Marine nutrient contributions to freshwater apex predators

Abstract

Recent investigations into the nutrient cycling of coastal ecosystems have suggested that migratory or anadromous fish could be important vectors of marine nutrients. Anadromous fish have assimilated marine nutrients that would contribute to the nutrient budgets of freshwater systems by excretion, gamete release, or the decay of post-reproductive carcasses. However, the extent to which freshwater predators utilize marine material is not well understood. In systems where anadromous fish temporarily constitute a major portion of the fish community, they may contribute substantially to the diet of piscivorous fish and other predators. Here we show the contribution of anadromous blueback herring, shad, and alewife (Alosa) to diets of large, non-indigenous piscivorous catfish (Ictalurus furcatus) using δS and δC. The spawning anadromous Alosa, captured in tidal freshwater, had enriched δS and δC values compared to resident, native freshwater species. As a result of consuming the anadromous Alosa, the I. furcatus isotope signature shifted towards the marine signal. The isotope analysis revealed that anadromous fish contribute substantially to the diet of most captured I. furcatus. The percentage of anadromous Alosa carbon and sulfur that was incorporated into I. furcatus (≥38 cm total length) ranged from 0 to 84% and 10 to 69%, and had means (±SD) of 42 (±24) and 43 (±16)%, respectively. Although the δN signal of marine-derived biomass is enriched by approximately 3‰ relative to terrestrial or freshwater biomass, it was not as useful as δS and δC for nutrient source owing to trophic fractionation. This study demonstrates that anadromous fish may be a significant source of nutrients to tidal freshwater apex predators.

Dietary breadth and trophic position of introduced European catfish Silurus glanis in the River Tarn (Garonne River basin), southwest France

“…Therefore, any catfish heavily relying on this prey source ought to show corresponding decrease in δ 15 N values, which was not evident. Catfish are known to feed on many anadromous species, which would reflect marine δ 13 C values when migrating from marine to freshwater habitats, and feeding on prey with such distinct δ 13 C values can quickly elevate the δ 13 C values of catfish (MacAvoy et al 2000). But migrations of anadromous fish are effectively prevented by damming in the Tarn River, so any dietary contribution from anadromous fish with elevated δ 13 C values is unlikely.…”

Natural variations of copper and sulfur stable isotopes in blood of hepatocellular carcinoma patients

“…The body 65 Cu/ 63 Cu ratio varies according to that of diet (11) and also seems to be age dependent (12). In life sciences, sulfur isotopic ratios are mainly used to trace animals' diet in wildlife (13) and in stockbreeding (14) contexts. To this date, one study reports on bodily sulfur isotopic systematics, which shows no significant variations relative to diet in a murine model (15).…”

Habitat-specific variation in stable C and N isotope ratios of pond smelt (Hypomesus nipponensis)

“…Generally, in marine systems, studies have shown that both d 13 C values and d 15 N values of fish were higher than d 13 C and d 15 N of freshwater fish (France 1994;Doucett et al 1999;MacAvoy et al 2000;Garcia et al 2007). These patterns support the hypothesis that if pond smelt migrate between freshwater zone and coastal zone, pond smelt d 13 C values would change with growth.…”