Removal of Macroalgal-Derived Organic Matter from Suspension by Green-Lipped Mussels (Perna canaliculus): Potential Influence of Phlorotannin Concentrations and Nutritional Profiles

To test the effects of initial concentration and age of macroalgal-derived particulate material (MDPM) on removal rates by the green-lipped mussel (Perna canaliculus), two, no-choice feeding experiments were performed. Macroalgal-derived particulate material originating from common large brown algae with relatively high (fucoids: Cystophora retroflexa, Cystophora torulosa) and low (laminarians: Macrocystis pyrifera, Undaria pinnatifida) initial phlorotannin concentrations from southern New Zealand was selected for use in experimentation. Mussels were removed fresh MDPM originating from each species, but removal rates of MDPM were higher for the low phlorotannin species than for the higher phlorotannin species. Removal rates of MDPM ranging from fresh, 14, and 28-day-old material decreased with age in C. retroflexa and M. pyrifera, but not for MDPM from C. torulosa and U. pinnatifida. Initial MDPM concentrations presented to mussels ranged from 0.017 to 0.126 g L–1, and removal rates were positively correlated with increasing concentrations of fresh MDPM from three macroalgal species. A relationship was not observed between increasing concentration and removal rates of MDPM from C. retroflexa. In addition, carbon-to-nitrogen mass ratios (C:N) and nutritional profiles of mature blade material collected from C. retroflexa, C. torulosa, M. pyrifera, and U. pinnatifida were reported to consider the implications of potential consumption of MDPM on seston quality provided by macroalgal detritus in mussel diets. The two laminarian species had lower median C:N ratios than the fucoids, which were largely reflective of significant differences in total carbohydrate and crude protein content. Interspecific differences in phlorotannin concentrations and nutritional quality of organic matter produced by large brown algae have important consequences for the availability of organic matter originating from macroalgal communities and ecosystem function of coastal food webs.