Shifts in species composition in kelp forest communities: implications of differences in total phenolic composition among species

ABSTRACT: The purpose of our study was to measure total phenolic concentrations (TPC) of 14 species in the Phaeophyceae comprising kelp beds in the Otago Harbour Region (New Zealand). Our survey included 9 fucoids (order Fucales), 4 ‘true kelps’ (order Laminariales), and 1 species in the order Desmarestiales over 4 seasons from multiple sheltered and wave-exposed sites. TPC observed among species varied by 2 orders of magnitude from the most concentrated in Carpophyllum flexuosum (estimated marginal mean [emmean] 212.6 ± 24.77 µmol per gram dry tissue weight [g DTW^-1]) to the least concentrated in Lessonia variegata (emmean 10.88 ± 2.84 µmol g DTW^-1). Within the sheltered kelp bed communities of the Otago Harbour, TPC was higher in the warmer months and lower in the cooler months within species. In the wave-exposed communities, TPC was on average higher in the spring compared to the summer within the observed community. Lastly, within one species across both inner and outer Harbour communities, a Vargha and Delaney’s A measure suggests a specimen collected from the sheltered inner harbour sites would have a higher probability of being more concentrated in TPC than a specimen from the wave-exposed sites in the spring and summer (A-estimates 0.90 and 0.76, respectively) and a high probability of being more concentrated in the winter (A-estimate 0.70). Overall, variation in TPC among species within macroalgal communities suggests shifts toward more opportunistic species may impact community-wide TPC. Changes in species composition have important implications for the palatability of organic matter produced from macroalgal communities and the pathways for macroalgal-derived organic matter into coastal food webs.