Transport and mixing of gametes in three free-spawning polychaete annelids, Phragmatopoma californica (Fewkes), Sabellaria cementarium (Moore), and Schizobranchia insignis (Bush)

Abstract

Invertebrates that free-spawn (release their gametes into the water column) are dependent on the movement of water for transport and mixing of gametes in order to achieve successful fertilization. Therefore, rates of transport and mixing of gametes in the water column and the behavior of animals during spawning may have significant reproductive consequences. In this study, rates of advection (horizontal transport), convection (vertical transport) and mixing in the water column of gametes of the polychaete annelid Phragmatopoma californica (Fewkes) were quantified. Spawning behavior in this polychaete was also examined. Rates of P. californica gamete transport and mixing were compared with those of two other polychaete species, Sabelleria cementarium (Moore) and Schizobranchia insignis (Bush). Gametes of P. californica have mixing rates below those of water, are advected at a similar rate as the ambient water flow but convected at a higher rate. Comparisons of the transport and mixing rates of P. californica gametes with those of two other polychaetes, Sabelleria cementarium and Schizobranchia insignis indicate that the sperm of all three species mix in the water column at a similar rate whereas eggs do not. Phragmatopoma californica was observed releasing eggs in a single clump and sperm in clumps, strings, or as a plume. Eggs were released below structures on worm's tubes that protrude above surfaces of P. californica aggregations. Some sperm was released below these structures while some was ejected above them. Therefore, simple models or experiments that assume gametes of free-spawning invertebrates are released in plumes may be inadequate for predicting fertilization success in this species.