Alterations in hydrological variables and substrate qualities and its impacts on a critical conservation reserve in the southwest coast of India

Tracing microplastics in environmental sources and migratory shorebirds along the Central Asian Flyway

Microplastic pollution poses a significant threat to coastal ecosystems worldwide. Despite its widespread occurrence, knowledge on the prevalence and fate of microplastics across food webs is limited. To bridge this gap, we conducted an extensive study on microplastic contamination in mudflats, mangroves, and sand beaches being key habitats for wintering shorebirds on the west coast of India. Using a comprehensive multi-matrix approach covering water, sediment, biofilm, plankton, benthic macroinvertebrates, and migratory shorebird droppings, we analysed microplastic contamination across ten coastal sites from 2020 to 2022. Our findings show spatial and temporal variations in microplastics widespread in water and sediments, influenced by human activities. Notably, an increase in microplastics within prey and shorebird droppings coincide with a decline in prey abundance and shorebird populations. The prevalence of fibre-shaped microplastics indicates that common sources include discarded fishing gear and domestic sewage. The types of microplastics ingested by shorebirds varied depending on their feeding strategies, with biofilms serving as significant reservoirs of microplastics, facilitating their transfer to shorebirds. Epibenthic feeders, with a more limited foraging range, displayed the lowest levels of microplastics, while species foraging through multiple sediment layers exhibited higher concentrations. These findings underscore the urgent need for stricter conservation measures to tackle plastic pollution at its source. The study raises concerns about the potential harmful effects of microplastic contamination on the population of migratory shorebirds along the west coast of India. Continued research is crucial to understand the ecological impacts of microplastics on wintering shorebirds and to develop effective conservation strategies.

Bio-concentration of hazardous metals in migrant shorebirds in a key conservation reserve and adjoining areas on the west coast of India

Heavy metal pollution is a growing environmental concern as it causes the degradation of wetlands by affecting the organisms at different trophic levels. Shorebirds typically feed on benthic invertebrates including polychaete worms, crustaceans and molluscs. Thus, the assessment of bioconcentration of heavy metals in shorebirds provides an insight into the extent of bioaccumulation of these hazardous metals in the upper trophic levels. We studied the variation in the bioconcentration of hazardous heavy metals (chromium, lead and cadmium) in the faeces of 12 species of shorebirds (belonging to different foraging guilds including Endangered Great Knot, Vulnerable Grey Plover, Broad billed Sandpiper and Curlew Sandpiper and Near Threatened Eurasian Oystercatcher, Ruddy Turnstone and Dunlin) in relation to trends in their abundance over a period of five years (2019-2023). The study spanned over three different habitats (mudflats, mangroves and sand beaches) of Kadalundi Vallikkunnu Community Reserve (KVCR) and adjoining sand beaches, which are important wintering/ stop-over sites for the migrant shorebirds that provide abundant nutritional resources for the foraging shorebirds. We demonstrate that there has been a drastic increase in the heavy metal concentration in shorebird faeces from 2019 to 2023. Further, the findings indicate that predating and biofilm-grazing shorebirds in mangrove habitats, as well as small-bodied shorebirds in general are exposed to high levels of heavy metals. This study highlights that heavy metals in the coastal habitats are increasing and that there are potential risks from exposure to foraging shorebirds. Heavy metals have known adverse effects on shorebirds. Our study shows that reducing pollution and protecting community reserves alongside their surrounding habitats are crucial to combat biodiversity loss and maintain diversity in these areas.

