Aquatic Communities Midterm 2 Flashcards
What are the five primary requirments of Giant Kelp?
- High light
- Cool temperature
- High nutrient flux (N, P)
- Sufficient water motion
- Hard substratum
Kelp forests are most extensive on _____ margins of ocean basins.
eastern; this is caused by:
- Upwelling
- Ocean circulation patterns
Hermatypic
Term used to describe reef-forming corals, which usually contain symbiotic dinoflagellate called symbiodinium (i.e., zooxanthellae)
What are the 4 abiotic conditions that are necessary for reef-forming corals to persist?
- Annual mean water temperature > 18ºC
- High enough calcification rates require warm water (for CaCO3 deposition > erosion)
- High light levels
- Corals requre the nutrition from Symbiodinium via photosynthesis.
- No active reef formation at depths > 25-50 m (too little light)
- Clear water
- Turbidity reduces light and hinders photosynthesis
- Sediments smother coral polyps
- A reason why coral reefs are rare directly adjacent to large land masses.
- Constant marine salinity
- No estuarine or fresh water coral reefs
- Another reason for no large coal reefs near river mouths
Where are the tropics located?
Between the Tropic of Cancer at 23.5° N and the Tropic of Capricorn at 23.5° S.
Why is it warmer near the equator than toward the poles?
The solar rays become increasingly dispersed toward the polar caps due to the curvature of the planet.
The sun is directly overhead some time during the year between ___ N and ___ S of the equator.
23.5°
Reefs can expand beyond the Tropics at the _____ margins of oceans but remain very close to the equator at the _____ margins.
Western; Eastern
Air pressure moves from ____ to ____ pressure areas.
high; low
This macroscopic flux of air creates the air circuits that are responsible for surface winds.
Direction of surface winds alternate every ___° of latitude.
30
- The Coriolis effect causes the winds to seem to veer from our perspective.
Due to the Ekman Transport and Coriolis Effects, surface water moves at a ___° from the apparent wind direction.
45;
- Can also be thought of as 90° from the “original” wind direction before the Coriolis Effect’s influence has been considered.
Not considering the effect of continents, warm water flows toward the _____ near the equator and poles, and cold water flows toward the _____ in between the two.
west; east
Major land masses deflect warm water away from the equator at _____ margins of ocean basins, and deflect cool water toward the equator at _____ margins.
western; eastern
What are the 7 primary ways that coral reefs differ from temperate reefs?
-
Predominant biogenic structure
- Temperate reef: macroalgae
- Tropical reef: stony coral
- Coral reefs have a lower standing crop of macroalgae, despite the fact that macroalgae grows > 50 times faster than coral
- Greater number and diversity of herbivores (particularly fish)
- Detritus-based food web less important (little algal material left unconsumed by herbivores)
- Lower nutrient concentration in water
- More constant and benign environmental conditions
- Higher overall species diversity
Coral Reef
A wave-resistant structure built by Hermatypic corals (containing Symbiodinium) that are cemented together by secreted limestone.
- Forms when conditions allow CaCO3 deposition to be faster than erosion.
What are the two major categories of coral reefs based on location?
-
Coastal Reefs: elongate structures that border a continental coast.
- Form anywhere conditions are favorable
- Atolls: ring-shaped reefs around volcanoes in the open ocean. Uniquely formed
Describe Darwin’s Subsidence Theory of Atoll Formation and explain the steps involved.
A theory that accounts for the flux between upward coral growth and sea floor depression. The slow accumulation of coral limestone moves living surface upward and seaward. The steps are:
- Formation of a fringing reef
- Formation of a barrier reef that creates lagoons
- Formation of an atoll as the island subsides completely
Theory supported 100 years after proposition when scientists drilled holes in atolls and hit volcanic rock under hundreds of m of limestone.
What are the six main habitat zones within a barrier reef / lagoon system?
From shore to ocean:
- Fringing reef
- Patch reefs
- Lagoon pinnacle
- Barrier back reef
- Barrier reef crest
- Outer reef slope
What benthic organisms are largely responible for the extraordinary level of primary productivity within coral reefs?
- Symbiodinium (Zooxanthellae)
- Turfing and filamentous algae
Considering the low nutrient content of water surrounding coral reefs, how can primary production be so high?
- Incredibly efficient nutrient recycling (particularly between coral and Symbiodinium)
- Nitrogen fixation by blue-green algae (cyanobacteria)
- Herbivore-algal interactions
- Nutrient flux can be high due to high water flow
- New nutrient-laden water can access coral reef systems via terrestrial runoff to coastal reefs or though reef breakage from internal waves
Coral reefs support ___-___% of all species of marine fish.
25–33%
What are the main factors that promote high diversity within coral reef communities?
- High speciation and niche diversification
- Intermediate disturbance hypothesis (caused by such things as hurricanes)
- Biotic interactions that prevent competitive exclusion
- No keystone or frequency-dependent predator yet identified
- Mechanisms involving settlement in open populations
- Equal chance (lottery) hypothesis
- Storage effect
- Recruitment limitation hypothesis
What are two coral forms that demonstrate growth-susceptibility trade offs?
- Massive and encrusting forms
- Resistant to storm damage
- Slow growing colonies
- Slow to colonize
- Branching forms
- Highly vulnerable to storm damage
- Fast growing colonies
- Rapid colonizers (by asexual reproduction)
What growth strategy confers the best ability to compete for light with other corals?
Tall structures that grow quickly can exclude understory corals via shading.
What are mesenterial filaments and what are their function?
Mesenterial filaments are a coral’s digestive organs and are used for defense.
- The filaments are extruded onto a neigbor to digest enchroacing tissue
- Creates a buffer zone between adjacent colonies
Typically, _____ growing corals are most resistant to digestion, while _____ growing corals are the least resistant.
slow; fast
What is the greatest factor in promoting competitive exclusion of coral by algae?
Lack of herbivores
