Meiofaunal Groups Research Articles

Nematode and copepod diversity (2012) from Louisiana near the Deepwater Horizon oil spill

Abstract Meiofauna were sampled from the NOAA ship Gordon Gunter during Fall 2012 off the coast of Louisiana. At five locations near the Deepwater Horizon drilling site (located 54–115 km away) box core samples and Shipek® grab samples were collected for subsurface meiofauna and sediment analysis. The goals of this study were to: 1) perform a taxonomic analysis of the meiofauna groups Nematoda and Copepoda, 2) perform statistical analyses of animal densities and sediment characteristics, and 3) compare sampling results using two different collection devices. Nematodes were the most abundant animals recovered, ranging from 88–791 animals per 10 cm2 area. Nematodes were represented by 60 genera in 23 families. The nematode community was dominated by one genus at the deepest location. Cluster analysis showed that there were two major groups for the five sites; nematodes from two shallow sites 81 and 84, and those from two shallow sites 85 and 86 along with deep site 82. Copepods were represented by 35 specie...

Meiofauna and Trace Metals From Sediment Collections in Florida After the Deepwater Horizon Oil Spill

Sediment from the Florida Gulf continental shelf was collected from 18 sites during October and November 2010 for meiofauna and trace-metals analysis. Collections were obtained using a Shipek® grab on the National Oceanic and Atmospheric Administration ship Pisces and spanned from the head of the DeSoto Canyon to off the southern end of the Florida peninsula approximately following the 100–200-m contour. Mean abundance of the dominant meiofaunal groups (nematodes, copepods, and polychaetes) was unchanged when compared with 2007–2009 data. Nematodes and copepods correlated positively with each other, and negatively with latitude and longitude, suggesting that there were higher densities in southern Florida. These results contrast with those from 2007–2009 in that previously nematodes had no correlation with latitude or longitude in Florida. Nickel (Ni) and vanadium (V) concentrations were higher in the western Florida locations and correlated positively with increasing depth. No relationship was found between Ni, V, and meiofauna densities.

Grazing effects on nematodes and other components of the periphyton at three depths in Lake Erken

The periphyton of stony hard substrates in the littoral zone of lakes is inhabited by an abundant and diverse algae and meiofauna assemblage that is regulated by grazing. The objective of our study was to examine the effect of macroinvertebrate grazers on periphytic algae and meiofaunal organisms at different depths in the littoral zone of Lake Erken (Sweden). To this end, a 2-factorial field experiment was carried out in which macrofaunal access to the periphyton was manipulated at 3 different water depths (30, 70, and 200 cm). Grazing effects on algal biomass varied among depths and were highest in both deeper zones. Compared to algal biomass, the abundance of meiofaunal organisms was less affected by grazing because macrograzers significantly reduced meiofauna only at the 200-cm depth. The organism mainly responsible for the depth-dependent differences in grazer effects was the snail Theodoxus fluviatilis, which dominated macrofaunal assemblage at depths where grazing effects were the strongest (70 and 200 cm). The abundance of T. fluviatilis was positively correlated with the proportions of reduced algal biomass and reduced meiofaunal abundance. Meiofaunal groups and individual nematode species responded differently to grazing, so our results further revealed that grazing macroinvertebrates affected the composition of the meiofaunal assemblage. However, meiofaunal and nematode assemblages differed more across depths than across grazing treatments, suggesting that other depth-related factors (e.g., hydrodynamics or light) also were important for structuring periphytic meiofaunal assemblages.

Recovery of meiofauna following a short-term disturbance on coral reefs

The present study experimentally determined the short-term effect of different trampling intensities on the phytal habitat and associated meiofauna, and assessed the recovery of these communities on a coral reef. The experiment was conducted within the protected area on the reef of Porto de Galinhas Beach, northeastern Brazil. Within three areas, 30 × 30 cm2 plots were subjected to different experimental trampling intensities: 0 (control), 32 (low intensity) and 79 (high intensity) footsteps applied during 3 consecutive days. Samples were taken before trampling started and then 1 day and 1, 2 and 3 months after the end of trampling. Multivariate and univariate analyses were used to test for changes in the phytal substrate, the densities of the main meiofaunal major taxa, and the diversity, comparing the trampling intensities and the time periods. The immediate impact of trampling negatively affected the phytal substrate, causing large reductions in sediment content, total substrate weight, and algal turf height. Trampling also drastically decreased the density of the associated meiofauna and modified the community structure. The major meiofauna groups showed different patterns of recovery during the first and second months. However, 3 months after trampling ended, no impact was found for densities of total meiofauna and for most major taxa, and no differences were observed in the community structure among all trampling intensities. Finally, the results for trampling susceptibility and resilience allowed us to extend the discussion to management strategies for the use of reef areas for recreation.

