Kelp

The thallus (or body) consists of flat or leaf-like structures known as lamina (or blades) that originate from elongated stem-like structures, referred to as the stipes. A root-like structure (called the holdfast) anchors the kelp to the substrate of the ocean. Gas-filled bladders (pneumatocysts) form at the base of blades of American species, such as Nereocystis lueteana, to hold the kelp blades close to the surface to access light for photosynthesis. (Mert. & Post & Rupr.) The stipes are generally covered with a slimy mucilage layer, rather than a waxy cuticle.

Kelp may develop dense forests with high production, biodiversity and ecological function. Along the Norwegian coast these forests cover 5,800 km2, and they support large numbers of animals. Numerous sessile animals (sponges, bryozoans and ascidians) are found on kelp stipes and mobile invertebrate fauna are found in high densities on epiphytic algae on the kelp stipes and on kelp holdfasts. More than 100,000 mobile invertebrates per square meter are found on kelp stipes and holdfasts in well-developed kelp forests. While larger invertebrates and in particular sea urchins (Strongylocentrotus droebachiensis) are important secondary consumers controlling large barren ground areas on the Norwegian coast, they are scarce inside dense kelp forests.

Growth occurs at the base of the meristem, where the blades and stipe meet. Growth may be limited by grazing. Sea urchins, for example, can reduce entire ecosystems to kelp-less wastelands known as urchin barrens. The kelp life cycle involves a diploid sporophyte and haploid gametophyte stage. The haploid phase begins when the mature organism releases many spores, which then germinate to become male or female gametophytes. Sexual reproduction then results in the beginning of the diploid sporophyte stage, which will develop into a mature individual.

Overfishing nearshore ecosystems leads to the degradation of kelp forests. Herbivores are released from their usual population regulation, leading to over-grazing of kelp and other algae. This can quickly result in barren landscapes where only a small number of species can thrive. Other major factors which threaten kelp include marine pollution and the quality of water, climate changes and certain invasive species.

Kelp forests are some of the most productive ecosystems in the world - they are home to a great diversity of species. Many groups, like those at the Seattle Aquarium, are studying the health, habitat, and population trends in order to understand why certain kelp (like bull kelp) thrives in some areas and not others. Remotely Operated Vehicles are used in the surveying of sites and the data extracted is used to learn about which conditions are best suited for kelp restoration.