Marine Phytoplankton
of Kachemak Bay
By Jane Middleton and Catie Bursch
Kachemak Bay Research Reserve
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INTRODUCTION to PHYTOPLANKTON
This is a guide to aid in the identification of marine phytoplankton found in Kachemak Bay,
Alaska.
Phytoplankton are not really plants but close. They are classified under the Algae group which
sits just next door to plants in the classification of living things. Phytoplankton are one-celled
forms of life that float in sunlit surface water (freshwater and salt water), where they convert
solar energy into the food energy that sustains almost all life in marine and estuarine ecosystems. They are normally microscopic (less than 100 microns in diameter). A micron is a millionth of a meter; 1000 microns is a millimeter. There are two significant groups of phytoplankton in Kachemak Bay and adjacent coves, bays and estuaries. They are diatoms and
dinoflagellates.
Diatoms are comprised of a live cell surrounded by a glass cage that resembles a miniscule
box—a bottom that fits snugly into a tight-fitting lid—much like a hatbox or tube of lipstick.
The two box parts are called valves. Diatoms are loosely divided into two groups—centric and
pennate.
Centric diatom structure radiates out from the midpoint like a snowflake (radially symmetrical)
and they have a basic body shape that resembles a hockey puck or a gold coin. From the top
(valve view) it is round, becoming rectangular when viewed from the side (girdle view).
Typically, centric diatoms are not mobile—hence they flourish in the active surface waters
where waves and currents move them about, continually exposing them to new concentrations
of vital nutrients. Some centric diatoms form chains by joining adjacent cells. Chain formations,
as well as spines, are adaptations that increase floatation of diatoms in the surface water.
These three different centric diatom chains
with different cell lengths could look
like circles when viewed from the top.
Centric diatom_ side view
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Centric diatom_side view
Pennate diatoms are cigar or kayak shaped, tapered at both ends (bilaterally symmetrical).
Most pennates live on or near the bottom (benthic) in nearshore waters. Unlike centric diatoms,
some pennate diatoms can move. They may have a thin slit, called a raphe, which runs from one
end to the other and is open at both ends. The cytoplasm of the cell secretes ions into the water
of the slit at one end, creating an osmotic gradient along the raphe that pulls water into the slit
and moves it along to exit from the opposite end. This water action results in rather rapid motility of the diatom by “jet propulsion,” an important adaptation for obtaining nutrients in a benthic environment.
Pennate diatom_side view
Pennate diatom _top view
Dinoflalgellates are another form of phytoplankton, also one-celled, but with a shell of cellulose plates instead of glass. A dinoflagellate is basically round with a “waistline” groove circling the cell, and a second groove running from the waistline to the posterior or back of the
cell. One flagellum lies in the waistline groove and causes the cell to twirl, while a second flagellum in the posterior groove propels the cell forward. Most dinoflagellates are autotrophs
(produce their own food by photosynthesis), whereas a few are -heterotrophs (obtain their food
by capture of autotrophic cells). Some are both autotrophic and heterotrophic—in which case
they are called mixotrophes.
Protoperidinium_dinoflagellate
Identification of phytoplankton is accomplished by microscopic examination at 100x or 400x.
With the powerful lens of a microscope you lose depth of field. Therefore it helps to crank the
objective slowly up and down. This will allow you to gain a more distinct view of valve patterns, spines, chloroplasts, granules and, in pennate diatoms, the raphe. A common mistake
when viewing plankton is to allow too much light to hit your slide from the microscope lamp.
Adjust the light on your microscope so that the delicate clear borders of the cells become distinct.
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Ast erionello psis morpho typ e
Cylind rot heca closte rium
Ent omon eis spp.
Fragila riopsis spp.
Licmop hora spp.
Navicula morphot yp e
Nitzschia morph otype
Pleurosigma morph otype
Pseudo-nitzschia spp.
Th alassio nema spp.
PENNATE  DIATOMS ENTRIC
 DCIATOMS
Illustrations NO T to Scale: Illustra tions N OT to Scale : Cupp, E.E., 1943. Marine Plankton Di atoms of theWest
Coast of North Ameri ca, Uni versity of Cali fornia Berkeley. Tom as, C. (Ed.), 1997. Identifying Marine Phytoplankton. San Diego, CA. Cupp, E. E. , 1943. Mari nePl
ankton Diatoms of the West Coast of North America, Universi ty of Californi a Berkel ey. Tomas, C. (Ed.), 1997. Identifyi ng Mari ne Phytopl ankton. San Di ego, CA
Chaetoceros spp.
Coscin odiscus mo rp hotype
Ditylu m spp.
Lept ocylindrus spp .
Melosira sp.
Odonte lla sp p.
Rhizo solenia morphotype
Skeletone ma sp p.
Stephano pyxis spp .
Thalassiosira sp p.
Alexandrium sp p.
Cera tium f urca morphotype
Cera tium f usus mo rphotype
Ce rat iu m longip es mo rph otype
D INOFLAGELLATES Illustra tions N OT t o Scale : Tomas, C. (Ed.), 1997. Identifying Mari ne Phytoplankton. San Di ego, CA . Catie Bursch, Kac hemak BayResearc
h Reserve © Ca tie Bursch
© Cat ie Bu rsch
Din ophysis spp.
Protop eridinium spp.
Noctiluca spp .
© Catie Bu rsch
ZOOPLANKTON Barn acle na uplius
Ciliates
Copepod n auplius
Illustrations NO T to Scale: 4
Cati e Burs ch, Kachemak Bay Research Reserve Johnson, W.S., Allen, D. M. , 2005. Zoopl ankton of the Atlantic and Gul f Coasts A Guide to Their Identi fi cati on and Ecology. Baltimore, Maryl and. © Catie Bu rsch
©Catie
Bursch
©Catie
Bursch
Tintinnids
5/16/2013
PHYTOPLANKTON OF KACHEMAK BAY, ALASKA
DIATOMS
Asterionellopsis sp. 


