The Influence of Manila Clam (Ruditapes philippinarum) on Macrobenthos Communities in a Korean Tidal Ecosystem

We investigated the biological impact of extensive Manila clam (Ruditapes philippinarum) aquaculture on macrobenthic communities in a tidal ecosystem in Korea. We collected macrobenthos (>1 mm in length) samples seasonally in the intertidal zone in Geunsoman, Taean, Korea from April 2011 to December 2014. We identified 146 macrobenthos species, including 60 polychaetes, 53 crustaceans, and 16 mollusks. A biota–environment matching (BIO–ENV) analysis indicated that the benthic community was affected by mean sediment grain size (Mz), total organic carbon (TOC), and R. philippinarum biomass. We found no correlation between R. philippinarum and the main dominant species (Heteromastus filiformis, Ceratonereis erythraeensis, and Ampharete arctica), which have a different feeding strategy; thus, this may result in a lack of competition for food resources. In addition, we found that flourishing R. philippinarum positively affects the macrobenthos density but negatively affects the biodiversity index. Moreover, competition between species does not occur clearly, and environmental variables (sediment, organic carbon) are important.

Benthic macrofauna associated with decomposition of leaves in a mangrove forest in Ilhéus, State of Bahia, Brazil

We identified and quantified the benthic macrofauna associated with decomposing leaves of Rhizophora mangle and Laguncularia racemosa, to observe the differences in the abundance and composition of macrofauna between these mangrove species, and to examine whether the abundance and composition of organisms changed with different stations and collection times. Benthic macrofauna, mainly polychaetes and amphipods, were recorded from the fifth day after the installation of the experiment. Annelids including Oligochaeta and Polychaeta were the most numerous group. Crustacea were represented by peracarids (Amphipoda and Tanaidacea) and decapods. Of Hexapoda, only juvenile forms and pupae were present. The most abundant polychaete species was Perinereis brevicirrata, followed by Capitella cf. capitata, Heteromastus filiformis and Neanthes succinea. In one-way analysis of variance (ANOVA) there were no statistical differences between the macrofauna of mangrove species, seasons, or collection times, except among collection times for R. mangle litter bags. Two-way ANOVA showed homogeneity for macrofauna abundance between the groups of collection times for both mangrove species. The richness was similar for R. mangle litter bags, and showed a significant difference for L. racemosa. Abundance and richness were also similar between the mangrove species. The colonization of detritus by benthic invertebrates followed a successional sequence during the decomposition process. This suggests that the density of these organisms and their foraging behaviour affected the decomposition rates of leaves of R. mangle and L. racemosa.

Population structure and secondary production of Heteromastus filiformis (Polychaeta: Capitellidae) in the Loire estuary, France

A survey was carried out from April 1998 to June 2000 to study the structure and the secondary production of the population of Heteromastus filiformis in the Loire estuary. Each month, samples were collected in the intertidal zone of Mindin harbour. The length of the thorax (L12) was correlated with the fresh weight (FW) with the relation FW=1·49848 L12–3·62804 (r=0·92). In 1999, the mean density was 2184 ind m−2 with a minimum of 1104 ind m−2 in December and a maximum of 3328 ind m−2 in March. The mean annual biomass was 15·4 g m−2 with a minimum of 2·6 g m−2 in December and a maximum of 28·2 g m−2 in March. Most of the histograms of size–frequency are unimodal and could be considered a single cohort except in May and November/December 1999. The abundance and biomass of the population of H. filiformis decreased during summer and winter which are mortality periods and increase during spring and autumn which are recruitment periods for the population. The life time for a cohort was from six to nine months depending on the recruitment period and on the inter-annual variations. The secondary production was estimated by the method of Crisp (1971). The annual secondary production in 1999 was P=104·3 g m−2 with B¯=15·4 g m−2 and P:B¯=6·8. The quantity of sediment reworked by H. filiformis is about 116 l m−2 y−1 or 65 kg m−2 y−1 which is approximately a deep-sediment layer of 12 cm transported to the surface annually.