Lakshadweep Sea Research Articles

Physio-biochemical characteristics of Acrostichum aureum L. In the coir retting areas of Kadinamkulam Estuary, South India

The Kadinamkulam lake a temporary estuary lying in the southern part of Kerala, is the largest of its kind in Thiruvananthapuram district, Kerala. Connected with the Anchuthengu kayal on the north and the Veli kayal on the south, the north and the Veli kayal on the south, the Kadinamkulam kayal remains connected with the Lakshadweep Sea for varying periods depending on rain fall and river discharge. Acrostichum aureum L. is only pteridophyte genus fern in the mangrove ecosystem of Indian coast. So the present study was conducted in the plant Acrostichum aureum L. identified in the selected stations of Kadinamkulam estuary. The major objective of the study is to assess the changes in the physiological and biochemical characteristics of the plant Acrostichum aureum L in coir retting areas. For this, surface water samples and plant samples were collected from the six selected stations of the coir retting areas and one station in the non-retting area of Kadinamkulam estuary. The results show reduction in leaf pigments, total proteins, carbohydrates in the Acrostichum aureum L. plants in polluted stations compared to that of control station/non retting area. The malondialdehyde, antioxidants and proline were increased in the Acrostichum aureum plants in retting stations and it vividly points out the stressful environment in the study area. It may be due to the presence of pollutants in the coir retting effluents and sewage disposed to this lake. The results of the study in lake water samples show that the values of some water quality parameters in coir retting areas were above the permissible limits of surface water quality standards.

Population characteristics unravel occurrence of distinct stocks of yellowfin tuna (Thunnus albacares) population in the Indian seas

Fishery and biological observations of yellowfin tuna caught from seas surrounding theIndian mainland and its island territories have indicated the presence of biologically distinctstocks in the region. Those caught around the submerged mounts of Chagos-LaccadiveRidge in the Lakshadweep Sea, off Kerala-Karnataka coast exhibit early maturity, small sizeat maturity, short lifespan and a close association with sea mounts. In contrast, those caughtoff other coasts of the mainland, including Andaman waters, exhibit late maturity and largersizes at maturity indicating a fishery dominated by larger-sized individuals. These findingssuggest that the yellowfin tuna associated with the Lakshadweep Sea mounts constitutesa distinct stock, highlighting the necessity for comprehensive genetic, morphometric andpopulation investigations to confirm their stock status. Keywords:Chagos-Laccadive Ridge, Indian mainland,Lakshadweep Sea, Maturity, Stock, Sea mounts,Yellowfin tuna

Recovery of a tropical coral reef in the aftermath of a cyclone: insights into postdisturbance dynamics and conservation strategies

Over the past decade, the Arabian Sea has witnessed an increase in tropical cyclones during the pre-monsoon and post-monsoon months, resulting in heightened devastation across the vulnerable low-lying coral islands in the Lakshadweep Sea along the southwest coast of India. Our underwater survey-based study—focused on Kavaratti Atoll in the Lakshadweep group, India—provides groundbreaking evidence on the rapid recovery potential of coral reefs following severe cyclonic events, a globally relevant concern given increasing climate change impacts. The observed coral recovery rate was significantly faster than expected, showing that recovery rates can differ in coral reefs of different regions. The recovery was primarily facilitated by quick-growing coral genera such as Pocillopora and Acropora, leading to a shift in the coral assemblage. The recovery by these fast-growing corals highlights their role as early succession species, pivotal in the initial stages of reef recovery. The findings of this study underscore the crucial significance of ongoing monitoring, maintaining reef connectivity, and establishing marine protected areas for the conservation of less-studied remote reef systems.

