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Dr ters...
The
Main Story by
CABELL DAVIES PHD
Photography by
RUSS HOPCROFT PHD
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There are more animals in the sea than
on land…many times more. The dominant
forces behind all life on earth are the tiny,
minute beings that drift across the vast
expanse of the ocean.
EUCHAETA MARIN A is a common
shallow-water predatory copepod in
he term “Plankton”, for
VALDVIELLIA INSIGNIS is a deep-sea
tropical waters. This female carries a
predatory copepod. It attacks prey with
clutch of several dozen bright blue eggs.
by Victor Henson at the
“Edward scissor-hands” like mouthparts
Size 3-4 mm.
University of Kiel, Germany,
which are visible in this image. Her
is derived from the Greek
two large purple eggs are also visible.
microscopic, infinitesimal
animals, first coined in 1887
word “planktos,” meaning
“drifter”. Most offspring of
Size 11mm.
marine animals in larvae form
do not resemble their parents
such as tarpon, bonefish, and eels. However
there are some that are simply miniatures
Most offspring of marine animals
in larvae form do not resemble
their parents such as tarpon,
bonefish, and eels. However
there are some that are simply
miniatures of their parents like the
octopus, squids and anemone.
of their parents like the octopus, squids
and anemone. Plankton has evolved an
extremely diverse range of body shapes
(Front page) ATLANTA PERONI is a
and sizes in their attempt to adapt to
heteropod, one of the pelagic snails. It
the pelagic marine environment. Often
swims by rowing the 2 lobes of its foot,
wildly elaborated body forms of plankton
while using its well-developed eyes to
are reminiscent of creatures from George
Lucas‘s Star Wars series. George must have
search for other pelagic snails on which
been deeply inspired by the ocean.
it feeds. Size 1cm.
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THE DRIFTERS...
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25
T H E A M P H I P O D P H RO N E M A h a s
hollowed out a zooplankter called a salp
into which she will lay her eggs. She will
then swim this living nursery around
until her babies are large enough to leave
home. Size up to 3 cm
Copepods thrive in
the world’s ocean
and freshwater
environments, with
an estimated global
population of one
quintillion (1018).
That’s a half-billion
copepods for every
person on earth!
While the many familiar marine animals
Copepods have evolved to be the fastest
have larval stages, these species are not the
animals on earth relative to body size.
dominant members of the zooplankton.
Using a high-speed video microscope,
In fact, the vast majority of zooplankton
copepods have been clocked at 500 body
spend their entire lives as holoplankton
lengths per second. By comparison, an
and they are unfamiliar to the average folk.
F-16 fighter jet flies at best 50 body lengths
Important groups of holoplankton, are
per second. In that perspective, the cheetah
the copepods that are the most numerous
cannot be the fastest animal on earth! If a
animals on earth1, yet most of us have no
copepod is transformed in ratio to the size
clue of their existence. Copepods are small
of a cheetah, in comparison, the cheetah
crustaceans ranging in size as adults from
would run at 70 miles per hour (112
about ½ mm up to 10 mm ( see picture
km/h) at its top speed, and the copepod
of Valdvielia and Euchaeta). Copepods
would zoom past at 2,000 miles per hour
thrive in the world’s ocean and freshwater
(3219 km/h) through water which is 800
environments, with an estimated global
times denser than air. This mesmerizing
population of one quintillion (10 ). That’s
feat is achieved by the copepods when
a half-billion copepods for every person
they transform their bodies from a typical
on earth!
“T” feeding posture, with their antennules
18
spread wide (as illustrated in picture of
Copepods are a primary sustenance for
Valdvielia and Euchaeta), into a torpedo
many larger plankton, adult fish, and
shape with the antennules laying alongside
whales. As they are near the bottom of the
the body while the swimming legs propel
food chain, evading predators is a necessity.
the animal forward with blinding speed.
1
with the possible exception of roundworms
THE AMPHIPOD MIMONECTES SPHAERICUS
(formerly necto amphipod) is a commensal on
deep-sea jellyfish and their kin.The large knife-like
antennae indicate this is a male. Size 3 mm.
BASIN CIRCULATION: It reflects the connection between the surface and deep water flow,
in the global Ocean-conveyer belt that takes between 600 and 1600 years to complete.
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THE DRIFTERS...
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27
PELAGOBIA LONGICIRRATA is a
pelagic Polychaete worm, from
the deep Arctic Ocean; the orange
color comes from oil drops stored
in the body. Size 5 mm.
THIS GREEN POLYCHAETE
WORM has left the seafloor to
lay her clutch of pink eggs in
the plankton. Size 4-5 mm.
