Flatworm and horseshoe crab symbiosis

Last revised July 28, 2014

BIOL 181: Life in the Oceans – Lecture Notes

The text of these lecture notes for the Sea|mester courses Introduction to Marine Biology (v. 3.1),

by Chantale Bégin, Jessica Wurzbacher, Michael Cucknell, and Introduction to Oceanography

(v. 2.1), by Chantale Bégin and Jessica Wurzbacher, are used with the kind permission of the

authors. Images were researched and selected by UMUC BIOL and NSCI faculty.

Table of Contents

1. Introduction: Science and Marine Biology 2. Fundamentals of Ecology 3. Marine Provinces 4. Seawater 5. Tides 6. Biological Concepts 7. Marine Microorganisms 8. Multicellular Primary Producers 9. Sponges, Cnidarians, and Comb Jellies 10. Worms, Bryozoans, and Mollusks 11. Arthropods, Echinoderms, and Invertebrate Chordates 12. Marine Fish 13. Marine Reptiles and Birds 14. Marine Mammals 15. Intertidal Ecology 16. Estuaries 17. Coral Reef Communities 18. Continental Shelves and Neritic Zone 19. The Open Ocean 20. Life in the Ocean’s Depths 21. Marine Birds and Mammals in Polar Seas 22. Artificial Reefs 23. Marine Protected Areas 24. Impact of Tourism on the Marine Environment 25. The Global Trade of Marine Ornamental Species

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1. Introduction: Science and Marine Biology (The majority of the text below originally appeared as chapter 1 of Introduction to Marine Biology)

1.1. Science and Marine Biology

Oceans cover 71 percent of the earth, and affect climate and weather patterns that in turn impact

the terrestrial environments. They are very important for transportation and as a source of food,

yet are largely unexplored; it is commonly said that we know more about the surface of the moon

than we do about the deepest parts of the oceans!

Oceanography is the study of the oceans and their phenomena, and involves sciences such as

biology, chemistry, physics, geology, and meteorology. Marine biology is the study of the

organisms that inhabit the seas and their interactions with each other and their environment.

1.2. Brief History of Marine Biology

Marine biology is a younger science than terrestrial biology, as early scientists were limited in

their study of aquatic organisms by lack of technology to observe and sample them. The Greek

philosopher Aristotle was one of the firsts to design a classification scheme for living organisms,

which he called ―the ladder of life‖ and in which he described 500 species, several of which were

marine. He also studied fish gills and cuttlefish. The Roman naturalist Pliny the Elder published

a 37-volume work called Natural History, which contained several marine species.

Little work on natural history was conducted during the middle ages, and it wasn’t until the late

eighteenth century and early nineteenth century that interest in the marine environment was

renewed, fueled by explorations now made possible by better ships and improved navigation

techniques. In 1831, Darwin set sail for a five-year circumnavigation on the HMS Beagle, and

his observations of organisms during this voyage later led to his elaboration of the theory of

evolution by natural selection. Darwin also developed theories on the formation of atolls, which

turned out to be correct. In the early nineteenth century, the English naturalist Edward Forbes

suggested that no life could survive in the cold, dark ocean depths. There was little basis for this

statement, and he was proven wrong when telegraph cables were retrieved from depths

exceeding 1.7 km deep, with unknown life-forms growing on them. In 1877, Alexander Agassiz

collected and catalogued marine animals as deep as 4,240 m. He studied their coloration patterns

and theorized the absorption of different wavelengths at depth. He also noted similarities

between deepwater organisms on the east and west coast of Central America and suggested that

the Pacific and Caribbean were once connected.

Modern marine science is generally considered to have started with the HMS Challenger

expedition, led by the British Admiralty between 1872 and 1876. During a circumnavigation that

lasted 3.5 years, the Challenger sailed on the world’s oceans, taking samples in various

locations. The information collected was enough to fill 50 volumes that took 20 years to write.

The samples taken during the Challenger expedition led to the identification of over 4,700 new

species, many from great depths, and the chief scientist, Charles Wyville Thomson, collected

plankton samples for the first time.

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The Challenger expedition was the start of modern marine biology and oceanography, and is still

to date the longest oceanography expedition ever undertaken. However, modern technology has

allowed us to sample organisms more easily and more effectively and to quantify things more

accurately. Scuba diving and submersibles are used to directly observe and sample marine life;

remote sampling can be done with nets, bottles, and grabs from research vessels, and satellites

are used extensively for remote sensing.

1.3. Why Study Marine Biology?

1.3.1. To Dispel Misunderstandings about Marine Life

Though many people fear sharks, in reality 80 percent of shark species grow to less than 1.6 m

and are unable to hurt humans. Only three species have been identified repeatedly in attacks

(great white, tiger and bull sharks). There are typically only about eight to 12 shark attack

fatalities every year, which is far less than the number of people killed each year by elephants,

bees, crocodiles, or lightning.