(pennate diatom)
Cells have one end thicker than the other.
Held together in radial fashion by the thicker, “plunger” ends.
Chloroplasts are clustered in the “plunger” ends. Rarely seen.
Chaetoceros spp. (centric diatom)
 We see several species. Chaetoceros spp. is the dominant







group seen in Kachemak Bay in June-July.
Every cell has 2 spines on each valve. (photo on right)
Chains form when spines of adjacent cells fuse together.
Adjacent cells in the chain don’t touch—there is a space between them.
Cells are round or elliptical in top view, rectangular in side
view.
Important in marine food cycle—no apparent harm to the digestive tracts of predators. Cultured for food for bi-valves.
Extremely damaging to salmon smolt in the Nick Dudiak Fishing Lagoon.
 Spines lacerate delicate gills of small fish.
 During a Chaetoceros bloom, cells accumulate in and
clog the gills.
 Spines introduce bacteria to the bloodstream.
 Irritation by spines stimulates mucus production that
cuts off O2 supply.
Separate chains of Chaetoceros socialis (right) held in globular
formation by invisible tendrils radiating from a structure at the
center of an invisible sphere.
Coscinodiscus sp.
(centric diatom)
 Large round cell when seen from top-view.
 Not often seen in side view, but shaped like a hockey puck
 Coscinodiscus sp. controls its buoyancy by releasing oil droplets through large central pore and smaller pores aligned radially and around the circumference.
 Sometimes filled with chloroplasts and sometimes empty.
 May be confused with single cells of Thallasiosira sp, but is
larger. Coscinodiscus sp. do not form chains.
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DIATOMS
Ditylum sp.
(centric diatom)
 Rectangular looking cells with single spine at each end.
 Valve is actually triangular when seen from end-view.
Entomoneis sp.
(pennate diatom)
 Distinguished by rectangular chloroplast and cell shape.
 Like all pennates, mostly benthic but may get swirled into upper water layer.
Fragilariopsis sp.
(pennate diatom)
 Cells flattened, chloroplasts central.
 May occur singly, but chain of cells joined side by side is
more common.
 Mostly benthic.
Leptocylindrus sp.
(centric diatom)
 Cells long, straight.
 United in chains with full surface of valves joined.
 No spines nor horns.
 Important oyster food.
 Common in Kachemak Bay in late July and August.
Licmophora sp.
(pennate diatom)
 Wedge shaped.
 Normally grows attached to seaweed or zooplankton but sometimes breaks loose and floats as plankton.
 Chloroplasts tend to be olive-green.
Melosira sp.
(centric diatom)
 Pairs and triplets of cells are united in chains at their valve
centers.
 Cells drum-shaped.
Navicula morphotype
(pennate diatom)
 Over 1000 pennate species have this morphotype (shape).
 Most very small but a few quite large.
 Solitary. Kayak shaped with somewhat rounded ends.
 Very active. The raphe is usually visible.
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DIATOMS
Nitzschia sp.
(pennate diatom)

Elongated cell with pointed ends.

