plankton diversity

Plankton Diversity and the Ocean’s Food Webs Planktos is Greek for wanderer. Not only is it the root word applied to the points of light that wander in the night sky in a path apart from that of the constellations, but it is where the word plankton comes from. Plankton are small organisms that drift on the currents, and are found not just in oceans but in bays, lakes, and even small ponds. Some plankton are animals, and some are plants. There are even some single-celled organisms, having characteristics of both plants and animals. Almost all marine invertebrates and most fish (except sharks) are planktonic in their early stages. All marine plants have a planktonic stage. Plankton are of interest to ecologists because they are the base of the food web for the ocean. Almost all life in the oceans depends upon the plankton, so an appreciation of this microscopic diversity is important to understanding why little things are such a big deal.

In this lab we’ll examine plankton collected from our coastal waters. The types of organisms captured depends upon numerous factors: the location where the sample is collected, the time of day the collection is made, the size of the plankton net mesh used, and the time of year.

These microscopic organisms typically are transparent, so look into their bodies and see what parts are actively pumping, contracting, or flowing. Hearts, cilia, flagella, jaws, and circulatory fluids are just some moving components of these life machines.

Obtaining Plankton

Our trusty lab assistant has already obtained plankton samples by doing a tow off of the Cabrillo Biology Department's 100ft oceanographic research vessel, the cement ship at Seacliff State Beach. This state-of-the-art, zero-budget vessel is ideal for collecting near-shore samples of plankton during regular park hours. Samples are best freshly obtained the morning of the lab period, and contained in refrigerated bottles until lab starts. Why must it be refrigerated? When the specimens are ready for examination, use an pipette to extract a sample. DO NOT agitate the container, but rather, suck up a SMALL amount - just a drop or two - from the surface and examine it. Next, examine a sample from the middle of the bottle, and finally take a sample from the bottom. Since organisms tend to stratify themselves, you should see some differences in which organisms occur in which strata. There will be two different samples taken, one with a very fine mesh for sampling the smaller phytoplankton, and a second sample using a coarser net that only catches the larger phytoplankton and zooplankton.

Biology 11C Laboratory Experiments In Ecology

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Keying Out Microplankton

Shape is the first thing that one notices when trying to identify a planktonic organism. Size is not a good characteristic, and under a microscope it can be a difficult thing for a novice to determine. 11 a) Kite- or tablet-shaped, with

paired projections; large, active and common..............2

b) Not as above.............................3 2 a) Three pair of short legs, two

long, laterally-projecting antennae .................copepod

b) As above, but antennae absent .......................nauplius stage

33 a) Wine glass shape with stem

broken off; tiny; if alive, lip is ciliated................ tintinnid

b) Not as above.............................4 44 a) Barrel shape with paired,

ciliated "wheels"; perhaps with a forked, telescoping tail; contracting jaws look like beating heart; highly active ............................ rotifer

b) Not as above.............................5 5 a) Shape is round, globular, or

spherical ................................6 b) Not as above...........................12 6 a) Spinning or rolling very

rapidly .....................blastula b) Not as above.............................7 7 a) Looks like a clear lily pad,

with a slowly moving stalk .............................Noctiluca

b) Not as above.............................8

copepod

nauplius

tintinniddead

alive

blastula Noctiluca

some rotifers


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8 a) Jellyfish-like, with tentacles ......................Obelia medusa

b) Not as above.............................9 9 a) Spines radiating from central

globular mass..... radiolarian b) Not as above...........................10 10 a) Aspirin-shaped or flattened,

looks like a CD & may show same iridescence diatom

b) Not as above...........................11 11 a) Sphere shape, with cilia in

rows..................... ctenophore b) Sphere within a sphere, no

obvious features .............. egg 1212 a) Triangular shape ...................13 b) Not as above...........................15 13 a) Non-motile, golden-brown,

with radiating lines...diatom b) Not as above...........................14 14 a) Has anterior ciliated band

.......polychaete trochophore b) Shaped like shield, 3 pairs of

legs ..........barnacle nauplius 1515 a) Worm-like ..............................16 b) Not as above...........................21 16 a) Segmented; has bristles or

setae; very active if alive ..............................polychaete

b) Non-segmented .....................17 17 a) Tube-like, ends tapered

................................nematode b) Arrow-like, with anterior jaws

........................... chaetognath

barnacle nauplius

Obelia medusa

radiolarian

diatoms

ctenophore

egg

diatom

trochophore larva

nematode

polychaete

chaetognath


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18 a) Shaped like shooting star or comet: rounded front and rear protruding "legs" …echinoderm pluteus b) Not as above...........................19 19 a) Has notochord and tail ........20 b) Not as above...........................21 20 a) Has large eyes, looks like

larval fish.............. larval fish b) Tadpole-like ......tunicate larva 21 a) Chain-like or segmented .....22 b) Not as above...........................24 22 a) Has bristles ............................23 b) No bristles; may be spiral or

circular .............chain diatom 23 a) Moves about ..........polychaete b) Symmetrical, non-motile

............................Chaetoceros 24 a) Body compact, spiny ............25 b) Not as above...........................32 25 a) Like a swimming mustache

.................. larval polychaete b) Not as above...........................26 26 a) Has spines radiating out from

central globular mass ............................. radiolarian

b) Not as above...........................27 27 a) Tiny, cup-shaped with spines

on lip & base; girdlegroove; spins ...............dinoflagellate

b) Not as above...........................28 28 a) Shaped as peach pit or shield;

paired legs; may have large antennae and eyespot ........29

b) Not as above...........................31

polychaete

echinoderm pluteus larva

larval fish

tunicate larva

chain diatoms

Chaetoceros

larval polychaetes

radiolarian

dinoflagellates


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29 a) Very large, twitching antennae ....... adult copepod

b) Lacking antennae ..................31 30 a) Shield with two "horns"

