Ecological distribution of benthic polychaeta in coastal mangrove swamps of Fujian Province

Abstract

Numerous biotic surveys in mangrove swamps have been conducted throughout the whole world, and these studies have demonstrated that macrobenthos is among the most diverse biological group. Although benthic polychaetes, together with mollusks and crustaceans, constitute the main component of macrobenthos in mangroves, their diversity and abundance have been relatively poorly studies or even neglected, leading to a poor understanding of the ecological characteristics of this faunal group. In spite of the great spatial distribution variation of polychaetes, most previous studies located at certain area or one single location, were inadequately to reflect the spatial distribution of polychaetes. Aiming to describe the polychaete diversity and its distribution pattern in mangrove swamps in Fujian province, the present study carried out investigations along 11 transects in 5 typical mangrove swamps, namely Yaojiayu(FDH), Yundan Island(YDH), Luoyang River(QZH), Jiulong River(LHH) and Zhang River(YXH), in spring and autumn from 2009 to 2012. Macrobenthic samples were attained using digging method with 0.25 cm × 0.25 cm sampling square, and the fauna was retained by sieving sediment through 0.5 mm mesh screen. A total of 45 polychaete species were recorded, and the diversity was richer in spring than in autumn. The faunal assemblage was mainly consisting of three families— Nereididae, Spionidae and Capitellidae, which accounted for 64.4% of all speices, and the recorded species were mainly of euryhaline and hypohaline species. Some species, such as Parheteromastus tenuis and Mastobranchus indicus seems to exclusively inhabit in mangrove areas as they have not been recorded in non-mangrove mudflat in previous studies. Although the species richness was similar among all the sampling locations, species compositions and dominant species showed great difference and only 3 species occured at all the 5 locations. The average density and biomass of benthic polychaeta in these investigated areas were 190 ind/ m2and 2.17 g/ m2, respectively. Results of two-way ANOVA analysis showed that seasonal variations of both density and biomass were significant, with values significantly higher in spring than in autumn, probably due to the fact that most polychaete species reproduce in spring. Moreover, significant difference in density were also found among sampling locations, but the biomass were comparable among these mangroves. Polychaete densities recorded in this study were higher than those reported in the mangroves of Fujian in 1980s while their biomass were lower. Mann-Whitney U test showed that both polychaete density and biomass in foreshore mudflat were significantly higher than those in mangrove forests, indicating that the habitat environments in mudflat is more suitable for polychaete group. Such conclusion also agrees with those reported by previous researchers. In terms of the structure of feeding guilds, the five mangrove swamps in this study had different composition although carnivores and deposit feeders dominated these mangrove areas, which was partly related to the available food supply. Univariate analysis showed that biotic parameters such as the average species richness and Shannon-Weaver diversity indices were negatively correlated with content of clay in sediment. Multivariate analysis showed that polychaete assemblages varied with mangrove swamps and sampling seasons. In addition, characteristics of polychaete assemblages in spring was generally attributed to the latitude using BIO-ENV analysis. These results suggested that the large-scale distribution pattern of polychaete assemblage in mangroves of Fujian Province may be affected by environmental factors associated with latitude.