ALACIA VALDIVIAE is a deepwater Ostracod or clamshrimp, a small crustacean
protected by two clam-like
shells. They are important
scavengers in the deep-sea.
Size 4-5 mm.
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THE DRIFTERS...
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29
THE SEA-ANGEL CLIONE LIMACINA is
a predatory pteropod, another shell-less
pelagic snail that flies through the water
with it’s tow wings, hunting for other
snails to eat. Size up to 3 cm.
There are many other groups of
holoplankton with equally fascinating
life histories and behaviors. An example
includes the amphipods (Phronema and
Necto amphipod), which are voracious
predators of copepods. The amphipod
Phronema with large compound eyes
and scythe-like appendages is actually a
crustacean that breeds it young inside a salp,
CARINARIA LEMARCKI is another
species of heteropod (pelagic
snail), but unlike Atlanta it is no
longer able to fit inside its shell.
The end of the snout is equipped
with strong hook-like teeth used
The amphipod Phronema with large
compound eyes and scythe-like
appendages is actually a crustacean
that breeds it young inside a salp,
a jelly like animal.
or extracts other snails from
a jelly like animal. It t has to kill the salp
their shells. Size 3-4 cm.
first, and then move in and use its jellish
body as nest to breed. Another interesting
crustacean group is the Ostracods (Alacia
valdiviae) which are active swimmers
and have a clam-like shell for protection.
Many of the deep-dwelling zooplankton,
like that of Ostracods are red, which make
them nearly invisible at depth as the red is
readily absorbed by seawater. By contrast,
species that live near the surface in tropical
regions are often blue, matching the colour
of the ocean’s surface. Marine worms
called Polychaetes, (Green Ploy, Pelagobia
longicirrata), equipped with rows of
swimming appendages for rapid movement
are also the copepods’ predators.
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THE DRIFTERS...
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31
THE SHELLED PTEROPOD DIACRIA TRISPINOSA
feeds by secreting a bubble of mucus from its large
fleshy wings. As it sinks from the weight of the shell,
food gets stuck to the bubble, then both the bubble and
the attached food are eaten. It then uses the wings to
swim back to shallower water and start the process
over again. Size up to 2 cm.
The Pteropods are marine snails that have
adapted to life in the ocean by using a
“foot” to swim swiftly through the water
column. Some pteropods have little or
no shell and they are slug-like predators
(Carinaria and Clione) of the shelled
Pteropods (Limacina, Janthina, Diacria,
and Atlanta). The pelagic nudibranch,
Phylliroe atlantica, has a larval stage that
burrows into a jellyfish, eats it from the
inside out, and becomes a free-living adult.
Larger plankton includes various kinds
of shrimp, which feed on Phytoplankton
(plants plankton) as well as on smaller
zoo- plankton such as the Eusirus. Jellyfish,
which can grow up be up to a meter in
The pelagic nudibranch, Phylliroe
atlantica, has a larval stage that
burrows into a jellyfish, eats it from
the inside out, and becomes a freeliving adult.
diameter are considered planktonic since
they drift with ocean currents, and there is
JANTHINA UMBILICATA is a snail that
lives in a unique habit within the ocean
called the neuston. It secretes a mat of
sticky bubbles that keep it attached to
the ocean’s surface, where it hunts for
jellyfish that live in the same special
habitat. Size 6-7 mm.
LIMACINA HELICINA is a shelled pelagic snail
a wide variety of these important predatory
common in temperate through polar waters.
species. Siphonophores (see picture of
They are sometimes observed to gather
Abyla duck siph and Hippodius) are colonial
together into swarms. Size up to 1 cm.
animals, related to jellyfish that include the
deadly Portuguese Man of War (Physalia
utriculus) commonly known as the blue
bottles in Australia.
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THE DRIFTERS...
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The diversity of zooplankton is enormous,
comprising of species from all animal
phylum. Zooplankton includes most of
the nearly half-million non-insect animal
THE PELAGIC SNAIL PHYLLIROE
species on earth. In addition to its diversity,
ATLANTICA begins life as a parasite
the shear mass of zooplankton in the
within jellyfish, but as it grows, it
ocean is of colossal proportions; if all the
zooplanktons were sieved from the sea
becomes a predator on them. It
and spread across the USA, Australia and
swims using its flattened tail. Size up
China, the resulting layer would be meters
to 4 cm.
deep and the vast majority will be copepods.
These ocean drifters impact not
only upon the yield of global
fisheries but more importantly the
global carbon and nitrogen cycles.
