Download Marine Ecology

Daniel Coffey & Gregory Edward Phillips
BIOE 108: Marine Ecology
Professor Mark Carr
Kendra Karr, T.A.
March 17, 2009
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Causation of Harmful Algal Blooms in the Gulf of Mexico
Introduction:
Background:4/4
Marine productivity is largely controlled by nutrient availabilities and processes
that retain them in the ocean environment. New inputs of micronutrients such as iron
have been proven to have effects on the overall photosynthetic abilities of phytoplankton.
In the Atlantic Ocean periodic Saharan dust storms that blow over the southern Atlantic,
have been shown to increase iron levels in surface waters up to 300 times greater then
previous concentrations. Certain photosynthetic bacteria Trichodesmium, have also been
shown to bloom in correlation with periods of high Saharan dust input. Trichodesmium is
a marine bacterium that can utilize nitrogen gas (N2) for the nitrogen demands required
for growth. The utilization of dissolved nitrogen gas (N2) is a unique characteristic that
very few marine photosynthetic organisms possess. Phytoplankton species and even
many photosynthetic bacterial species can only utilize nitrogenous compounds found in
sea water to fulfill their nitrogen requirements. Trichodesmium, on the other hand,
contain the enzyme nitrogenase which is responsible for this ability to convert dissolved
nitrogen gas (N2) to a form usable in cell functions. Nitrogenase requires iron to function
and thus as iron increases in the marine environment via Saharan dust input,
Trichodesmium convert more and more nitrogen gas (N2) to different organic nitrogen
compounds. These new nitrogen compounds are now in a form usable by other marine
fauna and reflect new sources of nitrogen not normally available to the system.
After large Saharan dust events are followed by Trichodesmium explosions,
studies have shown that nutrient concentrations in the area spike up to 300 fold seemingly
in an identical pattern to the increase in iron concentrations caused by the dust storms
input. Extremely high nutrient levels then allow optimal bloom conditions for
phytoplankton species. A recent study connected the phytoplankton blooms to
Trichodesmium blooms and explained they were due to the dust storms coming off of
Africa and fertilizing the ocean with iron. Particularly interesting, however, is the study
led by Jason Lenes of the University of South Florida that observed a large bloom of
toxic algae in the study area. Lenes explained that an 8,100 square mile bloom of Karenia
brevis, a red algae, was observed in the Gulf of Mexico off Florida following the
Trichodesmium bloom. This provided some of the first possible evidence suggesting that
toxic algal blooms could be predicted by monitoring Saharan dust influxes and
subsequent Trichodesmium blooms.
Toxic algal blooms can be very severe and have extensive effects on local
fisheries, marine ecological diversity, ecosystem resiliency, and even human health risks.
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Daniel Coffey & Gregory Edward Phillips
Understanding what causes them and how to predict or even prevent them would have
incredible significance for not only the Gulf of Mexico area but the entire world.
Pattern:
2/2
Toxic algal blooms (Karenia brevis) in the Gulf of Mexico, particularly abundant
off the west coast of Florida, have been shown to correlate temporally with blooms of the
marine cyano-bacterium Trichodesmium. These photosynthetic bacterial blooms result
from events where Saharan dust storms blow over into the Atlantic Ocean, fertilizing its
waters with iron rich dust particles.
Figures: 4/4
Figure 1. The correlation between iron concentrations by the influx of Saharan dust. As
Saharan dust influxes become more abundant, iron concentrations increase.
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Daniel Coffey & Gregory Edward Phillips
Figure 2. The correlation between Trichodesmium populations by iron concentration.
Trich. populations increase with the growing abundance of iron concentrations until they
reach stable bloom capacity.
Figure 3. The correlation between dissolved organic nitrogen concentrations by Trich.
population density. As Trich. populations grow, dissolved organic nitrogen
concentrations increase.
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Daniel Coffey & Gregory Edward Phillips
Figure 4. The correlation between toxic algae (Karenia brevis) population densities by
dissolved organic nitrogen concentrations. Trich. populations increase with the growing
abundance of dissolved organic nitrogen concentrations until they reach stable bloom
capacity.
Goal: 2/2
Understanding the causal mechanisms and indicative warnings that could lead to
prevention of some of the impacts harmful algal blooms have on marine ecosystems is
the overwhelming drive behind the proposed research project. Such accomplishments
however, must be reached in sequenced analyses that are proven by more then one study
with multiple angles of perspective. To begin this process the mechanism that causes the
Trichodesmium blooms must be further examined. In general, Saharan dust has been
observationally proven to increase Trichodesmium productivity, and the release from iron
limitation has been experimentally proven necessary in the synthesis of the nitrogenase
enzyme. The direct relationship of the Saharan dust’s efficiency to provide dissolved iron
to Trichodesmium, however, has not been experimentally proven. Thus, a laboratory
experiment relating the stable population size of Trichodesmium to both Saharan dust and
simple dissolved iron must be achieved. This could reveal whether the contents of the
Saharan dust may have other important ingredients essential to Trichodesmium blooms
that simple dissolved iron could not supply.
