Importance of the riparian zone to the conservation and management of freshwater fish: a review Author Pusey, BJ, Arthington, AH Published 2003 Journal Title Marine and Freshwater Research DOI https://doi.org/10.1071/MF02041 Copyright Statement © 2003 CSIRO. This is the author-manuscript version of this paper. Reproduced in accordance with the copyright policy of the publisher. Downloaded from http://hdl.handle.net/10072/6041 Link to published version http://www.publish.csiro.au/nid/126.htm Griffith Research Online https://research-repository.griffith.edu.au CSIRO PUBLISHING www.publish.csiro.au/journals/mfr Marine and Freshwater Research, 2003, 54, 1–16 Review Importance of the riparian zone to the conservation and management of freshwater fish: a review Bradley J. PuseyA,B and Angela H. ArthingtonA ACo-operative Research Centre for Tropical Rainforest Ecology and Management, Griffith University, Nathan, Qld 4111, Australia. BCorresponding author; email: [email protected] Abstract. The relationship between freshwater fish and the integrity of the riparian zone is reviewed with special emphasis on the fauna of northern Australia. Linkages between freshwater fish and riparian zone processes are diverse and important. The riparian zone occurs at the interface between terrestrial and aquatic ecosystems and it may, therefore, regulate the transfer of energy and material between these systems, as well as regulating the transmission of solar energy into the aquatic ecosystem. Riparian influences on light quantity, quality and shade in streams are discussed and predictions are made about the likely impacts associated with changes in light quality. Increased rates of transfer of thermal energy between the atmosphere and the aquatic environment in the absence of an intact riparian zone may potentially disrupt reproduction by desynchronizing the thermal regimen from regional factors, such as the flow regimen, as well as having direct effects on mortality rates, body morphology, disease resistance and metabolic rates. Impacts associated with changes in light quality range from increased egg and larval mortality due to increased ultraviolet (UV) B irradiation and a decreased ability to discriminate between potential mates to increased conspicuousness to predators. Increased insolation and proliferation of exotic pasture grasses, an increasing threat in northern Australia, are shown to have a range of impacts, including changes in habitat structure, food-web structure and the facilitation of invasion by exotic fish species. The interception of terrestrial sediments and nutrients by the riparian zone has important consequences for stream fish, maintaining habitat structure, water clarity and food-web structure. Coarse organic matter donated to the aquatic environment by the riparian zones has a large range of influences on stream habitat, which, in turn, affect biodiversity and a range of process, such as fish reproduction and predation. Terrestrial matter is also consumed directly by fish and may be a very important source of energy in some Australian systems and under certain circumstances. Attention to the linkages between fish and riparian systems is essential in efforts to rehabilitate degraded stream environments and to prevent further deterioration in freshwater fish populations in northern Australia. Extra keywords: foodwebs, habitat diversity, habitat structure, riparian subsidy, sexual selection. Introduction The importance of riparian zones to aquatic ecosystems Naiman and Decamps (1997) define the riparian zone as is well recognized (Welcomme 1979; Bunn 1993; Naiman encompassing ‘… the stream channel between the low and and Decamps 1997). Terrestrial primary production derived high water marks and that portion of the terrestrial land- from the riparian zone and floodplains is acknowledged as a scape from the high water mark toward the uplands where vital source of energy in riverine food webs (Vannote et al. vegetation may be influenced by elevated water tables or 1980; Junk et al. 1989; Bunn 1993; Thorpe and Delong flooding and by the ability of the soils to hold water’.Whereas 1994). Terrestrial secondary production may also be a sig- the width of the riparian zone and the extent to which it nificant contributor of energy to riverine food webs (Chloe exerts an influence on the aquatic environment will vary and Garman 1996; Nakano et al. 1999). Other important greatly according stream size, landscape context and hydro- influences include thermal buffering (Lynch et al. 1984), the logic regime (Naiman and Decamps 1997), riparian zones are provision of shade and its influence on in-stream primary recognized as areas of biological, physical and chemical inter- production (Bunn et al. 1999a, 1999b), nutrient intercep- action