Seasonal and spatial distribution of mesozooplankton in a tropical estuary, Nha Phu, South Central Viet Nam

Abstract

This study provides a description of mesozooplankton (holo-and meroplankton) abundance, biomass and diversity patterns inside and outside a tropical estuary (Nha Phu Estuary, Khanh Hoa, Viet Nam). In total 185 zooplankton species have been recorded during the study period (2009)(2010), copepods contribute with the largest share of species (more than 100), Tunicata with 20, Cnidaria with 17 and Chaetognatha with 9 species. At the most species rich site the number of zooplankton species varies between 55 and 123. The number of species and the annual variation in numbers declines towards the head of the estuary (14-37 species). In contrast, the highest numbers of individuals occur in the inner part of NPE. Calanoids that are the most abundant group of the copepods occur in densities up to 28.2 ind. L −1 (Aug. 9). At 'Outer NPE' and 'Outside NPE' the maximum density of calanoids is 5.8 and 10.7 ind. L −1 , respectively. The declining diversity of zooplankton towards the head of the estuary is also supported by various indices (Shannon's index, Margalef's index). A cluster analysis on similarity of species supports a clustering of the inner NPE sites vs the other sites. There is a general separation between the dominant copepod species in the inner (Bestiola sp., Acartia pacifica, Pseudodiaptomus incisus) and outer (Paracalanus gracilis, Acrocalanus gibber, Subeucalanus subcrassus, Oithona rigida, Corycaeus andrewsi, Oithona plumifera) part of the estuary though a few species are common in both areas (Paracalanus crassirostris and Euterpina acutifrons). The zooplankton community at the inner NPE is subjected to more variable hydrographic conditions (salinity in particular) than the communities at the other sites where more stable conditions prevail. A short residence time in the inner part of the estuary due to the tide is supposed to impede a strong horizontal structuring of the zooplankton community.

Copepod Assemblages at the Base of Mangrove Food Webs during a Severe Drought

“…A particular feature of this tropical drought-prone estuary is the low number of species (n = 20) when compared to other estuaries in Brazil ( [52] (n = 49); [53] (n = 30); [54] (n = 37)) and elsewhere in the world ( [55] (n > 100); [56] (n = 47), [57] (n = 32)). Increased salinity can modify the structure and dynamics of planktonic communities through the selection of predominantly stress-tolerant marine species [58] and consequent simplification of planktonic communities, as observed in hypersaline estuaries, which have low numbers of species with high densities [14,59].…”

Transgenerational exposure to marine heatwaves ameliorates the lethal effect on tropical copepods regardless of predation stress

“…Pseudodiaptomus incisus is a calanoid copepod that can be found abundantly in aquaculture ponds, bays, lagoons, mangroves, and estuaries in Vietnam (BISMAL, 2020 ; Truong et al, 2014 ). They develop from the first nauplii to adults in 8–14 days, depending on temperatures (25–35°C) and salinity (5–40 PSU) (Nguyen, Le, Doan, Nguyen, et al, 2020 ).…”

Transgenerational exposure to marine heatwaves ameliorates the lethal effect on tropical copepods regardless of predation stress

“…Pseudodiaptomus incisus is a calanoid copepod that can be found abundantly in aquaculture ponds, bays, lagoons, mangroves, and estuaries in Vietnam (BISMAL, 2020;Truong et al, 2014). They develop from the first nauplii to adults in 8-14 days, depending on temperatures (25-35°C) and salinity (5-40 PSU) (Nguyen, Le, Doan, Nguyen, et al, 2020).…”