Variación espacio-temporal de la meiofauna submareal en una playa arenosa nororiental de Venezuela

Meiofauna organisms that play an important role in the trophic ecology of soft bottom benthos, have short life cycles and they respond quickly to disturbance and pollution. The present study shows the spatio-temporal variation ofsubtidal meiofauna (metazoans passing a 500im sieve but retained on meshes of 40-63micro m) in four shallow subtidal stations. Samples were taken in the sandy beach of San Luis, in the Northeastern coast of Venezuela, from October 2005 until September 2006. For this, three replicate sediment core samples (4.91cm2), were collected monthly to a depth of 10cm into the sediment, and preserved in 6% formalin stained with rose Bengal. Specimens of 14 meiofaunal groups (Foraminifera excluded) were collected, being the nematodes, ostracods and harpacticoid copepods the most abundant. Monthly density was comprised between 64 and 503ind./10cm2, and mean density of stations between 173 and 449ind./10cm2. There is a trend of low densities from October to February (end of the rainy season until the middle of the dry season). The San Luis beach control of the meiofaunal community is shared by climatic conditions and by the biology of the species found. The meiofauna mean density in San Luis beach (263ind./10cm2) was low when compared to other studies in tropical areas.

CellTracker Green labelling vs. rose bengal staining: CTG wins by points in distinguishing living from dead anoxia-impacted copepods and nematodes

Abstract. Hypoxia and anoxia have become a key threat to shallow coastal seas. Much is known about their impact on macrofauna, less on meiofauna. In an attempt to shed more light on the latter group, in particular from a process-oriented view, we experimentally induced short-term anoxia (1 week) in the northern Adriatic Sea (Mediterranean) and examined the two most abundant meiofauna taxa – harpacticoid copepods and nematodes. Both taxa also represent different ends of the tolerance spectrum, with copepods being the most sensitive and nematodes among the most tolerant. We compared two methods: CellTracker Green (CTG) – new labelling approach for meiofauna – with the traditional rose bengal (RB) staining method. CTG binds to active enzymes and therefore colours live organisms only. The two methods show considerable differences in the number of living and dead individuals of both meiofauna taxa. Generally, RB will stain dead but not yet decomposed copepods and nematodes equally as it does live ones. Specifically, RB significantly overestimated the number of living copepods in all sediment layers in anoxic samples, but not in any normoxic samples. In contrast, for nematodes, the methods did not show such a clear difference between anoxia and normoxia. RB overestimated the number of living nematodes in the top sediment layer of normoxic samples, which implies an overestimation of the overall live nematofauna. For monitoring and biodiversity studies, the RB method might be sufficient, but for more precise quantification of community degradation, especially after an oxygen depletion event, CTG labelling is a better tool. Moreover, it clearly highlights the surviving species within the copepod or nematode community. As already accepted for foraminiferal research, we demonstrate that the CTG labelling is also valid for other meiofauna groups.

Assessing the Response of Nematode Communities to Climate Change-Driven Warming: A Microcosm Experiment

Biodiversity has diminished over the past decades with climate change being among the main responsible factors. One consequence of climate change is the increase in sea surface temperature, which, together with long exposure periods in intertidal areas, may exceed the tolerance level of benthic organisms. Benthic communities may suffer structural changes due to the loss of species or functional groups, putting ecological services at risk. In sandy beaches, free-living marine nematodes usually are the most abundant and diverse group of intertidal meiofauna, playing an important role in the benthic food web. While apparently many functionally similar nematode species co-exist temporally and spatially, experimental results on selected bacterivore species suggest no functional overlap, but rather an idiosyncratic contribution to ecosystem functioning. However, we hypothesize that functional redundancy is more likely to observe when taking into account the entire diversity of natural assemblages. We conducted a microcosm experiment with two natural communities to assess their stress response to elevated temperature. The two communities differed in diversity (high [HD] vs. low [LD]) and environmental origin (harsh vs. moderate conditions). We assessed their stress resistance to the experimental treatment in terms of species and diversity changes, and their function in terms of abundance, biomass, and trophic diversity. According to the Insurance Hypothesis, we hypothesized that the HD community would cope better with the stressful treatment due to species functional overlap, whereas the LD community functioning would benefit from species better adapted to harsh conditions. Our results indicate no evidence of functional redundancy in the studied nematofaunal communities. The species loss was more prominent and size specific in the HD; large predators and omnivores were lost, which may have important consequences for the benthic food web. Yet, we found evidence for alternative diversity–ecosystem functioning relationships, such as the Rivets and the Idiosyncrasy Model.