Sea Bed Mining

The seabed is surely one of the last mining frontiers on earth remaining for mankind, to extract economic mineral deposits. It is hence imperative that India with its Obvious Geological Potential (OGP) area on the land surface amounting to 0.57 million km, for which baseline geoscience data has been generated and mineral exploration activities are ongoing, needs to be supplemented with mineral wealth on our sea beds, within our Territorial Waters (TW) and Exclusive Economic Zone (EEZ). Studies by the Geological Survey of India (GSI) and other agencies for mineralized horizons in the terrestrial OGP areas have been a continuous process. The baseline geoscience and mineral exploration data are published regularly by GSI and Indian Bureau of Mines (IBM) and made available to respective stakeholders. India has a 2.02 million km area under its TW and EEZ. Our East and West Coasts of the Peninsular India are endowed with phosphate, manganese nodules, lime mud and monazite sands with rare earth elements (REE) and thorium that have been surveyed by the Marine and Coastal Survey Division (MCSD) of the GSI with their research vessels to establish the potentiality. According to the data available, 1,53,996 million tons of lime mud within the EEZ off Gujarat and Maharashtra coasts, 745 million tons of construction grade sand, off Kerala coast, 79 million tons of heavy mineral placers in the inner-shelf and mid-shelf, off Odisha, Andhra Pradesh, Kerala, Tamil Nadu and Maharashtra, phosphorite in the Eastern and Western continental margins, polymetallic ferromanganese nodules and crusts in Andaman Sea and Lakshadweep Sea have been reported. The CSIR- National Institute of Oceanography has been embarking on research for seabed mineral deposits. The Offshore Areas Mineral (Development and Regulation) Amendment Bill, 2023, passed by Lok Sabha on 01.08.2023, has amendments to the Offshore Areas Mineral (Development and Regulation) Act, 2002, OAMDR Act (Ministry of Mines, Govt. of India, 2002). It envisages major initiatives to allow auction of mineral blocks 45° X 45° (latitude and longitude) in respect of any mineral or prescribed group of associated minerals, under one or more operating rights (taken together). The Act has a provision for setting up of a non-lapsable Offshore Areas Mineral Trust to maintain a fund under the Public Account of India. This fund will be financed by a yet to be determined, additional levy on the production of offshore minerals that will be used for exploration, research, disaster relief and for mitigation of adverse impacts of seabed mining. We have the National Exploration Trust and the District Mineral Foundation Trust funds, to which royalties are paid by stakeholders for onshore mining.

Population dynamics of Bentfin devil ray, Mobula thurstoni (Lloyd, 1908), from Lakshadweep Sea, south-west coast of India

Population dynamics of Bentfin devil ray, Mobula thurstoni (Lloyd, 1908), from Lakshadweep Sea, south-west coast of India

The giant clam commensal shrimp Anchistus miersi (de Man, 1888) (Decapoda: Palaemonoidae) new to Lakshadweep Sea, India

The genus Anchistus Borradaile, 1898 is a colourful shrimp from the commensal group. In this study, we are reporting a new occurrence of Giant Clam commensal shrimp Anchistus miersi (de Man, 1888 [in de Man, 1887–1888]) caught from Agatti Island, Lakshadweep Sea during February 2020. The present specimens (one each matured male and female) were collected from the mantle cavity of the Giant Clam, Tridacna maxima (Roding, 1798) in the coral lagoon at a depth of 4 m. Anchistus miersi is morphologically very similar to Anchistus demani, which is easily distinguished by the presence of a strong antennal spine and conspicuous accessory spinules in the third─fifth pereopods and presence of small blue spots all over the body. The molecular analysis confirms that, the morphological identification of the present Indian specimens displays an intraspecific genetic divergence of 0.3─1.2%. Besides, the remarkable taxonomic features and colour patterns, distributional ranges are also attested with the report of the species from the present area.

A Comparison of Stochastic and Deterministic Downscaling in Eddy Resolving Ocean Modelling: The Lakshadweep Sea Case Study

This study compares the skills of two numerical models at the same horizontal resolution but based on different principles in representing meso- and sub-mesoscale ocean features. The first model, titled LD20-NEMO, was based on solving primitive equations of ocean dynamics. The second model, titled LD20-SDD, used a newer stochastic–deterministic downscaling (SDD) method. Both models had 1/20° resolution, the same meteo forcing, and used outputs from a data assimilating global model at 1/12° resolution available from Copernicus Marine Service (CMEMS). The LD20 models did not assimilate observational data but were physically aware of observations via the parent model. The LD20-NEMO only used a 2D set of data from CMEMS as the lateral boundary conditions. The LD20-SDD consumed the full 3D set of data from CMEMS and exploited the stochastic properties of these data to generate the downscaled field variables at higher resolution than the parent model. The skills of the three models were assessed against remotely sensed and in situ observations for the four-year period 2015–2018. The models showed similar skills in reproducing temperature and salinity, however the SDD version performed slightly better than the NEMO, and was more computationally efficient by a large margin.

