Distribution of mesopredatory fish determined by habitat variables in a predator-depleted coastal system

Abstract

Shallow nearshore habitats are highly valued for supporting marine ecosystems, but are subject to intense human-induced pressures. Mesopredatory fish are key components in coastal food webs, and alterations in their abundance may have evident effects also on other parts of the ecosystem. The aim of this study was to clarify the relationship between the abundance of coastal mesopredatory fish, defined as mid-trophic level demersal and benthic species with a diet consisting predominantly of invertebrates, and ambient environmental variables in a fjord system influenced by both eutrophication and overfishing. A field survey was conducted over a coastal gradient comprising 300 data points sampled consistently for fish community and environmental data. Results from multivariate and univariate analyses supported each other, demonstrating that mesopredatory fish abundance at species and functional group level was positively related to the cover of structurally complex vegetation and negatively related to eutrophication, as measured by water transparency. Contrary to other studies showing an inverse relationship to piscivore abundance over time, the spatial distribution of mesopredatory fish was not locally regulated by the abundance of piscivorous fish, probably attributed to piscivores being at historically low levels due to previous overfishing. Mesopredatory fish abundance was highest in areas with high habitat quality and positively related to the abundance of piscivores, suggesting a predominance of bottom-up processes. We conclude that, in parallel with ongoing regulations of fishing pressure, measures to restore habitat function and food web productivity are important for the recovery of coastal fish communities in the area.Electronic supplementary materialThe online version of this article (doi:10.1007/s00227-016-2977-9) contains supplementary material, which is available to authorized users.

Top-down release of mesopredatory fish is a weaker structuring driver of temperate rocky shore communities than bottom-up nutrient enrichment

“…By gillnet fishing in different habitats, Moy et al (2007) showed labrids, and particularly the goldsinny wrasse, Ctenolabrus rupestris, to be the most abundant fish species in rocky shore communities dominated by kelps or other macroalgal vegetation. Similar results were presented by Bergström et al (2016) and Kraufvelin et al (2017) for both the goldsinny and for the corkwing wrasse, Symphodus melops, from fyke net fishing on the Swedish part of the Skagerrak coast. The wrasses are found to prey on a variety of small grazers in seaweeds (Norderhaug et al 2005) and may thus contribute to reducing herbivory/grazing and hence the community control imposed by small-sized consumer species.…”

“…for the foundation species F. serratus and Z. marina. Although this lack of clear-cut responses to the mesopredatory fish partly opposes the ones previously reported, it is to some extent supported by observations from field studies by Bergström et al (2016) and Kraufvelin et al (2017) on the Swedish west coast, where wrasses were more common in the structurally most complex habitats with the densest cover of perennial macrophytes. The lack of clear negative responses to mesopredator release among macrophytes is also important from a management perspective as it may have implications for the ongoing wrasse fishery in Swedish and Norwegian waters (Skiftesvik et al 2014;Halvorsen et al 2017;Olsen et al 2018).…”

“…The density of goldsinny wrasse was in this experiment ca 2.5-4 fish per m 3 of water at high and low tide, respectively. Moy et al (2007) got more than 50 wrasses in 20 m long gillnets with fine mesh size in kelp and seaweed beds in southern Norway and from the Swedish part of Skagerrak, Bergström et al (2016) and Kraufvelin et al (2017) report 7-15 goldsinny wrasses per fyke net and night. These results together with the data from Halvorsen et al (2017) and the beach seine data from Gjøsaeter and Paulsen (2004) give, however, insufficient background for a determination of realistic densities per m 2 , although the applied numbers in the present experiment may be defended with the abovementioned recordings and own personal observation of densities from shore areas close to the Solbergstrand mesocosm facility.…”

Persistent differences between coastal and offshore kelp forest communities in a warming Gulf of Maine

“…We hypothesized that the shallow kelp forest on Cashes Ledge supports unique, high biomass assemblages of fish as kelp habitats provide a complex three-dimensional habitat for demersal and mid-water rocky reef fishes [ 37 ]. In other areas, kelp forest fish distributions correlate with the availability of suitable habitat [ 38 , 39 ], as well as with the abundance of associated benthic invertebrates and other food resources [ 40 , 41 ]. As an offshore ridge in the midst of a gyre [ 42 ], Cashes Ledge is isolated, which may separate fish, kelp and benthic invertebrate populations living on Cashes Ledge from coastal areas.…”

Essential coastal habitats for fish in the Baltic Sea

“…important for providing surfaces for habitat-forming macroalgae and sessile animals, which serve as food and refuge from predation (Pihl and Wennhage 2002, Seaman 2007, Fabi et al 2011, Bergström et al 2016c. Finally, seabeds without macroscopic vegetation as well as open shallow waters are often highly productive, both with regard to primary and secondary production (Gerbersdorf et al 2005, Engelsen et al 2008.…”