This huge mass of zooplankton turns over
several times per year through birth, growth
and death. Zooplankton, together with the
even larger masses of bacterioplankton,
protozoa, and phytoplankton, are at the
base of the ocean’s food web. These ocean
drifters impact not only upon the yield of
global fisheries but more importantly the
global carbon and nitrogen cycles.
As the majority of marine species do not
provide parental care for their young, the
ocean becomes an organic soup nourishing
the eggs and larvae of sea animals. However
ABYLA sp. is a deep-sea Siphonophore,
HIPPOPODIUS HIPPOPUS is a colonial
Siphonophore, closely related to
jellyfish. The swimming bells along
the side of the colony move it around,
the sea does not always provide sufficient
food, and the young animals suffer
closely related to jellyfish. This is a
great losses to a variety of predators. To
colony of two individuals, that swim by
compensate, marine species generally lay
pumping water, and capture food like
a long-line fisherman. Size 30mm.
large masses of eggs. The numbers reaching
adulthood can vary by a factor of hundreds
from one generation to the next, greatly
affecting the adult population size. The
while the orange and yellow tentacles
factor affecting survivorship from egg to
are normally stretched out trying to
adult, or “recruitment” in scientific terms,
capture other zooplankton as prey.
Size up to 2 cm.
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THE DRIFTERS...
remains poorly understood and is the
subject of intensive study.
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THIS BABY OCTOPUS spends its
early life hunting in the plankton, soon
it will move to the seafloor beginning
the cryptic life-style of the adult. Some
Planktons are passive drifters where
their distribution is affected by oceanic
circulation. Biological and physical
of the color-changing cells are already
visible. Size 1 cm.
oceanographers are working together
to unravel the underlying mechanisms
controlling zooplankton diversity and
distributions. A combination of traditional
sampling methods, using plankton nets
THE MULTI-NET is a modern collecting tool for
zooplankton. It allows us to electronically open and close
nets at different depths within the ocean to determine
where different species live and how many of them are
found at each depth. It operates down to 6000m depth.
The vast array of
animal life in the ocean
is truly remarkable
to behold, and it is
incumbent upon us
to understand and
preserve this vital
component of
our planet.
THE ARCTIC AMPHIPOD EUSIRUS HOLMII
uses its praying-mantis like clams to capture
prey.They have been observed attached to sea
ice, on the deep-sea floor and swimming in
between the 2 habitats. Size up to 3 cm.
and new high tech DNA methods and
digital imaging tools such as a VPR (video
plankton recorder) are shedding new light
on zooplankton diversity and how they are
affected by natural environmental factors
and human impact. These new tools
allow for automated measurement and
development of ocean observing systems,
which, together with computer models of
plankton biology and ocean circulation,
pave the way for a new era in understanding
and predicting how marine life is impacted
THIS BABY SEA-ANEMONE
has spent its early life feeding on
by pollution, over-harvesting, and climate
zooplankton. Soon it will settle to
change. The vast array of animal life in the
the seafloor to begin the remainder
ocean is truly remarkable to behold, and
it is incumbent upon us to understand
of its life. Size 2-3 mm.
and preserve this vital component of
our planet.
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THE DRIFTERS...
OCEAN GEOGRAPHIC 5:3/2008
37
n
u
r
i
g
a
t
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Drifters...
The ways they go about their lives,
hunt for, capture, and ingest their
food are frequently unimaginable.
I often believe the inspiration for
many of the creatures in science
fiction movies come from animals
that live within the plankton.
RUSS HOPCROFT PHD
For the most
part, zooplankton
are translucent
creatures. Many are
vividly pigmented,
ith a bit of thought, one then thinks of the animals
appearing as bizarre
that crawl or are anchored to the seafloor, such as
as they are beautiful. There are currently about 7000 recognized
corals and the massive reef structure that they build.
species of full-time zooplankton, and an even greater number
A far more important part of ocean exists hidden from
that live in the plankton only for the early part of their lives
your perspective, the realm of the zooplankton – small drifting
before moving to the seafloor. Nonetheless, the range of body
animals found throughout the world’s oceans. Zooplankton are
the primary conduits between the tiny floating algae that capture
(Left) THE PELAGIC POLYCHAETE WORM
design is extreme: some have hard shells, while others are literally
bags of water. Some are peaceful grazers while others are viscous
the sun’s energy and the larger animals such as fish, seabirds and
TOMOPTERUS (formerly Pl1) is a predator on
marine mammals.
other soft-bodied zooplankton. It swims using
and ingest their food are frequently unimaginable. I often believe
the flattened paddles along the side of its body
the inspiration for many of the creatures in science fiction movies
Everyone knows at
least one type of
zooplankton, the
jellyfish. Although
jellyfish
are
sometimes meters
in length, like all
Everyone knows at least one type of zooplankton,
the jellyfish. Although jellyfish are sometimes
meters in length, like all zooplankton they have
little control over where they are carried by the
ocean’s currents.
called parapodia. Size usually up to 4-5 cm, but
some species can exceed 1 m.
predators. The ways they go about their lives, hunt for, capture,
come from animals that live within the plankton.
