Award: OCE-1155628

Larval connectivity of fishes and invertebrates has broad implications for population dynamics (e.g., recruitment pulses to fisheries), stock delineation, and mechanisms of evolution. Therefore, a major challenge in marine ecology and marine resource management is describing patterns of larval dispersal and population connectivity in the sea. The goal of this study was to gain insight into the larval connectivity and dispersal of a commercially and ecologically important invertebrate, the Eastern oyster (Crassostrea virginica), within a large estuarine system along the eastern US (Pamlico Sound, NC). To accomplish this, we applied two approaches: geochemical tags stored in the shell of oysters formed during the larval stage, and computer model simulations that accounted for physical transport processes and larval swimming behaviors. Studies utilizing natural or artificial tagging methods have greatly enhanced our quantitative understanding of larval connectivity in the ocean. Geochemical markers (e.g., Strontium, Barium, Manganese) stored within growing calcified structures, such as fish "ear stones" and bivalve shells, are useful for examining marine larval connectivity as many marine organisms begin recording environmental signatures with these "hard parts" soon after egg fertilization. Thus, provided that there are spatial gradients in environmental conditions, these hard parts can carry a permanent record/tag that allows researchers to retroactively track individuals through time and space (i.e., a flight data recorder). Estuarine systems provide an ideal setting in which to apply geochemical tagging methods and explore larval connectivity as they are characterized by high environmental variation, encompass complex and patchy habitat landscapes, and function as important nursery, juvenile, and adult habitats for many marine organisms of ecological and economic value. We began by evaluating the utility of geochemical tagging methods to discern oyster larval connectivity among reefs across Pamlico Sound. We used both laboratory incubations and field surveys to assess how gradients in temperature, salinity, and trace metal concentrations affect the incorporation of geochemical signals in larval oyster shells. Our studies demonstrated that across regional (35 km) scales within Pamlico Sound, spanning salinity and temperature gradients, there were distinct multi-elemental signatures between potential natal sites for oysters. For instance, we observed higher Sr concentrations within larval shells in cooler and fresher water, such as occurs in the northwestern portion of the Sound. Following these ground-truthing efforts, we used geochemical tagging to assess estuarine-scale larval connectivity among subpopulations of oysters. To generate ?atlases? of geochemical signatures associated with potential spawning sites, we outplanted/incubated recently spawned oyster larvae at multiple stations across Pamlico Sound. Using these atlases, we predicted the natal origin (i.e., connectivity) for newly settled oysters (spat) during three field trials conducted over two summers (2013- 2014). Patterns of larval connectivity varied both seasonally and annually, but were predominately directed south to north following wind patterns. Predicted self-recruitment was variable, as 0-100% of spat in a given region displayed signatures consistent with natal origin within that same region. We also used a biophysical model to simulate dispersal of eastern oyster larvae and connectivity among an existing network of 10 oyster reserves in Pamlico Sound. Modeling parameters were varied to assess the relative importance of spawning location, spawning date, larval behavior, larval mortality, and adult reproductive output to predicted dispersal and connectivity patterns. Spawning location and date of spawning relative to physical processes, particularly frequency of wind reversals, were the dominant drivers of dispersal and connectivity patterns. To a lesser extent, larval behavior (i.e., vertical depth regulation) and mortality modified dispersal and connectivity, whereas spatiotemporal variability in adult reproductive output was of minimal importance. Over a 21-day larval duration, mean dispersal distance of passive surface particles ranged from 5-40 km. Reserves were too small (<1 km2) relative to mean dispersal distances to promote extensive local retention or promote extensive inter-reserve connectivity. Reserves did, however, serve as notable "sources" for larval oysters that dispersed to non-reserve sites throughout Pamlico Sound. Collectively, these results highlight that oyster sub-populations (reefs) in Pamlico Sound are well connected and demographically "open" over annual (or longer) timescales. Thus, fewer large or several small reserves could both perform well in this system. Broadly speaking, natal sources in the southern half of Pamlico Sound were more typically larval source areas, and therefore could be targeted for the siting of future oyster reserve sites. To date, the project has supported 10 publications appearing in Ecology, Frontiers in Ecology and the Environment, Ecological Applications, Fisheries Oceanography, Journal of Applied Ecology, Marine Ecology Progress Series, Nature Climate Change, Restoration Ecology, Scientific Reports, and Proceedings of the Royal Society B, as well as 2 additional submitted manuscripts (Limnology and Oceanography, and Marine Ecology Progress Series). Two Ph.D. students worked on this study, with both students having published first-authored papers that acknowledge NSF support. One student has accepted a tenure-track position at East Carolina University, while the other currently works as a Knauss Fellow for the US Fish and Wildlife Service. Last Modified: 06/23/2017 Submitted by: Fredrick J Fodrie