.................barnacle nauplius b) Shield lacks "horns"

.................copepod nauplius 31 a) Large and obvious eyespot;

perhaps looking shrimp- or crab-like ........................ decapod larva

b) Lacks large, obvious eyespot; looks like adult copepod viewed from the side with antennae at its sides ........adult copepod side view

32 a) Shell shape is tear-drop or

elliptical ..............................33 b) Not as above............go back to 1 33 a) Two-part shell .......................34 b) Spiral shell ..............................36 34 a) Looks just like transparent,

tiny clam ........larval bivalve b) Not as above...........................36 35 a) Has large compound eye and

two branched swimming appendages .........cladoceran

b) Lacks large compound eye, has jointed legs extending out of shell ...... cyprid larva of barnacle

36 a) Test of ever-larger chambers;

pores may be visible ........................ foraminiferan

b) Shell resembles a snail's; animal may be ciliated ....................larval gastropod

copepod

barnacle nauplius

copepod nauplius

decapod larvae

larval bivalve

Cladocera

cyprid

larval gastropod

foraminiferans


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Notes On Commonly-Seen Creatures

Barnacle larvae We think of them as sessile, but barnacles pass their early larval stages in the plankton. Like most crustaceans, their first larval stage is called a nauplius. They then molt into a mid-stage that settles to transform into an adult barnacle.

Bivalve larvae These look like transparent clams. They also have the band of beating cilia for locomotion, which is typical of many zooplankton.

Blastula After fertilization, an egg cell cleaves into two, four, eight, 16, and many cells. Using up yolk energy in this process makes the egg become a hollow ball of cells called a blastula. It is covered with cilia that make it spin fast, aiding diffusion of respiratory gases, nutrients, and wastes. Chaetoceros This chain diatom has with many long projecting spines. Its name means bristle (Chaeto) horn (ceros: as in the three-horned dinosaur, Triceratops). These protect them from predators and increase its surface area so it doesn't sink.

Copepods The most abundant animals in the plankton, these cows of the sea eat phytoplankton, and pass through a nauplius stage. They move with a jerky motion as their large anterior antennae thrust rearward like giant oars to propel them forward.

Decapod larvae Coming in many forms, these larvae usually have projecting spines, helping to protect them from predators by making them too sharp or too big to swallow.

Diatoms These single-celled marine plants have a two-part test of silica (glass), and often form chains that are straight, spiral, and may (as with Chaetoceros) be adorned with spines.

Dinoflagellates Tiny and single-celled, these creatures swim with one flagellum and spin on their axis with another that’s wrapped around their characteristic girdle. They often contain toxins and huge blooms produce "red tides". Bivalves eat them in great numbers in the warmer months: the resulting biological magnification of their toxins makes shellfish dangerous to eat and hence quarantined at these times.

Egg What every animal starts out as. They are spherical, and the nucleus, yolk, or oil droplets can typically be seen in them. Sometimes they are found in a cluster.

Foraminiferans These "window bearers" have perforated tests made of CaCO3 - chalk. Indeed, this is where chalk comes from. They are single-celled photosynthesizers.

Gastropod larva These have a light, transparent snail shell. Some pelagic species retain it into adulthood. Note the beating cilia used in locomotion.


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Larval fish Most fish start out as planktonic predators. Early stages will still have a colored yolk sac integral with the abdomen

Nauplius stage See Barnacles and Copepods.

Noctiluca A single celled creature that has animal and plant features. It is photosynthetic, but its "stalk" wiggles about actively, perhaps to increase diffusion by disrupting the surface boundary layer. Noctiluca (night light) is named for its bioluminescence. Their glow is seen at night when they are jarred by a physical disturbance such as a breaking wave or the bow wave of a boat. During heat spells they undergo "blooms"; population explosions which can turn the ocean's surface a cloudy pink color.

Obelia medusa Looking like a miniature jellyfish, as adults they settle benthically to form branching clonal colonies. Observe the contracting bell margin, a movement used for swimming. Oikopleura These organisms look like a fish larva and are equally large, translucent, but with a longer tail. They are filter-feeders, and while closely related to tunicates, they remain in the plankton.

Polychaetes These "many bristled" segmented worms are active and obvious, although their early larval stages can be confusing at first. Like a puppy's feet, their bristles are oversized for their bodies but they will grow into them. As noted, some look like gliding mustaches. Examine the apical ciliary band used for locomotion. In mature specimens, look for dorsal blood vessels pumping blood.

Radiolarians Back before the days of TV, radiolarians were a popular form of entertainment for marine biologists. Their projecting spines likely serve the usual functions: flotation and predator defense.

Rotifera These "wheel bearers" cruise through the water like small spaceships, propelled by wheel-like cilia clusters. Look for contraction of their jaws inside their body - it looks like a beating heart. Tintinnid Tiny and delicate, these are normally found dead in a plankton tow. But scan carefully for a live one and you can see the crown of cilia beating.

Trochophore A larval stage of both annelids and molluscs, which reflects their common ancestry. Characterized by a "top" shape and a band of cilia.

Tunicate larva Actually called a tadpole larva due to their striking similarity to a tadpole, they of course are quite similar to Oikopleura (see above). However, they are darkly pigmented. As with Obelia medusae, they will settle and become clonal colonies incapable of swimming.

plankton diversity

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