Seaweed – A cornerstone of life

Far from being the obnoxious, unwanted plants the poorly chosen name suggests, the “weeds” of the sea play an essential role in our ecosystems. Seaweeds are marine macroalgae that live attached to rock and other structures in coastal areas. They are one of the foundations of New Zealand’s abundant underwater life and contribute a great deal to the wellbeing of us landlubbers as well.

Habitat. Anchored to the reef with their amazing holdfasts, seaweeds form three-dimensional structures in the shallow waters close to shore, which provide room for a myriad of life forms to settle in. Subtidal forests have some species grow into canapés, which change the conditions of their environment and create opportunities for other species. Large kelp can grow so long that it builds underwater forests.

Shelter. Algal beds and turfs provide refuge and disguise for invertebrates and many different fishes. Breeding nurseries rely on seaweed gardens and forests for protection. Some fishes are so adapted to seaweeds, they look like fronds themselves.

Food source. Seaweeds can be eaten directly by fishes and invertebrates. Also, pieces break off in the drift and get snatched up by critters in the currents. In addition, seaweeds produce mucilage that feeds small organisms which are themselves vital to coastal food chains. The slimes also dissolve in the water and provide food for bacteria, fungi and protozoans, which sustain filter feeders in their turn. Eventually, drifting plant matter gets washed up onto the beach, where bugs enjoy a feast before they provide nutrition to birds like seagulls, weka or even kiwi.

Protection from erosion. A strong growth of macroalgae can absorb wave energy and thus protect the coast from the elements. Some species can withstand prolonged burial under sand, enduring the ever-changing conditions of coastlines.

Carbon sinks. Kelps are very productive in the amount of carbon they fix, known as Blue Carbon. This also helps to reduce ocean acidification, a very serious problem we face in this time of climate change. In this, seaweeds are playing a vital role for the global atmosphere.

Oxygen production. As part of the carbon cycle, ocean plants also produce a huge amount of oxygen. Some number say that more than half of the oxygen we breathe comes from the sea, the blue lungs of our planet.

Human consumption, fertilizer, biofuels and other uses. From seaweed crackers to growth stimulants for vineyards, there is a wide range of uses to explore and discover. Seaweed farming can provide us with important nutrients, fight climate change and provide for underwater ecosystems all at once.


The Wellington Underwater Club is diving deep into seaweed and its coastal ecosystem and will share information in a series of articles. We will also let you know about threats to underwater gardens and forests, as well as events and actions you can undertake to help support seaweeds.

By Kat Mager



Wendy Nelson: New Zealand Seaweeds: An Illustrated Guide, Independent Publishing Group, 2013
School of Oceanography, Washington:
Blue Carbon Portal:




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