Hernandez et al.: Variability in ichthyoplankton abundance and composition in the northern Gulf of Mexico 
205 
a suite of environmental parameters. First, tempera- 
ture has long been proposed as an important factor in 
the initiation of spawning for marine fishes (Orton, 
1920), and numerous field and laboratory (primarily 
aquaculture-related) studies have provided support for 
temperature as a primary influence (Arnold et al., 2002; 
Sheaves, 2006). Second, water temperature varies pre- 
dictably at seasonal scales (e.g., months), as opposed 
to other factors that vary at shorter time scales. Our 
salinity data (Fig. 3), for example, showed no seasonal 
trends and were not correlated with egg or larval fish 
concentrations. The monthly mean salinity values cal- 
culated during each cruise likely reflect short-term 
variability related to tidal flow, riverine outflow, local 
wind conditions, and related factors that affect salinity 
at our sampling station. In addition, salinity, although 
an important factor for many estuarine-spawning spe- 
cies, is generally considered less important than tem- 
perature to the timing of marine fish spawning (Bye, 
1984; Sheaves, 2006). 
Defining seasonality in terms of water temperature 
also provides a framework for monitoring fisheries dy- 
namics with respect to anticipated rises in sea tem- 
perature due to global climate change. Our monthly 
observed depth-integrated temperatures were relatively 
consistent with those for the previous ten-year aver- 
age for the region, although winter (December- Janu- 
ary) and late summer (August-October) values were 
generally higher (Fig. 2). Fodrie et al. (2009) noted a 
significant increase in sea surface temperature near 
the mouth of Mobile Bay over a 20-year period (1987- 
2007). The authors also noted a concurrent increase in 
the number and occurrence of juvenile subtropical and 
tropical fishes collected in seagrass meadows along the 
northern Gulf of Mexico. For example, in 2006-2007 
surveys, juveniles of tropical species such as Chaetodon 
ocellatus (Chaetodontidae), Fistularia tabaccu'ia (Fistu- 
laridae), Ocyurus chrysurus (Lutjanidae), Thalassoma 
bifasciatum (Labridae), Sparisoma viride (Scaridae), 
and unidentified acanthurids were collected in coastal 
habitats where they were not collected during previous 
surveys (1971-79) (Livingston, 1985). Notably, in our 
ichthyoplankton survey larvae from all of these fami- 
lies, except Chaetodontidae, were collected but regret- 
tably, comparable ichthyoplankton data from the 1970s 
were not available and our identifications were made 
only to the family level. 
Conclusions 
Increases in regional water temperatures may have sig- 
nificant impacts on the reproductive success of marine 
fishes and the subsequent survival of early life stages, 
including early gonad maturation and spawning in 
adults, altered larval transport pathways, extended 
pelagic larval durations, changes in larval assemblage 
structure, and mismatched timing of larval fish occur- 
rence with food resources and physiological optima, 
among other effects (Sheaves, 2006; O’Conner et al., 
2007; Genner et al., 2009). Establishment of long-term 
baseline surveys provides a means of monitoring larval 
fish assemblages and the factors that influence larval 
fish dynamics in order to provide early indicators of 
ecosystem changes due to environmental perturbations. 
The ichthyoplankton survey efforts described here for 
the October 2004-October 2005 period have since con- 
tinued and expanded to include near monthly (depth- 
discrete) ichthyoplankton sampling at five stations along 
a cross-shelf transect from inside Mobile Bay extending 
offshore to a station approximately 54 km south of Dau- 
phin Island. The expanded survey program (Fisheries 
Oceanography of Coastal Alabama, or FOCAL) will allow 
us to estimate and monitor the variability in ichthyo- 
plankton seasonality, abundance, assemblage structure, 
and vertical distribution over multiple temporal and 
spatial scales. 
Acknowledgments 
We would like to thank the technicians and graduate 
students that participated on our research cruises: 
A. Beck, S. Bosarge, L. Chiaverano, T. Clardy, D. del 
Valle, N. Geraldi, J. Goff, E. Goldman, J. E. Herrmann, 
J. M. Herrmann, J. Higgins, L. Kramer, B. Lacour, C. 
Martin, M. Miller, S. Muffelman, C. Newton, C. Pabody, 
D. Ploetz, C. Schobernd, Z. Schobernd, R. Shiplett, and 
D. Vivian. We especially thank the captains and crew of 
the RV Verrill and RV E.O. Wilson (R. Collier, T. Guoba, 
C. Lollar, and R. Wilson) and the Dauphin Island Sea 
Laboratory technical support team (M. Dardeau, A. 
Gunter, and K. Weiss). We also thank M. Konieczna 
and the scientific staff at the Plankton Sorting and 
Identification Center in Szczecin, Poland, for larval 
fish identifications. K. Park provided assistance with 
the CTD data. H. Fletcher and L. Hu provided data- 
base management support. S. Bosarge produced the 
station map (Fig. 1). Valuable comments and guidance 
throughout the course of our survey were provided by J. 
Lyczkowski-Shultz (NOAA/NMFS/SEFSC, Pascagoula 
Laboratory, MS) and S. Heath (Alabama Department of 
Conservation and Natural Resources, Marine Resources 
Division, Dauphin Island, AL). We also thank R. Bro- 
deur and three anonymous reviewers for comments 
on a previous version of this manuscript. A portion of 
these data were collected as part of contract # 2004- 
GPS-MSA-NC-0085 from ConocoPhillips Corporation, 
Houston, TX. 
Literature cited 
Arnold, C. R., J. B. Kaiser, and G. J. Holt. 
2002. Spawning of cobia Rachycentron canadum in 
captivity. J. World Aquacult. Soc. 33:205-208. 
Auth, T.D. 
2008. Distribution and community structure of ichthyo- 
plankton from the northern and central California Cur- 
rent in May 2004-06. Fish. Oceanogr. 17:316-331. 
