In a groundbreaking study published in Scientific Reports, an international team of researchers examined over 4,400 museum specimens from around the world, revealing that soft corals harbor two distinct diversity hotspots. One of these hotspots, stretching along the coasts of Madagascar and Southeast Africa, came as an unexpected discovery, challenging longstanding assumptions about coral distribution. Led by Catherine McFadden, a professor at Harvey Mudd College, this study marks the largest global survey of soft corals to date and offers fresh insights into the evolutionary history of marine ecosystems.
The complex world of soft corals
Unlike their stony counterparts, soft corals lack rigid skeletons, making them particularly challenging to identify. Scientists often rely on visual characteristics of polyps, yet many species display nearly identical growth forms. Gustav Paulay, co-author of the study and curator at the Florida Museum of Natural History, describes soft corals as a “taxonomic nightmare.” On the field, differentiating one species from another often seems impossible, as colonies are made up of similar-looking polyps with subtle variations.
Soft corals maintain structure through internal cavities that pump water, effectively creating a flexible liquid skeleton. Tiny calcium deposits, called sclerites, provide additional support, yet these sclerites vary greatly from one specimen to another. McFadden explains, “They’re called snowflakes because no two sclerites are the same.” This incredible diversity has long complicated attempts to catalog soft coral species accurately.
The role of DNA in uncovering diversity
Before the advent of DNA sequencing, researchers depended on sclerite morphology to distinguish species. However, appearances often proved misleading. “We would assume a species was widespread, but genetic analysis would reveal six or eight distinct lineages,” says McFadden. This highlights the hidden complexity of soft corals, where visual similarities can mask significant genetic differences.
Interestingly, some corals displayed different growth forms in varying environments, yet DNA analysis revealed no genetic distinction. Such discrepancies between morphology and genetics challenge traditional classification systems. Still, using DNA sequencing in this study allowed researchers to clarify evolutionary relationships and identify previously unrecognized diversity among soft corals.
Unexpected biodiversity hotspots
For years, scientists believed soft corals had a single diversity center in the Indo-Pacific. This new research shows they actually have two major hotspots. Unsurprisingly, one is the Coral Triangle, spanning parts of Indonesia, the Philippines, and Papua New Guinea—a region already famed for hosting over 70% of the world’s coral species.
The second hotspot, along the coasts of Madagascar and Southeast Africa, was a revelation. Long overlooked in coral biodiversity studies, this region is surprisingly rich, sometimes even rivaling the Coral Triangle. McFadden notes, “We sampled this area more thoroughly than the Coral Triangle, so there may be a sampling bias.” Nonetheless, the findings underscore the need to explore under-studied regions of the western Indian Ocean to understand their true biodiversity potential.
The ancient influence of the Tethys Sea
These findings also shed light on historical forces shaping coral distribution. Millions of years ago, the Tethys Sea spanned much of today’s continents, providing a continuous habitat for marine life. As continents drifted and the Tethys closed, coral reefs were forced into new regions, fragmenting once-connected ecosystems.
The emergence of the Indonesian archipelago dramatically shifted coral distribution. Paulay explains, “When the islands formed, reefs colonized them, and diversity moved along with the new geography.” Meanwhile, regions like Madagascar and East Africa became isolated, leading to independently evolving coral communities with high levels of endemism.
This study highlights how past oceans continue to shape modern marine life. Soft corals in isolated regions evolved separately for millions of years, giving rise to unique species adapted to their local environments. Understanding this deep evolutionary history is critical for conservation efforts, particularly as climate change threatens coral ecosystems worldwide.
The research offers a vivid reminder that even tiny, seemingly simple organisms carry a rich evolutionary story. It also challenges us to look beyond familiar biodiversity hotspots and explore less-studied regions, where undiscovered treasures of life may still thrive.
Have you ever thought about how ancient seas influence the life around us today ? Share your thoughts and experiences—what hidden corners of nature have surprised you the most ? Let’s start a conversation about the remarkable resilience and diversity of our oceans, and the lessons they hold for our future.
