Bruce H. Comyns

Habitat use by early life-history stages of fishes and crustaceans along a changing estuarine landscape: differences between natural and altered shoreline sites

The recent population explosion along the coastal zoneof the southeast United States and the Gulf of Mexicohas accelerated the development rate of waterfrontproperty, and particularly along the Gulf Coast ofMississippi. We compared use of pristine and alteredshoreline habitat by early life-history stages of fishand crustaceans to assess the potential effects ofthis development. Monthly beam trawls were taken at13 sites along shoreline habitats characterized byJuncus/Spartinamarsh, natural beach, and areasaltered by bulkheads and rubble. A total of 52,068fish (n = 48 taxa) and 288,715 crustaceans (n = 24taxa) were collected during a two year study. The mostabundant fish groups included gobiids, sciaenids,clupeids, and engraulids. Crustaceans, excluding thecopepods, were numerically dominated by mysids, bothcaridean and penaeid shrimps, and crabs (Callinectesspp.). Demersal residents were dominatedby Gobiosoma boscand Palaemonetessp.whereas clupeiformes, sciaenids and penaeid shrimpswere dominant among the nektonic and demersaltransient species. These taxa were least abundantalong stretches of shoreline altered with bulkheads orrubble, and were generally most abundant in shorelinehabitats fringed with Juncus/Spartinagrasses.This general pattern in nekton relative abundanceparallel the low diversity (reciprocal of SimpsonsDominance Index) values adjacent to altered marsh tohigh values adjacent to pristine marsh or beachhabitats, suggesting that habitats adjacent to alteredmarsh sites are less frequently used as nurseryhabitat compared to natural sites. These data supportthe hypothesis that shorelines adjacent to marshhabitat are critical to various life history stages ofecologically- and commercially-important species,illustrate the influence of altering natural marshhabitat on resident/transient nekton, and providequantitative data for resource managers in thecontinued efforts to preserve the complex estuarinemarsh landscape.

Does salinity affect somatic growth in early juvenile Atlantic croaker, Micropogonias undulatus (L.)?

Abstract Factors affecting recruitment of fishes remain one of the most studied but least understood issues of fisheries science. Understanding the causes of recruitment variability remains elusive because factors that affect the growth and survivorship of young fishes are complex and dynamic. Here we focus on the influence of salinity on growth of early juvenile Atlantic croaker, Micropogonias undulatus under laboratory conditions as part of a larger study to relate short-term fluctuations in growth rates of young estuarine-dependent fishes with variability in abiotic environmental factors. Body growth of juvenile Atlantic croaker was significantly ( P 20–5‰=20‰. A linear response to the changing treatment suggests an additive effect of changing salinity on body wet weight (WW) growth. Juvenile Atlantic croaker in the 5‰ treatment grew in WW by a factor of 3.88 relative to initial WW. Fish in the 20–5‰ treatment grew in WW by a factor of 2.90, while fish in the 20‰ treatment grew in WW by a factor of 2.17. Otolith diameter also varied significantly with salinity, and there was a significant positive relationship between changes in body WW and changes in otolith diameter growth ( r =0.68, P n =12). The correlation between body and otolith growth justified our use of otolith data to infer that substantial fluctuation in the early growth of early juvenile Atlantic croaker from field collections was inversely cross-correlated with salinity and water temperature. Assuming that the probability of survival during the nursery period increases as postlarval fish grow, salinity-induced plasticity in growth rates implies that the site and habitat into which post-larval fish settle can potentially influence recruitment dynamics. This study demonstrates that there is the potential for fluctuations and spatial variability in salinity to cause significant variability in short-term growth rates for juvenile fishes within estuarine nursery areas.

Defining the Fundamental Physiological Niche of Young Estuarine Fishes and Its Relationship to Understanding Distribution, Vital Metrics, and Optimal Nursery Conditions

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.

