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Early juvenile spotted seatrout Cynoscion nebulosus (n = 199) were collected during late summer and autumn 2001 from shoreline habitats within 9 coastal regions bordering Mississippi Sound in the north-central Gulf of Mexico to ascertain how well fish could be spatially classified based on otolith chemistry. Left otoliths were assayed for trace element:Ca ratios of Ba, Li, Mg, Mn and Sr, and right otoliths for δ 13 C and δ 18 O. Significant overall differences in otolith chemistry existed among the 9 regions; 61% of the joint variance in the 7 otolith chemistry variables was explained by the regional factor in a multivariate analysis of variance (MANOVA). All 7 otolith chemistry variables differed significantly among the 9 regions. The isotopes δ 13 C and δ 18 O showed the highest regional affinities, and Li showed the strongest regional association of all the trace elements. Canonical discriminant function analysis (CDFA) maximally separated regional groups of early juvenile fish. The first 3 of 7 discriminant functions accounted for 97.5% of the cumulative variance in the 7 otolith chemistry variables. CDF 1 was influenced primarily by δ 18 O and Li, CDF 2 by Mn and δ 13 C, and CDF 3 by Mg and Ba. In the all-inclusive CDFA, 93.4% of cases were classified correctly, and classification success among regions ranged from 83.3 to 100%. The influence of freshwater discharge from 7 rivers along the Mississippi coastline likely made it possible to detect the relatively fine-scale spatial differences seen in this study, as defined by a mean interregional distance of only 25 km.

SynopsisBecause estuarine nekton are 'integrators of the environment' abiotic and biotic factors can influence or constrain the relative value of estuarine nursery zones. Recent laboratory experiments on young spot, Leiostomus xanthurus, indicate that both water temperature and salinity significantly affect somatic growth. These experimental data contrast with previous work on young Atlantic croaker, Micropogonias undulatus, white trout, Cynoscion arenarius, and mullet, Mugil sp. Together these results suggest that quantifying vital metrics of nekton, such as survival and growth, along realistic environmental gradients through critical laboratory experiments, allows a more accurate definition of constraints on habitat use. Our studies of factors influencing recruitment success in both winter-and spring/summer-spawning fishes illustrate seasonal as well as intrafamilial differences in growth. Effective management of coastal ecosystems must take into account both variability in abiotic conditions and the nested habitat component, both of which can be modified by coastal development, which could lead to reduced productivity and sustainability of these estuarine landscapes.

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