Macrobenthic community structure of coastal Arabian Sea during the fall intermonsoon (original) (raw)
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Deep Sea Research Part II: Topical Studies in Oceanography, 1999
Zooplankton communities, studied in the surface mixed layer on a 1600 m transect across the Arabian Sea, were found to differ in their temporal and spatial response to seasonal forcing. The transect studied, spanned seasonally eutrophic upwelling, mesotrophic downwelling and aseasonal oligotrophic waters. The nano-and microzooplankton communities constituted a relatively constant compartment in the tropical monsoon ecosystem, whilst the mesozooplankton showed a clear response to both upwelling and season. The heterotrophic nanoflagellates were concentrated in the surface mixed layer, except in the eutrophic upwelling waters of the SW monsoon. They reached maximum cell concentrations of 855 ml\ during the SW monsoon and a maximum biomass of 8.4 mg C m\ during the intermonsoon. Nanozooplankton standing stocks, in the surface mixed layer, ranged between 7 and 333 mg C m\, with highest stocks found during the intermonsoon. The microzooplankton community was dominated by Protozoa, particularly aloricate ciliates and heterotrophic dinoflagellates, which accounted for up to 99% in terms of numbers and up to 71% of the biomass. Sarcodines and metazoan nauplii were recorded in lower numbers ((400 l\). The microzooplankton were also concentrated in the surface mixed layer during both periods, except in the eutrophic coastal waters during the SW monsoon, when relatively high biomass values were found below the mixed layer depth. Their standing stocks, in the surface mixed layer, ranged between 50 and 182 mg C m\, with the highest concentration found in the mesotrophic offshore waters during the late monsoon period. Total mesozooplankton standing stocks, in the surface 100 m, decreased with distance from the coastal to offshore waters and between seasons, decreasing from 1248 to 238 mg C m\ during the late SW monsoon and 656-89 mg C m\ during the 0967-0645/99/$ -see front matter 1999 Elsevier Science Ltd. All rights reserved. PII: S 0 9 6 7 -0 6 4 5 ( 9 8 ) 0 0 1 2 9 -5 following intermonsoon. The largest size class, of 1000-2000 m sized organisms, dominated throughout except at the oligotrophic station during the intermonsoon period, when the smallest class, of 200-500 m, were more important. The shift in size structure from large to small zooplankton occurred in response to a shift in dominance from large to small phytoplankton cells both spatially, along a eutrophic-oligotrophic gradient, and seasonally. These responses are a result of the physical forcing associated with the monsoon seasons in the Arabian Sea.
Macrobenthic Community Structure Response to Coastal Hypoxia off Southeastern Arabian Sea
Journal of Coastal Zone Management, 2016
The analysis of changes in macrobenthic community using multivariate statistical techniques has been applied to find the structure by the environmental condition. The aim of the study was to evaluate macrofaunal community patterns between natural occurrence of coastal hypoxia condition (30 to 100 m depth) and normoxic bottom waters over the Southeastern Arabian Sea (SEAS). The macrofaunal communities patterns were analyzed by using various statistical methods (e.g. rank correlation, hierarchical clustering, nMDS, BIO-ENV). A clear seasonal difference was found in macrofaunal abundance, biomass, taxonomic composition, diversity and their relation to environmental conditions. Multivariate analysis of Non Multidimensional Scaling (nMDS) showed two major groups macrofaunal communities and ANOSIM results showed a significant difference between macrofaunal community structure in between nornaxia and hypoxia conditions (R=0.913). Spearman rank correlation (using BIO-ENV procedure included in PRIMER, V.6) showed the highest correlation of dissolved oxygen (R=0.678) with community structure. The SIMPER analysis illustrated community pattern changed seasonally with Paraprionospia cordifolia (20.03%) dominated during hypoxia whereas Tharyx sp. (22.63%) dominated in nornaxia conditions. The macrofaunal community patterns revealed contrasting pattern with two seasons, perhaps due to the dissolved oxygen (DO).