Short duration performance of floating heave buoy WEC in the Lakshadweep Sea

In the wake of a proposed installation of two-body floating heave buoy wave energy convertor (WEC) off coast of Vizhinjam in peninsular India, this paper analyses functional estimates of short duration mean power generation and associated variability at a site in deepwater vicinity of the port town. The work is motivated by two aspects that are of interest to project planners and academics.First, the recently proposed concept of capture width function allows a convenient, functional approach to estimate power output by a WEC unit, as well as the associated variability. However, the approach remains to be applied to WEC technologies that capture energy specifically through oscillatory dynamics of masses, given that the concept has no implicit representation for mechanical oscillations within a WEC.Second, power conversion by heave motion is often augmented by alternate dynamic modes in commercial makes of heave buoy WEC technology. Impact of multi-mode power capture, particularly on short duration output power variability, is of considerable interest in the context of network integration.Comparison to the well tested Pelamis WEC shows the latter to be a competitive alternative in terms of output power variability, and hence in some ways a better option than floating heave buoys.

Crisis Ocean Modelling with a Relocatable Operational Forecasting System and Its Application to the Lakshadweep Sea (Indian Ocean)

This study presents the Relocatable Operational Ocean Model (ReOMo), which can be used as a Crisis Ocean Modelling System in any region of the global ocean that is free from ice. ReOMo can be quickly nested into an existing coarser resolution (parent) model. The core components of ReOMo are the NEMO hydrodynamic model and Rose-Cylc workflow management software. The principal innovative feature of ReOMo is the use of the Nesting with Data Assimilation (NDA) algorithm, which is based on the model-to-model assimilation technique. The NDA utilises the full 3D set of field variables from the parent model rather than just the 2D boundary conditions. Therefore, ReOMo becomes physically aware of observations that have been assimilated and dynamically balanced in the external model. The NDA also reduces the spatial phase shift of ocean features known as the ‘double penalty effect’. In this study, ReOMo was implemented for the Lakshadweep Sea in the Indian Ocean at 1/20°, 1/60°, or 1/120° resolution with and without model-to-model data assimilation. ReOMo is computationally efficient, and it was validated against a number of observational data sets to show good skills with an additional benefit of having better resolution than the parent model.

A new species of six-gilled hagfish (Myxinidae: Eptatretus) from the Lakshadweep Sea.

A new species of hagfish, Eptatretus wadgensis sp. nov., is described from the Wadge Bank, Lakshadweep Sea, India, obtained from a depth of ~250300 m through deep-sea trawling. It is diagnosed by having six pairs of gill pouches and gill apertures, 3/3 multicusp teeth, total slime pores 6769, six branchial slime pores, and ventral aorta bifurcating at the 4th or between 4th and 5th gill pouch. The new species has significant morphological differences in total dental cusps, total slime pores, body proportions and the absence of the nasal-sinus papilla when compared to congeners and formed a distinct clade in phylogenetic reconstruction and a genetic distance of 3.414.00% when comparing K2P parameters with the nearest species. A key to the Eptatretus species of the Indian Ocean is provided.

Characterization and antibacterial activity of violacein producing deep purple pigmented bacterium Pseudoalteromonas luteoviolacea (Gauthier, 1982) isolated from coral reef ecosystems

The present study describes the isolation, characterization and antibacterial activity of two strains of the deep purple pigmented bacterium Pseudoalteromonas luteoviolacea designated P42 (Accession no. MN647538) and M64 (Accession no. MN647537), isolated from two coral reef regions viz . Minicoy Lagoon in the Lakshadweep Sea and Palk Bay, off Olaikuda village in Tamil Nadu, India. Ultrastructural examinations were done using scanning and transmission electron microscopy. Presence of violacein pigment was qualitatively analysed by chemical methods; UV-VIS spectrophotometry and FTIR spectroscopy. The strains, P42 and M64 were found to have antibacterial activity against 13 out of the 36 marine bacterial species tested. Antibiogram analysis revealed the sensitivity of both the strains to all the antibiotics tested, except for the resistance of P42 to Penicillin G and Trimethoprim. This study reports the isolation and characterization of P. luteoviolacea for the first time from India. Since both the isolated strains have shown clear evidence for the presence of violacein as well as antibacterial activity against selected marine bacteria, both P42 and M64 can be suggested as potent antibacterial agents.

