Chapter 2
MARINE ECOLOGY
I. Marine Environment: there are fewer marine species than land species because ocean
conditions are less variable than land conditions
A. Continental margin: place where most sea life is found due to higher nutrient availability
B. Upwelling: supports plants with nutrients that have come up from deep waters; it can also
hold more dissolved gases, because it is colder
C. Water color: green or yellow in coastal areas due to high organic material concentrations;
blue in open ocean due to low life and particulate concentrations
D. Light Sections
1. photic zone: light is visible here
a. euphotic zone (0-100 m): extends from surface to the compensation depth; thinner
where turbidity decreases light penetration (ex. coast)
i. critical depth: depth above which the total respiration equals the total
photosynthesis
i. compensation depth: depth where the rates of plant respiration and
photosynthesis are equal, so the net primary productivity is zero
b. disphotic zone (100-1000 m): zone where photosynthesis cannot occur, but light
is detected
2. aphotic zone (1000+ m): depths where there is no light
E. Life of the Shore: species are more soft-bodied as you go seaward from the shore
1. rocky shore: contains more life compared to any other shore type
2. supralittoral zone [spray zone] life: shelled organisms, such as the periwinkle snail,
isopods (rock lice, sea roaches), limpets
3. littoral zone life
i. high-tide zone: buckshot barnacles
ii. middle-tide zone: goose barnacles, mussels (form mussel beds), dog-whelk
carnivorous snail
iii. low-tide zone: mostly plants and seaweed/algae, crabs
iv. tide pools: these pools of water formed in depressions during a receding tide
include small fish, hermit crabs, sea urchins
4. sediment-covered shore (beach, salt marsh, mud flat): burrowing is common behavior
a. sandy beach: good for life because water and air can permeate through sand easily
i. inhabitants: bivalve molluscs (clams), annelids (lugworm), crustaceans (beach
hoppers, sand crabs), echinoderms (starfish, burrowing sea urchins),
meiofauna (small invertebrates that feed on bacteria; includes several phyla)
b. mud flat
i. inhabitants: eel grass, turtle grass, fiddler crabs
5. sublittoral zone life
a. rocky bottom: nudibranchs (sea hare), sea urchins, lobsters, oysters, starfish,
crabs, fishes
i. kelp forests: brown algae [phaeophytes] found in cold, nutrient-rich waters
ii. seagrass beds: found in the tropics
II. Basic Ocean Sections
A. benthic environment: ocean bottom; 98% of ocean species live here
1. subneritic province: sea floor on or above continental shelf (above 200 m)
a. supralittoral zone [spray zone]: region above high tide line; rarely covered with
water
b. littoral zone [intertidal zone]: region between high and low tide lines
c. sublittoral zone: region extending from low tide line to the edge of the continental
shelf (200 m deep)
i. inner sublittoral zone: goes down to the depth where plants no longer grow
ii. outer sublittoral zone: extends from edge of inner sublittoral zone to shelf
break
2. suboceanic province: sea floor below the continental shelf (200 m)
a. bathyal zone: sea floor between 200 and 4000 m; corresponds to continental slope
b. abyssal zone: sea floor between 4000 and 6000 m; corresponds to abyssal plains
c. hadal zone (in Greek mythology, Hades = the underworld): sea floor below 6000
m; only found in trenches; sea cucumbers are numerous at these depths
B. pelagic environment: open ocean water; more biomass because this is where the plankton
are
1. neritic province: ocean above 200 m
2. oceanic province: water below the shelf break
a. epipelagic zone (0-200 m depth): dissolved oxygen decreases abruptly below this
zone because there are no plants below these depths
i. oxygen compensation depth: depth at which oxygen production is equal to
oxygen consumption
ii. nutricline: depth zone where there is a maximum amount of nutrients; the
depth changes from season to season; its location affects the timing of algal
blooms
b. mesopelagic zone (200-1000 m depth): coincides with part of disphotic zone
i. dissolved oxygen minimum (700-1000 m): depth of minimum amount of
oxygen; occurs because deeper water is colder and can hold more oxygen, but
shallower water is the home to producers [autotrophs]
ii. deep scattering layer [DSL]: layer of water that reflects sonar, producing false
readings, because it has many organisms in it; the organisms migrate based on
the time of day, possibly to follow food, alter light exposure, or for
reproduction; deeper during the day (900 m) and shallower at night (100-200
m); this movement is called vertical migration [diel migration]
iii. fish in this zone have large, sensitive eyes
iv. bioluminescence is most common in this zone
c. bathypelagic zone (1000-4000 m depth): blind organisms
d. abyssopelagic zone (4000-6000 m depth): blind organisms
