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Vol. 45, N. 1 : pp. 67 - 72, March, 2002 ISSN 1516-8913 Printed in BRAZILIAN ARCHIVES OF BIOLOGY AND TECHNOLOGY

AN INTERNATIONAL JOURNAL

Food Plants Eaten by Amazonian (Trichechus inunguis, Mammalia : )

Ioni G. Colares1* and Elton P. Colares2 1Depto. de Ciências Morfo-Biológicas - Fundação Universidade Federal do Rio Grande (FURG), Av. Italia km 8; 2Depto. de Ciências Fisiológicas, FURG – Rua Eng. Alfredo Huch, 475, 96201-900 – Rio Grande-RS, Brazil

ABSTRACT

To determine the feeding habits of the Amazonian Trichechus inunguis in some Central Amazonian rivers and lakes, we compared plant epidermis found in the stomach contents and/or faeces of with a reference collection of plants present in the studied areas. Twenty five samples from digestive tracts of animals found dead and 25 faeces samples found floating were analyzed. From these samples, 24 aquatic macrophytes were identified. The Gramineae family was identified in 96% of the samples, Paspalum repens and Echinochloa polystachya being the most abundant in the samples. The second most frequent family was the Pontederiaceae primarily . During the high water period, the animals showed a more selective diet (eight identified ). In the low water period, when food was more scarce, the animals showed a larger diversity of species in their diet (21 species of plants). Differences in the diet among the two studied areas reflected the physiographics characteristics of the region. Amazonian manatees fed mostly on emergent plants.

Key words : Amazonian manatee, trichechus, food, plants eaten, Amazon

INTRODUCTION probably their preferred food (Montgomery et al. 1981; Best, 1984; Gonçalves-Colares & Colares, The Amazonian manatee (Trichechus inunguis) is 1992). Previous studies on the food habits of other the only exclusively fresh water sirenian and it is sirenian species, Trichechus manatus, T. endemic to the Amazon region. It ranges from senegalensis and dugon, were carried out, Marajó Island (Brazil) to the sources of the both by direct observation (Hartman, 1979; rivers in Columbia, and Bengtson, 1981; Packard, 1981; Anderson, 1998), (Timm et al., 1986). It is present in all the by analyzing the digestive tract contents (Marsh et major draining system tributaries of the Amazon al., 1982; Ledder, 1986) and using the stable river, where its distribution is apparently carbon isotope d13C in captive animals (Ames et restricted to two locations: calm waters and lakes al.,1996). with aquatic vegetation (Best, 1984; Rosas et Direct observation of a manatee in the Amazon is al.,1991; Rosas, 1994). Amazonian manatees are nearly impossible due to the turbid, dark water, herbivorous, non-ruminant, and feed on a large which limits the visibility to no more than 60 cm. variety of aquatic and semi-aquatic plants (Timm In clear water rivers, such as the Tapajós (Pará), et al., 1986). However, aquatic grasses are for example, sightings of manatees are rare (Husar, 1977). Therefore, studies on the feeding habits of

* Author for correspondence

Brazilian Archives of Biology and Technology 68 Colares, Ioni G. et al.

Amazonian manatees are only possible by the method of Heinsohn & Birch (1972). Plant analyses of the digestive tract contents of dead species were identified by means of comparison animals or of faeces collected in the wild, as well with epidermal layers of previously identified as partially consumed foods (parts of plants left by plants which were mounted as a reference the animal) or through observation of captive collection, following Storr (1961). Identifications animals (Gonçalves-Colares & Colares, 1992). were based on size and shape of the epidermal Domning (1981) quoted observations made by cells, presence and distribution of silica deposits, local fisherman in the regions of Pará, Maranhão, distribution and types of stomata, and distribution, Amazonas and Amapá (Brazil), who confirmed types and sizes of trichomes and veins. Totally having seen animals feeding on different species transparent epidermal layers were identified of submerged, floating, and emergent plants. The immediately. Those which were not transparent, availability of aquatic and semi-aquatic plants on which still had remains of mesophyll, were first which the manatee feeds (Best, 1984) varies cleaned with a fine brush or immersed in a mixture greatly depending on the levels of the rivers of 10% nitric acid (HNO3) and 10% chromic acid between the low and high water periods of the (HCrO3) (cold acid digestion), for an average of Amazon basin (Junk, 1970; Colares & Colares, two minutes, depending on the quantity of 1987), and is believed that seasonal variation in mesophyll present. The presence of algae or non- their diet is due to variation in the availability of vegetative material was also noted. these plants (Best, 1981). Data were grouped taking into consideration The main objective of this study was to determine possible variations between the times of year (low the feeding habits of the Amazonian manatees (T. water: September to February, and high water: inunguis) in some rivers and lakes of the central March to August), and different regions (areas 1 Amazon. and 2).