The occurrence of phosphorites on the Calicut mount, off Kerala, Lakshadweep Sea, India

A highly altered carbonate rock was recovered from the mount, off Calicut, Kerala. Bulk chemical analysis of the rock showed that it contains ~ 21 % P2O5. The rock consists of fine to coarse lithic and bio-clasts embedded in brown to the yellow coloured phosphatic matrix. Detailed SEM-EDS of the rock piece indicates micro-globular and nodular growth of phosphorite around calcite to form a core-rim structure, with P2O5 as high as 31.67 weight percentage. The X-ray elemental mapping carried out using EPMA indicates highest P2O5 (29.87 %) on the altered surfaces. Microstructural and geochemical analyses suggest authigenic/diagenetic precipitation of phosphorite on the carbonate rock.

New Geographical Record of Plesiothyreus cinnamomeus (Gould, 1846) (Gastropoda: Neritoidea: Phenacolepadidae) from the Central Indian Ocean

The neritiform gastropods Plesiothyreus cinnamomeus (Gould, 1846) was collected from Indian coast for the first time and Zacalantica galathea (Lamarck, 1819) for the first time from the recorded from Lakshadweep Sea, west coast of India. The record of Plesiothyreus cinnamomeus confirms the extended distribution of the species from the Pacific Ocean to the Arabian Sea.

Near reef abundance and on–offshore distribution of tuna larvae around Minicoy Island in Lakshadweep Sea, India

ABSTRACTNear reef abundance and coast–offshore distribution of tuna larvae around Minicoy Island were studied based on three cruises carried out on board FORV Sagar Sampada during 2014–15. The samples were collected by oblique tows using bongo twin nets (300 micron) for three seasons (Fall inter-monsoon (FIM), Spring inter-monsoon (SIM) and Summer monsoon (SM)) in six on–offshore stations ranging from 1 to 20 km off-shore of the Minicoy. Results indicated that the tuna larvae aggregate in the near reef waters and total tuna larvae abundance (all the species combined) shows a decreasing trend towards off-shore. Tuna larvae are found to be more abundant during SM and FIM. Comparison of the species-wise variation in tuna larvae for one season (SM) indicated that the larvae of Euthunnus affinis (32.5%) dominated among the tuna species, followed by Auxis spp. (31.6%), Thunnus spp. (3.9%) and Katsuwonus pelamis (2.7%). A pattern of highest larvae abundance in the near reef areas was observed except for Thunnus larvae. GAM indicated that mean seawater temperature and mean seawater salinity are the major environmental factors that significantly influence the larvae abundance, particularly for Thunnus followed by Katsuwonus pelamis, E. affinis and Auxis spp. The study confirms that the environmental parameters show high variation between stations and among transects as a result of the complex oceanographic characteristics around the islands. Further studies with better understanding of the larvae dynamics and their association with the environmental parameters including physical processes are essential to elucidate these relationships more clearly.

