Effects of post-settlement habitat use and biotic interactions on survival of the seagrass-associated fish red drum (Sciaenops ocellatus)

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Title: Effects of post-settlement habitat use and biotic interactions on survival of the seagrass-associated fish red drum (Sciaenops ocellatus)
Author: Fencil, Megan Christine
Abstract: Due to high mortality encountered by marine fish larvae during their first weeks of life , small changes in the number of individuals surviving through this period can cause large fluctuations in year -class strength . Larval Red Drum (Sciaenops ocellatus ) are dependent upon structured estuarine habitat to avoid predation . A study of post -settlement larval Red Drum distribution in a subtropical seagrass meadow in Mission -Aransas Estuary , Texas , USA indicates that larvae settle over approximately two months . Abundance of larger settled larvae was significantly different among sites . The areas of highest larval abundance varied temporally , indicating that the entire extent of the seagrass bed is utilized . Regression analysis of abiotic environmental factors did not explain why larvae were more abundant at particular sites . To characterize the structure and variability of the fish species assemblage that Red Drum encounter upon settlement , larvae and juveniles were captured in the seagrass meadow during weekly collections . Of the 32 fish species collected , seven represented 92 % of the assemblage . Multivariate species analysis indicated that collections widely separated in time and space shared the lowest Bray -Curtis similarity . Because Red Drum settle over a relatively long period and co -occur at body sizes known to cause cannibalism under laboratory conditions , I tested combinations of small and large Red Drum larvae at various field -realistic densities and at different levels of seagrass habitat structure to determine potential for cannibalism . Artificial seagrass did not protect small (5 – 6 mm SL ) larvae from cannibalism , but natural dense seagrass had a protective effect relative to edge habitat . The final component of this research examined the emergent impacts of a common predator pinfish (Lagodon rhomboides ) on mortality and cannibalistic interactions between small and large Red Drum larvae . Both pinfish and large Red Drum larvae alone readily consumed small Red Drum in all seagrass habitat structures tested . However , the combined treatment of pinfish and large Red Drum together led to reduced mortality of small Red Drum . Predation can significantly affect Red Drum survival during the post -settlement period , and multiple predators may have a protective effect on the smallest settlers if predation pressure is re -directed towards a larger size class .
URI: http : / /hdl .handle .net /2152 /ETD -UT -2009 -12 -668
Date: 2010-08-23

Citation

Effects of post-settlement habitat use and biotic interactions on survival of the seagrass-associated fish red drum (Sciaenops ocellatus). Doctoral dissertation, The University of Texas at Austin. Available electronically from http : / /hdl .handle .net /2152 /ETD -UT -2009 -12 -668 .

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