Marine and Coastal Ecosystems Practice Test 2026 – The All-in-One Guide to Mastering Zones, Features, and Processes!

Unlock all questions

This demo includes only 20 questions. Upgrade to access hundreds of questions, flashcards, exam simulations, and disable ads.

Full question bankExam simulationsFlashcards

From $12.50Unlock all

Session length

1 / 20

Explain why coral bleaching occurs in the absence of zooxanthellae and what alternatives can support coral survival?

Without zooxanthellae, corals rely on heterotrophy but productivity and calcification drop; some corals can survive longer by capturing plankton, yet long-term survival is unlikely; recovery requires recolonization with symbionts.

Coral bleaching happens when corals lose their symbiotic zooxanthellae, which live in the coral tissue and provide most of the coral’s energy through photosynthesis. Without those algae, the coral must switch to heterotrophic feeding on plankton and organic particles to meet its energy needs. This can keep the coral alive for a while, but the energy from feeding alone is much lower than what the symbionts supply, so growth and calcification slow or stop. Some corals can persist longer by increasing plankton capture, but long-term survival without symbionts is unlikely. Recovery depends on recolonization or reacquisition of zooxanthellae, which restores the energy flow from photosynthesis and allows normal calcification and growth again.

Bleaching occurs because corals cannot photosynthesize; alternatives include heterotrophy; but long-term survival is guaranteed.

Bleaching happens due to pollution; alternatives include increasing nutrient input.

Corals without zooxanthellae cannot survive at all.