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.

Ingestion and elimination of anthropogenic fibres and microplastic fragments by the European anchovy (Engraulis encrasicolus) of the NW Mediterranean Sea

This study analysed the anthropogenic microparticles in the stomach content of the European anchovy (Engraulis encrasicolus) in the Ligurian Sea (NW Mediterranean). The results showed that 30–40% of the anchovies had ingested anthropogenic microparticles (on average, 0.34 ± 0.29 fibres ind−1 and 0.12 ± 0.12 fragments ind−1). The fibres were probably ingested via filtration, and were significantly correlated with the gut fullness. Fibres were mostly dark, but the presence of other colours was frequent, indicating a general lack of selectivity. Plastic fragments composed of polyethylene and polypropylene were prevalently transparent, suggesting active predation, especially for larger fragments resembling zooplankton. No significant differences were recorded for the frequency of fish containing particles among females, males, and undetermined individuals. The presence of, generally, only one anthropogenic item per fish, as observed for 95.8% of fish containing microparticles, indicated that the permanence of these particles in the stomachs was short, likely no more than 1 day, although it could also depend on low environmental concentrations. The evaluation of the intestinal lumen indicated that a portion of the plastic fragments found in the stomach could not be ejected. Hard fragments that were larger than the intestinal lumen could be held for longer times, but probably regurgitation, fragmentation, and embedding in a biological matrix may facilitate their quick elimination. It is pivotal to understand the processes that regulate the abundance and the residential time of anthropogenic particles in commercial organisms captured for human nutrition, given the potential biomagnification of toxic substances carried by ingested particles.

Expectancy of ergogenicity from sodium bicarbonate ingestion increases high-intensity cycling capacity

This study examined whether expectancy of ergogenicity of a commonly used nutritional supplement (sodium bicarbonate; NaHCO3) influenced subsequent high-intensity cycling capacity. Eight recreationally active males (age, 21 ± 1 years; body mass, 75 ± 8 kg; height, 178 ± 4 cm; WPEAK = 205 ± 22 W) performed a graded incremental test to assess peak power output (WPEAK), one familiarisation trial and two experimental trials. Experimental trials consisted of cycling at 100% WPEAK to volitional exhaustion (TLIM) 60 min after ingesting either a placebo (PLA: 0.1 g·kg−1 sodium chloride (NaCl), 4 mL·kg−1 tap water, and 1 mL·kg−1 squash) or a sham placebo (SHAM: 0.1 g·kg−1 NaCl, 4 mL·kg−1 carbonated water, and 1 mL·kg−1 squash). SHAM aimed to replicate the previously reported symptoms of gut fullness (GF) and abdominal discomfort (AD) associated with NaHCO3 ingestion. Treatments were administered double blind and accompanied by written scripts designed to remain neutral (PLA) or induce expectancy of ergogenicity (SHAM). After SHAM mean TLIM increased by 9.5% compared to PLA (461 ± 148 s versus 421 ± 150 s; P = 0.048, d = 0.3). Ratings of GF and AD were mild but ∼1 unit higher post-ingestion for SHAM. After 3 min TLIM overall ratings of perceived exertion were 1.4 ± 1.3 units lower for SHAM compared to PLA (P = 0.020, d = 0.6). There were no differences between treatments for blood lactate, blood glucose, or heart rate. In summary, ergogenicity after NaHCO3 ingestion may be influenced by expectancy, which mediates perception of effort during subsequent exercise. The observed ergogenicity with SHAM did not affect our measures of cardiorespiratory physiology or metabolic flux.

Feeding ecology of two sympatric species of Acetes (Decapoda: Sergestidae) in Panguil Bay, the Philippines

Sergestid shrimps of the genus Acetes are important in global shrimp fisheries and nearshore food-webs. The feeding habits of the sympatric species Acetes erythraeus and A. intermedius from Panguil Bay, Philippines were studied using gut contents and stable isotopes analyses. Both species are omnivorous suspension feeders of plankton, macrophyte detritus, and amorphous particulate organic materials. However, the diet of adults and juveniles differed by prey type. Gut fullness differed over 24h with a night-time peak in A. erythraeus and morning and midnight peaks in A. intermedius. Over 1 year gut fullness peaked during July to September for both species, with a minor peak during January for A. intermedius. Stable isotope analysis revealed similar δ15N values, but both species showed ontogenetic and interspecific separation of δ13C. A. erythraeus seemed to assimilate highly depleted carbon food sources by mangrove-based detrital and plankton trophic pathways, whereas A. intermedius relied on plankton and macroalgal and seagrass detrital pathways. These trophic differences may be mechanisms of partitioning the feeding niche, but allotopy in the two species with A. erythraeus confined to more brackish waters and A. intermedius dwelling in more saline marine waters may indicate that habitat niche segregation underlies these contrasting carbon trophic pathways.