1.3.2. To Preserve Our Fisheries and Food Source

Fish supply the greatest percentage of the world’s protein consumed by humans, yet about 70

percent of the world’s fisheries are currently overfished and not harvested in a sustainable way.

Fisheries biologists work to estimate a maximum sustainable yield, the theoretical maximum

quantity of fish that can be continuously harvested each year from a stock under existing

(average) environmental conditions, without significantly interfering with the regeneration of

fishing stocks (i.e., fishing sustainably).

1.3.3. To Conserve Marine Biodiversity

Life began in the sea (roughly 3-3.5 billion years ago), and about 80 percent of life on earth is

found in the oceans. A mouthful of seawater may contain millions of bacterial cells, hundreds of

thousands of phytoplankton, and tens of thousands of zooplankton. The Great Barrier Reef alone

is made of 400 species of coral and supports over 2,000 species of fish and thousands of

invertebrates.

1.3.4. To Conserve the Marine Environment

Each year, three times as much trash is dumped into the world’s oceans as the weight of the fish

caught. There are areas in the North Pacific where plastic pellets are six times more abundant

than zooplankton. Plastic is not biodegradable and can kill organisms that ingest it. Many

industrial chemicals biomagnify up the food chain and kill top predators. Some chemicals can

bind with hormone receptors and cause sex changes or infertility in fish. Understanding these

links allow us to better regulate harmful activities.

1.3.5. To Conserve the Terrestrial Environment

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Phytoplankton and algae use CO2 dissolved in seawater in the process of photosynthesis, and

together are much more important than land plants in global photosynthetic rates. Marine

photosynthesizers therefore have the ability to reduce the amount of CO2 dissolved in the oceans

and consequently in the atmosphere, which has important implications for the entire biosphere.

Many marine habitats, such as coral reefs and mangroves, also serve to directly protect coastlines

by acting as a buffer zone, reducing the impact of storm surges and tsunamis that may threaten

human settlements.

1.3.6. For Medical Purposes

Because the architecture and chemistry of coral is very similar to human bone, it has been used

in bone grafting, helping bones to heal quickly and cleanly. Echinoderms and many other

invertebrates are used in research on regeneration. Chemicals found in sponges and many other

invertebrates are used to produce several pharmaceutical products. New compounds are found

regularly in marine species.

1.3.7. For Human Health

Several species of plankton are toxic and responsible for shellfish poisoning or ciguatera.

Understanding the biology of those species allows biologists to control outbreaks and reduce

their impact on human health.

1.3.8. Because Marine Organisms Are Really Cool

Many fish are hermaphrodites and can change sex during their lives. Others, including several

deep-sea species, are simultaneous hermaphrodites and have both male and female sex organs at

the same time.

The blue whale is the largest animal to have ever live on earth, and has a heart the size of a

Volkswagen Beetle.

An octopus recently discovered and as of yet unnamed has the ability to mimic the color and

behavior of sole fish, lionfish, and sea snakes, all toxic animals, which greatly reduces its

likelihood of encountering predators.

1.4. How Is Marine Biology Studied? Using the Scientific Method

1.4.1. Science

The word science comes from the Latin (scientia) and means ―knowledge.‖ Science is a

systematic enterprise that builds and organizes knowledge in the form of testable explanations

and predictions about the world.

1.4.2. The Scientific Method

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The scientific method is widely used in the process of conducting science. Its general steps are to

make observations, form a hypothesis to explain the patterns seen, perform experiments to test

the hypothesis, and then draw conclusions (Figure 1.1).

Diagram showing the steps of the scientific method

by Erik Ong is licensed under CC BY-SA 3.0

Figure 1.1. Scientific method. Steps of the scientific method.

1.5. Review Questions: Introduction to Marine Biology

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1. What percentage of the earth is covered with oceans? 2. What was the driving force behind the initial studies into oceanography? 3. Who was the scientist on board the HMS Beagle in 1831? 4. What theories did this scientist develop? 5. In the early nineteenth century, who proposed that no life could live in the deep ocean? 6. Who was the chief scientist on board the HMS Challenger from 1872 to 1876? 7. What theories did Alexander Agassiz develop? 8. Why study marine biology? Give three reasons. 9. Explain the process of the scientific method.

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2. Fundamentals of Ecology (The majority of the text below originally appeared as chapter 2 of Introduction to Marine Biology)

2.1. Study of Ecology

Ecology (from Greek oikos meaning home) is the study of interactions of organisms with each

other and with their environment.

