Transcript ENVI 21 Life in the Ocean

I.
Phytoplankton
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A.
Over 4000 described species
Bacillariophyceae (Diatoms)
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Dominant in temperate and high-latitude waters
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Prefer well-mixed, nutrient-rich conditions
Pelagic and benthic forms
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Pelagic forms generally non-motile
Unicellular, though some may form chains, which then
may form mats
Test composed of two silica valves
Tests are important components of marine sediments in
some areas - diatomaceous oozes
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An ooze is any sediment that contains more than 30%
tests, the rest typically terrigenous
Fig. 2.1
I.
Phytoplankton
A.
Bacillariophyceae (Diatoms)
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Two basic body shapes
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Pennate – Elongate, typically motile, mostly benthic
(Exception – Nitzschia)
Centric – Mostly planktonic (Ex – Coscinodiscus,
Chaetoceros)
I.
Phytoplankton
A.
Bacillariophyceae (Diatoms)
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Planktonic forms typically non-motile with anti-sinking
mechanisms
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Reduced body size
Structural elaborations – increase drag
Formation of chains
Reduction of internal ion concentration
Sequestration of low-density ions, e.g. NH4+
Production and storage of oils
Many of these mechanisms are generally applicable to planktonic
organisms
Living cells typically sink 0-30 m d-1, while dead cells may sink
twice as rapidly
Senescent or near-senescent cells may
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Lose ability to regulate ion content or sequester low-density ions
Lose ability to produce and store oils
Release a chemical (e.g. a polysaccharide) that lowers viscosity of
water immediately surrounding cell
I.
Phytoplankton
B.
Dinophyceae (Dinoflagellates)
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Motile forms possess two flagella
Not all dinoflagellates are motile and not all are
autotrophic
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Some lack flagella
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Some heterotrophic (~50%)
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Some mixotrophic (auto- and heterotrophic)
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Some symbiotic (e.g. zooxanthellae)
Two basic forms
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Thecate – Covered with theca made of cellulose
plates
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Theca may have spines
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Athecate – Less common
Fig. 2.3
I.
Phytoplankton
B.
Dinophyceae (Dinoflagellates)
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Important open-water primary producers, especially in
tropical regions
More tolerant of low nutrients and low light than diatoms
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Advantage for thriving under post-diatom-bloom
conditions
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Often abundant in summer/autumn following spring and
summer blooms of diatoms
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Motility allows individuals to maintain position in water
column under low-turbulence conditions
Motility also allows individuals to spend daylight hours in
surface waters (light for photosynthesis) and night hours in
deeper waters (nutrients more plentiful)
Most abundant phytoplankton in stratified, nutrient-poor
tropical and subtropical waters
Thecate species of heterotrophic
dinoflagellates use pallium feeding
Feed on other plankton
with a pallium (sac)
extruded from a
microtubular basket.
Siana and Montrasor
(Eur. J. Phycol. 2005)
reported ingestion rates
up to 36 diatoms/
Protoperidinium vorax
/hr
Other reports are lower
http://chbr.noaa.gov/pmn/images/PhytoplanktonPics/Protoper
idinium/ProtoperidiniumSEM02.jpg
•Protoperidinum feeding on
Ceratium furca
•Arrow shows pallium
•Arrowheads show multiple
Protoperidinium feeding on
the same prey
•Olseng, et al. 2002 Mar
Ecol Prog Series
•Other species of
dinoflagellates use a tube
inserted into prey to
consume the cytoplasm
•Only naked dinoflagellate
species engulf prey
Olseng, et al. (2002) Mar Ecol Prog Series
Swimming with bioluminescent dinoflagellates
Campbell and Reece Figure 28.12x2
Dinoflagellates often cause Harmful Algal Blooms
http://www.whoi.edu/redtide/
I.
Phytoplankton
C.
Haptophyceae (Coccolithophorids)
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Very small (typically less than 20 μm)
Covered by calcium carbonate coccoliths
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Coccoliths may be important components of
sediments
Typically motile at some life stage (have flagella)
Most species occur in warm water at relatively low
light intensities
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Most abundant at depths of ca. 100 m in clear,
tropical, oceanic water
Blooms may cover extensive areas
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Ex – Bloom covering 1000 x 500 km of sea surface
in North Atlantic (area roughly equivalent in size to
Great Britain)
I.
Phytoplankton
D.
Chrysophyceae (Silicoflagellates)
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E.
