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The population dynamics and morphological traits of the new species Alpheus Gatari in the Gulf of Cadiz (Spain)
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Abstract(s)
There are about more than 600 of Alpheus species have been identified under the 36 genera. Alpheus species are possible to be found in tropical, subtropical, and temperate seas and inhibiting a wide range of habitats, from tidal pool to deep sea areas, in both temperate and tropical areas. Some of them live in cool-temperate waters and few have colonized freshwater habitats, as well as mangroves and estuarine areas Major prominent feature of Alpheus species in enlarged or modified major chelea of the male organism. This group of species is highly abundant in spring and summer (warmer seasons) probably because the high nutrient availability and high primary production typical of those seasons help to maintain a high survival rate. Alpheus qatari, in the Persian Gulf, inhabiting the muddy substrate in the mangroves, in channels under rocks, and in the intertidal zone. The genetic analysis demonstrated that Alpheus qatari n. sp. is a new species, genetically different from the closest congeners A. buckupi and A. lobidens. Widely distributed Alpheus species are morphologicalyy divers group. The immense diversity of orbital hoods and chelipeds likely facilitated the diversification of snapping alpheids. Most of Alpheus species are burrowing organisms and In the alpheid group, one of the first pereiopods (chelipeds) bears a large claw with a snapping mechanism on the fingers, known as the snapping claw.
No studies to date have examined the relationship between food availability and distribution patterns in alpheid shrimp populations. Some species are detritus feeders. the amount and quality of food present in the sediments could influence where they decide to construct a burrow. Snapping shrimp have different feeding habits, however most of them are omnivores. Usually feeding is occurred during night time, while day time they are staying in the burrows. Epiphytes on sea grass leaves are also possible food for the shrimp. These algae to be a primary source of organic matter for higher top levels in tropical sea grass beds. Despite the high number of Alpheus species, there are few studies about their population biology, especially in comparison with the extensive knowledge about the taxonomy and diversity of the family Alpheidae. There is a lack of information on the biological, ecological, and behavioral aspects of Alpheidae species. Information on population biology, such as the sex ratio, reproductive period, recruitment and the size at first maturity is essential to understand a species’ life history.
Since A. qatari is a new exotic species in the Bay of Cadiz, we explore which factors (both biotic and abiotic) shape the distribution of this species. The main objective of this study is to analyse the A. qatari population structure on the San Pedro River (SW Atlantic Spanish coast) focusing on: (a) studying the population size distribution and sex-ratio during an annual period; (b) assessing whether a temperate region could shape the population dynamic of a tropical species. Bearing in mind that this is a new species, the morphological traits in males and females will also be analysed.
Individuals of the snapping shrimp Alpheus qatari were collected along the 275 m stretch of the San Pedro River right bank, Cadiz, Spain (36°32’03.4”N 6°12’50.8”W) from June 2021 to April 2022, and carried alive to the laboratory at the Institute of Marine Science of Andalusia (CSIC) for further analysis. The sampling periods covered all four seasons: Summer (June to September), Autumn (September to December), Winter (December to March), and Spring (March to May).
Total 383 organisms were recorded during sampling times July-2021 to May 2022, of which 174 were females (50 non-ovigerous and 124 ovigerous) and 188 were males. Ovigerous females were observed during the study period July-2021 to May 2022 .The average Sex ratio (Male:Female) was 1:0.92, i.e., its value did not differ significantly from the expected equal proportion ( X2 = 1.43, df =1, P >0.05). There is significant difference between male and females for the cephalothorax length (M–nn - Whitney = 15060, P < 0.05), while there was no significant difference for the cephalothorax length between non-ovigerous and ovigerous females (M–nn - Whitney = 3802, P > 0.05). The largest individuals were observed during the months of August, September, October, and March (male=14 -14.99mm CL). For the ovigerous females, the largest individuals were observed in April (ovigerous female = 15.66mm CL) and the largest non-ovigerous females were observed in August (–on - ovigerous female = 14.75 mm CL). the percentage of females increased from July -to December in 2021. The maximum percentage of females was recorded during December 2021. With regards to males, the percentage increased from July to October and gradually decreased up to December. In the case of Females with eggs, the percentage of individuals was higher in summer and in spring.
The size of females gradually decreased from July 2021 to November 2021 and increased from December 2021 to 2022 May. Ovigerous females were collected during the entire sampling period, with the smallest ones appearing mainly in summer (July) and the largest ones in spring (April-May). Two cohorts could be identified in males and females from July to October and, from November to May of the following year. The relationships between weight and lengths and the correlation coefficients were analyzed for all the demographic categories of Alpheus qatari during the 11-month study period at the San Pedro River. The significant correlation between the total weight and cephalothorax length was found to be a power function (P<0.05).
Results from the morphological analysis showed that there is a significant difference between the relative chela length of males and females (W= 33473, p<0.05).A Kruskal-wallis test was performed to determine significant difference of the relative chela length between the three demography categories (H=155.58(2), p<0.001). Males showed a significantly larger chela than females. Female and ovigerous females did not show significant differences among their length.
The Fulton´s condition factor (K index) was calculated for the males, females and ovigerous females at each month. A PERMANOVA test was performed for the factors Sex, Month, and Position of Chela, and the covariate cephalotorax length. Among these factors, Sex, Month and cephalothorax length showed significant differences, and there was no evidence for a two and three-way significant interactions. The Hureau Index was calculated for the males, females and ovigerous females for each month. A PERMANOVA test was performed for the factors Sex, Month, and Position of Chela, and the covariate cephalothorax length. Among these factors, Sex and Month showed significant differences. Overall, the fullness index (FI) of the stomach showed the highest values in autumn and, among the different demographic categories, the highest values occurred in females.
The population traits of A. qatari in the San Pedro River are similar to other Alpheus populations. According to the results obtained, the sex ratio of the Alpheus qatari is not significantly different from the 1:1 ratio characteristic of other Alpheus species. In this study, most of the individuals collected were adults and only few of them had a small size, similar to other populations (Moraes et al, 2020). According to Costa-Zouza et al (2018), adults and juveniles are available during the whole annual period with a dominance of adults in most months. Thus, it could be assumed that adults are reproducing in another ground and migrate to the sampling area to grow. The significant correlation between the total weight and total length was found to be a power function in both sexes of A. qatari in the San Pedro River with a high correlation between both covariates. For instance, the values obtained from the length/weight relationship (LWR) of some shrimp species in the Iko River estuary showed that there was a high and significant correlation between both covariates. Our results revealed that A. qatari displayed a sexual dimorphism of the snapping claw with males having larger claws than females and showing a steeper allometric claw-body relation than females. The highest condition factor was recorded in summer, especially in August 2021. Males chela were heavier than the female ones at a similar size. These differences could explain that they are capable to reproduce or mate several times per year and protect females in their galleries. The fullness index value in this study also showed the fullness of gut of the organisms and, according to the results, the highest gut fullness value occurred in summer-autumn and the lowest one in winter, similar to other studies. During spring and summer, the seasonal food availability increases and enhances productivity (primary and secondary) within the coastal area, perhaps explaining the greater feeding intensity of the Alpheus species. This news Alpheus Qatari also follow some common feature of the family Alpheadea as sex ratio is not significantly apart from 1:1, males have significantly large chelea and Males are relatively larger than females.
Description
Keywords
Alpheus qatari Sex ratio Population dynamics Condition factor Fullness index