M. P. Puglisi · V. J. Paul Intraspeciﬁc variation in the red alga Portieria hornemannii : monoterpene concentrations are not inﬂuenced by nitrogen or phosphorus enrichment Received 11 June 1996 / Accepted 20 July 1996 Abstract The red alga Portieria hornemannii (Lyngbye) Silva was selected to test the eﬀects of enhanced nutrient availability on the production of carbon-based second- ary metabolites, because of its notable site-to-site var- iation in monoterpene production. On Guam, the major secondary metabolite produced by this alga is ochto- dene, a cyclic monoterpene. Quantitative high-perfor- mance liquid-chromatography analysis of the extracts of P. hornemannii collected from six sites on Guam showed that both ochtodene and triglyceride concentrations diﬀered signiﬁcantly among sites. Internal nitrogen and phosphorus content of the algae did not correlate with the observed variation in chemistry. Experimental en- hancement of N-alone, P-alone or N + P in the ﬁeld for 5 wk failed to induce a signiﬁcant change in ochtodene concentrations in the alga, while triglyceride concentra- tions increased signiﬁcantly in the N + P treatment. Ochtodene and triglyceride concentrations did not change among similar treatments in shaded (18 d) and unshaded (11 d) fertilization experiments conducted in the laboratory. Variation in ochtodene concentrations in P. hornemannii cannot be attributed to N and P avail- ability; however, the decrease in ochtodene and trigly- ceride concentrations during the shaded laboratory ex- periment suggests that light may be a factor inﬂuencing monoterpene biosynthesis. The diﬀerence in ochtodene concentration between the initial and ﬁnal sets of ﬁeld controls collected for the unshaded laboratory experi- ment suggests that temporal variation might also con- tribute to diﬀerences observed among the algae at the diﬀerent sites. Introduction Intraspeciﬁc chemical variation in secondary metabolite production has been noted for a variety of plants in marine and terrestrial environments (Hay and Steinberg 1992). Recent studies focus mostly on hypotheses that attribute this variation to phenotypic responses (Tuomi 1992). One of these hypotheses, the carbon/nutrient- balance hypothesis, suggests that the allocation of re- sources to the production of secondary metabolites in a plant depends primarily on the resource regime available (Bryant et al. 1983, 1987a,b; Baldwin and Ohnmeiss 1994; Baldwin et al. 1994). The hypothesis postulates that the concentration of secondary metabolites in a plant will vary quantitatively with resource availability, i.e. carbon and nitrogen (Bryant et al. 1983; Price et al. 1989). For plants that produce carbon-based secondary metabolites (such as terpenes or polyphenolics), condi- tions that increase the C:N ratio (e.g. high light, low nutrients) should result in an increase in the concentra- tion of secondary metabolites and a decrease in growth rate, while conditions that decrease the C:N ratio (e.g. shade, high nutrients) should result in a decrease in growth rate accompanied by a decrease in the con- centration of secondary metabolites. For plants that produce nitrogen-based secondary metabolites (such as alkaloids), conditions that increase the C:N ratio should result in a decrease in the concentration of secondary metabolites and the growth rate, while conditions that decrease the C:N ratio should result in a decrease in growth rate and an accumulation of secondary meta- bolites (Bryant et al. 1983). Resource enhancement and depletion experiments with carbon, nitrogen and combined nitrogen and phosphorus treatments conducted with plants and brown algae that synthesize carbon-based compounds such as polyphenolics and tannins achieve results well within the predictions of the carbon/nutrient-balance hypothesis (Coley et al. 1985; Bryant et al. 1987a; Yates and Peckol 1993; Arnold et al. 1995; Hartley et al. 1995). Marine Biology (1997) 128: 161–170  Springer-Verlag 1997 Communicated by M.F. Strathmann, Friday Harbor M.P. Puglisi · V.J. Paul (&) University of Guam Marine Laboratory, Mangilao, Guam 96923, USA