water Review Review of Methods to Repair and Maintain Lithophilic Fish Spawning Habitat 1, , 1 2 3,4 4,5 Audrey Baetz * y , Taaja R. Tucker , Robin L. DeBruyne , Alex Gatch , Tomas Höök , Jason L. Fischer 6 and Edward F. Roseman 1,* 1 U.S. Geological Survey Great Lakes Science Center, 1451 Green Rd, Ann Arbor, MI 48105, USA; [email protected] 2 Department of Environmental Sciences, University of Toledo, 2801 W. Bancroft St., Toledo, OH 43606, USA; [email protected] 3 U.S. Fish and Wildlife Service, Lower Great Lakes Fish and Wildlife Conservation Office, 1101 Casey Road, Basom, NY 14103, USA; [email protected] 4 Department of Forestry and Natural Resources, Purdue University, Forestry Building, 195 Marsteller Street, West Lafayette, IN 47907, USA; [email protected] 5 Illinois-Indiana Sea Grant College Program, 195 Marsteller Street, West Lafayette, IN 47907, USA 6 U.S. Fish and Wildlife Service, Alpena Fish and Wildlife Conservation Office, 5437 West Jefferson Ave., Trenton, MI 48183, USA; jason_fi[email protected] * Correspondence: [email protected] (A.B.); [email protected] (E.F.R.); Tel.: +1-248-912-7545 (A.B.); +1-734-214-7237 (E.F.R.) Under contract with U.S.G.S. y Received: 8 July 2020; Accepted: 24 August 2020; Published: 8 September 2020 Abstract: Rocky reefs provide important spawning and refuge habitats for lithophilic spawning fishes. However, many reefs have been lost or severely degraded through anthropogenic effects like dredging, channelization, or sedimentation. Constructed reefs have been used to mitigate these effects in some systems, but these reefs are also subject to degradation which may warrant custodial maintenance. Monitoring and maintenance of natural or constructed spawning reefs are not common practices; therefore, few methodologies have been created to test the effectiveness of such tools. We conducted a literature review to assess available information on maintenance of rocky spawning habitats used by lithophilic fishes. We identified 54 rocky spawning habitat maintenance projects, most of which aimed to improve fish spawning habitats through the addition of spawning substrate (n = 33) or cleaning of substrate (n = 23). In comparison to shallow riverine studies focused on salmonids, we found little information on deep-water reefs, marine reefs, or other fish species. We discuss the possible application of potential spawning habitat cleaning methods from other disciplines (e.g., treasure hunting; archeology) that may provide effective means of reef maintenance that can be used by restoration practitioners. Keywords: reef; custodial maintenance; fish spawning; restoration; sediment removal; anthropogenic impacts 1. Introduction Rocky reefs are historically important fish habitats that can increase fish abundance locally [1], serve as biodiversity hotspots [2,3], and provide spawning, nursery, and refuge habitats [4–6]. Habitat requirements vary by species and life stage (e.g., egg, larvae, juvenile, or adult); thus, different fishes and life history stages benefit from rocky reefs differently. Habitat requirements for egg and larval stages are constrained due to increased sensitivity to stochastic processes, smaller energy stores, and reduced mobility compared to adults [7]. For many species, clean rocky substrates in the Water 2020, 12, 2501; doi:10.3390/w12092501 www.mdpi.com/journal/water Water 2020, 12, 2501 2 of 37 Water 2020, 12, x FOR PEER REVIEW 2 of 31 influenceform of reefs recruitment are particularly potential important in deeper spawning waters and[8]. nurseryGravel habitatsbeds serve and the may same strongly purpose influence for salmonidsrecruitment and potential other riverine in deeper species waters in shallow [8]. Gravel water beds environments serve the same [9,10]. purpose Despite for their salmonids importance, and manyother riverinereefs and species other inrocky shallow spawni waterng environmentsareas have been [9,10 lost]. Despiteor degraded their importance,due to habitat many destruction reefs and fromother anthropogenic rocky spawning stressors areas have [11,12]. been Anthropogenic lost or degraded destruction due to habitat of fish destruction habitats fromis widespread anthropogenic and isstressors implicated [11, 12in ].