Larval Behavior and Natural Trace Element Signatures as Indicators of Crustacean Population Connectivity

In Chapters 1 and 2, I focused on investigating the role of swimming behavior in regulating larval transport in upwelling regimes. I observed in the laboratory the larvae of four crab species from open coast and estuarine habitats that develop either nearshore or offshore. Larval vertical positions in acrylic columns were recorded for up to three days, and I determined whether (1) depth preferences differed for the four species, (2) larvae undertook tidal and diel vertical migrations, (3) vertical migrations were timed endogenously or exogenously, and (4) maternal habitat influenced larval swimming behavior. Regardless of light or tidal phase, larvae of three species (Hemigrapsus oregonensis, Lophopanopeus bellus bellus, and Pachygrapsus crassipes) that develop offshore stayed high in the water column, where they would be transported seaward in the field. In contrast, larvae of one species (Petrolisthes cinctipes) that develop nearshore stayed low in the water column, where they would remain in shoreward-flowing bottom waters. None of the species from the open coast exhibited tidal or diel vertical migrations, but one estuarine species (H. oregonensis ) exhibited reverse tidal vertical migrations that would expedite their transport to the open ocean. Furthermore, larvae hatched from estuarine populations of P. crassipes exhibited tidal swimming behaviors, while larvae hatched from coastal populations showed no tidally based behavior. Thus, larvae of species that hatch in different locations and develop different distances from shore exhibited diverse larval swimming behaviors that regulate transport, and these behaviors are phenotypically plastic.;A successful trace element study requires a natal site atlas with high reclassification success, but selecting sites to create an atlas is time consuming and expensive, with no guarantee that trace element signatures will differ among sites and remain consistent over time. In Chapter 3, I determined whether natal site atlases could be used repeatedly and identified site characteristics that yielded the best results by building atlases in five consecutive years using crab embryos from 15 sites that spanned 190 km of the northern California coast. I analyzed the elemental composition of 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 element or group of elements was useful 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 three areas or two regions improved overall reclassification success to 72.5% to 97.7% correct. Sites with unique geology, consistent freshwater runoff, or high anthropogenic influences had the highest individual reclassification success (up to 86.7% correct), and variation in these factors helped account for the variability in reclassification success among sites. Targeting differences in these factors when selecting sites in future trace element studies will increase the resolution of population connectivity estimates and inform explorations on the usefulness of these types of studies in a given area.;Finally, Chapter 4 focused on whether or not trace element signatures were retained in larval soft tissues throughout their pelagic development, to determine whether trace element analysis could be applied to larvae of the vast majority of species that do not retain larval calcified structures. To determine whether natal signatures are retained in soft tissues throughout larval development, I collected embryos of the porcelain crab, Petrolisthes cinctipes, from two to four locations along the coast of northern California in two years and reared larvae in a common water source for 6-8 weeks until they metamorphosed to postlarvae. Twenty elements were analyzed in extractions of soft tissues from embryos for the two larval and one postlarval stages. Elemental signatures of these planktonic stages were compared to those of embryos from the different collection sites using discriminant function analysis to determine if they could be accurately assigned to their site of origin. Overall reclassification success of postlarvae was poor (average 39.7% correct), though individual site success ranged from 86.2% correct to 0% correct. Reclassification success improved to 81.7% correct overall (ranging from 35.7% correct to 94.4% correct) when using each larval stage as a training set for the same larval stage. Thus, the same trace element signatures were not consistently maintained from embryos to postlarvae, but differences in signatures among natal sites were maintained. Trace element signatures in soft tissues could be useful in tracking dispersal from one stage to the next and determining how many sites, rather than which sites, contributed to a cohort of settlers. (Abstract shortened by UMI.)...