erosion (i.e., bed load and suspended load), under different hydrodynamic forcing that was created using a wave flume. Belowground biomass played an important role preventing bed‐load erosion, by roughly halving the amount of sediment transported after being exposed to maximal orbital velocities of 27 cm s−1, with and without canopy. Surprisingly, for suspended sediment transport, we found opposite effects. In the presence of eelgrass, the critical erosion threshold started at lower velocities than on bare sediment, including sand and mud treatments. Moreover, in muddy systems, such resuspension reduced the light level below the minimum requirement of Z. marina. This surprising result for sediment resuspension was ascribed to a too small eelgrass patch for reducing waves but rather showing enhanced turbulence and scouring at meadow edges. Overall, we conclude that the conservation of the existent eelgrass meadows with developed roots and rhizomes is important for the sediment stabilization and the meadow scale should be taken into account to decrease sediment resuspension.

Pacific geoduck (Panopea generosa) resilience to natural pH variation

Pacific geoduck aquaculture is a growing industry, however, little is known about how geoduck respond to varying environmental conditions, or how the industry will fare under projected climate conditions. To understand how geoduck production may be impacted by low pH associated with ocean acidification, multi-faceted environmental heterogeneity needs to be included to understand species and community responses. In this study, eelgrass habitats and environmental heterogeneity across four estuarine bays were leveraged to examine low pH effects on geoduck under different natural regimes, using targeted proteomics to assess physiology. Juvenile geoduck were deployed in eelgrass and adjacent unvegetated habitats for 30 days while pH, temperature, dissolved oxygen, and salinity were monitored. Across the four bays, pH was lower in unvegetated habitats compared to eelgrass habitats. However this did not impact geoduck growth, survival, or proteomic abundance patterns in gill tissue. Temperature and dissolved oxygen differences across all locations corresponded to differences in growth and targeted protein abundance patterns. Specifically, three protein abundance levels (trifunctional-enzyme β-subunit, puromycin-sensitive aminopeptidase, and heat shock protein 90-α) and shell growth positively correlated with dissolved oxygen variability and inversely correlated with mean temperature. These results demonstrate that geoduck may be resilient to low pH in a natural setting, but other abiotic factors (i.e. temperature, dissolved oxygen variability) may have a greater influence on geoduck physiology. In addition this study contributes to the understanding of how eelgrass patches influences water chemistry.

An effective seed protection method for planting Zostera marina (eelgrass) seeds: Implications for their large-scale restoration

We describe an innovative method of planting Zostera marina (eelgrass) seeds in which hessian bags filled with high-silted sediments are used as a seed protecting device. Here, we evaluated the effectiveness of the method through a field seed-sowing experiment over a three year period. The suitable seed planting density required by the seeds of Z. marina in this method was also investigated. In the spring following seed distribution, seedling establishment rate of Z. marina subjected to different seed densities of 200–500seedsbag−1 ranged from 16% to 26%. New eelgrass patches from seed were fully developed and well maintained after 2–3years following distribution. The seed planting density of 400seedsbag−1 may be the most suitable for the establishment of new eelgrass patches. Our results demonstrate that seed-based restoration can be an effective restoration tool and the technique presented should be considered for future large-scale Z. marina restoration projects.

Impact of submerged herbaceous vegetation on wind-induced current in shallow water

