Study on the presence and density of three types of Brachyuran crabs in Shatt Al-Basra Canal, Basrah, Iraq

TL;DR

This study investigates the presence and density of three Brachyuran crab species in the polluted Shatt Al-Basra Canal, highlighting temperature's role in their distribution and the impact of environmental pollutants on biodiversity.

Contribution

It provides new data on crab species distribution and density in a heavily polluted environment, emphasizing temperature's influence on their presence.

Findings

N. dotilliformis was present throughout the study period.

L. kuwaitensis had lower density and was absent in many months.

Temperature significantly affected crab presence and density.

Abstract

The environment of the Shatt Al-Basra Canal suffers from many pollutants like is a sewage channel for all areas of Basra Governorate, in addition, the riverbanks are a dumping ground for butchery waste, dirt, construction waste, and spoiled medicines thrown into the river and its banks, leading to a lack of biodiversity in the region and the low density of existing organisms. The river banks are characterized by their dryness at low tide due to the high temperature, so they are not suitable for the life of many organisms except the eurythermal and euryhaline organisms. Samples of crabs were collected monthly from September 2023 to June 2024 by using a quadrate with a 1 m length end drilled to a depth of 15 cm, the air temperature at the time of sample collection ranged from 8 to 38{\deg}C, While the BOD ranged between 3.5 to 7.3 mg/L, As for TOC, it ranged from 0.25 to 0.54. The highest density recorded for the species Nasima dotilliformis was in December and reached 6ind/m2 , as the highest density of the species Leptochryseus kuwaitensis was 4ind/m2 in February, and the highest density of the species Ilyoplax stevensi was in December and January, reaching 4ind/m2. The species N. dotilloformis was characterized by its appearance throughout the study period, while the other two species were absent for many months, while the the species L. kuwaitensis was characterized by a lower appearance and lower density. Temperature had the greatest impact on the presence and density of the crab community and was the greatest controller of the rest of the other factors and a basic factor in the dryness of the riverbank soil. The statistical analysis results also showed a significant inverse correlation between temperature and biological oxygen demand (BOD) and a non-significant direct correlation between temperature and total organic carbon (TOC).