By Phebe Fidge
If you thought corals were warm-water spectacles exclusive to distant underwater seascapes, think again. Shellharbour scuba instructor Bob McKee has corrected many a tourist who's assumed it’s too cold for corals on the South Coast.
Local divers can attest to the wonders waiting in offshore kelp beds, from massive rays to weedy sea dragons. However, with a mask, fins and scuba tank you can also spot several species of hard and soft corals on the temperate reefs of the Illawarra.
Here are just two of the corals that adorn our coastline.
First up is small knob coral (Plesiastrea versipora), a hard coral that encrusts rocks and debris.
It has a wide distribution across tropical and cold waters of the Indian and Pacific Oceans, and can survive for hundreds of years! Small knob corals range in colour depending on the algae (called zooxanthellae) that they adopt into their tissues, providing the corals with the sugars they need to grow and reproduce. This symbiotic relationship is common to many coral species.
Pictured below is a small knob coral off the Gutter at Bass Point Reserve. If you look closely, you can see the coral polyps that make up the colony of animals inhabiting its skeleton. You may notice that they resemble little upside-down jellyfish and that is because they are closely related on the evolutionary tree.
Melithaea zimmeri is a kind of Gorgonian or “fan coral” (pictured at top). Branches fan out from flexible nodes on a central “trunk”, so these soft corals look like bushes exploding against the blue ocean in vivid reds and oranges. Their spectacular appearance makes them popular subjects for underwater photography and distinctive landmarks for navigating dive sites. Like many corals, they are also popular habitats for small fish, as their intricate structures offer protection from predators.
Corals are not only beautiful, but also incredibly useful! With the global average sea surface temperature expected to rise by up to 4.8°C by the end of this century, it will be important to detect changes in our beloved temperate reef systems.
Using corals as “warning systems” will help us better manage the impacts of climate change. Corals are sensitive to environmental conditions, which regulate their growth and internal composition. In this way, the skeletons of long-lived corals record historical climate information and provide clues as to how environments are changing.
Other clues can be found in the composition of coral communities. ‘Tropicalisation’ or replacement of temperate corals with warm-water species has been observed in Western Australian temperate reefs after repetitive marine heatwaves in 2010 to 2012. Research is needed to characterise the baseline condition of the Illawarra’s unique temperate reef systems and to monitor their responses to future environmental change.
Want to see them for yourself?
If you are ready to explore the corals of the Illawarra coast and meet some local legends, Shellharbour Scuba offers social dives every Saturday and Sunday (weather permitting) at 8.30am. Dive Near Me also offers weekly social dives at 8am on Sundays. Not a diver (yet)? Learning to scuba dive is one of the best things you will ever do. Become PADI-certified with a local provider and discover new blue horizons.