A combined wind tunnel and water flume experiment was performed to study the effect of an aquatic herbaceous plant patch on the turbulent structure and flow field of wind-induced currents. Eel grass was chosen as the test plant. The plants were settled in patch form. Three-dimensional instantaneous velocities were measured using an acoustic doppler velocimeter (ADV). The results indicate that in the non-eel grass patch flow, turbulent shear stress −u′w′¯has a local minimum near the flow reverse point, turbulent intensity has the tendency to decrease continually from surface to bottom, and the dominant turbulent event is sweeping. In the eel grass patch with wind-induced flow, reverse flow occurs more quickly than in the non-eel grass patch case, and the reverse point shifts downward. Turbulent shear stress −u′w′¯ has two maxima below the canopy. Turbulent intensity u′2¯ decreases generally from water surface to flume bed, but there are maxima below the canopy. The dominant turbulent event is the fourth quadrant event below the canopy, and the two relative contributions of the second and the fourth quadrant event have similar values above the canopy. The mean bias and RMS values at centre of the eel grass patch are almost as two times larger as that at other measuring lines in non-eel grass region. This indicates that not only the shear stress and turbulent intensity become larger, and the vertical variations of the shear stress and turbulent intensity are also larger due to the effect of vegetation. The differences in the effects of submerged herbaceous vegetation on open channel flow and wind-induced flow were discussed in relation to time averaged velocity, turbulent shear stress, turbulent intensity and coherent structure based on the present test data and previous data.

Disturbance facilitates the coexistence of antagonistic ecosystem engineers in California estuaries.

Ecological theory predicts that interactions between antagonistic ecosystem engineers can lead to local competitive exclusion, but disturbance can facilitate broader coexistence. However, few empirical studies have tested the potential for disturbance to mediate competition between engineers. We examined the capacity for disturbance and habitat modification to explain the disjunct distributions of two benthic ecosystem engineers, eelgrass Zostera marina and the burrowing ghost shrimp Neotrypaea californiensis, in two California estuaries. Sediment sampling in eelgrass and ghost shrimp patches revealed that ghost shrimp change benthic biogeochemistry over small scales (centimeters) but not patch scales (meters to tens of meters), suggesting a limited capacity for sediment modification to explain species distributions. To determine the relative competitive abilities of engineers, we conducted reciprocal transplantations of ghost shrimp and eelgrass. Local ghost shrimp densities declined rapidly following the addition of eelgrass, and transplanted eelgrass expanded laterally into the surrounding ghost shrimp-dominated areas. When transplanted into eelgrass patches, ghost shrimp failed to persist. Ghost shrimp were also displaced from plots with structural mimics of eelgrass rhizomes and roots, suggesting that autogenic habitat modification by eelgrass is an important mechanism determining ghost shrimp distributions. However, ghost shrimp were able to rapidly colonize experimental disturbances to eelgrass patch edges, which are common in shallow estuaries. We conclude that coexistence in this system is maintained by spatiotemporally asynchronous disturbances and a competition-colonization trade-off: eelgrass is a competitively superior ecosystem engineer, but benthic disturbances permit the coexistence of ghost shrimp at the landscape scale by modulating the availability of space.

Sexual reproduction and seed dispersal pattern of annual and perennial Zostera marina in a heterogeneous habitat

The sexual reproduction of annual and perennial Zostera marina was investigated in Moon Lake, Shandong, China. Based on the disturbance and stress regimes, the Z. marina beds were classified into five types: intertidal annual (IA) and perennial (IP) eelgrass patches, subtidal patch area (PA), meadow margin (MM) and meadow center (MC). Seed dispersal was investigated using artificial seagrass units in the five areas and another two areas [adjacent bare area and Zostera japonica meadow (Zj)]. Total and flowering shoot density and aboveground biomass of flowering shoots per unit area were higher in PA and MM, and lower in IA and IP, whereas the total biomass per unit area in MC showed the highest value. Reproductive effort (RE) in IA showed negative response to intertidal stress, while in perennial IP, PA and MM it showed significantly positive response to anthropogenic or natural disturbances. The density-based RE in perennial IP, PA and MM was 1.1-, 5.1- and 5.1-fold higher than that in MC, while in annual IA it was 0.46-fold lower. Additionally, the biomass-based RE in IP, PA and MM was 1.8-, 3.5- and 3.8-fold higher than that in MC, while the RE in IA was 0.84-fold lower. The estimated seed production per unit area was much greater in PA (60,793 ± 9,843 seeds m−2) and MM (43,414 ± 8,718 seeds m−2) than in IA (416 ± 83 seeds m−2), IP (3,820 ± 1,470 seeds m−2) and MC (9,779 ± 631 seeds m−2), while the seed density ranged from 24 ± 6 to 584 ± 56 seeds m−2. Results suggested that in response to disturbances and stress, Z. marina in subtidal areas increased their RE and seed production and thus seeds were available to be dispersed into areas where seed production was limited.

