Regulation of eelgrass (Zostera marina) cover along depth gradients in Danish coastal waters

Krause‐Jensen, Dorte; Pedersen, Morten Foldager; Jensen, Chris

doi:10.1007/bf02803345

Cited by 63 publications

(29 citation statements)

References 30 publications

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“…One may be that the regression assumes that the relation between eelgrass cover and number of waterbirds is the same throughout the time series and this may not be the case, as birds could exert topdown control during periods with sparse eelgrass populations. Eelgrass meadows at 0-1 m are also more affected than those at 1-2 m by physical disturbances from ice scour in winter, wave action (Krause-Jensen et al, 2003) and possibly also from drifting macroalgae and burrowing fauna which may hamper the establishment of seedlings (Valdemarsen et al, 2010). As eelgrass meadows become sparse they also loose resilience, and feed-back mechanisms may act to maintain the state of reduced cover, e.g., through increased sediment resuspension (Maxwell et al, 2016).…”

Section: Relationships Between Abundances Of Eelgrass and Water Birdsmentioning

confidence: 99%

Long-term Patterns of Eelgrass (Zostera marina) Occurrence and Associated Herbivorous Waterbirds in a Danish Coastal Inlet

et al. 2017

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Seagrasses in coastal areas have substantial importance for the marine environment and also serve as food for herbivorous waterbirds. We investigated potential relationships between the autumn population of herbivorous waterbirds and eelgrass (Zostera marina) abundance in the EU protected area, Nibe-Gjøl Bredning, a broad of the Limfjorden estuarine complex in Denmark.This is an important site for migratory herbivorous waterbirds such as mute swan (Cygnus olor), coot (Fulica atra), brent goose (Branta bernicla), and wigeon (Anas penelope). We explored long-term (27 years) changes in eelgrass and bird-populations and relationships between eelgrass-and bird abundance. We applied trend-and correlative analyses of yearly monitoring data on eelgrass and waterbirds between 1989 and 2015 coupled with estimates of the potential grazing pressure exerted by the birds. Around 1990 eelgrass was abundant in this area covering more than 40 km 2 , but eelgrass coverage and biomass declined drastically around 1995 and remained low until 2011 when natural recolonization accelerated and by 2015 had restored the lost meadows. The number of herbivorous waterbirds also fluctuated substantially during the monitoring period with large abundance until the mid-end 1990s followed by reduced abundance in the 2000s and recovery after 2010. The number of bird-days showed a positive relationship with the same year's eelgrass abundance in the 1-2 m depth stratum. For the 0-1 m depth stratum, where the eelgrass meadows are most exposed to bird grazing but also to physical control from e.g., wind and ice, only a particularly detailed eelgrass data set available for a subset of the study period, showed a significant relationship with bird grazing. The potential waterbird consumption of eelgrass, estimated by multiplying average intake rate and number of bird-days for each species, ranged from less than 16% of the eelgrass biomass in most years to more than 40% of the eelgrass biomass in years with extremely sparse eelgrass populations. Hence, the study suggests that dense eelgrass populations stimulate herbivorous waterbirds whereas top-down control is only likely when abundant bird populations graze on sparse eelgrass populations.

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Section: Relationships Between Abundances Of Eelgrass and Water Birdsmentioning

confidence: 99%

Long-term Patterns of Eelgrass (Zostera marina) Occurrence and Associated Herbivorous Waterbirds in a Danish Coastal Inlet

et al. 2017

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“…It is probable that unfavorable chemical sediment conditions are more of a problem for deep, shaded eelgrass populations than for populations living in shallow light saturated habitats; while soft sediments with low anchorage support are more problematic for shallow eelgrass populations in exposed environments. A combination of unfavorable physico-chemical sediment conditions across the entire depth range may, therefore, further accentuate the pattern of eelgrass being constrained to intermediate water depths where moderate light levels are combined with moderate levels of physical exposure (Krause-Jensen et al 2003). If depth limits rose to exclude eelgrass from all but very shallow waters, due to extremely high turbidity, plants growing within the depth limit would be highly vulnerable to higher drag forces in the shallow waters.…”

Section: The Sea Bottom Exerts a Threshold Effect On Eelgrass Depth Lmentioning

confidence: 99%

Sea bottom characteristics affect depth limits of eelgrass Zostera marina

Krause‐Jensen¹,

Carstensen²,

Nielsen³

et al. 2011

Mar. Ecol. Prog. Ser.

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This study tested the hypothesis that sea bottom characteristics interact with light attenuation in the water column to regulate the depth limit of eelgrass Zostera marina L. A large-scale field data set on eelgrass depth limits, light climate and physico-chemical sea bottom characteristics was collected from Danish coastal waters and analyzed by statistical models. The results confirmed that light attenuation is the main predictor of eelgrass depth limits, but indicated that sediments characteristic of eutrophic conditions and physically protected environments also play a regulating role. Depth limits were moderately shallower when the sea bottom was rich in organic material, had high concentrations of nutrients and hydrogen sulfide, and had a physical structure characterized by fine particles, high porosity, high water content and low density. The effect of sediment variables was non-linear, and the sediment only affected depth limits beyond certain threshold levels characteristic of eutrophic conditions and physically protected environments. We argue that further reductions in nutrient loads can improve the state of eelgrass beds by ameliorating not only light conditions but also sediment quality and associated oxygen concentrations in the water column.

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“…Reinke (1889), Waern (1952) andvon Wachenfeldt (1975) as well as Boström et al (2003), Martin (1999), and Krause-Jensen et al (2003).…”

Section: Refconmentioning

confidence: 99%

Getting the measure of eutrophication in the Baltic Sea: towards improved assessment principles and methods

Andersen

Axe²,

Backer

et al. 2010

Biogeochemistry

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Regulation of eelgrass (Zostera marina) cover along depth gradients in Danish coastal waters

Cited by 63 publications

References 30 publications

Long-term Patterns of Eelgrass (Zostera marina) Occurrence and Associated Herbivorous Waterbirds in a Danish Coastal Inlet

Long-term Patterns of Eelgrass (Zostera marina) Occurrence and Associated Herbivorous Waterbirds in a Danish Coastal Inlet

Sea bottom characteristics affect depth limits of eelgrass Zostera marina

Getting the measure of eutrophication in the Baltic Sea: towards improved assessment principles and methods

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