Phytoplankton community structure in the Arabian Sea during and after the SW monsoon, 1994
Deep Sea Research Part II: Topical Studies in Oceanography, 1999
Diatoms, dinoflagellates, coccolithophores, nanoflagellates, picophytoplankton and procaryote algae (Synechococcus spp. and prochlorophytes) were quantified by microscopy and flow cytometry, and their biomass determined, at 12 stations along a 1600 km transect across the Arabian Sea at the end of the SW monsoon in September, and during the inter-monsoon period of November/December 1994. The transect spanned contrasting oceanic conditions that varied from seasonally eutrophic, upwelling waters through mesotrophic, downwelling waters to permanently oligotrophic, stratified waters. The overall diversity of diatoms, dinoflagellates and coccolithophores along the transect was not significantly different between the SW monsoon and inter-monsoon. However, diatoms showed greatest diversity during the SW monsoon and coccolithophores were most diverse during the inter-monsoon. Integrated phytoplankton standing stocks during the SW monsoon ranged from 3 to 9 g C m\ in the upwelling eutrophic waters, from 3 to 5 g C m\ in downwelling waters, and from 1 to 2 g C m\ in oligotrophic waters. Similar phytoplankton standing stocks were found in oligotrophic waters during the inter-monsoon, but were ca. 40% lower compared to the SW monsoon in the more physically dynamic waters. Phytoplankton abundance and biomass was dominated by procaryote taxa. Synechococcus spp. were abundant (often '10 cells l\) during both the SW monsoon and inter-monsoon, where the nitrate concentration was *0.1 mol l\, and often dominated the phytoplankton standing stocks. Prochlorophytes were restricted to oligotrophic stratified waters during the SW monsoon period but were found at all stations along the transect during the inter-monsoon, dominating the phytoplankton standing stocks ('40%) in the oligotrophic region during this period. Of the nano-and micro-phytoplankton, only diatoms contributed significantly to phytoplankton standing stocks, and then only in near-shore upwelling waters during the SW monsoon. There were 0967-0645/99/$ -see front matter 1999 Elsevier Science Ltd. All rights reserved. PII: S 0 9 6 7 -0 6 4 5 ( 9 8 ) 0 0 1 2 2 -2 significant changes in the temporal composition of the phytoplankton community. In nearshore waters a mixed community of diatoms and Synechococcus spp. dominated during the SW monsoon. This gave way to a community dominated by Synechococcus spp. in the intermonsoon. In the downwelling zone, a Synechococcus spp. dominated community was replaced by a mixed procaryote community of Synechococcus spp. and prochlorophytes. In the oligotrophic stratified waters, the mix of procaryote algae was replaced by one dominated by prochlorophytes alone.
Macrobenthic community structure within and beneath the oxygen minimum zone, NW Arabian Sea
Deep Sea Research Part II: Topical Studies in Oceanography, 2000
Investigations of macrobenthos were carried out within and beneath the oxygen minimum zone (OMZ, (0.5 ml l\) during Fall 1994 on the Oman margin, NW Arabian Sea. Six stations (400, 700, 850, 1000, 1250 and 3400 m) were characterized with respect to macrofaunal abundance, biomass, body size, taxonomic composition, diversity and lifestyles, and the relation of these parameters to environmental conditions. The OMZ (400}1000 m) was dominated by a dense (5818}19,183 ind m\), soft-bodied assemblage consisting largely (86}99%) of surface-feeding polychaetes. Spionids and cirratulids dominated at the 400-and 700-m stations, paraonids and ampharetids at the 850-and 1000-m stations. Molluscs and most crustaceans were common only below the OMZ (*1250 m); a species of the amphipod Ampelisca was abundant within the OMZ, however. Both density and biomass were elevated within the OMZ relative to stations below but body size did not di!er signi"cantly among stations. The lower OMZ boundary (0.5 ml l\) was not a zone of enhanced macrofaunal standing stock, as originally hypothesized. However, abundance maxima at 700}850 m may re#ect an oxygen threshold (0.15}0.20 ml l\) above which macrofauna take advantage of organically enriched sediments. Incidence of burrowing and subsurface-deposit feeding increased below the OMZ. Species richness (E[S ]), diversity (H) and evenness (J) were lower and dominance (R1D) was higher within than beneath the OMZ. Within-station (between-boxcore) faunal heterogeneity increased markedly below the OMZ. Surface sediment pigment concentrations and oxygen together explained 96}99% of the variance in measures of E [S ], H and J across the transect; 0967-0645/00/$ -see front matter 1999 Elsevier Science Ltd. All rights reserved. PII: S 0 9 6 7 -0 6 4 5 ( 9 9 ) 0 0 1 0 3 -4 grain size and % TOC did not yield signi"cant regressions. Pigments, assumed to re#ect food availability and possibly oxygen e!ects on organic matter preservation, were negatively correlated with species richness and evenness, and positively correlated with dominance. The reverse was true for water depth. Macrobenthic patterns of calci"cation and lifestyle within the Oman margin OMZ (0.13}0.3 ml l\) match the dysaerobic biofacies of paleo-environmental reconstruction models.