Turbulence structure and flow field of shallow water with a submerged eel grass patch

A flume experiment was conducted to investigate the effect of the aquatic herbaceous plant patch on the turbulent structure and flow field of shallow water. The eel grass that is widely distributed in the shallow lakes in China was chosen as the targeted plant. The plants were settled in patch form with three groups of densities and flow velocities. The three-dimensional instantaneous velocities were measured using an Audio Doppler Velocitimeter (ADV). The results indicate that the vertical velocity profile in the plant patch exhibits an S-shape from the canopy to the root of the eel grass. A secondary maximum in the vertical profile of velocity near the plant root is observed. The turbulent intensity increases from the water surface to the canopy, then decreases to the plant root; there is an inflection point around canopy, where the turbulent intensity deceases from the inner region to the side boundary of the patch. The vertical profiles of the eel grass resistance coefficient CP have different forms at different positions in the patch in general, but the forms of the CP profiles are similar along the boundary of the patch, and the forms of the CP profiles are similar in the inner part of the patch. In the patch area, the turbulent flow corresponds to the Quadrant 2 event (ejection event) above the canopy, the turbulent flow corresponds to the Quadrant 4 event (sweep event) below the canopy, but near the bed the Quadrant 1 event (outward interaction), the Quadrant 2 event and the Quadrant 4 event coexist. In the lateral boundary area of the patch the Quadrant 2 event and the Quadrant 3 event (inward interaction event) coexist due to presence of a strong shear layer.

Spatial distribution and nutritional requirements of the endosymbiont-bearing bivalve Loripes lacteus (sensu Poli, 1791) in a Mediterranean Nanozostera noltii (Hornemann) meadow

Sulphur-oxidising endosymbiont-bearing bivalves often inhabit seagrass meadows, where they can control sulphide levels and variably contribute to carbon cycling, by feeding on endosymbiotic bacteria and/or on particulate organic matter from the water column. The patterns of variability in their feeding mode and their spatial distribution within the seagrass meadows are however poorly studied. Seagrass beds form naturally patchy habitats with seagrass-sand edges that may have variable effects on different organisms. The present study aims at understanding differences in feeding mode and abundance of the endosymbiont-bearing bivalve Loripes lacteus (sensu Poli, 1791) as well as the physiological conditions of its endosymbiotic populations between edge and inner portion of meadows of the eelgrass Nanozostera noltii (Hornemann). In July 2010, Loripes specimens were sampled in 4 eelgrass patches at 2 different locations in the Thau lagoon, South of France. There was a clear negative edge effect on the abundance of small individuals of Loripes, while large individuals were homogeneously distributed between edge and inner part of the meadow. Although Loripes isotopic signatures (δ13C and δ15N) were always closer to those of its symbiotic bacteria than to those of suspension-feeding bivalves, eelgrass edge enhanced mixotrophic behaviour of small animals, which assimilated less bacterial carbon and nitrogen at the edge than in the inner part of the eelgrass meadow. No differences related to eelgrass edges were instead found for the bacterial populations harboured by Loripes. Rather, flow cytometry revealed large variability at small spatial scales. Although bacteria were always important for the nutrition of Loripes, these findings showed that seagrass edges may contribute to regulate feeding mode and population structure of Loripes, which may have implications for seagrass functioning.