Bill Length of Non-breeding Shorebirds Influences the Water Depth Preferences for Foraging in the West Coast of India

Body size, bill length and shape determine foraging techniques, habitat selection and diet among shorebirds. In this study, water depth preferences of different shorebirds with different bill sizes in various habitats including mudflats, mangroves at Kadalundi-Vallikkunnu Community Reserve (KVCR) (19 shorebird species) and adjacent agroecosystems at Vazhakkad (12 species) were studied between 2017 and 2020. The bill length of the shorebirds was significantly and positively associated with the average water depth, where shorebirds were observed to forage. Shorebirds with shorter bill lengths preferred shallow waters and those with longer bills preferred deep waters for their foraging activities. Habitat type also had a significant effect on the shorebird occurrence. Eurasian Curlews in both mangroves and mudflats were observed in areas with a higher water depth compared to other species. This is due to the fact that shorebirds tend to specialise in feeding habitats or in prey items to reduce intraspecific competition and distribute themselves in space and time in accordance with the availability of their resources. The occurrence of some species in agroecosystems is attributed to the reduced food availability, habitat quality and other disturbances for shorebirds on tidal flats, which are critical for sustaining migratory phenology. The differences in bill morphology are crucial in determining diet, water depth, niche preferences and segregation. Morphological characters and hydrological rhythms determine specialisation in diet and habitat preference in shorebirds.

The threat of microplastics: Exploring pollution in coastal ecosystems and migratory shorebirds along the west coast of India

To evaluate the exposure risk and ingestion of microplastics by migratory shorebirds, which are regarded as apex predators in the coastal ecosystem, this study investigated the ubiquitous presence of microplastics in estuarine and coastal habitats and their potential to be transferred in the food chains. We analysed the presence of microplastics in water, sediment, major macroinvertebrate prey and the guano samples of ten shorebird species from ten important wintering grounds in the west coast of India. Our results revealed that water is the primary source through which microplastics disseminate into various ecosystem components. Microplastic debris in various forms were reported in all samples analysed, with microfibres being the most abundant form. While polyethylene and polypropylene were found as the major microplastic types in water, sediment, and prey samples, polystyrene was most abundant in guano samples. Microplastic transfer and impacts in this delicate ecosystem demand further investigations.

Heavy metals in wetlands of southwestern India: from sediments through invertebrates to migratory shorebirds

Heavy metal pollution in Indian wetlands is rising due to industrial, agricultural and urban development activities. Shorebirds occupy upper trophic levels and are therefore especially vulnerable to heavy metal pollution. We evaluated the concentration of heavy metals (zinc, copper, cobalt, chromium, lead and cadmium) in 22 common species of migrant shorebirds (220 shorebird dropping samples) with diverse foraging behaviors, in their different prey (55 prey samples) and in the sediments (90 sediment samples) in different habitat types (mudflats, mangroves and sand beaches) between 2019 and 2021. Further, we analyzed a total of 10 biofilm samples from mudflats and mangroves. We detected relatively low concentrations of heavy metals in the sediments (Zn concentration range: 9.11-40.91 mg/kg; Cu: 5.74-21.38 mg/kg; Co: 2.00-4.04 mg/kg; Cr: 4.05-41.03 mg/kg; Pb: 1.02-7.19 mg/kg; Cd: 0.56-4.35 mg/kg). However, we measured relatively high concentrations of heavy metals in invertebrate prey species (Zn concentration range: 84.72-224.74 mg/kg; Cu: 26.63-170.36 mg/kg; Co: 13.98-14.42 mg/kg; Cr: 14.78-98.16 mg/kg; Pb: 18.95-157.29 mg/kg; Cd: 9.33-60.56 mg/kg). In addition, we found high concentrations of heavy metals in shorebird droppings (Zn concentration range: 41.33-58.8 mg/kg; Cu: 31.42-52.11 mg/kg; Co: 36.34-55.68 mg/kg; Cr: 52.3-68.21 mg/kg; Pb: 25.94-43.13 mg/kg; Cd: 5.53-16.4 mg/kg). It is evident that concentration of heavy metals increased successively moving from sediment to prey to shorebird species, likely through trophic transfer. The biofilm samples contained very high concentrations of Cr, Pb and Cd (22.64, 28.09 and 18.46 mg/kg respectively) which could be harmful to biofilm grazing shorebirds. Since bioaccumulation of heavy metals entail risks in living species, we suggest that increasing concentrations may detrimentally affect physiological processes in invertebrates and shorebirds. There is an urgent need to identify the sources of pollution and to reduce the discharge of heavy metals and other pollutants into coastal and inland wetlands.