Major Meiofaunal Taxa Research Articles

Microalgal–meiofaunal interactions in a sublittoral site of the Gulf of Trieste (northern Adriatic Sea, Italy): A three-year study

Monthly sediment sampling was carried out from February 1999 to December 2001 at a 21-m deep station. Benthic diatom biomass and meiobenthic abundance were estimated together with abiotic parameters (PAR irradiance, temperature, salinity and dissolved oxygen). During the three-year study average microphytobenthic abundance (ABU) and biomass (BIOM) were 4.7 ± 2.6 × 10 4 cell cm − 3 and 14.3 ± 8.1 µg C cm − 3 , respectively, while the mean meiofaunal abundance was 923 ± 210 ind 10 cm − 2 . The microphytobenthic community was mainly composed of Bacillariophyceae (99.3%) with a smaller percentage of phytoflagellates (0.7%). Among diatoms 39 genera were observed with a total of 110 taxa and 100 species. The main benthic diatom genera were Navicula, Paralia, Nitzschia and Diploneis. A total of 18 meiobenthic taxa were detected: 7 taxa belonged to permanent meiofauna (Nematoda, Copepoda Harpacticoida and their nauplius stages, Kinorhyncha, Turbellaria, Gastrotricha, Ostracoda and Acarina). The remaining 11 taxa belonged to temporary meiofauna (juvenile macrofauna: Polychaeta, Cumacea, Amphipoda, Isopoda, Nemertea, Decapoda, Sipunculida, Ophiurida, Gastropoda, Bivalvia and Cnidaria). Positive correlations between PAR and the biomass of the major diatom genera were revealed. Temperature did not seem to influence the microphytobenthic community as a whole, although we found statistically significant correlation between temperature and the genera Nitzschia and Amphora. Salinity showed significant positive correlation only with the genus Pleurosigma, in contrast, dissolved oxygen did not seem to affect the microalgal community. The major meiofaunal taxa were not correlated with abiotic variables, but were positively correlated with most diatom genera. Paralia was negatively correlated with the three main meiofaunal taxa. The three-point moving average applied to our biotic data allowed us to better the signal without the background noise which hid the actual variations of the studied communities. Applying the three-point moving average to the main taxa, it resulted that microphyto- and meiobenthos were in phase. The principal component analysis (PCA), constructed considering both biotic and abiotic variables, accounted for 58% of the total variance. PC1 axis explained 39.74% of the total variance and was correlated with Navicula, Diploneis and Nitzschia. PC2 axis explained 18.40% of the remaining variance and was correlated with Copepoda, Paralia and PAR. In contrast to 1999 and 2001, a mucilage event occurred in 2000, which resulted in the formation of a false bottom and a decrease in the abundance of microphyto- and meiobenthos.

Effects of intensive seaweed farming on the meiobenthos in a tropical lagoon

Open water aquaculture of the seaweed Eucheuma spinosum, imported to Zanzibar from the Philippines in 1989, is presently a large scale operation on the island, with algal farms covering around a 1000 ha of the intertidal area. To assess the effects of the farming on benthic communities both field and laboratory studies were conducted. Two field studies conducted at different times showed that all major meiofaunal taxa were found in significantly lower numbers within the farm area compared with control areas. Multidimensional scaling ordination of nematode species, genera and family abundance data separated samples from farmed and control areas. There was a significant difference in the nematode assemblage structure among areas in pairwise comparisons using ANOSIM. The trophic structure of the nematode assemblage was characterised by a high number of epistrate feeders in all areas ranging from 73 to 96% of total numbers in the samples. To test the hypothesis that toxic substances excreted by the seaweed were responsible for lower abundance inside the farm area, a laboratory experiment was conducted. Eucheuma plants were added to several microcosms and allowed to grow there for 40 days. The results indicated no effects of the seaweed on the density of the major infauna taxa as no significant difference was found among the treatments. It is concluded that other factors such as increased predation by benthic feeding fish and the mechanical disturbance of the sediments may better explain the observed differences in infauna abundance inside and outside the algal culture farms.

Analysis of community attributes of the benthic meiofauna of Frierfjord/Langesundfjord

Sublittoral meiofauna was sampled for the GEEP Workshop along a putative pollution gradient at 6 sites in Frierfjord/Langesundfjord, Norway. Data were subjected to multivariate statistical analyses which discriminate between sites on their faunistic attributes, and univariate measures of community stress were determined. Most multivariate techniques produced similar results. The copepod component of the meiofauna discriminated between sites better than the nematodes at the species level, but nematodes were more robust to analyses based on data aggregated to higher taxonomic levels. It is concluded that pollution monitoring at the community level using higher taxonomic groupings of meiofauna is viable, and renders such studies much less time-consuming and more cost-effective than more standard procedures. Appropriate taxonomic levels tor the 2 major meiofaunal taxa (nematodes and copepods) and for the total meiofauna are discussed. There is a paucity of validated univariate measures of community perturbation available for use with meiofauna. Traditional diversity measures were rather uninformative, but the community at one site was identified as being adversely affected by pollution.

Monitoring with meiofauna—A reply to Coull, Hicks and Wells (1981) and additional data

The usefulness of the ratio of two major meiofaunal taxa, nematodes and copepods, for marine pollution advocated by Raffaelli & Mason has been challenged by Coull, Hicks & Wells. The present paper answers their criticisms and provides additional information relevant for assessing the potential of this ratio for biomonitoring.