Sadly, these animals are easy damaged by the process of collection,
and both their unique transparency and rich colors cannot be
(Top) BRANCHIOSTOMA (old name was
maintained for long. The only way to appreciate the wonder of
these animals is to see them alive, either directly in the water diving,
zooplankton they
Amphioxus) larvae are filter-feeders with
through electronic eyes on underwater robots, or immediately
have little control over where they are carried by the ocean’s
many of the characteristics of the most
after they are collected with specialized nets. For several years, I
currents. Most zooplankton are smaller, and many are just specks
to the naked eye. This small size is unfortunate, because within
primitive vertebrates (hagfish and lampreys).
the zooplankton there is an incredible range of life.
Size 2 cm.
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THE DRIFTERS...
have been working to share my fascination of zooplankton with
people by capturing them as digital images. Through projects
within the Census of Marine Life, I’ve been fortunate to participate
OCEAN GEOGRAPHIC 5:3/2008
39
About the authors
Cabell Davis PHD
Ocean Geographic Oceanographer in Residence
Dr Davis is a Senior Scientist at Woods Hole
Oceanographic Institution and is the Director
of WHOI’s Ocean Life Institute with over 30
years experience in plankton ecology. He has
conducted research on 50 oceanographic cruises and co-developed
the Video Plankton Recorder, an underwater video microscope
with automatic imaging of high-resolution fragile plankton data.
He recently worked with MIT engineers to develop a small
underwater digital holographic camera for imaging plankton. He
is now modeling the impact of climate change on the fisheries
ecosystem. His current interests are in developing, modeling
and observing systems in support of ecosystem approaches
to managing ocean resources.
Russ Hopcroft PHD
THE LEPTOCEPHALUS
LARVAE of moray eels are
ribbon-like and completely
transparent, with only tiny
heads. Size up to 15 cm.
on research cruises scattered around the
globe, from the tropics to both poles. I’ve
collected from the ocean’s surface waters to
depths of several kilometers. What started
out as an activity during my ‘spare time’
on cruises can become a full-time activity,
either hunting for larger zooplankton
with ROVs (remotely operated vehicles)
or sifting through net samples to find
healthy undamaged subjects. Expert coworkers help me identify animals when
they are unfamiliar. I then spend hours
trying to capture the perfect picture, of a
moving animal, on a moving ship. It’s a
challenge, but I hope you agree, it’s worth
the effort.
*all photography by Russ Hopcroft
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THE DRIFTERS...
Associate Professor
Institute of Marine Science, University of
Alaska, Fairbanks
Dr. Russ Hopcroft is an Associate Professor
at the University of Alaska’s Institute of Marine
Science in Fairbanks. He grew up fascinated by aquatic
life (and Jacques Cousteau specials), pursuing the sciences during his
education. Dr. Hopcroft received his Masters degree in 1988, and his Ph.D. in
1997 from the University of Guelph, Ontario, Canada. The focus of his graduate
research was on marine plankton ecology in the tropical waters surrounding
Jamaica, West Indies. From 1997 to 1999, he was a Post-doctoral Fellow at
the Monterey Bay Aquarium Research Institute (MBARI). At MBARI he was
heavily involved in the use of ROVs, as well as traditional oceanographic
surveys, to study the oceans.
Dr. Hopcroft pursues a broad array of research interests, concentrating on the
composition, production and energy flow of the planktonic trophic levels that
ultimately shape the structure of all marine communities. Since joining UAF in
2000, most of his research focuses on copepod and euphausiid crustaceans
in Alaskan waters. He also specializes on the taxonomy, biology and ecology
of the tadpole-like pelagic tunicates, and most recently the pelagic snails. He
serves on the steering committee of several Census of Marine Life projects:
the Arctic Ocean Biodiversity (ArcOD) project, the Census of Antarctic marine
Life (CAML), and the global Census of Marine Zooplankton (CMarZ). He is
increasingly recognized for his images of live zooplankton that are widely
distributed in the media and on the web. He is an active contributor to ongoing
global efforts to molecular barcode all zooplankton species. Visit his web site,
http://www.sfos.uaf.edu/directory/faculty/hopcroft/ and http://www.
sfos.uaf.edu/research/arcdiv/index.html