Thermal effects on swimming activity and habitat choice in juvenile Pacific cod (Gadus macrocephalus)

The behavioral responses of fishes to temperature variation have received less attention than physiological responses, despite their direct implications for predator–prey dynamics in aquatic ecosystems. In this paper, we describe the temperature dependence of swimming performance and behavioral characteristics of juvenile Pacific cod (Gadus macrocephalus; 75–125 mm total length). Maximum swimming speeds increased with temperature and body size. Routine swimming speeds of Pacific cod in small groups of similarly sized fish (N = 6) increased with body size and were 34 % faster at 9 °C than at 2 °C. The response to temperature was opposite that previously described for juvenile walleye pollock (Theragra chalcogramma), reflecting species-specific differences in behavioral responses. In a separate experiment, we demonstrated the effect of temperature on habitat selection of juvenile Pacific cod: Use of an artificial eelgrass patch in a 5-m-long laboratory tank was significantly greater at 9 °C than at 2 °C. These results illustrate that temperature affects a range of behavioral traits that play important roles in determining the frequency and outcomes of predator–prey interactions.

Recolonization of intertidal Zostera marina L. (eelgrass) following experimental shoot removal

The recovery of eelgrass ( Zostera marina) from physical disturbances is understudied and no attention has been given to the likely differences in damage recovery rates between the continuous lower intertidal perennial meadows and higher intertidal eelgrass patches. In the present study, 4 m 2 plots were treated by removing all eelgrass shoots and followed over a 3 year period until they attained control (untreated) plot shoot densities. The number and types of shoots (vegetative, reproductive, and seedling) were counted semi-monthly with comparisons made between experimental and control plots. In the second year of the study additional plots were denuded and sown with Z. marina seeds to evaluate the importance of seedlings in the recovery process. Our results suggest that recovery in both low and high intertidal plots was due exclusively to rhizome growth from adjacent perennial eelgrass. This recovery began immediately within the permanent eelgrass meadow and was complete within 24 months. Denuded transition zone patches took almost twice as long to recover to control densities. Natural seedling production appeared to play no part in recovery. When larger numbers of seeds were planted into denuded plots in the winter, only a small portion of them produced seedlings in the spring and none appear to survive through the summer. These experimental eelgrass recovery rates were similar to recovery rates determined from aerial photographs of an eelgrass meadow damaged by a boat grounding near the study site. We suggest that transition zone perennial patches are more vulnerable to natural and anthropogenic disturbance events than lower intertidal eelgrass meadows.

Eelgrass patch size and proximity to the patch edge affect predation risk of recently settled age 0 cod ( Gadus)

Postsettled age 0 Atlantic cod ( Gadus morhua) seek refuge from predation in eelgrass ( Zostera marina) habitat within shallow, coastal nurseries. Laboratory and field experiments have demonstrated that predation risk on small fish is reduced in habitats of greater structure compared to less complex or barren environs. To determine if predation risk is linked to the areal extent of eelgrass coverage, we tested the hypothesis that predation risk of age 0 cod decreases with increasing eelgrass patch size. Predation on tethered age 0 cod ( G. morhua and G. ogac) was quantified in eelgrass patches (1–80 m 2) at three sites in northeastern Newfoundland, Canada, during September and October 1999 and 2000. Based on evidence of edge effects in terrestrial landscapes, we also tested the hypothesis that predation is elevated at ecotones separating eelgrass from adjacent barren mud substrate. We examined predation at the edge (i.e., 0 m) and both 5 and 10 m from this edge into and away from eelgrass cover along an 18 m long barren mud-gravel and eelgrass boundary, at two sites. Logistic regression analysis showed that the risk of predation, as measured by the odds ratio, increased with area over a small range of patch sizes (1–35 m 2 in 1999). When the study was extended to a wider range of patch sizes (1–80 m 2) in 2000, a parabolic relationship emerged, with patches on the order of 25 m 2 providing the least safety and the largest patches (80 m 2) providing the most safety. Predation on tethered cod was highest at the edge of eelgrass patches, compared with barren and eelgrass locations; predation generally decreased with distance from the eelgrass boundary. Our results are consistent with the hypothesis that predators are drawn to large patches of eelgrass because of increased prey numbers, that predators increase their success by searching edges, and that this results in greatest predation risk to prey in isolated patches of intermediate size.