Small-scale patterns of meiofauna in a bryophyte covered tufa barrier (Plitvice Lakes, Croatia)

Meiobenthic fauna is complex and essential part of the stream benthos and it is known as intermediaries from bacteria to higher trophic levels. However, the dynamics and mechanisms regulating this community at small-scale largely have been neglected. This study was carried out to determine meiofaunal dynamics in a small scale-patterns influenced by flow velocity and other abiotic and biotic factors. We examined meiofauna within bryophytes on a tufa barrier in Plitvice Lakes National Park using a detailed taxonomic approach of various meiofaunal groups and their feeding guilds. We choose three microhabitats (slow, medium, fast) differing significantly in flow velocity above bryophytes. Bdelloid rotifers were the most abundant group in microhabitat with highest flow velocity, while in other two microhabitats nematodes and monogonont rotifers prevailed in abundance. Data on environmental variables and main meiofaunal taxa and feeding guilds were analyzed using redundancy analysis. This analysis indicated that microfilter feeding guild (e.g. bdelloid rotifers) was strongly affected by interaction of flow velocity and POM fractions. Other feeding guilds were influenced by temperature, oxygen and/or pH and did not prefer high flow velocity. Suction-feeder nematodes and microfilter-feeder rotifers were dominant on temporal and spatial scale, indicating their good adaptations on frequently disturbed conditions that prevailed on bryophyte covered tufa barrier. Our results provide comprehensive survey of diversity, density as well as trophic structure of meiofauna in aquatic bryophytes. Differences in meiofaunal composition and density between three microhabitats suggest that the meiofauna is relevant indicator of environmental changes even at small-scale pattern.

Analyzing changes in sediment meiofauna communities using the image analysis software ZooImage

We here propose a novel method of automatic classification of higher taxa from benthic meiofaunal communities using the image analysis software ZooImage. Meiofauna was extracted from sediment at five sites at different depths in the Gullmar Fjord on the Swedish west-coast, and digitalized through scanning. The resulting images were analyzed with the image analysis software, by comparing them to a reference image library of meiofaunal groups of higher taxa, as well as non-faunal groups consisting of different types of debris. The accuracy of the analyses was tested using ZooImage internal cross-validation method, and by comparing digitalized samples from the different sites with manually classified samples. The internal validation accuracy (82–93%) was comparable to prior published studies on zooplankton. The largest errors in classification were within the non-faunal groups and accuracy for classification of faunal groups was as high as 93%. Misclassification within the faunal groups was mainly due to either too few images of some classes in the training set, or to when fauna could not be sufficiently separated from debris in the images used for the library, causing interference in the learning algorithm. Comparison with manual classification confirmed the errors revealed in the internal cross-validation. Statistical analysis revealed differences in the meiofauna communities between different depths as well as a temporal change.

Evaluating the Relative Effectiveness of Sampling Methods for Reef Meiofauna Community Structure Studies

Despite their potentially important role in ecosystem functioning, meiofauna are possibly the least studied animals associated with hard bottoms such as coral and sandstone reefs. A significant limitation in meiofauna research has been the lack of standardized sampling methods for species inhabiting hard surfaces. To address this problem we tested four different sampling methods proposed for the reef meiofauna community: a suction pump at three different suction treatments (20 s, 1 min, and 5 min) and substrate scraping. Significant differences were observed in the abundance of meiofauna groups, and the composition and diversity of Nematoda genera. The highest values were always generated by substrate scraping. We conclude that scraping is a more accurate method of sampling (among the methods tested) and we recommend the adoption of this method for future hard bottom meiofauna studies.