>70% Anthropogenic of North American destruction fish ofextinctions fish habitats and is includes widespread habitat and loss is implicated or degradation in >70% or reducedof North access American to spawning fish extinctions areas [13]. and includes habitat loss or degradation or reduced access to spawningWhile areasmarine [13 ].coral reefs are the focus of many restoration initiatives, both marine and freshwaterWhile rocky marine reefs coral are reefs not are as thewell focus studied of many as co restorationral reefs, despite initiatives, having both both marine high and biodiversity freshwater androcky similar reefs arelevels not of as degradation well studied [14]. as coral Causes reefs, of despite destruction having or both degradation high biodiversity of rockyand spawning similar habitatslevels of include degradation physical [14 ].factors Causes such of destructionas sedimentation or degradation [15–17], channelization of rocky spawning [18,19], habitats and resource include extractionphysical factors [20–22], such while as sedimentation biological factors [15–17 include], channelization periphyton [18 ,19accumulation], and resource (e.g., extraction Cladophora [20– 22or], Didymospheniawhile biological) [23–25] factors includeand biofouling periphyton by invasive accumulation species (e.g., (e.g.,Cladophora musselsor [26,27]).Didymosphenia Sedimentation)[23–25] is and a naturalbiofouling process by invasive in freshwater species and (e.g., marine mussels systems; [26,27 ]).however, Sedimentation anthropogenic is a natural stressors process have in freshwaterincreased theand rate marine at which systems; this process however, can anthropogenic occur [15,28]. stressorsAccumulation have increasedof fine sediments the rate such at which as silt this and process sand cancan lead occur to [egg15,28 mortality]. Accumulation via infilling of fine of interstitial sediments spaces such as that silt help and sandprotect can fish lead eggs to eggand mortality larvae from via predatorsinfilling of and interstitial displacement spaces that[29] helpwhile protect allowing fish for eggs adequate and larvae water from flow predators and oxygenation and displacement [17,30,31]. [29] Biofoulingwhile allowing occurs for when adequate the habitat water flow is degraded and oxygenation through [biological17,30,31]. processes, Biofouling such occurs as whencolonization the habitat by Dreissenais degraded polymorpha through biologicaland D. bugensis processes, mussels such as colonization(hereafter referred by Dreissena to as polymorpha dreissenidand mussels)D. bugensis or periphyton.mussels (hereafter Biofouling referred can also to asreduce dreissenid the intersti mussels)tial spaces or periphyton. required for Biofouling egg incubation, can also deplete reduce oxygen,the interstitial and create spaces waste required build-up for [27]. egg Many incubation, lithophilic deplete spawners oxygen, pr andefer createsubstrate waste free build-up of epiphytic [27]. growthMany lithophilicand debris spawners [29,32] and prefer select substrate spawning free habi of epiphytictats with growthwater velocities and debris that [29 maintain,32] and selectsuch habitatsspawning [33,34]. habitats Historic with waterdestruction velocities of reefs that for maintain resource such extraction habitats or [33 development,,34]. Historic destructioncoupled with of alteredreefs for ecosystem resource extractionprocesses that or development, increase rates coupled of physical with degradation, altered ecosystem have led processes to the loss that of increase viable fishrates spawning of physical habitats degradation, and reduction have led of toother the ecosystem loss of viable services fish spawning [15,35–37] habitats (Figure and1). reduction of other ecosystem services [15,35–37] (Figure1). Figure 1. Conceptual diagram of the causes and effects of rocky fish spawning habitat degradation. ToFigure mitigate 1. Conceptual impacts diagram of degradation, of the causes construction and effects of of rocky rocky fish reefs spawning to improve habitat spawningdegradation. habitat increased during the 1980s [38] and spawning reefs have been constructed across the globe, with a majorityTo mitigate located inimpacts North Americaof degradation, and Europe constructi [11,39].on Construction of rocky reefs of reefsto improve to attract spawning fish has occurred habitat increasedin Japan for during centuries, the 1980s and construction [38] and spawning of similar reef reefss have began been in the constructed early 1800s across in North the America globe, with [25,40 a], majority located in North America and Europe [11,39]. Construction of reefs to attract fish has occurred in Japan for centuries, and construction of similar reefs began in the early 1800s in North America [25,40], but the emphasis on creating spawning-specific reef habitats has been more recent. Water 2020, 12, 2501 3 of 37 but the emphasis on creating spawning-specific reef habitats has been more recent. In freshwater systems such as the Laurentian Great Lakes (hereafter referred to as the Great Lakes), rocky reefs were constructed to provide spawning habitats for lithophilic spawning fishes such as lake sturgeon Acipenser fulvescens [24,41], lake trout Salvelinus namaycush [37], walleye Sander vitreus, and lake whitefish Coregonus clupeaformis