Dr Mangesh Gauns - Academia.edu (original) (raw)

Papers by Dr Mangesh Gauns

Asian fisheries science, Jun 30, 2014

Pseudodiaptomus serricaudatus (Scott, T. 1894), a planktonic copepod belonging to the family Pseu... more Pseudodiaptomus serricaudatus (Scott, T. 1894), a planktonic copepod belonging to the family Pseudodiaptomidae, though has worldwide distribution, has been reported only from estuarine and coastal waters. This is the first report of the occurrence of demersal calanoid copepod, P.serricaudatus in the open oceanic waters of the Equatorial Indian Ocean (EIO; 4ºN, 77ºE). This species, collected during September 2010, was found to be one of the most abundant copepods with a density of 113 ind•m¯3. We suggest that this species might have advected from the estuarine and coastal waters off the southern parts of the west coast of India under the influence of prevailing monsoon currents.

Research Square (Research Square), Feb 21, 2023

The seasonal variations of δ 15 N and δ 13 C of copepods and suspended particulate organic matter... more The seasonal variations of δ 15 N and δ 13 C of copepods and suspended particulate organic matter is examined to comprehend the feeding habits of copepods of the marine food web over the western continental shelf of India. This study provides baseline information on seasonal variation of the isotopic composition in copepods. Seasonal divergence in δ 15 N and δ 13 C values in Paracalanidae, Oncaeidae, Subeucalanus spp., Acartia spp. and Temora spp. conspicuously revealed herbivorous/omnivorous feeding habit. Such omnivorous feeding habit of copepods seems to play important role in trophodynamics of zooplankton and transfer of carbon and nitrogen to other trophic levels over the western continental shelf of India.

Indian Journal of Marine Sciences, Jun 1, 1999

The Arabian Sea is one of the most productive regions of the world oceans. This productivity main... more The Arabian Sea is one of the most productive regions of the world oceans. This productivity mainly results from coastal and open ocean upwelling in summer and cooling effects during winter. Earlier and more recent studies showed that there are considerable spatial and temporal variations in the area in primary productivity. Nonetheless, contrary to ,earlier thinking, it would seem that the mesozooplankton abundance in the Arabian Sea is fairly high in the mixed layer all through the year. This paradox of the Arabian Sea could be partly resolved by explaining the microbial loop and a fresh set of data is presented here in support. This is because most of the herbivorous forms are either small filter feeders like copepods or larger mucous filter feeders like tunicates which are able to feed on very small particles. It would seem that the Arabian Sea sustains a large biomass of mesopelagic fishes (about 100 million tonnes), mainly myctophids. They mostly live in the core of oxygen minimum layer and ascend to the surface layers during night to feed on the abundant zooplankton.

Marine Pollution Bulletin, Apr 1, 2023

Indian Journal of Marine Sciences, 1996

Research Square (Research Square), Aug 24, 2022

We studied the community composition of microzooplankton (MZP) from the surface waters off Candol... more We studied the community composition of microzooplankton (MZP) from the surface waters off Candolim, Goa. The MZP communities were examined for the year 2013, covering different seasons and four stations (Near-shore: G3 & G4, offshore: G5 & G6). A total of 30 species belonging to 24 genera were recorded, which include loricate ciliates (LC: 14 species of 13 genera), aloricate ciliates (ALC: 5 species of 3 genera), heterotrophic dino agellates (HDS: 11 species of 8 genera) and copepod nauplii. The MZP abundance in the coastal waters varied spatially irrespective of different seasons, with higher abundance in the offshore stations (G5 & G6, 38-127 cells L-1) and lower abundance in the near-shore stations (G3 & G4, 20-97 cells L-1). The MZP community composition showed the dominance of HDS (16-85%) in the near-shore stations during most of the seasons and inferiority during NEM (16-18%,). Moreover, all the coastal waters (near and offshore) were dominated by HDS (58-85%) during spring inter-monsoon. The dominant species of HDS were Dinophysis apicata, Dinophysis caudata, Porocentrum micans, Protoperidinium breve, Protoperidinium latistriatum, and Protoperidinium granii. The statistical analysis (Spearman's rank correlation) depicts that the MZP abundance and community composition were mainly controlled by salinity (r = 0.4-0.7). Whereas the dominance of HDS in the coastal waters could be the reason for its mixotrophic nature and diverse feeding mechanism. Thus, a strong positive correlation between the HDS and LC (r = 0.73-0.92) showed the feeding ability of HDS in their relative community.

