Effects of the 1983-El Niño on growth and carbon and nitrogen metabolism ofPleurophycus gardneri (Phaeopyceae: Laminariales) in the northeastern Pacific

Growth and compounds of carbon and nitrogen of the northeast Pacific kelpPleurophycus gardneri (Laminariales, Laminariaceae) were assessed before, during and after the 1983-El Niño Souther Oscillation event. This 2-yr study provides evidence that reduced ambient levels of nitrate and phosphate from March until August/September, 1983, in combination with elevated seawater temperature, caused a significant impairment of growth. Blade surface area, blade length, total fresh weight, and dry weight on an areal basis were significantly reduced in 1983 compared to 1982 (P<0.01). They were also significantly smaller in 1984 than in 1983 (P<0.05). The C:N values obtained both in May and July 1983 were considerably higher than in 1982, while those in May 1984 were strikingly smaller than in both 1982 and 1983. Mannitol content of the mibrid in May 1983, exhibited the highest levels recorded during the 2-yr study period, with ca. 19% dry weight and significantly exceeded mannitol content measured in May 1982 (average: 13%) and in May 1984 (average: 8%). The concentration factor for internal vs external nitrate in the midrib was 700 x ambient in May 1982 and 1984 compared with 20 x in May 1983. Ninhydrin positive substances (NPS) averaged 117 mol g dry wt^-1 in May 1984 compared with ca. 50 mol in May 1982 and 1983. The pigment ratios chlorophyllc: chlorophylla and fucoxanthin: chlorophylla in May 1983 were similar to those obtained in 1982, but were significantly different in May 1984. It is suggested that the interactive effects of temperature stress and nutrient limitation in 1983 caused a disruptive influence on C- and N-metabolism ofPleurophycus gardneri, which still affected growth performance in 1984.