Effects of Refuge Size and Complexity on Recrnitment and Fish Assemblage Formation on Small Artificial Reefs ROBIN L SHEPJVIAN, D.S. QI LLIAM and R.E. SPIELER NovaSotttheastern University Oaeanographic Center 8NN North Ocean Drive Bania Beach, Fl33904 USA ABSIRACI' There have beena numberof natu' and artificialreef studiesexamining possiblecorielatian's between refuge size and complexity and the associatedfish assemblages. Results of these studies have been contradictory indicating possiblesite dependentdifferences, We examinedthe role of refugesize and complexity in fish recruitmentand the formation of associatedfish assemblages, using artificial reef modules,at two different depthsoff Fort Lauden9a1e,Hloidd, USA. The 1 m3 reef modules Swiss Cheesereefs! were constructedof poured concrete with 12 tunnels running through the block, six tunnels in each direction pexpenthcularto eachother. Twenty teplicateswere canslriictedof eachof three different refugeconfigurations, 12 largetunnels squareopening, 15 cm per side!, 12 small tunnels .5 cin per side! or six large and six small tunnels Ten replicatesof each reef designwere deployedat each depth m and 20 m! on sandysubstrate. Significant differenceswere found far recruits fishes0 - 5 cm TL!, total fish abundance, and species richness between refuge contiguiations as well as depths. Additionally, this study was designed,in part, to replicatework done previously by others,in the Catibbeanexamining the effectsof refugesize on fish abundance and species richnem. Differences were found between the studies. This may be due, in part, to differences in local fish species composition and population structure, KEY WORDS: Refuge,site dependentdifferences, substrate INTRODUCTION Many aspect of artificial structurehave been examined in eIT'artsto identify ways to increasefish abundanceand diversity, improve catch rates of targeted species,manipulate habitats, and restoredamaged caral reefs far referencessee: Sahnsack and Sutherland 1985, Bohnsack 1990, B~k et al. 1991, Seajrnan 1997, Spieler et al. in press!. A number of ~ and artificial reef studies examined possible cortelation's between refuge size and complexity and the associatedfish assemblages Molles 1978,Gascon and Miller 1982,Roberls and Ormond 1987, Brack and Norris 1989, Hixon and Beets 1989, Hdund 1996, Friedlander and Fairish 1998, Spieler 1998, Spieler in press, Authors unpublished!. Resultsof these studies have been conttadictoty indicating 455 Proceedin s of the 52nd Gtitf end Caribbean FIeheriee Institute possiblesite dependentdifferences. We examinedthe role of refugesize and complexityin fishiucruitment and the formation of associatedfish assemblages, usingartificial reef modules, attwo diff+mt depths off FortLauderdale, Florida. MATERIALS AND METHODS Experimental Design This iesearchfocused on threecentral hypotheses: i! therecruitment and aggregation af a diverseassemblage of fishes to artificial reefscan be effected by thesize of therefuges available, ii! diverserefuge sizes are superiorto uniformrefuge sizes for the recruitment andaggregation of a diverseassemblage of fishes to an artificial reef, and iii! deploymentsite selection i.e. depth!will effect the formationand maintenanceof thelish assemblageon a smallartificial reef. Briefly, the experimentaldesign consisted af comparingfish abundance, speciesrichness, and species composition among three groups of reefs0 Swiss Cheesereefs each! with eitherlarge holes only Large refugereefs!, small holes only Small refugereefs!, or largeand smallholes Mixed refugereefs!, at two diffetent depths.The hypothesesabove allowed us to make three specific predictionsthat were statistically verifiable: i! Artificialreefs with largerefuges will havedifferent fish abundance, species richness,and species composition than reefs with smallrefuges ii! Reefswith mixed sized refuges will havegreater fish abundatice, and species richnessthan either large refuge reefs or smailrefuge reefs, and iii! Reefsdeployed at differentdepths will havedifferent fish abundance, species richness,and species composition. Construction «nd Deployment The reefs Swiss Cheesereefs! were constructedat the CSR Rinker Concise Plant, ~broke Pines,Florida usingwaste concrete concrete remaining in truckswhen returningfrom a job! pouredinto reusablemolds made from pressuretreated plywood. Tunnels were formedin the ccncteteusing wooden dowelsof either 3.5 cm squateor 10 cm squarewrapped in 2 cm thick Styrofoam.When assembled, this form contained approximately I m~ of poured concretewith 12 tunnels refuges! running through the block,six tunnelsin each directionperpendicular to each other Fiiguie 1!. Twenty replicateswere constructedof each of threedifferent refuge configurations, 12 large refuges squareopening, 