Two chloroplasts centrally located.

Cytoplasm extends into points of the cell.
Ends tend to curve a bit, but curvature may not be apparent.
Odontella sp. (centric diatom)

Note terminal horns in the enlarged photo at right.

Cells may occur singly or in straight or zigzag chains.

Numerous chloroplasts lay against the valve walls.
Pleurosigma morphotype (pennate diatom)
 Name from Gr. Pleura=rib and sigma=S-shaped.
 Very large pennate diatom.
 Ends always blunt—never pointed—and they usually flex in
opposite directions. Bending and direction may not be visible
when viewed sideways.
Pseudo-nitzschia sp. (pennate diatom)
 Elongated cells with two chloroplasts in the center. Usually
joined in chains with overlapping ends, but the overlap may
not be obvious if specimen is oriented somewhat sideways.
There are five cells in chain in photo on right.
 Single cells do occur.
 Only diatom that is toxic to humans by producing domoic
acid (DA). Humans may develop Amnesic Shellfish Poisoning (ASP) after eating shellfish (crabs, clams, mussels) contaminated with domoic acid.
 All species of Pseudo-nitzschia produce domoic acid, but at
different levels and times.
 One of the species found in Kachemak Bay; Pseudo-nitzschia
australis, is a typical DA producer.
 P. australis is found all around the world.
 Photo close-up shows the distinct overlapping feature.
Rhizosolenia sp. (centric diatom)
 Cylindrical, sometimes clear with no chloroplasts.
 Local species seem to be very large and long, but some species are short.
 Spines on end look slightly crooked or bent.
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DIATOMS
Skeletonema sp. (centric diatom)
 In photo, slanted downward across the top from upper left.
 Cells are very tiny but may be confused with larger Stephano-
pyxis (in photo at right, slanting upward from lower left).
 Adjacent cells do not touch but are connected by a cluster of
hollow spines.
 Good food source for oysters and zooplankton.
Stephanopyxis sp.
(centric diatom)
 In photo above, slanting sharply upward from lower left.
 Valve margins circled by ring of stout spines nearly parallel
with the central axis.
 Adjacent cells do not touch .
Thalassionema sp.
(pennate diatom)
 Rectangular cells joined randomly in zigzag chains by gelatinous cushion at valve corners.
 Internal structure usually not visible, but chloroplasts scattered
throughout.
Thalassiosira sp.
(centric diatom)
 United in flexible chains by single strand of gelatinous thread
connecting center of adjacent cells. (chain at right)
 Single cells resemble Coscinodiscus in top-view, but chloroplasts larger in comparison to cell size in Thalassiosira sp.
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DINOFLAGELLATES
Alexandrium sp.
 Very small cell.
 Like most dinoflagellates, Alexandrium has two flagella. One
lies in a groove circling the “waistline” of the cell, while the
other lies in a backward facing groove.
 The two flagella are responsible for spinning motion that propels the cell through the water.
 Waistline groove is deep and cell is densely pigmented reddish
-brown.
 May occur singly or in chains and (like other dinoflagellates)
may be bioluminescent, occasionally producing a red or brown
glow in the water (red tide).
Ceratium furca morphotype
 Ceratium is a genus of dinoflagellates with three horns—one at
the anterior pole of the cell and two at the posterior pole.
 The two posterior horns of C. furca are relatively straight and
apear parallel to one another, but may be flexed outward somewhat.
Ceratium fusus morphotype
 C. fusus has two prominent horns, the third horn is a rudimentary stub.
Ceratium longipes morphotype
 The posterior horns on this species are severely flexed forward
and are sometimes long and curved.
Dinophysis sp.
 Has unique collar and wing-like structure on the side.
 Common in Kachemak Bay tows and are very active.
 Multiple species of Dinophysis produce a toxin, okadaic acid,
which causes Diarrhetic Shellfish Poisoning, DSP.
 DSP is not fatal but causes intestinal discomfort in humans
