Studies on the Giant Kelp, Macrocystis. II. Reproduction
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Neushul, M. (U. Washington, Seattle.) Studies on the giant kelp, Macrocystis. II. Reproduction. Amer. Jour. Bot. 50(4): 354–359. Illus. 1963.—The reproduction of Macrocystis pyrifera was studied in the sea and in the laboratory. The estimated minimum time needed for the completion of the sexual life history of Macrocystis pyrifera in La Jolla, California, is from 12 to 14 months. Young sporophytes begin fruiting when they have from 4 to 8 stipes and a somatic frond weight of from 8 to 10 kg. The behavior of abscised sporophylls in laboratory tanks, as well as their morphology and coloration, strongly suggests an interrelationship between the translocation of photosynthetic products and fructification.Keywords:
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Neushul, M. (U. Washington, Seattle.) Studies on the giant kelp, Macrocystis. II. Reproduction. Amer. Jour. Bot. 50(4): 354–359. Illus. 1963.—The reproduction of Macrocystis pyrifera was studied in the sea and in the laboratory. The estimated minimum time needed for the completion of the sexual life history of Macrocystis pyrifera in La Jolla, California, is from 12 to 14 months. Young sporophytes begin fruiting when they have from 4 to 8 stipes and a somatic frond weight of from 8 to 10 kg. The behavior of abscised sporophylls in laboratory tanks, as well as their morphology and coloration, strongly suggests an interrelationship between the translocation of photosynthetic products and fructification.
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Anthropogenic disturbances, including coastal habitat modification and climate change are threatening the stability of kelp beds, one of the most diverse and productive marine ecosystems. To test the effect of temperature and irradiance on the microscopic gametophyte and juvenile sporophyte stages of the rare kelp, Saccharina angustissima, from Casco Bay, Maine, USA, we carried out two sets of experiments using a temperature gradient table. The first set of experiments combined temperatures between 7–18°C with irradiance at 20, 40, and 80 μmol photons m−2 s−1. The second set combined temperatures of 3–13°C with irradiance of 10, 100, and 200 μmol photons m−2 s−1. Over two separate 4-week trials, in 2014 and again in 2015, we monitored gametogenesis, the early growth stages of the gametophytes, and early sporophyte development of this kelp. Gametophytes grew best at temperatures of 8–13°C at the lowest irradiance of 10-μmol photons m−2 s−1. Light had a significant effect on both male and female gametophyte growth only at the higher temperatures. Temperatures of 8–15°C and irradiance levels of 10–100 μmol photons m−2 s−1 were conditions for the highest sporophyte growth. Sporophyte and male gametophyte growth was reduced at both temperature extremes—the hottest and coldest temperatures tested. S. angustissima is a unique kelp species known only from a very narrow geographic region along the coast of Maine, USA. The coupling of global warming with high light intensity effects might pose stress on the early life-history stages of this kelp, although, as an intertidal species, it could also be better adapted to temperature and light extremes than its subtidal counterpart, Saccharina latissima. Key words: gametophyte; irradiance; kelp; north Atlantic; Saccharina angustissima; sporophyte; temperature
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Morphological relationships among fronds of giant kelp Macrocystis pyrifera off La Jolla, California
Giant kelp Macrocystispyrifera is the dominant macrophyte along much of the California coast.Each plant is composed of several fronds, each of which can have more than 100 blades.We have developed equations which describe relationships between size and distance which account for variations in frond size and blade node number The most successful descriptions involve the separation of within-frond patterns from between-frond patterns.One useful within-frond description is the relationsh~p between the area of blade relative to the largest blade on its frond (e.g. a fractional area of 0.1) as a function of its relative position on the frond (e.g. the blade's node posit~on is 0.1 of the total number of nodes from the apex).A useful between-frond description is the relationship between the area of the largest blade on a frond and the frond size.The 2 types of descriptions used together form a compact description of frond morphology that accounts for most of the variability in blade size and position for a range of frond sizes.Similar relationships hold for the distributions of frond lengths within a kelp plant.The morphological relationships are expressed used power series that were fit to the data.The existence of power series relationships describing kelp morphology can be used for modelling studies of such factors as the light field around a plant.
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Deepened isotherms associated with El Niño resulted in severe nutrient limitation and very low kelp productivity during the last half of 1983. Frond growth rates were so low that terminal blades formed before reaching the surface, eliminating the canopy. Frond initiation rates were also extremely low, resulting in significant reductions in mean plant size. Plants growing above 10 m were more severely affected than plants at 20 m. These results suggest that nutrient pulses associated with internal waves are critical for survival of Macrocystis pyrifera in nutritionally marginal habitats in southern California.
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N eushul , M. (U. Washington, Seattle.) Studies on the giant kelp, Macrocystis. II. Reproduction. Amer. Jour. Bot. 50(4): 354–359. Illus. 1963.—The reproduction of Macrocystis pyrifera was studied in the sea and in the laboratory. The estimated minimum time needed for the completion of the sexual life history of Macrocystis pyrifera in La Jolla, California, is from 12 to 14 months. Young sporophytes begin fruiting when they have from 4 to 8 stipes and a somatic frond weight of from 8 to 10 kg. The behavior of abscised sporophylls in laboratory tanks, as well as their morphology and coloration, strongly suggests an interrelationship between the translocation of photosynthetic products and fructification.
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Delayed recruitment of microscopic stages in response to cyclical cues is critical to the population dynamics of many annual and seasonally reproducing perennial seaweeds. Microscopic stages may play a similar role in continuously reproducing perennials in which adult sporophytes are subject to episodic mortality, if they can respond directly to the unpredictable onset and relaxation of unfavorable conditions. We experimentally evaluated the potential for temporary reduction in limiting resources (light, nutrients) to directly delay recruitment of giant kelp ( Macrocystis pyrifera (L.) C.A. Agardh) gametophytes and embryonic sporophytes. Laboratory cultures were subjected to limiting conditions of light and nutrients for 1 month and then exposed to nonlimiting conditions for 10 days. Gametophytes in all treatments failed to recruit to sporophytes after 2 weeks, suggesting they are not a source of delayed recruitment in giant kelp. Sporophytes in light‐limited treatments, however, survived and grew significantly slower than non–light‐limited controls. When stimulated with light, light‐limited sporophytes grew from 2 to>10 times faster than unstimulated controls depending on nutrient availability. These results suggest that limiting resources can delay recruitment of embryonic giant kelp sporophytes for at least 1 month. Flexible timing of recruitment from embryonic sporophytes may enhance persistence of continuously reproducing perennial species when mac‐ roscopic adults are subject to episodic large‐scale removals.
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