Kelp Forests: An Overlooked Carbon Sink

Introduction

Giant kelp, known scientifically as Macrocystis pyrifera, builds dense floating canopies along cold temperate coastlines. This document covers its range, growth cycle, the species most often surveyed, and what the beds contribute to coastal carbon storage.

Range and Habitat

Kelp anchors to rocky substrate in water between 6 and 17 °C, rarely deeper than 38 metres. The Pacific belt runs from Baja California to the Aleutian chain, with a second stronghold off Tasmania and southern Chile.

Common Species

Roughly 31 genera are currently recognised. The four most surveyed are giant kelp, bull kelp, sugar kelp, and oarweed, which differ mainly in holdfast structure, blade shape, and how far the canopy reaches toward the surface.

Carbon Capture

A mature bed fixes carbon at about 1.8 kg per square metre each year — comparable to temperate woodland — and a measurable share of that detaches, sinks, and is buried in deep sediment rather than returning to the atmosphere.

Pressures and Decline

Marine heatwaves, urchin barrens, and sediment runoff have thinned northern California beds by 62% since 2014. Recovery is uneven: sites with intact sea otter populations regrew within four seasons, while barren sites have not returned.

Restoration Work

Current programmes fall into three groups — urchin removal, green gravel seeding, and translocation of reproductive fronds. Cost per restored hectare ranges from 4,300 to 27,500 USD depending on depth and boat access.