Settlement of blue crab (C. sapidus rathbun) megalopae varies over distance and time in Aransas-Redfish Bay, Texas
Abstract
Description
A thesis Submitted in Partial Fulfillment of the Requirements for the Degree of MASTER OF SCIENCE in FISHERIES AND MARICULTURE from Texas A&M University-Corpus Christi in Corpus Christi, Texas.
Blue crab (Callinectes sapidus Rathbun) are both a keystone species and an important fishery throughout its U.S. range. Extensive research of the life history and ecology of blue crab has been undertaken. However, limited research into postlarval recruitment dynamics in Texas estuaries has been conducted, providing impetus for this study. To describe the spatiotemporal occurrence and use of the Aransas-Redfish Bay Complex (ARBC), Texas, by blue crab megalopae, settlement was monitored via passive collectors at five sites along the periphery of the complex for 40 weeks (24 h week-1) from August 2012 through September 2013. Barometric pressure, flood time, fractional illumination, salinity, water temperature, and wind direction and speed were determined for each sampling period. Regression of a zero-inflated negative binomial model of settlement indicated that date, location, and east-west wind strength were significantly influential on settlement of blue crab megalopae. Settlement was episodic and varied over time with a majority of settlement, 63.5%, occurring during 2012 sampling dates. Settlement occurred at low levels at all sites from August 2012 through March 2013, becoming confined to the site located within the Aransas Pass from April through August 2013. Peak settlement events (mean count ≥ 25.2 day-1) were observed in all months of the study except for January, August, and September 2013. Significant differences in mean settlement with distance from the tidal inlet was found with 97% of settlement occurring within 8.2 km of the Aransas Pass tidal inlet and 94% of settlement occurring along the Aransas Ship Channel. The greatest numbers of megalopae were collected within the Aransas Pass, accounting for 71% of total megalopae count. Settlement occurred primarily on ESE-SE mean winds between 6-9 m sec-1. Peak settlement events coinciding with predominantly SSE-ESE winds, but varied by site, dependent upon wind speed from a given direction. The results of this study indicate that 1) blue crab megalopal settlement within the ARBC exhibits intra- and interannual variation consistent with related studies; 2) surface currents associated with onshore wind forcing primarily drive blue crab megalopal settlement within the ARBC; and 3) that settlement is secondarily driven by location, with vegetated bottom closer to the Aransas Pass tidal inlet serving as preferential nursery grounds.
Life Sciences
College of Science and Engineering
Blue crab (Callinectes sapidus Rathbun) are both a keystone species and an important fishery throughout its U.S. range. Extensive research of the life history and ecology of blue crab has been undertaken. However, limited research into postlarval recruitment dynamics in Texas estuaries has been conducted, providing impetus for this study. To describe the spatiotemporal occurrence and use of the Aransas-Redfish Bay Complex (ARBC), Texas, by blue crab megalopae, settlement was monitored via passive collectors at five sites along the periphery of the complex for 40 weeks (24 h week-1) from August 2012 through September 2013. Barometric pressure, flood time, fractional illumination, salinity, water temperature, and wind direction and speed were determined for each sampling period. Regression of a zero-inflated negative binomial model of settlement indicated that date, location, and east-west wind strength were significantly influential on settlement of blue crab megalopae. Settlement was episodic and varied over time with a majority of settlement, 63.5%, occurring during 2012 sampling dates. Settlement occurred at low levels at all sites from August 2012 through March 2013, becoming confined to the site located within the Aransas Pass from April through August 2013. Peak settlement events (mean count ≥ 25.2 day-1) were observed in all months of the study except for January, August, and September 2013. Significant differences in mean settlement with distance from the tidal inlet was found with 97% of settlement occurring within 8.2 km of the Aransas Pass tidal inlet and 94% of settlement occurring along the Aransas Ship Channel. The greatest numbers of megalopae were collected within the Aransas Pass, accounting for 71% of total megalopae count. Settlement occurred primarily on ESE-SE mean winds between 6-9 m sec-1. Peak settlement events coinciding with predominantly SSE-ESE winds, but varied by site, dependent upon wind speed from a given direction. The results of this study indicate that 1) blue crab megalopal settlement within the ARBC exhibits intra- and interannual variation consistent with related studies; 2) surface currents associated with onshore wind forcing primarily drive blue crab megalopal settlement within the ARBC; and 3) that settlement is secondarily driven by location, with vegetated bottom closer to the Aransas Pass tidal inlet serving as preferential nursery grounds.
Life Sciences
College of Science and Engineering