A Viability study on the use of enriched sediment verses natural sediment to increase growth and survival rates of Zostera marina. Daniel j. Flint FdSc Marine Science Falmouth Marine School May 2012
Abstract Zostera marina is a key habitat in Northern European coastal waters due to the nursery grounds that it provides for many juvenile species. Unfortunately due to the naturally occurring fungal disease found within Zostera marina whipping out over 90% of the naturally occurring eelgrass beds in northern European waters in the 1930’s. This naturally occurring disease which normally has no effect on the eelgrass due to its natural defence of phenoic acid was able to take such a devastating effect due to the very poor weather conditions in the 3 years prior to the epidemic resulted in the eelgrass not being able to build the nitrogen reserves and therefore the phenoic acid as a natural defence against pathogens. This study has looked into the viability of the most effective methods of cultivating eelgrass, with the long term goal of reintroduction in to the natural environment, either replenishing existing Zostera m. beds or possibly seeding new Zostera m. beds. This study looks at the effect of nutrient enriched sediment verses natural sediment of the effect of growth rate and therefore net nitrogen gain/reserves. By creating a system in which both populations of Zostera m. where exposed to the same environmental conditions, with only one being in nutrient enriched sediment the sole effect of the sediments can be reliably measured. Through statistical tests of the comparative growth rates of both populations of Zostera m. it is proven that enriched nutrient sediments increases
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growth and survival rates of Zostera m. and therefore the viability of reintroduction into the natural environment.
Introduction
waters (Borum & Greve 2004) Z.
The lower Fal and Helford intertidal
marina inhabit from the intertidal
areas are classified as SSSIs (Natural
sones down to 5 - 15 meters depth in
England, 2011). Within these areas
northern European waters (J. Borum et
there are habitats designated as SACs.
al. 2004) being able to do so has
Special Areas of Conservation (SACs)
resulted in Zostera marina or Eelgrass
are sites that have been adopted by the
is the most dominant species of
European Commission and formally
seagrass in northern temperate coastal
designated by the government of each
waters. Eelgrass (Zostera marina)
country in whose territory the site lies
inhabits these areas due to its
(Natural England, 2011). Zostera
preference to grow in sheltered
marina, Eelgrass is one of four closely
intertidal zones and down to 5-15
related species of seagrass in European
meters in northern European waters. (J.
water. Seagrasses have evolved from
Borum et al, 2004). With the fal having
different freshwater species, some
wide areas of shallow sheltered water
being more related than others. There
produced from the tin mining further
are other species of aquatic plants that
up stream producing fine sand, mud
inhabit the marine areas of low to
and silt deposits, producing anoxic
moderate salinity however the only
conditions under the sediment. This is
group that can be classified as seagrass
favourable for Zostera as typical
are found in high salinity oceanic
growth occurs in highly reducing
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sediments. Photosynthesis-mediated 02
primary production. (McMillan and
supplied to below-ground tissues
McRory. 1977) and (Zieman and
sustains aerobic respiration during
Witzel. 1980) Studies have shown that
photosynthetic periods. (R.D. Smith,
zosteras physiological responses of
1998). Zostera is able to survive and
temperate seagrass, Zostera marina,
thrive in these conditions through
ability to absorb light. These factors
being able to obtain O2. Strict
have been expanded upon by the fact
anaerobic conditions inhibit plant
that over the past 10 years 62% of all
growth in all but a few species of plant.
published journals on seagrass have
The ecological success of eelgrass in
purely focused on light intensity and
anoxic sediments must rely
epiphytes while only 18% have
predominantly on anatomical and
focused on hydrodynamics, now
physiological features that prevent
thought to be one of the key factors in
below ground tissues from becoming
eelgrass growth. 17% have focused on
permanently anaerobic. (Armstrong
sediment characteristics only major
1978, Crawford 1978, Davies 1980).
factor contributing to eelgrass growth
However the physiological adaptive
that previously was thought to be a less
features of this ecologically important
significant factor. Only 3 % of the
species are not well understood.
