Copepods are the dominant marine zooplankton and perform important functions in the marine food web. However, copepod traits have not been studied in many waters. We studied the copepod community under influence of the Mekong River and the Southern Vietnamese coastal upwelling, based on their functional traits, during the southwest monsoon period in 2016. Fourteen trait categories of four key functional traits (trophic-groups, feeding-types, reproductive-strategies and diel migration) of copepod data were analyzed to investigate how environmental gradients impact on their distribution and abundance among the four defined habitats: Mekong River (MKW), upwelling (UpW), nearshore (OnSW) and offshore waters (OSW). There were seven functional groups identified in the study waters based on multiple correspondence analysis of distribution, abundance and traits of 139 copepod species. Herbivorous, current-feeding and sac-spawning copepods were dominant in all habitats with the highest abundance in OSW. Specifically, herbivorous species dominated in MKW and UpW, whereas omnivorous species dominated in OnSW and OSW. Sac-spawners dominated in all habitats, but decreased from MKW and UpW to OnSW and lowest in OSW. Cruise feeders were 2-fold higher than ambush feeders in the UpW, but the opposite was observed in the other habitats. The results suggest that impacts of Mekong River and coastal upwelling led to distinctive copepod assemblages with specific functional traits.
Zooplankton samples were collected at 16 stations in the coastal waters of Son Tra peninsula, Da Nang city in dry season (7/2016). At each station, zooplankton samples were collected by using Juday net (mouth diameter: 37 cm, mesh-zise: 200 µm) from 1 m above bottom to surface. 112 species belonging to 11 zooplankton groups were identified. Copepod was a dominant group with 67 species, followed by Tunicate (13) and Gastropod (7). The Northeast and Northwest areas of Son Tra peninsula have a higher biodiversity than the South and Southeast based on number of species, species richness value. An average density of zooplankton was 7.768 ins.m-3 and was decided by copepod density (3.759 inds.m-3 on average). Station 4 had the highest number of individual and station 18 had the lowest zooplankton density. Oikopleura fusiformis was dominant in most of stations in the north area (22.16%) and in the northwest (15.97%), while copepod species Paracalanus crassirostris was dominant in the northwest (16.51%) and in the south (24.57%) of Son Tra based on SIMPER analysis (90%).
This paper presents the results of the surveys on zooplankton in Thi Nai lagoon from 2001 to 2020. There were 179 species found in the lagoon, among which Copepod was the dominant group with 97 species (50.78% of total species), followed by Cladocera with 20 species (10.36%), Hydrozoa with 18 species (9.33%), Tunicata with 11 species (5.7%) and Siphonophora with 10 species (5.18%). Based on Bray-Curtis similarity analysis of zooplankton community and the station position, the sampling stations in the lagoon were grouped into three areas: The upper lagoon (UP), the middle (MI), and the mouth of the lagoon (MO). Among the surveyed years, there was a slight variation in the species number, while the density decreased by time and was especially low in 2020. Zooplankton density was much lower in the rainy season compared to that in the dry season, while the species number was less varied. Analysis of the differences between the areas in the lagoon demonstrated a clear distribution pattern of zooplankton with a decreasing density and an increasing number of species from upper lagoon to the mouth of the lagoon. Zooplankton diversity was less affected by time and only the Pielou index in the MI area between 2004 and 2009 was significantly different. Analysis of the various indices between seasons showed that the MO area was less volatile than the two other regions. The multi-dimensional scaling analysis demonstrated that zooplankton community was less variable by regions (50% similarity) compared to by the years (only 30% of similarity), except in 2009 and 2020 when differences among the areas were significant. Seasonal community change between the dry and rainy seasons was 30%.
Zooplankton samples in the biosphere reserve of Cu Lao Cham - Hoi An were collected at 20 stations belonging to 3 ecosystems: Mangrove palm - seagrass, transition area and coral reef in rainy season (11/2015) and dry season (6/2016) to determine biodiversity of the biosphere reserve of Cu Lao Cham - Hoi An. 161 species belonging to 16 zooplankton groups were recognized, copepoda was a dominant group with 92 species, followed by cladocera (15 species) and tunicata (13 species). Mangrove palm - sea grass had a different zooplankton structure compared with transition area and coral reef with a lower number of species and similarity index about 40%. The average density of zooplankton in study areas in dry season (24,559 ± 24,700 inds.m-3) were 4 times higher than in rainy season (6,124 ± 6.554 inds.m-3) and dominated by copepoda. The euryhaline cladocera (Bosmina longirostris), freshwater cladocera (Ceriodaphnia rigaudi) and freshwater copepoda (Microcyclops varicans) were dominant in mangrove palm - seagrass ecosystem. Meanwhile, in coral reef ecosystem, the small copepods (genus Oncaea, Oithona) and Tunicata were dominant. Biodiversity indices were low in mangrove - palm and increase from transition area to coral reef ecosystem.
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