What are Kelps?

• What are Kelps?
• Species of Kelp
  

Kelps are large brown seaweeds or algae (Class Phaeophyceae) which belong to the Order Laminariales. The Order Laminariales is characterised by individuals with a hetermorphic alternation of generations, comprising 2 free-living life phases (a macroscopic sporophyte generation and a microscopic gametophyte generations. The sporophytes are typically differentiated into a holdfast, stipe and one or more blades.

Growth is by intercalary meristems that are primarily active at the base of the blades. As each strand of kelp grows, new blades are added by splitting of the blade at the very tip of the strand.

Members of the Laminariales are typically cold-water species, richly developed in the cold temperate and Arctic waters of the northern hemisphere, less so in the southern hemisphere and absent from the Antarctic. Four families are recognised worldwide (Alariaceae, Chordaceae, Laminariaceae and Lessoniaceae), two of which occur on southern Australian coasts (Lessoniaceae and Alariaceae), where they are often conspicuous elements of the mid to upper sublittoral zones.

Kelp forests occur in cold, nutrient-rich waters and are among the most beautiful and biologically productive habitats in the marine environment. They are found throughout the world in shallow open coastal waters, and the larger forests are restricted to temperatures less than 20^oC, extending to the Antarctic and Artic Circles. A dependence upon light for photosynthesis restricts them to clear shallow water and they rarely occur much deeper than 15-40m.

Species of Kelp
In Australia, 3 genera (and 4 species) of Laminariales occur: Macrocystis and Lessonia (Order Lessoniaceae) and Ecklonia (Order Alariaceae). In the genus Macrocystis, 2 species are recognised: M.pyrifera and M.angustifolia. Only one species of Lessonia (L.corrugata) and Ecklonia (E.radiata) occur in Australia. Macrocystis angustifolia and Lessonia corrugata are endemic to Tasmania.

Interestingly, Bull Kelp (Durvilleae potatorum) which is found in the sublittoral fringe, along much of the cold temperate waters of southern Australia, is not a 'true' kelp (ie. a member of the Laminariales), but rather is a member of the Order Fucales. The Fucales is a diverse group of large brown seaweed, which have only one life stage (compared with two in true kelps). The Fucales is particularly species rich in southern Australia, particularly in the genera Sargassum and Cystophora.

Macrocystis is in the family Lessoniaceae. The characteristics of the family include branched stipes, each branch terminating in a single blade, and blades that split at an intercalary meristem. Some of the genera, like Macrocystis, have gas-filled floats called pneumatocysts that hold the plant erect in the water. Other genera in the Lessoniaceae include Lessonia, Postelsia, Pelagophycus and Nereocystis.