journals published have been focused
Extensive reviews by McRoy and
on seagrass geochemistry. (E. W. Koch
Mcmillan and Zieman and Witzel have
2001). Though the understanding of
stated that there is very little
eelgrass hydrodynamics it has become
experimental data available on
clear that there are far more
photosynthetic characteristics on these
understanding needed than purely the
species beyond the estimates of plant
light intensity required as even with
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high light intensity if the flow rate is
factor governing seagrass production
too high (above 150 cm/s there will be
in moderately nutrient enriched
reduced average growth rates due to
environments. (K. A. Moore & R. L.
self shading from neighbouring
Wetzel). As is apparent there is still
eelgrass. (E. W. Koch 2001) however a
much debate between the effects and
flow rate lower than 18 cm/s will result
causes of Zostera standing stock
in a increased DBL thickness in turn
diminishment. These factors have to be
reducing the CO2 absorption resulting
further understood as to provide
in reduced photosynthesis, over
adequate conservation. The first step in
prolonged periods can be the cause of
conservation is understanding the
death in the species. (Jones et al.
biological makeup and physical
2000). Having said these studies still
identification of Zostera marina.
have shown that light intensity is a
Zostera marina has leaf bundles with
major contributing factor, as light
terminal shoots on horizontal
shading studies indicated a massive
rhizomes. Branching of the rhizomes
reduction in standing stock of Zostera
occurs during the growth season
marina due to light irradiance,
forming the new terminal shoots. (J.
(Dennison 1979). Though studies
Borum and T. M. Greve. 2004). Each
carried out on light intensity and
new leaf formed produces a new
nutrient enrichment it was clear that
rhizome segment (internode) and two
only in light saturated conditions were
bundles of roots develop from the
nutrients an additional factor in
nodes between the segments. The roots
increased seagrass production. The
themselves are thin (0.2-1mm),
results of the experiment suggested
covered in fine hairs that may be up to
that the available light is the principle
20cm long. The rhizomes segments on
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which the roots develop are generally
Nitrogen and phosphate. The Redfield
2-6mm in thickness and vary from 5-
ratio of C:N at 106:16 of carbon to
40mmin length. Begin as a white/green
nitrogen (Redfeild et al. 1963) being a
colour and change to dark brown in the
marine primary producer one might
older segments. (J. Borum and T. M.
expect that eelgrass would contain the
Greve. 2004). Male and female flowers
same ratio of carbon to nitrogen
are found on the same individual. Male
however it considerably lower than in
and female flowers of Zostera marina
other marine species such as
are small, greenish and hidden in
phytoplankton. (Atkinson & Smith.
pockets within leaf sheaths. Zostera
1984, Duarte 1990). Although this is
marina may produce thousands of
the case overall nitrogen requirement
seeds per square meter and flower
for maximum eelgrass production per
regularly under optimum conditions
m2 is still 3 time higher than that of
predominantly flowering from early
phytoplankton production. (M. F.
spring till autumn. During this period
Pedersen. J. Borum. 1992). Eelgrass
the Zostera begins to change
unlike most angiosperms not only
morphology to produce more leaf
absorb nutrients from the sediment
bundles separated by long thin stem
they also uptake nutrients from the
segments. (J. Borum and T. M. Greve.
water column. (Iizumi & Hattori, 1982,
2004). Being an angiosperm Zostera
Thursby & Harlin, 1982, Short &
marina has the same nutrient
McRoy, 1984). Sediments where
requirements as terrestrial plants, but
Zostera can be located have generally a
obviously with a few key differences.
much high concentration of nitrogen
The major nutrients required for
than in the water column. (Lizumi &
Zostera growth are Carbon dioxide,
Hattori, 1982, Boon 1986, Dennison et
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al. 1987) although this is the case
However due to a disease in the 1930’s
Zostera marina leaves have a much
sweeping across Europe depleting the
higher uptake affinity than root
population by 90% (Koch 2001) only
rhizomes (Short & McRoy 1984)
those in brackish waters survived.
suggesting that the sediment is not the
Zostera marina is under huge amounts
primary source of nutrients. however
of pressure still due to human activity,
later studies have shown that nutrient
sediment disturbance is a massive
uptake can be accredited to both the
influence to the growth and well being
leaves and roots-rhizomes as both
of Z.marina if the sediment is
contribute significantly to overall
disturbed, the turbidity increases, this
nitrogen uptake in eelgrass (Iizumi &
reduces light intensity to the Z.marina
Hattori, 1982, Short & McRoy 1984,
leaves this as we know from Zosteras
Zimmerman et al, 1987).
high light intensity requirements very detrimental to growth rates. For these reasons, this study was carried out to in a bid to asses the viability of culturing Zostera marina in the lab, with the idea to reintroduce Zostera m. back into the natural environment either
Fig 1. Depiction of natural geographical distribution of Zostera marina.
reseeding existing Zostera m. beds or potentially seeding new Zostera m. beds.
