Adult/juvenile interactions of infaunal bivalves:contrasting outcomes in different habitats

Abstract

Field experiments were used to assess the influence of density vanatlons of adult bivalves on recruitment of juveniles. The generality of these results was tested by running the experiment concurrently at 2 sltes of different sediment grain size and wave exposure. Adults of 2 bivalve species, the deposit-feedlng tellinid Macomona lillana and the suspension-feeding venerid Austrorienus stutchburj~i, were used in the experiment. The experiment consisted of 14 treatments of vanous combinations of densities of live adults or the empty articulated shells of the 2 species. Three species of juvenile bivalve (M. liliana, A. stutchburyi and Nucula hartvigiana) were sampled from the experiment on 3 occasions over a 9 wk period. Treatment effects were consistent over lime, but reflected only small changes In the mean density of juvenile bivalves. The presence of empty articulated shells of adult M. liliana or A stutchburyi, positioned at localities within the sediment which reflected normal living conditions, had no detectable influence on the density of juvenile bivalves. Treatments ~nvolving adult A stutchburyi ~nfluenced only the density of juvenile conspecifics at the muddy-sand site. Treatments involving adult M. liliana produced significant effects on the density of both M. l~liana and N. hartvlgiana juveniles a t both sites. However, these effects occurred in opposite directions a t the 2 sites. At the muddy-sand site, highest juvenile densities were associated with high adult densities, but, at the sandy site, they were associated with the absence of adult M. liliana. The identification of subtle density changes a t the sandy site was unexpected because sediment transport is frequent at this site and associated passive movement of juveniles has the potential to mask local biotic interactions. The change found in the direction of interactions between adult and juvenile bivalves between sltes has irnplications for the generality of such interactions: in particular it highlights the influence that habitat may have on ecolog~cal interactions.

Integrating heterogeneity across spatial scales: interactions between Atrina zelandica and benthic macrofauna

“…Marine soft-sediment studies investigating interspecific relationships often focus on density effects (see 124 Olafsson et al 1994 for a review, also more recently Thrush et al 1996a, Alfaro & Carpenter 1999, Botto & Iribarne 1999, Crooks & Khim 1999, Manderson et al 1999 (Table 6). This makes designing manipulative experiments more complex and suggests that before conducting manipulative experiments, a survey of natural communities is required to determine the range of spatial distributions available and the variables that are most important (e.g.…”

The sandflat habitat: scaling from experiments to conclusions

“…However, many important ecological questions and pressing environmental problems concern integration over a wide range of spatial and temporal scales-especially the larger ones (Livingston, 1991;Carpenter et al, 1995;Thrush et al, 1995). Even where processes are operating on scales amenable to experimental manipulation, individual experiments frequently are conducted at only one location and the results of similar experiments in different locations are not always consistent (Thrush et al, 1996). Interpolating the results of studies by either extending the size of the area in which phenomena operate (i.e.…”

“…On the Wiroa Island sandflat, recolonisation of small defaunated plots is influenced by resident adult infauna. In particular, low adult densities of Macomona liliana can facilitate recruitment of conspecifics, while high adult densities can inhibit conspecific recruitment (Thrush et al, 1992(Thrush et al, , 1996. Evidence of further interactions involving this species came from an experiment designed to assess the effects of large vertebrate predators on macrofaunal community structure (Thrush et al, 1994b).…”

Variable effect of a large suspension-feeding bivalve on infauna: experimenting in a complex system

“…Wiens et al 1986, Irlandi et al 1995, Irlandi 1996, Thrush et al 1996, 1997a,b, Micheli 1997. In marine benthic systems, results of experiments may differ in time or space due to interactions with broader scale phenomena associated with habitat or oceanographic variability.…”