Seasonal biomass and composition of mesozooplankton communities in Sea of Oman and Arabian Sea

Samples of mesozooplankton were collected and analysed from two contrasting coastal regions; Muscat (Sea of Oman) and Salalah (Arabian Sea). Copepods represented 41-44% of total biomass. Small species such as Temora turbinata, Oithona spp., Oncaea spp. and Microsetella spp. were abundant but their contribution to total biomass was small compared with the much rarer but larger species such as Eucalanidae, Calanoides natalis or Labidocera pavo. In Muscat, T. turbinata was particularly abundant, whereas C. natalis and Eucalanidae were more abundant in Salalah. Biomass in Muscat seems to be associated with a series of different species peaks showing no clear seasonality. However, biomass in Salalah followed a distinct seasonality with higher biomass during southwest monsoon., a seasonality pattern was observed with the meroplankton/holoplankton ratio in Salalah but not in Muscat. PERMANOVA analysis indicated that the communities structure showed geographic and seasonal differences. The effect of seasonality was particularly visible when the dataset included non-copepods, highlighting the role of this group in structuring mesozooplankton communities. Non-copepods such as chaetognaths and doliolids had a high biomass contribution to both geographic areas. normalized size spectra in both regions were similar and suggested that smaller species were underestimated Whereas, large species, especially chaetognaths, were over-represented.