Cheсklist of gastropod molluscs in mangroves of Khanh Hoa province, Vietnam.

Gastropod molluscs are one of the most important components of mangrove ecosystem. Mangroves in Central Vietnam have a rather limited distribution due to peculiarities of the coastline morphology and presently their fauna remains understudied. Extensive surveys were conducted in both natural vegetation and artificial mangrove plantations in several localities in Nha Trang Bay from 2005 to 2015. In total 65 species of gastropod molluscs were found alive, 17 of which can be considered as predominantly mangrove-associated. An illustrated guide is provided, with short synonymies and data on ecology and distribution. The recorded molluscan diversity is compared with published data on mangrove gastropods in different regions of the Indo-Pacific. Total species number and the proportion of mangrove-associated species are similar to studied faunas in Hong Kong, Malaysia and Thailand, but the diversity is much lower than that of the mangal fauna of the Philippines.

Long-term monitoring of Gastropoda (Mollusca) fauna in planted mangroves in central Vietnam.

BACKGROUND: The aim of the research was to study the gastropod assemblage associated with a planted mangrove consisting of Rhizophora apiculata in Dam Bay (Tre Island, Nha Trang Bay, central Vietnam). Long-term changes in species composition, density, and biomass of gastropod assemblages in a planted mangrove were compared to those associated with natural mangroves. RESULTS: The gastropod assemblages in one planted and two natural mangrove associations were studied. Long-term monitoring (2005 to 2013) of assemblages associated with planted mangroves was also carried out. In total, 53 gastropod species in 21 families were recorded. This is comparable or even higher than in other areas of South-East Asia. In planted mangroves, R. apiculata trees were planted in mid (in 2004) and lower (2007) intertidal zones. Composition of gastropod fauna during the early period of observations (2005 to 2006) differed significantly in species richness, biomass, and abundance from the later period (2008 to 2013). Initially, the values of these parameters were low in the upper, and mid-intertidal zones and negligible in low intertidal zone. In 2008 to 2013, the values increased in the upper and mid-intertidal zones. R. apiculata planting in mid-intertidal zone and changes in its gastropod assemblage strongly affected those of upper intertidal zone as well. Comparison of gastropod fauna in planted mangroves and natural associations revealed significant differences. In planted mangroves, gastropods were mostly represented by eurybiotic species, also found in other not mangrove intertidal habitats, while in natural association many species were predominantly mangrove inhabitants, e.g., Potamididae, Littorinidae, and Ellobiidae. The fact that mangrove plantations in Dam Bay are highly dominated by opportunistic species, together with a paucity of predominantly mangrove-associated gastropods, suggest that the whole ecosystem is not balanced yet. CONCLUSIONS: Thegastropod assemblage found in a 9-year old mangrove plantation differed from natural mangrove associations in that the former is dominated by opportunistic eurybiotic gastropod species. This could mean that the ecosystem of planted mangroves is unbalanced and is still in a transitional state.