Climate change and deepening of the North Sea fish assemblage: a biotic indicator of warming seas

Abstract

Summary 1.Climate change impacts have been observed on individual species and species subsets; however, it remains to be seen whether there are systematic, coherent assemblage-wide responses to climate change that could be used as a representative indicator of changing biological state. 2. European shelf seas are warming faster than the adjacent land masses and faster than the global average. We explore the year-by-year distributional response of North Sea bottom-dwelling (demersal) fishes to temperature change over the 25 years from 1980 to 2004. The centres of latitudinal and depth distributions of 28 fishes were estimated from species-abundance-location data collected on an annual fish monitoring survey. 3. Individual species responses were aggregated into 19 assemblages reflecting physiology (thermal preference and range), ecology (body size and abundance-occupancy patterns), biogeography (northern, southern and presence of range boundaries), and susceptibility to human impact (fishery target, bycatch and non-target species). 4. North Sea winter bottom temperature has increased by 1·6 ° C over 25 years, with a 1 ° C increase in 1988-1989 alone. During this period, the whole demersal fish assemblage deepened by ~3·6 m decade -1 and the deepening was coherent for most assemblages. 5. The latitudinal response to warming was heterogeneous, and reflects (i) a northward shift in the mean latitude of abundant, widespread thermal specialists, and (ii) the southward shift of relatively small, abundant southerly species with limited occupancy and a northern range boundary in the North Sea. 6. Synthesis and applications. The deepening of North Sea bottom-dwelling fishes in response to climate change is the marine analogue of the upward movement of terrestrial species to higher altitudes. The assemblage-level depth responses, and both latitudinal responses, covary with temperature and environmental variability in a manner diagnostic of a climate change impact. The deepening of the demersal fish assemblage in response to temperature could be used as a biotic indicator of the effects of climate change in the North Sea and other semi-enclosed seas.

Chapter 1 Impacts of the Oceans on Climate Change

“…Prior to 2003 this fish Impacts of the Oceans on Climate Change 37 Author's personal copy was confined to the south and west of the British Isles, but it now extends as far north as the Barents Sea and Spitzbergen (Kirby et al, 2006;Harris et al, 2007). The pelagic environment is of course three-dimensional and recent research has observed a movement of fish species towards deeper cooler waters in response to climate warming (Dulvy et al, 2008). This change can be seen as analogous to the upward altitudinal movement of terrestrial organisms in alpine environments.…”

Transitional states in marine fisheries: adapting to predicted global change

“…On average, the assemblage has deepened by 3.6 m decade 21 , belying exceptional changes in species such as cod Gadus morhua (figure 4c) and anglerfish Lophius piscatorius (figure 4a; Dulvy et al 2008). A widespread change in depth is a predictably efficient response for species as tracking the movement of their thermal optima requires smaller movements with depth or elevation than for latitude (Colwell et al 2008).…”

“…Because the northward emigration of larger, cold-water species progressed more gradually (Perry et al 2005), diversity increased within the North Sea ( figure 4e,f ). Southward movements of warm-water species such as sole Solea solea and scaldfish Arnoglossus laterna into the shallow southern North Sea have also occurred owing to earlier springtime warming (Dulvy et al 2008).…”

“…Between 1982 and 2006, North Sea temperatures rose by 1.318C (Sherman et al 2009), including a dramatic 0.98C increase in 1989 (Dulvy et al 2008) that led to major biogeographical shifts in community structure. From 1977 to 2001, almost two-thirds of fished species in the North Sea changed their spatial distribution in response to warming (e.g.…”

Fish physiology and ecology: the contribution of the Leigh Laboratory to the collision of paradigms

“…Major biogeographical shifts have been observed in recent years (Perry et al 2005;Dulvy et al 2008) but the cause and effect of such change remains poorly understood. For example, a poleward shift in North Sea fishes appears to occur at subcritical temperatures (Perry et al 2005), but it is still not known whether biogeographical shifts occur as a result of behavioural redistributions (behavioural thermoregulation), localised extinctions or community-level interactions.…”