Ecosystems are composed of living organisms and their nonliving environment, while the

biosphere includes all of the earth’s ecosystems taken together.

The environment is all the external factors that act on an organism:

 physical (abiotic): temperature, salinity, pH, sunlight, currents, wave action, and sediment

 biological (biotic): other living organisms and their interactions, e.g., competition and reproduction

The habitat is the specific place in the environment where the organism lives; e.g., rocky or

sandy shore, mangrove, coral reefs. Different habitats have different chemical and physical

properties that dictate which organisms can live there.

Niche: what an organism does in its environment—range of environmental and biological factors

that affect its ability to survive and reproduce

 physical: force of waves, temperature, salinity, moisture (intertidal)

 biological: predator/prey relationships, parasitism, competition, organisms as shelter

 behavioral: feeding time, mating, social behavior, young bearing

2.2. Environmental Factors that Affect the Distribution of Marine Organisms

2.2.1. Maintaining Homeostasis

All organisms need to maintain a stable internal environment, even though their external

environment may be changing continuously. Factors such as internal temperature, salinity, waste

products, and water content all need to be regulated within a relatively narrow range if the

organism is to survive. This regulation of the internal environment by an organism is termed

homeostasis. The ability to maintain homeostasis limits the environments where an organism can

survive and reproduce. Each species has an optimal range of each environmental factor that

affects it. Outside of this optimum, zones of stress exist where the organism may fail to

reproduce. At even more extremes lie zones of intolerance, where the environment is too extreme

for the organism to survive at all.

2.2.2. Physical Environment

Sunlight

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Sunlight plays an essential role in the marine environment. Photosynthetic organisms are the

base of nearly every food web in the ocean and are dependent upon sunlight to provide energy to

produce organic molecules. Light is also necessary for vision, as many organisms rely on this to

capture prey, avoid predation, and communicate, and for species recognition in reproduction.

Excessive sunlight can, however, be detrimental to some life forms, as it may increase

desiccation in intertidal areas and induce photo-inhibition through pigment damage to

photosynthetic organisms in the very top of the water column.

Click the link to see a graph showing the ranges of environmental "comfort zone." Where planets

are concerned, the central location is referred to as the "Goldilocks Zone": not too hot, not too

cold range of conditions for organisms.

Temperature

Most marine organisms are ectotherms (meaning that they rely on environmental heat sources)

and as such are increasingly active in warmer temperatures. Marine mammals and birds, on the

other hand, are endotherms and obtain heat from their metabolism. To keep this heat, they often

have anatomical adaptations such as insulation. The temperature of shallow subtidal and

intertidal areas may be constantly changing, and organisms living in these environments need to

be able to adapt to these changes. Conversely, in the open oceans and deep seas, the temperatures

may remain relatively constant, so organisms do not need to be as adaptable.

Salinity

Salinity is the measure of the concentration of dissolved organic salts in the water column and is

measured in parts per thousand (‰). Organisms must maintain a proper balance of water and

salts within their tissue. Semipermeable membranes allow water but not solutes to move across

in a process called osmosis. If too much water is lost from body cells, organisms become

dehydrated and may die. Some organisms cannot regulate their internal salt balance and will

have the same salinity as their external environment; these are termed osmoconformers. These

organisms are most common in the open ocean, which has a relatively stable salinity. In coastal

areas where the salinity may change considerably, osmoregulators are more common.

Pressure

At sea level, pressure is 1 atm. Water is much denser than air, and for every 10 meters descent

below sea level, the pressure increases by 1 atm. Thus, the pressure at 4,000 m will be 401 atm,

and in the deepest part of the oceans at nearly 11,000 m, the pressure will be about 1,101 atm.

The pressure of the water may affect organisms that both live in or visit these depths. Organisms

found in the deep oceans require adaptations to allow them to survive at great pressures.

Metabolic Requirements

Organisms need a variety of organic and inorganic materials to metabolize, grow, and reproduce.

The chemical composition of saltwater provides several of the nutrients required by marine

organisms. Nitrogen and phosphorous are required by all photosynthesizing plants or plant-like

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organisms. Other minerals such as calcium are essential for the synthesis of mollusk shells and

coral skeletons. Although nutrients are essential for life, excessively high levels of nutrients in

sea water can cause eutrophication. This process of nutrient enrichment can lead to vast algal

blooms that eventually die and start to decompose. The decomposition may deplete the available

dissolved oxygen in the water, killing fish and other organisms.

2.3. Populations and Ecology

Population: a group of organisms of the same species that occupies a specific area. Different

populations are separated from each other by barriers that prevent organisms from breeding.

Biological community: populations of different species that occupy one habitat at the same

time. The species that make up a community are linked in some way through competition,

predator/prey relationships and symbiosis.

