Waterfowl grazing in autumn enhances spring seedling recruitment of intertidal Zostera noltii

Zipperle, Andreas M.; Coyer, James A.; Reise, Karsten; Stam, Wytze T.; Olsen, Jeanine L.

doi:10.1016/j.aquabot.2010.05.002

Cited by 17 publications

(19 citation statements)

References 16 publications

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“…Both Medby and Sørkjosen are dense meadows, suggesting that recruitment may be limited. Creation of a large area of distinct substructure requires the opening of large gaps that favor new recruitment, such as destructive (as opposed to normal) waterfowl grazing (Zipperle et al 2010) or past habitat destruction by anchors or fishing traps. Although destructive waterfowl grazing could be an explanation applied to the intertidal Medby sites, it is unlikely at the subtidal (2.5 to 5 m deep at low tide) Sørkjosen-deep site which is too deep.…”

Section: Substructure Within Meadows -Stochastic Processes or Habitatmentioning

confidence: 99%

Eelgrass Zostera marina populations in northern Norwegian fjords are genetically isolated and diverse

Olsen¹,

Coyer

Stam³

et al. 2013

Mar. Ecol. Prog. Ser.

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Populations along the northern boundary of a marine species' distributional range in the NE Atlantic are expected to harbor lower standing genetic variation as a consequence of postglacial expansion following the last glacial maximum. Founder events and marginal habitat availability may render the edge populations more vulnerable to anthropogenic stress and less capable of rapid adaptation to global climate change, a concern for conservation and management. We analyzed meadow architecture, persistence and connectivity within and among 15 locations (600 samples genotyped with 8 microsatellite loci) in 3 fjords in Troms County, Norway (69°N). Whereas global mean allelic diversity (standardized for sample size) was in accordance with previous studies using the same markers, more extensive sampling revealed a broader range of allelic richness (mean = 2.85; range = 1.84 to 4.21) in the regional pool. Genotypic diversity was typically high, whereas large genets were rare (2 out of 15 locations). Population differentiation (F ST ) was 2 to 6 times higher between fjords than within fjords. A Bayesian (STRUCTURE) analysis also strongly supported the genetic distinctness of each fjord. Although 9 locations within the 60 km long Balsfjord were connected by gene flow, demographic connectivity may actually be low, as fixed differences were observed at 6 of the 9 locations, along with significantly positive inbreeding coefficients and strong substructure. Overall, our results suggest that these northern, leading-edge meadows are healthy, but vigilance is required to avoid further losses. Fjord-level management, especially of the larger fjords, will be sufficient to capture the range of variation.

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Section: Substructure Within Meadows -Stochastic Processes or Habitatmentioning

confidence: 99%

Eelgrass Zostera marina populations in northern Norwegian fjords are genetically isolated and diverse

Olsen¹,

Coyer

Stam³

et al. 2013

Mar. Ecol. Prog. Ser.

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“…In this sub-tidal environment, there are no large grazing species, such as the geese that affect inter-tidal seagrass populations [46], [47], or the marine turtles and sirenians of tropical seagrass habitats [48], [49]. In addition, our choice of location is an archipelago with little industrial or agricultural impact or urbanization (Fig.…”

Section: Introductionmentioning

confidence: 99%

Local Competition and Metapopulation Processes Drive Long-Term Seagrass-Epiphyte Population Dynamics

et al. 2013

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It is well known that ecological processes such as population regulation and natural enemy interactions potentially occur over a range of spatial scales, and there is a substantial body of literature developing theoretical understanding of the interplay between these processes. However, there are comparatively few studies quantifying the long-term effects of spatial scaling in natural ecosystems. A key challenge is that trophic complexity in real-world biological communities quickly obscures the signal from a focal process. Seagrass meadows provide an excellent opportunity in this respect: in many instances, seagrasses effectively form extensive natural monocultures, in which hypotheses about endogenous dynamics can be formulated and tested. We present amongst the longest unbroken, spatially explict time series of seagrass abundance published to date. Data include annual measures of shoot density, total above-ground abundance, and associated epiphyte cover from five Zostera marina meadows distributed around the Isles of Scilly, UK, from 1996 to 2011. We explore empirical patterns at the local and metapopulation scale using standard time series analysis and develop a simple population dynamic model, testing the hypothesis that both local and metapopulation scale feedback processes are important. We find little evidence of an interaction between scales in seagrass dynamics but that both scales contribute approximately equally to observed local epiphyte abundance. By quantifying the long-term dynamics of seagrass-epiphyte interactions we show how measures of density and extent are both important in establishing baseline information relevant to predicting responses to environmental change and developing management plans. We hope that this study complements existing mechanistic studies of physiology, genetics and productivity in seagrass, whilst highlighting the potential of seagrass as a model ecosystem. More generally, this study provides a rare opportunity to test some of the predictions of ecological theory in a natural ecosystem of global conservation and economic value.

