Estuarine Seascape Research Articles

Using stable CNS isotopes to evaluate estuarine fisheries condition and health

Humans are modifying estuaries of the coastal zone and ecologists have begun measuring ecosystem responses in an attempt to preserve natural ecological conditions and health. Traditional approaches to assessing structural and functional responses of coastal systems include measures of species composition and water quality, but fisheries assessments are often left out because of the perception that fisheries species are too mobile and cannot easily be linked to local conditions. Stable isotopes have emerged as a new and useful way to understand movements and productivity of mobile shrimp and fish species across estuarine seascapes. Two case studies from Louisiana, USA, suggest that estuaries with healthy fishery food webs might be identified using isotope indicators that show low anthropogenic N inputs, strong benthic contributions, and moderate to high fisheries residency and productivity in marsh and mid- salinity areas.

Fine‐scale movements and habitat use of juvenile southern flounder Paralichthys lethostigma in an estuarine seascape

Habitat use of juvenile southern flounder Paralichthys lethostigma was examined within a shallow estuarine seascape during June and July 2011 using acoustic telemetry. Fine-scale movement and habitat use of P. lethostigma was investigated with an acoustic positioning system placed in a seascape that varied in habitat type, physicochemical conditions and bathymetry. The use of different habitat types was examined with Euclidean distance-based analyses, and generalized additive models were used to determine the relative importance of habitat type relative to physicochemical conditions and bathymetry. Tracks of P. lethostigma ranged in distance between 1477 and 8582 m and speed was 4·2 ± 1·1 m min⁻¹ (mean ± s.e.) for all P. lethostigma combined. Depth, slope and habitat type had the most influence on P. lethostigma occurrence and deep sandy areas with shallow slopes were used most frequently. In addition, depth use by P. lethostigma was influenced by tidal cycles, indicating habitat use varies temporally and is dynamic. Finally, temperatures <30·5° C were used more than warmer waters within the study area. The results successfully identify movements by juvenile P. lethostigma, and indicate that definitions of essential habitats need to account for dynamics in habitat use.

CASCADING OF HABITAT DEGRADATION: OYSTER REEFS INVADED BY REFUGEE FISHES ESCAPING STRESS

Mobile consumers have potential to cause a cascading of habitat degradation beyond the region that is directly stressed, by concentrating in refuges where they intensify biological interactions and can deplete prey resources. We tested this hypothesis on structurally complex, species-rich biogenic reefs created by the eastern oyster, Crassostrea virginica, in the Neuse River estuary, North Carolina, USA. We (1) sampled fishes and invertebrates on natural and restored reefs and on sand bottom to compare fish utilization of these different habitats and to characterize the trophic relations among large reef-associated fishes and benthic invertebrates, and (2) tested whether bottom-water hypoxia and fishery-caused degradation of reef habitat combine to induce mass emigration of fish that then modify community composition in refuges across an estuarine seascape. Experimentally restored oyster reefs of two heights (1 m tall “degraded” or 2 m tall “natural” reefs) were constructed at 3 and 6 m depths. We sampled...