e. hadopelagic zone (6000 m and below): blind organisms
III. Freshwater Bodies
A. epilimnion
B. hypolimnion
IV. Terminology and Ecology Basics
A. species: group of interbreeding individuals that is reproductively isolated from other
species
B. population: group of individuals of one species in a particular area
C. community: members of multiple species living in an area and interacting
D. ecosystem: all the biotic (living) and abiotic (non-living) components of an area that
interact
E. ecotone: the transition between two different ecosystems; an ecosystem interface
F. biome: a collection of similar ecosystems; similar climates
G. trophic levels: classification of organisms based on where they get their energy from
1. producer: autotrophs; group with the greatest biomass normally, but in the oceans, the
biomass of producers is less than primary consumers’ biomass
2. consumers: heterotrophs that eat producers or other consumers; starts with primary
consumers, which eat producers, then secondary consumers, which eat primary
consumers, and so on
3. decomposers: mostly bacteria, these heterotrophs break down organic compounds
from waste or dead organisms into inorganic compounds to get energy
a. bacterial decomposition is slow on the sea floor
H. food web: diagram of all energy flow between organisms of a community
I. food chain: simplified linear diagram of energy flow from producer to final consumer
J. microbial loop: bacteria decompose detritus and are then eaten by consumers
K. symbiosis: dependent biological relationship between two organisms that one or both of
them need to survive
1. types of symbiotic relationships
a. commensalism (+ 0): only one organism is benefited; the other is not affected
significantly
b. mutualism (+ +): both members benefit
i. lichen: mutualistic relationship between fungi and cyanobacteria or algae
ii. clownfish-sea anemones: provide protection for each other; clownfish have
mucus that protect them from being stung by sea anemones
c. parasitism (+ –): one organism benefits at the expense of the host
L. keystone species: species that has a large impact on an ecosystem; if its population is
altered, it will affect many other species
M. life history patterns
1. r-selected: common to opportunistic species that have high birth rates but are not
competitive; r is the intrinsic rate of growth of a species
2. K-selected: common to equilibrium species that are competitive but don’t have high
birth rates; do well at the carrying capacity (K), the maximum population that can
be supported by the environment
3. growth curves
a. s-curve [logistic growth]: reaches a maximum asymptotically
b. j-curve [exponential growth]: grows faster and faster
V. Deep-Sea Habitats
A. hydrothermal vent communities
1. varieties: cold seeps (water is not hot), black smokers (contain metal sulfides),
hypersaline seeps (46 ppt), hydrocarbon seeps (bacteria do chemosynthesis with
methane)
2. inhabitants: giant clams, large mussels, giant tube worms, and white crabs
3. around black smokers, most organisms rely on a symbiotic relationship with
archaeabacteria, which do chemosynthesis using hydrogen sulfide gas [H2S] or
methane [CH4] as their energy source
B. brine pools
VI. Coastal Habitats: coastal water appears yellow-green because these colors are scattered by
algae; coral reefs and algae beds are the two most productive underwater ocean ecosystems,
but wetlands are the most productive marine ecosystems
A. lagoon: a shallow body of salt or brackish water partially or completely isolated from the
open ocean by a barrier island (or similar sand feature) or a coral reef (in an atoll);
protected from effects of tides; may be associated with an estuary, wetland, or reef
1. Laguna Madre: long, narrow, shallow, hypersaline lagoon off the coast of Texas that
has the opposite of normal estuarine circulation
2. inhabitants: fish, sea cucumbers, worms, molluscs
B. estuary: discussed more in “Coastal Geography and Waters;” ecological characteristics
include:
1. brown and green in color
2. consist of brackish water (mix of freshwater and saltwater) with an average salinity of
17 ppt
3. occur past the river delta, the part of the river that water flows from
4. low biodiversity, but high ecological productivity due to large amounts of nutrients
coming from river runoff and deep, cold water
5. it may provide a calm refuge from the open sea if it partially enclosed
C. wetlands: partially submerged, sheltered shore areas with lots of plant life and a water
table close to the surface, resulting in saturated ground most of the time; human
development destroys wetlands in the US at a rate of 8,100 hectares/yr (20,000 acres/yr);
salt marshes and mangrove swamps have slow rates of decomposition
1. benefits
a. remove pollutants from runoff
b. control floods
c. reduce erosion
2. salt marsh (30-65° latitude): contains a variety of grasses
