Population parameters of the non-indigenous invasive shrimp Palaemon macrodactylus Rathbun, 1902 (Caridea: Palaemonidae) from the southeastern Caspian Sea, with implications for range expansions, threats and conservation

Abstract

Knowledge on invasive species is critical for the conservation. This study is the first documentation on population parameters of oriental shrimp (Palaemon macrodactylus) in the southern Caspian Sea, where the occurrence of invasive species is of great importance. The samples were collected using a small beach seine (35 m long and 2.5 m height) monthly from April 2019 to March 2020, and a total of 1643 specimens of P. macrodactylus were sampled. The growth form of the males was negative and that of females positive allometric nature. From the size-frequency distributions, the shrimp's lifespan was estimated to be about 2 years for both sexes. High recruitment can take place over nearly all months of late summer and autumn. The VBGF parameters were L_∞ = 65.00 mm, K = 0.82 y^-1, and t₀ = -0.80 for males, and TL_∞ = 71.00 mm, K = 0.51 y^-1 and t₀ = -0.59 for females. The estimated Z was 3.65 and 3.10 year^-1 for males and females, respectively. The total sex ratio was significantly biased toward females in the population. Length group analysis showed a clear pattern of female dominance in lengths larger than 29 mm. Based on the occurrence of ovigerous females, the reproductive period lasts for seven months (April-October). Fecundity, as the number of both eyed and non-eyed eggs per clutch of females, varied from 71 to 2308 eggs shrimp^-1 with a mean of 1074 ± 553.8 (±SD) eggs shrimp^-1. The estimated relative number of eggs in a clutch of ovigerous females varies between 1208.8 and 1714, with a mean value of 889.1 eggs. female^-1. The egg diameter averaged 0.675 ± 0.063 mm (±SD), ranging from 0.512 to 0.812 mm. The relationships of the total and relative number of eggs in a clutch of ovigerous females with their size were statistically significant, while the egg diameter in ovigerous females was independent of shrimp size (length and weight). P. macrodactylus underwent a life-history strategy including high abundance, short life span, high mortality rate, long reproductive season, and female dominance that showed characteristics of r-strategist species, promoting the invasion of this shrimp in the Caspian Sea as a new area of introduction. We are convinced that P. macrodactylus established in the Caspian Sea it is in the last stage of invasion (impact on the ecosystem).

Keywords: Caspian sea; Invasion; Life history; P. macrodactylus; r-strategy.