One of our most abundant kelps, Sugar Kelp can be found in the lower part of the intertidal zone well below a band of Ribbon Kelp (Alaria marginata) in many areas. It occurs both in protected waters and on the outer coast, although it does not thrive in heavy surf. In Southern California, it can grow in rather sandy areas. It is often found on mixed substrata, where the haptera attach to rock, shell and other debris.
Members of this family have a single, terminal blade that is divided in some species. The stipe is rarely branched. Blades are smooth or undulate, entire or with holes, of uniform thickness or with a central, thickened region (midrib). Sori develop directly on the blades.
Species description: Sugar Kelp is a rich medium brown, and, like other members of the genus Laminaria, has no midrib in its blade. It has a profusely branched holdfast. A single cylindrical stipe up to 50 cm (20 in) long and perhaps 9 mm (0.3 in) in diameter lacks the internal mucilage ducts present in older individuals of Split Kelp. In Sugar Kelp, the stipe supports one undivided (but often distally tattered), smooth blade that is moderately thick, up to 3.5 m (10 feet) long and 18 cm (7 in) broad. The blade often has two rows of bullations (blisterlike swellings). This is reported to be a perennial species that dies back to its holdfast and stipe in winter and then resprouts the following spring, but some workers think that only subtidal specimens can do this (and live up to 3 years) while intertidal ones are just annuals. This conspicuous phase is the sporophyte, and spores are produced in a sorus that covers much of the surface of this blade.
Much research has been performed on the relationship between light levels, temperature, and the availability of nutrients on the growth of Sugar Kelp, and we summarize those findings here briefly. Light is, of course, necessary for photosynthesis, and declining levels of light in the fall prevent the further growth of Sugar Kelp even if nutrient levels increase at that time. Also, the period of maximum growth of this kelp at higher latitudes is delayed behind that further south. On the other hand, young sporophytes are especially sensitive to high levels of light, so a canopy of adult sporophytes can provide critical shade to these young plants. During low tides, light levels are also much higher, which is probably why this species cannot grow above the low intertidal zone on the shore. As for the effects of temperature, Sugar Kelp is generally adapted to live at the local temperature ranges, but cannot grow above certain critical temperatures. For example, on the east coast of the United States, the southern boundary of the distribution of this kelp is marked by the 19°C (66°F) summer isotherm. At higher temperatures, growth ceases and most sporophytes disappear. Higher temperatures also affect gametophyte formation, favoring males over females. Nutrients are essential for growth, and nitrogen availability is usually critical (when nitrogen is added to the environment, growth is enhanced). At some latitudes, and perhaps throughout the range of this kelp, carbohydrates stored as mannitol and laminarin are used to support the growth of new tissues.
Spore formation peaks in the spring and again in the fall, but individuals that form spores in the fall are themselves the offspring of individuals that lived the previous fall and are not the offspring of individuals that formed spores in the spring. Spore release is severely inhibited by such pollutants as petroleum products.
Sugar Kelp is eaten by such herbivores as the Dusky Tegula snail (Tegula pulligo) and sea urchins on our coast. A chemical released by Laminaria is thought to attract the urchins.
Bathymetry: lower intertidal and upper subtidal (to perhaps 30 meters or 98 feet) World Distribution: Aleutian Islands, Alaska, to Santa Catalina Island, California; Japan; Arctic Ocean; Russia; North Atlantic; North Sea
Recommended citation: Author, Date. Page title. In Klinkenberg, Brian. (Editor) 2019. E-Flora BC:
Electronic Atlas of the Plants of British Columbia [eflora.bc.ca]. Lab for
Advanced Spatial Analysis, Department of Geography, University of British
Columbia, Vancouver. [Accessed:
2020-02-28 8:30:42 PM
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