Journal of Tropical Ecology (2003) 19:333–336. Copyright  2003 Cambridge University Press DOI:10.1017/S0266467403003365 Printed in the United Kingdom SHORT COMMUNICATION Macrophyte rafts as dispersal vectors for fishes and amphibians in the Lower Solimões River, Central Amazon Luis Schiesari*1, Jansen Zuanon†, Claudia Azevedo-Ramos‡, Marcelo Garcia§, Marcelo Gordo§, Mariluce Messias¶ and Emerson Monteiro Vieira# *Departamento de Zoologia, Instituto de Biociências, Universidade de São Paulo, CP 20520, 01452-990, São Paulo-SP, Brazil †Coordenação de Pesquisas em Biologia Aquática, Caixa Postal 478, Instituto Nacional de Pesquisas da Amazônia, 69083–970, Manaus-AM, Brazil ‡Núcleo de Altos Estudos Amazônicos-NAEA, Universidade Federal do Pará 67070-100, Belém-PA, Brazil §Departamento de Biologia, Universidade do Amazonas, 69970-000, Manaus-AM, Brazil ¶UNESP-Rio Claro, PG Zoologia, Avenida 24-A, 1515, C.P. 199, 13506-900, Rio Claro-SP, Brazil #Laboratório de Ecologia de Mamı́feros, Centro de Ciências da Saúde, UNISINOS, CP 275, 93022-000, São Leopoldo-RS, Brazil (Accepted 9 June 2002) Key Words: Amazon, amphibians, biodiversity, biogeography, dispersal, fishes, macrophytes, várzea floodplains Large rivers have played a prominent role in biogeo- graphic theory for their potential to act as barriers for the dispersal of terrestrial organisms, and therefore be involved in the generation of species diversity (Brown & Lomolino 1998). In this paper, we document the potential role of macrophyte rafts as a mechanism by which Ama- zonian rivers could act as dispersal agents rather than bar- riers, transferring organisms across banks and possibly across very large distances. These vectors could therefore act against speciation and towards homogenization of the local biota. These rafts originate from extensive macrophyte stands that grow along the margins and banks of the nutrient- rich, white-water rivers and lakes in the Amazonian várzea floodplains (Junk 1970, 1973; Junk & Piedade 1993, 1997; Junk et al. 1989). Macrophyte stands support an extremely rich community of over 380 species of herbs of floating and rooted habits, but are commonly domin- ated by the grasses Paspalum repens Berg. and Echinoch- loa polystachya (H.B.K.) Hitch. and floating vegetation such as the water hyacinth (Eichhornia crassipes (Mart.) Solms.) and the pteridophyte Salvinia auriculata Aubl. (Junk & Piedade 1993). Macrophyte stands constitute a peculiar habitat encompassing aquatic and terrestrial biotopes. The rapid growth and production of detritus, and shelter availability in the root zone of macrophyte stands 1 Corresponding author. Present address: Department of Ecology and Evolutionary Biology, University of Michigan, 48109-1048, Ann Arbor-MI, USA. Email: lschiesa@umich.edu provide conditions for the development of an abundant aquatic fauna of invertebrates (especially microcrustace- ans, molluscs and insects; Junk & Robertson 1997) and vertebrates (mostly fish; Henderson & Hamilton 1995, Junk et al. 1997). The aerial portion is habitat for inver- tebrates (mostly insects and arachnids), anuran amphi- bians, which use the stands of floating macrophytes as calling and breeding sites (Hödl 1977), and for other ver- tebrates such as birds (Petermann 1997). After explosive growth during the period of rising water levels, stalks of floating meadows often get weak and break, forming drifting rafts that may flush into the main river channel and be carried away by wind and water currents (Junk & Piedade 1997). Field work was conducted on 20 and 21 August 