174 The Open Sea
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THE OPEN SEA
Chapter Outline
LIFE IN THE OPEN SEA
Classification of Plankton
Taxonomic Groups
Motility
Size
Nekton
Invertebrates
Fish
Competing for Limited Resources
Remaining Afloat
Swimming Methods
Reduction of Sinking Rates
Avoiding Predation
Efficiency of Open-Ocean Food Webs
KEY CONCEPTS
ARE YOU STILL WONDERING?
Chapter Objectives
• Describe the different ways to classify plankton.
• Explain how and why plankton migrate.
Key Terms
epipelagic zone
seston
tripton
bacterioplankton
mesoplankton
megaplankton
holoplankton
meroplankton
salps
larvaceans
pyrosomes
labial flaps
Chapter Summary
1. Although the open sea appears uniform and without divisions, it can be divided into regions
2. The open sea lacks well-defined communities and is termed a pelagic ecosystem. Living
components of this ecosystem are the drifting plankton and strongly swimming nekton.
3. One of the challenges to life in the open sea is to remain afloat. Plankton and nekton have
4. The primary producers of the open sea are mainly phytoplankton. Even though the open sea
5. Our understanding of community production and dynamics continues to improve with the
application of new techniques for open-ocean studies.
Chapter Outline
I. Life in the Open Sea
A. Classification of plankton.
1. Taxonomic groups.
B. Patchiness in the open sea.
C. Plankton migrations.
D. Megaplankton.
1. Cnidarian zooplankton.
1. Invertebrates.
2. Fish.
a. Billfish.
b. Tuna.
II. Survival in the Open Sea
A. Competing for limited resources.
B. Remaining afloat.
1. Swimming methods.
a. Flagella, cilia, and jet propulsion.
C. Avoiding predation.
1. Benefit of being less conspicuous.
2. Reduced nutritional quality.
3. Safety in numbers.
a. Impact bubble—plastics in the ocean.
Chapter 17 177
Suggestions for Presenting the Material
1. Have students create a table organizing different planktonic organisms into
categories based on life history, size, and taxonomic group.
2. If students live near the coast, collecting plankton is an easy process, and examining
3. To help students recognize common marine larval forms, have them create
4. Have students create a concept map using open-ocean communities as the starting
Classroom Discussion Ideas
1. What is the adaptive benefit of vertical migration for the zooplankton that conduct
it?
2. Outline a typical open-ocean food chain, and contrast it with that of a coastal
upwelling zone.
3. What is the deep scattering layer, and how was it discovered?
4. Compare and contrast modes of locomotion in various planktonic organisms.
5. What would the global consequences be if plankton populations greatly declined
due to pollution or other human impacts?
Videos, Animations, and Websites
Videos
Ocean Drifters. (VHS, National Geographic, 58 min, 1997)
Program follows the travels of a young loggerhead turtle throughout the North Atlantic
The Blue Planet: Seas of Life (Open Oceans). (set of five DVDs, BBC, 2002)
David Attenborough narrates the Emmy-award winning documentary examining
Ocean Odyssey. (DVD, BBC, 2006)
Follows the lives of sperm whales as they travel across the ocean basins.
Wild Pacific: Endless Blue. (DVD, BBC, 2009)
Explores the large, expansive ecosystems of the world’s largest ocean.
Plankton: Ocean Drifters.
This Oceanic Research Group educational film takes viewers under the ocean to look at
Websites
National Marine Sanctuaries Media Library.
Searchable database of photographs and video clips from America’s marine sanctuaries.
Tagging of Pacific Predators.
Follow the real-time migrations and movements of tagged oceanic nekton through
How to Make a Plankton Net.
Easy-to-follow instructions for making a net to collect coastal samples.
Suggested Answers to End of Chapter Questions
Multiple Choice
1. b. photic zone
2. c. nekton
3. d. nutrients
Matching
1. d.
1. b.
Short Answer
1. What are some adaptations in open-ocean plankton that allow them to be productive
despite the nutrient-poor environment?
Adaptations of open-ocean plankton that allow them to be productive include:
2. What is marine snow, and what is its significance?
Marine snow is a fluffy, cotton-candy-like aggregate of bacteria and decomposed
3. What are some adaptations that help organisms in the open ocean remain afloat?
Adaptations for flotation include: structures to increase surface area and frictional
4. What aspects of reproduction in pelagic sharks indicate adaptations to life in the open
sea?
Internal fertilization is an adaptation that increases the likelihood of fertilization,
5. Describe some of the ways animals living in the open sea hide from predators.
Pelagic animals hide from predators with cryptic coloration (such as
180 The Open Sea
6. Describe some of the strategies animals use to increase their survival in the open sea.
Survival strategies of open-ocean animals include: high reproductive output
7. Describe how the upside-down lifestyle of the purple sea snail and the nudibranch
Glaucus has influenced their coloration.
Coloration of both these “upside–down” pleustonic organisms demonstrates
8. Describe how a swordfish feeds.
Swordfish feed by slashing their bills from side to side through schools of fish,
9. Describe how tunas are adapted for fast swimming.
Adaptations of tuna for fast swimming include: a keeled, lunate tail; finlets on the
10. Why is the photic zone of the open ocean not as productive as the photic zone of
coastal seas?
The low productivity in the open ocean is due to the lack of key nutrients (nitrogen
Thinking Critically
1. Why does it make good ecological sense for the largest sharks to be plankton feeders
rather than predators of other nekton?
It makes sense that the largest sharks (the basking shark and whale shark) are
2. The water of the North Atlantic Ocean is colder than that of the tropical Atlantic
Ocean. Do you think this difference affects the shape of phytoplankton living in the
two areas? Explain your answer.
In general, water density is inversely related to water temperature, and thus warm,
3. Why is it difficult to keep large tunas alive in public aquariums?
Tuna usually die in captivity since these pelagic animals are adapted for
4. What problems in feeding mechanics, digestion, physiology, or nutrition might be
encountered by predators that feed on gelatinous zooplankton? What additional
problems might they face in today’s seas with drifting bottles and plastic bags?
Predators on gelatinous zooplankton may experience the following nutritional
problems: Since gelatinous zooplankton are mostly water, there is little protein and
Suggested InfoTrac® Articles
“Ecosystem Engineers in the Pelagic Realm: Alteration of Habitat by Species Ranging
from Microbes to Jellyfish.” Breitburg, D.L., B.C. Crump, J.O. Dabiri, and C.L. Gallegos.
Integrative and Comparative Biology, (2010).