Abstract
ABSTRACT We analyzed the microhabitat preferences of Macrobrachium jelskii (Miers, 1877) males and females inhabiting an urban water reservoir in Cruz das Almas, Bahia, Brazil. Prawns were collected monthly, from March 2015 to February 2016, in three microhabitats, using a sieve. Each microhabitat was dominated by one macrophyte species: Eleocharis sp. (M1), Cabomba sp. (M2), and Nymphaea sp. (M3). The prawns were measured (carapace length), and categorized as juvenile males, adult males, juvenile females, non-ovigerous adult females and ovigerous adult females. An analysis of variance (ANOVA) was used to compare the number and size of individuals. The sex ratio and frequency of ovigerous females in the three microhabitats were also calculated. The sex ratio was biased towards females in M1 and did not deviate from 1:1 in M2 and M3. When prawns were separated into five categories we observed that non-ovigerous adult females were more abundant in M1, while adult males were the most abundant demographic category in M2 and M3. Juveniles of both sexes and ovigerous females showed no microhabitat preference, although M1 and M2 appeared to be more suitable for the latter. Adult females were the largest individuals in all microhabitats. Food availability, lower depth and lower predation pressure in M1 are the main factors that make M1 more suitable for M. jelskii, particularly non-ovigerous adult females and larger adult males. Intraspecific competition for shelter in M1 might also occur and adult females win this competition due to their larger body size. Therefore, adult males are found in higher abundance in M2 and M3 and the juvenile of both sexes spread evenly across all microhabitats. Our results help to understand the ecological role and the niche used by M. jelskii. Future studies on the habitat choice and predation under laboratory conditions should help to understand the behavior of this species.
Highlights
Macrobrachium jelskii is popularly known in Brazil as “camarão-sossego” (Paiva & Barreto, 1960) and it is among the 19 species of Macrobrachium Spence Bate, 1868 occurring in the Brazilian territory (De Grave & Fransen, 2011; Maciel et al, 2011; Pileggi & Mantelatto, 2012; De Grave & Ashelby, 2013; Santos et al, 2013; Vera-Silva et al, 2016)
When the data were separated into five demographic categories (Fig. 3) adult males were the most abundant demographic group in M2 and M3 (F = 5.055; P < 0.001), and there was no predominance of a demographic group in M1
analysis of variance (ANOVA) demonstrated that there were no statistical differences between the total numbers of individuals in each microhabitat, M. jelskii were more abundant in M1 and M2
Summary
A disponibilidade de alimento, a menor profundidade e a menor pressão de predação em M1 são os principais fatores que tornam este micro-habitat mais adequado para M. jelskii, particularmente para fêmeas adultas não ovígeras e machos adultos e fêmeas jovens de maiores tamanhos. In freshwater environments there is a stratification of the fauna directly related to the environmental conditions and shelter availability (Thomazi et al, 2008; Giuliatti & Carvalho, 2009) This stratification occurs due to predation pressure and food resources that are exploited by different species throughout their life phases (Merrit & Cummins, 1996; Marques et al, 1999; Thomazi et al, 2008; Ferreira et al, 2010). The occurrence of M. jelskii in hydrographic basins of Northeast and Southeast Brazil might be considered the result of anthropogenic actions (Magalhães et al, 2005; Vera-Silva et al, 2016, 2017)
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