Identification of Sphaeroma terebrans via morphology and the mitochondrial cytochrome c oxidase subunit I (COI) gene.

Sphaeroma terebrans, a wood-boring isopoda, is distributed worldwide in tropical and subtropical mangroves. The taxonomy of S. terebrans is usually based on morphological characteristics, with its molecular identification still poorly understood. The number of teeth on the uropodal exopod and the length of the propodus of the seventh pereopod are considered as the major morphological characteristics in S. terebrans, which can cause difficulty in regards to accurate identification. In this study, we identified S. terebrans via molecular and morphological data. Furthermore, the validity of the mitochondrial cytochrome c oxidase subunit I (COI) gene as a DNA barcode for the identification of genus Sphaeroma, including species S. terebrans, S. retrolaeve, and S. serratum, was examined. The mitochondrial COI gene sequences of all specimens were sequenced and analysed. The interspecific Kimura 2-parameter distances were higher than intraspecific distances and no intraspecific-interspecific distance overlaps were observed. In addition, genetic distance and nucleotide diversity (π) exhibited no differences within S. terebrans. Our results revealed that the mitochondrial COI gene can serve as a valid DNA barcode for the identification of S. terebrans. Furthermore, the number of teeth on the uropodal exopod and the length of the propodus of the seventh pereopod were found to be unreliable taxonomic characteristics for S. terebrans.

[Wind-attenuation effect of Sonneratia apetala and Kandelia obovata plantations].

A field monitoring was conducted to examine the wind-attenuation effect of mangrove plantations at the Sanjiang Bay of Dongzhai Harbor, Hainan Province of South China. The wind speed and wind direction were measured at a site 50 m away from the offshore forest fringes of Sonneratia apetala and Kandelia obovata plantations and 2 m above the ground. Both the S. apetala and the K. obovata plantations had obvious effect in attenuating the speed of the wind from northerly to the shore, with the mean wind speed decreased by > 85% and the better effect of K. obovata plantation. With the increase of the wind speed, the wind-attenuation effect of the plantations presented a trend of decreasing first and remained stable then. At 50 m away from the offshore forest fringe of S. apetala plantation, the wind-attenuation rate was higher than 89.8% when the mean wind speed was lower than 5 m x s(-1), tended to be stable when the mean wind speed was 10 m x s(-1), and turned to be 58.9%-63.6% when the mean wind speed was higher than 15 m x s(-1). The S. apetala plantation had better wind attenuation effect in warmer season than in colder season. Under the extremely adverse weather like typhoon, the mean wind speed and extreme wind speed at 50 m away from the offshore forest fringe of S. apetala plantation were decreased by 59.4% and 53.2%, respectively.

[Effects of divergent habitat on genetic structure of population of Excoecaria agallocha, a mangrove associate].

Genetic diversity and population genetic structure of Excoecaria agallocha, a typical mangrove associate species,were surveyed at divergent habitats (intertidal and inland). In general, intertidal populations had higher genetic diversity than inland populations. Genetic differentiation among intertidal populations (G(ST) = 0.191) were smaller than that among inland populations (G(ST) = 0.218), suggesting that gene flow via seed among intertidal populations were stronger. In an analysis of molecular variance (AMOVA), we found that 15.13% of the genetic variance could be explained by the differentiation between habitats, as compared to only 11.63% to geographical effects among five sits 181 -759 km distant from each other. This implies that markedly selection regimes result in habitat adaptation. Isolation-by-distance, Southwest Monsoon Current,China Coastal Current and genetic drift played important role in genetic differentiation of China population of Excoecaria agalocha.