Transcript Ecosystems and Biodiversity

Marine Ecosystems and Biodiversity
•The connection between environment, biodiversity and
ecological niches
Learning Outcomes
• Describe shoaling and explain why
shoaling may be a successful strategy for
feeding, reproduction and predator
avoidance, with reference to tuna and
sardines
• Shoal - any group of fishes that remains
together for social reasons
• School - a polarized, synchronized shoal
(has coordinated, directed movements)
– schooling is an extreme form of shoaling
– fish move into and out of schools all the time
Shoaling and commercial fish
• Many commercially important fish shoal and this
behavior makes them more vulnerable to fishing
pressure and capture in large numbers
• In many commercial species the largest shoaling
occurs during migrations, when smaller shoals
join together.
• Some North Atlantic herring shoals have been
measured to be 279 million to 4,580 million m3
with densities of .5-1.0 fish per/m3
• Migrating mullet shoals in the Caspian Sea have
been documented 100 km long
Shoals and Predators
• One strategy is to attack at low light levels
• Another strategy is to swim along shoal
and pick off fish that are sick, don’t stay in
form, or make an error in responding
• More effective is the to attack in schools –
schooling fish cannot avoid another school
as effectively as they can a lone predator
How do Schools Work?
• Requires great deal of coordination among
individuals in the school
• Vision is primary sensory cue for
coordinating movement
• Use of optomotor reaction - individual
movement is coordinated with movement
of some other visually distinctive object e.g. a spot or a stripe
Functions of Schooling Behavior
1.
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3.
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increased hydrodynamic efficiency
increased efficiency finding food
increased reproductive success
reduced risk of predation
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Dilution and confusion effect
More eyes to detect danger
Functions of Schooling Behavior
• Hydrodynamic efficiency
– individuals obtain reduction in drag by
following in “slip-stream” of neighbors
– limited evidence in support of this
Functions of Schooling Behavior
• Reduced predation risk
– creates patchy distribution of prey - large
areas with no prey
– once school is found, individual risk of being
captured is reduced by dilution
– confusion of prey by protean displays,
encirclement, other behaviors
Functions of Schooling Behavior
• Feeding
– increases effective search space for the
individual (more eyes, separated by greater
distance)
– coordinated movements to help break up
schools of prey - analogous to pack behavior
in wolves - by tunas, jacks
Functions of Schooling Behavior
• Reproduction
– increases likelihood of finding a mate
– facilitates coordination of preparedness
(behavioral and pheromonal cues)
– facilitates arriving at right spawning site at
right time
Fish Behavior & Communication
• Shoaling
• A social grouping of fish
• Occurs throughout life in about 25% of fish
species
• Half of all fish shoal at some time
• Benefits of Shoaling
• Gives a predator many moving targets
– Confuses predators
– Increases chances at the individual level
– Increases food finding ability
• Keeps potential mates in close proximity
Fish Behavior & Communication
• Pods
• Tightly grouped school
• Move as a single unit (including making
quick turns)
• Makes the school appear like one large
organism
– Protection from predators
Liabilities of Grouping Behavior
• Increased likelihood of disease & parasite
transmission
• Becoming more conspicuous to some
predators
– Harvested more easily by man
Sortment
Fish sort by parasite load
-This is due to the parasites leaving black spots on the skin
of the fish
-When the fish have too many parasites on them they
become phenotypically different and end up standing out
from the rest of the school ….ie: the cootie effect
Fish sort by size
-Because of the “confusion effect”, they tend to swim with
similar size fish
-large fish tend to swim along the outside edges of the
school but move to the center when a predator was near
-With small fish the opposite was true. They tended to stay
near the center and then forced to the outside when a
predator was near by
-If a fish is dissimilar in size from the rest of the group they
tend to forage less when they are the large-odd fish
Holy Crap, there’s life there?
• Bill Nye interviews Bob Ballard
• Significance?
