Kelp is nature’s most complex algae and the Giant kelp, Macrocystis pyrifera, reach lengths in excess of 80m. They have an astounding growth rate, growing up to 50 centimetres, a day. These giant kelp form vast and dense forests and beds along the coasts of the temperate and cooler waters of the world and house a rich treasure trove of life. Found mainly along the coasts of the Northeast and Southeastern Pacific, Southern Australia, South Africa, Southern California, Western Europe and West South America they grow down to 30 metres depth and thrive in these cool, nutrient rich waters. They are recognised as one of the most dynamic and productive ecosystems on earth, influencing oceanographic patterns around the coasts and providing many ecosystem services.
Although kelp have root like structures (holfasts) they are unlike terrestrial plants that draw in water and nutrients, and these roots. Holdfasts, provide only anchorage points for the plant. This means that giant kelps must have a rocky shore where they have plenty of substrate for anchorage and it makes then particularly secure against the storms and waves they are regularly subject to. Their fronds (leaves) have pneumatocysts; gas filled bladders attached to the base of each frond to provide the all-important buoyancy needed in the underwater world, These allow them to obtain maximum sunlight for nutrition and growth.
Kelp Forests Have Distinct Biological Zones
Like forests on land, kelps forests have distinct biological zones, each of which are packed with life. These dense vertical zones form microenvironments similar to those of terrestrial forests and provide shelter and food and a home to a myriad of plant and animal life, from the tiniest algae to the world’s largest marine mammals. The forest canopy is home to animals feeding directly on the fronds; such as bivalves, nudibranchs (such as the sea hare) and crabs. The most distinctive of creatures living alongside, and on the fronds are sea mats; the bryozoans-tiny colonies of animals encrusting the fronds in a dazzling variety of hues. Fronds can become so heavy with these mats, that sunlight is blocked to the fronds. But nature balances perfectly and these rich sea mats are grazed by other animals in their turn.
The leaves of kelp are unpalatable to most animals. Fronds are tough and rubbery and produce chemicals, including acids, that make them unattractive to a would be grazer. As the kelp grows and fronds are lost in storms and wave action, they rot and decay sinking to the seabed. And here, a soup rich in nutrients is formed that is essential for the bacterial and microscopic life on the forest floor. These crucial filter feeders and scavengers wait patiently on the sea bed for manna from heaven.
And the forest is not without its larger predators; visitors come looking for short term shelter and food while others make the kelp forest their home. Sharks for example, generally feed and hunt in open waters but the blue shark in the Pacific is often found patrolling the fringes of kelp forests. Whales, sea lions and seals all use the kelp forests to search for food and the sea otter, in the forests of the northern hemisphere, is particularly associated with kelp forests.
Giant Kelp Forests in Decline Globally
Declines of kelp forests around the world has caused concern over the past few decades. As well as pollution, kelp harvest and climate change impacts, disruption of the delicate balance of life due to over fishing has caused dramatic changes in kelp forests.
The disappearance of vast areas of kelp forests in the sea otters range (including Northern Japan, Alaska and Western North America) has been directly linked to the demise of sea otters.The overharvest of sea otters in the last century caused an increase in the population of sea urchins. This is turn led to a sea urchin bloom once their main predator (the sea otter) was removed. The subsequent grazing pressure, from sea urchins on the kelp forest, was dramatic. Although sea otters have recovered through much of their range, it has been a cautionary tale. The sea otter is a keystone species in these kelp forest ecosystems - a species that is crucial in controlling the food web.
There have been similar kelp forest declines when other top predators such as fish and lobsters are removed. Kelp forests are still poorly understood and yet they provide us with one of the world’s richest environments. The complex relationships within the forest provide new insights into marine dynamics and yet we may be losing them before we fully know what magic they harbour.
Sources
Kelp Research (University of California, Santa Cruz)
Sarah Curran-Ragan - Science journalist and marine biologist, Sarah Curran Ragan, keeps you informed about our Oceans.
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