Eelgrass seed dispersal via floating generative shoots in the Dutch Wadden Sea: a model approach

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 358:115-124 (2008) - DOI: https://doi.org/10.3354/meps07304 Eelgrass seed dispersal via floating generative shoots in the Dutch Wadden Sea: a model approach Paul L. A. Erftemeijer1,*, Jan K. L. van Beek1, Caroline A. Ochieng2, Zwanette Jager3, Hans J. Los1 1WL/Delft Hydraulics, PO Box 177, 2600 MH Delft, The Netherlands 2Jackson Estuarine Laboratory, University of New Hampshire, 85 Adams Point Road, Durham, New Hampshire 03824, USA 3National Institute for Coastal and Marine Management/RIKZ, PO Box 207, 9750 AE Haren, The Netherlands *Email: paul.erftemeijer@wldelft.nl ABSTRACT: Potential long-distance dispersal of eelgrass seeds via floating generative shoots from a 256 ha meadow in the Ems Estuary (Wadden Sea) was studied by means of computer-simulation modelling. Flowering shoot density (peaking at 7.8 m–2) and total seed production (1094 million seeds yr–1) of this meadow was determined in the field and used as model input. Dispersal of floating generative shoots dislodged by increased water turbulence during autumn was modelled using a 3D transport model (Delft3D-WAQ). Transport of eelgrass seeds contained in floating reproductive shoots with the prevailing hydrodynamic regime revealed maximum dispersal distances of up to 130 km from the source of seed production. The effect of wind speed and direction on seed transport was assessed by applying a wind drag function (3% of wind speed) on surface currents in the model using actual wind data from 10 consecutive years (1993 to 2002). Main transport direction under average autumn wind conditions was northeastward. Easterly winds (occurring at an average frequency of 15%) were responsible for some westward transport of eelgrass seeds (at densities >0.2 seeds m–2) up to 20 km from the estuary. Westward eelgrass colonization of suitable areas in the Dutch Wadden Sea appears to be limited by seed supply due to transport limitations posed by the prevailing hydrodynamic regime. Extreme events, such as prolonged Eastern storms, might promote seed dispersal further westwards, allowing for natural recovery of eelgrass in this area; this theory is supported by observations of localized eelgrass patches up to 40 km west of the estuary. KEY WORDS: Seed dispersal · Zostera marina · Transport modelling · Wind effects · Recruitment limitation · Wadden Sea Full text in pdf format PreviousNextCite this article as: Erftemeijer PLA, van Beek JKL, Ochieng CA, Jager Z, Los HJ (2008) Eelgrass seed dispersal via floating generative shoots in the Dutch Wadden Sea: a model approach. Mar Ecol Prog Ser 358:115-124. https://doi.org/10.3354/meps07304 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 358. Online publication date: April 21, 2008 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2008 Inter-Research.

Importance of genetic diversity in eelgrass Zostera marina for its resilience to global warming

