Enhanced production of Pacific dulse ( Palmaria mollis) for co-culture with abalone in a land-based system: nitrogen, phosphorus, and trace metal nutrition

Abstract

Pacific dulse ( Palmaria mollis) is a high-quality algal feed for both red abalone ( Haliotis rufescens) and Japanese abalone ( Haliotis discus hannai); however, culture techniques capable of producing commercial quantities of P. mollis are still in development. This study was undertaken to improve our understanding of nutrient requirements and management strategies for P. mollis production in intensive, land-based systems. All experiments were conducted under moderate to high artificial light of 24–52 mol photons m −2 day −1 and low seawater exchange (1 vol day −1), in order to minimize seawater pumping costs. Application of nutrients every 5–7 days resulted in no significant difference in P. mollis growth compared with daily applications. Nutrient additions during the dark cycle compared with the light cycle were found to be effective in controlling epiphytes. The addition of f medium trace metals (Gran. Can. J. Microbiol. 8 (1962) 229) significantly increased growth rates compared with those of cultures supplied with just nitrate and phosphate alone. The concentration of Zn was increased to equal that of Mn (1.37 μM day −1), with resulting improvement in yields. NaNO 3 as a source of nitrogen was found to be superior for long-term growth (9 weeks) compared with NH 4NO 3, although NH 4NO 3 was superior on a short-term basis (first 2–5 weeks). This was likely due to NH 4 +–N toxicity resulting from the experimental design. While P. mollis growth was not significantly different between additions of 1176–2942 μM day −1 NO 3 −–N (average daily N load), an increasing trend in growth was observed with increasing N loads up to 2942 μM day −1 NO 3 −–N. P. mollis showed a sharp decline in growth with P additions above 83.3 μM day −1 (average daily P load). Tissue nutrient concentrations and molar ratios (N, P, trace metals, N/P and C/N) can be used in the development of optimal nutrient management strategies to ensure maximum dulse growth rates.