Environmental variables and nutrients in selected islands of Lakshadweep Sea; Addressing coral bleaching

An observational investigation on the environmental variables in the coral reef ecosystem of the Lakshadweep Sea was made with reference to coral bleaching. The investigation was done during 2014–2015 in selected islands of Lakshadweep Sea. The environmental variables recorded were sea surface temperature (SST; 28.1–31.5 ° C), salinity (34.0–38.36 psu), pH (7.9–8.3), dissolved oxygen (DO; 3.19–7.70 mg/L), total organic carbon of water (WTOC; 1.6–3.20 ppm) and net primary productivity (NPP; 0.440–2.060 mgC/m3/hr). Nutrients of nitrite (NO2; 0.052–1.522μmol/L), nitrate (NO3; 0.293–14.867μmol/L), in-organic phosphate (IP; 0.287–2.070μmol/L), total phosphorous (TP; 1.919–5.200μmol/L) and reactive silicate (RS; 3.791–19.422μmol/L) were also recorded. PCA showed positive loadings for salinity, DO, NO2, IP, TP, and RS in the Lakshadweep Sea. Currents and their divergence patterns influencing the upwelling in the nearshore islands might be the sources for the availability of nutrients. Data were treated statistically (linear regression) to understand the interrelationship between the variables. DO was found normal, indicating that the waters of the Lakshadweep Sea are well mixed and aerated. Nutrients such as NO2, NO3, IP and RS in Kavaratti and Agatti islands were found higher indicating that these islands are under the influence of anthropogenic activities. Cluster analysis revealed clear groupings among the islands. Agatti and Kalpetti islands were grouped together indicating more similarity in the values of environmental variables than with other islands. SST was found in the higher range over a study period and also over to the past ∼5 decades as per records and pH was found at the lower level in majority of the assessments. The unvaried ranges of SST and pH (P >0.01) might have favored bleaching of the corals in the Lakshadweep Sea. The nutrient levels recorded presently besides the other variables will serve as the baseline data for future investigations in the Lakshadweep Sea.

On the Seasonal Variability of Sea Surface Temperature and Air–Sea Fluxes in the Lakshadweep Sea

Using satellite-sensed sea surface temperature (SST), winds, and air–sea fluxes, we studied seasonal variability of SST and air–sea fluxes in the Lakshadweep Sea (LS) and quantified their relations. Seasonal variability of SST exhibits a bimodal nature, for that air–sea fluxes and oceanic processes operate differently. Analysis demonstrates that seasonal SST variability due to air–sea fluxes in the LS arises with a time lag of 1 or 2 months. For winter cooling, low solar insolation plays a cardinal role and the effects due to net longwave radiation (NLWR) and latent heat flux (LHF) are surpassed. Although net shortwave radiation (NSWR) is minimum in December, low winter SST with a lag of 1 month occurs in January. All air–sea fluxes are favorable for summer monsoon cooling though cooling is also set by several oceanic processes such as advection, vertical overturning, and turbulent mixing. During pre-monsoon warming months March–April, all air–sea fluxes are favorable. But during intense warming in May, though SST is high (> 29.8 °C) in the LS, air–sea fluxes are not supportive as incoming solar insolation is low and evaporative heat loss is high. This indicates that warming during May is the resultant of the expansion of Indian Ocean warm pool into the LS and westward propagation of the Lakshadweep high (LH) as downwelling Rossby wave. For the post-monsoonal warming during October–November, low NSWR is unfavorable but distributions of LHF and NLWR demonstrate suitable condition. For warming during November, vertical ocean heat convergence and less evaporation act favorably.

Morphological and molecular identification of marine copepod Dioithona rigida Giesbrecht, 1896 (Crustacea:Cyclopoida) based on mitochondrial COI gene sequences, from Lakshadweep sea, India

Morphological identification of the marine cyclopoid copepod Dioithona rigida in combination with sequencing a 645 bp fragment of mitochondrial cytochrome oxidase c subunit I (mtCOI) gene, collected from offshore waters of Kavarathi Island, Lakshadweep Sea, is presented in this study. Kiefer in 1935 classified Dioithona as a separate genus from Oithona. The main distinguishing characters observed in the collected samples, such as the presence of well-developed P5 with 2 setae, 5 segmented urosome, 12 segmented antennule, compact dagger-like setae on the inner margin of proximal segment of exopod ramus in P1–P4 and engorged portion of P1-bearing a spine, confirmed their morphology to D. rigida. A comparison of setal formulae of the exopod and endopod of D. rigida with those recorded previously by various authors are also presented here. Maximum likelihood Tree analysis exhibited the clustering of D. rigida sequences into a single clade (accession numbers KP972540.1-KR528588.1), which in contrast was 37–42% divergent from other Oithona species. Further intra-specific divergence values of 0–2% also confirmed the genetic identity of D. rigida species. Paracyclopina nana was selected as an out group displayed a diverged array. The present results distinctly differentiated D. rigida from other Oithona species.