1994 in the Ilha da Marchantaria (03°14′S, 59°57′W), near Manaus, Central Amazon, Brazil. This island is located in the lower Solimões river, 15 km above the confluence with the Rio Negro. Following the yearly peak in water level in June (Irion et al. 1997), around August the strong- est water currents occur and many macrophyte rafts drift down the river. We approached the rafts by boat, and measured their length and width. Rafts were encircled with a 7-m × 3.5-m (mesh 0.5 cm) seine net. Rafts were not compact and therefore could be entirely encircled even if their perimeter exceeded net length (7 m). The net was subsequently brought to the boat, where every plant was carefully screened for vertebrates. All vertebrates were collected, identified whenever possible to species, L. SCHIESARI ET AL.334 and counted. Fish were identified as adults or juveniles according to Géry (1977), Kullander (1986), Burgess (1989) and Botero & Araújo-Lima (2001). Voucher speci- mens were deposited in the collections of the Instituto Nacional de Pesquisas da Amazônia, Manaus, Brazil. We sampled eight floating macrophyte rafts of 3.02– 24.7 m2 (mean ± SD: 9.11 ± 6.30 m2) which were found drifting down the river. Two rafts were constituted pre- dominantly of Eichhornia crassipes, and six of Paspalum repens. Associated vertebrates were represented by fishes and amphibians (Table 1). Fishes were present in the root zone of all rafts. We found 286 individuals of 39 species and 19 families (Table 1). Characidae were the most abundant (32.9% of all individuals, n = 94) and species-rich (35.9% of all spe- cies, n = 14) family, followed closely by Cichlidae in abundance (29.0%, n = 83), but not species richness (10.2%, n = 4). Hypopomidae were represented by 35 individuals (12.2%) and three species (7.7%). Apteronoti- dae and Serrasalmidae were represented by two species each, while the 14 remaining families were represented by only one species and most commonly by less than four individuals each. The most common species were Apisto- gramma agassizi (Cichlidae), Hyphessobrycon eques (Characidae) and Pyrrhulina sp. (brevis species group) (Lebiasinidae), with respectively 49 (17.1%), 24 (8.4%) and 23 (8.0%) individuals. Fish species richness was significantly related to raft area (number of species = 3.87 + 0.81 × area; r2 = 0.70, P = 0.01). No significant relationship was found between fish abundance and raft area. Nearly half (49.30%) of individual fish collected were juveniles. Amphibians occurred on six rafts. We found 42 indi- viduals of nine species belonging to five families, four of Anura (Hylidae, Leptodactylidae, Pseudidae and Bufonidae) and one of Gymnophiona (Typhlonectidae) (Table 1). Hylidae were the most abundant (83.3% of all individuals, n = 35) and species-rich (55.5% of all species, n = 5) family. The four remaining families were each rep- resented by a single species and 1–3 individuals. The tree- frog Hyla walfordi was by far the most abundant species (45.2% of all individuals, n = 19). In one single raft, with an area of 8.48 m2, we found 11 individuals of H. wal- fordi, two of them gravid females. A gravid female of Hyla leucophyllata was found in another raft. Only five anurans (11.9%) collected were immatures (three tadpoles and two metamorphs). We did not find any significant relationship between raft area and amphibian species rich- ness or abundance. A rich and abundant invertebrate fauna was found asso- ciated to these rafts, including: a leech, pulmonate mol- luscs, spiders, crustaceans (shrimps and crabs), and insects