Wanderlust World Wanderlust World Coral reefs start with a microscopic larva and end, millennia later, as massive limestone structures visible from space. The process:
Most corals are broadcast spawners: on specific nights (cued by temperature, lunar cycle), colonies release eggs and sperm into the water. Fertilization produces planula larvae—tiny, ciliated, free-swimming organisms. They drift in the plankton for days to weeks, carried by currents.
A planula seeks a hard, clean substrate (bare rock, dead coral, rubble) with suitable light, flow, and low sedimentation. It secretes adhesive, attaches, and metamorphoses into a primary polyp (1–2 mm).
The polyp extracts calcium (Ca²⁺) and carbonate (CO₃²⁻) from seawater, precipitating aragonite (CaCO₃) as a basal cup (corallite). This is the reef's first grain of "bone."
The primary polyp divides repeatedly, forming a colony of genetically identical polyps connected by living tissue (coenosarc) over a shared skeleton. The colony grows upward and outward.
Over years, colonies of framework builders (branching Acropora, massive Porites, foliaceous Montipora) create a complex 3D lattice. Dead skeleton is colonized by coralline algae, sponges, and new coral larvae—cementing the structure.
As the framework rises toward the surface, zones develop: reef flat, crest, slope, lagoon. Biodiversity explodes. A mature reef may be thousands of years old (Great Barrier Reef: ~20,000 years on current shelf).
Key requirements: Warm (23–29°C), clear, sunlit, saline, nutrient-poor water; hard bottom; low sedimentation. Climate change (bleaching, acidification) now threatens every stage.