Larval settlement of Sabellaria cementarium Moore, and comparisons with other species of sabellariid polychaetes

Tube-building marine worms of the polychaete family Sabellariidae exhibit a wide range of settlement strategies; the larvae of some species settle with near-absolute specificity on the sandy tubes of conspecific adults to build extensive reefs, while others are not gregarious and construct solitary or paired tubes. Sabellaria cementarium forms aggregations in some localities, but it is nongregarious throughout much of its range. Larvae of S. cementarium were competent to metamorphose in 25 days at 15 °C, much sooner than previously reported and within the range of other sabellariids cultured under the same conditions. In two of three experiments, there were no significant differences in larval settlement on conspecific tube sand versus control sand or tube sand extracted with organic solvents, suggesting that this species does not aggregate in response to a chemical cue. Settlement was not enhanced in response to free fatty acids, naturally occurring inducers of settlement for two reef-forming sabellariids, Phragmatopoma lapidosa lapidosa and P. l. californica. In reciprocal assays, larvae of S. cementarium and P. l. californica did not significantly discriminate between conspecific and heterospecific tube sand; yet, where they co-occur, the tubes of the former species are not found in aggregations of the latter. The two species were not interfertile, although one cross resulted in ~ 14% fertilization with larvae dying shortly after hatching. The processes by which larvae of S. cementarium avoid settlement on the tubes of P. l. californica (and the reverse for the latter species) remain unclear.