2.3.1. Population Range and Size

Since biologists can’t count every single individual in a population, they must instead estimate

size by sampling. One common way to sample a population is to count all individuals within a

few representative areas, and then extrapolate to the total number of individuals that are likely to

be in the entire range. Of course, this method only works well if the samples are representative of

the overall density of the population; if you happen to sample areas of exceptionally high

density, you would overestimate population size. Another common method to estimate

population size is the mark-recapture method. In this process, a certain number of individuals are

captured and tagged, then released back and allowed to mingle with the rest of the population.

After a certain period, a second sample is taken. As long as the marked individuals are dispersed

well within the population and haven’t suffered mortality from the first capture, the ratio of

marked: unmarked individuals in the second capture should reflect the ratio of marked: unmarked

individuals in the entire population. (Click the link to see a graphic demonstrating a simple mark

and recapture model for determining population density and distribution.) Therefore, we can

estimate population size with the following formula:

M m

----- = -----

N R

where:

N = Population size

M = Number of animals captured and marked in first sample

R = Number of animals captured in resampling event

m = Number of "R" that were already marked

2.3.2. Distribution of Organisms in a Population

Population density refers to the number of individuals per unit area or volume. In many

populations, individuals are not distributed evenly, and the dispersion (pattern of spacing among

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individuals) can tell a lot about the spacing of resources and interactions between individuals. A

clumped dispersion pattern may reflect variations in the physical environment, or a clumped food

source; a uniform distribution is often the result of strong intraspecific competition; random

dispersion reflects weak interactions among individuals.

2.3.3. Changes in Population Size

Populations change in size over time. They acquire new individuals through immigration and

births, and lose individuals through emigration and deaths. Different species can have varying

reproductive outputs, life span and generation times, all of which can affect how quickly

populations of that species can grow. Collectively, these traits and others that impact births,

deaths and reproduction are referred to as life history traits. On each extreme of a continuum of

life history, strategies are r-selected species (those that have short generation times, high

reproductive potential) and K-selected species (those that have much longer generation time and

are long-lived, but have low reproductive outputs and low population growth potential. The

typical traits of r- and K-selected species are outlined in table 2.1.

Table 2.1. Characteristics of Organisms that Are Extreme r or K Strategists

r

Unstable Environment; Density-

Independent

K

Stable Environment; Density-Dependent

Interactions

organism is small organism is large

energy used to make each individual is low energy used to make each individual is high

many offspring are produced few offspring are produced

organisms have early maturity organisms have late maturity, often after a

prolonged period of parental care

organisms have a short life expectancy organisms have a long life expectancy

each individual reproduces only once individuals can reproduce more than once in a

lifetime

organisms have a type III survivorship pattern,

in which most die within a short time, but a

few live much longer

organisms have a type I or II survivorship

pattern, in which most live to near the

maximum life span

Source: Adapted from University of Miami Department of Biology. Accessed July 15, 2014, from

http://www.bio.miami.edu/tom/courses/bil160/bil160goods/16_rKselection.html

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Populations change in size due to births, deaths, immigration, and emigration. Click here for a

graphic showing various factors that influence population size.

2.3.4. Population Growth

There are many ways in which a population can increase in size, including reproduction and

immigration. When a population has sufficient food or nutrients and is not greatly affected by

predation, it can grow rapidly in an exponential curve. However, no population can maintain this

growth forever—at some point resources become limited and slow down population growth

(either through lower birth rate or increased death rate). That population growth model is called

logistic growth. Here, the population levels off at size which the environment can sustain, known

as the carrying capacity of the environment. The carrying capacity is a dynamic point which may

fluctuate with changes in resource availability and predator behavior. Predator abundance often

mirrors prey abundance with somewhat of a lag in time. Click here to see a graph of exponential

(geometric) and logistic growth curves.

2.4. Communities

A biological community comprises the various populations of different species that interact

together in the same place at the same time. Organisms in a community interact with one another

in a variety of ways.

2.4.1. Niche

The niche of an organism is often described as its role in the community. It refers to the

environmental conditions and resources that define the requirements of an organism. The

broadest niche that an organism can occupy (defined mostly by resource availability and

tolerance to abiotic factors, e.g., pH, salinity) is called its fundamental niche. In reality,

organisms often occupy a smaller subset of their fundamental niche because of biological

interactions with other species such as competition and predation. This subset is called the

realized niche. Click the link to see a graphic indicating the difference between realized and

fundamental niches in nature and how these zones are determined.