MATERIALS AND METHODS RESULTS AND DISCUSSION

Samples of digestive tract contents of 25 animals The number of plant species found in a sample found dead and 25 faeces samples found floating varied from one to seven, with a predominance of were collected from two study areas. Area 1 two or three plant species per animal (30.6% and included Amanã Lake, of 145.3 km2 (2046’ S and 34.7% respectively). During high water, a 64039’ W), 67 km north of the city of Tefé (state maximum of three species per sample was of Amazonas – AM). Area 2 included the lakes observed, while during the low water this number and proximities of Marchantaria Island, of 320 reached to seven distinct species. During high km2, (3015’ S and 60000’ W), in the Solimões water, all species of aquatic plants were more River (AM), as well as Rei Lake, of 100 km2, abundant, suggesting higher food availability located in the Careiro Island (3005’ S and 59035’ (Colares & Colares, 1987). Faeces during low W), in the Amazonas River, close to the City of water when food availability was lower, suggested Manaus (AM). Amongst the total of 50 samples that Amazon manatee had not a selective diet, analyzed, 35 (70%) came from area 1 and 15 eating all available species. With more abundant (30%) from area 2. Of this total, 40 samples (80%) food sources, the number of eaten species were collected in the low water period and 10 decreased, indicating a more selective diet. samples (20%) in the high water period. In (D. dugon) and West Indian manatees The digestive tract of each animal was removed (T. manatus), several plant species were also and samples were collected from the stomach, the found, mixed together in their digestive tracts small and large intestines and the caecum. They (Heinsohn & Birch, 1972; Ledder, 1986). were preserved in FAA (85% ethyl alcohol, 10% According to Reynolds (1977) and Hartman formalin at 10%, 5% glacial acetic acid). Faeces (1979), West Indian manatees apparently did not found floating were also collected and stored in select their feeding grounds – at times they FAA. remained in one place until food species were Each sample was homogenized and a sub-sample totally destroyed, or they passed casually from one removed. From the sub-sample, five microscope area to another. This could also happen with the slides were prepared and analyzed, according to Amazonian manatee, explaining the variation in

Brazilian Archives of Biology and Technology Food Plants Eaten by Amazonian Manatees 69

the number of plants encountered in the digestive according to Sioli (1968), most of the aquatic tracts and faeces analyzed. Samples made up of plants are floating or emergent, favour this different plant species could represent a nutritional situation. Domning (1978a) suggested that complement or feeding in wide-spread feeding different degrees of deflection in sirenian skulls grounds made up of different plant species. The could be adaptations to feed at different levels in sample which only contained one plant species the water column. According to Domning (1978 could represent a specific preference for that a), the degrees of deflection in T. manatus and T. species or feeding in one dense, monospecific inunguis were similar. These animals were to feed feeding ground. T. inunguis kept captive at INPA efficiently anywhere in the water column, which (National Institute of Amazonian Research, Brazil) could provide a greater variety of food. However, showed a specific preference for Paspalum repens, muscular and articulation peculiarities in the neck and fed casually on other species when the of T. inunguis provided support for the hypothesis preferred one was totally consumed (Gonçalves- that it was more specialized than the West Indian Colares & Colares, 1992). manatee to feed near the water surface (Domning, Table 1 shows the accumulated number of plants 1978b). Of the plants identified, the Gramineae encountered in samples. Twenty two species were family was the most common, being found in 96% identified, of which the animals fed more of the samples analyzed. The more frequent frequently on emergent plants (65.1%) than species was Paspalum repens (17.5%), followed floating (31.3%) or submerged (3.6%). This high by Echinochloa polystachya (13.8%). consumption of emergent plants may be related to feeding adaptation or availability. The surroundings in which this species lives, where,

Table 1 - Percentage of plants identified in samples collected in the digestive tract and faeces from Amazonian manatee. Emergent % Floating % Submerged %

