Science topics
Microalgae—minute jewels of the ocean - Jeannie-Marie LeRoi
The Scientist
Jeannie-Marie LeRoi is a microalgal biologist with over fifteen
years experience with microalgae. Based at CSIRO Marine Laboratories,
she recently completed her Masters project in collaboration with
Assoc Professor Gustaaf Hallegraeff at the University of Tasmania.
Jeannie-Marie was also selected to attend the IOC Advanced Phytoplankton
Course in Naples, Italy, where she had the opportunity to work with
international experts and to study microalgae from all over the
world.
When she is not playing with microalgae, Jeannie-Marie is involved
with producing plays about microalgae, in collaboration with students
from Double Helix Drama. Recent performances have included "The
Deadly Dinoflagellate" at the Ninth International Conference
on Harmful Algal Blooms, as well as presentations at the International
Science Festival in New Zealand, and the Australian Science Festival.
Jeannie-Marie's collaboration is with artist Helen
Wright.
The Research
Microalgae are the minute jewels of the ocean, microscopic floating
plants and vital for all marine life. Without microalgae, there
would be no life on earth - the oceans would be sterile and the
land uncolonised.
What are Microalgae?
Microalgae are tiny single-celled plants found in oceans, lakes,
rivers and ponds. If they float or are carried along by currents,
they are known collectively as phytoplankton.
Microalgae are at the base of the food chain — they are food
for small animals of the zooplankton which are then fed on by larger
animals. Without this primary food source ("primary productivity"),
there would be no marine or freshwater life.
Microalgae also play a signficant role in contributing to the earth’s
atmospheric oxgyen, with up to 70 per cent of this oxygen being
produced by the tiny cells of the marine phytoplankton.
There are thousands of different microalgal species, ranging in
size from one thousandth of a millimetre (or one micron) to over
2 mm. Under the microscope, many of these species have amazingly
beautiful shapes and structures.
In contrast to the well known microalgae, diatoms and dinoflagellates,
many other groups have been found in recent decades through such
techniques as electron microscopy, careful preservation and ship-board
cell-flow cytometry.
Nanoflagellates
Nanoflagellates are the "hidden" flora of phytoplankton populations.
These small organisms, 2 - 20 microns (µm) in size, are not usually
seen when standard methods are used for plankton collection, preservation
and examination under the light microscope. But they are a major
part of the phytoplankton, accounting for up to 90% of the total
biomass and responsible for more than 50% of primary productivity.
Nanoflagellates are an important food source for zooplankton, including
larval stages of molluscs, crustaceans and finfish, both in nature
and in aquaculture operations. However, nanoflagellate blooms can
also cause invertebrate and fish mortalities due to the formation
of anoxic conditions or the production of toxins.
My work focuses on those marine nanoflagellates which have minute
scales covering the cell, and in some cases, the flagella. There
is an enormous variety of scale size and structure, ranging from
long spined scales, over 30 µm in length, to tiny delicate flagellar
scales, less than 0.3 µm. Certain scale types are unique to particular
species or genera, and consequently, scales are key taxonomic characters.
While the function of these scales is largely unknown, it has been
suggested that they have a protective role by isolating the cell
membrane from the immediate environment, thus shielding the cell
from mechanical, chemical or osmotic shock. Long spine scales increase
the overall cell size, and may prevent predation by smaller zooplankton.
Other possible functions include providing structural support, regulating
the position of the cell in the water column, and shielding the
cell from high light intensities
As part of my Masters project, I undertook a survey of scale-bearing
nanoflagellates from southern Tasmanian coastal waters, using transmission
electron microscopy to examine scale morphology and identify species.
Over 70 species of scale-bearing nanoflagellates were identified,
with 17 of these species being new records for Australian waters.
In addition, over 30 previously unreported scale types were observed,
highlighting the biodiversity of scale-bearing nanoflagellates in
Tasmanian waters.
Examples of scale-bearing nanoflagellates
from southern Tasmanian waters:
Paraphysomonas butcheri
This was a very common species in Tasmanian coastal waters.
Image 1— P. butcheri cell (2.5 µm) from the Derwent
River, with two flagella of unequal length. Note the fine hairs
on the longer flagellum.
Image 2— P. butcheri plate scales (0.7 x 0.5µm) and
crown scales (0.6 x 0.4 µm) from Storm Bay.
Chrysochromulina sp.
This species has distinctive spine scales, and has not been previously
reported. It was found in samples from the Derwent River, Pipeclay
Lagoon and Southport and Dru Point.
Image 3— Chrysochromulina sp. cell (3 µm) showing spines,
from the Derwent River.
Image 4— Chrysochromulina sp. spine scales (1.5 µm),
from PipeClay Lagoon.
Chrysochromulina sp. "eyelash"
This species has yet to be named. It was first described from New
Zealand waters from a partially obscured scale that did look like
an eyelash. But when the entire scale was seen in later samples
it looked more like a small sunshine! Since its first record, this
species has been reported from the Red Sea, South Africa, Japan
and south-east Australia.
Image 5- Chrysochromulina sp. "eyelash"
(0.8 µm) and plate scales (0.9 x 0.7 µm), from the Derwent River.
Image 6- Chrysochromulina sp. large plate scales
(0.9 x 0.7 µm), showing different patterning on each surface; also
from the Derwent River.
Prymnesium patelliferum
This species produces toxins and has been implicated in harmful
bloom events resulting in fish mortalities. In this study, P.
patelliferum was found to be toxic to hatchery-reared oyster
larvae and to Derwent River decapod zoea.
Image 7— P. patelliferum cells (4 µm) from a Pipeclay
Lagoon sample.
Image 8- P. patelliferum scales (0.35 µm) showing different
patterning on each surface, from the same Pipeclay Lagoon sample.
Pavlova sp.
Pavlova is a widespread but infrequently recorded group
from various habitats from freshwater lakes to marine environments,
although most species thrive in brackish waters. Originally named
after the ballerina Anna Pavlov, because of their graceful swimming
motion, Pavlova species are widely used as larval food in
aquaculture.
Image 9 - Pavlova sp. cell (5 µm), from Pipeclay Lagoon.
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