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Marine Biodiversity
Comparison of Biodiversity on Land and in the
Ocean.
Physical and chemical differences:
1. Greater density and viscosity
2. Sound transmitted 4 times faster
3. Water absorbs light
Results:
•
Larger animals suspended in H2O, plankton community,
suspension feeding
•
Less structural material (skeletons)
•
Autotrophs limited to the upper levels of the seas
•
Sonar, communication by animals over great distances.
Comparison of Biodiversity on Land and in the
Ocean.
Life history differences:
•Spawning- shed both female and male gametes. On Land,
plants shed male, but never female gametes.
•No pollinators in marine systems
•Little parental care (less)
Comparison of Biodiversity on Land and in the Ocean.
Structural and Functional differences:
1.
Lack of large plants. Dominant autotrophs are microscopic organisms.
2.
On land the structures habitat are often plants; we discuss redwood forests,
grasslands. In the seas, we discuss coral reefs, oyster beds, rocky reefs.
3.
So, dominant herbivores are also microscopic (copepods).
4.
Land plants are rarely entirely consumed; microscopic sea plants always
consumed entirely
5.
On Land: long-lived plants and short-lived fauna. In the Sea, short lived
plants and long-lived fauna
6.
Most large animals are carnivores
7.
Filter feeders confuse trophic levels, and animals often change trophic levels
in the seas.
Comparison of Biodiversity on Land and in the
Ocean.
Of species known today 85%
are terrestrial.
There are more phyla and
classes in the oceans (32 phyla
found in the sea, only 12 found
on land).
90% of all species belong to
one phyla- ??
Species are more evenly
distributed among phyla.
Some say only 2% to 15
%of the species on Earth are
marine.
21 phyla are exclusively
marine.
Where do you think
biodiversity is higherland or sea??
Comparison of Biodiversity on Land and in the
Ocean.
Estimated described marine species = 250,000
Estimated described land species = 1.5 million
Now, which do you think is more diverse??
Comparison of Biodiversity on Land and in the
Ocean.
•There are similar latitudinal gradients on land and sea: more
species near the equators
•In the Oceans, there are also longitudinal gradients: In the
Atlantic there are more species in the west. The Indo-Pacific has
the highest diversity which falls off as you move east and west.
•Most diverse community in the Oceans: CORAL REEFS
Biodiversity and Conservation of the Ocean:
The Speciation-Extinction Balance
Although local patterns of diversity are explained by shortterm dynamic interactions (disturbance, competition, etc…),
regional patterns of biodiversity are explained by the balance
of speciation and extinction.
•For a new species to develop, some degree of isolation
must occur.
•Extinction is caused by climate or environmental change,
diseases, and random fluctuations of population size.
Therefore, total number of species in a region is the net result
of the rate of speciation and the rate of extinction.
Biodiversity and Conservation of the Ocean:
The Speciation-Extinction Balance
In areas where the environment is unstable (large disturbances,
fluctuations in climate) newly isolated species are likely to go
extinct. The rate of extinction is higher than the rate of
speciation = low biodiversity. (areas of the Hawaiian Islands)
In areas with recent geographic isolation and a stable
environment, the rate of speciation is higher than the rate of
extinction = higher diversity. (Ex. Gulf of California)
In areas where with little recent geographic isolation, and high
stability, the rate of speciation and extinction would be lower
than the above example = lower diversity. (Ex. Florida coast)
The most diverse
regions of the sea:
Coral Reefs
Coral Reefs
Importance of Reefs
• Geological Importance: massive physical
structures (1950 km Great Barrier Reef), islands
and archipelagos, old and well-preserved fossil
communities
• Biological Importance: High diversity, many
phyla, organisms with both very wide and
sometimes very localized geographic
distributions.
• Economic Importance: shoreline protection,
harbors, fishing in developing world, tourism
Coral Reefs
• Compacted and cemented assemblages of
skeletons and sediment of sedentary organisms
• Constructional, wave-resistant features
• Built up principally by corals, coralline algae,
sponges and other organisms, but also
cemented together
• Reef-building corals have symbiotic algae
known as zooxanthellae; these corals can
calcify at high rates
• Coral reefs are topographically complex nad
make up the largest biogenic structures on
EARTH!
Great Barrier Reef from outer space
Coral Reefs - Limiting Factors
• Warm sea temperature (current problem
of global sea surface temperature rise)
• High light (symbiosis with algae)
• Open marine salinities usually
• Low turbidity - coral reefs do poorly in
near-continent areas with suspended
sediment
Coral Reef Biogeography
• Current division between Pacific and Atlantic
provinces
• Strong Pacific diversity gradient: (1) diversity
drops with increasing longitude, away from
center of diversity near Philippines and
Indonesia; (2) also a latitudinal diversity
gradient, with diversity dropping with
increasing latitude, north and south from near
equator
Tentacle
Mouth
Digestive
Filament
Septum
Pharynx
Septum
Gastrovascular
Cavity
Basal plate
Polyp of a scleractinian coral
Closeup view of expanded polyps of Caribbean
coral Montastrea cavernosa
Hermatypic vs. Ahermatypic corals
• Hermatypic: Reef framework building,
have many zooxanthellae, hi calcification
• Ahermatypic: not framework builders,
low calcification
Mass Spawning on Coral Reefs
• Most corals have planktonic gametes
• On Great Barrier Reef, reefs off of Texas: many
species of corals spawn at same time
• Facilitates gamete union, perhaps a mechanism to
flood the sea with gametes to avoid all being
ingested by predators
• Facilitiates release of gametes at time when
currents are minimal and gametes can unite
Biological Interactions
• Competition - shading, overgrowth,
interspecific digestion, sweeper tentacles
• Predation and grazing - some common coral
predators (e.g., crown-of-thorns starfish),
grazers (e.g., surgeon fish, parrotfish, urchins)
• Disturbance - e.g., storms, hurricanes, cyclones
• Larval recruitment - mass spawning, question
of currents and recruitment of larvae
• Disease - spread by currents, can cause mass
mortality of some species (e.g., common black
sea urchin Diadema antillarum in 1980s)
Predation and Grazing 1
• Role of predation on reefs poorly known
• Caribbean: Urchin Diadema antillarum feeds both
on sea grasses surrounding patch reefs and on
algae on reefs. Experimental removal results in
strong seaweed growth. Disease in 1980s
eliminated most urchins and this resulted in
strong growth of seaweeds
Predation and Grazing
100
1990s
80
Jamaican Coral
Reefs
60
40
20
0
1970s
20
40 60
80
100
Percent coral cover
Die-off of Diadema: Seems to have flipped Jamaican reefs into
alternative stable state (also a result of storm damage). Instead of
rich coral cover, you now have poor coral cover and lots of algae
Predation and Grazing 3
• Pacific Ocean: Crown-of-thorns starfish
Acanthaster planci feeds on corals
• Outbreaks all over Indo-Pacific starting
in 1960s
• Formerly rare, they changed behavior:
herding instead of dispersed, changed
from nocturnal to diurnal in feeding
Crown-of-thorns sea star
Predation and Grazing 4
• Explanations for Crown-of-thorns starfish
outbreaks?
1. Blasting of harbors in WWII, resulting in enhanced
sites for larval settlement
2. Overcollection by shell collectors of starfish’s main
predator, Giant triton Charonia tritonus
3. Storms, which wash out nutrients, stimulate
phytoplankton growth and enhance larval survival of
the starfish (some question this, as larvae can do well
Under starvation)