CHANGES IN FISH POPULATION REGARDING FISH LARVAL ABUNDANCE IN RESPONSE TO ACIDIFICATION AT THE BAKKHALI RIVER, COX'S BAZAR COAST, BANGLADESH

Abstract

The uptake of atmospheric CO2 by the oceans since the beginning of the industrial revolution is considered to be a significant threat to marine ecosystems due to the resulting carbonate chemistry changes. This study tried to evaluate the level of acidity and the larval abundance of the Bakkhali River in Cox's Bazar. Fish larval abundance fluctuates directly in response to the rising acidity of river water. The potential impact of rising atmospheric CO2 levels on fish larvae caused by ocean acidification is receiving a lot of attention. This research was conducted in the Bakkhali River estuary with monthly sampling from January to December 2021. The key ocean acidification factor, pCO2, ranged from 19.3642 to 360.6499 μatm. The pH of the water was always found to be alkaline and varied between 8.0 and 8.8 (8.267±0.2146). The range of the DIC (mol/kg) concentration was 0.0005 to 0.001 with a mean of 0.00094686±0.00038532. The aragonite ranges from 0.86174819 to 3.4318 with mean of 2.2771±0.7552 and the calcite ranges from 1.3987 to 5.2121 with a mean of 3.5397±1.1109. Throughout the study, 555 larvae were recorded from the study region. The maximum and minimum number of fish larvae was 109 in August and 11 in February, respectively. The levels of pCO2 and fish larvae were inversely related. A decline in the quantity of fish larvae had been associated with rising pCO2 levels and decreasing seawater pH. Fish larvae had significant positive relationships with pH (R2 =0.5290, p<0.05), and fish larvae had significant negative relationships with pCO2 (R2 =0.2056, p<0.05). The growth and survival of marine organisms during their larval stages could be hampered by ocean acidification. The early life stage was substantially more sensitive to elevated pCO2 induced mortality than the post larval stage. The results showed that a higher pCO2 may negative impact on larval fish survival. It is still entirely unknown whether wild populations of marine species are capable of adapting to elevated pCO2. This finding will stimulate interest in fish biology research in regions where fish larvae are particularly vulnerable to acidification.