Local dispersal of juvenile bivalves: implications for sandflat ecology

Abstract

Dispersal has profound influences on population dynamics and is a key process maintaining spatial and temporal patterns. For many benthic marine invertebrates dispersal occurs primarily during the planktonic larval stages. It is now widely recognised that post-larval and juvenile stages of benthic invertebrate species can also exhibit high rates of dispersal. In particular, post-settlement dispersal has been demonstrated for many bivalve species. Despite this appreciation, no studies to date have analysed the direct dispersal rates and the spatial distribution of dispersing individuals in situ. We used a fluorescent stain for marking bivalves in vivo and a mark-and-recapture methodology to investigate dispersal patterns of post-larval and juvenile bivalves on a sandflat. Wave-induced energy dissipation on the seafloor was measured using a DOBIE wave gauge. Tracer sediment and bedload transport was used as a template for bivalve movement. The experiment was conducted over a short-time span (60 h) and encompassed spatial scales relevant to many sampling designs and manipulative experiments. Our results show that juvenile bivalves dispersed over scales of meters within one tidal cycle. Modelling the half-life of juvenile bivalve retention using radioactive decay equations provided insight into the local persistence of individuals. These models indicate a 50% turnover within an area of 0.25 m 2 for post-larval (<1 mm) bivalves within the first 17.4 h, whereas juvenile (1-4 mm) bivalves persist longer with a 50% turnover after 31.5 h. Considering the very calm hydrodynamic conditions during the experiment, these dispersal rates are remarkable. Bivalve dispersal was decoupled from sediment bedload transport, illustrating the importance of active dispersal behaviour under the prevailing hydrodynamic conditions. Our results suggest that dispersal is potentially more important than mortality for the population dynamics of juvenile bivalves over small and meso spatial-time scales.KEY WORDS: Bivalve dispersal · Post-settlement transport · Wind waves · Disturbance · Scale · Sediment bedload transport · Intertidal sandflats Resale or republication not permitted without written consent of the publisher

Spatial and temporal variability in juvenile bivalve dispersal: effects of sediment transport and flow regime

“…High rates of dispersal of juvenile bivalves have also been observed in other systems. Turnover of bivalves has been estimated to occur within one to several days in a number of soft bottom habitats (Armonies 1994, Commito et al 1995a, Norkko et al 2001. Rapid turnover also has been observed for other groups of macrofauna and meiofauna on tidal flats (e.g.…”

“…As a result, field measurements of rates of dispersal of some bivalves may be uncoupled from sediment transport (e.g. Norkko et al 2001). …”

“…Thrush et al 1996, Hewitt et al 2003, Zajac & Whitlatch 2003, and for bivalves it has been suggested to result in rapid turnover of individuals (e.g. Norkko et al 2001) and changes in spatial distribution with age (e.g. Bouma et al 2001).…”

The effect of eutrophication abatement on the bivalve Scrobicularia plana

“…Although recruitment was higher, the most eutrophic area exhibited less adult individuals, probably related to a spatial dispersion towards the other two areas. Despite the restricted mobility of this species, there are several references to dispersion of S. plana (Hughes, 1969(Hughes, , 1970aGuelorget and Mazoyer-Maye´re, 1983;Sola, 1997;Guerreiro, 1998) and among other bivalve species (Norkko et al, 2001) over short and medium distances.…”

Predicting suitability of cockleAustrovenus stutchburyirestoration sites using hydrodynamic models of larval dispersal

“…Ciliated larvae such as bivalve veligers cannot swim sufficiently fast in a horizontal direction to influence their distribution (young 1995); but they may control their horizontal position through occupying selected depths, allowing them to exploit flow regimes that may advect them toward suitable settlement habitat (Wood & hargis 1971;Shanks 1995;Baker & mann 2003). many bivalves also move considerable distances as postsettlement juveniles via bedload or watercolumn transport, thus influencing colonisation rates of disturbed sites (armonies 1996;Norkko et al 2001;Petuha et al 2006). However, we expected postsettlement dispersal to be on a smaller scale than larval dispersal because of physiological and behavioural characteristics that limit transport (Lundquist et al 2004b;Petuha et al 2006), and thus only considered larval dispersal in the current model.…”