5 research outputs found
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Complex Tidal Marsh Dynamics Structure Fish Foraging Patterns in the San Francisco Estuary
Mechanisms driving the consumption and transport of tidal marsh nutrients and energy by fishes are of key interest in the San Francisco Estuary, CA, USA. By combining multiple data sources (gill-net catches, gut contents, channel morphology, tides), we modeled spatial and temporal patterns of fish abundance and gut fullness across a tidal marsh elevation gradient. Channel depth, microhabitat, and tide were important predictors of fish abundance and gut fullness. Species, feeding guild, and season were also important to fish abundance but not to gut fullness, suggesting that abundance was more related to physical constraints of shallow water than to prey availability. Multiple feeding guilds overlapped in space and time at interaction hotspots in subtidal channel habitat near the marsh entrance. In contrast, fish use of shallow intertidal marsh channels was more variable and indicated tradeoffs between foraging and predation. Gut content analysis revealed moderate-to-high gut fullness for all feeding guilds and models predicted high gut fullness in subtidal reaches during tidal flooding, after which fish fed intensively throughout the marsh. While mysids, amphipods, and detritus were common prey among feeding guilds, variation in prey consumption was apparent. Overall, complex tidal marsh hydrogeomorphology driving land-water exchange and residence time may diversify and enhance benthic and pelagic food web pathways to fishes and invertebrates. Furthermore, these findings substantiate the notion that dynamic tidal marshes in this system can support robust secondary production, foraging by multiple feeding guilds, and trophic transfer by fishes to the estuarine mosaic
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Tidal effects on marsh habitat use by three fishes in the San Francisco Estuary
Little is known about the ecological importance of low-order tidal marsh channels to fishes in the San Francisco Estuary, California. We conducted a passive mark-recapture study to compare residency, site fidelity, and movement patterns of fishes in a small intertidal channel (0.1 km2) in a large tidal marsh reserve (4.25 km2). We coupled continuous, high-frequency data on movements of fish tagged with Passive Integrated Transponder (PIT) tags and abiotic conditions from a PIT-detector and datasonde, respectively. Novel insights were gained by employing TidalTrend, a software program that characterizes tidal time-series data for ecological interpretation. Overall, we found that fishes exhibited different patterns of intertidal habitat use: the resident species, tule perch (Hysterocarpus traski), consistently spent more time per visit, per day, and per season using the intertidal channel, except during the reproductive window in spring; the transient species, Sacramento splittail (Pogonichthys macrolepidotus) and striped bass (Morone saxatilis), were more opportunistic and exhibited higher individual variation in movement patterns. Generalized additive mixed models indicated that tide height, rate of change in tide height, tidal inequality, time of day, lunar phase, and water temperature better predicted fish detections than other variables, but their effects varied across species. Based on our findings, we posit that time, through tides, allows habitat partitioning among fish species and individuals with different life-history types. Furthermore, functional connectivity between subtidal and intertidal channels in tidal marshes is a feature of the estuarine mosaic that should be integrated into habitat restoration designs in the San Francisco Estuary
Henneguya sp. in yellowfin goby Acanthogobius flavimanus from the San Francisco Estuary
Myxozoan spores were observed in yellowfin goby Acanthogobius flavimanus collected from Suisun Marsh, San Francisco Estuary (SFE). Although histopathological changes associated with the parasite were not observed, the spores formed plasmodia that partially blocked the gastric and intestinal mucosa and gut lumen and may affect the perfomance and survival of the yellowfin goby. Morphological features of the spores resembled Henneguya sp. and molecular analysis of the 18S ribosomal DNA (Domain III) confirmed close similarity to H. rhinogobii and H. pseudorhinogobii isolated from the Japanese freshwater goby. The yellowfin goby myxozoan however, is likely an undescribed species based on phylogenetic analysis and morphologic features. Detailed description of vegetative and spore stages are currently lacking for proposal to a new species of Henneguya. A specific PCR test was developed, which confirmed a 100% prevalence of the parasite among randomly collected gobies in group 1 (N = 30) and group 2 (N = 15) at termination of the study at one month in captivity. The myxozoan was also detected from 18 gobies (12%) that died in the first group within two weeks in captivity. Apparently healthy gobies that served as controls did not reveal the presence of the myxozoan by PCR. This study documents the occurrence of a potentially new species of myxozoan in the yellowfin goby and underscores the detection of a parasitic infection in an introduced fish in the SFE. Although the pathogenesis of the myxozoan was not assessed and the prevalence as reported here is restricted to a comparatively small collection site in Suisun slough, the reemergence, identification, and ecological relevance of the parasite on goby populations in the SFE may be investigated in the future using the specific diagnostic tool developed in this study. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1186/2193-1801-2-420) contains supplementary material, which is available to authorized users