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“…This has consequences at the community level because subordinate aquatic plants increase in abundance as a result (Santamaría , Hidding et al ). It is known that foraging pits can enhance chances of successful seed germination in macrophytes; this has for instance been shown in the seagrass Zostera noltii (Zipperle et al ). And, although the effect of autumn herbivory on the biomass in summer is rather limited (Hidding et al ), four years of Bewick ‘s swan exclusion changes the burial depth of tubers: tubers are produced deeper in the sediment when Bewick's swans feast annually on them, and hence the plant follows an escape strategy (Hidding et al ).…”

Section: Discussionmentioning

confidence: 98%

“…Our results indicate that repeated seedling recruitment (RSR) plays a role, and that sexual propagation takes place locally, because we observed spatial genetic structure even when clonal ramets are omitted from the analysis. Given that the competitive advantage of existing genets over seeds must be considerable, recruitment from seeds may not have happened at a constant rate, as also observed in the seagrass Zostera noltii (Zipperle et al 2009(Zipperle et al , 2010. Th e most likely opportunities for sexual propagation may occur through episodic recruitment.…”

Section: Discussionmentioning

confidence: 99%

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The effect of herbivores on genotypic diversity in a clonal aquatic plant

Hidding¹,

Meirmans

Klaassen³

et al. 2014

Oikos

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In clonal plants, vegetative parts may outcompete seeds in the absence of disturbance, limiting the build-up of genotypic diversity through repeated seedling recruitment (RSR). Herbivory may provide disturbance and trigger establishment of strong colonizers (seeds) at the expense of strong competitors (clonal propagules). In the clonal aquatic fennel pondweed Potamogeton pectinatus , two distinct herbivore guilds may modify the dynamics of propagation. In winter, Bewick's swans may deplete patches of tubers, promoting seedling establishment in spring. In summer, seed consumption by waterfowl can reduce the density of viable seeds but grazing may also reduce tuber production and hence facilitate seedling establishment. Th is study is among the fi rst to experimentally test herbivore impact on plant genotypic diversity. We assess the separate and combined eff ects of both herbivore guilds on genotypic diversity and structure of fennel pondweed beds. Using microsatellites, we genotyped P. pectinatus from an exclosure experiment and assessed the contribution of herbivory, dispersal and sexual reproduction to the population genetic structure. Despite the predominance of clonal propagation in P. pectinatus , we found considerable genotypic diversity. Within the experimental blocks, kinship among genets decreased with geographic distance, clearly identifying a role for RSR in the maintenance of genotypic diversity within the fennel pondweed beds. However, over a period of fi ve years, none of the herbivory treatments aff ected genotypic diversity. Hence, sexual reproduction on a local scale is important in this putatively clonal plant and possibly suffi cient to ensure a relatively high genotypic diversity even in the absence of herbivores. Although we cannot preclude a role of herbivory in shaping genotypic diversity of a clonal plant, after fi ve years of exclusion of the two investigated herbivore guilds no measurable eff ect on genotypic diversity was detected.

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Waterfowl grazing in autumn enhances spring seedling recruitment of intertidal Zostera noltii

Cited by 17 publications

References 16 publications

Eelgrass Zostera marina populations in northern Norwegian fjords are genetically isolated and diverse

Eelgrass Zostera marina populations in northern Norwegian fjords are genetically isolated and diverse

Local Competition and Metapopulation Processes Drive Long-Term Seagrass-Epiphyte Population Dynamics

The effect of herbivores on genotypic diversity in a clonal aquatic plant

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