The Consequences of Short‐Distance Larval Dispersal in a Sessile Marine Invertebrate

Abstract

The colonial ascidian—algal symbiosis Didemnum molle Herdman occurs in large numbers (densities of >100 colonies/m2) on shallow patch reefs in the lagoon at Lizard Island, Australia. Shallow—water currents in the lagoon are driven unidirectionally by the southeast trade winds most of the year. The patch reefs are several hundred metres apart and are separated by sand flats. The largest populations of D. molle occur on the upstream ends of the patch reefs. D. molle larvae, followed underwater, dispersed invariably downstream in the direction of the water current at °1—2 m/min. Although larvae were capable of swimming for up to 2 h, they generally settled in 10—15 min when given a suitable substratum such as a dark surface. Larvae experimentally denied a suitable substratum for 40 min settled rapidly when provided with a dark surface, suggesting that when larvae encounter a reef after drifting over sand flats, they probably settle immediately. A qualitative model of larval dispersal was developed to predict the settlement pattern of D. molle in the lagoon at Lizard Island. Three predictions of the model were tested by measuring larval recruitment upstream and downstream of an experimental patch reef for 1 wk before, then 1 wk after denuding the reef of all reproductive D. molle colonies. The results agree with the model, indicating that larval recruitment of D. molle in the lizard Island lagoon is a highly predictable process. The settlement pattern that results from the dispersal model describes the upstream distribution of adult D. molle colonies on patch reefs in the Lizard Island lagoon.

The influence of stage-dependent dispersal on the population dynamics of three amphipod species

“…These include the dispersal of broadcast spawned gametes (Scheltema 1986;Grosberg 1991;Swearer et al 1999;Gilg and Hilbish 2003), the release of brooded larvae from maternal adults (Olson 1985;Sotka et al 2004), and the movement of both juveniles (Martel and Chia 1991;Olivier et al 1996) and adults (Junkins et al 2006). The consequence of stage-speciWc dispersal is stage-speciWc colonization.…”

Dispersal of an introduced larval cohort in a coastal lagoon

“…Researchers have been able to track relatively large larvae (e.g., Olson 1985) or unusually distinctive patches of larvae (Willis and Oliver 1990), but such situations are not representative of most larval dispersal scenarios. For most broadcast spawning invertebrates, including many economically important species (Thorson 1950), the fate of a larval cohort is unknown.…”

Biofouling likely serves as a major mode of dispersal for the polychaete tubewormHydroides elegansas inferred from microsatellite loci

“…It is often assumed that, over similar important factor influencing the amount of migration distances, species with short-lived larvae will show between adult populations (e.g. Thorson, 1950; greater genetic differentiation between populations Olson, 1985;Strathmann, 1985;Wares et al 2001).…”

“…The potential for relatively large, short-lived larvae (e.g. Olson, 1985). adults to travel great distances by rafting on natural Previous research on marine invertebrates employing objects and on artificial objects such as ships' hulls genetic markers to investigate dispersal potential has (i.e.…”