Age and Growth of Red Drum Larvae in the North-Central Gulf of Mexico

Abstract Otolith growth increments were used to estimate the age of 113 larval red drum Sciaenops ocellatus collected in the north-central Gulf of Mexico in October 1983, October 1984, and September 1985. Larval growth, as estimated by correlating age with length and dry weight measurements, was exponential and positively associated with water temperature. Mean growth in length of larvae smaller than 4 mm was relatively slow (≈0.3 mm/d), but at sizes larger than 4 mm, length increased rapidly. Based on growth equations, the mean increases in length of 4–6-mm larvae in October 1984, October 1983, and September 1985, were 0.4, 0.5, and 0.6 mm/d, respectively. These increases in larval growth were associated with increasing water temperature at time of capture; ranges in temperature during the three periods were 24.5–25A, 25.5–26.5, and 27.8–29.0°C, respectively. Larvae that developed in October 1984 grew to a length of 6 mm in about 15.0 d, whereas in September 1985, at the warmest temperatures, larvae grew...

Feeding Habits and Mouth Morphology of Young Silver Perch (Bairdiella chrysoura) from the North-Central Gulf of Mexico

Abstract We examined predator-prey relationships of young Bairdiella chrysoura (Silver Perch) collected in Mississippi Sound by comparing the diet to fish standard length (2.5–30.0 mm SL) and mouth width (MW). Silver Perch displayed a diel feeding pattern, with the most active feeding occurring from midnight until noon. As Silver Perch SL increased, prey number, frequency, and volume plus prey width increased. Calanoid copepods and mysid shrimp were the dominant prey, with mysids becoming prominent as Silver Perch SL increased. Cluster analysis supported this pattern as Silver Perch ≤5 mm SL consumed a homogenous material and a few copepods, fish 5–10 mm SL preyed upon calanoid copepods, and then fish in larger size classes shifted their diet to mysid shrimp as MW increased and fish became more robust. Silver Perch SL was linearly related to MW (MW = 0.097 [SL] + 0.245; r2 = 0.891).

Relating Environmental Fluctuation and the Early Growth of Estuarine Fishes: Ontogenetic Standardization

Abstract Variability in early growth rates of estuarine-dependent juvenile fishes in relation to large-scale meteorological forcing may be detected following the removal of ontogenetic growth trends. Here we develop a general approach for the ontogenetic standardization of otolith daily records and demonstrate the usefulness of this approach in terms of relating the early growth of juvenile Atlantic croaker Micropogonias undulatus to concurrent environmental fluctuation. For these data, a linear/constant ontogenetic growth function provided the best fit to the inferred growth histories of individual fish. Whereas daily proportional growth declined linearly during the presettlement period, constant proportional growth ensued during the postsettlement phase of the first 50 d of early life. The recognition of such stage-specific shifts in growth trajectories is essential for accurate ontogenetic standardization. Daily postsettlement growth could be ontogenetically standardized for individual Atlantic croaker...

Regional Patterns in the Otolith Chemistry of Juvenile Spotted Seatrout(Cynoscion nebulosus) Differ under Contrasting Hydrological Regimes

The value of using otolith chemistry to characterize recruitment in terms of natal source regions depends on how consistently spatio-temporal variation can be resolved. The objective of this study was to compare regional classifica- tion patterns in the otolith chemistry of juvenile Spotted Seatrout (Cynoscion nebulosus) between two years experiencing disparate hydrological regimes, and separated by a five year interlude. Spatial patterns in the whole-otolith chemistry of juveniles of this estuarine-dependent species were compared between years using five otolith elements and two stable iso- topes. Consistent size-related trends in uptake and deposition were evidenced by parallel ontogenetic relationships for six otolith variables. Nine natal regions were discerned equally well in both years; and region accounted for similar overall amounts of variation in the seven otolith variables in both years. However, the otolith variables did not distinguish the nine regions in the same manner in both years, and natal regions varied in how similar they were in otolith chemistry be- tween years. Consequently, between-year cross-classification accuracy varied widely among regions, and geographic dis- tance per se was unimportant for explaining regional patterns in otolith chemistry. Salinity correlated significantly with regional patterns in otolith chemistry in 2001, but not at all in 2006 when conditions were much drier. Regional patterns in individual otolith variables reflected either a general trend based on hydrology, a regional-local effect whereby geographi- cally closer regions exhibited similar otolith chemistry, or a location-specific effect for which there was either no correla- tion in otolith concentration among regions between years, or a significant but individualistic relationship. In addition to elucidating limitations of using otolith chemistry to identify natal source regions or for tracking fish movements, knowing more about how and why otolith chemistry varies could be used to address specific questions about early recruitment dy- namics, or to aid in the development of more reliable instruments for discerning natal source contributions.