Coral bleaching revision qs

Some symbionts are more 'thermally tolerant' than others, what molecular differences might these tolerant algae have?

They might have a more stable D1 protein that doesn't break as easily under heat, or they might produce higher concentrations of SOD and APX to clean up the ROS before it leaks to the host.

Which coral morphologies are most susceptible to bleach first and which last?

most susceptible = fast, growing branching corals like acropora and pocillopora as have thin tissues and high metabolic rates (use of P fast).

least = slow growing massive corals like porites/ favia as have thicker tissues that can shade symbionts and larger lipid reserves to survive periods with no photosynthesis.

How do ocean acidification and coral bleaching interact?

Calcification Cost: OA forces corals to spend more energy (ATP) to maintain internal pH for skeleton building.

This "metabolic drain" leaves the coral with fewer lipid reserves and energy

When thermal stress occurs, the coral lacks the energy to run its antioxidant systems (to fight ROS), leading to faster bleaching and higher mortality rates.

What are the general bleaching susceptibility of atoll vs barrier vs fringing?

Atoll = high susceptibility in middle in the central lagoon water can become trapped, without tidal flushing continues to get hotter. Lagoon areas of barrier reefs are susceptible to bleaching as water is shallow and still so heats up quickly. Fringing reefs are generally lower as used to bad conditions as right next to coastline.

What is the difference between symbiont shuffling and symbiont shifting?

Why are 'Back-to-Back' bleaching events significantly more lethal than isolated events spaced several years apart?

Corals have not yet replenished their energy and lipid stores, leading to rapid metabolic exhaustion and death during second event. e.g. The GBR suffered mass bleaching in 2024 and again in 2025. This is part of the 4th Global Bleaching Event.

Why is the 2023-2026 period significant in the history of coral reef monitoring?

It makes the occurence of the fourth coral bleaching event, impacting over 60 countries and both hemispheres,

Why does clear white corals signal that the coral is still alive?

Living coral tissue produces a constant layer of mucus and has an active immune system that prevents anything from growing on it. It’s like a "non-stick" coating.

As soon as the coral tissue dies and this mucus isnt produced, that "non-stick" coating is gone. Within days algae will colonise it and settle on top.

Why is increased CO2 a double whammy problem?

Increased atmospheric CO2 acts as a dual threat to reefs: it functions as a greenhouse gas that traps infrared radiation, leading to marine heatwaves and coral bleaching, while simultaneously dissolving into the ocean to lower the calcium carbonate saturation state, hindering skeletal growth.