A study on microzooplankton community from the coastal waters of eastern Arabian Sea: emphasis on the dominance of heterotrophic dinoflagellates.

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 dinoflagellates (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, Prorocentrum micans, Protoperidinium breve, Protoperidinium latistriatum, and Protoperidinium granii. The statistical analysis (Canonical correspondence analysis and 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.

Microbial diversity from the continental shelf regions of the Eastern Arabian Sea: A metagenomic approach.

The marine microbiome is a complex and least-understood habitat, which play a significant role in global biogeochemical cycles. The present study reported the culture-independent assessment of microbial diversity from the Arabian Sea (AS) sediments (from Gujarat to Malabar; at 30 m depth) by using metagenome sequence analysis. Our results elucidated that bacterial communities in the Malabar coastal region are highly diverse than the Gujarat coast. Moreover, Statistical analysis (Spearman rank correlation) showed a significant correlation co-efficient value (r = P < 0.001) between microbial communities and physicochemical parameters (salinity and dissolved oxygen) in the water column. A total of 39 bacterial phyla were recorded from the eastern side of AS, of which six phyla Proteobacteria, Bacteroidetes, Actinobacteria, Cyanobacteria, Firmicutes, and Planctomycetes were found to be the most dominant group. The most dominant genus from Valapad region (Malabar Coast) was found to be Halomonas sp., while other regions were dominated with Psychrobacter pulmonis. The subsequent Principal Coordinate Analysis (PCoA) showed 99.53% variance, which suggests that, highly distinct microbial communities at Valapad (Malabar Coast) sampling location than other sites. Moreover, the microbial metabolic activity analysis revealed the important functions of microbial communities in the AS are hydrocarbon degradation, polymer degradation, nutrient oxidation and sulphate reduction (biodegradation process). Further extended studies are needed to be carried out for better understanding the functional diversity of microbial communities from the marine sediments.

A checklist of tintinnids (loricate ciliates) from the coastal zone of India.

We report here a checklist of tintinnids (loricate ciliates) for the coastal zone of India. Based on available literature (1978 to 2017), a total of 25 stations were studied from 5 distinct areas of Indian coastal waters. A total of 151 species of 33 genera belonging to 14 families of tintinnids were documented. Diversity patterns of tintinnids were recorded higher along the west coast (30 genera and 106 species) than the east coast of India (20 genera and 93 species). Among tintinnids families, the Codonellidae (2 genera and 52 species, 20%) and the Tintinnidae (8 genera and 21 species, 19%) are the major contributors to the total tintinnids diversity in the Indian coastal zone.

Diversity and distribution of heterotrophic dinoflagellates from the coastal waters of Port Blair, South Andaman.

The interaction between the environment and heterotrophic dinoflagellates inhabiting coastal waters of South Andaman was studied based on year round collections made during September 2012-August 2013 in the bay, eastern, and western region of South Andaman. The distribution pattern of microzooplankton in South Andaman showed high abundance in eutrophic waters (bay region) and gradually decreased towards the off shore region. Microzooplankton community comprised of six different taxa, viz. tintinnids, heterotrophic dinoflagellates, non-loricate ciliates, Foraminifera, Rotifera, and Copepoda (nauplii). Tintinnids were the major component of the microzooplankton (43.8 ± 7%) followed by heterotrophic dinoflagellates (34 ± 12%) and copepod nauplii (18.8 ± 4.0%). This study focused on heterotrophic dinoflagellates which ranked next to tintinnids in overall abundance and contributed 38-42% in the bay, 22-37% in the eastern, and 15-29% in the western region to the microzooplankton community. Dinoflagellates showed a positive correlation with salinity and a negative correlation with dissolved oxygen and chlorophyll a (r = - 0.3). Abundance of heterotrophic dinoflagellates in this area may be due to their diverse and advantageous mode of nutrition. A total of 35 species belonging to 8 genera of heterotrophic dinoflagellates were recorded during the study period. Heterotrophic dinoflagellates showed a great potential to thrive in low oxygenated and low productive area (p < 0.001, Mann-Whitney test). Relatively higher diversity (H') in the dinoflagellates population was found in the bay region (avg. H' = 3.46).

Comparison between microzooplankton population in polluted and moderately polluted coastal waters of Port Blair, South Andaman.

We report on the seasonal and spatial variations of microzooplankton between polluted and moderately polluted coastal waters of South Andaman Island, in relation to certain physicochemical and biological parameters. Microzooplankton communities were studied and recorded for 1 year (September 2011 to August 2012) during the northeast monsoon, the intermonsoon, and the southwest monsoon periods. We recorded a total of 75 species belonging to 29 genera, of which polluted waters encompassed 71 species (28 genera). In contrast, only 59 species (22 genera) were recorded in the moderately polluted waters. We discovered that taxonomic composition, biomass, and abundance of microzooplankton not only varied spatially but also altered seasonally. It is noteworthy to state that the northeast monsoon played a significant role in controlling the abundance of microzooplankton in South Andaman coastal waters.

Abundance, species composition of microzooplankton from the coastal waters of Port Blair, South Andaman Island.

BACKGROUND: Microzooplankton consisting of protists and metazoa <200 µm. It displays unique feeding mechanisms and behaviours that allow them to graze cells up to five times their own volume. They can grow at rates which equal or exceed prey growth and can serve as a viable food source for metazoans. Moreover, they are individually inconspicuous, their recognition as significant consumers of oceanic primary production. The microzooplankton can be the dominant consumers of phytoplankton production in both oligo- and eutrophic regions of the ocean and are capable of consuming >100% of primary production. RESULTS: The microzooplankton of the South Andaman Sea were investigated during September 2011 to January 2012. A total of 44 species belong to 19 genera were recorded in this study. Tintinnids made larger contribution to the total abundance (34%) followed in order by dinoflagellates (24%), ciliates (20%) and copepod nauplii (18%). Foraminifera were numerically less (4%). Tintinnids were represented by 20 species belong to 13 genera, Heterotrophic dinoflagellates were represented by 17 species belong to 3 genera and Ciliates comprised 5 species belong to 3 genera. Eutintinus tineus, Tintinnopsis cylindrical, T. incertum, Protoperidinium divergens, Lomaniella oviformes, Strombidium minimum were the most prevalent microzooplankton. Standing stock of tintinnids ranged from 30-80 cells.L-1 and showed a reverse distribution with the distribution of chlorophyll a relatively higher species diversity and equitability was found in polluted harbour areas. CONCLUSIONS: The change of environmental variability affects the species composition and abundance of microzooplankton varied spatially and temporarily. The observations clearly demonstrated that the harbor area differed considerably from other area in terms of species present and phytoplankton biomass. Further, the phytoplankton abundance is showed to be strongly influenced by tintinnid with respect to the relationship of prey-predator. Consequently, further investigation on microzooplankton grazing would shed light on food web dynamics.