2.4.2. Biological Interactions

Competition—occurs when organisms require the same limiting resources such as food, space

or mates. Interspecific competition occurs between organisms of different species, whereas

intraspecific competition is between organisms of the same species. Interspecific competition for

resources prevents different species from occupying exactly the same niche; if two species have

the same requirements, one will outcompete the other with several possible results: local

extinction (also known as competitive exclusion), displacement of the less successful competitor,

or selection for speciation that would lessen the competition.

To efficiently take advantage of a common resource, organisms may have unique anatomical and

behavioral specializations. This is commonly seen on coral reefs. For example, fairy basslets,

brown chromis, and soldierfish are all plankton feeders, but they do not directly compete with

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each other. Fairy basslets feed close to the reef, chromic feed in the water column, and

soldierfish feed mainly at night. Another strategy to lessen competition is to take advantage of a

resource not in demand by other species, e.g., angelfish are one of the only reef fish that eat

sponges.

Predator-prey relationship—may determine the abundance of different trophic levels. The

amount of vegetation in a given area may determine the number of herbivores, which in turn may

limit or be limited by the amount of primary consumers and so on and so forth up the trophic

ladder. In some situations, if the population of primary consumers becomes large and consumes

many of the herbivores, then the vegetation of the area may thrive in a process known as a

trophic cascade. This would be an example of a top-down process in which the abundance of

prey taxa is dependent upon the actions of consumers from higher trophic levels. Bottom-up

processes are functioning when the abundance or diversity of members of higher trophic levels is

dependent upon the availability or quality of resources from lower levels. For example, the

amount of algae produced determines the amount of herbivorous fish produced, and this in turn

determines the amount of piscivorous fish the ecosystem will support.

A keystone species is an organism whose effect on the biological diversity of an area is

disproportionate to its abundance. For instance, the ochre sea star (Pisaster ochraceus) in the

intertidal zone of western North America is a keystone predator and makes it possible for many

other organisms to live through its predation on the mussel. Without the ochre sea star, the

intertidal zone becomes dominated by mussels, which outcompete most other species.

Symbiosis—occurs where organisms develop close relationships to each other, to the extent that

one frequently depends on the other for survival. There are three types of symbioses:

(a) Mutualism: both organisms benefit from the relationship; e.g., corals and zooxanthellae; clown fish and sea anemones

(b) Commensalism: one organism benefits while the other is not harmed but doesn’t benefit; e.g., remoras and sharks

(c) Parasitism: parasites live off a host, which is harmed; e.g., worms in digestive tract

2.5. Ecosystems

Ecosystems include the biological communities and their physical environment. Examples of

ecosystems include coral reefs, mangroves, rocky shores, sandy beaches, estuaries, kelp forests,

or the open ocean. Since different ecosystems don’t exist in complete isolation from one another,

important interactions between different ecosystems often exist (e.g., many coral reef fish spend

their juvenile stages in nearby mangroves).

2.5.1. Producers (Autotrophs)

Most producers obtain their energy from the sun or some form of chemicals. The vast majority of

primary producers photosynthesizes using a pigment called chlorophyll, which absorbs the sun’s

energy and convert it into an organic molecule called glucose (C6H12O6). Other autotrophs may

be chemosynthetic, using the energy from chemical reactions to produce organic compounds.

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The glucose produced by autotrophs may be used by the organism for its own metabolic needs or

is available for higher trophic levels.

2.5.2. Consumers (Heterotrophs)

Organisms that rely on other organisms for food are collectively known as heterotrophs. Primary

consumers are herbivores, feeding on plants. Secondary consumers are carnivores feeding on the

herbivores. Tertiary consumers then feed on the secondary consumers and so on until the top

carnivores are at the top of the food chain. There are also omnivores, which feed on both

producers and heterotrophs, and then decomposers, which feed on all organic matter, breaking it

back down to simple molecules.

Click here for a graphic showing the difference between a terrestrial food chain and a marine

food chain.

2.5.3. Food Chains and Food Webs

Food chains are simple representations of the feeding relationships in an ecosystem. They show

one organism feeding on one prey while being devoured by one predator. In reality, these

interactions may be much more complex with one organism feeding on several prey at different

trophic levels while having several potential predators. This more complex relationship is called

a food web.

2.5.4. Other Energy Pathways

Not all energy pathways in the marine environment involve one organism feeding on another.

Through several inefficient feeding and metabolic mechanisms, organic matter is released into

the marine environment in the form of dissolved organic matter (DOM). These energy-rich

organic molecules can be incorporated by bacteria and other small plankton, which in turn are

eaten by larger organisms. In this way DOM, which would otherwise be lost to the environment,

is funneled back into the food web. Detritus from feces and decaying plants and animals is also

an extremely important food source for organisms in the marine environment. Detritivores, such

as bacteria and zooplankton in the pelagic zone or animals in the benthos, feed on this detritus,

returning energy back into the food chains.

