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 higher- land 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 short-term 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 ReefsImportance 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

Polyp of a scleractinian coral

Mouth

Pharynx

Septum

Basal plate

Tentacle

DigestiveFilament

Septum

GastrovascularCavity

Closeup view of expanded polyps of Caribbeancoral 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

Die-off of Diadema: Seems to have flipped Jamaican reefs intoalternative stable state (also a result of storm damage). Instead of rich coral cover, you now have poor coral cover and lots of algae

0 20 40 60 80 100Percent coral cover

100

80

60

40

20

Per

cen

t al

gal c

over

1990s

1970s

Jamaican CoralReefs

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 settlement2. Overcollection by shell collectors of starfish’s main predator, Giant triton Charonia tritonus3. Storms, which wash out nutrients, stimulate phytoplankton growth and enhance larval survival ofthe starfish (some question this, as larvae can do wellUnder starvation)