For organisms with planktonic larvae, the early post-settlement stage is a particularly vulnerable one, likely to influence distribution patterns in subsequent life stages. Although substantial post-settlement mortality is well known in several marine invertebrate taxa (e.g. barnacles), few estimates exist for benthic invertebrates, such as mussels, that have mobile settlers. Furthermore, estimates of early post-settlement mortality (within 2 d of settlement) are sparse for most groups. In addressing the difficulties involved with quantifying early mortality of mobile settlers, the present study builds on a sequential-deployment method to estimate the post-settlement mortality of the intertidal mussel Perna perna. Trials were run at 16 sites, split evenly between bay and open coast locations, and were repeated over 2 sampling cycles. By comparing post-settlement mortality estimates from bays and open coast sites, we investigated whether such topographic features produce differential mortality. Post-settlement mortality estimates showed substantial levels of mortality but did not differ significantly between bay and open coast sites. Early post-settlement mortality (i.e. mortality of primary settlers up to 2 d old) ranged from 31 to 94% but averaged 54 and 64% in the 2 sampling cycles. Estimates of total post-settlement mortality (i.e. inclusive of primary and secondary settlers) had a similar range and averaged 66% in Cycle 1 and 67% in Cycle 2. Apart from confirming significant mortality rates of early mussel settlers, these findings suggest that intertidal abundance patterns of recruits and adults, often associated with topographic features of coastlines, are more likely a result of initial settlement patterns than of differences in post-settlement mortality.KEY WORDS: Post-settlement mortality · Coastline topography · Bays · Perna perna · Intertidal mussels · Pelagic-benthic coupling 463: 193-204, 2012 parameter to quantify, particularly for invertebrate organisms with mobile settlers. In general, monitoring of early settlers must be frequent enough to allow separation of the initial settlement pattern from the mortality-altered post-settlement pattern (Hunt & Scheibling 1997). This requirement of high frequency sampling (Minchinton & Scheibling 1993), together with the small size of early settlers makes studies of mortality within the first 24 to 48 h exceedingly difficult (Hunt & Scheibling 1997). Much of our knowledge of post-settlement processes and their importance to benthic invertebrate populations comes from the study of barnacles (Foster 1971, Connell 1985, Wethey 1985, Jarrett 2000, Chan & Williams 2003. Some direct estimates of mortality within 2 to 4 d of settlement are available for several other taxa, including ascidians, bryozoans, oysters and gastropods (Davis 1987, Stoner 1990, Ray & Stoner 1995, Gosselin & Qian 1996, Walters & Wethey 1996, Naylor & McShane 2001. For many groups, including bivalves, post-settlement mortality estimates pertain largely to older settlers and recruit...