Spatio-temporal variation in sediment biochemistry alters larval habitat selection and juvenile performance in the polychaete Capitella sp. I

The aim of the present study was to understand how larvae and juveniles of the opportunistic polychaete Capitella sp. I respond to natural sediments with varying biochemical properties. Muddy sediments of a similar particle size spectrum were collected from 5 sites in Hong Kong along a pollution gradient of domestic sewage on 4 sampling occasions in both wet and dry seasons. The sediments were used to study the influence of organic matter quantity and composition (i.e. total organic carbon [TOC], total nitrogen [TN], chlorophyll a, biopolymeric carbon and enzymatically hydrolysable amino acid contents) on larval metamorphosis (i.e. habitat selection) and juvenile performance (i.e. growth and survivorship). Organic matter quantity and composition varied with sampling date and site. Still water multiple-choice experiments showed that larval choice at settlement varied with spatial and temporal variations in sediment biochemical properties. A series of experiments in the study also showed that both the quantity and the composition of organic matter affect the attractiveness of substrates to larvae and appear to play a key role in determining larval behavior at the time of settlement. Further laboratory experiments showed that larvae did not choose to settle on sediments from sites where juvenile growth was poor and mortality was higher. Our field data indicated that both larval metamorphosis and juvenile performance patterns observed in this laboratory study partially corroborate data on the abundance of adult Capitella spp. in the field. Overall, this study suggests that the field distribution of Capitella sp. 1, and consequently species composition in a community, could be determined by the habitat selection by larvae and early juvenile performance.