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What are corals?
What are corals?
Coral reefs 🪸, often referred to as the "rainforests of the sea," are intricate ecosystems teeming with life and color. They are built by tiny organisms called coral polyps, which belong to the phylum Cnidaria, the same family as jellyfish. A symbiotic algae, zooxanthellae, inhabits its cells and, by photosynthesis, converts sunlight into nutrients which the coral feeds on.
Within coral reefs, there are two main types of corals: hard corals (hexacorrallia) and soft corals (octocorrallia).
Hard corals, also known as stony corals, have rigid skeletons made of calcium carbonate and form the backbone of reef structures.
Soft corals, on the other hand, lack hard skeletons and instead have flexible structures supported by tiny spicules or proteinaceous material.
Corals reproduce both sexually and asexually. Sexual reproduction involves the release of eggs and sperm into the water column, a process known as spawning. This typically occurs in synchrony with lunar cycles. Fertilized eggs develop into free-swimming larvae called planulae, which eventually settle onto a substrate and form new polyps. Asexual reproduction (similar to cloning) occurs through budding or fragmentation, allowing corals to spread and repair damaged parts of the reef. That is why a coral formation is considered a single living organism as all polyps are genetically identical.
📷 Photo tip
Coral reefs provide near-infinite photo opportunities. Take your macro lens 🔍, go low or eye-level ⬇️, then get intimate and close ❤️. But don't touch ✋🏼 these sensitive creatures. Prepare for the annual coral spawning period in Nha Trang, from March to May, after the full-moon.
Life on the reef
Life on the reef
Coral reefs form vibrant and diverse habitats that support a myriad of marine life. Home to 25% of all marine life, these reef ecosystems provide crucial shelter, and feeding areas for a vast array of species. These reefs also serve as vital breeding grounds and nurseries for remarkable species of fish, providing protection for juvenile individuals as they grow and mature. The complex reef formations create a mosaic of microhabitats, offering niches for various organisms to flourish, from tiny invertebrates to majestic reef sharks.
The iconic marine turtles graze the seagrass bordering the reefs (Chelonia mydas) or forage through the coral in search of sponges (Eretmochelys imbricata) while the small cleaner Wrasse turns the reef into a spa servicing larger animals in exchange for food.
Vietnam boasts a rich diversity of coral species, with over 350 species of hard corals distributed across the Central and Southern Coastline by the Eastern Sea and the Gulf of Thailand. The species include the Acroporidae (branching coral), Faviidae (brain coral), and Poritidae (boulder coral) families.
Besides looking pretty, are corals any useful?
Besides looking pretty, are corals any useful?
Besides being home to a quarter of all marine life, they provide us with many benefits that we may not even realize.
Support to marine life: they host thousands of different species and also act as breeding grounds to replenish the fisheries stocks. Many of these animals are important for our food supply. Without the reefs and sustainable harvest practices, fish stock will perish. 🐠
Climate Regulation: Coral reefs play a vital role in carbon sequestration and storage, helping mitigate the impacts of climate change. Coral polyps absorb dissolved carbon dioxide from seawater during photosynthesis, thereby reducing the concentration of greenhouse gases in the atmosphere. Additionally, coral reefs contribute to the formation of coastal habitats, such as mangroves and seagrasses, which also sequester carbon and stabilize coastal ecosystems. ♻️
Coastal Protection: Coral reefs act as natural barriers, reducing the impact of waves, storms, and erosion on coastal communities. The complex structure of coral reefs absorbs wave energy, dissipating its force before it reaches the shore, thereby safeguarding the livelihoods of coastal residents. 🚧
Economic Benefits: Coral reefs support thriving marine ecosystems that also attract tourists and support recreational activities such as diving. In Palau, a single live shark is estimated to generate $180k of tourism revenue each year, or $1.9Mn over its lifetime, compared to a mere $400 worth of shark fins when fished. This economic diversity helps 47Mn people from coastal communities become more resilient and provides alternative sources of income. 💸
Innovative medicine: They contain compounds that have been used to develop treatments for various diseases, such as cancer, arthritis, and infections. Scientists are still discovering new potential drugs from coral reefs, which could help us fight against future health challenges. 💊
🧑🏻🔬 The science of coral bleaching
When corals are under stress from elevated water temperatures ♨️, chemical pollution ☠️, or excessive sunlight radiation 🥵, the photosynthetic ability of the symbiotic zooxanthellae 🦠 is disrupted. This disruption leads to an overload of electron ⚡️ production. Under normal conditions, these electrons are processed to produce the nutrients the coral requires 🍜.
However, when unprocessed and leaking into the coral tissues, these electrons attach to the oxygen (O₂) produced during photosynthesis, forming oxidising ions (such as O₂⁻). These ions cause damage ⛓️💥 to both the coral and the algae at a cellular level. As a defence mechanism, the coral expels 🚀 the algae to reduce the production of electrons and the accumulation of harmful oxidising ions. This expulsion results in the loss of color in the coral, turning it pale or even white ⚪️, the phenomenon known as bleaching. As long as zooxanthellae fail to recolonize the coral, bleaching is sustained and the coral starves to death.
How long it can survive ⏲️ without the zooxanthellae depends on the species of coral: Acropora is more susceptible and may only last a few weeks, while Porites (such as the one in the photo), generally known to be more resilient 💪🏼, may survive a few months at most.
Bleached boulder coral located on the Northern side of hòn Tằm, Nha Trang. 4th Global Bleaching Event. June 2024
What can you do to help protect the reefs?
What can you do to help protect the reefs?
At Bubbles & Lenses, we are committed to spreading our knowledge and expertise in sustainable photography and diving practices. All our team members are certified GreenFins Eco-dive-guides and are dedicated to making your photography experiences respectful of the environment in general, and the coral reefs in particular. Coral reefs are not only a breathtaking spectacle for divers and snorkelers but also a cornerstone of marine biodiversity, supporting a delicate balance of life along its expansive shores.
The team notably volunteers to collect data and capture images during important community impact and citizen science activities in Vietnam, supporting the local marine park authorities by providing the observations required for effective park management and policies.
To know more:
To know more:
Coral Reefs 101, Coral Reef Alliance 🪸📚
US Coral Reefs Fast Facts, NOAA 🪸 📚
Threats to coral reefs, NOAA 🪸☣️☠️
Coral Reef Watch, NOAA's bleaching alert online platform 🪸☠️
Coral Reefs & Tourism, GreenFins 🏖️🧑🏻🏫
Save The Reef's guide to reef safe sunscreen. 🧴🧑🏻🔬
Treeline Review's guide to reef safe sunscreen. 🧴🧑🏻🔬
#CORALWATCHVIETNAM, Saigon Divers Club's Sea Surface Temperature monitoring database 🪸🇻🇳
« Benthic fauna of the Bay of Nha Trang », by Britayev & Palov, KMK Scientific Press, 2007. 🐠🐚🦀
« Varied spawning patterns of reef corals in Nha Trang Bay, Vietnam, western South China Sea », by Võ Sĩ Tuấn et al., Regional Studies in Marine Science Vol. 55, 2022. Pub: Elsevier 🪸🪺
« The extreme truth about the coral situation in Phú Quốc », 2023, OnBird.vn ‼️
B&L covers Saigon Divers Club's Conservation Trip
Scripps Institution of Oceanography developped a diver-operated underwater microscope to study millimeter-scale processes as they occur naturally on the seafloor such as in vivo coral polyps life cycle and interactions.
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