Landform Analysis, Vo/. 3: 35-40 (2002)

The environmental impact ofcrayfish biopedoturbation on a floodplain:

Roanoke River, North Carolina Coastal Plain, D.S.A.

David R. Butler

The James and Marilyn Lovell Center forEnvironmental Geography and Hazards ResearchDepartment a/Geography. Southwest Texas State UniversitySan Marcos. TX 78666-4616, U.S.A.e-mail: db25@swt.edu

LA~­-

AbsfrflCI: A terrestrial crustacean. the crayfish, creates widespread fine-scale landfonns (mounds or "chimneys'")on the floodplain oflhe Roanoke River in eastern Nonh Carolina, U.S.A. These mounds are typically 12 cm highand 8 cm in diameter. and are composed of extremely high ooncenlrations ofday, Non-crayfish-affectcd soils onthe noodplain, regardless of coarser-scale Iandform type, are dominated by sand. illustrating that crayfish an: I

primary mechanism for concentrating clay and creating spatial heterogeneity on the Ooodplain.

Kq words: zoogeomorpbology, biopedoturbation. crayfish, Roanoke River, North Carolina

Introduction

Zoogeomorphology is the study of the role ofanimals as geomorphic agents (Butler, 1995). Re­cent years have seen a surge of interest in tbe meth­ods by wbich animals geomorpbically influence theirenvironment. Examples include several papers thatexamine tbe gcomorphological role of dam-build­ing and excavations by beavers in orth Americaand Europe (Butler & Malanson, 1995; Bums &McDonnell, 1998; Gumell, 1998; Hillman, 1998;Mcentemeycr el al., 1998; Meentemeyer & Butler,1999); burrowing by ground squirrels (Andersen,1996), arctic foxes (Anthony, 1996), pocket gophers(Inouye el al., 1997), rabbits (pickard, 1999), andvoles (G6mez-Garcia et al., 1999); grazing and dig­ging for food (Boeken et aJ., 1995; MaUick el al.,1997; Manson, 1997; Mauson & Reinhart, 1997;Evans, 1998; Tardiff & Stanford, 1998); tramplingby large berbivores such as bison, cattle, and sheep(Govers & Poesen, 1998; Fritz et al., 1999; Hallet al., 1999); geophagy (soil-eating) (Mahaney etal., 1996a, 1996b); and the effects of fish on sedi­mentation paltcrns in tropical streams (Flecker,1996).

5'

In spite of this recent interest in tbe role of largeranimals as geomorphic agents, however, it isnoteworthy that little attention has been paid to tbegeomorphic impact of invertebrates, althoughinvertebrates are among the most widespread andcommon ofaU animals on the planet (Butler, 1995).Exceptions include works that have examined thegeomorphic and hydrologic effects of earthwonns(Haria, 1995), ants (Hululgalle. 1995; Butler, 1996;Green el al., 1999), scorpions (Rutin, 1996, 1998).snails and isopods (Shachak el al., 1995), river crabs(Onda and Itakura, 1997), and salt-water mud shrimp(Ziebis et al., 1996). This paper describes thegeomorphology of crayfish mounds ("chimneys"),and examines the mound particle-size texture,compared to non-crayfisb·afTected soils on portionsof the floodplain oftbe Roanoke River, on the CoastalPlain of eastern North Carolina, USA.

Background

Crayfish are terrestrial crustaceans found in low­lying terrain throughout the GulfCoast region of thesouthem United States, as well as in such diverse

35

David R. Butler Crayfish biopedoturbation, flood plain, Roanoke River, u.s.A.

The study area

The lower Roanoke River floodplain is located ineastern NQrth Carolina, on the Coastal Plain physio­graphic province of the southeastern United States(Fig. 2). The floodplain contains a mosaic ofalluvialbottomland forests that have developed as a conse­quence ofcQmplex and interrelated gcomorphje, hy­drologic and ecological processes. Floodplaintopography is sublle, but small elevational differenc­es can result in major differences in drainage, soils,and vegetation community composition. The annu­al flooding cycle constitutes the dominant geornor­phic process influencing floodplain topography. Geo­morphic features of the floodplain include oxbowlakes, natural levees, meander scrolls (ridge and

of crayfish in "mixing the surface of a very poorlydrained soil seems comparable to that of largeearthworms such as Lumbricus terrestris L (aloneor together with burrowing predators)". Theseconclusions about the hydrological effects of crayfishecho those presented by Onda and ltakura (1997)concerning river crabs, and illustrate the profoundeffects thal terrestrial crustaceans can have onlhe geomorphology and hydrology onow-lying flood­plains around the world.