Absolute Calibration of SARAL/AltiKa in Kavaratti During its Initial Calibration-Validation Phase

The Kavaratti calibration-validation site in India at Lakshadweep Sea has been improved to carry out absolute calibration of SARAL/AltiKa altimeter. This site is augmented with a down-looking radar gauge and a permanent GPS receiver. The Kavaratti Island is located near a repeating ground track of SARAL/AltiKa and ∼12 km away from the point of closest measurement of Jason-2, SARAL/AltiKa crossover point. Additionally, the altimeter and radiometer footprints do not experience any land contamination. This article aims at presenting the initial calibration-validation results over cycles 001-011 of AltiKa. The absolute sea surface height bias has been found to be −48 mm at Kavaratti calibration site. In this preliminary study the effect of environmental variables such as winds and pressure are not considered in calculations.

Shark bycatch in the experimental tuna longline fishery in Lakshadweep Sea, India

Bycatch from the experimental longline operations in the Lakshadweep Sea were studied. The experiments were conducted on converted Pablo boats, originally used for pole and line fishing operations, to capture skipjack tuna in the Lakshadweep Islands. The overall bycatch rate was very high, with a mean hooking rate of 8.05/1000 hooks compared to the targeted tuna catch (1.75/1000 hooks). Bycatch contributed 82.4% of the catch in comparison to the tuna (17.6%) Thunnus albacares, in the longline operations. Silky shark (Carcharhinus falciformes) with 89.9% was the dominant shark species followed by C. amblyrhynchos, Galeocerdo cuvier, Alopias pelagicus, Negapriion acutedens and Sphyrna lewinii with 4.7, 2.7, 1.4, 0.7 and 0.7%, respectively. Sharks contributed to 74.1% of the catch, followed by 15.7% sailfishes and 10.2% miscellaneous fishes. Higher bycatch rates were evident during evening hours compared to mornings, but the results were not significant statistically. Studies on the effects of depth on the overall fishing performance and species selectivity failed to establish any significant relationship at a depth range of 35–100 m. Soaking time had a significant effect on bycatch rates. The hooking rate of sharks declined with an increase in soaking time. Considering the high shark bycatch in the fishery, an accurate monitoring of the longline fish catches in the Lakshadweep waters is an important step towards ensuring the sustainability of other populations, especially sharks.

Wave Transformation along Southwest Coast of India Using MIKE 21

Nearshore wave transformation is a complex coastal process of shoaling, refraction, diffraction, reflection, and energy dissipation due to bed friction and breaking contributing variations in the wave height, period and direction. A well defined sediment cell of about 45 km extending from Kovalam headland to Varkala cliff which forms a part of Thiruvananthapuram coast along the southwest coast of India, is selected for the wave transformation studies. In the present study MIKE 21 Spectral Wave model (DHI, 2011) was used. The model simulates the growth, decay and transformation of wind generated waves and swells both in offshore and coastal areas. Providing MIKE 21 SW with a suitable bathymetry is essential for obtaining reliable results from the model. Usually the offshore bathymetry is derived from C-MAP, ETOPO, GEBCO etc. and the nearshore bathymetry is generated from close grid bathymetric surveys. In this study offshore bathymetry was generated from GEBCO-08 grid which is a freely available software with 30 arc (∼ 1 km) resolution. In the nearshore zone, surveyed close grid bathymetric data were used. The other inputs such as wave measurements and wind data provided in the model were from observations in Lakshadweep Sea. Model result is calibrated with field observations along this sector. The model has efficiently simulated the process of shoaling and refraction along the coast. The percentage of observed shoaling is 12.7% at a distance of 24 km from the shoreline at a depth of 70m and it was seen to be increasing to 27.9% when it reached around 2.4 km from the shore at a depth of 10m. The model result also shows that the wave is almost aligned parallel to the coast as wave approaches the coast. This model result can be used for further applications in designing along this coast.