– Discovery of new marine ecosystems which
were independent of the photosynthetic food
chain
Chemosynthesis
• Prior to 1977, biologists thought that without the energy of
sunlight to support a food chain, organisms in the deep sea
ate only what debris fell from surface waters. Scarce food
meant that organisms were few and far between.
Deep sea is food limited
• Insufficient light below 250 m depths in
the ocean (the mixed layer).
– Reduced biomass
– Reduced diversity
– Little biogenic CaCO3 precipitation-nothing
but ooze
• The abyss as desert-(results of HMS
Challenger expedition)
Background geology
• Geologists knew that cold water sunk into cracks in the ocean
floor and hypothesized that this water was heated beneath the
ocean crust. During heating, the hot water would dissolve
minerals from surrounding rocks. The heated, mineral-laden
water, hypothesized geologists, would rise from the seafloor at
a vent.
What is a hydrothermal vent?
• At a hydrothermal vent, sea
water that has sunken into
cracks in the ocean crust and
been heated (sometimes to over
180 degrees Farenheit!) by the
interior of the earth escapes
through crust cracks back into
the ocean.
• Superheated water beneath the
oceanic crust often dissolves
minerals from nearby rocks. As
hot vent fluids meet cold ocean
water, minerals precipitate out
of vent fluids.
• Precipitating minerals
often give vent fluids
different colored “smoky”
appearances.
• Precipitating minerals can
fall out of vent fluids to
form “chimneys”(like the
one on the left) and other
formations on the sea
floor.
Geologists test a hypothesis
• In order to test their
hypothesis, geologists
decided send remotecontrolled equipment to
look for vents where
oceanic plates pulled
away from each other at
the Galapagos Rift.
• Since the temperature of
the deep sea varies very
little from 35.6 degrees
Farenheit, geologists
searched for small
changes in temperature.
Geologists find a vent!
• After temperature-sensitive equipment returned small
temperature changes at one site along the Rift, cameras were sent
to the same site and returned with pictures of heaps of clam
shells.
• Repeated submarine dives to the same site revealed temperatures
as high as 46.4 degrees and a variety of unusual organisms.
What are these thriving animals?
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Jones (1980) proposes a new phylum: Vestimentifera
Cavanaugh et al. (1981) prokaryotic cells in tubeworm sectionssymbionts?
The Base of the Food Web:
Sulfur-Oxidizing Bacteria
• Compared to the surrounding sea floor, upon which
organic matter rains from above, hydrothermal vents
boast a community of organisms that is 10,000 to
100,000 times denser.
The reason for this: the presence of sulfur-oxidizing
bacteria as a food source either directly or through a
kind of cooperative "agreement" between the bacteria
and a particular vent organism.
Tube worms and giant white clams
• Tube worms and giant
white clams are unique
because they do not have
a digestive tract. They
have no way of “eating”
food. Both organisms
harbor symbiotic
bacteria. The worms and
clams transfer hydrogen
sulfide and oxygen to a
special area of their body
filled with bacteria.
Through chemosynthesis,
the bacteria make
carbohydrates to fuel
themselves as well as
their larger hosts.
These bacteria are able to oxidize (remove
electrons) compounds such as hydrogen
sulfide and store energy in the form of ATP
(adenosine triphosphate), which is the
universal "energy" molecule in all
organisms, including humans.
These bacteria use this energy to transform
carbon dioxide into simple sugars and
other molecules, just like plants.
Nowhere is the importance of symbiosis
better demonstrated than in the giant tube
worm, Riftia pachyptila. When these
worms were collected and examined in
greater detail, some important parts were
missing.
These worms have no mouth, no gut, and
no anus. They are completely devoid of any
digestive system whatsoever.
The tubeworm provides all the chemicals
necessary for the bacteria to make food,
including sulfur, oxygen, and carbon
dioxide, and the bacteria manufacture
sugars or some other form of energy-rich
molecules that provide nutrition to the
tubeworm.
The unusual vent life forms were different from any others recorded by scientists to date.
