Publication Date

2014-07-29

Availability

Embargoed

Embargo Period

2015-07-29

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PHD)

Department

Marine Biology and Fisheries (Marine)

Date of Defense

2014-06-19

First Committee Member

Claire B. Paris

Second Committee Member

Mark J. Butler, IV

Third Committee Member

Lynne A. Fieber

Fourth Committee Member

Michael C. Schmale

Fifth Committee Member

Joseph Serafy

Abstract

Studies of movement, fundamental to most life on earth, become complicated in the ocean. Many marine organisms have a complex lifecycle with a larval phase, giving them vast dispersal potential from powerful ocean currents while obscuring direct observation by virtue of their minute size. These research challenges are beginning to be circumvented through biophysical modeling of larval transport. Modeling simulates the potential pathways of larvae, but not fine-scale spatial movements. Despite their small size, larvae actively participate in their dispersive journey, detecting and responding to environmental cues. Orientation behavior has a great impact on a larva’s survival and journey, and links dispersal and settlement. A thorough examination of larval movement encompasses two scales: investigating small-scale orientation behavior in situ and broad dispersal through modeling. Comprehensive studies spanning a range of spatial scales are rare, thus there is a knowledge gap between modeling dispersal and studying behavioral ecology. This dissertation bridges the gap by addressing both scales of movement for the Caribbean spiny lobster, Panulirus argus, and asking: what are the consequences of larval lobster movement? Caribbean larval movement and connectivity were explored using Lagrangian stochastic modeling of larval dispersal. The first focus was on how variation in modeled biological traits impacted connectivity networks, to provide a template for setting up and evaluating future models of larval dispersal. Any linkage of modeled larvae between two habitat sites was defined as a connection. Connections were rare in time, associated with mesoscale features in both time and space, and vertical migration behavior increased the stability of connections. Next a dispersal model was parameterized, validated with observed average monthly settlement at multiple sites, and used to determine the probabilistic larval connectivity of lobster; translating connectivity into fisheries management strategy. The majority of larval exchanges cross international boundaries, and management scenarios focused on international exchange yielded the most settlement potential. However, self-recruitment still dominated in some areas. Management scenarios focused on preserving connectivity from self-recruitment caused a near universal increase in modeled larval settlement across the Caribbean. Simulations including behavior and realistic spawning biology performed best when compared with empirical data. Modeled pelagic nurseries were identified that entrained lobster larvae across age classes, and may be important features for conservation. Previous studies suggest that as a larva moves towards appropriate settlement habitat, it is exposed to environmental cues including sound, odor, pressure, and light. If, when, and how a settling larva integrates this information to influence its journey remains a mystery. The Drifting In Situ Chamber (DISC) allows glimpses into this process; while imbedded in the ocean current it simultaneously observes the environment, and quantifies the orientation behavior of larvae. This study deployed this new instrumentation in a novel manner, investigating the orientation behavior preceding settlement of postlarval lobsters in situ and nocturnally for the first time. Postlarvae oriented differently relative to the tide. During ebb tide postlarvae oriented using partial compensation into the current and towards the shore, potentially facilitating transport towards settlement habitat. Postlarvae may orient using the wind while at the surface, using a seabreeze as a compass to swim towards settlement habitat. Investigating the specific movement patterns during settlement and the far-flung dispersal of a species throughout its range gives this study a comprehensive examination of marine larval movement ecology over multiple spaciotemporal scales. The dynamics of spiny lobster dispersal throughout the Caribbean are necessary information for managing an internationally important fishery. Understanding the cues that guide the postlarvae of lobster, and likely a broad range of other species, into settlement habitat is important to better conserve nursery habitats.

Keywords

LaGrangian Individual-Based Model; Orientation; Larva; Panulirus argus; Spiny lobster; postlarva

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