The bivalves Mytilus chilensis, Venus antiqua, Mulinia edulis and Tagelus dombeii inhabit different levels of the tidal flats in Yaldad Bay, southern Chile. Mytilus chilensis is an epifaunal bivalve, which, at this location, is also farmed in culture rafts; whereas the other species belong to the infauna. The objective of this study was to compare filtering capacity of these species; in order to do this, measurements of food consumption were taken by quantifying clearance rates, as well as taking morphological measurements of their feeding systems (gills and labial palps), and endoscopic observations to determine the velocity of particle transport within the gills. All of these parameters were related to the sediments present in environments occupied by these species. In Mytilus chilensis, both wild and farmed, gill area was significantly higher than in the three infaunal species. Mulinia edulis and Venus antiqua did not show any significant differences in gill area. As far as Tagelus dombeii is concerned, the species presented the lowest values among all species studied. Weight of labial palps was significantly higher in Mulinia edulis compared to the other species. There were no significant differences between labial palps of either wild or farmed Mytilus chilensis or in those of Venus antiqua and Tagelus dombeii. A positive, significant relationship was identified between labial palps size and mud sediment content. Both culture-rafts and intertidal Mytilus chilensis displayed a clearance rate that was significantly higher than the infaunal species, concurring with a significant relationship between clearance rate and gill area in the different species studied. Clearance rates displayed by Venus antiqua, Mulinia edulis and Tagelus dombeii did not show significantly different results among them. Mytilus chilensis from both culture-rafts and intertidal zone displayed higher values of particle transport velocity than the infaunal species. Particle transport was not observed in the dorsal canal of any of the species studied. The conclusion is that in these species filtering capacity is determined mostly by gill size and that labial palp size displays a strong relationship with sediment content in the mud of Yaldad tidal flats.

We consider adaptive importance sampling for a Markov chain with scoring. It is shown that convergence to the zero-variance importance sampling chain for the mean total score occurs exponentially fast under general conditions. These results extend previous work in Kollman (1993) and in Kollman et al. (1999) for finite state spaces.