Paspalum repens 17.5 Eichhornia crassipes 11.2 foliosa 1.8 Echinochloa polystachya 13.8 Salvinia auriculata 8.3 Cabomba sp. 1.8 Luziola spruceana 7.4 stratiotes 6.4 Phaseolus pilosus 6.4 Ludwigia helmintorriza 2.7 Paspalum fasciculatum 5.6 Ipomoea aquatica 1.8 Panicum chloroticum 2.7 Neptunia oleracea 0.9 Hymenachne amplexicaulis 2.7 Panicum chlorantum 1.8 Panicum laxum 1.8 Panicum sp. 1.8 Oryza latifolia 0.9 Oryza perennis 0.9 Oryza grandiglumis 0.9 Polygonum spectabile 0.9 Total 65.1 31.3 3.6

Figure 1 shows that plant consumption varied Samples of two manatees collected during the low according to time of year (low or high water). water period consisted of only Paspalum repens, During the low water period, a larger number of while Echinochloa polystachya was found as the vegetable species was consumed (21), while only food item during high water. This not only during high water only eight species were suggested a food preference of the Amazonian identified, of which seven were the same as those manatee for these species, but also reflected their identified during low water. abundance in the habitat of these animals. Paspalum repens and Echinochloa polystachya are

Brazilian Archives of Biology and Technology 70 Colares, Ioni G. et al.

the two most frequent aquatic grasses in the same. In Area 1 the animals fed on 16 species of Amazon rivers (Junk, 1970; Colares & Colares, plants, while in Area 2, they fed on 14 species, of 1987; Piedade, 1988). which eight were common for the animals in both of these areas. In the samples from Area 1, the most frequent plant was Paspalum repens, followed by Eichhornia crassipes. In Area 2, the most frequent plants were the grasses Echinochloa polystachya and Paspalum repens, followed by Paspalum fasciculatum. This variation almost reflected the physiographics characteristics of these two areas. The vegetation in the northward of lake Amanã (Area 1) is typical of black waters “igapó” forests. In the southward, the vegetation is “varzea” typical, with aquatic and semi-aquatic macrophytes (Rodrigues & Nelson 1984). In Area 2, the vegetation is predominantly herbaceous, composed of aquatic and semi-aquatic Figure 1 - Plants identified in the digestive tract and/or macrophytes typical of “varzea” forests (Colares faeces of the animals in the different times of year. Low & Colares 1987; Piedade 1988). water: September to February, and high water: March to August.

Floating Ipomoea aquatica was also identified as the only food item encountered in one sample collected during the low water period, when this species was more abundant in the studied areas (Rodrigues & Nelson, 1984; Colares & Colares, 1987). In dugongs, Wake (1975) showed that the percentage of grasses found in the stomach contents and faeces reflected almost perfectly the grass bed composition where they occurred. The hyacinth Eichornia crassipes was the third Figure 2 - Plants identified in the digestive tract and/or most frequent plant in the digestive tracts and faeces of the animals from the two large studied areas. faeces analyzed, constituting 11.2% of the Amazonian manatees diet. Marmol (1976) in Peru and Timm et al. (1986) in Ecuador, also found Terrestrial grasses also contribute to the diet of Amazonian manatee feeding on this species. Some Amazonian manatee, although in small quantities. have noted that the West Indian manatees only ate This may be a reflection grass abundance along the emergent part of hyacinth, ignoring the roots the edges of the rivers, lakes and streams. Two (Lomolino, 1977). Hartman (1979) noted that T. species of land grasses, Panicum laxum and manatus rarely ate this plant but that when it ate, it Panicum chloroticum, were encountered in the usually ate the entire plant. We found this species samples from Area 1 during the low water period. quite frequently in the digestive tract and faeces of Ledder (1986) found a nearly 6% contribution of the animals with the entire plant being consumed. land grasses in the diet of West Indian manatees, T. inunguis captive at INPA ate the entire plant. reflecting their distribution along the rivers and But when feeding only on the hyacinth Eichhornia canals where the animals live. The submerged plants Utricularia foliosa and crassipes, intestinal disturbance was evident, since Cabomba sp. were identified in samples from Area this plant was of difficult digestibility (Colares et 1 during the low water period. However, the al., 1990). frequency of occurrence was quite low (1.8% There were some variations in the type of food each), which supported the hypothesis that T. consumed when comparing both studied areas inunguis mainly consumed emergent plants. (Fig. 2), though the most frequent species were the Besides this, during the low water period, plant