A new age in deep sea biology and ecology had begun!
Spaghetti worms
How does a vent food web begin?
• In areas of the earth that receive sunlight or are near areas that
receive sunlight, photosynthesizing plants are the basis of the
food chain. Using the energy of the sun, plants turn water and
carbon dioxide into carbohydrates. Carbohydrates are energy
for plants and for the organisms who eat plants.
• Bacteria are the green plants of hydrothermal vents. Through a
process known as “chemosynthesis”, bacteria use the energy in
hydrogen sulfide dissolved in vent
fluids to join water and carbon
dioxide into carbohydrates. Vent
communities food chains are based
on these bacteria!
Who else is in the food web besides bacteria?
• Most deep sea animals can not tolerate the
chemicals or hot temperatures near vents.
Vent animals are unique because they can
withstand and even thrive upon conditions
that kill most life. Some vent animals are
related to more familiar organisms, but
some, like the fluffy ball that vaguely
resembles a dandelion, are not..
• Grazing vent animals include snails, crabs, and limpets.
These animals graze on bacteria. Suspension feeders such
as mussels, barnacles, and feather-duster worms remove
food from the water. One kind of predator is the
anemone. Anemones capture prey with their tentacles.
White crabs and brittle stars are examples of scavengers
that eat whatever live or dead animals and bacteria they
can find
Mussels
Feather-duster worms
How are vents populated?
• Vents are often far apart. They often exist for just a few decades
or years. New vents are populated very quickly.
• Vent bacteria live in deep ocean water and in pores of deep ocean
rocks all of the time in low numbers. When a vent pops up,
bacteria populations flourish.
• Hot water streaming out of vents often plumes for 200 meters
above the sea floor because it is less dense than surrounding cold
water. Plumes probably carry larva into nearby currents.
However, this still may not account for the great distances
between vents. Scientists continue to test other hypotheses that
consider “stepping stones”, or intermediate sites, where vent
animals may grow without a vent and release larvae.
Where are the vents and how many are there?
• Nobody knows how many vents exist or where they all are.
Hydrothermal vents are constantly being formed and destroyed,
and many parts of the deep sea floor have yet to be seen by
human eyes. Some of the known sites are marked on the map
below. Most occur on or near boundaries between tectonic
plates.
(f) Explain the meaning of the term succession and
describe examples, including the tube worms
Tevnia and Riftia.
• Succession: to the gradual process of change that
occurs in community structure over a period of
time.
• This can be illustrated by the change which occurs
in abandoned grassland. After a period of time,
shrubby perennial plants become established and
these are eventually replaced by tree seedlings,
giving rise to woodland. As the plant communities
change, there are corresponding changes in the
animal communities associated with them.
Succession
(f) Explain the meaning of the term succession and
describe examples, including the tube worms
Tevnia and Riftia.
• Succession also occurs around hydrothermal vents in the
deep oceans.
• 1st organisms to grow around a vent are bacteria  
small crustaceans, mollusks, crabs and fish  a complex
community consisting of many different species is
established.
• One of the first animal species to inhabit the area around a
hydrothermal vent is the tube worm Tevnia. This species is replaced by
the larger and faster growing tube worm Riftia. Tube worms form
symbiotic relationships with chemosynthetic bacteria, which provide
organic substances directly to the tissues of the tube worms.
• GOOGLE SCHOLAR Assignment
Tubeworm Succession
• Succession also occurs around hydrothermal vents in the
deep oceans. The first organisms to grow around a vent are
bacteria, which are followed by small crustaceans,
mollusks, crabs and fish. Eventually, a complex
community consisting of many different species is
established. One of the first animal species to inhabit the
area around a hydrothermal vent is the tube worm Tevnia.
This species is replaced by the larger and faster growing
tube worm Riftia. Tube worms form symbiotic
relationships with chemosynthetic bacteria, which provide
organic substances directly to the tissues of the tube
worms.
