Pacific dulse (Palmaria mollis) as a food and biofilter in recirculated, land-based abalone culture systems

Abstract

Palmaria mollis (Pacific dulse) is increasingly being used as an in situ biofilter and feed in land-based abalone culture. This work reviews physical and nutrient requirements for P. mollis culture and its nutritional value for three abalone species, the Japanese abalone Haliotis discus hannai, the red abalone Haliotis rufescens, and the U.S. Federally endangered white abalone Haliotis sorenseni.P. mollis growth was positively correlated with light over specific light densities (SLD) ranging from 0.0048 to 0.036molphotonsg−1fresh weightd−1, under tumble culture conditions. Under low light conditions, growth was greatest at a temperature of 12°C (SGR=8.69±0.29%d−1), while under high light conditions growth was greatest at a temperature of 14–18°C (SGR=10.5±0.12%d−1). Addition of Guillard's f nutrient medium [Guillard, R.R.L., Ryther, J.H., 1962. Studies on marine plankton diatoms. I. Cyclothella nana Huntedt and Detonula confercacae (Cleve). Gran. Can. J. Microbiol. 8, 229–239] significantly increased Pacific dulse growth in cultures receiving one seawater exchange per day; furthermore, growth was significantly improved by addition of trace metals. The use of NaNO3 as an N source in the f medium resulted in better growth compared with NH4NO3. The use of phosphorus additions above 83.3μMPd−1 depressed P. mollis growth rates. P. mollis growth was positively correlated with concentrations of dissolved inorganic carbon, including HCO3−. Growth rates were not significantly different over a pH range of 8.3–8.9.There were no significant toxic effects on Japanese abalone, H. discus hannai cultured in seawater supplemented with (0.75f+1.37μM Zn) trace metals d−1. H. discus hannai showed the highest growth rates when fed on P. mollis fertilized with f medium and nitrate (NO3−-N) loads ranging from 1176 to 2353μMd−1 while red abalone, H. rufescens, grew best when fed on P. mollis fertilized with f medium and nitrate loads of 2353–2942μMd−1. Both abalone species grew better on P. mollis fertilized with (0.75f+1.37μM Zn) d−1 trace metal solution compared with P. mollis without trace metal additions. H. sorenseni, grew well when fed on P. mollis, showing higher linear shell growth rates and higher survival rates compared with those of abalone fed on commercially harvested and abundant giant kelp, Macrocystis pyrifera.