2.5.5. Trophic Levels

Energy flows from the sun through producers to higher orders of consumers. Energy received

from photosynthesis, or from food, is temporarily stored until the organism is eaten or dies and is

decomposed. Thus energy storage in an organism can be portrayed as a trophic level. Primary

producers represent the first trophic level; primary consumers the second, secondary consumer

the third, and so on. Energy transfer between trophic levels is inefficient; primary producers

capture and store less than 1 percent of the sun’s energy. From there, an average of only 10

percent of the energy is passed on to successive higher trophic levels while the rest is used for

feeding, metabolism, reproduction, etc.

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2.6. The Biosphere

2.6.1. Distribution of Marine Communities

Marine communities and ecosystems can be designated by the regions of the oceans that they

inhabit (click here for a simple representation of the ecological energy pyramid, showing energy

loss at different trophic levels). In the water column, known as the pelagic zone, the area of water

overlying the continental shelf is known as the neritic zone, whereas the area above deep ocean

basins is known as the oceanic zone. The organisms that inhabit the pelagic division exhibit one

of two different lifestyles. Plankton drift with the currents, whereas nekton are active swimmers

that can move against the currents. The benthic realm can be divided into the intertidal area, the

continental shelf, and the deep. Organisms in the benthic division are either epifauna, organisms

that live on the sediment, or infauna, organisms that live within the sediment.

2.7. Review Questions: Fundamentals of Ecology

1. Define the term ecology. 2. Define the term ecosystems. 3. Give an example of abiotic factors affecting marine organisms. 4. Give an example of biotic factors affecting marine organisms. 5. Define the term habitat. 6. Define the term niche. 7. Define the term homeostasis. 8. What is an ectotherm? 9. What is an endotherm? 10. What does it mean if an organism is anaerobic? 11. What is eutrophication? 12. What is the difference between interspecific and intraspecific competition? 13. What is resource partitioning, and give an example on a coral reef? 14. Define a keystone predator and give an example of one. 15. Name and describe the three types of symbiotic relationships. 16. What is osmosis? 17. What are osmoconformers? 18. In which type of symbiotic relationship does one organism benefit and the other is not

harmed in any way but does not benefit?

19. Define the term population. 20. What is the carrying capacity of a population? 21. What does the term neritic refer to? 22. What is plankton? 23. What does benthic refer to? 24. What does pelagic refer to? 25. What is the difference between epifauna and infauna? 26. What is an autotroph? 27. What is the equation for photosynthesis? 28. What is the primary energy source for autotrophs? 29. What inorganic nutrients do photosynthetic organisms require?

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30. How do chemosynthetic organisms generate energy? 31. What do detritivores feed on? 32. What is the average percent of energy passed from one trophic level to another in a food

chain? What is the rest used for?

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3. Marine Provinces (The majority of the text below originally appeared as chapter 3 of Introduction to Oceanography)

3.1. Introduction

Why study the oceans? To understand "Life in the Oceans" (our course title), we need to

understand the ocean environments. They cover 71% of our planet (Figure 3.1), and play an

important role in regulating global climate through their interaction with the atmosphere.

Map data: Google, NASA

Figure 3.1. Pacific Ocean from space. Here is an image you probably have not seen before. This

is the Pacific Ocean, with California in the upper-right corner and New Zealand in the lower-left

corner. Perhaps our planet should be named "Water" instead of "Earth" because oceans cover

71% of the planet. The Pacific Ocean is the largest ocean.

Oceans have been present for about 4 billion years, and are thought to be where life originated.

Moreover, the majority of the human population lives by the sea, and modern societies use

biological and mineral resources from the sea. Understanding the oceans is critical for optimal

and sustainable harvest of these resources.

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Four major oceans have traditionally been recognized, with one additional ocean newly

recognized (Figure 3.2).

World map of oceans (English version) by Pinpin is licensed under CC BY-SA 3.0

Figure 3.2. The world's oceans.

The average depth of all oceans is 3.5 km. Pacific means peaceful or tranquil, but is inaccurately

named as the Pacific Ocean has numerous earthquakes and volcanoes along its edge (the Ring of

Fire). The Pacific is the oldest ocean, about 200 million years old, and the deepest, with an

average depth of 4.2 km. It is the largest (13,000 km wide) and covers 1/3 of the earth’s surface.

The Atlantic Ocean is half as old as the Pacific, and much smaller (6,600 km wide). It is 3.6 km

deep on average. The Indian Ocean is 7,000 km wide and has an average depth of 3.7 km. It is

confined to the Southern hemisphere. The Arctic Ocean is frozen but does not have any land

masses. It has an average depth of 1.1 km. Most oceanographers now also recognize the

Southern Ocean as a separate ocean. Although it is physically connected to the Pacific, Atlantic,

and Indian Oceans, this body of water, south of about 50 degrees south, is defined by the distinct

circulation of the Antarctic convergence.