15cm per side!,12 smallrefuges .5 cm per side!or six large andsix smallrefuges. Ten replicatcsof eachieef designwere deployed at eachof twodepths in and20 m! on sandysubstrate, The deepsite was approximately Sherman R.L. et al. GCFlr52 2001 one kilometer eastof the shallow site. Thirty reefswere deployedat eachsite, in sandysubstrate, with 35 metersbetween each reef. Figure 1. Nxed refuge size reel being deployedoffshore Broward County, Rorida, USA Monitoring In an effort to examine seasonal differences the reefs were monitored approximatelyquarterly eight times! from October1996 through January 1999, Divers, using SCUBA, counted,and reccmh8census data on slatesmarked on one edge with five size intervals: < 5, 5 10, 10 20, and 20+ cm to aid in length estimation. The reefs are small enough to allow for an accuratetotal count without sub-sampling, Species, numbers of fish per species, aud estimatedtotal length, by size class,of all fishes within 1 m of each reef 8 m3, tolal volume including reef! were recorded. The size classeswere also used Proceedin s of the 52nd Gulf and Caribbean Fisheries Institute to calculatefish biomasson the reefs. The meantotal length TL! for eachsize classwas usedin length-weightequations published by Bohnsackaad Harper {1988!. When a length-weightequation for an identifiedspecies was not available, the equationfor a congenericwas used. Datawere analyzed with non-parunetricanalysis of variancetechniques usiagStatistical Analysis Systems SAS! software SAS InstituteInc., Cary, NC, VSA! PROC GLM of rankeddata Kruskai-Wallisk-sample test, and a Student-Newman-Keulstest between iaeans! Refuge Size With the followingexceptions, Iitrle differencewas noted in the numberof fishes all speciescoinbincd! among the three refuge sizes for anysize class. At boththe shallowaad deep sites there were more 20+ cm fish aadmore total fish all sizescombined! associate with largeor mixedrefuge reefs than small refuge reefs p < 0.05. ANOVA/SNK! Figute 2, 3!. At Theshallow site therewere alsomore juvenile fishes 5 cm TL! on the largerefuge reefs than those with small refuges p 0.05, ANOVA/SNK!. 14 ~~12 10 8 6 I 4 2 0-5 5-lt! 10-20 . 20+ Total Sizeclass cra! Figure 2. Meannumber of totalfishes {+/- 1 SEM!by sizechss on deepreefs with one of three treatments:large, small or mixedrefuge sizes. Asterisked treatmentsare significantlydifferent from other treatments within a sizeclass {p < 0.05, SNK!. Sherman R L et al. GCFI:52 2001 45 40 5.5 39 ti 25 sa 20 8 15 100-5 5-10 20+ Total Size class cm! Figure 3. Mean number of total fishes +/- 1 SEM! by size class on shaNow reefs with one of three treatments: large, slnalf or mixed refuge sizes. Asterlsked treatments are significantly different from other treatments within a size class p < 0.05, SNK!. Likewise, the numberof species,by size class,did not differ much among the three treatments. Both shallow and deepreefs had more speciesin the 20+ cm size classon the large and mixed refugereefs and at the shaliow site, there were also more total specieson the large and mixed refuge reefs p < 0.05, ANOVA/SNK! Rgure 4, 5!. There were more <Scm TL specieson large and mixed refugeshallow reefsvs. deep. Large size classfishes >10 crn!, as well as total species aH sizescombined!, were more abundantdeep on large and mixed refuge reefs p < 0.05, ANOVA/SNK!. Throughout the year, total species ali size classescombined! were not significantly different on the deepreefs among months p > 0.05! but were highest on the shallow reefs in July and November p < 0.05, ANOVA/SNK!. SHe Dependent Differences Seventy-seven species were recorded at the deep site and 49 species at the shallow site. Of the 88 total speciesrecorded, 40 were found exclusivelydeep all refuge sizes combined! and 11 were only found shallow Table 1!, Proceedin s of the 52nd Gulf and Caribbean Fisheries institute 7 ~ 6 5 tl 4 4 0-5 5-10 10-20 Total Size class cm! Figure 4. Mean numbercf total specm +/- 1 SEM! by size class on deep asefs with one ol three treatments; large, small or mixed refuge sizes, Asterlsked treatments are significantly dNerent from other treatments within a size class p < 0.05, SNlq. + 4 I 53 4 2 0-5 5-10 10-20 20+ Total Size class cm! Figure 5. Mean number af total species +1- 1 SEM! by size chas on shallow reefs with one of three treatments: large, small or mixed refuge sizes. Asterisked treatments are significantly different from other treatments within a size chss p < 0.05, SNlq. Sherman R.L. et al. GCFI:52 2001 Table 1. List of fishes Common Name Scientific Name Deep Shallow STING RAYS DASYATIDAE Southern stingray Oasyatis amencana MORAY EELS MURAENIDAE Purplemouth Moray Gymnothorax vicinus SEA BASSES SERRANIDAE Black Grouper h5eteroperca bonaci Scamp Mycteroperca phenax Red Grouper Epinephelus