•-­•. 0

Roanoke River Soil Sample Sites

< Ridge,Levee.,Terrace

D Bluff

Fig. 2. Map of the soil sampling sites, Roaooke River. North Carolina. The location of the BroadneckSwamp intensive study area is labeled

10 a tower more than 30 cm high". The most detaileddescriptions of crayfish mounds were provided byHobbs and Whiteman (1991). They reported densitiesof2,730 mounds per hectare from onc site in easternTexas, with average mound heights of 12 cm anddiameters of28 cm. They reported that >17.000 kgofsoil and 40 kg ofsodium per hectare were broughtto the surface each ycar, such that the entire surface"must have exhibited some stage ofmound construc­lion or erosion over a period of <3 years" (p. 128).At six other cast Texas study sites described by Hobbsand Wbiteman (1991), the estimated number ofmounds per hectare was 44,124 (averaging 7 cm taUand 15 cm in diameter), 63,505, 31,214, 62,676,61,775 (eQvering 15% of the surface area), and 42,470(with >40,000 kg of soil moved per hectare). ]ndivi­dual mounds examined weighed up to 40 kg, allhoughI I-25 kg was the normal range.

The density of crayfish burrows and tunnels inareas oflhe southern GulfCoast ofeast Texas, westernMississippi, and eastern Alabama is in fact so grealthat crayfish are a primary factor in the hydrology ofthe region. Stone (1993, p. 1,099) stated that, in poorlydrained areas, "[w]hen water tables are near thesurface, however, the network of large-diametercrayfish tunnels [... ] allows lateral flow at ratesunlikely to be equaled by the activity of any otherburrowing organism", and noted that the effectiveness

and chamber develQpment, and spend much time outof lhe burrow (Hobbs, 1981; Hasiotis & Mtt~hell,

1993); and• Tertiary: Crayfish spend most oftheir lives in openwater, burrowing only 10 reproduce or to escapedesiccation (Hobbs, 1981).

The digging ofburrows by crayfish results in theexcavalion and subsequent deposition ofsurface sed­iment. These deposits typically lake the form ofsteep, conical mounds also known as crayfish "chim­neys" or "turrets" (Fig. 1). The chimneys arc sur­face entry points to a tunnel system frequently over1 m in depth and chiefly 4-8 cm in diameter (Stone,1993). In many eases the mounds, reportedly com~

posed of silt and/or clay, become case-hardened bythe sun SQ that they are an impediment to farm ma­chinery. Burrows may so penneate Ihe subsurfacethat farm machinery and livestock break through thesurface and collapse into the underlying burrow sys­tem (Hobbs & \Vhiteman, 1991; Stone, 1993). Thepcdoturbational activities in burrow excavation andmound emplacement also, in some cases, bring del­eterious levels of sodium salts to the surface, harm­ing agricultural usage of the area (Hobbs & White­man, 1991).

The morphology and density ofernyfish chimneyshave been described in some detail. Hobbs (1884)reponed a typical mound size as ]5 cm wide and 10cm high, and Grow and Merchant (1980, p. 231)reported mounds ranging in height from "a low mound

habitats as the midwestern United States, easternCanada, and Australia (Hobbs. 1981; Butler, 1995).Many crayfish species dig deep vertical and complexshafts leading to long-lasting underground burrows.Crayfish burrowing has occurred as a geomorphic andpedoturbational activity since at least the Triassicperiod (Hasiotis & Mitchell, 1993; Hasiotis et al.,1993).

The significance ofcrayfish as agents of zoogeo­morphological landscape modification was first dc­scribed in detail by Tarr (1884). His illustrations ofcrayfish mounds and burrows remain the standard,as witnessed by their ulilization in a modified fonnby Grow (1981) in her examination of the burrowingbehavior of crayfish (Figs. 2-4).

Crayfish burrows arc cQmplex and may be as IQngas 4-5 m (HQbbs, 1981; Hasiotis, Mitchell & Dubiel,1993). Hobbs (1981) identified three categories ofcray­fish burrowers and burrows based Qn the amount oftime spent in the burrow, ilS architecture, :lIld its con­nection to open water:• Primary: Crayfish construct burrows with com­plex architecture, unattached to open water, andspend the majority of their tife in the burrow. Bur­rows are vertical, obtain great length, and branchout horizontally below the local water table (Hobbs& White man, 1991; Hasiotis & Mitchell, 1993;Stone, 1993);• Secondary: Crayfish construct burrows that arca"ached to open water and exhibit some branching

Fig. I. Typical crayfish mound on the Roaookc Rivcr floodplam. lens cap is 49 mm in diameter

36 37

David R. Butler Crayfish biopedoturbation, flood plain, Roanoke River, U.S.A.

swale topography), point bars, sloughs (arcas ofstagnant or sluggish water in meander scroll depres­sions), backswamp deposits, and terraces (Townsend& BUller, 1996).

