Temporal and small-scale spatial variation in distribution, abundance, and reproduction of Australian hijiki analogues in southwest Victoria

Abstract Exploration of Australian fucoids for aquaculture production has been limited, despite globally high regional diversity and endemism. Sargassum fusiforme (hijiki in Japanese) is amongst the most highly valued seaweeds worldwide for human consumption, but concerns about high arsenic concentrations limit importation into countries with strict safe-food regulations and standards. We investigated the temporal and small-scale spatial variation in distribution, abundance, growth (estimated by changes in length), reproduction (estimated from the number of fertile conceptacles per receptacle and/or percentage of reproductive branches) and biofouling of two Australian sargassaceous fucoids, Cystophora torulosa and Caulocystis uvifera, that show promise as low-arsenic alternatives to hijiki. Temporal variation was assessed by seasonal surveys in a single year, in which small-scale spatial variation was assessed at a single site for each species, comparing high-shore and low-shore for intertidal C. torulosa and distance from the shore for subtidal C. uvifera. For C. torulosa, no significant variation in distribution, abundance or reproduction was observed; however, growth peaked in winter. Moreover, biofouling of C. torulosa was minimal throughout the study. In contrast, significant temporal variation was observed for C. uvifera with peaks in growth and reproduction in spring, and biofouling in summer. In both species, reproductive output increased with thallus length. Whilst both species might be promising Australian hijiki analogues, the temporal and spatial consistency in reproduction and minimal biofouling may render cultivation of C. torulosa more practical for successful commercialisation than for C. uvifera. However, generality of our findings should be assessed at larger spatial and temporal scales.