10.5061/DRYAD.HMGQNK9D2
James, Rebecca K.
0000-0002-3679-8531
Royal Netherlands Institute for Sea Research
Christianen, Marjolijn J. A.
Wageningen University & Research
van Katwijk, Marieke
Radboud University Nijmegen
de Smit, Jaco
Royal Netherlands Institute for Sea Research
Bakker, Elisabeth (Liesbeth)
Nederlands Instituut voor Ecologie
Herman, Peter
Delft University of Technology
Bouma, Tjeerd
Royal Netherlands Institute for Sea Research
Data from: Seagrass coastal protection services reduced by invasive
species expansion and megaherbivore grazing
Dryad
dataset
2020
Invasion ecology
Thalassia
Halophila
Storm resilience
exotic species
Dutch Research Council
https://ror.org/04jsz6e67
858.14.063
Dutch Research Council
https://ror.org/04jsz6e67
858.14.063
2020-04-29T00:00:00Z
2020-04-29T00:00:00Z
en
566021 bytes
2
CC0 1.0 Universal (CC0 1.0) Public Domain Dedication
1. Seagrasses provide an important ecosystem service by creating a stable
erosion-resistant seabed that contributes to effective coastal protection.
Variable morphologies and life history strategies, however, are likely to
impact the sediment stabilisation capacity of different seagrass species.
We question how opportunistic invasive species and increasing grazing by
megaherbivores may alter sediment stabilisation services provided by
established seagrass meadows, using the Caribbean as a case study. 2.
Utilising two portable field-flumes that simulate unidirectional and
oscillatory flow regimes, we compared the sediment stabilisation capacity
of natural seagrass meadows in situ under current- and wave-dominated
regimes. Monospecific patches of a native (Thalassia testudinum) and an
invasive (Halophila stipulacea) seagrass species were compared, along with
the effect of three levels of megaherbivore grazing on T. testudinum:
ungrazed, lightly-grazed and intensively-grazed. 3. For both hydrodynamic
regimes, the long-leaved, dense meadows of the climax species, T.
testudinum, provided the highest stabilisation. However, the loss of
above-ground biomass by intensive grazing reduced the capacity of the
native seagrass to stabilise the surface sediment. Caribbean seagrass
meadows are presently threatened by the rapid spread of the invasive
opportunistic seagrass, H. stipulacea. The dense meadows of H. stipulacea
were found to accumulate fine sediment, and thereby, appear to be
effective in reducing bottom shear stress during calm periods. This fine
sediment within the invasive meadows, however, is easily resuspended by
hydrodynamic forces, and the low below-ground biomass of H. stipulacea
make it susceptible to uprooting during storm events, potentially leaving
large regions vulnerable to erosion. Overall, this present study
highlights that intensive megaherbivore grazing and opportunistic invasive
species threaten the coastal protection services provided by mildly grazed
native species. 4. Synthesis: Seagrass meadows of dense, long-leaved
species stabilise the sediment surface and maintain the seabed integrity,
thereby contributing to coastal protection. These services are threatened
by intensive megaherbivore grazing, which reduces the stability of the
surface sediment, and opportunistic invasive species, which are
susceptible to uprooting in storms and thereby can leave the seabed
vulnerable to erosion.
This dataset contains data collected in Lac Bay, Bonaire where the
critical erosion threshold was measured within vegetation patches of
varying seagrass species and different levels of grazing. Erosion
threshold measurements: Measurements were conducted with field flumes that
simulated unidirectional and oscillatory flow. The critical erosion
threshold was considered the flow velocity at which sediment began to
move. Sediment grain size analysis: Sediment samples were freeze-dried and
sieved through a one mm sieve, sediment grain size distribution was
measured by laser diffraction on a Malvern Mastersizer 2000 (McCave and
others 1986). Biomass: Five replicate cores of 15 cm (for Thalassia) and
10 cm for (Halophila) diameter and length were taken from each vegetation
patch. Sediment was washed from the biomass, and the biomass was separated
into above-ground biomass (leaves and shoots), and below-ground biomass
(roots and rhizomes). The biomass was dried in a 60°C drying oven and
weighed. Seagrass bendability: Seagrass shoots were placed in the fume
with the broadest part of the leaf positioned adjacent to the flow, to
allow for the natural bending direction of the seagrass. The flow within
the flume was increased at 10 cm s^-1 increments, from 0 - 50 cm s^-1, and
a digital photograph was taken of the individuals at each flow speed.
