Short answer: Oceans are a frequent IELTS reading topic and feed environment essays, so precise words such as acidification, biodiversity, overfishing and salinity raise your Lexical Resource quickly.
Each replaces a vague phrase — "the sea getting more acid", "variety of sea life", "catching too many fish" — with the exact term examiners expect at Band 7.
Marine biology, ocean exploration, pollution and overfishing are common IELTS reading themes, and the sea also appears in Task 2 essays on the environment and conservation.
Because the topic recurs so often, its vocabulary is learnable in advance — a candidate who writes about ocean acidification, coral bleaching or the collapse of fish stocks reads as far more precise than one who writes "the sea getting worse".
This guide gives you 30 genuine Band 7+ ocean words, each with a natural collocation and an example sentence you can adapt.
Why topic vocabulary lifts your Lexical Resource band
In both Writing and Speaking, Lexical Resource is one of four marking criteria, each carrying equal weight — so it is worth a full quarter of your mark on those papers.
The public band descriptors state that Band 7 needs "a sufficient range of vocabulary to allow some flexibility and precision" and the use of "less common lexical items… with some awareness of style and collocation".
Preparing topic language in advance is the most efficient way to meet that standard.
The descriptors reward accuracy, not decoration. A less common word dropped into the wrong collocation — "make a pollution" or "a big overfishing of the sea" — reads as reach without control and can lower your band rather than raise it.
That is why every entry below is paired with its natural partners: learn the collocation, not the isolated word. For a structured month of building vocabulary like this across topics, follow our 30-day vocabulary plan.
30 Band 7+ ocean words
Read down each row for the meaning, then across to the collocation and an example sentence that shows the word doing the job it would do in a real answer.
| Word | Meaning | Collocation / common usage | Example sentence |
|---|---|---|---|
| marine | relating to the sea and its life | marine life, a marine ecosystem | Plastic waste poses a growing threat to marine life. |
| ecosystem | a community of organisms and their physical environment | a marine ecosystem, a fragile ecosystem | Coral reefs support one of the richest ecosystems on Earth. |
| biodiversity | the variety of living things in a habitat | marine biodiversity, loss of biodiversity | Overfishing has sharply reduced the biodiversity of coastal waters. |
| coral reef | an underwater ridge built by coral organisms | a coral reef, coral bleaching | Rising sea temperatures have triggered widespread coral bleaching. |
| overfishing | catching fish faster than stocks can replace themselves | combat overfishing | Overfishing has driven several species close to collapse. |
| sustainable | able to continue without depleting a resource | sustainable fishing, sustainable quotas | Sustainable fishing quotas give depleted stocks time to recover. |
| acidification | the process of the ocean becoming more acidic | ocean acidification | Ocean acidification makes it harder for shellfish to form their shells. |
| current | a continuous, directed flow of seawater | an ocean current, a warm current | Ocean currents carry heat around the globe and shape regional climates. |
| tidal | relating to the rise and fall of the sea | tidal energy, tidal range | Tidal energy offers a predictable source of renewable power. |
| salinity | the amount of salt dissolved in water | high salinity, water salinity | Melting glaciers reduce the salinity of the surrounding seawater. |
| plankton | tiny organisms that drift in the sea | microscopic plankton, a plankton bloom | Plankton forms the base of almost every marine food chain. |
| habitat | the natural home of an organism | a marine habitat, habitat destruction | Bottom trawling destroys the seabed habitat that many species need. |
| sediment | solid particles that settle on the seabed | ocean sediment, layers of sediment | Layers of sediment on the seabed preserve a record of the ancient climate. |
| buoyancy | the ability to float in water | control buoyancy, neutral buoyancy | Divers adjust their buoyancy to hover motionless above the reef. |
| estuary | the tidal mouth where a river meets the sea | a tidal estuary | The estuary serves as a nursery where young fish can grow safely. |
| abyssal | relating to the deep ocean floor | the abyssal plain, abyssal depths | Strange creatures endure the crushing pressure of the abyssal depths. |
| migration | the seasonal movement of animals | fish migration, migratory routes | Warming seas are disrupting the migration of many fish species. |
| depletion | the reduction of a resource to a low level | stock depletion, depletion of fisheries | The depletion of tuna stocks has alarmed marine biologists. |
| runoff | water draining from land into the sea | agricultural runoff | Fertiliser in agricultural runoff triggers harmful blooms along the coast. |
| algal bloom | a rapid overgrowth of algae in water | a toxic algal bloom | A toxic algal bloom can strip the water of oxygen and kill fish. |
| crustacean | a hard-shelled marine animal such as a crab | a crustacean | Crabs, lobsters and other crustaceans thrive along the rocky shore. |
| desalination | the removal of salt from seawater to make it drinkable | a desalination plant | Desalination plants now supply fresh water to many coastal cities. |
| hydrothermal vent | an opening in the seabed that releases hot, mineral-rich water | a hydrothermal vent | Entire communities of organisms cluster around hydrothermal vents. |
| continental shelf | the shallow seabed bordering a continent | the continental shelf | Most commercial fishing takes place over the continental shelf. |
| submersible | a small vessel built for deep-sea exploration | a crewed submersible | A submersible descended two kilometres to film life on the ocean floor. |
| pollution | the presence of harmful substances in the sea | plastic pollution, marine pollution | Plastic pollution now reaches even the deepest ocean trenches. |
| conservation | the protection of the sea and its wildlife | marine conservation | Marine conservation zones give fragile habitats a chance to recover. |
| trawling | fishing by dragging a large net through the water or along the seabed | bottom trawling | Bottom trawling scrapes the seabed and destroys slow-growing habitats. |
| mollusc | a soft-bodied animal, often with a shell, such as a mussel | molluscs such as mussels | Molluscs such as mussels filter and help to clean the surrounding water. |
| coastal | relating to the coast | coastal waters, coastal erosion | Coastal erosion is accelerating as sea levels continue to rise. |
How to turn these words into marks
Commit each word inside its collocation, not on its own: the bare word "acidification" is fragile, but "ocean acidification" gives you a ready-made phrase you can drop into a sentence without a grammar risk.
Use one or two of these words per paragraph, where they are natural — accuracy beats quantity, and a single wrong collocation is more visible to an examiner than three plain sentences.
Meet the words in context with our ocean reading practice, then make them active with a word a day on Word Coach.