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Potential larval dispersal and population connectivity of deep-sea methane seep invertebrates

Potential larval dispersal and population connectivity of deep-sea methane seep invertebrates
Doreen Miriam Anne McVeigh

2016

Department of Marine, Earth, and Atmospheric Sciences, North Carolina State University, Raleigh, NC 27695, UNITED STATES OF AMERICA.

ABSTRACT

Since their discovery, deep-sea chemosynthetic ecosystems have been novel systems within which to test the generality of paradigms developed for shallow-water species. The first part of this study explored the roles of larval behavior, pelagic larval duration (PLD), and spawning locations on dispersal potential of seep invertebrates. The goal was to assess the dispersal trajectories of the polychaete, Lamellibrachia luymesi, the gastropod, Bathynerita naticoidea, and the crustacean, Alvinocaris muricola among seep-sites in the Gulf of Mexico (GOM) and Western Atlantic Ocean (WAO) using a coupled biophysical model. Larval particles were programmed with species-specific PLDs and swimming behaviors that best matched empirical data, and released into a flow field that accurately characterizes climatological conditions at ~7-kilometer horizontal resolution. While there was variation, the overall trend was consistent, with the greatest dispersal observed for A. muricola, followed by B. naticoidea, and L. luymesi. L. luymesi mean particle distance travelled was significantly higher when released from western GOM (274 km ± 0.82), followed by the eastern GOM (171 km ± 0.82). B. naticoidea mean particle distance travelled was significantly higher when released from western GOM (670 km ± 1.27), followed by WAO (287 km ± 1.27), northern WAO (286 km ± 1.27), central GOM (241 km ± 0.15), and western GOM (268 km ± 1.27). A. muricola mean particle distance travelled was significantly higher when released from eastern GOM (854 km ± 2.53), followed by central GOM (846 km ± 1.27), western GOM (757 km ± 1.27), WAO (616 km ± 1.27), and northern WAO (612 km ± 1.27). In Chapter 2, the dissertation explored potential larval dispersal and population connectivity of the deep-sea mussel, “Bathymodioluschildressi among three methane seep sites in the Gulf of Mexico. Three possible larval dispersal simulations were evaluated: (1) demersal drift of larvae, (2) variable larval vertical distribution with near surface dispersal, and (3) variable larval vertical distribution with near-surface dispersal. Particles with Simulation 3 behavior had the greatest dispersal distance (1173 km ±2.00), followed by Simulation 2 (921 km ±2.00), and Simulation 1 behavior (237 km ±1.43). In Chapter 3, the dissertation quantified potential population connectivity using Lagrangian Particle Density Functions (LPDFs) and connectivity matrices for the five methane seep species. There were marked differences in the strength of larval dispersal pathways and LPDFs among the different species and release sites, with a majority of larval particles remaining near their natal site. The LPDFs of particles released from the GOM with surface seeking “B.” childressi behavior readily dispersed throughout the eastern GOM and WAO. Conversely, L. luymesi and “B.” childressi demersal drifting particles were spatially constrained to the northern and western GOM, with no connection to the WAO. The majority of A. muricola and B. naticoidea particles released from WAO dispersed south of the release sites along the shelf-break depth contour toward the Caribbean (southward). Patterns of population connectivity varied greatly among species, with the greatest amount of connectivity by B. naticoidea and A. muricola, and the least amount of connectivity exhibited by surfacing seeking “B.” childressi and L. luymesi. Despite the extensive dispersal of particles, no other sites exhibited any degree of connectivity. These results are the first known attempt to use empirically observed behavior of larval seep invertebrates to assess dominant pathways and connectivity in a coupled biophysical model, and assess self- recruitment from release sites despite wide variation in PLD and behavior. Collectively, the three chapters of this dissertation provide an initial and quantitative understanding of the potential population connectivity for four species of methane seep invertebrates found throughout the GOM and WAO and the significance of coupled biophysical models to test connectivity hypotheses.