Silica test, usually with spines
Single flagellum
Relatively rare but more common in colder water than
tropics
Cyanobacteria (Blue-Green Bacteria)
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Most relatively minor primary producers
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Certain species may be important in particular areas
for limited periods of time
Some can fix nitrogen (e.g. mats of Oscillatoria)
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Attribute may explain relatively high abundances of
Oscillatoria in tropical waters which often have low
concentrations of nitrogen sources generally used by
algae (e.g. ammonia, nitrite, nitrate)
Cyanophyceae (Cyanobacteria)
•Phycoerythrin and phycobilin
accesory pigments.
•Nitrogen Fixation
•Some symbiotic
•Some filamentous or colonial
A.
Katagnymene spiralis
B.
Two colonies of Trichodesmium
C.
Aphanizomenon sp. colony [note heterocyst (H)]
D.
Benthic Rivularia atra
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Lichen Lichina confinis
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Diatom with cyanobacterial symbiont Richelia
intracellularis (R)
G.
Dinoflagellate with a "collar" specialised for
Synechococcus (S) cyanobionts.
http://www.bom.hik.se/~njasv/mcb.html#pics%20cyano
I.
Phytoplankton
F.
Prochlorophytes
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Very small (0.6-0.8 μm diameter)
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Components of nanoplankton and picoplankton
Resemble bacteria in some respects and algae in others
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Structurally, resemble large chloroplasts with internal
membranes that facilitate photosynthesis
Appear to be closely related to cyanobacteria and may be
ancestors of modern algae
In some areas, e.g. oceanic equatorial Pacific, production by
prochlorophytes may constitute a substantial fraction of total
phytoplankton chlorophyll (up to 60%) and primary
production
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Cell densities may be comparable to those for bacteria
(ca. 106 ml-1)
Phytoplankton community in some areas may change from
diatom- or dinoflagellate-dominated assemblages to
prochlorophyte-dominated assemblages
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Shift has profound consequences for entire food web
I.
Phytoplankton
F.
Prochlorophytes
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Very small (0.6-0.8 μm diameter)
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Components of nanoplankton and picoplankton
Resemble bacteria in some respects and algae in others
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Structurally, resemble large chloroplasts with internal
membranes that facilitate photosynthesis
Appear to be closely related to cyanobacteria and may be
ancestors of modern algae
In some areas, e.g. oceanic equatorial Pacific, production by
prochlorophytes may constitute a substantial fraction of total
phytoplankton chlorophyll (up to 60%) and primary
production
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Cell densities may be comparable to those for bacteria
(ca. 106 ml-1)
Phytoplankton community in some areas may change from
diatom- or dinoflagellate-dominated assemblages to
prochlorophyte-dominated assemblages
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Shift has profound consequences for entire food web
I.
Phytoplankton
G.
Blooms
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Occur when conditions become favorable for one
species or group of phytoplankton
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Population of that species or group increases
rapidly and suddenly
If bloom species is a dinoflagellate, densities
sometimes increase so rapidly and reach such high
levels that reddish-brown pigment they produce may
color the water and cause a red tide
http://www.whoi.edu/redtide/
I.
Phytoplankton
G.
Blooms
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Red tides typically become visibly apparent when cell
concentrations reach 2-8 x 106 cells l-1
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Cell concentrations may exceed 108 cells l-1
As nutrients are depleted and bloom begins to break
down, bacteria begin to decompose the remaining
organic material
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If material is sufficiently abundant, bacterial
decomposition may deplete oxygen in surface
waters, negatively impacting local fauna
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Phenomenon applies to any large phytoplankton
bloom, not just red tides
Red tides may involve species that produce pigments
but are not toxic or may involve species that produce
compounds that are toxic to marine life
I.
Phytoplankton
G.
Blooms
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Toxin (Saxitoxin) may be
1) Released into water, where it may be consumed directly
by organisms that graze on phytoplankton (e.g.
zooplankton) and indirectly at higher trophic levels
2) Transmitted from dinoflagellates directly to higher
organisms, e.g. clams, mussels, scallops, oysters, which
then may be food for larger animals
Result of consuming tainted fish or bivalves is Paralytic
Shellfish Poisoning (PSP) - may be fatal
Some forms can be extremely toxic
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Ex – Pfiesteria
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Blooms triggered by coastal pollution
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Causes extensive fish kills
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Toxin can cause memory loss in humans