Do changes in the water regime determine the abundance of the copepod trophic group in a Neotropical floodplain?

Lino, Lenin Medeiros de Almeida; Mantovano, Tatiane; Tibúrcio, Vanessa G.; Lansac-Tôha, Fábio Amodêo

doi:10.1590/S2179-975X4220

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Thematic Section: Limnology of Subtropical Aquatic Environments • Acta Limnol. Bras. 33 • 2021 • https://doi.org/10.1590/S2179-975X4220 linkcopy

Do changes in the water regime determine the abundance of the copepod trophic group in a Neotropical floodplain?

Mudanças no regime das águas determinam a abundância de grupos tróficos de copépodes em uma planície de inundação Neotropical?

Authorship SCIMAGO INSTITUTIONS RANKINGS

Abstract

Aim Our study evaluated the effects of extreme weather events and environmental conditions on the trophic groups of copepods (herbivores and omnivores) in the upper Paraná River floodplain.

Methods The zooplankton were collected and Copepods and Rotifers were analyzed in nine environments of the upper Paraná River floodplain during 2000 and 2010, during which time the La Niña (drought) and El Niño (flood) climatic events occurred, respectively.

Results The results suggest that in periods of extreme drought productivity-related variables act as determining forces on abundance of copepod trophic groups due to the contraction of aquatic ecosystems. Although the abundance of trophic groups is associated with system productivity, the responses between them differ, since herbivore abundance was associated with chlorophyll-a and total phosphorus and omnivores with rotifer abundance. In extreme flood (El Niño), no significant relationship was found between environmental variables and any trophic group.

Conclusions In general, it is believed that in periods of extreme drought the variables associated with productivity act as determining forces on the abundance of trophic groups of copepods due to the contraction of aquatic ecosystems. According to the results found, it is suggested that other works be carried out with a greater number of extreme events to corroborate our results and, and also to extrapolate to other aquatic communities.

Keywords: climate events; microcrustaceans; trophic guilds; floodplain

Lakes	Environmental characterization
Paraná River sub-basin
Parana River (22°45' S; 53°15' W)	It presents varied width, with the presence of islands. Average depth: 4.0 m. Maximum depth: 15 m. Vegetation composed of fields, the dikes being occupied by sparse trees, remnants of the original vegetation. Occupied areas occur along the left bank, Paraná. Some islands still have arboreal vegetation, moderately explored.
Pau Véio ressaco (22°44' S; 53°15' W)	Average depth: 1.8 m - area: 3.0 ha; communicates with the right bank of the Paraná River. Its length is 1,146.4 m. On its right bank there are Ingás (Inga uruguensis) and pasture fields, in addition to Croton.
Garças Lake (22°43' S; 53°13' W)	Average depth: 2.03 m - area: 14.08 ha; it presents riparian forest in its surroundings and extensive multispecific banks of aquatic macrophytes in almost all its extension, with the predominance of Eichhornia azurea, and submerged macrophyte banks; it also presents communication with the river through a 5m long winding channel.
Osmar Lake(22°46’ S; 53°19’ W)	Average depth: 1.13 m - area: 0.006 ha; temporary lagoon located on an island in the gutter of the Paraná River, it presents terrestrial vegetation on its margin that prevents the action of the wind in the water column, and reduced banks of emerged and floating aquatic macrophytes; it has no communication with the river, and it is 100 m away from its channel.
Baia River sub-basin
Baia river (22°43' S; 53°17' W)	Average depth: 3.2 m. It has varied width and narrower stretches with higher dikes occupied by riparian vegetation or man-made fields. In the wider stretches, the dikes are lower and the vegetation consists of flooded fields (floodplain). Winding river and moderately lotic water. Sampling was carried out in wider areas, with less speed and with aquatic macrophytes and slopes occupied by grasses.
Guaraná Lake (22º43' S; 53º18' W)	Average depth: 2.06 m - area: 4.21 ha; it does not present riparian vegetation in its surroundings and it has extensive multispecific banks of aquatic macrophytes in almost all its extension, with the predominance of Eichhornia azurea. It also presents communication with the river through a short 70m long channel.
Fechada Lake (22º42' S; 53º16' W)	Average depth: 2.46 m - area: 7.46 ha; absence of riparian forest in its surroundings, and reduced multispecific banks of aquatic macrophytes on its banks, with the predominance of Eichhornia azurea. It has no communication with the river and is 100m away from its channel. However, during the flood period it connects with the river quickly due to the absence of a high slope on the river bank.
Ivinhema river sub-basin
Ivinhema River
Patos´Lake (22º49' S; 53º33’ W)	Average depth: 3.50 m - area: 113.80 ha; it does not present large extensions of riparian forest in its surroundings. It presents multispecific banks of aquatic macrophytes in some stretches of its banks, with the predominance of Eichhornia azurea, and communication with the river through an 8 m long winding channel.
Ventura Lake (22º51' S; 53º36' W)	Average depth: 2.16 m - area: 89.79 ha; it presents riparian forest in its surroundings and multispecific banks of aquatic macrophytes in some stretches of its banks, with the predominance of Eichhornia azurea. Has no communication with the river and is 200m away from its gutter