such as odonates (naiads and adults), blattarians, orthopterans (ensiferans and caeliferans), homopterans, belostomatid heteropterans, hymenopterans (ants), lepid- opterans (larvae and adults) and coleopterans (larvae, pupae and adults). Particularly abundant were shrimps, spiders and orthopterans. Aquatic macrophyte rafts have been suggested to act as dispersal vectors in large lakes (Lake Mamiraua: Hender- son & Hamilton 1995; Lake Malawi: Oliver & McKaye 1982) and rivers (Parana River: Achaval et al. 1979) for both aquatic and terrestrial faunas, although the effect- iveness can vary depending on the fish group considered (Henderson & Hamilton 1995). Albeit preliminary, our sampling in the Solimões River indicates that floating macrophyte rafts can transport a remarkably diverse and abundant vertebrate assemblage. In addition to the 39 spe- cies of fishes and nine of amphibians found (Table 1), at least 13 other species of fish and seven of amphibians live in aquatic macrophyte stands (Hödl 1977, Junk 1973). Many of the fish and amphibian species that we found in the floating rafts show very wide distributional ranges in the floodplains of the Amazon basin (Burgess 1989, Frost 1985, Géry 1977, Kullander 1986). Dispersal of ver- tebrates through the Amazon River seems to be a common phenomenon and floating macrophyte rafts may be acting as important vectors. Moreover, transportation by floating rafts may represent an unusually predictable vector of long-distance dispersal both from spatial (unidirectional) and temporal (seasonal) standpoints (see also Hender- son & Hamilton 1995). This predictability could have favoured selection for the utilization of macrophyte stands as breeding sites and nursery grounds for several fish species. Rafts could trans- port juveniles and therefore return individuals to the popu- lations of the several fish species that migrate upriver to breed. Consistent with these hypotheses, Sazima & Zam- progno (1985) observed that young piranhas sheltering among the roots of water hyacinths had no fin damage, in contrast to larger juveniles and adults. They also sug- gested that, apart from shelter, young piranhas might profit from water hyacinth transportation. This could explain why piranhas, which spawn during the annual floods, have a wide distribution despite the absence of known migratory movements by the adults in Amazonian rivers (Goulding 1980). The effectiveness of the rafts as a long-distance dis- persal vector is further reinforced by the observation that average current velocities in the Amazon River range from 1.0 to 1.5 m s−1 in the wet season (Sioli 1975). Under such conditions a raft could travel 86–130 km per day, or, in other words, travel the whole extension of the Solimões/Amazonas River system (4000 km) in as little as 31 d. The probability of establishing viable populations upon arrival could be enhanced both by the synchroniza- tion of the drift and reproductive period, and by the large observed densities of fishes (up to 10.5 m−2) and amphibians (up to 1.65 m−2). In summary, drifting of many rafts containing dense vertebrate populations in Animal dispersal by macrophyte rafts in the Amazon 335 Table 1. Absolute frequency of fish and amphibian families and species found in eight macrophyte rafts in the lower Solimões river, Amazonas, Brazil. Individuals classified as adults (A) or juveniles (J) (a = tadpoles; b = metamorphs). Family Species Number of individuals Number of rafts Individuals in which the species per J A Total was found family FISHES Ageneiosidae Ageneiosus