Coral and Reefs

I always think corals are a colourful plant because they seem they have ‘taken root’ on the seafloor. Those with hardened surfaces can even be mistaken for rocks. But corals are alive, and corals are in fact animals.

How many main types of corals are there?

There are two main classifications: the first are hard corals, which form reefs by forming a calcium carbonate exoskeleton they create for protection, the second is soft corals that are flexible and often resemble plants or trees. The latter do not have stony skeletons, don’t take part in reef-building, and are held together by a jelly-like goo called mesoglea and rigid, spiny structures called sclerites.

Food and habitat

The branch or mound that we often call ‘coral’ is actually made up of thousands of polyps, some no bigger than a pinhead, others to up 30cms in diameter. Each polyp has a saclike body and a mouth that is encircled by stinging tentacles. The polyp uses calcium carbonate (limestone) from seawater to build a hard, cup-shaped skeleton to protect the soft, delicate body of the polyp. All species of soft coral have eight tentacles that provide defence, capture food, and clean debris. Nematocysts, or stinging cells in the tentacles release an often fatal toxin to prey or threats. Reefs are a vital ecosystem, supporting an estimated 25 percent of ocean species.

What’s killing coral?

It’s the usual suspects – pollution, overfishing, illegal collection of coral, destructive fishing practices using dynamite or cyanide, and the global warming crisis are all things that are damaging reefs all around the world. Pollution can be caused by fuels and other chemicals leaking into the water and can be caused by dredging, coastal development, agricultural and deforestation activities, plus sewage treatment plant operations. Petroleum spills do not always appear to affect corals directly because the oil usually stays near the surface of the water, but if an oil spill occurs while corals are spawning, the eggs and sperm can be damaged as they float near the surface before they fertilise and settle.

Is it OK to touch coral?

Tempting though it may be, touching corals can remove their outer protective layer, spread infectious diseases, and expose them to foreign bacteria and oils from your fingers, which could negatively impact their health. They might sting too! The golden rule is ‘look don’t touch’ for both your safety and that of the coral. Corals that appear white have suffered from ‘bleaching’, meaning that their primary food source, microscopic algae called zooxanthellae has left when the coral is stressed. As the algae leaves, the coral fades until it looks like it's been bleached. And without the algae, the coral will die.

Why should we care about coral reefs?

We should care about coral because these reefs are essential to the health of our oceans and our planet. They provide a home and a source of food for many species of marine creatures. They protect coastlines from erosion and storms and play a vital role in regulating the earth’s climate by absorbing and storing carbon dioxide. Record-breaking marine heatwaves are causing mass coral bleaching in places like the Great Barrier Reef of Australia and on coral reefs globally. Since 2016 the Great Barrier Reef has suffered four mass bleaching events. In March 2022 91% of the Reef was impacted by bleaching, and it was the first time the Reef bleached during a La Niña weather event, which typically creates cooler, cloudier conditions. So yes, we should care, and UNEP (United National Environmental Programme) predicts that unless we reduce emissions, all of the world's reefs will bleach and be dead by the end of the century.

Did you know Portugal has a reef?

Off the coast of Albufeira, Lagoa, and Silves, lies one of the largest natural coastal reefs in Portugal, benefiting from its unique natural conditions and marine biodiversity, and is classified as a Marine Protected Area. Once part of the original Algarve coastline, the reef is believed to house 70% of the species indigenous to the coastline, as well as 45 species newly discovered in Portugal and, incredibly, 12 species newly discovered in the world.

Marilyn writes regularly for The Portugal News, and has lived in the Algarve for some years. A dog-lover, she has lived in Ireland, UK, Bermuda and the Isle of Man. 

Marilyn Sheridan