Marine Biology Field Trip
Plankton Sampling
Introduction
To fully appreciate the complexities of marine ecosystems and their food webs we
should examine the often-overlooked organisms of the plankton. Plankton is simply
defined as organisms that are at the mercy of the ocean's winds and currents. These
organisms have limited powers of locomotion. One common misconception is that
plankton must be microscopic. It is true that most of what we will examine on this field
trip will be viewed with the use of a microscope, but there is plenty of macro plankton.
The Portuguese Man-O-War responsible for a painful sting is an example of large
plankton.
Plankton can be classified into two different types: phytoplankton and
zooplankton. Phytoplankton is the base of many marine ecosystem food webs and
vitally important. This assemblage of organisms is analogous to plants and grasses of
terrestrial habitats. By definition, phytoplankton is considered autotrophic - they create
energy through the process of photosynthesis. Chlorophyll is the crucial pigment
necessary for photosynthesis to occur. Just as most terrestrial vegetation contains green
chlorophyll (giving them a green color), phytoplankton contains chlorophyll of varying
colors. For example, the much-publicized Red Tides are toxic dinoflagellates that
contain red chlorophyll. When conditions are right, these microorganisms can bloom and
occur in such densities that they turn the water red. On our field trip today, the most
common phytoplankton representative will be diatoms. It should be re-emphasized that
phytoplankton is the base of marine ecosystem food webs. Again, just as terrestrial
plants and grasses have animals which graze upon them, phytoplankton provides
sustenance for our next group, zooplankton.
Zooplankton is considered heterotrophic - they obtain energy by eating other
organisms. For example herbivores eat autotrophs and carnivores eat other
heterotrophs. The zooplankton community is extremely diverse, every known phyla is
represented. To appreciate this assemblage, we need to further classify zooplankton into
two groups: holoplankton and meroplankton.
Holoplanktonic organisms spend their entire existence drifting in the plankton;
they are created and die in the planktonic community. Holoplanktonic examples include
diatoms (phytoplankton) and copepods (zooplankton). Copepods are analogous to
insects in their abundance; some scientists believe they are the most abundant animals on
earth. These will be the most numerous specimens we see on our field trip. Copepods
are important for another reason; they are the primary grazers of phytoplankton and
therefore are another important link in marine food webs.
Meroplanktonic animals spend only part of their lifecycle drifting in the plankton.
This is usually a developmental period typically called larvae. These larva are unique,
since they do not resemble the adult and require metamorphosis when they reach a
suitable habitat. As mentioned earlier, nearly all phyla are represented as meroplankton
and a single species can have multiple larval stages. Examples include the developmental
stages of fish, and countless species of benthic invertebrates (worms, clams, crabs, etc.).
Below is a table to summarize the differences between holoplankton and meroplankton.
Holoplankton
Spend entire life in the plankton
Examples: copepods, and diatoms
Meroplankton
Spend only part of life in the plankton
Examples: fish and invertebrate larvae
Plankton Collection
Plankton has been collected in the same manner for years - through the
deployment of nets. Like most sampling gear, there are different types for various
purposes. First, plankton nets can have an assortment of mesh sizes expressed in microns
(1 m = 0.001 mm.). Typically, smaller mesh sizes are used to collect phytoplankton,
and larger mesh sizes used for various sizes of zooplankton. Neuston nets are
rectangular plankton nets towed half in-half out of the water, and collect organisms in the
neuston layer (the top meter of the water column). On the DAN MOORE we will deploy
a tucker trawl, which is a multiple net gear. When the trawl is deployed, one net is
positioned open; once it has completed fishing, a messenger is sent to close the net. The
trawl is then moved to a different depth and an additional messenger deploys the second
net. For this field trip we will use a single opening plankton net. We will attach a planer
so the net will fish deeper in the water.
Regardless of the net type, plankton nets should be towed from the side of a ship
whenever possible. When dragged off the stern of a vessel there is the possibility of prop
wash interfering with the net.
Goals
On this trip you'll have an opportunity to view a host of marine plankton sampled
from the Cape Fear River. We will have several dissection microscopes to view the
collections. Unfortunately, there will not be enough scopes for everyone, so you will
have to share. Please view and draw several specimens and then give other students a
chance while you attempt identification using the field guides provided. Attached to this
lab are identification boxes for your drawings.
The grading for this lab is as follows:
A - 6 drawings and identifications
B - 5 drawings and identifications
C - 4 drawings and identifications
D - 3 drawings and identifications
F - 2 or less drawings and identifications
Extra space has been added for additional information (Class, Order, Family, Genus,
Species), if it can be ascertained. If the review questions are not complete, one letter
grade will be subtracted from your lab grade. Complete sentences are required.
Drawings are required to be as detailed as the following:
Barnacle Larvae
Cydippid
Calanoid
Copepod
Crab larvae
Megalop
Medusa
Zoea Crab Larvae
Mysid Shrimp
Review Questions
1. During our sampling trip on the MARTECH which microscope type did we utilize
the most?
2. Ideally, plankton nets should be towed from what area on a ship? Why?
3. Briefly, describe what a neuston net is and what area of the water column it samples.
4. What units are used when measuring the mesh size of plankton nets?
5. What is the difference between meroplankton and holoplankton? Give examples of
each.
R/V MARTECH I
ESTUARINE / NEAR SHORE RESEARCH VESSEL
The R/V Martech I was acquired from Federal Surplus in December of 1994. Beginning
in January 1995 the vessel underwent a complete overhaul and conversion into a research
vessel. The conversion was a school project involving the Marine Technology program
students and staff as well as students in several other programs (welding, electrical,
machining, engineering and boatbuilding) at CFCC.
DESCRIPTION:
SPECIFICATIONS
53’ welded aluminum catamaran
17’ beam
34 gross tons, 27 net tons
4’ draft
PROPULSION:
Twin Detroit Diesel 671’s
Cruising Speed - 10 knots
FUEL CAPACITY:
720 gallons
ELECTRICAL:
15 KW generator for AC power
12 VDC system
Clean power for computers & electronics
EQUIPMENT:
Compass
GPS
DGPS
Radar
VHF w/ hailer & intercom
Digital & paper fathometers
Meteorological system
Cellular phone
WINCHES/DECK GEAR:
Anchor windlass
Stern deck capstan
Hydraulic trawl winch, “A” frame & light duty davit
FACILITIES:
Interior is heated & air conditioned
150 sq ft Interior lab space [10’ x 15’]
180 sq ft Bow work deck [1l’x17’]
300 sq ft Aft work deck [18’xl7’]
Small refrigerator
Microwave
Head. No shower facilities
CAPACITY:
20 passengers
Phylum
Drawing:
Common Name
Holo or Mero?
Phyto or Zoo?
Additional Information:
Phylum
Drawing:
Common Name
Holo or Mero?
Phyto or Zoo?
Additional Information:
Phylum
Drawing:
Common Name
Holo or Mero?
Phyto or Zoo?
Additional Information:
Phylum
Drawing:
Common Name
Holo or Mero?
Phyto or Zoo?
Additional Information:
Phylum
Drawing:
Common Name
Holo or Mero?
Phyto or Zoo?
Additional Information:
Phylum
Drawing:
Common Name
Holo or Mero?
Phyto or Zoo?
Additional Information: