Light Stress and TEP Production in Phytoplankton Communities in Turbid Coastal Waters

1
Light Stress and TEP Production in Phytoplankton
Communities in Turbid Coastal Waters
Light Stress and TEP Production in Phytoplankton
Communities in Turbid Coastal Waters
Jessie Sebbo, Trisha Bergmann, John B. Kerfoot,
Sasha Tozzi Oscar Schofield Institute Of
Marine and Coastal Sciences, Rutgers University,
New Brunswick, NJ
Abstract
TEP Production, Light Stress and Upwelling

TEP Determination
Different Dye Batch
The effect of light stress on the production of
transparent exopolymer particles (TEP) was
studied in natural phytoplankton populations off
the New Jersey coast during the 2001HyCODE/COMOP
Coastal Predictive Skill Experiments. Nearshore
waters generally are optically turbid and the
resident phytoplankton populations are often
low-light adapted. TEP production is generally
enhanced when cells are stressed.
Given this, we
Initial TEP Abundance per Volume
Figure 3 As seen in these slides, the
transparent particles can be made visible when
stained with Alcian Blue, a cationic hydrophyllic
dye. Cells and other materials are not stained
due to the specificity of the dye. TEP were
stained and measured colormetrically using a
modified version of the spectrophotometric method
of Passow and Alldredge (1995). There is a
linear correlation between TEP concentration and
the absorbance of a stained sample
B
A
.000
.005
.010
.015
.020
.025
Absorbance/ml
Final TEP Abundance per Volume
B
Figure 9 There is a correlation between TEP
and the in situ absorption at 676 nm for the
majority of the natural samples (red diamonds).
Samples from day 204 (blue diamonds) are outliers
most likely due to the fact a different batch of
stain was used for these samples.
A
at 767nm (the absorbance maximum of alcian blue).
The use of calibration standards for different
batches of dye was omitted. This was not a
problem since most of the samples were stained
using the same batch.
Figure 6 Vertical profiles of relative
concentrations of phytoplankton, detritus and
colored dissolved organic material (CDOM) for
Stations A and B on the day of sampling. At the
sampling depth there is greater signal for all
three measurements at the inshore station A than
at B. These profiles were obtained by inverting
AC-9 measurements (see Oliver et al. OS21E-90).
hypothesized that coastal communities should be
particularly sensitive to high light stress and
thus potentially produce a great deal of TEP when
they are mixed to surface waters. Secondarily, we
predicted that surface light stress should be
greater for inshore communities compared to
offshore communities who reside in clearer
waters. Discrete samples were collected from
offshore and inshore stations at 8 m depth, and
were incubated for 24 hours outdoors under
ambient light. Ambient light levels were
comparable to light levels just below the surface
at both offshore and inshore sampling sites.
Nearshore populations were very low light adapted
as indicated by significantly lower Ik values
(factor of 2) and were heavily light stressed,
compared to their offshore counterparts, by
surface irradiance. The TEP abundance and TEP
production rates were an order of magnitude
greater than the offshore community. This
confirmed that light stress is positively
correlated with TEP production in natural
populations. In this area, topographic variations
associated with ancient river deltas cause
upwelled water to evolve into an alongshore line
of three recurrent upwelling centers that are
co-located with historical regions of low
Dissolved Oxygen (DO). Upwelling results in the
Ekman transport of water offshore and the
transport of mid- and bottom water phytoplankton
communities to the surface. Satellite and ship
data confirm that significant phytoplankton
blooms are associated with these upwelling
events. Furthermore, SCUBA divers often observe
marine snow. Given our findings of the
potentially large TEP production rates in the
nearshore populations, we hypothesize that TEP
formation, via light-stressed populations, may
strongly influence the hypoxic/anoxic zones off
the coast of New Jersey.
.000
.005
.010
.015
.020
.025
Absorbance/ml
Figure 12 While TEP production over the
incubation varied little in the offshore sample,
the inshore sample increased by over 150. The
inshore community, initially adapted to lower
light than the offshore community, experienced
greater stress when exposed to surface light
conditions. The effect of this light inhibition
was positively correlated with greater TEP
production.
Field Sampling
Outdoor Incubation
Figure 12 Phytoplankton communities advected
toward the surface during upwelling, experience a
similar light change as simulated in this
experiment. Exposed to the higher light
environment, the cells are light saturated until
they acclimate. Enhanced TEP production caused
by inhibition would therefore correspond to the
initial phase of an upwelling induced bloom,
leading to potential higher aggregation rates,
and marine snow formation.
Upwelling, TEP and Hypoxia
Figure 4 Locations of sampling sites A and B on
August 2nd, 2001 overlayed on chlorophyll
concentrations from the SeaWiFS Satellite. The
colormetric scale shows the steep decline in
chlorophyll moving from inshore to offshore. In
situ data from the R/V Walford confirm a drastic
difference in the chlorophyll concentrations of
station A and B of 6.61 and 4.20 (mg/m3)
respectively.
Figure 7 Water collected from depth at stations
A and B was incubated for 24 h in natural light.
The incubation system mimicked light (725 µmol
photons) conditions in surface waters. The
natural samples were effectively upwelled from
low light (thermocline depth of about 8 m) to the
high light environment of the surface.
Figure 10 Using the correlation between TEP and
a676, TEP can be plotted for the entire summer
experiment from a676 data measured by the optical
profiler (at site A). High concentrations
observed at days 208 to 215 were correlated with
Hudson River plume.
Conclusions
Variance in TEP in Coastal Zone

• Concentration of TEP can be correlated with
  absorption at 676 nm
• TEP Production is enhanced when cells are light
  saturated
• Phytoplankton blooms during upwelling events
  are initially light saturated leading to enhanced
  TEP production, more aggregate formation and
  greater transport of carbon to the benthos

Photosynthesis Irradiance Curves
Different Dye Batch
Ik100
Ik37
Acknowledgements
Scott Glenn, Mark Moline, Paul Bisset, Matt
Oliver, Mike Crowley, Josh Kohut, Liz Creed, Cris
Orrico, Jessica Pearson, Meghann Horner, Shelly
Blackwell, Alex Kahl, Captain Jim, Mike Nunez,
All Your Base Are Belong To Us.
Figure 11 Photosynthesis Irradiance curves
were determined during the experiment for the two
samples. The offshore community was less light
saturated then the inshore community, as
reflected in the higher Ik for the offshore
community. This was a response to the turbid
optical conditions nearshore.
References
Alldredge, A. L., U. Passow, and B. Logan. 1993.
Deep-Sea Res. 40 1131-1140. Passow, U and
Alldredge, A. L. 1994. Marine Ecology Progress
Series 113135-198.
Figure 8 TEP amounts measured over the 2001 LEO
experiment varied widely. Day 204 samples were
stained with a different batch of dye which would
account for their higher than average values.
The only other value which stands out is the
final inshore incubation value which was not an
in situ sample.
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