Using ImageJ 1.50i, a straight line was drawn from the base of the stem to
the most outward part of the thallus, and the angle of this line was
recorded as the bending angle of the individual. Bending angles are
presented relative to the angle of the thallus at 0 cm s^-1. Seagrass leaf
strength: Three to four undamaged leaves of the four seagrass types were
measured with a tensometer (Instron Corporation, Canton, MA, USA,
precision ± 0.5%). Seagrass blades were individually clamped into Instron
screw side action grips (Cat. No. 2710-102), with the mountings 20 mm
apart. The leaves of the seagrass were stretched at a velocity of 5 mm
min^-1, while the force (measured in Newton, N) was recorded every 0.1
seconds until the blade broke. The maximum force (N) that the blades could
bear before breaking was recorded and reported as the ultimate strength.
Readme for: Data presented in the paper “ Seagrass coastal protection
services reduced by invasive species expansion and megaherbivore grazing”
***General Introduction*** This dataset contains data collected in Lac
Bay, Bonaire where the critical erosion threshold was measured within
vegetation patches of varying seagrass species and different levels of
grazing. The dataset is split into csv files containing data from within
each measured patch type (critical erosion threshold and grain size) and
data about the dominant vegetation types (biomass, leaf bending
properties, leaf strength). Seagrass species measured were: Ungrazed
Thalassia testudinum (T. testudinum), intermediately grazed T. testudinum
intensively grazed T. testudinum, and Halophila stipulacea (H. Stipulacea)
***Individual file information*** File:
JamesEtAl_SGSedimentStabilisation_Bonaire_Flume General Info: Measures of
critical erosions thresholds within different vegetation types in Lac Bay,
Bonaire. Column headings: Code: Code used in manuscript Species: Dominant
vegetation type Replicate: Replicate number Flume type: Either
unidirectional flow flume or oscillatory flow flume water_depth_cm: Depth
that measurements were conducted (cm) Canopy_length_cm: Average height of
the vegetation canopy at measurement position in (cm) %_plant_cover:
Estimated percent cover of all vegetation at the measurement position (%)
SGVol: canopy height (m) multiplied by plant cover (%) Uni_CritVel:
Unidirectional flow velocity at which sediment began to move (cm/s)
Wave_CritVel|: Oscillatory flow velocity at which sediment began to move
(cm/s) File: JamesEtAl_SGSedimentStabilisation_Bonaire_GrainSize General
Info: The grain size distribution of the sediment collected within the
different measurement positions. Column headings: Sample: Dominant
vegetation at measuring position SD(0.9)_2 (μm): 90% grains are bigger
than this (μm) SD50MUM_2 (μm): Median grain size (μm) SD50PHIM_2 (phi):
median grain size (phi) SMODE_2 (μm): Modus grain size (μm)
SCOARSE%_500-1000μm (%): percent of grains 500-1000 μm in size
SMEDIUM%_250-500μm (%): percent of grains 250-500 μm in size
SFINES%_125-250μm (%): percent of grains 125-250 μm in size
SVFINES%_63-125 (%): percent of grains 62.5-125 μm in size SSILT63_0-63
(%): percent of grains less than 63 μm in size File:
JamesEtAl_SGSedimentStabilisation_Bonaire_Biomass General: Biomass of the
different parts of the most dominant vegetation types within Lac Bay,
Bonaire. Column headings: Species: Species of vegetation Part: The part of
the plant rep: Replicate g_DW_m2: Dry weight per m2 (g ,m^-2) File:
JamesEtAl_SGSedimentStabilisation_Bonaire_Bending General: The angle of
bending of the dominant vegetation types in increasing unidirectional flow
speeds. Column headings: Species: Species of vegetation 0cm/s: Bending
angle of plant at a flow of 0 cm/s 10cm/s: Bending angle of plant at a
flow of 10 cm/s 20cm/s: Bending angle of plant at a flow of 20 cm/s
30cm/s: Bending angle of plant at a flow of 30 cm/s 40cm/s: Bending angle
of plant at a flow of 40 cm/s 50cm/s: Bending angle of plant at a flow of
50 cm/s File: JamesEtAl_SGSedimentStabilisation_Bonaire_Strength
General: Breaking point of the leaves of the dominant seagrass species at
Lac Bay, Bonaire. Column headings: Species: Species of vegetation No:
Replicate number Max load (kgs): Maximum load in kgs that the leaf
withstood before breaking (kgs) Max load (N): Maximum load in Newtons that
the leaf withstood before breaking (N)