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 355:1-7 (2008) - DOI: https://doi.org/10.3354/meps07369 Importance of genetic diversity in eelgrass Zostera marina for its resilience to global warming Anneli Ehlers1,2,*, Boris Worm1,3, Thorsten B. H. Reusch2,4 1Leibniz Institute for Marine Sciences, IfM-Geomar, Düsternbrooker Weg 20, 24105 Kiel, Germany 2Max-Planck-Institute for Limnology, August-Thienemann-Str. 2, 24306 Plön, Germany 3Biology Department, Dalhousie University, Halifax, Nova Scotia B3H 4J1, Canada 4Institute for Evolution and Biodiversity, University of Münster, Hüfferstr. 1, 48149 Münster, Germany *Email: aehlers@ifm-geomar.de ABSTRACT: Effects of global warming on marine ecosystems are far less understood than they are in terrestrial environments. Macrophyte-based coastal ecosystems are particularly vulnerable to global warming, because they often lack species redundancy. We tested whether summer heat waves have negative effects on an ecologically important ecosystem engineer, the eelgrass Zostera marina L., and whether high genotypic diversity may provide resilience in the face of climatic extremes. In a mesocosm experiment, we manipulated genotypic diversity of eelgrass patches fully crossed with water temperature (control vs. temperature stress) over 5 mo. We found a strong negative effect of warming and a positive effect of genotypic diversity on shoot densities of eelgrass. These results suggest that eelgrass meadows and associated ecosystem services will be negatively affected by predicted increases in summer temperature extremes. Genotypic diversity may provide critical response diversity for maintaining seagrass ecosystem functioning, and for adaptation to environmental change. KEY WORDS: Climate change · Ocean warming · Coastal ecosystem · Genotypic diversity · Intraspecific variation · Resilience · Zostera marina Full text in pdf format NextCite this article as: Ehlers A, Worm B, Reusch TBH (2008) Importance of genetic diversity in eelgrass Zostera marina for its resilience to global warming. Mar Ecol Prog Ser 355:1-7. https://doi.org/10.3354/meps07369 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 355. Online publication date: February 26, 2008 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2008 Inter-Research.

Recovery of the seagrass Zostera marina in a disturbed Mediterranean lagoon (Etang de Berre, Bouches-du-Rhône, Southern France)

Until 1966, Berre lagoon (Provence, southern France) was a salty lagoon with a highly diversified marine fauna and flora. Increased inputs of freshwater from a hydroelectric plant led to the desalination and stratification of the lagoon. Following these changes, a wide diversity of species disappeared, including the eelgrass Zostera marina, a keystone species which previously constituted extensive meadows in the lagoon. After almost three decades of absence, patches of eelgrass were observed in 2001 and 2002 but the success of future recolonization by this community is uncertain.

Disturbance of eelgrass Zostera marina by commercial mussel Mytilus edulis harvesting in Maine: dragging impacts and habitat recovery

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 285:57-73 (2005) - doi:10.3354/meps285057 Disturbance of eelgrass Zostera marina by commercial mussel Mytilus edulis harvesting in Maine: dragging impacts and habitat recovery Hilary A. Neckles1,*, Frederick T. Short2, Seth Barker3, Blaine S. Kopp1 1USGS Patuxent Wildlife Research Center, 196 Whitten Road, Augusta, Maine 04330, USA 2Jackson Estuarine Laboratory, University of New Hampshire, 85 Adams Point Road, Durham, New Hampshire 03824, USA 3Maine Department of Marine Resources, PO Box 8, West Boothbay Harbor, Maine 04575, USA *Email: hilary_neckles@usgs.gov ABSTRACT: We studied the effects of commercial harvest of blue mussels Mytilus edulis on eelgrass Zostera marina L. in Maquoit Bay, Maine, USA, at a hierarchy of scales. We used aerial photography, underwater video, and eelgrass population- and shoot-based measurements to quantify dragging impacts within 4 sites that had been disturbed at different times over an approximate 7 yr interval, and to project eelgrass meadow recovery rates. Dragging had disturbed 10% of the eelgrass cover in Maquoit Bay, with dragged sites ranging from 3.4 to 31.8 ha in size. Dragging removed above- and belowground plant material from the majority of the bottom in the disturbed sites. One year following dragging, eelgrass shoot density, shoot height and total biomass of disturbed sites averaged respectively 2 to 3%, 46 to 61% and <1% that of the reference sites. Substantial differences in eelgrass biomass persisted between disturbed and reference sites up to 7 yr after dragging. Dragging did not affect physical characteristics of the sediment. The pattern and rate of eelgrass bed recovery depended strongly on initial dragging intensity; areas of relatively light dragging with many remnant eelgrass patches (i.e. patches that were missed by the mussel dredge) showed considerable revegetation in 1 yr. However, by developing recovery trajectories from measurements at sites disturbed in different years, we projected that it would require a mean of 10.6 yr for recovery of eelgrass shoot density within the areas of intense dragging characterizing most of the disturbed sites. A spatial simulation model based on measured rates of lateral patch-expansion (mean 12.5 cm yr-1) and new-patch recruitment (mean 0.19 patches m-2 yr-1) yielded a mean bed recovery time of 9 to 11 yr following dragging, depending on initial degree of plant removal. Model simulations suggested that with favorable environmental conditions, eelgrass beds might recover from dragging disturbance in 6 yr; conversely, recovery under conditions less conducive to eelgrass growth could require 20 yr or longer. This study shows that mussel dragging poses a severe threat to eelgrass in this region and that regulations to protect eelgrass from dragging impacts would maintain the integrity of a substantial amount of habitat. KEY WORDS: Eelgrass · Zostera marina · Seagrass · Dragging impacts · Recovery · Patch recruitment · Patch expansion Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 285. Online publication date: January 19, 2005 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2005 Inter-Research.