between terrestrial and aquatic ecosystems (Gregory tion, storage and release (Omernik et al. 1981; Smith 1992; et al. 1991) and, consequently, are typified by unusually high Osborne and Kovacic 1993;Arthington et al. 1997), enhance- biodiversity and diversity of environmental processes. ment of bank stability (Beeson and Doyle 1995; Prosser et al. © CSIRO 2003 10.1071/MF02041 1323-1650/03/010001 2 Marine and Freshwater Research B. J. Pusey and A. H. Arthington RIPARIAN ZONE TRANSFER OF SOLAR EXCHANGE OF INORGANIC EXCHANGE OF ORGANIC ENERGY TO THE AQUATIC MATERIAL BETWEEN MATERIAL BETWEEN ECOSYSTEM TERRESTRIAL AND TERRESTRIAL AND AQUATIC AQUATIC ECOSYSTEMS ECOSYSTEMS Thermal energy Food Shade and in- stream habitat Interception Provision of Rootmasses of terrestrial bank contaminants stability Shade and the in-stream light Woody debris environment Community Leaf litter metabolism* HABITAT WATER TROPHIC QUALITY & QUALITY DYNAMICS DIVERSITY INDIVIDUAL SPECIES FITNESS DIVERSITY FISH ASSEMBLAGE COMPOSITION Fig. 1. Conceptual model depicting the mechanisms by which riparian regulation of energy and material transfer to the riverine ecosystem impacts on riverine fish communities. *This component will not be dealt with in detail here. 2001), the provision of coarse woody material as habitat and only when riparian integrity is re-established (Penczak 1997). substrate for fish, invertebrates and microalgae (Everett and Penczak et al. (1994) stressed that the mechanisms by which Ruiz 1993; Sheldon and Walker 1998; Crook and Robertson such relationships arise are difficult to ascertain due to the 1999), mediation of changes in channel morphology and multifactorial and highly interrelated nature of the linkages habitat diversity (Nakamura and Swanson 1993; Beechie and between freshwater fish and riparian zones. Sibley 1997) and refuge from disturbance at a variety of scales The present paper reviews the many linkages between the from that of the particle (i.e. individual pieces of wood) to aquatic ecosystem and the riparian zone and the mechanisms that of the watershed (Sedell et al. 1990). by which such linkages may affect lotic fish. We consider Given the number and importance of links between ripar- the various pathways by which changes in these linkages ian and lotic ecosystems, it is not surprising that spatial may lead to alterations in stream fish assemblages and the and temporal variation in fish assemblage composition and potential for their mitigation or reversal if riparian zones are characteristics (i.e. species richness, abundance, biomass) reforested. We develop a model (Fig. 1) in which the capac- have been linked to variation in riparian cover (Angermeier ity of the riparian zone to regulate the transfer of energy and Karr 1983; Davies 1989; Pusey et al. 1993, 1995a, (solar radiation) and material (both inorganic and organic) to 2000a; Amour et al. 1994; Penczak et al. 1994; Marsh- the aquatic ecosystem influences fish assemblage composi- Matthews and Matthews 2000) or that fish communities tion via impacts on individual fitness and species diversity are adversely affected by riparian destruction and recover mediated by changes in water quality, habitat quality and Importance of riparian zone to freshwater fish Marine and Freshwater Research 3 DISRUPTION OF THERMAL REGIMEN WATER QUALITY W A T TERRESTRIAL CONTAMINANTS E R Q DISRUPTION OF LIGHT ENVIRONMENT U TROPHIC DYNAMICS T A R L O I T REDUCED ALLOCHTHONOUS INPUTS P Y H I C DISRUPTED COMMUNITY METABOLISM HABITAT STRUCTURE H D A Y B N I A MACROPHYTE PROLIFERATION T M A T I C S WEED INVASION S T R U SEDIMENTATION C T U LOSS OF UNDERCUTS R E ? ? ? LOSS OF ROOTMASSES LOSS OF WOODY DEBRIS 1 10 100 TIME (years) Fig. 2. Temporal scale for the imposition of impacts on fish associated with riparian degradation. Broken boxes indicate that impacts are gradually imposed or gradually decrease in importance with time. diversity, and trophic dynamics. (The interception of light and to result in increased average summer water temperatures its influence on in-stream primary and secondary production (Lynch et al. 1984; Pearson and Penridge 1992; Quinn et al. and the influence that this may have on freshwater fish (and 1992), decreased winter water temperatures (Lynch et al. other biota), has been reviewed by Bunn et al. (1999b) and 1984; Amour et al. 1994) and an increase in the extent will not be dealt with here in detail.) The model allows a and rate of change of diel fluctuations of water temperature time sequence for impacts associated with reduced riparian (Lynch et al. 1984; Quinn et al. 1992). Seasonal patterns of integrity to be developed (Fig. 2), which may then be used temperature change may be obscured or modified and vari- to identify and compare effective