The south eastern Arabian Sea is characterized by moderate coastal upwelling, high biological production and subsurface oxygen depletion during the southwest monsoon (June–September). Concurrently, a seasonal closure to trawling activities (15th June–31st July) is implemented here, as a sustainable ecosystem management practise. The effects of monsoon driven environmental changes and consequences of trawling cessation on macrofauna were assessed, based on surveys at 12 sites (30–200 m) preceding and during different phases of the southwest monsoon. Macrofaunal density and biomass increased considerably towards the mid and late monsoon along the inner shelf (30–50 m) where trawling is intense , while no temporal changes were observed along the outer shelf (100–200 m). Density increased four-folds at the 30 m contour and three-folds at 50 m, while biomass nearly doubled at both depths, reflecting a marked increase in density of polychaetes (61–87% of macrofauna). The disproportionate increase in faunal density and biomass along the inner shelf (30–50 m) was due to abundance of juvenile polychaetes and dominance of small-sized opportunists towards late monsoon (August–September). A concurrent hike in nominal species count of polychaetes was also observed in the study area. The increase in polychaete standing stock and high density of planktonic larvae during onset and peak monsoon , coupled with occurrence of juveniles as well as gamete-bearing adults in sediments, indicates that the southwest monsoon is a peak breeding season for the dominant polychaetes in the region. The trawl-ban during this period facilitates the recoupment of benthos by maximising spawning success and larval settlement, thereby enhancing overall ecosystem integrity.
Continental Shelf Research, 2018
The spatio-temporal variation of mesozooplankton assemblages and the relative environmental variables were assessed in a coastal upwelling system. Remarkable seasonal variations were found in the mesozooplankton community structure and Chl-a concentration due to the seasonal shift in the environmental variables. Copepods were found to be the dominant group during the winter monsoon (WM) and spring inter monsoon (SIM) seasons whereas, cladocerans (Evadne tergestina and Penilia avirostris) were dominant during the summer monsoon (SM) which may be attributed to the availability of preferential food and favorable environmental conditions (viz., temperature and salinity etc.). Multivariate statistical analysis revealed that the distribution and their possible spatio-temporal pattern of dominant copepods (Acrocalanus gibber, Acartia danae, Nanocalanus minor and Oncaea venusta), siphonophores (Chelophyes appendiculata and Diphyes chamissonis) and pelagic tunicates (Doliolida sp.) synchronized with their specific food habits and adaptive mechanism. The present findings emphasize the significance of the trophic relationship between Chl-a concentration and mesozooplankton abundance in the coastal waters of Kochi, southeastern Arabian Sea.