Full of eggs and no place to lay them: hidden cost of benthic development

The scarcity of sites suitable for attaching eggs may be a hidden cost to depositing embryos in benthic aggregations. We tested this hypothesis with the bubble-shell snail Haminaea vesicula, which lives on mud or sand but requires firm substrata for attaching its eggs. In pools on a sandflat where firm substrata were scarce, the preferred substrata were but a small fraction of the total available firm substrata. Abundant drifting green algal blades comprised 1 to 11% cover but were rarely used for egg deposition. Substrata commonly used for egg deposition totaled less than 1% cover, and included attached and drifting eelgrass, drifting branched red algae, bivalve shells, and attached green algal blades. In choice experiments, the snails preferred to deposit eggs on branched red algae and eelgrass, with bivalve shells next and green algal blades last. To test the hypothesis that substratum availability limits egg deposition, we added artificial eelgrass made of duct tape to tidepools inhabited by the snails. The mean number of egg ribbons laid m -2 in the exper- imental areas was 20 to 360 times that in control areas, and the mean number of adult snails present and egg ribbons per adult snail were greater in the experimental areas. Also, more egg ribbons per adult were deposited on artificial eelgrass when it was positioned away from natural eelgrass patches, indicating that distances of a few meters affect availability of substrata for deposition. The results imply that in this habitat the snails travel to scarce substrata for egg deposition, with whatever costs in time, energy, or risk that may be associated with travel. Scarcity of suitable sites for benthic egg masses can limit an apparently safe mode of development. Habitats that regularly support adult populations can differ greatly in suitability for egg deposition, but this limitation may not be appar- ent without experimental intervention.

Predator distribution and habitat patch area determine predation rates on Age-0 juvenile cod Gadus spp.

Eelgrass Zostera marina provides refuge to numerous fish species but is vulnerable to fragmentation through natural and anthropogenic disturbance. In Bonavista Bay, Newfoundland, eelgrass patch size was altered to measure changes in predation risk in Age-0 juvenile cod, Gadus morhua. Artificial eelgrass mats of 5 sizes (0.32, 1.1, 5.5, 11 and 22 m2) were deployed in duplicate at each of 2 sites in Newman Sound in Terra Nova National Park during summer/autumn in 1999 and 2000. Predator distribution was determined using a combination of weekly underwater transect surveys and biweekly seining. Relative predation rates were measured by tethering Age-0 cod at the center of each patch and recording the incidence of predation (n = 1116 tether sets). Predation rates were negatively correlated with patch size during both years, suggesting that larger patches reduce predator foraging ability. However, high predator densities in the largest eelgrass patch resulted in higher than expected rates of predation. Therefore, habitat dimension affected predation risk in juvenile cod via 2 opposing mechanisms. Our results stress the importance of considering both habitat areal extent and predator distribution when estimating the effects of habitat fragmentation on predation rates.