Seas are bodies of salt water that are smaller than oceans. They have a direct connection to an

ocean and are often indentations into continents, or delineated by an island arc. There are many

seas around the world, including the Caribbean, Mediterranean and Red Sea

3.2. Determining Ocean Bathymetry

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Bathymetry is the study of the depth and shape of the bottom of the ocean. Depth can be

measured in various ways. The earliest depth readings were done using soundings: lowering a

heavy weight on a line until it reached the bottom. In the early 1900s, the first echo sounders

measured ocean depth by sending a sound signal to the bottom and measuring how long it takes

for its echo to return to the surface. Modern echo sounders have tremendously increased the

precision of the measurements, but these measurements are severely limited by ship time and

resources. For this reason, satellite remote-sensing is increasingly used to infer bathymetry.

Features on the ocean floor create sea level abnormalities above them, which can be measured

accurately by satellites after correcting for waves, tides and other interferences (Figure 3.3).

Because satellites can obtain much more data than ships, bathymetric charts derived from

satellite data are more much detailed than those produced by acoustics alone (Figure 3.4).

The Jason-1 Measurement System by NASA

is in the public domain in the United States.

Figure 3.3. The Jason-1 measurement system.

http://en.wikipedia.org/wiki/Satellite_geodesy#mediaviewer/File:Jason-1_measurement_system.gif
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Global seafloor topographic map by NOAA

is in the public domain in the United States.

Figure 3.4. Global bathymetric chart derived from sea surface abnormalities, which reveals

continental shelves and other shallow areas in pink, mid-ocean ridges in yellow-green and the

deepest parts of the ocean in blue.

3.3. Features of the Continental Margins

The ocean floor can generally be divided in three regions: continental margins, the ocean basins,

and mid-ocean ridges (Figure 3.5). The submerged edges of continents and the steep slopes that

lead to the sea floor, both made of continental crust, are the continental margins. Continental

margins may be passive or active. Passive margins are found where continents have rifted apart

(e.g., the Atlantic). Passive margins show little seismic or volcanic activity, and the transition

from continental to oceanic crust occurs on the same plate. They are typically wide. Active

continental margins, on the other hand, are associated with convergent plate boundaries and

subduction of oceanic crust beneath continental crust (e.g., Pacific Ocean). Active continental

margins are associated with earthquakes and volcanoes, and are typically narrow.

http://www.ngdc.noaa.gov/mgg/bathymetry/predicted/predict_images.HTML
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Diagram Representing Oceanic Basin by Chris_Huh

is in the public domain in the United States.

Figure 3.5. Oceanic basin features.

Continental margins are made up of several sections (Figure 3.6). The continental shelf lies right

at the edge of the continent and is nearly flat, with an average depth of 130 m. The width of the

continental shelf varies greatly, and is much greater in passive continental margins. Continental

shelves have been alternately submerged and uncovered through fluctuations in sea level during

glacial ages, and when inundated, they may accumulate sediment derived from land and carried

by rivers. The shelf break marks the abrupt change in slope from the nearly flat continental shelf

to the continental slope. The angle of the slope varies greatly. Continental slopes have submarine

canyons that were formed during periods of low sea level (Figure 3.7). These canyons are V-

shaped with steep walls and transport sediments from the shelves to the deep sea floor. Caused

by earthquakes or overloading of sediments on the shelf, turbidity currents are a fast moving

flows of sediments on the continental slope that may travel to speeds of 90 km/hr and carry

enormous quantities of sediments. At the base of the continental slope the accumulation of

sediment creates a gentle slope. This portion of the continental margin is known as the

continental rise, and is most prominent on passive continental margins. The continental rise

marks the beginning of true deep ocean basins.

http://commons.wikimedia.org/wiki/File:Oceanic_basin.svg
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Continental Shelf by the Office of Naval Research,

U.S. Department of the Navy, is in the public domain in the United States.

Figure 3.6. Continental margin, with continental shelf, slope, and rise.

Los Angeles Margin: Perspective View Looking North

by USGS is in the public domain in the United States.

Figure 3.7. Perspective view looking north over the San Gabriel (A) and Newport (B) submarine

canyons. The distance across the bottom of the image is about 17 km with a vertical exaggeration

of 6x. Both canyons formed when the San Gabriel River and the Santa Ana River flowed out

across the Los Angeles Basin and offshore shelf when it was exposed during lower eustatic sea

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http://walrus.wr.usgs.gov/pacmaps/la-persp3.html
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level. Newport Canyon begins less than 360 m from shore at the north end of Newport Harbor

and is composed of individual channels that braid down the slope over a width of about 9 km.

