Is a walrus a homeothermic endotherm

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.