Reviews in Fish Biology and Fisheries, Oct 26, 2010

Myctophids are mesopelagic fishes belonging to family Myctophidae. They are represented by approx... more Myctophids are mesopelagic fishes belonging to family Myctophidae. They are represented by approx. 250 species in 33 genera. Called as "Lanternfishes", they inhabit all oceans except the Arctic. They are well-known for exhibiting adaptations to oxygen minimum zones (OMZ-in the upper 2000m) and also performing diel vertical migration between the meso-and epipelagic regions. True to their name, lanternfishes possess glowing effect due to the presence of the photophores systematically arranged on their body, one of the important characteristic adding to their unique ecological features. Mid-water trawling is a conventional method of catching these fishes which usually accounts for biomass approx. in million tones as seen in Arabian Sea (20-100 million) or Southern ocean (70-200 million). Ecologically, myctophids link primary consumers like copepods, euphausiids and top predators like squids, whales and penguins in a typical food web. Lantern fishes become a major part of deep scattering layers (DSL) during migration along with other fauna such as euphausiids, medusae, fish juveniles, etc. Like any other marine organisms, Myctophids are susceptible to parasites like siphonostomatoid copepods, nematode larvae etc in natural habitats. They are important contributors of organic carbon in the form of their remnants and fast sinking faeces, which get deposited on ocean beds. Economically, they are a good source of protein, lipids and minerals, which is used as fishmeal for poultry and animal feed and as crop fertilizers. Few species are considered edible, but proper processing difficulties on a higher scale limit myctophids as human food. Myctophids have a life span of approx. 1-5 years and low fecundity rates (100-2000 eggs per spawn). This trait is a disadvantage, if continuous utilization of their population, for e.g. for fish meal industries etc, occurs without giving them a chance to revive and recover. Hence, research in this area also should be given utmost importance. In this paper, we have tried to compile information and ideas from various sources of myctophid research around the world, particularly from the Indian Ocean, to understand their ecological and economic importance and also to put forth new ideas to bring about conservation and restoration of this vulnerable resource.

Research Square (Research Square), Dec 14, 2022

In the present study, four species of commercial sh species namely Rastrelligar kanarguta, Tenual... more In the present study, four species of commercial sh species namely Rastrelligar kanarguta, Tenualosa ilisha, Mugil cephalus and Sardinella longiceps were studied to understand their planktonic gut composition. This investigation was carried out by collecting locally caught fresh sh specimens from Coco beach at Nerul, Bardez-Goa, India from October 2019 to March 2020. These specimens were caught using the shing gears such as cast net/gill net/seine nets operated from motorized canoes/crafts in the near shoreline region. Fishes mentioned in this report feed mainly on zooplankton i.e., copepods and bivalves. The copepod that dominated the gut content most of which were in semi-digested form apart from diatom and bivalve larvae. However, during the winter period, February and March, gut content was full of non-motile, marine dino agellates (ca. 200-500µm in size) represented by Pyrocystic sp. The study concludes that these commercial shes show seasonal variation in feeding patterns and food selection (zooplankton ← → phytoplankton)

ABSTRACT Coastal upwelling is known to bring nutrient rich bottom waters to the surface. This cha... more ABSTRACT Coastal upwelling is known to bring nutrient rich bottom waters to the surface. This change in chemistry triggers a series of cascading effects on the trophic levels of coastal ecosystems. Phytoplankton, besides being primary producers and carbon sink also produce a tertiary sulfonium compound dimethylsulphoniopropionate (DMSP), which breaks down mostly by bacterial mediation to a climatically relevant volatile compound dimethylsulphide (DMS). In order to probe the dynamics of DMSP in post upwelling coastal waters, we monitored variations in phytoplankton biomass, abundance and diversity along with DMSPt (total = particulate + dissolved) and DMS concentration in seawater over a period of 5 days at 6 hour intervals off Trivandrum located along the southern west coast of Indian subcontinent in November 2010. Physicochemical parameters and zooplankton abundance were also measured. Chlorophyll a averaged 1.39 µg l -1 and phaeophytin 0.49 µg l -1 . Average phytoplankton abundance was 1.17E+05 l -1 and was mainly composed of diatoms ~78% and dinoflagellates ~21%. The most abundant diatom was Pseudonitzschia spp. while dinoflagellates were represented by Gymnodinum spp. Average DMSPt concentration was 103.2 nM while DMS was 1.11nM. Highest DMSPt and DMS concentrations were in the subsurface waters at 25m depth with an average value of ~297nM and ~3nM respectively. Intriguingly, the lowest