Method and materials
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A 130 litre tank was divided into two
sediment of Zostera m. beds in this that
sections by the use of a purpose built
area.
Perspex divider see fig. 2. This allowed the separation of the two sediment types, natural sediment. Both sections where then filed with a base layer of coral sand this was placed on the bottom of both sections to enable water flow to prevent excess anoxic conditions. This can be seen on the left of Fig. 2.
Fig. 3 Google maps, location for source of natural sediment.
The second section was filled with a nutrient enriched sediment, (Aquatic fertiliser). On top of these sediments a second layer of fine coral gravel and sand was placed this was to prevent the water movement causing the sediments to be stirred into the water column causing a increase in turbidity and therefore effecting light intensity and
Fig. 2 Cultivation tank set up. (D.Flint 2011)
Once the base layer was in place and levelled out, the sediments where then put into place one side containing the natural sediment a mud/slit mixture that was taken from Deveron mudflats, see fig. 3 for details of specific area. The sediment was taken from this area as this is consistent with the natural 7|Page
therefore growth rates. Also the use of coral gravel provides a natural buffering of the water to help maintain the natural pH of the water maintaining a level between 7.4 and 8.0 recreating the natural conditions (J. Borum and T. M. Greve. 2004). The lighting required to recreate the natural light conditions, a Halide lighting system with a 150
watt 5000k bulb alongside two 24watt
by (J. Borum. 2004) Zostera m.
T5 bulbs. These were put on a
requires a wave period of 0.4-0.7
electronic timer which was set for 16
seconds. Once set up the Zostera m.
hours a day for recreate the natural
may be planted placed into the
light duration at the time of the start of
sediment only up to the crown under
the study. The filtration system used
low light intensity to establish the
was a canister filter to provide good
growth of the root systems. Once
water quality and decent water flow
established and any non viable
without reducing aquarium space or
specimens removed form the tank and
causing shading. To increase water
the study may begin.
flow as recommended by (J. Borum
Measurements were taken on a weekly
and T. M. Greve. 2004) two 1600lph
basis measurement to be taken from
power heads were placed on opposite
the crown to the tip of the tall frond.
ends of the tank on a waver maker
Each specimen was numbered by a
system this allowed not only increased
small cable tie being numbered and
water flow but intermittent water flow
placed around the base of the
causing a wave motion in the tank
specimen. The number of fronds is to
preventing the build up of macroalgaes
be recorded this together with the
and filamentous algae which would
labelling system will allow reliable
reduced growth of Zostera m. as stated
record to be kept.
Results. From the data collected from the
the graph in Fig. 4 taking into account
cultivation tanks, the overall growth
the loss of the samples in the natural
has been established and placed on to
sediment as opposed to no losses in the
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enriched sediment once the trial had
sediment type was not the sole
begun. As can been seen form the 2.