Responses of macroinvertebrate drift, benthic assemblages, and trout foraging to hydropeaking

We utilized both hydropeaking and experimental flows to quantify responses of macroinvertebrate drift, benthic assemblages, and fish consumption to double-peak release patterns. Our results suggest that changes in discharge may have a greater impact on macroinvertebrate drift than absolute flow levels, such that mean daily drift biomass was significantly higher during double-peaking; however, drift increases were sustained for only 30–60 days despite ongoing hydropeaking. Drift increases were proportional to peak magnitude, with drift biomass peaking during the rising limb of the hydrograph and declining prior to the cessation of peak flows. Both within- and among-day drift hysteresis appeared related to patterns in vegetative export, principally Cladophora and Amblystegium. Increases in macroinvertebrate drift were not associated with detectable reductions in benthic densities, while we observed inconsistent and modest taxa richness reductions. Lastly, gut fullness for both brown and rainbow trout increased significantly following periods of hydropeaking, suggesting that the effects of double-peaking can propagate through tail-water food webs.

Trophic ecology of two non-native hydrozoan medusae in the upper San Francisco Estuary

Blooms of some gelatinous zooplankton are increasing worldwide, often disrupting foodwebs. Invasions of non-native jellyfish are a growing problem in many estuaries, including the San Francisco Estuary, where at least two species of Ponto-Caspian hydrozoans, Maeotias marginata Modeer, 1791 and Moerisia sp., are abundant. The present study investigated their trophic ecology, testing the following hypotheses: (1) diets over the bloom and at the diel scale are comprised of a variety of prey items; (2) hydrozoans are generalist feeders; (3) hydrozoans feed on the larvae of declining fish species; and (4) the potential for prey competition exists between the hydrozoans and two declining planktivorous fishes, striped bass (Morone saxatilis) and threadfin shad (Dorosoma petenense). Both hydrozoans ate a variety of crustaceans, most notably calanoid copepods, which were found in greater proportion in the guts than in the environment. The only fish larvae consumed were gobies. Density of Moerisia sp., was negatively correlated with gut fullness for both fishes, and diet overlap was high between shad and hydrozoans, but low for bass. Because of strong spatial and temporal overlap between hydrozoans and shad, competition for zooplankton may be occurring. These hydrozoans have invaded other systems, and should be monitored to assess potential ecological interactions in these locations.

Diet and feeding daily rhythm of Pimelodella lateristriga (Osteichthyes, Siluriformes) in a coastal stream from Serra do Mar - RJ

The present study was carried out in Mato Grosso fluvial system, a costal drainage from Serra do Mar. We analysed the diet and the feeding daily rhythm of Pimelodella lateristriga from samples carried out during 24 hours over a 4 hour fishing interval, in June, July and September, 2006 as well as in January and February, 2007. Diet was described from the Feeding Index (IAi) and feeding daily rhythm was verified through the Gut Fullness Index (GFI). Pimelodella lateristriga diet was composed of 37 items, being aquatic insects the most important ones. IAi analysis revealed that Diptera, Trichoptera and Ephemeroptera amounted to 90% of the diet. Autochthonous invertebrates were the most important consumed items. Pimelodella lateristriga concentrated its feeding activities in the nocturnal period (10:00 PM to 2:00 AM) with marked significant differences (F = 16.11; gl = 5; p < 0.05) between each diurnal and nocturnal periods. Between 6:00 AM and 6:00 PM, foraging activity was gradually reduced. We concluded that P. lateristriga has an insectivorous diet and a nocturnal feeding habit with greater activity between 10:00 PM to 2:00 AM.

Feeding ecology of the Brazilian silverside Atherinella brasiliensis (Atherinopsidae) in a sub-tropical estuarine ecosystem

The feeding ecology of the Brazilian silverside, Atherinella brasiliensis, in a sub-tropical estuary of Brazil was investigated through the gut analysis of 1431 individuals. We described dietary composition and analysed seasonal, estuarine habitat, and body size variations in the diet; trophic level; feeding diversity; and gut fullness indices. Results reveal that A. brasiliensis is a typical, generalistic and opportunistic predator that makes use of a wide array of prey types (at least 89 different types), with zooplankton (mainly calanoids), diatoms, terrestrial insects, and plant detritus making up the bulk of the overall diet. The exotic calanoid Temora turbinata ranked as the primary prey. A wide feeding diversity (mean H′ = 2.26), low trophic level (mean TROPH = 2.57), and high gut replenishment were persistent across seasons and habitats. Diet composition varied largely and significantly with respect to habitat, season, and body size. A closer assessment showed that habitat and season had a stronger effect on diet than fish size.