Effects of drought on fish across axes of space, time and ecological complexity

Abstract

Summary We evaluate the position of 50 previously published studies of fish and drought with respect to spatial scale of study (individual stream pools to subcontinents), length of the dry period (weeks to centuries), and level of system complexity (individual fish to ecosystems). Most papers address short (months to a year) droughts or dry periods, in local reaches of streams, and impacts on populations or local assemblages. In these 50 papers, the most frequently demonstrated effects of drought were population declines, loss of habitat, changes in the community, negative effects from changes in water quality, movement within catchments, and crowding of fish in reduced microhabitats. Thirteen other less frequent effects also were identified. Gaps in knowledge exist on effects of long‐term droughts (decades to centuries), influence of drought on fish effects in ecosystems, and at the spatial scale of river basins to subcontinents. However, some of these gaps have recently been addressed, particularly additive effects of repeated drying episodes and whole‐lake or basin‐wide effects of drought, and in using molecular techniques to seek signals of drought at wide geographic scales because of events in the deep past. Gaps in knowledge remain for effects of very short dry periods, on drought effects on higher levels of complexity, and on the manner in which droughts at the scale of decades affect fish. Data from streams in Oklahoma and elsewhere in the south‐western U.S.A. suggest that most droughts may leave little persistent signal in the existing fish fauna, i.e. that recovery from drought by fish populations or assemblages in the region can be rapid. However, species that are vulnerable to drought or water loss in streams may have disappeared from some basins in the region before the mid‐1900s, and recent evidence also suggests that extreme droughts do sometimes alter fish assemblages. Little is known about mechanisms by which droughts have direct or indirect effects on fish, the roles of droughts in the evolution of fish species, and the ways droughts alter effects of fish in ecosystems. Global climate changes may have serious consequences for future local or regional fish faunas, but ongoing studies of fish experiencing drought may aid in future conservation of what will become species at risk under climate‐change scenarios.

Recent perspectives on temporary river ecology

“…Although the effects of flow intermittence on biota have been well-described in previous studies (e.g., Lake 2003; Matthews and Marsh-Matthews 2003;Boulton 2003), this special issue highlights a number of community and speciesspecific responses of aquatic and terrestrial animals to flow cessation and rewetting. Skoulikidis et al (2011) described the effects flow cessation on a Greek river.…”

Bottom‐up nutrient and top‐down fish impacts on insect‐mediated mercury flux from aquatic ecosystems

“…This has important implications because humans have dramatically altered fish communities directly through purposefully stocking and accidentally introducing native and non-native fish species [44] and overfishing [45] and indirectly through enhanced frequency of drought and associated drying of small water bodies as a result of anthropogenic climate change [46]. Anthropogenic alterations of fish communities directly affect aquatic communities and aquatic ecosystem function but may also indirectly impact terrestrial ecosystems by altering aquatic subsidies [47].…”

Long-term changes in fish assemblages of the Widawka and Grabia Rivers (Poland): pattern recognition with a Kohonen artificial neural network

“…In small streams, the environmental conditions are less stable. Especially frost penetration in winter, draughts in hot summers or episodes of severe water pollution or intensified engineering works increase the risk of fish extirpation (Prowse 2001, Hoffsten 2003, Matthews & Marsh-Matthews 2003. The natural mechanism of compensating these losses is recolonisation from downstream river fragments, where larger volumes of water form a more stable environment.…”

“…about 2/3 in the Widawka and 1/3 in the Grabia, in order to avoid recording changes in fish resulting from different spatial allocation. Also, in both rivers, the source sections were ignored because fish assemblages in such habitats often are unstable as a result of frost penetration in winters and low water levels in hot summers (Prowse 2001, Hoffsten 2003, Matthews & Marsh-Matthews 2003, which can lead to extreme events in fish assemblages including extinction of certain cohorts, certain species or all fish, thereby masking long-term changes.…”