Metbods

Crayfish construct conspicuous entrance mounds,and these chimneys are particularly ubiquitous inbackswamps of the lower Roanoke River, typicallyassociated with the low-lying swalcs between adjacent"swells" or ridges. High numbers of mounds arelocated in the areas of Broadneck Swamp, and soilswere collected from 30 crayfish mounds within a 10m x 30 m plot in this area. An additional 13 moundswere randomly selected from a variety of additionalfloodplain sites, in order to detenninc the degree ofspatial heterogeneity of crayfish mounds. Moundswere also photographcd in the field, and the diameterand height were determined. An additional 102 soilsamples, taken from four characteristic landform­types of the floodplain, were also collected forcomparison with crayfish-affected soils. Particle sizcdistribution of mounds and non-mound floodplainsoils was determined using hydromcler analysis.

Results

The morphology ofcrayfish mounds in the studyarea arc broadly similar to thosc reported for cray­fish elsewhere in the literature, about 12 cm aver­age height and 8 cm average diameter (N = 30 inboth cases). These mounds are larger in diameterthan those reported in the literature for other bur­rowing crustaceans. Onda and ltakura (1997) report­ed that river crab mounds are about 5 cm in diameter(no height data was given); and Ziebis et al. (1996)described the conical mounds produced by mudshrimp as averaging 4 cm in height (9 cm maximum).Although Ziebis et af. did not provide an averagemound diameter. extrapolating from !.heir Fig. 2 sug­gests an average ofabaut 6-8 cm, flaring to 10 cmat the base where particles collect at the angle ofrepose.

Soils comprising crayfish mounds in the Broad­neck Swamp area showed strong within·site similar­ity (Table 1). The mounds contain extraordinarily highlevels of clay, which when dry, becomes case-hard·ened and extremely difficult to break apart. Al!.houghthe mounds were collected wi!.hin a backswamp areawhere clay concentration would naturally be some­what high, non-crayfish soil samples from through·out the backswamp laodform (Table I) do not begin

38

Table I. Textural Data, Crayfish Mound Soils vs.Non-Mound Soils

s... ,... c.,u.-dr_

1%1 1%' 1%'Crayfish MOIIOds,Broadntck SwamP

(N-30) 4.8 (2.5)- 4.601) 90.6 (5.1)

Cl'1vflSb Mounds. Olhcr Sila(N- 13) 31.4 (18.4) 121 (IOJ) 56.4 (23.3)

IlIlIIf>(N'" 27) 62.5 (17.6 13.9 (9.2) 23.6 (15.4

:l<IIJw(N-") 61.6 (10.0 14.6 (8.1) 23.7 (9.4)

Lma(N-7) 63.3 (16.8 20.5 (7.1) 16.2 (10.8

Bad.swamp Ridges and SWJI"(N- 20) 59.0 (J 1.2) 16J (7.0) 1',.7 (122

10 approach these levels of clay conceDlration. Thepedoturbational activities of the crayfish clearly con­centrated the clay in extremely elevated levels thatare statistically significantly different (alpha = .01)than the levels ofnon·mound soils. These results alsocorroborate those ofGrow and Merchant (1980), whoexamined 40 crayfish mounds for particle size distri­bution, and classified all of those mounds as clay orsilty clay in tcxturc.

Between-site variability existed for crayfishmounds sampled from other locations (Tablc 1).These mounds were collected from a more diverselandforms assemblage, although primarily fromwithin meander·bend, low-lying swales. The spa­tial hctcrogeneity of the crayfish mounds is a re­flection of the diversity of soil textures on similarlandforms along the length of tbe study reach.Even so, however, the crayfish mounds spatiallyconcentrate clay in statistically significantly greateramounts than in any non-crayfish·affected soils inthe study area, and are more similar to otber cray­fish soils (i.e., the Broadneck Swamp crayfishmound soils) tban to non-crayfisb soils. Non­crayfish soils contain high amounts ofsand. in spiteof the fact that those soils come from a variety ofcoarser landform types, some of which (e.g .•backswamp ridges and swales) provide the primarysurfaces upon which the crayfish mounds are lo­cated The concentration of high levels ofclay, andthus the creation of spatial heterogeneity at a finescale, is thus clearly attributable to the mound­building activities of the cra.yfish.