3. mangrove swamp (0-30° latitude): contains mangrove trees, which have adapted to
survive in salty, hypoxic waters; their root structure [mangal] provides a home for
many other organisms and causes sediment to build up around them, which can lead
to the formation of an island or an extension of land
a. pneumatophores [mangrove knees]: tubular extensions from horizontal roots that
pop above the water’s surface and provide oxygen for the buried roots
b. aerial roots [prop roots] (see picture): prop the tree up and give it oxygen; these
extend from the trunk of the tree
c. Everglades, Florida: largest area of mangrove swamps in North America;
dominant species along the shores is the red mangrove
d. Sundarbans Mangrove Forest, India: largest mangrove ecosystem in the world
4. mudflat: ecosystem seaward of a salt marsh; inhabited by epipsammic algae,
including diatoms and dinoflagellates, that are adapted to grow on sediment particles;
covered during high tide but open during low tide
5. peat deposit: remains of marsh plants that get buried and can be burned later
D. coral reef: organically constructed, wave-resistant, mineral structure created by
carbonate-secreting corals (cnidarians); most productive and biodiverse marine
ecosystem; many reef organisms produce chemicals that are being studied for their
medical benefits
1. found only where temperatures exceed 18°C, between latitudes of 35°N and S, and
where there are few nutrients
2. inhabitants: reef-building corals, molluscs, foraminifers, algae, anemones, crustaceans
3. coral polyps form calcium carbonate (CaCO3) exoskeletons called corallites;
successive generations of cnidarians grow and produce limestone foundations
4. buttress zone: coral above 20 m depth with the most light and wave action
5. living conditions
a. low nutrients
b. high light transmittance
c. average monthly temperature must exceed 18° C
6. stages of development: theorized by Charles Darwin
a. fringing reef: youngest type of reef; borders coastline closely
b. barrier reef: reef separated from coast by lagoon; caused by the sinking of the
island from erosion or the rise of sea level
i. Great Barrier Reef (Australia): longest reef in the world; 2000 km long
c. atoll: oldest type of reef; caused by complete submersion of island due to further
sinking of island due to erosion or the rise of sea level; common in equatorial
Pacific; a shallow lagoon forms in the middle
i. Great Blue Hole: deep lagoon in an atoll east of Belize that is good for diving
E. shoreline habitats
1. sandy shores: low biodiversity, low productivity; most organisms in this ecosystem
are infauna, so they live in the sand
2. rocky shores: high biodiversity; have vertical zonation, which is determined by
predation, grazing, food availability, and ability to resist desiccation
VII. Biogeochemical Cycling [nutrient cycling]: cycling of nutrients through the biosphere,
lithosphere, and atmosphere
A. carbon
1. bicarbonate [HCO3-]: most common form of carbon in the ocean
B.
VIII.
A.
B.
C.
D.
E.
F.
2. calcification: calcium is combined with carbonate ions to make calcium carbonate for
a shell
nitrogen cycle: most processes are carried out by bacteria, such as cyanobacteria
1. nitrogen fixation: conversion of atmospheric nitrogen [N2] into other nitrogen
compounds, such as ammonia [NH3]
2. nitrification: conversion of ammonia [NH3] into nitrate [NO3-] and nitrite [NO2-]
Fisheries: most are found in upwelling regions above non-tropical continental shelves
top fishing nations
1. China
2. Peru: high yields because of local upwelling; anchovies are plentiful
3. USA
overfishing: damages marine ecosystems so that they cannot sustain populations, which
results in lower fishing yields later
1. maximum sustainable yield: amount of fish that can be harvested while still
maintaining a safe number of fish to reproduce
2. recruitment rate: rate of young fish becoming adults; highest mortality occurs in
larval stages
bycatch [incidental catch]: unwanted fish or other animals unintentionally caught by
fishers; they usually die; includes dolphins, sea turtles, and birds
1. dolphins were once used to locate schools of tuna, so many dolphins were killed by
tuna fishers because they were enclosed in nets; this is now illegal
fishing methods
1. long-line fishing: a long line with many hooks is dragged through the water with
floats
2. purse seine fishing: a net is drawn around a school of fish; mesh size depends on
target fish; high bycatch
3. trawling: dragging a net along the sea floor in order to get demersal and benthic
organisms; causes great damage to benthic environment; high bycatch
4. gillnet/driftnet fishing: a driftnet/gillnet is invisible to fish because it is very thin, so
fish swim through and get caught
5. cyanide fishing: cyanide stuns fish, which can be caught for aquariums; this greatly
damages ecosystems
6. dynamite fishing: using dynamite to stun fish
