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BIODIVERSITY FLOODPLAIN
IN THE HIGH PARANA RIVER
A.A. Agostinhol*, S.M. Thomazl, C."\/: Minte-Veral and K.O. Winemiller2 1Nucleo de Pesquisas em Limnologia, Ictiologia e Aquicultura (NUPELIA), Universidade Estadual de Maringa, Av. Colombo 5790, Bloco H-90, CEP 87.020-900, Maringa, Parana, Brasil 2 Department of Wildlife and Fisheries Sciences, Texas A&M University, College Station, Texas, 77843, USA Corresponding Author; E-mail:
[email protected]
*
Abstract Despitebeing the most regulatedriver in the world, the high ParanaRiver in Brazil supportsa great wealth of biological diversity.An extensiveregion of floodplain habitat remainswithin the high Parana River betweenthe Porto Primaveraand Itaipu reservoirs,but it now experiencesa modified flood regime due to the influence of the upstreamreservoirs.Annual flooding and drying of the floodplain occurs,andthis regimeis greatly influencedby tributary rivers, especiallythe Ivinheima River which entersfrom the west.Most groupsof aquaticorganismsshowhigh speciesdiversityand strongpatternsof ecologicaldynamicsin responseto habitatheterogeneityand water level fluctuations. Physicochemicalattributes and primary production show high spatiotemporalvariation in both river and floodplain habitats.In general,the floodpulsereducesphytoplanktondensities,promotesperiphytonandaquaticinvertebrateproductionin the floodplain which supportsjuvenile fish feeding, growth, and development.Most fishes of the region are stimulatedto spawnduring the early stagesof the annualflood pulsebut somefishes reproduceover extendedperiods.The abundanceof most speciesis positively associatedwith the timing and durationof the flood, and this is especiallythe casefor migratory specieswith high fecundity.Severalimportant iliophagous,herbivorous,and omnivorousfishes are amongthoseshowingevidenceof enhancedrecruitmentduring very high flood years.Somebrood-guardingandpiscivorousfishes showpatternsof increased abundancein associationwith low flood years.We demonstratehow the integrity of the river-floodplain ecosystemof the high Paranais dependenton the maintenanceof some degreeof annual flooding. Severalconservationareashavebeen establishedto protect the biological diversity supported by the floodplain region that remainsin a relatively naturalcondition.
Introduction The Parana basin has a drainage area of 28 xl06 kIn2, the second largest in South America, and drains the south-central region of the continent from the Andes to the Serra do Mar close to the Atlantic Ocean. From its source in the central plateau to its mouth in the La Plata estuary, this river runs 4,495 kIn. Its headwaters (the Paranaiba river, 1070 kIn long), its upper reaches (the confluence of the rivers Paranaiba and Grande up to the former Sete Quedas Falls, 619 kIn) and part of the middle section (from the former Sete Quedas falls to the mouth of the Igua~u river,
Biodiversity in wetlands:assessment, junction and conservation,volume1 editedby B. Gopal, W:J.Junk and J.A. Davis,pp. 89-118 ~ 2000 BackhuysPublishers,Leiden,TheNetherlands
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190 kIn) are within Brazil where the river drains 891,000 km2 i.e., about 10.5% of the country's area. The falls that formerly separatedthe high and middle sections are now submerged beneath the Itaipu reservoir. The two rivers that form Parana river (Grande and Paranaiba) are typical plateau rivers, with average gradients of about 0.8 m kIn-I, decreasing towards their lower reaches (0.3 and 0.4 m kIn-I, respectively) (Paiva 1982). With an average declivity of 0.18 m kIn-I, the high Parana river had an extensive floodplain between Tres Lagoas city, State of Mato Grosso do SuI, and Guaira, State of Parana(a 480 km stretch,
