The spatial variability of mesozooplankton (MZ) community characteristics, with an emphasis on the predominant taxa, copepods, were evaluated between two distinct coastal water environments of Mangalore: the Netravati-Gurupura estuarine system (NGES) and the adjacent nearshore waters (<20 m depth) on the southwest coast of India during winter 2018. The nearshore waters were characterised by uniformly distributed hydrographic properties, particularly in terms of water column temperature, salinity and turbidity. This well-mixed water column likely stimulated increased phytoplankton chlorophyll a concentrations (av. 2.9±2.2 mg/m3), which in turn supported higher MZ biomass (av. 0.4±0.15 mL/m3) and abundance (av. 6889±3387 ind./m3) in the nearshore waters. In contrast, the NGES exhibited highly variable hydrographic conditions, leading to inconsistent chlorophyll a (av. 3.2±3.7 mg/m3), along with significantly lower MZ biomass (av. 0.1±0.2 mL/m3) and abundance (av. 238±339 ind./m3). The MZ community was dominated by herbivorous copepods (HCs), particularly Bestiolina similis, in the entire study region; however, the nearshore waters supported a more diverse taxon. The overall dominance of HCs, e.g., B. similis and Pseudodiaptomous aurivillii, in the nearshore waters, indicates the presence of stable hydrographic conditions, especially consistently higher salinity and chlorophyll a level. In contrast, the unstable hydrographic conditions in the NGES, primarily reflected in the uneven salinity distributions, likely contributed to the reduced MZ biomass and abundance. The relative increase in the abundance of B. similis observed exclusively in the euhaline zones of the estuary highlights the significant influence of neritic waters.
Figure 1. The details of study region (near shore waters of Mangalore and Netravati-Gurupura estuarine system-NGES) and sampling locations.
Figure 2. Vertical distribution of water column temperature (℃) (a and d), salinity (b and e) and turbidity (NTU) (c and f) in the near shore waters of Mangalore and NGES.
Figure 3. Spatial distribution of DO, ammonium, nitrate, phosphate and silicate in the near shore waters (surface) and NGES.
Figure 4. Spatial distribution of phytoplankton chlorophyll a in the nearshore waters (surface) of Mangalore (a) and NGES (b).
Figure 5. Spatial distribution of MZ biomass and abundance in the near shore waters (surface) of Mangalore (a) and NGES (b).
Figure 6. Spatial distribution of major MZ taxa and copepod species in the nearshore waters (surface) of Mangalore (a and b) and NGES (c and d).
Figure 7. Percentage composition of various copepod species based on their feeding guilds.
Figure 8. Representation of sampling stations by Dendrogram (a) and NMDS ordination (b) based MZ abundance and composition in the study region.
Figure 9. Bubble plots representing the abundance of major copepod characterizing species (SIMPER analysis) in the nearshore waters of Mangalore and NGES superimposed in the NMDS ordination.
Figure 10. RDA triplots depicting the interrelationships between MZ biomass and abundance of dominant taxa, and environmental variables in the nearshore waters of Mangalore (a) and the NGES (b). Sampling stations are indicated by blue circles; environmental parameters are represented by red arrows; MZ parameters (Bio-Biomass, Cpd-Copepod, Cdc-Cladocera, Dcp-Decapoda larvae, Luc-Lucifer, Ctg-Chaetognatha, Bvl-Bivalve larvae, Npl-Nauplius larvae, Cpl-Copepodite) are represented by green arrows.
Figure 11. RDA triplots depicting the interrelationships between major copepod species and environmental variables in the nearshore waters of Mangalore (a) and the NGES (b). Sampling stations are indicated by blue circles; environmental parameters are represented by red arrows; Copepods (BS-Bestiolina similis, PSA-Pseudodiaptomus aurivillii, CC-Onychocorycaeus catus, TT-Temora turbinata, EA-Euterpina acutifrons, UV-Undinula vulgaris AD-Acartia danae, CF-Centropages furcatus, PS-Pseudodiaptomus serricaudatus) are represented by green arrows.
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