Frequently Asked Questions
The most-asked questions about brain and merulinid corals.
What are brain corals, and why are they called that?
Brain corals are a group of reef-building stony corals whose colonies develop a deeply grooved, winding surface pattern that closely resembles the convoluted folds of a mammalian brain. The common name comes entirely from that distinctive topography, which is produced by the way individual polyps grow and divide over time.
Which taxonomic family do merulinid corals belong to?
They are members of the family Merulinidae within the order Scleractinia (stony corals). The family groups together several genera that share a massive growth habit, small calices, and that characteristic meandering surface ridges.
What are the main genera in the family Merulinidae?
The core genera most people encounter include Merulina, Favia, Pseudofavia, Diploastrea, and Pavona. Each differs in ridge spacing, polyp size, and colony shape, but all produce the familiar brain-like or lumpy boulder form.
Where in the world can you find merulinid corals?
They are distributed across tropical and subtropical shallow seas on every continent, with particularly diverse assemblages in the Indo-Pacific, the Caribbean, and the western Atlantic. Most species live on reef flats, fore-reef slopes, or lagoon floors at depths of roughly 1 to 30 metres.
How big can a single brain coral colony grow?
Many Merulinidae species form boulders one to two metres across, and some Diploastrea or Favia colonies in the Pacific have been documented exceeding three metres in diameter. Growth is slow—often only a few millimetres per year—so a large boulder can represent centuries of continuous polyp activity.
How do merulinid corals reproduce?
They use both asexual and sexual strategies. Asexually, colonies expand by budding new polyps or by breaking off fragments that settle elsewhere. Sexually, many species release clouds of eggs and sperm into the water column, a process called broadcast spawning, often timed to lunar or seasonal cues.
What role do brain corals play in a reef ecosystem?
As long-lived, massive framework builders, they create the three-dimensional structure that shelters countless fish, invertebrates, and algae. Their grooved surfaces also host specialized microbial communities and provide attachment points for other sessile organisms, making them keystone structural elements of coral reefs.
Are merulinid corals threatened, and by what?
Yes. Like most reef corals, they are vulnerable to mass bleaching driven by marine heatwaves, ocean acidification that weakens their calcium carbonate skeletons, and physical damage from storms or anchoring. In some regions, overfishing of herbivorous fish that keep algae in check further limits their ability to recover.
How can I tell a Favia from a Pseudofavia or a Merulina?
The distinction rests on subtle differences in ridge width, calice (polyp cup) size, and the arrangement of septa inside the calices. Favia tends to have broader, more irregular ridges; Pseudofavia shows finer, more regular meanders; Merulina often has a smoother, more continuous surface with fewer sharp ridges. A hand lens and a good regional key are usually needed for a confident ID.
Where should a newcomer start learning about brain and merulinid corals?
A good first step is to browse a regional coral identification guide for your local waters, then supplement it with the WoRMS (World Register of Marine Species) entries for each genus to see accepted names and synonymies. From there, watching time-lapse footage of polyp extension at night and reading a few papers on Merulinidae spawning ecology will round out both the visual and biological picture.