The second connection that should be examined is the relationship between the
combination of Saharan dust influxes and Trichodesmium blooms on causing toxic algal
blooms. Here, it must be determined whether the toxic algae are blooming in response to
both of the components or exclusively one of the two. In other words, even though the
toxic algae blooms occur when both components are present, this fact alone does not
prove the reliance on both as the algae may only need Trichodesmium or Saharan dust
influxes.
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Daniel Coffey & Gregory Edward Phillips
Finally, it must be determined whether toxic algae are favored over non-toxic
species following the Saharan dust and Trichodesmium bloom. This observation may
have been an artifact of the study mentioned before, or have to do with the phytoplankton
community structure present when the blooms are triggered, or even another mechanism
such as relative predation pressures between toxic and non-toxic species. By studying the
relative population growth rates normalized to certain individual species’ population
growth rates it could be determined whether toxic species are preferentially favored in the
Gulf of Mexico following an episode of dust input and Trichodesmium blooms. This
could suggest the need for further research on what nutrient circumstances toxic algae
require to bloom. On the other hand, it may show that the link between the toxic blooms,
Trichodesmium, and dust events are not driven by mechanisms relating to delivery of
nutrients, thus suggesting something else may have caused a selection pressure favoring
the toxic red algae Karenia brevis.
Hypothesis: 6/6
General Hypothesis 1:
HA: Trich. blooms directly result from the input of Saharan dust into the surface waters of
the Gulf of Mexico and not just a release from iron limitation.
H0: Trich. blooms are caused via a general release from iron limitation
Specific Hypothesis1:
HA: If Trich. cultures are fertilized with Saharan dust, then they will have a higher
population growth than cultures exclusively fertilized with dissolved iron equivalent to
the concentrations present in Saharan dust.
H0: If Trich. cultures are fertilized with Saharan dust, then they will not have a higher
population growth than cultures exclusively fertilized with dissolved iron equivalent to
the concentrations present in Saharan dust.
General Hypothesis 2:
HA: The toxic red algal (Karenia brevis) blooms, observed in the Gulf of Mexico, are
directly caused by Trich. blooms and/or Saharan dust influxes.
H0: The toxic red algal blooms are not correlated to the combination of Trich. blooms and
Saharan dust influxes.
Specific Hypothesis 2:
HA: If isolated cultures of K. brevis are given inoculations of Trich. in observed bloom
concentrations they will exhibit a higher population growth than in cultures given only
Saharan dust.
H0: Isolated cultures of K. brevis given inoculations of Trich. do not exhibit a higher
population growth than cultures given only Saharan dust.
Specifc Hypothesis 3:
HA: If isolated cultures of Karenia brevis are given inoculations of both Trich. in
observed bloom concentrations and Saharan dust they will exhibit a higher population
growth than in cultures given each treatment separately.
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Daniel Coffey & Gregory Edward Phillips
H0: Isolated cultures of K. brevis given inoculations of both Trich. and Saharan dust do
not exhibit a higher population growth than in cultures given each treatment separately.
General Hypothesis 3:
HA: The mechanism creating the selection for the toxic species is not due to a specific
relationship between the Trich. and Saharan dust influx.
H0: The mechanism creating the selection for the toxic species is due to a specific
relationship between the Trich. and Saharan dust influx.
Specific Hypothesis 4:
HA: If K. brevis and other known Gulf Coast species of phytoplankton are inoculated
with Trich. and Saharan dust, then there will be relatively similar increases in population
growth in each species.
H0: If K. brevis and other known Gulf Coast species of phytoplankton are inoculated with
Trich. and Saharan dust, then K. brevis will have the only significant increase in
population growth.
Material and Methods
Species Description:
4/4
K. brevis is a dinoflagellate that lives in the Gulf of Mexico and Caribbean
throughout the year. It is a toxic algae that produces brevetoxin, which leads to
neurotoxic shellfish poisoning. Toxic algae like K. brevis are often very resilient to
fluctuating environmental factors. K. brevis in particular, can tolerate a wide range of
salinities and often out-competes other phytoplankton species in the gulf. When released
from nutrient limitation it is thus likely for K. brevis to out-bloom other species
essentially becoming the competitive dominant. This competitive dominance is
complemented with Trichodesmium’s ability to supply nutrients to the system through
nitrogen fixation, which is carried out with the nitrogenase enzyme. So the system is not
only characterized by a competitive dominant, K. brevis, but also by a possible
commensal bacterium that gives the system resources when its blooms die out.
Trichodesmium does however, have a high requirement for iron which limits it from
blooming for most of the year. Following Saharan dust storm events, this requirement is
fulfilled and the bacteria bloom. The dust storms blow off the coast of west Africa during
the late-spring to early fall almost annually. Their frequency and intensity depend on
different global climate patterns, notably El Niño Southern Oscillation and The North
Atlantic Oscillation. Other ecological factors that characterize the system and its
phytoplankton assemblages are markedly predation by zooplankton, oceanographic
western boundary current fluctuations, pollution and hypoxic events, and seasonal
variability in cloud cover among others.
