Abstract
Interactive effects of settlement density, nutrient concentration and temperature on growth and survival of Sargassum muticum germlings were recorded over 45 days in laboratory cultures, using a factorial experimental design. Germling growth was stimulated by high temperature (17 °C compared to 7 °C) and nutrient enrichment (seawater enriched with 32 μmol nitrogen and 2 μmol phosphorus per litre), and negatively related to settlement density (in the range of 10–100 germlings cm−2). Survival was reduced when high settlement density was combined with high temperature and nutrient enrichment. After 45 days the size-distribution of germlings became positively skewed in some of the high-density stands, probably as a result of a few large individuals gaining dominance and suppressing many small plants. Intraspecific competition, defined as the relative reduction of germling growth and survival in high-density cultures compared with low-density cultures, increased during the course of the experiment, and depended on temperature and nutrient regime. As biomass accumulated in the stands competition increased more per biomass-unit at 7 °C than at 17 °C, which indicates a reduced tolerance to competition in germlings at the lower temperature. These results suggest the presence of intraspecific competition in stands of young S. muticum germlings, and a reduced growth and competition ability of germlings at low temperatures.
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