contributor to this as the time that the
Growth (mm) Nutrient Enriched Natural 9 5 10 9 10 XXX 3 12 14 XXX 10 9 10 12 13 10 11 9 8 XXX 7 12 10 11 10 10 Averages Nutrient Natural
9.875 O 9.875 4.125
Critical value Statistical value
4.125 E 7 7
O-E 2.875 -2.875
(O-E)2 8.265625 8.265625
(O-E)2/E 1.180803571 1.180803571 2.361607143
3.841 2.362
Table 1. Chi Squared Statistical test of overall growth rates
study was carried out coincided with
of the two populations of Zostera marina
the time of year Zostera m begins graph there is not the same amount of
to stop growth, as well as the fact that
data for each sediment type, this is due
Zostera is a protected species could
to in the settlement period there was
not be harvested for this study due to
considerably more loss of Zostera m
Zostera m being a Protected species
samples within the natural sediment
within the Fal under SSSI and SAC
that in the enriched sediment. However
legislation. The Zostera m. had to be
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collected form specimens that had been
significantly different. Due to the
washed ashore is rough weather
limited amount of data that could be
therefore prior damage to the Zostera
collect from this study it would appear
may have occurred that may not have
that enriched sediment does have a
been apparent, degradation of the
huge bearing on the growth and
Zostera may have already begun. This
survival rates of Zostera which is
being the case the Zostera samples in
reinforces the hypothesis of (J. Bourm
the nitrogen rich, nutrient enriched
2004) who stated that the only effect of
sediment did show a marked
higher nitrogen levels within the
improvement in the survival of the
sediment will only replace the nitrogen
specimens, as show in table 1, this may
lost from nitrogen recycling by the
be due to the nitrogen deficit normally
Zostera as the species is very effective
occurred in nitrogen recycling by the
at recapturing any nitrogen lost from
Zostera (J. Borum. 2004). Carrying out
decaying leaves and roots. To back up
a chi squared statistical test on the
these results a much more
samples as shown in table 2. shows a
comprehensive study on a larger
significant difference in the growth
scales would be needed to qualify
rates of the two populations favouring
these results.
the enriched sediment see table 2 for details. The statistical value is lower than that of the Critical value therefore
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Overall Growth measurements. 16
Growth in mm
14 12 Nutrient enriched sediment
10 8
Natural sediment
6 4 2 0 1
2
3
4
5
6
7
8
9 10 11 12 13 14 15 16
Specimen number
Fig. 4 A graph to show the Overall growth rates of the Two populations of Zostera marina.
The three troughs in the graph of the
and resulted in several specimens
natural sediment show the number of
being uprooted. These specimens had
species that did not survive in the
to be replanted this would have set
cultivation tank. This may be due to
back growths rate and may very well
the bridging of the nitrogen deficit of
have resulted in the loss for specimens
nitrogen recycling (J. Bourm 2004).
in this section. Problems were also
However this may also be due to the
experienced with the lighting system, a
several contributing factor that affected
malfunction in the electronic timers
the results that were collected, firstly
resulted in the constant output of high
one of the power heads designed to
intensity light. This resulted in excess
created irregular water flow preventing
algae within the tank, lots of macro
shelf shading (Koch, 2001) fell of its
and filamentous algae was produced
placement into the sediment on the
which has a hugely negative effect on
natural sediment section. This caused
the growth of Zostera marina. (J.
massive disturbance of the sediment
Bourm, 2004).
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Discussion Through this study it is apparent that
each sediment sample. Also it would
the theory proposed by (J. Bourm,
be advisable to collect Zoster m. in
2004) that increased levels of nitrogen
early spring to summer as this is in
in the sediment will provide the small
Zostera m primary growth period
percentage of nitrogen that is lost to
therefore being healthier, stronger and
the environment from nitrogen
have larger nitrogen and phenoic acid
recycling by Zostera marina. Enabling
reserves (Koch 2001). It would also be
Zostera not only to survive stressful
advisable to use larger power heads to
conditions i.e. uprooting and replanting
create a larger intermittent flow
but to also show a growth pattern
reducing shelf shading and a more
larger than that of natural sediment.
adequate wave period of 0.4-0.7
Having said that it may also the case
seconds (J. Bourm, 2004). This would
that the contributing factors in this
result in more accurate and reliable
study such. The contributing factors in
results to more accurately identify the
this study being the power head
importance of using a nutrient enrich
disturbance and the faulty lighting
sediment to increase growth and
timer may have had adverse effects on
survival rates. As (Borum et al, 1989)
the natural sediment populations
suggested that nitrogen conservation
causing a less pronounced growth and
i.e. reclamation could potentially be an
survival rate seen in the enriched
important mechanism for eelgrass
sediment population. If this study were
nitrogen nutrition, as studies have
to be carried out again, suggestions
shown that this is the case, even with
would be to carry out the study on a
deciduous terrestrial, evergreen plants
larger scale using more specimens in
living in nutrient poor environment
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therefore providing the nitrogen to the
Zostera marina in the nutrient enriched
eelgrass that would normally have
sediment to be healthier than the
been lost though this almost
population in the natural sediment.
completely effective process can explain the reason for the population of
Acknowledgements I gratefully acknowledge the help and support provided by Craig Baldwin, Falmouth Marine School for help, advice and concerns with aquaculture as well as use of lab and equipment with funding from Southampton University, Falmouth Harbour commission and Falmouth Marine School. I would also like to thank Luke Marsh, Falmouth Marine School, for his help taking measurements and helping with maintenance of the study tank.
