Productivity and life history of Laminaria longicruris at its southern limit in the Western Atlantic Ocean

The seasonal population dynamics of Laminaria longicruris de la Pyl. were studied in Long Island Sound (Connecticut, USA). Llnear growth rates were minimal during August and September, subsequently increased through the remainder of the year and reached a maximum (2.5 cm d-') in May. Productivity per plant (fresh weight) was maximal January to May (11.4 to 15.7 mg g-' d-'); productivity m-2 was maximum in May (110.53 g m-2 d-' in 1986 and 413.32 g m-2 d-' in 1987).Production was 10.6 kg m-2 m 1986 and was estimated to have been 46 to 50 kg m-2 in 1987. Maximum standing crop was observed In May (1986: 24 kg m-2; 1987: 47 kg m2)M. aximum densities of new recruits were 1000 ind m-'.

Densities of plants with blades > 50 g were 92 and 167 plants m-2 in January and May, respectively. Carbon and nitrogen contents were minimal and maximal, respectively, in winter; the reverse was true for summer measurements. Highest percentages of fertile plants were observed during October to December. Succession in generations of plants behaving as either annuals or biennials is also noted and Iscussed.