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Connectivity among estuarine habitats can influence nekton vital rates, and studying these processes requires the ability to track individuals effectively. Passive integrated transponder (PIT) tags have been used to evaluate movement of juvenile fishes in estuaries, yet this technique remains untested for penaeid shrimp . We evaluated survival, growth, and feeding behavior of juvenile white shrimp ( Litopenaeus setiferus ), an ecologically and economically important penaeid species along the US Atlantic and Gulf coasts, implanted with 8-mm PIT tags. Daily survival and tag retention observations and weekly length and weight measurements were made of tagged individuals (n = 18) kept in individual seawater tanks for 28 days, and compared with similarly housed untagged (control) individuals (n = 18). After four weeks, tagged and control shrimp were offered varying densities of a common estuarine prey item, grass shrimp ( Palaemonetes spp.), in feeding trials. Tagged white shrimp exhibited 100% tag retention and an estimated probability of survival after 28 d that was not significantly different from control shrimp (0.81 and 0.94, respectively). We found no evidence of a relationship between tagging treatment or initial shrimp size on the probability of survival. Tagged shrimp demonstrated growth at rates that were not significantly different from control shrimp, and tagged and control shrimp exhibited nearly identical feeding rates on grass shrimp (Palaemonetes spp.) prey. Our results suggest PIT tag technology represents an effective tool to study the movement and vital rates of juvenile white shrimp during their estuarine residence.

article i nfo Climate change is expected to cause a poleward shift of many temperate species, however, a mechanistic un- derstanding of how temperature and species' life histories interact to produce observed adult range is often lacking. We evaluated the hypothesis that juvenile thermal tolerance determines northern range in gray snapper (Lutjanus griseus), a species commonly caught as juveniles along the US Atlantic coast well north of their adult distribution, using a combined laboratory, field and modeling approach. The cumulative degree days below 17 °C (CDDb17) survived by individuals maintained in the laboratory under ambient seasonal cooling conditions were used to quantify the chronic effects of prolonged but non-lethal low temperatures. Under ambient conditions, juveniles stopped feeding below 11.3 °C, and the mean temperature at death was 10.2 °C (+/−0.74 S.D.). The CDDb17 endured by individuals ranged from 61.9 to 138.8 (83.54+/− 22.44 S.D.), and was positively related to fish size. The relation between CDDb17 and fish size was extrapo- lated to the maximum juvenile size in fall to provide an upper limit for survival in the wild (CDDb17= 210 days). Acute low temperature tolerance was evaluated in a second experiment that exposed juveniles to a constant rate of temperature decline (3 °C d −1

article i nfo Structurally complex habitats are often associated with more diverse and abundant species assemblages in both aquatic and terrestrial ecosystems. Biogenic reefs formed by the eastern oyster (Crassostrea virginica) are complex in nature and are recognized for their potential habitat value in estuarine systems along the US Atlantic and Gulf of Mexico coasts. Few studies, however, have examined the response of nekton to structural complexity within oyster reefs. We used a quantitative sampling technique to examine how the presence and complexity of experimental oyster reefs influence the abundance, biomass, and distribution of nekton by sampling reefs 4 months and 16 months post-construction. Experimental oyster reefs were colonized immediately by resident fishes and decapod crustaceans, and reefs supported a distinct nekton assemblage compared to mud-bottom habitat. Neither increased reef complexity, nor age of the experimental reef resulted in further changes in nekton assemblages or increases in nekton abundance or diversity. The presence of oyster reefs per se was the most important factor determining nekton usage.

Water control structures (WCSs) installed to regulate water levels can alter both the hydrology and ecology of salt marshes. WCSs are thought to limit nekton ingress into, and egress from, managed marshes. Slots (vertical openings that span most of the water column) incorporated into WCSs are thought to facilitate nekton passage through structures, but little research has directly examined how slot size affects passage rates. We used dual-frequency identification sonar (DIDSON) acoustic imaging to examine the effect of slot width (10, 15, 30, or 60 cm), tidal cycle, diel period, and season on nekton passage at a WCS located in a tidal salt marsh canal. Few individuals (total numbers and relative percentages) used the slots for passage through the structure during any stage of the tidal cycle, day or night, or seasonally. The number and size of migrants were similar for all four slot sizes examined. Nekton used the slots most often on flood tides to access the managed marsh (i.e., swim inside), primarily at night. Individuals entering the managed marsh were larger than those observed leaving the managed marsh. Whereas the majority of migrants were observed during winter months, season did not affect nekton passage in our study. Acoustic imaging allowed a unique and comprehensive evaluation of nekton passage by permitting an examination of factors such as swimming direction and proportion of migrants that are unobservable with other sampling techniques.

Intertidal creeks provide an extensive and direct interface with the marsh surface during periods of tidal inundation, and as such they represent a critically important corridor between the marsh surface and subtidal habitats. However, invasion by Phragmites can potentially alter this intertidal creek function. Habitat restoration was conducted in the oligohaline Alloway Creek watershed of Delaware Bay, USA, to ameliorate the deleterious effects of Phragmites invasion and restore marshes to pre-invasion form and function. Intertidal creeks in three marsh habitat types (natural Spartina-dominated, sites treated for Phragmites removal and now dominated by Spartina, and invasive Phragmites-dominated) were sampled during summer 2004 with seines during ebb and flood tides to determine juvenile nekton habitat and tidal utilization patterns and identify possible effects of marsh restoration efforts on intertidal nekton. Total nekton abundance was greater at Spartina and Treated marshes than Phragmites marshes. The overall nekton assemblage did not vary between habitat types, but the nekton assemblage did vary between tide stages, with low tide stages dominated by resident nekton (primarily Fundulus heteroclitus) and high tide stages consisting of a mix of transient and resident species (e.g., Anchoa mitchilli, Morone americana, Anguilla rostrata, Morone saxatilis). The effect of marsh restoration efforts on intertidal creek nekton was inconsistent, but most metrics examined indicated that restoration efforts had little effect in intertidal creek habitats, likely because the intertidal assemblage in all creek types was greatly influenced by many species moving from subtidal habitats and primarily a single (but abundant) species, F. heteroclitus, moving from the marsh surface.