Regional Studies in Marine Science

Environmental Monitoring and Assessment

Environmental Science and Pollution Research, Jan 17, 2023

Environmental Monitoring and Assessment, 2021

A correction to this paper has been published: https://doi.org/10.1007/s10661-021-08983-6

Journal of Sea Research, 2021

Abstract Benthic biogeochemistry and its coupling with pelagic ecology are less understood in tro... more Abstract Benthic biogeochemistry and its coupling with pelagic ecology are less understood in tropical than in temperate estuaries, which have significant implications for global carbon and nutrient cycling. In dry season, the Mandovi Estuary of Western India develops a prominent salinity gradient (0–35 psu), and remains nutrient-limited but most productive, which stands in contrast to wet season. To understand the role of benthic exchange in the sustenance of estuarine biogeochemistry and ecosystem, we carried out biogeochemical measurements in the water column and a series of intact-core incubations along the estuarine salinity gradient, during the dry season of 2014. We observed that the lower estuary was nitrogen (N)-limited whereas the middle and upper estuary were phosphorus (P)-limited. The benthic respiration (38.6–82.87 mmol O2 m−2 d−1), organic carbon (Corg) mineralization (34.3–79.8 mmol C m−2 d−1) and nutrient exchange rates considerably varied along the salinity gradient. Variability in benthic respiration was apparently controlled by labile Corg content and faunal abundance in the sediments. Benthic exchange of NH4+ and NOx− were mainly controlled by salinity and NOx− of the water column, respectively. Benthic PO43− exchange was predominantly controlled by sedimentary Fe content and bottom water O2, whereas benthic SiO44− exchange was primarily controlled by sediment-water SiO44− gradient. Abiotic processes accounted for 37-79% of sediment O2 consumption (SOC). Benthic metabolism accounted for 34–60% of total community respiration and mineralized 43–145% equivalent of C fixed through primary production (PP). Of dissolved inorganic nitrogen (DIN) efflux (0.67–2.59 mmol m−2 d−1), NH4+ comprised 91% in the lower estuary but NOx− (NO3− + NO2−) comprised 97% in the upper estuary, and benthic nitrification apparently determined the dominant N species released from the sediments. Coupled nitrification-denitrification apparently caused the loss of 30–69% of NH4+ diffusing from the deeper sediments. The estuarine sediments were a net source of DIN and SiO44−, potentially meeting up to 31% of N and 40% of Si demand of the phytoplankton, but acted as a net PO43− sink owing to high sedimentary Fe and normoxia, and tended to buffer the estuarine water PO43− to 0.05–0.19 μM. Benthic PO43− influx (0.006–0.026 mmol m−2 d−1) apparently caused the P-limiting condition in the middle and upper estuary. Particularly, the role benthic DIN supply was crucial for the sustenance of estuarine PP as the estuary receives some PO43− from the sea and sufficient SiO44− from the river but not sufficient DIN. The sediments potentially immobilized up to 25% and 20% of riverine DIN and PO43− load, respectively. Overall, the study revealed an efficient benthic carbon recycling and a tight benthic-pelagic coupling in the estuary during the dry season.