Conclusions

Crayfish mounds are comprised largcly of clay­size particles, and are typically about 12 cm high and8cm in diameter in the study area. These dimensions,the first reponed from the North Carolina CoastalPlain, place the Roanoke River crayfish moundswithin a typieal range for such landfonns. They are adominant fine-scale landform imposed on the coarser­scale landforms of the floodplain. Given that thebackwater sites of the Roanoke River floodplainclearly qualify as locations wbere the water table isnear the surface, crayfish clearly must play an integralrole in lateral througbflow and soil aeration in thisenvirorunent. Crayfish may be a keystone species ininducing spatial heterogeneity of soil characteristicsin an environment where soils of great similarityotherwise exist regardless of landform type.

Acknowledgments

This study was funded by a grant from The NatureConservancy to Stephen J. Walsh, David R. Butler,Charles E. Konrad 11, and Robcrt K. Peel. Assistancein the field for crayfish mounds and soil data collectionwas provided by Ms. Marilyn Wyrick and Mr. JobnVogler. Ms. Wyrick and Mr. Michael Brown providedassistance in laboratory analysis of the non-crayfishsoils data, and Mr. Vogler assisted with the laboratoryanalysis of the crayfish mounds.

References

Andersen, D. C., 1996: A spatially-explicit model ofsearch path and soil disturbance by a fossorial her­bivore. Ecological Modelling 89: 99-108.

Anthony, R. M., 1996: Den use by arctic foxes (Ala­pex lagopus) in a subarctic region of westernAlaska. Canadian Journal ojZoology 74: 627­631.

Bocken, 8., Sha.chak. M. & Brand, S. 1995: Patchi­ness and disturbance: plant community responsesto porcupine diggings in the central Negev. Eca­grophy 18: 41<>-422.

Bums, D. A. & McDonnell, J. J., 1998: Effects ofabeaver pond on runoff processes: comparison oftwo headwater catchments. Journal ojHydrology205: 248-264.

Butler, D. R., 1995: Zoogeomorphology: Animals asGeomorphic Agents. Cambridge, Cambridge Uni­vcrsity Press.

Butler, D. R., 1996: The Carolina Invasion of theFire Ants. In: Snapshors ofrhe Carolinas: Land·scopes and Cultures D. G. Benneu. (Ed.). Asso-

ciation of American Geographcrs, Washington,D.C., 95-97.

Butler, D. R. & Malanson, G. P., 1995; Sedimenta­tion rates and pauems in beaver ponds in a moun­tain environment. Geomorphology 13: 255-269.

Evans, R., 1998: The erosional impacts of grazinganimals. Progress in Physical Geography 22: 251­268.

Flecker, A. S., 1996: Ecosystem engineering by a de.minant detritivorc in a diverse tropical stream.Ecology 77: 1845-1854.

Fritz, K. M., Dodds, W. K. & Pontius, J., 19"·. Theeffects ofbison crossings on the macroinvertcbra­te community in a tallgrass prairie stream. Amen·­can Midland Naturalist 141: 253--265.

G6mez-Garcia, D., Giannoni. S. M., Reine, R. & Gor·gbi, C. E., 1999: Movementofseeds by the burro­wing activity ofmole·volcs on distwbed soil moundsin tbe Spanish Pyrenees. Arctic. Antarctic, andAlpine Research 31: 407-411.

Govers, G. & Poesen, J., 1998: Field experiments onthe transport of rock fragments by animal tram­pling on scree slopes. Geomorphology 23: 193-­203.

Green, W. P., Pettry, D. E. & Switzer, R. E.• 1999:Structure and hydrology of mounds of the impor­ted firc ants in the southeastern United States.Geodenna 93: 1-17.

Grow, L., 198): Burrowing behaviour in the crayfish.Cambarus diogenes diogenes Girard. AnimalBehaviour 29: 351-356.

Grow, L. & Merchant, H., 1980: The burrow habitatof the crayfish. Cambarw; diogenes diogenes (Gi·rard). American Midland Naturalist 103: 231-237.

Gumell, A., 1998: The hydrogeomorphoJogical cf·feets ofbcavcr dam-building activity. Progress inPhysical Geography 22: 167-189.

Hall, K., Boclhouwers, J. & Driscoll, K., 1999: Ani­mals as erosion agcnts in the alpine zone: somedata and observations from Canada, Lesotbo. andTibet. Arclic. Antarctic, and Alpine Research 31:436-446.

Haria, A. H., 1995: Hydrological and environmentalimpact ofearthworm depletion by the New Zealandnatwonn (Artioposrhia triangulata). Journal ofHydrology 171: 1-3.

Hasiotis, S. T. & Mitchell, C. E., 1993: A compari·son ofcrayfish burrow morphologies: Triassic andHolocene fossil~ paleo· and neo-icbnological evi­dence, and the identification of their burrowingsignatures.lchnos 2: 291-314.