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Koch, E.W., 1996. Hydrodynamics of shallow Thalassia testudinum beds in Florida, USA. In: Kuo, J., Phillips, R.C., Walker, D.I., Kirkman, H. (Eds.), Seagrass Biology: Proceedings of an International Workshop, Rottnest Island, Western Australia, 25±29 January 1996. Sciences UW, Nedlands, Western Australia, pp. 105±110. Krause-Jensen D, Middelboe AL, Christensen PB,Rasmussen MB, Hollebeek P (2001) Benthic Vegetation Zostera marina, Ruppia spp., and Laminaria saccharina. TheAuthorities’ Control and Mmonitoring Programme for the fixed link across Øresund. Benthic vegetation. Status report 2000. 115 pp Krause-Jensen D, Pedersen MF, Jensen C (2003) Regulation of eelgrass (Zostera marina) cover along depth gradients in Danish coastal waters. Estuaries 26:866-877 McRoy, C. P., McMillan, C. (1977). Production ecology and physiology of seagrasses. In McRoy, C. P., Helfferich. C. (eds.) Seagrass ecosystems, a scientific perspective. Marcel Dekker, New York, p. 53-88 Muehlstein, L.K., Porter, D. and Short, F.T., 1991. Labyrinthula zosterae sp. nov., the causative agent of wasting disease of eelgrass, Zostera marina. Mycologia, 83: 180-191. Patriquin, D. G. (1972). The origin of nitrogen and phosphorus for growth of the marine angiosperm Thalassia testudinum. Mar. Biol. 15: 35-46 Pedersen, M. F., Borum, J. (1992). Nitrogen dynamics of eelgrass Zostera marina during a late summer period of high growth and low nutrient availability. Mar. Ecol. Prog. Ser. 80: 6573 Phillips RC, McRoy CP (1990) Seagrass research methods. Monographs on oceanographic methodology. UNESCO, Paris. 210 pp Rasmussen, E., 1977. The wasting disease of eelgrass (Zostera marina) and its effects on environmental factors and fauna. In: C.P. McRoy and C. Helfferich (Editors), Seagrass Ecosystems. A Scientific Perspective. Marcel Dekker, New York/Basel, pp. 1-52 Renn, C.E., 1936. The wasting disease of Zostera marina: I. A phytological investigation of the diseased plant. Biol. Bull., 70: 148-158. Short, F.T., Mathieson, A.C. and Nelson, J.I., 1986. Recurrence of the eelgrass wasting disease at the border of New Hampshire and Maine, U.S.A. Mar. Ecol. Prog. Set. 29: 88--92.ng, E.L., 1938. Labyrinthula on Pacific coast eelgrass. Can. J. Res., 16:115-117. Thayer, G.W., Engel, D.W., LaCroix, M.W., 1977. Seasonal distribution and changes in the nutritional quality of living, dead, and detrital fractions of Zostera marina L. J. Exp. Mar. Biol. Ecol. 30, 109–127 Tutin, T.G., 1938. The autecology of Zostera marina in relation to its wasting disease. New Phytol., 37: 50-71. Vergeer, L.H.T. and den Hartog, C., 1991. Occurrence of wasting disease in Zostera noltii. Aquat. Bot., 40: 155163. Vergeer, L.H.T. and den Hartog, C., 1994. Omnipresence of Labyrinthulaceae in seagrasses. Aquat. Bot., 48: 120.
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Fig. 1. Natural Geographical Distribution of Zostera marina, D. Flint 2012, map sourced from google maps.
Fig. 2 Cultivation tank set up sediment set up through to filling. D. Flint 2011. Fig 3. Google maps Deveron mudflats [Online] available at: http://maps.google.co.uk/maps?hl=en&tab=wl (Accessed on 29th April). Fig. 4. A graph to show the Overall growth rates of the Two populations of Zostera marina
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