Multiple fish predators: effects of identity, density, and nutrients on lower trophic levels

Karlsson

et al. 2018

Ambio

Understanding the relative impacts of pressures on coastal ecosystems is central for implementing relevant measures to reach environmental management objectives. Here, survey data on the species and size composition of coastal fish are evaluated in relation to fishing and eutrophication, by comparing a long-standing no-take area to an environmental gradient in the Baltic Sea. The no-take area represents an intermediate eutrophication level, but the species composition resembles that seen at low eutrophication in areas with fishing. The catch biomass of piscivores is 2–3 times higher in the no-take area than in the other areas, while the biomass of Cyprinids, generally benefitted by eutrophication, corresponds to that of areas with low eutrophication. The results support that fishing may generate eutrophication-like effects, and, conversely, that no-take areas may contribute to improving environmental status in impacted areas by enhancing piscivores, which in turn may contribute to further improvement in the food web. Electronic supplementary material The online version of this article (10.1007/s13280-018-1133-9) contains supplementary material, which is available to authorized users.

Section: Discussionmentioning

confidence: 99%

Relative impacts of fishing and eutrophication on coastal fish assessed by comparing a no-take area with an environmental gradient

Karlsson

et al. 2018

Ambio

“…Individual biomass was calculated using length : weight conversion factors (Swedish national database for coastal fish, http://www.slu.se/kul). Catch per unit effort (CPUE) was calculated as biomass (kg) per net and night of piscivores ( perch and pike pooled), three-spined stickleback (the dominant mesopredator in the system, with the potential to control macroalgal grazers [38,47]) and roach (Rutilus rutilus), another common mesopredator feeding mainly on gastropods [37]. Stomachs of perch (n ¼ 634) and pike (n ¼ 34) were dissected and the relative contribution ( percentage volume) of three-spined stickleback to total stomach content was estimated visually [48].…”

Section: (B) Field Surveymentioning

confidence: 99%

A cross-scale trophic cascade from large predatory fish to algae in coastal ecosystems

Donadi

Austin²,

et al. 2017

Proc. R. Soc. B.

Trophic cascades occur in many ecosystems, but the factors regulating them are still elusive. We suggest that an overlooked factor is that trophic interactions (TIs) are often scale-dependent and possibly interact across spatial scales. To explore the role of spatial scale for trophic cascades, and particularly the occurrence of cross-scale interactions (CSIs), we collected and analysed food-web data from 139 stations across 32 bays in the Baltic Sea. We found evidence of a four-level trophic cascade linking TIs across two spatial scales: at bay scale, piscivores (perch and pike) controlled mesopredators (three-spined stickleback), which in turn negatively affected epifaunal grazers. At station scale (within bays), grazers on average suppressed epiphytic algae, and indirectly benefitted habitat-forming vegetation. Moreover, the direction and strength of the grazer-algae relationship at station scale depended on the piscivore biomass at bay scale, indicating a cross-scale interaction effect, potentially caused by a shift in grazer assemblage composition. In summary, the trophic cascade from piscivores to algae appears to involve TIs that occur at, but also interact across, different spatial scales. Considering scale-dependence in general, and CSIs in particular, could therefore enhance our understanding of trophic cascades.

Journal of Fish Biology

“…Prey community composition has the potential to affect predation rates of larval fish through indirect effects. Indirect effects can be mediated by predator switching, which occurs as prey items change in density and predators focus foraging efforts on more abundant prey (McPhee et al ., ; Murdoch, ; Murdoch et al ., ; Reiss et al ., ; Willette et al ., ). Abundance and biomass of larval fishes is often highly variable through time and space (Kallasvuo et al ., ; Reiss et al ., ; Smith & King, ), making prey switching behaviours in predator species likely, as the availability of prey fishes and encounter rates between predators and prey change spatially ( e.g ., among habitats) or temporally ( e.g ., seasonally).…”

Section: Introductionmentioning

confidence: 99%

“…Species composition and size‐classes of predatory fish in a community can have important effects on predation levels of larval prey (Chalcraft & Resetarits, ; Parke et al ., ). Prey preferences (Silbernagel & Sorenson, ; Reiss et al ., ), foraging efficiencies (Scharf et al ., ) and consumption rates (Gosch & Pope, ) can vary greatly among predators. Recognition of certain species as important predators of larval fish can inform management decisions about harvest regulations, targeted removals, biological controls, or other strategies of predator control to improve recruitment of a target species (Carpenter & Mueller, ).…”

Section: Introductionmentioning

confidence: 99%

Molecular diet analysis reveals predator–prey community dynamics and environmental factors affecting predation of larval lake sturgeon Acipenser fulvescens in a natural system

Waraniak

Baker

Scribner

2018

This study utilized molecular tools to quantify the prevalence of predation during the vulnerable drifting larval life-history stage of lake sturgeon Acipenser fulvescens. How predators, the co-distributed prey community and abiotic environmental conditions (e.g., stream substrata) affected predation levels was quantified. Nightly D-frame drift net surveys were used to estimate the biomass of A. fulvescens and co-distributed prey. Gastrointestinal diet samples (n = 1,140) from 28 species of potential fish predators were collected during electrofishing surveys. Sampling was conducted for 17 days across 2015 and 2016. Based on DNA barcode analysis using sturgeon-specific mtDNA cytochrome oxidase I primers, A. fulvescens DNA was detected in 73 of 1,140 diet samples (6.40%) from 16 of the 28 predator species examined. A logistic regression model was used to analyse the effects of biotic and abiotic variables associated with the likelihood a predator had consumed larval A. fulvescens. Increasing lunar illumination and biomass of larval A. fulvescens increased predation rates on larval A. fulvescens. Higher discharge and greater biomass and proportions of alternative prey decreased predation rates of larval A. fulvescens. Predation rates were slightly higher in habitats with sand substrata. Most predator species preyed upon larval A. fulvescens at similar rates. The study revealed considerably higher incidence of predation on larval A. fulvescens than previous studies had documented using traditional morphological diet analysis. Co-distributed prey and abiotic environmental variables that affected the predation rates of a species of regional conservation concern can inform future management actions.