Environmental variables	Years and study periods
Environmental variables	2000	2010
	Mean (Min-Max)	Mean (Min-Max)
Depth (m)	2.6 (0.95-5)	3.8 (0.8-9)
Water temperature (° C)	23.2 (17.7-29.8)	26.05(22.3-29.6)
Dissolved oxygen (mg L^-1)	7.2 (1.5-10.87)	5.9 (0.18-9.64)
pH	6.6 (5.73-8.85)	7.08 (6.23-8.52)
Electrical Conductivity (μS cm^-1)	44.7 (24- 50)	47.9 (22.3-70.2)
Transparency (m)	0.87 (0.1-3.25)	1.5 (0.4-5.2)
Total Suspension Material (μg L^-1)	7.01 (1.1-27.2)	2.43 (0.33-10.7)
Chlorophyll-a (μg L^-1)	10.4 (0.0-89.5)	8.39 (0.41-50.2)
Total Nitrogen (μg L^-1)	389.6 (243-902.5)	780.9 (396.6-1768.6)
Nitrate (μg L^-1)	73.5 (0.0-229)	68.3 (0.0-216.86)
Ammonia (μg L^-1)	9.4 (0.0-37)	14.2 (0.0-82.59)
Total Phosphorus (μg L^-1)	51.9 (4.94-289.5)	35.8 (7.38-400.4)
Phosphate (μg L^-1)	6.8 (0.0-25.7)	7.6 (0.4-18.85)

Taxons	Omnivores		Herbivores
	2000 (Drough)	2010 (Flood)	2000 (Drough)	2010 (Flood)
Argyrodiaptomus furcatus (Sars, 1901)			333
Eucyclops solitarius Herbst, 1959	251
Eucyclops sp.	2
Mesocyclops longisetus (Thiébaud, 1912)		2.7
Mesocyclops longisetus curvatus Dussart, 1987	3
Mesocyclops meridianus (Kiefer, 1926)	3,278	356.2
Mesocyclops ogunus Onabamiro, 1957		51.9
Microcyclops anceps (Richard, 1897)	266
Notodiaptomus deitersi (Poppe, 1891)				49.1
Notodiaptomus henseni (Dahl, 1894)			56,011
Notodiaptomus iheringi (Wright, 1935)			1,309
Notodiaptomus cf. spinuliferus (Dussart, 1986)			4.9
Paracyclops sp.		2
Thermocyclops decipiens (Kiefer, 1929)	9,167	4,552
Thermocyclops minutus (Lowndes, 1934)	5,189	26,717
Total	18,143	31,691	62.6	49.1

Year/ Trophic group	Model equation	R² adjusted	F	N	P
2000/ Herbivores	Abh00=0.0016* chlorophyll-a +0.03370^* * Abh = Abundance of herbivores; Abo = Abundance of omnivores. Total phosphorus	0.99	42.6	35	<0.01
2000/ Omnivores	Abo10=0.0451*rotifers (abundance)	0.64	31.5	27	<0.01

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[1] Source: Souza-Filho & Stevaux (2002).