guano: excrement from birds that feed on fish; it is rich in phosphorus and nitrogen and is
used in fertilizer
aquaculture: the growth and harvesting of organisms in controlled water environments
1. mariculture [marine aquaculture]: cultivation of marine organisms, such as:
a. algae (seaweed)
b. bivalves (oysters, mussels)
c. crustaceans (shrimp, lobster)
d. fish (salmon, mullet, milkfish)
2. ocean ranching: rearing fish eggs in hatcheries, then releasing the young fish into the
sea; usually done with salmon
3. polyculture: advanced cultivation of many species in order to provide a range of
necessary ecological functions and increase efficiency
4. monoculture: simple cultivation of one species
IX. Other
A. biodiversity (relative) gives a good measure of the health of an ecosystem
B. algal bloom: rapid growth of algae populations
1. red tide: large abundance of harmful dinoflagellates that secrete toxins
a. saxitoxin: deadly neurotoxin produced by some dinoflagellate species, causing
paralytic shellfish poisoning
2. spring bloom: exponential growth of algae population in the spring due to greater
light availability; ends when nutrients are depleted
3. autumn bloom: lower-magnitude growth of algae populations due to nutrient
replenishment by strong trade winds; ends when sun goes away
4. dead zone: area of water with low oxygen because it has been used by decomposers
to decompose algal blooms
a. Mississippi River mouth: location of the most prominent dead zone in the US that
forms annually and grows bigger each year
C. dimethyl sulfide [DMS]: gas produced by plants at the ocean’s surface; causes the
characteristic smell of the sea
D. pollution: introduction of man-made substances or energy that harm the environment
1. eutrophication: the input of excessive nutrients into a body of water which leads to
high productivity; may cause algal blooms
2. oligotrophication: a reduced nutrient availability which leads to low productivity
3. bioassay: determination of the concentration of pollutants that harm marine life
4. bioremediation: method of using microorganisms to help clean up pollution
E. ecological efficiency: the ratio of energy obtained by a given trophic level to the amount
of energy available to that trophic level; averages 10% in nature; limits the size of
communities
F. cohort: one generation of a population or a group of organisms born together
G. mineralization: breakdown of organic materials into inorganic forms of elements; can be
done by decomposers or other processes
H. ocean productivity
1. gross primary productivity: rate of production of organic matter by photosynthesis or
chemosynthesis in a certain place in a given amount of time; primarily determined by
the light and nutrient availability
2. net primary productivity: gross primary productivity minus the rate of cellular
respiration done by the producers that produce the organic matter
3. for positive net primary productivity to occur, the mixing depth must be above the
critical depth
4. secondary productivity: rate of accumulation of consumer biomass
5. related concepts:
a. standing stock: number of organisms or biomass present in an area or volume at a
given time; it is called standing crop for plants
b. biological pump: movement of carbon and other nutrients from the euphotic zone
to deeper water and deep sediment; 1% of the mass accumulates
c. productivity near the poles is limited most by light availability rather than nutrient
availability; polar productivity is high in the summer because of this
d. productivity is low in the tropics because it’s limited by nutrient availability rather
than light availability, because nutrients are blocked from coming up by
pycnocline; tropical production is increased by upwelling; tropical water is blue
because it lacks organisms and nutrients
e. productivity in the temperate region is limited by light availability and is higher in
the summer
f. the centers of gyres are like deserts because they have relatively low productivity
due to low nutrient availability
I. Algal poisoning
1. paralytic shellfish poisoning [PSP]: human paralysis caused by eating too many
shellfish with saxitoxin in them
2. amnesic shellfish poisoning: condition caused by ingesting domoic acid from
shellfish, a toxin produced by certain diatom species; this poison causes birds to act
abnormal, which is what inspired Alfred Hitchcock’s film, The Birds
3. ciguatera: seafood poisoning that causes the most human illness; caused by eating
reef fish with dinoflagellate toxins
4. Pfiesteria: genus of algae responsible for massive fish kills, especially on the NC
coast; appears in large numbers due to nitrogen eutrophication
J. deepest captured fish came from 7230 m in the Kurile-Kamchatka trench
K. Taylor column: column of rotating water similar to an eddy that traps nutrients and
plankton above a seamount; it is caused by the coriolis effect and deflection of water
around the seamount