MEPS 298:101-114 (2005)  -  doi:10.3354/meps298101

ABSTRACT: The effect of nitrogen (N) load and irradiance on morphology, growth and photosynthetic performance was studied in the green macroalga Caulerpa prolifera (Forsskål) J.V. Lamouroux from the Gulf of Cádiz (south Spain). Constant growth rates were obtained for thalli growing at different N loads, which could be fitted to tissue N using the Droop equation, rendering a maximum growth rate of 0.09 d^–1, a minimum tissue N level of 1.71% dry weight (DW) and a critical tissue N of 5.2% DW. N limitation had no effects on F_v/F_m (maximum quantum yield of chlorophyll a fluorescence). Stolon production was significantly highest at low N loads; a reverse trend was observed for assimilator production. In a second experiment, algae were subjected to combinations of high and low N loads (HN and LN) and irradiance (HL and LL) levels. Highest growth rates were observed in the HNLL treatment, whereas the reverse combination rendered the lowest growth rate. High irradiance and high N load both led to increased biomass allocation to assimilators; at low N, the bulk of the biomass (>75% in the HLLN treatment) was allocated to the stolons. HN had a positive effect on F_v/F_m, and HL had a negative effect. HL algae had a higher capacity for non-photochemical quenching. Despite its prolific nature, C. prolifera should be characterised as a slow-growing, but highly nitrophilic alga which has the capacity to forage for nutrients by allocating biomass to the stolons.

KEY WORDS: Caulerpa prolifera · Clonal growth · Morphology · Nitrogen foraging · Growth rate · Photosynthesis