San Gabriel Canyon begins as a series of channels that join together midway down the slope and

then split into two channels at the base of the slope. The width of San Gabriel Canyon at "C" is

815 m and incises about 25 m into the slope. Lasuen Knoll can be seen in the foreground.

(Caption from USGS)

3.4. Features of Deep Ocean Basins

The deep sea floor covers a huge area of the oceans, and most of it consists of vast flat plains

known as the abyssal plains (Figure 3.8). Sediments carried from continental shelves are

eventually deposited on the deep sea floor, covering irregular topography and forming this flat

abyssal plain. Abyssal hills and seamounts are scattered throughout the sea floor. Abyssal hills

are short (less than 1,000 m high) and are a very common feature of the deep oceans. Most are

volcanic in origin. Seamounts are steep volcanoes that sometimes pierce the surface of the water

and become islands. Submerged seamounts that have a flat top are known as guyots, and were

formed by wave erosion when they were at the surface (Figure 3.8). Deep sea trenches occur

along convergent plate boundaries and typically have steep sides. The deepest part of the oceans,

known as the Challenger Deep, occurs in the Mariana trench off Japan and is 11,020 m deep.

Ocean trenches are associated with volcanic arcs, on the side of the overriding plate, as material

from the subducted plate melts and rises. These volcanoes can form island arcs such as the

eastern Caribbean or volcanic mountain ranges such as the Andes. The Pacific Ocean is lined

with such trenches, which create volcanoes and earthquakes around its perimeter, which has been

dubbed the Pacific Ring of Fire (Figure 3.9).

Image courtesy of Prof. Denny Whitford, UMUC.

Figure 3.8. Ocean floor features. Abyssal plains comprise about 40% of the total area in the

oceans.

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Pacific Ring of Fire by Gringer is in

the public domain in the United States.

Figure 3.9. Deep sea trenches are especially common around the perimeter of the Pacific Ocean,

but are also found in the Indian and Atlantic Oceans. The perimeter of the Pacific Ocean is

known as "The Ring of Fire" because of earthquake activity resulting from tectonic plate

movement.

3.5. Features of the Mid-Ocean Ridges

Mid-ocean ridges and rises are the longest continuous mountain chain on earth and are

approximately 75,000 km long. Mid-ocean ridges are typically 2–3 km high and have a central

rift valley along the axis of spreading (Figure 3.10). A prominent feature of the rift valley is

hydrothermal vents (Figure 3.11a and b). These unique features are created when water seeps

down in cracks in the crust, gains heat and dissolved substances and is released by through the

seafloor. Hydrothermal vents can reach temperatures of over 350 °C and contain energy-rich

inorganic compounds such as hydrogen sulfides which can be used as a source of energy by

specialized communities than inhabit the vents. Volcanic seamounts can also be associated with

mid-ocean ridges, as magma can escape through the oceanic crust by side chambers (Figure

3.12).

http://commons.wikimedia.org/wiki/File:Pacific_Ring_of_Fire.svg
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Age of the Sea Floor with Shaded Vegetation by

NOAA is in the public domain in the United States.

Figure 3.10. Sea floor bathymetric features and tectonic plate names. Mid-ocean ridges are

shown in red with a black line. Red indicates youngest sea floor age.

New Model for Water Dynamics of Deep-Sea Hydrothermal Vents

by Zena Deretsky, NSF, is in the public domain in the United States.

Black Smoker at a Mid-Ocean

Ridge Hydrothermal Vent by P.

Rona, NOAA, is in the public

domain in the United States.

Figure 3.11a and b. Structure and image of a hydrothermal vent.

http://sos.noaa.gov/ge/land/sea_floor_age/shaded_veg/4096.png
http://www.nsf.gov/mobile/discoveries/disc_images.jsp?cntn_id=110976&org=NSF
http://www.photolib.noaa.gov/htmls/nur04506.htm
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A Map of Seamount in the Arctic Ocean by

NOAA/NOS is licensed under CC BY 2.0

Figure 3.12. Seamounts rising from the seafloor. Color code indicates depth, with red and yellow

being the shallowest depth, and purple representing the deepest depths.

Mid-ocean ridges are cut by a number of fracture zones, parallel series of linear valleys

perpendicular to the ridge. Transform faults are the region of the fracture zone where plates

move in opposite direction (Figure 3.13). Earthquakes are frequent along transform faults.

https://www.flickr.com/photos/usoceangov/5369581627/
https://www.flickr.com/people/usoceangov/
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BIOL 181: Life in the Oceans – Lecture Notes