MESOZOOPLANKTON DISTRIBUTION IN THE NORTHEASTERN ARABIAN SEA DURING SPRING INTERMONSOON

Authors

JANI MOL, M., PILLAI, H. U. K.

Abstract

ABSTRACTMesozooplankton forms a vital part of the pelagic food web and plays a significant role in the coastal and oceanic biogeochemical cycle of carbon and other elements. They are the connecting link between primary producers and higher trophic levels. The materials for the present study form part of the in-house marine research project of the Zoological Survey of India, Kolkata. Sampling and data collection of Mesozooplankton as well as environmental variables were carried out on board FORV Sagar Sampada in March 2019.Samplings were carried out from fourteen stations including both coastal ($>50text{m}$) and oceanic ($<1000text{m}$) waters along the Northeastern Arabian Sea (NEAS) covering $15^circtext{N} - 21^circtext{N}$ Latitude. Mesozooplankton samples were collected with a Bongo Net, and related hydrographic parameters (temperature, salinity, dissolved oxygen, and chlorophyll a) were collected using a CTD profiler (SEABIRD).Key Findings:Sea Surface Temperature (SST): Showed a sharp decrease towards the northern transects in both coastal and oceanic waters. Coastal SST ranged from $24.33^circtext{C}$ to $27.79^circtext{C}$; oceanic SST ranged from $25.13^circtext{C}$ to $28.68^circtext{C}$.Sea Surface Salinity (SSS): Showed a sharp decrease towards northern transects. Coastal SSS ranged from $35.25$ to $36.62$; oceanic SSS ranged from $35.51$ to $36.65$.Dissolved Oxygen (DO): Displayed an increasing trend towards the northern transects, ranging from $4.55text{ ml/l}$ to $5.24text{ ml/l}$ in coastal waters and $4.79text{ ml/l}$ to $5.15text{ ml/l}$ in oceanic waters.Chlorophyll a: Recorded higher values in coastal regions ($0.18text{ mg/l}$ to $2.31text{ mg/l}$, av: $1.45text{ mg/l}$) compared to oceanic waters ($0.02text{ mg/l}$ to $2.02text{ mg/l}$, av: $0.36text{ mg/l}$).Biovolume & Abundance: Average mesozooplankton biovolume (excluding large gelatinous components) showed a threefold increase in coastal waters ($text{av. } 1.39text{ ml}cdottext{m}^{-3}$) compared to oceanic regions ($text{av. } 0.38text{ ml}cdottext{m}^{-3}$). Numerical abundance was higher in coastal waters ($text{av. } 605text{ No.}cdottext{m}^{-3}$, range: $82 - 1354text{ No.}cdottext{m}^{-3}$) than in oceanic waters ($text{av. } 524text{ No.}cdottext{m}^{-3}$, range: $108 - 1069text{ No.}cdottext{m}^{-3}$). Gelatinous blooms (salps and siphonophores) were prominent in coastal waters ($17^circtext{N}, 18^circtext{N}, text{and } 19^circtext{N}$ Latitudes).Community Structure: A total of 21 mesozooplankton taxa (holo- and meroplankton) were recorded (19 taxa in coastal, 21 in oceanic). Copepods were the dominant group overall (Coastal: $text{av. } 61.07%$, Oceanic: $text{av. } 56.69%$). Secondary dominant groups in coastal waters included Chaetognaths ($14.76%$), Cladocerans ($9.39%$), Decapod larvae ($5.69%$), Lucifer ($2.63%$), Stomatopod larvae ($2.30%$), and Salps ($1.37%$). In oceanic waters, Ostracods were the second most dominant ($22.93%$), followed by Salps ($12.51%$), Chaetognaths ($2.84%$), and Decapods ($1.23%$).

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The authors list and abstract were imported from bioRxiv on 06 Aug 2026.

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