Marine Ecology

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Marine Ecology

• Coral reefs

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Global distribution of coral reefs
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Productivity and diversity
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Structure of coral
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Coral anatomy
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Coral anatomy

• Zooxanthellae are within the gastrodermal layer
  lining the gastrovascular cavity.

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What does the coral animal provide to the
zooxanthellae?

• Nutrients, especially nitrogen and
  phosphorus-containing compounds
• Carbon dioxide
• Location in the photic zone
• Protection

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What do the zooxanthellae provide to the coral?

• Organic molecules (carbohydrates, proteins, other
  organic molecules)
• End products of photosynthesis
• Radiolabelled C-14 experiments verify this
  transfer of organic molecules
• 98 of a corals nutrition comes from the
  zooxanthellae
• Oxygen
• Aids in calcification

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Calcification

• Active transport of calcium from seawater into
  epidermal cells of coral occurs.
• At peak of calcium deposition, a cell must
  transport 50-100 times its own volume.
• Calcium carbonate deposition is 14X greater in
  light than in dark, so role of zooxanthellae
  proposed to be important
• Highest deposition on sunny days at noon.
• Mechanism of coupling not well-understood.

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Calcified coral skeleton
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Other coral basics

• Feeding
• Shape vs. depth

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Role of coral in food web

• Primary producers
• Primary consumers
• Secondary consumers, and up
• Detritovores?

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Factors affecting reef growth

• Temperature
• Depth
• Salinity
• Sediment
• Wave action
• Nutrients

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Paradox low nutrients, high productivity

• Hypotheses
• Efficient coupling between coral and its
  symbionts
• High flow rate of water over reef integrated
  amount that flows over the reef is relatively
  high
• Nitrogen fixation by cyanobacteria creates a
  source of nitrate
• Nutrients in particulates are relatively high,
  and are efficiently sequestered by reef organisms.

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Reef structure

• Reef building
• Reef breakdown

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Types of coral reefs

• Fringing
• Barrier
• Atoll (Darwins other theory)

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Pacific vs. Atlantic reefs

• Differences in diversity
• Differences in species composition
• Hypotheses to explain these differences

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Key threats to coral reefs

• The scope of the problem
• Major threats (explained in some detail)
• Coral bleaching
• Overfishing
• Sewage and other pollutants
• Storms
• Implications of reef loss