Brazilian Archives of Biology and Technology Food Plants Eaten by Amazonian Manatees 71

abundance in rivers and lakes of the Amazon basin RESUMO was very low (Junk, 1970), what constituted an additional evidence of a generalist feeding-habit. Para determinar o hábito alimentar do peixe-boi da Non-identified algal filaments, animal fragments, Amazonia em alguns rios e lagos da Amazonia grains of sand, and decomposing vegetable matter Central, nós comparamos as epidermes de plantas were also identified in the samples. We believed encontradas nos conteúdos alimentares e/ou fezes that these items were attached to vegetation, thus de animais com uma coleção de referência de being accidentally ingested with food plants. Similar observations were made in dugongs and epidermes de plantas presentes nas áreas de West Indian manatees (Lipkin, 1975; Wake, 1975; estudo. Foram analisadas 25 amostras de trato Ledder, 1986). Hartman (1979) and Best (1981) digestivo de animais encontrados mortos e 25 reported that manatees consumed considerable amostras de fezes . A familia Gramineae foi quantities of organisms which were found in large encontrada em 96% das amostras, com maior numbers on the roots and leaves of aquatic ocorrência das espécies Paspalum repens e macrophytes. The presence of sand grains and Echinochloa polystachya. A segunda familia mais decomposing vegetable matter encountered in freqüente foi Pontederiaceae sendo Eichhornia samples during low water was supported by Best crassipes a espécie predominante. Durante o (1981), who indicated that when availability of período de água cheia, os animais apresentaram food decreased during this period, they used uma dieta mais seletiva (oito espécies decomposing material and mud as a food identificadas). Já na água baixa, com menor oferta supplement. de alimentos, os animais apresentam uma maior Grass seeds also were identified in the samples. diversidade de espécies em sua dieta (21 espécies The ingestion of grass seeds by Amazonian de plantas). Diferenças na dieta entre as duas áreas manatees was frequent (32% samples) during low amostrais refletem as características fisiográficas water. However, the majority of these seeds were das regiões. O peixe-boi alimenta-se broken, with degradation starting from the principalmente de plantas emergentes. stomach up to the large intestine. In previous observations (Colares, I.G.; pers. obs.), it was noted that when captive Amazonian manatees at INPA were offered branches of aquatic grasses REFERENCES with seeds, the animals ate the seeds first. However, Gonçalves-Colares et al. (1988) have Ames, A. L., E. S. Van Vleet and W. M. Sackett. (1996), observed that the Amazonian manatee probably The use of stable carbon isotope analysis for were not a good disperser of aquatic grasses. determining the dietary habits of the Florida manatee, In conclusion, the present data suggested that Trichechus manatus latirostris. Marine rivers and lakes with emergent aquatic vegetation, Science, 12(4), 555-563. especially aquatic grasses, were important for the Anderson, P. K. (1998), Shark Bay dugongs (Dugong species. However, the generalist feeding-habit dugon) in summer. II. Foragers in a Halodule- allowed to use the most varied resources, as dominated community. Mammalia, 62(3), 409-425. Trichechus demonstrated during the period of low water, Bengtson, J. L. (1981), Ecology of Manatees ( manatus) in the St. Johns River, Florida. Ph.D. Thesis, when abundance of emergent aquatic plants were University of Minnesota, Minneapolis, USA. very low. Best, R. C. (1981), Foods and feeding habits of wild and captive Sirenia. Mammal Review, 11(1), 3-29. Best, R. C. (1984), The aquatic and reptiles of ACKNOWLEDGEMENTS the Amazon. In-The Amazon. Limnology and Landscape Ecology of a mighty tropical river and its We thank Megumi Yamakoshi for her assistance basin, ed. H. Sioli, Netherlands, pp. 371-412. in the collection of the biological material; Dra. Colares, I. G. and E. P. Colares (1987), Variação anual de vegetais que servem de alimentação para o peixe -boi Olga Minura (São Paulo University-Brasil) for her th amazônico (Mammalia-Sirenia), Paper presented at 2 technical support; and all staff of the Aquatic Reunião de Trabalho de Especialistas em Mamíferos Mammals Laboratory of the National Institute of Aquáticos da América do Sul, Rio de Janeiro, Brasil, Amazonian Research (INPA) for their assistance pp. 42-44. and dedication during the study. The work was supported by the National Research Council of Brazil (CNPq) and INPA.

Brazilian Archives of Biology and Technology 72 Colares, Ioni G. et al.

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