from eating shellfish, which have eaten the toxic Dinophysis.
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DINOFLAGELLATES
Noctiluca scintillans
 This very large cell has atypical structure for dinoflagellate.
Photo shows size next to chain diatom.
 Two sticky food-gathering flagella extend from a slit along one
side.
 Feeds mostly on diatoms. Chloroplasts are absent.
 Often bioluminescent, greenish or blue, at night when water is
disturbed. Most common near shore in marine water.
 Does not produce a toxin, but following a large bloom the dying cells can release large amounts of ammonia which may kill
many fish.
Protoperidinium sp.
 Small, plump cells with two horns on the posterior pole and
one anterior horn.
 Waist groove prominent.
 Common in local tows—several species in Kachemak Bay.
 Protoperidinium is a heterotroph, meaning it feeds on other
organisms. The “polka dots” in the cytoplasm are undigested
pigments of the diatoms they consume.
Scrippsiella sp.
 Small cell with conical top and rounded bottom.
 Chloroplasts present.
 The little point on the top distinguishes it from Alexandrium.
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OTHER GROUPS OF MARINE MICROPLANKTON
PHYLUM CILIOPHORA
Tintinniopsis sp.
 This small zooplankton is a ciliate enclosed in an external case,
called a lorica, made of foreign particles.
 Collar of cilia (like small hairs) around the opening creates
currents that stir up the water, propelling the animal forward
and drawing food particles in.
 Very active and common locally in many different shapes.
PHYLUM SARCOMASTIGOPHORA, Subphylum Sarcodinia
Actinopods
 A zooplankton related to amoeba.
 The cell is encased in a sphere made of silica with holes
through which thin transparent feet extrude to capture food.
PHYLUM CHRYSOPHYTA, Class Dictyochophyceae
Dictyocha sp.
 Related to diatoms, this tiny phytoplankton is encased in silica
with holes and a wreath of 6 spines.
 Appears to be spherical when seen from valve view, but is actually fairly flat.
 Not common, but very distinctive.
PHYLUM PRYMNESIOPHYTA
Coccolithospore
 A tiny photosynthetic organism formerly classed with diatoms
in Phylum Chrysophyta.
 Very tiny and nearly colorless, the circular calcareous plates
are characteristic.
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Kachemak Bay Research Reserve
95 Sterling Hwy, Ste 2
Homer, AK 99603
www.kbayrr.org
907-235-4799
2013
The production of this guide was a cooperative effort by KBRR volunteer
Jane Middleton, KBRR staff Catie Bursch and Jeff Paternoster with NOAA
Phytoplankton Monitoring Network.
Photographs by Jane Middleton and Catie Bursch (all from Kachemak Bay
Plankton except Alexandrium photo from NOAA, PMN).
Cover illustration by Catie Bursch.
The Alaska Department of Fish and Game (ADF&G) administers all programs and activities free from
discrimination based on race, color, national origin, age, sex, religion, marital status, pregnancy, parenthood, or disability. The department administers all programs and activities in compliance with Title VI of
the Civil Rights Act of 1964, Section 504 of the Rehabilitation Act of 1973, Title II of the Americans with
Disabilities Act of 1990, the Age Discrimination Act of 1975, and Title IX of the Education Amendments
of 1972.
If you believe you have been discriminated against in any program, activity, or facility please write:
 ADF&G ADA Coordinator, P.O. Box 115526, Juneau, AK 99811-5526
 U.S. Fish and Wildlife Service, 4401 N. Fairfax Drive, MS 2042, Arlington, VA 22203
 Office of Equal Opportunity, U.S. Department of the Interior, 1849 C Street NW MS 5230, Washington DC 20240.
The department’s ADA Coordinator can be reached via phone at the following numbers:
 (VOICE) 907-465-6077
 (Statewide Telecommunication Device for the Deaf) 1-800-478-3648
 (Juneau TDD) 907-465-3646
 (FAX) 907-465-6078
This product can be downloaded as a PDF
on the Kachemak Bay Research Reserve
website; www.kbayrr.org
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