Seasonal variability in physicochemical parameters and fish larval abundance along the coastal waters of Dakshina Kannada, southwest coast of India

The study attempted to record the seasonal variability in the physicochemical parameters that influence the fish larval abundance in six stations from the Netravathi-Gurupura and the Mulki-Pavanje estuaries along the coast of Dakshina Kannada for a period of 36 months (2014-2016). Pronounced variations in the primary production, chlorophyll a, and physicochemical parameters such as water temperature, pH, salinity, dissolved oxygen, and nutrients were observed in the estuarine and coastal waters. Between stations, the one-way ANOVA revealed highly significant variations (p<0.001) in pH, salinity, Chlorophyll a, Nitrate-N, Ammonia- N, and Silicate-Si concentrations and significant differences in dissolved oxygen and chlorophyll c (p< 0.05) concentrations. Multivariate comparisons (Tukey HSD) revealed variations in the physicochemical parameters within the stations. Nearshore stations and estuarine waters were distinct concerning physicochemical parameters. Environmental factors influencing fish larval abundance in the nearshore waters include rainfall (r = 0.487, p< 0.01), river discharge (r = 0.444, p< 0.01), dissolved oxygen (r = 0.395, p< 0.05), and silicate-Si concentration (r = 0.423, p<0.05). Similarly, the tidal height (r= 0.536, p<0.01) also played an additional key role in influencing and determining the seasonal abundance of fish larvae in the estuarine waters. The water quality index (WQI) in estuaries and nearshore waters is indicated as Good to Poor state as per USEPA (2012) rating. Improving the quality of near-shore coastal waters can increase the survival of fish larvae, protect fish breeding sites, and ultimately contribute to enhanced fisheries productivit

Reviews and syntheses: Abrupt ocean biogeochemical change under human-made climatic forcing – warming, acidification, and deoxygenation

Abrupt changes in ocean biogeochemical variables occur as a result of human-induced climate forcing as well as those which are more gradual and occur over longer timescales. These abrupt changes have not yet been identified and quantified to the same extent as the more gradual ones. We review and synthesise abrupt changes in ocean biogeochemistry under human-induced climatic forcing. We specifically address the ocean carbon and oxygen cycles because the related processes of acidification and deoxygenation provide important ecosystem hazards. Since biogeochemical cycles depend also on the physical environment, we also describe the relevant changes in warming, circulation, and sea ice. We include an overview of the reversibility or irreversibility of abrupt marine biogeochemical changes. Important implications of abrupt biogeochemical changes for ecosystems are also discussed. We conclude that there is evidence for increasing occurrence and extent of abrupt changes in ocean biogeochemistry as a consequence of rising greenhouse gas emissions

Dwindling seagrasses: A multi-temporal analysis on Google Earth Engine

Seagrasses, a unique group of marine flowering plants, profoundly influence the marine environment by providing an array of critical ecological functions. They serve as the foundational habitat for several endangered and charismatic species, including sea cows, sea turtles, and sea horses, and are often referred to as coastal canaries. In comparison to boreal and tropical forests, they have an amazing ability for carbon storage. Despite their long evolutionary history, they are threatened by rapid environmental changes caused by climate change and human activity. Long-term monitoring is required to comprehend the changes in this fragile ecosystem. Conventional field survey methods for collecting long-term data are laborious, time-consuming, and expensive. Hence, this work builds a time-series dataset of the seagrass coverage in the Kalpeni lagoon from 2003 to 2020 by analysing Landsat data on Google Earth Engine. We also evaluated the temporal changes in the seagrass coverage of the study area and studied the influence of selected environmental factors on the seagrass coverage. We observed a negative relationship between sea surface temperature and seagrass coverage. The results revealed a decline in more than 99% of seagrass coverage, indicating an alarming threat to this seagrass ecosystem of the region. With such a drastic shrinkage in the seagrass coverage, the hysteresis must be strong, and the recovery of these meadows may require intensive interventions. By establishing a long-term time series database of seagrass coverage, our study also opens up new avenues for future ecological research on the seagrass meadows

Impact of marine debris on coral reef ecosystem of Palk Bay, Indian Ocean

Coral reef ecosystems are highly sensitive to pollution from marine debris, especially if the regions are noted for tourism and fishing. Palk Bay on the south east coast of India is a famous tourist and fishing region, where the marine debris accumulation poses a great threat to the coastal ecosystem. In this study during 2018–2020, the marine debris distribution and their interactions with coral reefs of Palk Bay were monitored from five stations. Derelict fishing gears (DFGs), including ropes (51 ± 2%) and fishing lines (43 ± 2.5%), were the dominant debris forms recorded. Among the reef-forming corals, Acropora sp. colonies experienced maximum physical injury and mortality from DFG entanglement. Plastic materials and anchors caused considerable physical damage and tissue loss in Porites sp, without any mortality. Manual debris removal as a potential debris management method was assessed by regularly removing the accumulated debris from the test reef locations of all five stations, whereas the control reef locations were left undisturbed. Test reef locations showed a significant increase in live coral cover and coral recruit density in 2020, against that in 2018, compared with the control locations. Continuous accumulation and interaction of marine debris with the coral colonies of control reef locations resulted in significant reduction of live coral cover and coral recruit density at the control reef locations. This study illustrates the impact of unsustainable fishing and other anthropogenic activities such as tourism and waste disposal on coral reef ecosystems like Palk Bay. The findings of this study demonstrates that manual removal of debris is an important strategy for marine debris management in coral reef ecosystem. Considering the importance of coral reefs in the livelihood of the coastal communities, it is important to tackle the marine debris issue through regular debris removal with stakeholder participation, awareness campaigns and strict legal and management measures

Coral disease prevalence in Gulf of Mannar and Lakshadweep Islands

1755-1762Coral disease prevalence was higher in Coral reefs of Gulf of Mannar (GOM) (Kurusadai= 23.42% and Manoli = 15.23%) than in the Lakshadweep group (Kavaratti = 11.2% and Agatti= 9.65%). white band, white pox, white plague, pink line syndrome, pink spot, yellow band, fungal blotch, black band and necrotic patches were all observed during the survey. Pink spot disease (35.08%) was the most prevalent disease among other observed infections. Massive corals especially Porites Spp. was highly affected (18.2%) and followed by Pocillopora (6%) Acropora (5.3%), Goniastrea (3.6%), Favia (3.5%), Montipora (2.3%) , Favia (3.5%), Galaxea (1.3%) and Fungia (0.89%) . Massive corals were found more susceptible to diseases than branching corals. High levels of new mortality and disease prevalence at Kavaratti and Agatti islands suggests that the coral reefs of Lakshadweep are facing increasing pressure from a variety of stresses