Hasiotis. S. T., Mitcbell, C. E. & Dubiel, R. E, 1993:Application ofmorphologic burrow interpretationsto discern continental burrow architects: lungfisbor crayfish? lchnos 2: 315-333.

39

David R. Butler

Hillman, G. R., 1998: Flood wave attenuation by awetland following a beaver dam failure on a se­cond order borcal stream. Wetlands 18: 21-34.

Hobbs, H. H., Jr., 1981: The crayfishes of Georgia.Smithsonian Contributions to Zoology 318: 1­549.

Hobbs, H. H., Jr. & Whiteman, M., 1991: Noteson the burrows, behavior, and color of the cray­fish FalJicambarus (F) devastator (Decapoda:Cambaridae). Southwestern Naturalist 36: 127­135.

Hululgalle, N. R., 1995: Effects of ant hills on soilphysical properties ofa Vertisol. Pedobiologia 39:34-41.

Inouyc, R. 5., Huntly, N. & Wasley, G. A., 1997: Ef­fects of pocket gophers (Geomys bursarius) onmicrotopographic variation. Journal ofMamma­logy 78: 1144-1148.

Mahaney, W. C., Bezada, M., Hancock, R. G. v., Au·freiter, S. & Percz, F. L., 1996a: Geophagy ofHolstein hybrid cattle in the northern Andes, Ve­nezuela. Mountain Research and Development 16:177-180.

Mahaney, W. C., Hancock, R. G. V. & Huffinan, M.A., 1996b: Geochemistry and clay mineralogy oftermite mound soil and the role of geophagy inchimpanzees of the Mahale Mountains, Tanzania.Primates 37: 121-134.

Mallick, S. A., Driessen, M. M. & Hocking, G. J.,1997: Diggings as a population index for theeastern barred bandicoot. Journal of Wildlife Ma­nagement 61: 1378-1383.

Mattson, D. 1., 1997: Selection ofmicrosites by griz­z.lybears to excavate biscuitroots. Journal ofMam­malogy 78: 228;-238.

Mattson, D. J. & Reinhart, D. P., 1997: Excavation ofred squirrel middens by grizzly bears in the white­bark pine zone. Journal ofApplied Ecology 34:926--940.

Meentemeycr, R. K. & Butler, D. R., 1999: Hydroge­omorphic effects ofbeaver dams in Glacier Natio­nal Park, Montana. Physical Geography 20:436--446.

40

Meentemeyer, R. K, Vogler, J. B. & Butler, D. R,1998: The geomorphic influences of burrowingbeavers on streambanks, Bolin Creek, North Ca­rolina. Zeitsehriji fUr Geomorphologie 42: 453­468.

Onda, Y. & Itakura, N., 1997: An experimental studyon the burrowing activity of river crabs on subsur­face water movement and piping erosion. Geomor~phology 20: 279-288.

Pickard, J., 1999: Tunnel erosion initiated by feralrabbits in gypsum, semi-arid New South Wales,Australia. Zeitsehriftfiir Geomorphologie 43: 155­166.

Rutin, J., 1996: The burrowing activity of scorpions(Scorpio maurus palmaws) and their potential con~tribution to the erosion of Hamra soils in Karkur,central Israel. Geomorphology 15: 159--168.

Rutin, J., 1998: The contribution of scorpions (Scor~

pio maurns palmalus) to the preparation ofavaila­ble sediment on a sandy slope in Karkur, centralIsrael. Geoiikodynamik 19: 89-101.

Shachak., M., Jones, C. G. & Brand, S., 1995: Therole of animals in an arid ecosystem: snails andisopods as controllers of soil formation, erosionand desalinization. Advances in GeoEcofogy 28:37-50.

Stone, E. L., 1993: Soil burrowing and mixing by acrayfish. Soil Science Society ofAmerica Journal57: 1096--1099.

Tardiff, S. E. & Stanford, J. A., 1998: Grizzly beardigging: effects on subalpine meadow plants in re­lation to mineral nitrogen availability. Ecology 79:2219-2228.

Tarr, R. S., 1884: Habits of burrowing crayfishes inthe United States. Nature 30: 127-128.

Townsend, P. A. & Butler, D. R., 1996: Patterns oflandscape use by beaver on the lower RoanokeRiver floodplain, North Carolina. Physical Geo­graphy 17: 253-269.

Ziebis, W., Forster, S. & Jorgenscn, B. 8., 1996: Com­plex burrows of the mud shrimp Callianassa trun­eata and their geochemical impact in the sea bed.Nature 382: 619-622.