Estuarine, Coastal and Shelf Science, 2018

In a mangrove environment, several groups of organisms are symbiotically associated with pneumato... more In a mangrove environment, several groups of organisms are symbiotically associated with pneumatophores (aerial roots). But whether these organisms are exclusively found in this habitat (uniqueness) or accidentally settled here from water or sedimentary habitat, is not clearly understood. This hampers our understanding of their functional ecology. Hence the present study aimed to characterise the epibiotic microalga and meiofauna from the pneumatophores of mangrove Avicennia officinalis. To determine the habitat influence, these communities were also compared with those found in water and sedimentary habitat. Four estuarine mangrove sites represented by brackish water (salinity varying from 5 to 12) and located at different spatial scales (5e50 km distance) were chosen to determine whether these communities are consistent or vary with sites. Overall, the microalgal community was found to vary both among the habitats as well as sites. In the pneumatophore habitat, several tychoplanktons such as Coscinodiscus, Thalassionema, Cyclotella, Fragilariopsis, and Biddulphia were observed instead of benthic ones. These diatoms are planktonic genera and might have settled on pneumatophores from the water column. The observed variability in the microalgal composition among the sites is possibly due to predatory interactions or the dominance of particular species of macroalga that govern the diatom community. On the other hand, among the meiofaunal community, diptera, halacarida, tanaidacea, and foraminifera were mainly found in the pneumatophore habitat than in the sediment. Because pneumatophores either provide refugee to meiofauna against predators or are saturated with oxygen that meiofauna can utilize for respiration. Pneumatophores were also found to harbour several rare (abundance <1%) epibionts, the ecological importance of which is discussed in this paper.

Marine Pollution Bulletin, 2019

The relative importance of organic nitrogen (ON) and inorganic nitrogen (IN) as nitrogen sources ... more The relative importance of organic nitrogen (ON) and inorganic nitrogen (IN) as nitrogen sources for the phytoplankton communities were studied through a seasonal time series of nitrogen species in the eastern Arabian Sea. Seasonal data on nitrogen species showed that ON dominates the system throughout the year and account for > 90% of the total nitrogen (TN) during north east monsoon (NEM). The average ON concentration in the study region was 11.5 μM during NEM as compared to 7.2 μM during south west monsoon (SWM). The contribution of picoplankton to the total phytoplankton pool (f pico) increased from 19% during SWM to 36% in NEM. Along with cyanobacteria, the diatoms Thalassionema nitzchoides and Thalassiosira sp. and among the dinoflagellates Pronoctiluca sp. were found to proliferate in ON rich waters. We suggest atmospheric deposition, riverine-input, resuspension of bottom sediment and ground water intrusion as the possible sources of ON in the study region. 1999). Glibert et al. (2004) gave evidences for dissolved organic nitrogen (DON) uptake during a cyanobacterial bloom in Florida Bay. Among all the nitrogen species, the DON comprises the largest component (60-69%) of total dissolved nitrogen in rivers, estuaries, coastal and open oceanic surface waters (Bronk, 2002; Sipler and Bronk, 2015), and could drive ecological shift. Previously, Parab et al. (2006) have reported a seasonal community shift in the eastern Arabian Sea from diatoms (SWM) to dinoflagellates (fall inter monsoon (FIM)) to cyanobacteria (NEM) associated with IN species. This would also have a profound effect on the oceanic CO 2 sequestration capacity as the composition of the phytoplankton community affects the magnitude and efficiency of carbon export (Durkin et al., 2016). Here we hypothesize that ON plays an important role in the seasonal phytoplankton community shift in the Arabian Sea coastal waters (ASCW). We present for the first time, the seasonal variation of ON in the ASCW, its possible sources and role in phytoplankton diversity. This study also

Marine Ecology, 2019

Microzooplankton (MZP) refers to a group of organisms defined by their size (20-200 µm), function... more Microzooplankton (MZP) refers to a group of organisms defined by their size (20-200 µm), function, and limited swimming ability (Dussart, 1965). These are classified into two groups, mixotrophic and heterotrophic (Protozoans and Metazoans). Protozoans include dinoflagellates, ciliates, radiolarians, and foraminifera, whereas metazoans contain rotifers, meroplankton, and holoplankton larvae (Calbert & Alcaraz, 2007). They are overall capable of exploiting pico-/nanoplankton, which in turn are utilized by other large trophic components such as mesozooplankton (Stoecker & Capuzzo, 1990). Their intermediary role between bacterioplankton and large mesozooplankton through grazing on bacterioplankton thus controls the bacterial community (Azam et al., 1983; Bernard & Rassoulzadegan, 1993; Gifford & Dagg, 1991). This is particularly important in stratified oligotrophic water, which is seasonally experienced in the study region in the central Arabian Sea. Most tropical ocean regions experience strong stratification seasonally and remains well mixed for