Lectures 14-15: Coral reefs Marine Biology Lectures 14-15: Coral reefs

Global distribution of coral reefs

Productivity and diversity

Structure of coral

Coral anatomy

Coral anatomy Zooxanthellae are within the gastrodermal layer lining the gastrovascular cavity.

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

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 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.

Calcified coral skeleton

Other coral basics Feeding Shape vs. depth

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

Factors affecting reef growth Temperature Depth Salinity Sediment Wave action Nutrients

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.

Reef structure Reef building Reef breakdown

Types of coral reefs Fringing Barrier Atoll (Darwin’s other theory…)

Pacific vs. Atlantic reefs Differences in diversity Differences in species composition Hypotheses to explain these differences

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