sp. 1 – 1 1 1 Anostomidae Leporinus fasciatus (Bloch, 1794) 1 – 1 1 1 Apteronotidae Apteronotus albifrons (Linnaeus, 1766) – 1 1 1 2 Apteronotus hasemani (Ellis, 1913) – 1 1 1 Auchenipteridae Parauchenipterus galeatus (Linnaeus, 1766) 3 1 4 4 4 Callichthyidae Megalechis thoracata (Valenciennes, 1840) 1 – 1 1 1 Characidae Aphyocharax sp. 8 5 13 3 94 Charax sp. 13 – 13 1 Ctenobrycon spilurus (Valenciennes, 1850) 3 – 3 3 Hemigrammus sp. 1 3 5 8 2 Hemigrammus sp. 2 – 1 1 1 Hemigrammus sp. 3 7 1 8 3 Hemigrammus sp. 4 1 – 1 1 Hyphessobrycon eques (Steindachner, 1882) 10 14 24 3 Hyphessobrycon sp. 1 5 5 10 5 Hyphessobrycon sp. 2 – 1 1 1 Hyphessobrycon sp. 3 – 2 2 1 Moenkhausia sp. (intermedia group) – 7 7 2 Prionobrama filigera (Cope, 1870) – 1 1 1 Roeboides sp. 2 – 2 2 Crenuchidae Crenuchus spilurus Günther, 1863 – 1 1 1 2 Klausewitzia sp. – 1 1 1 Cichlidae Apistogramma agassizi (Steindachner, 1875) 27 22 49 3 83 Apistogramma sp. 6 12 18 3 Cichlasoma amazonarum (Kullander, 1883) 6 6 12 6 Crenicichla inpa (Ploeg, 1991) 3 1 4 4 Erythrinidae Hoplias cf. malabaricus 3 – 3 3 3 Gymnotidae Gymnotus aff. stenoleucus 2 – 2 1 2 Hypopomidae Brachyhypopomus brevirostris (Steindachner, 6 12 18 3 35 1868) Brachyhypopomus pinnicaudatus (Hopkins, 1991) 3 13 16 3 Brachyhypopomus sp. n. 1 – 1 1 Lebiasinidae Pyrrhulina sp. (brevis group) 2 21 23 5 23 Lepidosirenidae Lepidosiren paradoxa (Fitzinger, 1837) – 1 1 1 1 Pimelodidae Paulicea luetkeni (Steindachner, 1875) 1 – 1 1 1 Rivulidae Rivulus aff. ornatus 1 1 2 2 2 Serrasalmidae Metynnis sp. 2 – 2 2 13 Serrasalmus sp. 11 – 11 4 Sternopygidae Eigenmannia sp. 5 5 10 3 10 Synbranchidae Synbranchus sp. 4 4 8 5 8 Total 19 39 141 145 286 – – AMPHIBIANS Bufonidae Bufo marinus (Linnaeus, 1758) 2b – 2 1 2 Leptodactylidae Leptodactylus aff. leptodactyloides – 1 1 1 1 Hylidae Hyla walfordi Bokermann, 1962 – 19 19 3 35 Hyla leucophyllata (Beireis, 1783) – 4 4 2 Hyla raniceps (Cope, 1862) – 2 2 2 Hyla punctata (Schneider, 1799) 2a 2 4 3 Sphaenorhynchus carneus (Cope, 1868) – 5 5 1 Unidentified species 1a – 1 1 Pseudidae Lysapsus laevis Parker, 1935 – 3 3 3 3 Typhlonectidae Typhlonectes compressicauda (Duméril and – 1 1 1 1 Bibron, 1841) Total 5 9–10 5 37 42 – – L. SCHIESARI ET AL.336 breeding condition provides a scenario consistent with the hypothesis of an effective long-distance dispersal vector. This reported dispersal system could be in part respons- ible for the wide distribution of many of the amphibian and fish species found associated to Amazonian white- water riverine systems. ACKNOWLEDGEMENTS This manuscript has been improved with the criticism of Walter Hödl, Richard Lehtinen, Woodruff Benson, Miguel Trefaut Rodrigues, Antonio Carlos Marques and Martin Henzl. This study was conducted during the field course Ecology of the Amazonian Forest, promoted by the Organization of Tropical Studies, Universidade Estadual de Campinas, Smithsonian Institution and Insti- tuto Nacional de Pesquisas da Amazônia. We are indebted to these institutions for financial and logistical support. LCS was funded by a grant of Conselho Nacional de Desenvolvimento Cientı́fico e Tecnológico (200093/97-5) during the final preparation of this manuscript. LITERATURE CITED ACHAVAL, F., GONZÁLES, J. G., MENEGHEL, M. & MELGA- REJO, A. 1979. Lista comentada del material recogido en costas urug- uayas, transportado por camalotes desde el rio Parana. Acta Zoologica Lilloana 35:195–200. BOTERO, J. I. S. & ARAÚJO-LIMA, C. A. R. M. 2001. As macrófitas aquáticas como berçário para a ictiofauna da várzea do rio Amazonas. Acta Amazonica 31:437–447. BROWN, J. H. & LOMOLINO, M. V. 1998. Biogeography. Second edition. Sinauer Associates, Sunderland. 