Intertidal crabs in diverse habitats worldwide release larvae synchronously during nocturnal spring high tides. This expedites seaward transport of the larvae to beyond high density areas of predatory fishes under the cover of darkness. We found that 4 species of intertidal crabs along the west coast of the USA shared this reproductive timing pattern. As in other mixed semidiurnal tidal regimes, biweekly patterns of larval release were more closely synchronized with the tidal amplitude cycle than the lunar cycle, and some crabs released larvae in daylight. However, unlike other places in the world, larval release was weakly synchronized to environmental cycles regardless of interspecific differences in vertical distributions on the shore. We provide evidence that weak synchrony in the timing of larval release in upwelling regimes can result from exposure to environmental variation over long incubation periods of externally brooded embryos. According to the prevailing paradigm, weaker synchrony in the timing of larval release will increase predation by planktivorous fishes in upwelling regimes. Weak synchrony in the timing of larval release should increase larval mortality in a wide array of animals that brood embryos in the intertidal zone, regardless of the selective force operating, and it could contribute to recruitment limitation in upwelling regimes. © Inter-Research 2011.

Trace elemental signatures incorporated into calcified structures in fish and mollusk larvae have been used to reveal population connectivity and larval dispersal trajectories. To determine whether trace element analysis could be applied to larvae that do not permanently retain calcified structures, we raised larvae of the porcelain crab Petrolisthes cinctipes from multiple locations along the northern California, USA, coast in a common water source for up to 8 wk. We analyzed 20 elements in extractions of soft tissues from embryos and the 2 larval and 1 postlarval stages. Elemental signatures of individuals in each developmental stage were compared to an atlas of signatures from each collection site using discriminant analysis to determine whether larvae could be accurately assigned to their site of origin in 2 ways. First, postlarvae were classified using a natal site atlas constructed using embryonic signatures from each site, and this classification had poor success (average 39.7% correct). Second, larvae of each stage were classified using a natal site atlas constructed using signatures of larvae from that same stage. This yielded considerably better classification success (81.7% correct overall). Thus, the same trace element signatures were not consistently maintained from embryos to postlarvae, but differences in signatures among natal sites were maintained during the larval period. Trace element signatures in soft tissues could be useful in tracking dispersal between stages and determining how many sites, rather than which sites, contributed to a cohort of larvae or settlers. © Inter-Research 2013.

Natural trace element signatures have increasingly been used to track the dispersal of marine larvae, and these studies require an atlas of potential source populations with distinctive elemental signatures. To determine whether natal site atlases could be used repeatedly and to identify site characteristics that yield the best results, we built atlases in 5 consecutive years using embryos of the porcelain crab Petrolisthes cinctipes that were collected from 15 sites spanning 190 km of the open coast of northern California, USA. We analyzed the elemental composition of the embryos using a discriminant function optimization procedure to determine the suite of elements that resulted in the best reclassification success for individual sites and groups of sites each year. No single element or group of elements succeeded in discriminating the origins of embryos every year, and the reclassification success of the atlas varied at all spatial scales among years. Average reclassification success at the site level ranged annually from 39.5 to 54.3% correct, and combining sites into 2 or 3 areas improved the overall reclassification success to 72.5 to 97.7% correct. Sites with (1) distinctive elemental compositions of rocks, (2) unusual habitats, (3) consistent freshwater input, (4) consistent anthropogenic inputs, or (5) complex local oceano graphy had the highest reclassification success (up to 86.7% correct), but interannual variation in runoff reduced the temporal stability of the atlas. To improve population connectivity estimates, future trace element studies should consider these 5 key characteristics when selecting sites and anticipate temporal variation in natal site signatures. © Inter-Research 2013.