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What are coral reefs and why are they so important?

If you’re an avid SEVENSEAS reader, you’ve probably dived or snorkelled beautiful coral reefs around the world; admiring their stunning colours and abundance of marine life. But how much do you actually know about coral reefs? What are they and why are they so important? We asked the team at The Reef-World Foundation to tell us more…

Coral reefs might look like colourful rocks or dazzling underwater plants but they’re actually a colony of animals all living and working together – a bit like the ants or bees of the underwater world.

One individual coral animal – called a coral polyp – is a tiny creature that looks a little like an upside-down jellyfish. It falls under the scientific classification Cnidaria, made up of animals which use special stinging cells – called cnidocytes – to capture their prey. In corals, these cnidocytes are located in their tentacles. The coral polyp can move, feed and reproduce; and it lives in a coral colony, which is a large group made up of lots of polyps, in the same way you or I might live with family members. That colony lives in a group with lots of other colonies (like a human town or neighbourhood), which is called a coral reef.

There are lots of different types of coral. Hard corals have hard skeletons and provide the building blocks of the entire reef ecosystem. Although they look like rocks, these slow-growing corals are fragile and can take a long time to recover from damage. Soft corals, which tend to look more like plants, have no skeleton – you’ve probably seen them wafting in the current.

Corals, you’ll remember, have special tentacles with stinging cells which they use to capture food. They prey on zooplankton: tiny animals that drift along in the water. At night, a coral will grab the zooplankton with their tentacles and pull them into its mouth. But this only accounts for 20% of a coral’s food source.

For the rest of its food, coral relies on a microscopic algae called zooxanthellae. These two organisms have a very special, symbiotic relationship: the zooxanthellae live inside the coral skeleton – benefitting from the shelter it receives – where it uses photosynthesis to convert sunlight into food and shares this with the coral. It’s actually the zooxanthellae which gives the coral its bright and beautiful colours.  Without the zooxanthellae, the coral would not only lose its colour but also the majority of its food source.

That’s what happens when coral bleaches. These sensitive zooxanthellae can only survive at very specific temperatures. Warming waters can stress the algae and trigger them to leave the coral looking for a more suitable home. If they don’t come back, the coral won’t have enough food and will die.

Bleaching is happening in oceans around the world. If current trends continue, it’s predicted severe bleaching will occur every year on 99% of the world’s coral reefs within the next 80 years. This is not just a problem for the coral because coral reefs are the building blocks of the entire marine ecosystem – they provide food and shelter for many fish and other types of marine life. In fact, they’re often called “the rainforests of the sea” because they’re one of the most valuable ecosystems on the planet. Despite only taking up less than one quarter of 1% of the marine environment, coral reefs are home to more than 25% of all known fish species. Put simply, without them, the ocean would be in trouble.

And if the ocean is in trouble, so are we. Reefs provide many local communities with fishing grounds; providing them with food and livelihoods. As well as fishing, there are a huge number of diving, snorkelling and other tourism-related jobs that exist thanks to coral reefs. Not to mention the protection they offer from coastal storms – which themselves are becoming more frequent thanks to climate change.

Whether or not you live by the ocean, coral reefs are a hugely important part of our planet – let’s work together to protect and conserve them for future generations.

The Reef-World Foundation leads the global implementation of the UN Environment’s Green Fins initiative, which focuses on driving environmentally friendly scuba diving and snorkelling practices across the industry globally. To keep up with our latest news and developments, please follow Reef-World on Facebook, Instagram and Twitter. You can also follow the Green Fins initiative on Facebook, Instagram and Twitter to keep up to date with new materials, updates and sustainability insights from Green Fins members.

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Aquacultures & Fisheries

What the Fish Are Telling Us About Marine Biodiversity and Ocean Health Around Tenerife

Tenerife sits in the eastern Atlantic like a crossroads. Positioned roughly 300 kilometres off the northwest coast of Africa, the island intersects the paths of the Canary Current, warm subtropical surface waters, and the deep cold upwellings of the Atlantic basin. The result is one of the most ecologically productive marine environments in the northern hemisphere, a place where bluefin tuna from the Mediterranean share waters with tropical reef species and migratory whales from the polar ocean. What lives in these waters, and how those populations are changing, tells us something important about the health of the broader Atlantic system.

The Anatomy of an Exceptional Marine Environment

The waters around Tenerife support approximately 400 species of fish, a number that reflects the unusual convergence of marine provinces that the island straddles. [1] Its seafloor topography is dramatic: the island drops away steeply from the coast, reaching oceanic depths within just a few kilometres of shore. This proximity of shallow coastal habitat to very deep water creates conditions that support both reef-associated species and the large pelagic predators of the open ocean, sometimes within sight of the same beach.

