phytoplankton community structure and the physiological ecology of the toxic, bloom-forming diatom...
TRANSCRIPT
PHYTOPLANKTON COMMUNITY STRUCTURE AND THE
PHYSIOLOGICAL ECOLOGY OF THE TOXIC, BLOOM-FORMING DIATOM
PSEUDO-NITZSCHIA SPP. IN COASTAL ALABAMA
Justin D. Liefer
OutlineI. Introduction
I. Interaction with LLPSII. Why are we interested in nutrients (nitrogen, phosphorus)III. What are harmful algal blooms (HABs)IV. What is Pseudo-nitzschia
Study Goals and overview of results
FindingsI. Occurrence Pseudo-nitzschia in Alabama watersII. Seasonal patterns in nutrients and grounwaterIII. Seasonal patterns in Pseudo-nitzschia and other
phytoplanktonIV. Toxicity of Pseudo-nitzschia
I. Conclusions
Definitions• Algae –
– General (and old) term for a wide range of simple organisms that are similar to plants
– They do photosynthesis, making their own food using light. Includes seaweeds and phytoplankton
• Phytoplankton – – Microscopic, single-celled algae
(microalgae) that live in the water column.
– They act as the “plants” and base of the food web in oceans and lakes.
Disclaimers
The sky is not falling. This work is motivated by general scientific interest (DISL) and understanding of the local environment to help manage and protect it (LLPS)
The presence of toxins in the water or in fish does not mean that poison is imminent or even likely
I am showing interesting biological patterns that contribute to science in general, not assessing ecosystem health or tracking pollution
I am high-lighting potential areas of concern
Interaction with LLPS Volunteers from LLPS have collected bi-weekly samples
since June 2007. About 140 sampling trips, almost 1000 samples.
This has greatly assisted our research efforts aside from sampling help Local access and knowledge Oppurtunity for community outreach Educational opportunities
In turn, Little Lagoon is now very well-studied and will soon be well-represented in the scientific literature
Why Are We Interested in Nutrients? Phytoplankton (like plants) need nutrients (fertilizer) to grow.
Nutrient inputs can control the amounts and kinds of phytoplankton
Nitrogen (N) and phosphorus (P) are the most important nutrients
Silicate (Si) can also be important (diatoms)
Nutrients can be delivered from outside the system (river or groundwater discharge, runoff, sewage)
Nutrients can be produced internally (nitrogen-fixation, recycling by bacteria)
Difference between total nutrients and dissolved (available)
Harmful Algal Blooms (HABs)
A broad term for any proliferation of phytoplankton with potentialnegative consequences for the rest of the ecosystem or human health
An increasing global problem Nutrient pollution is widely believed to be the
cause of this increase Also due to invasive/exotic species
Can be “harmful” due to: Production of toxins Reducing oxygen in the water Physical damage (like clogging fish gills) geo.brown.edu
Pseudo-nitzschia, the toxic diatom A diatom (a group of phytoplankton) which occurs in
temperate waters globally
Can produce the neurotoxin domoic acid (DA). Production of the toxin varies, depends on conditions
DA accumulates in plankton, fish, and shellfish and can poison the animals that eat them
Domoic acid poisoning (DAP) is observed on the US west coast in birds and marine mammals after consuming toxic fish. Contamination often causes costly fishery closures
Amnesic shellfish poisoning (ASP) in humans. 1987, PEI poisoning event
APTexas PWD
ADPH
Features of Pseudo-nitzschia
A global concern Occurs in a variety of
systems Upwelling systems Estuaries Open ocean Oceanic fronts
Similarities in bloom conditions Pulses of nutrients Mixing Likes variable conditions A ruderal (weedy) strategy
Pseudo-nitzschia in Alabama
Pseudo-nitzschia rarely described along NE Gulf Coast
Notable exceptions: Liefer et al. 2009; MacIntyre et al. 2011
Key QuestionsI. When and where does Pseudo-nitzschia occur in
Alabama waters?
