Marine Ecology Coral reefs

Global distribution of coral reefs

Productivity and diversity

Structure of coral

Coral anatomy

Zooxanthellae are within the gastrodermal layer lining the gastrovascular cavity.

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 coral’s nutrition comes from the zooxanthellae Oxygen Aids in calcification

Calcification Active transport of calcium from seawater into epidermal cells of coral occurs.  At peak of calcium deposition, a cell must transport 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.

Calcified coral skeleton

What does the coral animal provide to the zooxanthellae? Inorganic nutrients, especially nitrogen and phosphorus- containing compounds Carbon dioxide Location in the photic zone Protection

Role of coral in food web Primary producers Primary consumers Secondary consumers, and up Detritovores?

Reef building/structure Reef building  Spawning (sexual reproduction)  Settlement  Growth (asexual division)  Breakage  reef spread  Role of other organisms Reef breakdown  Abiotic  Biotic

Factors affecting reef growth Temperature Depth Salinity Sediment Wave action Nutrients

Paradox: low nutrients, high productivity Hypotheses  Efficient coupling between coral and its symbionts  Nutrients in particulates  efficiently processed by filter & deposit feeders  High flow rate of water over reef  high integrated amount of nutrients  Nitrogen fixation by cyanobacteria creates a source of nitrate

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