Mangrove is the most productive and biodiversity-rich ecosystem (Tomlinson 1986) rather than a halophyte growing in tropical or subtropical coastline areas (Giri et al. 2011; Hema and Devi 2015). Since they are located in the transition zone between two different ecosystems, mangroves have a higher genetic diversity than other vegetation types (Jithendra et al. 2014). Hence All the plant, animal, and microbial communities in this ecosystem are associated with these intertidal zones and can adapt to their changing environment (Edwin 2002).
According to the global Forest Resource Assessment (2020), mangroves represent a total of 14.79 billion hectares across 123 countries worldwide. India covers 4992 sq. km of mangrove forest, accounting for approximately 5% of the world's land area vegetation (CRZ 2019; FSI 2021). Kerala constitutes 17.82 sq. km of mangrove forests, scattered as small patches along the coastal and intertidal region (Sreelekshmi et al. 2021).
However, mangroves are rapidly disappearing on a global scale due to anthropogenic interventions such as aquaculture, urbanization, tourism, and agriculture (Peng et al. 2009; Hema and Devi 2015; Sreelekshmi et al. 2021). The digging and leveling of the mangrove habitats for shrimp farms' preparation have significantly impacted mangrove status worldwide (Giri et al. 2008; Jayanthi 2018). Shrimps positively correlate with mangrove ecosystems, and the habitats are ideal for farming (Barbier and Cox 2004). Traditional and non-traditional/scientific shrimp farms are two types of farming methods that have been well managed in Kerala. Traditional shrimp farms depend on diurnal tidal inundation to supply the larval shrimp and their food nutrients into the ponds. In contrast, non-traditional shrimp farming focuses on modern techniques such as intensification of culture operation by innovative changes in pond size, increasing stocking rate, employment of aeration, application of feed, etc. (Bhattacharya 2010).
The highest extent of mangrove forests in Kerala is distributed along the coastline of the Kannur district, known to be the capital of the mangroves in Kerala (Vidyasagaran and Madhusoodanan 2014). More than 60% of these forests in the Kannur district are privately owned and, therefore, highly threatened (Preethy 2019). The primary threat to the mangroves of Kannur is the continuous destruction due to the construction of shrimp ponds/aquaculture ponds (Bijith et al. 2022) and recorded that the mangroves in the vast intertidal tracts of Kannur district have been reclaimed for the construction of such farms. They reported 140 active shrimp farms with a total extent of 524.4 sq. km, including traditional and non-traditional shrimp farms.
The physical and chemical properties of the water and soil determine the welfare of organisms in the mangrove ecosystem. The construction of such shrimp ponds may alter the physicochemical characteristics of the soil and water of mangrove ecosystems and the dependent communities (Mishra et al. 2008). Mishra et al. (2008) studied water quality assessment of aquaculture ponds in Orissa's Bhitarkanika mangrove ecosystem. The significant findings were that the pH of the aquaculture ponds varied from 5.63 to 8.5 due to the application of chemical additives and that the DO contents of water samples were high compared to the standard (4 mg/L) because of mechanical aerators. They have investigated high levels of chlorine in water due to the inflow of waste and those aquaculture ponds showed more range in calcium and magnesium due to the addition of Lime and other pesticides. The observed nitrate concentration in aquaculture ponds is much below BIS's prescribed standard of 10 mg/L (Mishra et al. 2008). The quality of soil and water, the growth of floral-faunal components, and the entire structure and function of mangrove ecosystems are determinedly affected by shrimp farms (Primavera 1997; Primavera 2006; Ashton 2008; Biao et al. 2009; Hamilton 2011; Preethy 2019).
This study analyses the physicochemical characteristics of the soil and water of traditional and non-traditional shrimp ponds near the mangrove vegetation of the Kannur district to understand the critical variation from the natural mangrove ecosystems.