II. What are the seasonal patterns in water conditions and phytoplankton where Pseudo-nitzschia occurs?
III. What conditions control phytoplankton and promote blooms of Pseduo-nitzschia?
IV. What controls the toxicity of Pseudo-nitzschia? Does the toxin move up the food chain?
Groundwater discharge promotes Pseudo-nitzschia blooms at low temps
There is a local “hot-spot” for Pseudo-nitzschia blooms at Little Lagoon. Likely
caused by groundwater
Domoic acid accumulates in small fish, even when the toxicity of
blooms is low
Local Pseudo-nitzschia produces toxin, especially when
salinity and light are high,
phosphorus and silicate are low
Overview
When and where does Pseudo- nitzschia occur in Alabama waters?
Pseudo-nitzchia monitored by Alabama Dept. of Public Health since 2004
Samples of Pseudo-nitzschia abundance at 7 coastal sites were from 2004 – Oct 2008 were examined
A local hot-spot for Pseudo-nitzschia
Pseudo-nitzschia occurs more frequently and often in greater numbersw at Little Lagoon Pass (LLP)
Little Lagoon is a local hot-spot for Pseudo-nitzschia blooms
DIP
B
LL
P
DIE
E
GS
P
GS
PB
OB
AP
Liefer et al. 2009
Groundwater and Pseudo-nitzschia
Groundwater discharge was the most important factor examined
Styx River is an estimate for local groundwater discharge
Groundwater and Pseudo-nitzschia were highly correlatated from Apr 15-May 15 (bloom season) in each year.
Lo
cal
Gro
un
dw
ater
Lev
el
Local Hydrogeology
Dowling et al. 2004
Surface Flow 2/3 of nitrate
Groundwater 1/3 of nitrate
Water table is highest near Little Lagoon
Very high nitrate (important source of nitrogen) in local groundwater
Large local discharge of groundwater/nitrate to Gulf of Mexico
Unlikely that this would not effect the biology of local waters
Groundwater Discharge is Unique Very high in nitrogen,
low in phosphorus
Diffuse, difficult to measure directly
May add nutrients without large flushing/drop in salinity, unlike rivers
Pseudo-nitzschia was shown to prefer high salinity (30.1 ± 3.2). LLP may have ideal combination of high nutrients and high salinity
River DischargeSubmarine Groundwater Discharge
Nu
trie
nts
Fre
shw
ater
Seasonal patterns in phytoplankton and Pseudo-nitzschia
Preliminary work prompted closer look at Little Lagoon
Little Lagoon is a shallow, poorly-flushed coastal lagoon.
No river inputs. Connected to groundwater-fed lakes via canals
Determining conditions and phytoplankton dynamics in Little Lagoon
Approach
4 sites monitored bi-weekly from Jun 2007 – Jun 2010. Temperature, salinity, overall water conditions Nutrients Phytoplankton pigments
Pseudo-nitzschia monitored during April 2008 bloom and regularly at 2 sites from Jan 2009 – Jun 2010.
Groundwater is the source of freshwater to Little Lagoon
Patterns in freshwater to Little Lagoon follows patterns in groundwater
Surveys for Radon 222 (with W. Burnett, FSU), a conservative groundwater tracer, shows direct groundwater inputs and a high correlation with salinity (R = -0.745)
0
5
10
15
20
25
30
35
40
EW
Two Different Nutrient Seasons
Winter and SpringLow tempHigh GroundwaterLow total nutrientsAvailable nitrogen is
higher and variable
Summer and FallHigh tempLow GW dischargeHigh total nutrientsAvailable nutrient
consistently low
Jun
07
Dec
07
Jun
08
Dec
08
Jun
09
Dec
09
Jun
10
Sal
init
y 13
Sites
0
5
10
15
20
25
30
35
EW
Jun
07
Dec
07
Jun
08
Dec
08
Jun
09
Dec
09
Jun
10
Tem
per
atu
re (
°C)
0
5
10
15
20
25
30
35
Mea
n C
hl
a (μ
g l
-1)
Cyanobacteria-dominated
Diatom-dominated
Winter/spring, diatoms dominate, phytoplankton low
Cyanobacteria dominante, phytoplankton high, oxygen low
Benthic Benthic BenthicGW GW GW
Two Regimes for Phytoplankton and nutrients
Benthic nutrient regime
GW nutrient regime
13
Sites
Winter and SpringNutrients are low, but more of them are
availableGroundwater controls salinity and nitrogen Diatoms dominate
Groundwater
Detritus
Phytoplankon on the bottom
NP
Summer and FallNutrients are high in the lagoonNutrients likely come recycling of detritus
(dead stufff)Cyanobacteria (blue-green algae) dominate
Groundwater
Detritus
Phytoplankon on the bottomN P
Pseudo-nitzschia Blooms Occur in Winter and Spring Only
Pse
ud
o-n
itzs
chia
sp
p.