Succession in Hydrothermal Vents
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New vent forms at diverging plates
Chemosynthetic bacteria
Amphipods, copepods
Grazers/filter feeders: limpets, clams, mussels
Scavengers: vent crabs, worms, fish
Predators: vent crabs, octopi
Symbiotic with primary producers (bacteria): vestimentiferan
worms, giant clams
– 1. Tevnia jerichonana
– 2. Riftia pachyptilia
Longevity of vent itself estimated at years to decades
Deep Sea biota
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75% of sea floor is below 3000 m depth
Imported nutrients from photic zone
Seasonal pulses of organic matter
Seafloor communities low biomass but
surprisingly high biodiversity
• Most benthic organisms in the deep sea
(polychaetes, arthropods, molluscs, echinoderms)
survive on detritus in sediment
• Low biomass but high diversity of fish species
(why?): scavengers and predators
Factors Driving Methane Vent
(Cold Seep) Systems
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High pressure
Low temperature
Depth
Lack of sunlight
Lack of photosynthesis
Scarcity of food resources
Enormous volume of water further reduces encounter
probability
Counteracted by:
• Chemosynthetic bacteria (primary producers)
• Cold, mineral-rich water
• Location – advantages and disadvantages
Learning Outcomes
• Understand why extreme and unstable
environments tend to have relatively low
biodiversity, giving examples including
coral reefs (stable and not extreme), sand
on a reef slope (unstable), and
hydrothermal vents (extreme)
Tolerance and Need
• A proper balance of physical and biological factors
is important for the success of each organism and
the community.
• Different organisms have different tolerances for
specific factors and may be broadly or narrowly
tolerant of different conditions.
• Steno- is a prefix meaning “narrow”. It can be
used to describe organisms that have narrow
tolerances for specific factors, e.g. stenohaline.
• Eury- is a prefix meaning “wide”. It can be used to
describe organisms that have wide tolerances for
specific factors, e.g. eurythermal.
Diversity: richness, evenness & dominance
• Two communities with same
10 species;
• If we selected groups at
random from a & b, how
long would we have to
sample before we got all 10?
• What is the dominant species
in a, b?
• What happens to a & b if
each is affect by an elephant
disease?
(g) Understand why extreme and unstable environments
tend to have relatively low biodiversity, giving examples
including coral reefs (stable and not extreme), sand on a
reef slope (unstable) and hydrothermal vents (extreme).
• In general, environments that are unstable or extreme tend
to have a low biodiversity.
– Sand, for example, easily dries out and is easily eroded by wind
and water currents. Some organisms are able to survive by
burrowing into sand.
– The water surrounding hydrothermal vents is under very high
pressure and at a high temperature; relatively few organisms are
adapted to survive in these conditions.
– Coral reefs provide a stable and favorable environment for many
different organisms and have a correspondingly high biodiversity.
(h) Give examples of organisms that occupy specialized and
generalized niches, including coral-eating butterfly fish and tuna.
• Organisms with a specialized niche have
a narrow range of food requirements or
live in a specific habitat,
• those with a generalized niche can
exploit a wider range of food sources and
live in a wider range of habitats.
– Most species of butterfly fish feed on corals
and sea anemones. Many species are also
territorial and live closely associated with a
specific area of coral.
– Tuna feed on a range of different species of
fish, as well as squid and crustacean. Tuna are
also highly migratory fish, Bluefin Tuna, for
example, are widely distributed in the Atlantic
Ocean.
i) Explain why habitats with high biodiversity tend to
contain narrow ecological niches.
• Narrow niches tend to reduce the extent of overlap and therefore
reduce interspecific competition. Coral reefs have a high biodiversity
and include many species with narrow niches, including fish exploiting
a variety of different food sources such as corals, seaweeds, and small
animals living in the coral.
i) Explain why habitats with high biodiversity tend to
contain narrow ecological niches.
• High biodiversity means that many different species live
within one ecosystem.
• Each species of organism has its own niche within the
ecosystem; if niches overlap, one species will die out as a
result of interspecific competition.