Site Description:
4/4
Florida red tides occur in the Gulf of Mexico almost every year, generally in the
late summer or early fall. They are most common off the central and southwestern coasts
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Daniel Coffey & Gregory Edward Phillips
of Florida between Clearwater and Sanibel Island, but they may occur anywhere in the
gulf. Most blooms last three to five months and may affect hundreds of square miles.
Occasionally, however, blooms continue for as long as 18 months and may affect
thousands of square miles. K. brevis can sustain such long bloom periods due to its
tolerance of varying salinities that are common in the Gulf of Mexico. In addition, the sea
surface temperature does not vary much in the Gulf of Mexico which provides a suitable
environment for K. brevis.
Recent studies show that Florida red tides begin in nutrient-poor waters 18 to 74
kilometers offshore. Resting populations of K. brevis are believed to exist in the water
column or sediments in specific areas on the west Florida continental shelf. The seafloor
off the west coast of Florida is made up of widely spaced sediment ridges, separated by
hard limestone. K. brevis blooms along the southwestern coast of Florida may be
transported along the Gulf of Mexico coastline or via eddies into the Gulf Stream.
Methods:
General Hypothesis 1.
Specific Hypothesis 1:
In order to test the hypothesis that Trich. blooms are correlated to influxes of
Saharan dust and not just from iron limitation, we will set up three treatments of 30
individual isolated Trich cultures in one liter flasks. The first treatment will serve as a
control where the water sample is exclusively characteristic of Gulf coast waters prior to
dust storm events. For the second treatment, we will inoculate Saharan dust. For the third
treatment, we will inoculate standard dissolved iron equivalent to the concentration in
Saharan dust. If Trich. cultures treated with Saharan dust exhibit the highest population
growth than we can reject the null hypothesis.
General Hypothesis 2.
Specific Hypothesis 2:
In order to test the hypothesis that K. brevis blooms are exclusively correlated to
either Trich. blooms or Saharan dust, we will set up three treatments of 30 individual
isolated K. brevis cultures in one liter flasks. The first treatment will serve as a control
where the water sample is exclusively characteristic of Gulf coast waters prior to dust
storm events. For the second treatment, we will inoculate Saharan dust. For the third
treatment, we will inoculate Trich. If K. brevis exhibits the highest population growth
when treated with Trich. then we can reject the null hypothesis.
Specific Hypothesis 3:
In order to test the hypothesis that K. brevis blooms are correlated to both Trich.
blooms and Saharan dust, we will set up four treatments of 30 individual isolated K.
brevis cultures in one liter flasks. The first treatment will serve as a control where the
water sample is exclusively characteristic of Gulf coast waters prior to dust storm events.
For the second treatment, we will inoculate both Saharan dust and Trich. For the third
treatment, we will inoculate Saharan dust. Finally, for the fourth treatment, we will
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inoculate Trich. If K. brevis exhibits the highest population growth when treated with
both Trich. and Saharan dust then we can reject the null hypothesis.
General Hypothesis 3.
Specific Hypothesis 4.
In order to test the hypothesis that the mechanism creating the selection for the
toxic species is not due to a specific relationship between the Trich. and Saharan dust
influx, we will set up two treatments for each of four native Gulf coast phytoplankton
species, including K. brevis. The first treatment of each species will serve as a control
where the water sample is exclusively characteristic of Gulf coast waters prior to dust
storm events. For the second treatment, we will inoculate all species with both Saharan
dust and Trich. If all species of phytoplankton exhibit relatively similar increases in
population growth than we can reject the null hypothesis.
For all of our treatments we will simulate nutrient concentrations described in the
controls. We will use flow cytometry to measure population growth. In addition, our data
will be analyzed using regression analysis and analysis of variance (ANOVA) to
determine the significance of correlations (95% CI).
Literature Cited:
“Red Tides in Florida.” Fish and Wildlife Research Institute. 17 Mar 2009
<http://www.floridamarine.org/features/view_article.asp?id=24936>.
O’Carroll, Cynthia M. “Dust from Africa leads to large toxic algae blooms in Gulf of
Mexico, study finds.” Bio-Medicine 17 Mar 2009 <http://news.bio-medicine.org/biologynews-2/Dust-from-Africa-leads-to-large-toxic-algae-blooms-in-Gulf-of-Mexico--studyfinds-9266-1/>.
NASA/Goddard Space Flight Center – EOS Project Science Office. “Dust From Africa
Leads To Large Toxic Algae Blooms In Gulf Of Mexico, Study Finds.” ScienceDaily 29
August 2001. 17 March 2009 <http://www.sciencedaily.com
/releases/2001/08/010829082907.htm>.
No potential results 0/5 per hypo
No stats discussion
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