log
(cel
ls l-1
)
2
3
4
5
6
7
0
5
10
15
20
25
30
35
EW
Tem
per
atu
re (
°C)
Jun
07
Dec
07
Jun
08
Dec
08
Jun
09
Dec
09
Jun
10
GW-dominated periods (blue bars, diatom-dominated periods (yellow bars), toxic Pseudo-nitzschia blooms, and low temperatures all overlap
Does temperature or groundwater+nutrients drive blooms?
ND
Every bloom so far has produced low/moderate levels of toxin
Example from Apr 2008
Pseudo-nitzschia high across much of lagoon
Toxicity highest in Gulf Lower nutrients High light High salinity
PC 1 Score
-4.5 1.50-1.5-3
106105104103
Pseudo-nitzschiaspp. (cells l-1)
Toxicity (pg DA cell-1)
<1 1-2 5 1510<1 1-2 5 1510
3
Are These Blooms Toxic?
What Cuases The Toxicity?
Others have shown nutrient stress to cause toxicity in Pseudo-nitzschia
My results show the same, but also that light is important
Blooms are likely to be more toxic where water isSaltierClearerHas less phosphorus and silicate
Toxin can move up the food chain2009
ShorelineBloom
FM
LLBS
Bloom had low toxicity
Toxin detected in 98% of fish collected during bloom (shoreline seine)
Fish toxicity was low compared to poisonous events in other areas
CB
Implications of fish toxicity
Bloom of low toxicity was able to transfer toxin to higher trophic levels. Much higher cellular toxicity observed in other local blooms
Most fish collected are not considered primary consumers. Toxin was transferred at least 2 levels up the food chain
Texas PWD
Sinh Nhut Nguyen
Fishbase.org
Summary and Implications
May – Dec
Photos: Protist Information Server, WRoMS
High TempsLow Discharge
High Total Nutrients
Low TempsHigh Discharge
Low Total Nutrients
Jan – Apr
DiatomsCyanobacteria
Groundwater Discharge
Little LagoonNGOM
Groundwater Discharge
Little LagoonNGOM
N + DisturbanceTwo seasonal
phytoplankton/nutrient Seasons Groundwater discharge at low temps promotes
Pseudo-nitzschia blooms
Light and nutrient
stress promote toxicity
Low grazing pressure on Pseudo-nitzschia
Toxins can move up
the food chain
TP
Si
Domoic Acid Production
Regional considerations Local geology, population
growth, agriculture = higher groundwater nitrate in the future. Risks for future blooms
DA contamination unlikely for shellfish in fresher water (e.g. Mobile Bay oysters)
DA exposure should be considered when relaying oysters or attempting aquaculture in local high salinity waters
Probability of High Groundwater Nitrate
Nolan et al. 2002
Local health implications DA may pose a threat to
mullet and menhaden fisheries (herbivores)
Most likely threat is to wildlife such as birds or marine mammalsKnown to be poisoned in
other areasConsumers of
phytoplankton-eating fish
Low dose, chronic exposure is a concern for humans and wildlife
Sinh Nhut NguyenFishbase
Texas PWD
C. Pabody
Thank You
Justin Liefer, [email protected]
Check the LLPS website (www.littlelagoon.org) for research updates