691 pp. BURGESS, W. E. 1989. An atlas of freshwater and marine catfishes. TFH Publications, Neptune. 784 pp. FROST, D. R. 1985. Amphibian species of the world: a taxonomic and geographical reference. Allen Press and Association of Systematics Collections, Lawrence. 732 pp. GÉRY, J. 1977. Characoids of the world. TFH Publications, Neptune. 672 pp. GOULDING, M. 1980. The fishes and the forest: explorations in Amazo- nian natural history. University of California Press, Berkeley. 280 pp. HENDERSON, P. A. & HAMILTON, H. F. 1995. Standing crop and distribution of fish in drifting and attached floating meadow within an Upper Amazonian varzea lake. Journal of Fish Biology 47:266–276. HÖDL, W. 1977. Call differences and calling site segregation in anuran species from Central Amazonian floating meadows. Oecologia 28:351–363. IRION, G., JUNK, W. J. & DE MELLO, J. A. S. N. 1997. The large Central Amazonian River floodplains near Manaus: geological, clima- tological, hydrological, and geomorphological aspects. Pp. 23–46 in Junk, W. (ed.). Ecological Studies 126, The Central Amazon floodplain – ecology of a pulsing system. Springer-Verlag, Berlin. JUNK, W. 1970. Investigations on the ecology and production-biology of the ‘floating meadows’ (Paspalum-Echinochloetum) on the middle Amazon. Part I: the floating vegetation and its ecology. Amazoniana 2:449–495. JUNK, W. 1973. Investigations on the ecology and production-biology of the ‘floating meadows’ (Paspalum-Echinochloetum) on the middle Amazon. Part II: The aquatic fauna in the root zone of floating vegeta- tion. Amazoniana 4:9–102. JUNK, W., BAYLEY, P. B. & SPARKS, R. E. 1989. The flood pulse concept in river-floodplain systems. Pp. 110–127 in Dodge, D. P. (ed.). Proceedings of the International Large River Symposium (LARS). Canadian special publication of fisheries and aquatic sci- ences 106. JUNK, W. & PIEDADE, M. T. F. 1993. Herbaceous plants of the Amazon floodplain near Manaus: species diversity and adaptations to the flood pulse. Amazoniana 12:467–484. JUNK, W. & PIEDADE, M. T. F. 1997. Plant life in the floodplain with special reference to herbaceous plants. Pp. 147–186 in Junk, W. (ed.). Ecological Studies 126, The Central Amazon floodplain – ecology of a pulsing system. Springer-Verlag, Berlin. JUNK, W. J. & ROBERTSON, B. A. 1997. Aquatic invertebrates. Pp. 279–298 in Junk, W. (ed.). Ecological Studies 126, The Central Amazon floodplain – ecology of a pulsing system. Springer-Verlag, Berlin. JUNK, W., SOARES, M. G. M. & SAINT-PAUL, U. 1997. The fish. Pp. 385–408 in Junk, W. (ed.). Ecological Studies 126, The Central Amazon floodplain – ecology of a pulsing system. Springer-Verlag, Berlin. KULLANDER, S. O. 1986. Cichlid fishes of the Amazon River drainage of Peru. Swedish Museum of Natural History, Stockholm. 431 pp. OLIVER, M. K. & MCKAYE, K. R. 1982. Floating islands – a means of fish dispersal in Lake Malawi, Africa. Copeia 1982:748–754. PETERMANN, P. 1997. The birds. Pp. 419–452 in Junk, W. (ed.). Eco- logical Studies 126, The Central Amazon floodplain – ecology of a pulsing system. Springer-Verlag, Berlin. SAZIMA, I. & ZAMPROGNO, C. 1985. Use of water hyacinths as shel- ter, foraging place, and transport by young piranhas, Serrasalmus spil- opleura. Environmental Biology of Fishes 12:237–240. SIOLI, H. 1975. Tropical rivers: the Amazon. Pp. 461–488 in Whitton, B. A. (ed.). Studies in Ecology 2, River ecology. University of Cali- fornia Press, Los Angeles.