Marine Environmental Research, 2021
Coastal upwelling in the south eastern Arabian Sea (SEAS) leads to oxygen depletion over the continental shelf during the summer monsoon season (June-September), with latitudinal gradients in intensity. Based on two surveys in the onset (June) and peak (August) phases of the summer monsoon, the present study evaluates the response of macrozoobenthic communities (size >500 μm) to upwelling and consequent hypoxia (dissolved oxygen <0.2 ml/l) in the central sector of the SEAS shelf (10-12˚N, 30-200 m). From the onset to the peak monsoon, macrozoobenthic density increased five-fold in the mid-shelf (50 m water depth), and nearly doubled in the outer shelf (100 m water depth) and shelf edge (200 m water depth). This was found to be a direct consequence of recruitment and proliferation of opportunistic polychaetes, particularly the spionid Paraprionospio pinnata, which was the single dominant species (52-78%) at all depths during the peak monsoon. With the establishment of the monsoon, the shelf communities (particularly 50-100 m depth sites) are thus transformed from relatively diverse assemblages to dense, single-species dominated ones. The shelf-edge communities (150-200 m depths), which are impacted with the perennial Arabian Sea oxygen minimum zone, and therefore harbour opportunist-dominated communities year-round. It is postulated that larvae of hypoxia-tolerant taxa are transported from the shelf edge by the process of upwelling onto the shelf. The settlement and survival of these larvae are regulated by nature of shelf sediments and by the prevailing hypoxia. Thus, substantial recruitment of opportunists occurred in the outer and mid-shelf (50-100 m), but not in the inner shelf (30 m), where sedimentation from river discharge hindered settlement and survival of juveniles.
Deep Sea Research Part II: Topical Studies in Oceanography, 2018
This work examines the spatial variability among mesozooplankton abundance and copepod species diversity along the continental margin prior to the onset of southwest monsoon in the eastern Arabian Sea during the year 2011. The eastern Arabian Sea experiences seasonal hypoxia during the receding phase of monsoon that corresponds to low copepod abundance in the slope region. Collectively, fifty copepod species were identified over the continental margin where the diversity index (H') ranged between 2.59 and 3.73. Bray-Curtis cluster analysis clustered the stations into three groups that corresponded to the continental shelf, slope and break reaches of the eastern Arabian Sea. This spatial variability among the groups is mainly ascribed to changes in the relative contributions of the prevailing species. The distinct genera of the continental shelf were Microsetella spp. and Temora turbinata; at the slope region, Oncaea spp. and at shelfbreak, Pleuromamma indica. Overall, herbivorous copepods were numerically abundant at the continental shelf and carnivores at the slope. The discrepancy between the distributions of herbivorous versus carnivorous copepod assemblages may be attributed to environmental factors such as ambient water dissolved oxygen and phytoplankton biomass.
Status of macrobenthic communities in the hypersaline waters of the Gulf of Salwa, Arabian Gulf
Journal of Sea Research, 2015
The spatial extent of hypersaline marine ecosystems is very limited and therefore they have received only little scientific study. Here, we present the status of macrobenthic communities in a hypersaline water body, the Gulf of Salwa (Saudi Arabia part), in the Arabian Gulf and assess the natural stress, if any, in the communities. The Gulf of Salwa is nearly isolated from the main water body of the Arabian Gulf and shows a progressive southward increases in salinity (up to 63 during summer) and temperature (up to 40°C during summer) due to the southward decrease in tidal flushing. The study reveals that the benthic communities in the southern region (south of 25°10′ N) of the Gulf of Salwa are under natural stress, while the deeper, the northern, and the inner bay regions have healthier benthic communities than the south. In the southern region, there were 87 to 93% reduction in polychaete species, 49 to 57% reduction in species diversity of polychaetes and 70 to 71% in nonpolychaete taxa compared to the northern region. The present study identified some opportunistic taxa such as Fabricia sp., Heteromastus filiformis, Platynereis insolita and Nereis sp. 1 and non-polychaetes such as chironomid larvae, podocops and cumaceans capable of adapting to the hypersaline environment in the Gulf of Salwa when salinity exceeded 60 and temperature exceeded 35°C during summer.