Marine organisms and adaptations

Adaptation is an evolutionary process whereby an organism becomes increasingly well suited to living in a particular habitat. It is not a quick process! Natural selection over many generations results in helpful traits becoming more common in a population. This occurs because individuals with these traits are better adapted to the environment and therefore more likely to survive and breed.

Adaptation is also a common term to describe these helpful or adaptive traits. In other words, an adaptation is a feature of an organism that enables it to live in a particular habitat.

Different types of adaptations

Marine organisms have adapted to the great diversity of habitats and distinctive environmental conditions in the marine environment. Adaptations are many and varied but they are generally grouped into 3 main categories: structural, physiological and behavioural.

Structural adaptations

Structural (or morphological) adaptations are the physical features of the organism. These include things you can see, like its shape or body covering, as well as its internal organisation. Following are a few of the ways that marine organisms have adapted their physical features to suit a particular habitat.

Seawater is much denser than air – as a result, there are vast numbers of microscopic organisms suspended in it. Cockles, as well as many other bivalves, are filter feeders. They have adapted specialised siphon structures to filter these organisms and any other particles of food from the surrounding water.

Estuaries have quite variable conditions – tides, waves and salinity fluctuations affect the animals and plants that live there on a daily basis. Many animals, such as cockles, are adapted to live in these conditions. They have strong shells that protect them from wave action, drying out and the prying beaks of predators.

Coastal plants need special adaptations to survive. For example, many types of seaweed attach firmly to rocks so they are not swept away by waves. Their leaf-like fronds are tough and leathery, which helps protect them from being torn by the waves or dried out by the sun.

Dolphins are mammals, but they look very different to mammals that live on land, as they are adapted to living in water. They have a streamlined shape and fins instead of legs. They also have blowholes on the tops of their heads. They use these to breathe, rather than through their mouths and noses. Find out more about New Zealand’s two endemic dolphin species.

Physiological adaptations

Physiological adaptations relate to how the organism’s metabolism works. These adaptations enable the organism to regulate their bodily functions, such as breathing and temperature, and perform special functions like excreting chemicals as a defence mechanism.

Some marine mammals, such as whales, migrate over large distances and may spend time in a combination of arctic, tropical and temperate waters. To cope with these temperature changes, they are endothermic or ‘warm blooded’. This means that they are able to maintain a constant body temperature that is not dependent on the surrounding water.

Slow-moving species have adaptations that help protect them from predators. For example, many marine organisms can only move slowly or not all. This means they cannot easily get away from mobile predators, and they have other adaptations to protect them from being eaten. These can include chemical defences in their skin, for example, sea stars.

Behavioural adaptations

Behavioural adaptations are learned or inherited behaviours that help organisms to survive, for example, the sounds made by whales allow them to communicate, navigate and hunt prey. Crab larvae use sounds to help them find suitable habitats so they can settle and metamorphose (change into an adult form).

Bryozoan colonies are found in high numbers on the continental shelf in New Zealand. They look like plants but are actually made up of hundreds of tiny individual animals that have banded together in order to more successfully find food and survive predation,