In the deeper offshore waters, the Canary Islands are internationally recognised as one of the finest big game fishing destinations in the world, and for good reason. Atlantic bluefin tuna (Thunnus thynnus) pass through in their thousands between December and April, migrating northward toward Mediterranean spawning grounds. These are not small fish. Individuals regularly exceed 250 kilograms, and the largest bluefin recorded in these waters approach 450 kilograms. [2] Their spring passage coincides with dense schools of Atlantic mackerel (Scomber scombrus) and smaller baitfish that concentrate near the island, drawing the giants in from the open Atlantic.

Blue marlin (Makaira nigricans) and white marlin (Kajikia albida) are present from spring through autumn, the two billfish species that define Tenerife’s reputation among dedicated sport anglers. Spearfish (Tetrapturus belone) inhabit the deeper offshore trenches. Yellowfin tuna (Thunnus albacares), bigeye tuna (Thunnus obesus), wahoo (Acanthocybium solandri), and mahi-mahi (Coryphaena hippurus) complete a pelagic assemblage that few locations outside the tropics can match. [2]

Closer to shore, the volcanic reef structures support a different community. Atlantic amberjack (Seriola dumerili), barracuda (Sphyraena viridensis), grouper (Epinephelus spp.), and European sea bass (Dicentrarchus labrax) inhabit the rocky substrates, alongside numerous wrasse species, bream, and moray eels. The deeper sandy bottoms, where slow-jigging techniques are most effective, hold species less visible to tourists but central to local gastronomy: red porgy (Pagrus pagrus), sargo (Diplodus sargus), and various sparids that have been fished by Canarian communities for centuries. [3]

Reading the Signals: What Is Changing

The richness of this marine environment is not static, and the signals coming from the water are mixed. On one hand, the resident cetacean populations tell a story of relative stability. Whale Watch Tenerife, which has logged cetacean sightings systematically since 2018, recorded 17 different species in both 2018 and 2023, with short-finned pilot whales (Globicephala macrorhynchus) and bottlenose dolphins (Tursiops truncatus) present on nearly every survey day. [4] In 2025, orca sightings and encounters with fin whales were notable additions to the year’s record. [4] The continued presence of these apex predators is generally a positive indicator of ecosystem function.

On the other hand, the EU-funded OCEAN CITIZEN restoration project documented concerning trends at the base of the food web when it began its work on the island in 2024. Fish populations associated with rocky reef habitats have declined significantly compared to historical baselines. Seagrass meadows (Cymodocea nodosa), which serve as nurseries for juvenile fish and feeding grounds for sea turtles, have retreated across multiple coastal areas due to sedimentation, pollution, and rising water temperatures. Rocky reefs have been degraded by a combination of physical disturbance and the effects of ocean acidification. [5] These are not peripheral problems. Reef habitats and seagrass meadows are foundational to the productivity that ultimately supports the entire marine food web, from the smallest reef fish to the bluefin tuna and the pilot whales that hunt above them.

The Atlantic regulatory framework governing commercial fishing has also evolved. EU fisheries ministers, meeting in December 2025, set 2026 catch limits with 81 percent of total allowable catches in the northeast Atlantic at maximum sustainable yield levels — an improvement on previous years, though the failure to agree a mackerel quota for 2026 due to disputes with non-EU countries was a notable setback. [6] For sport and recreational fishing around Tenerife, a growing culture of catch and release has taken hold among charter operators, particularly for bluefin tuna, billfish, and other large pelagic species. Most reputable charters now apply mandatory release for bluefin tuna, reflecting both changing regulation and a shift in the values of visiting anglers. [3]

What the Fish Are Actually Telling Us

Marine ecosystems are exceptionally good at communicating ecological stress, if we know how to listen. The presence of 28 cetacean species, including year-round resident pilot whales, tells us that the deep-water food web west of Tenerife remains productive. The decline of reef fish populations and seagrass cover tells us that the shallower coastal zone is under sustained pressure from human activity. The continued migration of bluefin tuna past the island tells us that large-scale Atlantic management is beginning to take effect after decades of overfishing. The appearance of orcas and large baleen whales in 2025 tells us that the waters retain the biological richness to attract ocean wanderers from across the hemisphere.

Tenerife’s marine environment is neither pristine nor beyond recovery. It occupies a contested middle ground where genuinely exceptional natural heritage coexists with the pressures of one of Europe’s busiest tourist destinations. Paying attention to what lives here, in all its scientific specificity, is the first step toward deciding what kind of relationship the island will have with its sea.

Sources

  1. Wikipedia: Tenerife — fauna and marine ecology
  2. FishingBooker: Tenerife Fishing — The Complete Guide for 2026, fishingbooker.com, January 2026
  3. FishingBooker: Canary Islands Fishing — The Complete Guide for 2026, fishingbooker.com
  4. Whale Watch Tenerife: Tenerife Whale Watching Season — cetacean sighting data 2023-2025, whalewatchtenerife.org
  5. OceanCitizen EU: Reclaiming Tenerife’s Ocean, oceancitizen.eu, September 2024
  6. European Commission Oceans and Fisheries: Fisheries ministers agree fishing opportunities for 2026, December 2025, oceans-and-fisheries.ec.europa.eu
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