A new species of Pontarachna (Acari, Hydrachnidia, Pontarachnidae) from a mesophotic coral ecosystem off Vieques Island, Puerto Rico, Caribbean Sea

The water mite family Pontarachnidae Koenike, 1910, the only family of the Hydrachnidia occurring in the marine environment, represents a diverse and widespread, but still neglected group of marine meiofauna. Most marine species live nearshore with the exception of few freshwater species found in estuaries or locations near the sea (Smit 2002; Smit & Alberti 2010). In this paper we describe a new species, Pontarachna nemethi, from substrata collected from El Seco, a mesophotic site near Vieques Island off Puerto Rico, from 52–67 m depth, more than 2 times the depth at which Pontarachnidae have been previously collected. The finding of the new species remarkably extended the potential area of the world ocean occupied by the Pontarachnidae.

Biodiversity of meiofauna community in Da Nang bay and Son Tra peninsula, Da Nang province

The first result on meiofaunal community in the Da Nang bay and Son Tra peninsula was reported. Nine meiofaunal groups: Nematoda, Harpacticoids-Copepods, Turbelaria, Kinorhyncha, Polychaeta, Oligochaeta, Ostracoda, Halacaroidea and Insect larvae were recorded. Among them, Nematoda was the most predominant group with 96.36% of meiofaunal community of samples in term of individuals. Harpacticoids-Copepods followed with 1.84% and Polygochaeta and other groups occupied less than 1%. A total of 30 species marine nematodes belonging to 13 families of 3 orders were identified so far. The ratio of Nematoda/Copepoda (N/C) in all investigated stations was fluctuated between 16 and 78 according to the Warwick’s N/C ratio. With high diversity indexes, the environment quality seems to be good except two satations DN1 and DN3 that might be more disturbed.

Benthic ciliate and meiofaunal communities in two contrasting habitats of an intertidal estuarine wetland

Annual variations in benthic meiofaunal and ciliated protozoan communities were investigated using monthly samplings from June 2006 to May 2007 in two habitats characterized by different vegetal coverage in an estuarine intertidal wetland of Qingdao Jiaozhou Bay, China. The sediment composition was stable at each site: sediments densely covered with seagrass (Suaeda glauca) in the lower estuarine site (Station S) were finer, with higher content of organic matter, phaeopigments and water than sediments at the upper estuarine site (Station S-P) which was unvegetated other than for patches of S. glauca and common reed (Phragmites australis). Chlorophyll a exhibited a similar distribution in the two habitats. A total of 14 meiofaunal groups, and 249 species of ciliates belonging to 37 genera, 28 families and 16 orders, were isolated from the two sites. Univariate and multivariate measures of the communities were significantly different between the two habitats. There were higher abundances of ciliates and meiofauna, and a greater diversity of ciliates, at Station S than Station S-P (223 vs. 61 species). Herbivorous ciliates were numerically predominant in ciliate communities at both sites. The representative ciliates at Station S-P belonged to the Cyrtophorida and appeared to be a reduced subset of the assemblage at Station S, which was characterized by members of the Prostomatida, Cyrtophorida, Hypotrichida and Scuticociliatida. More than 96% of the total meiofauna were nematodes, accounting for 93% of the differences in the abundance compositions of the meiofaunal communities between habitats. The average individual weights of nematodes were nearly 3 times greater at Station S than Station S-P, indicating a distinctive species composition at each site. Temperature, salinity and food availability were key factors that regulated the ciliate and meiofaunal community structure. Nematodes were the dominant group in terms of the combined abundance, biomass and benthic metabolism of ciliates and meiofauna. With respect to the dominance of herbivorous ciliates and epistrate-feeder nematodes in seagrass sediment, predator–prey relationships and competition for food resources between nematodes and ciliates are likely to be important factors in controlling the abundances of these groups.

Meiofaunal responses to nutrient additions in a Mediterranean stream

Summary1. The effects of a moderate addition of nutrients (twofold N and threefold P) were examined during a 2‐year period to determine the response to nutrient addition in a meiofaunal community inhabiting sandy patches in a Mediterranean stream.2. The pattern of meiofaunal assemblages exhibits a high degree of intra‐ and interannual variability. This pattern alternates between periods of hydrological stability and disturbances, such as floods and droughts, which is a characteristic of Mediterranean systems.3. A before–after–control–impact (BACI) design was used to determine the outcome of the addition by comparing an upstream non‐enriched reach with an enriched downstream reach. Analysis of the study data by means of a nonparametric permutational procedure (permanova) showed that fertilisation had a significant effect. Density and biomass values increased in the most abundant meiofaunal groups, including microcrustaceans, oligochaetes and chironomids. Microcrustaceans were the dominant group in the permanent meiofauna.4. We also examined differences in microcrustacean secondary production in both reaches. Ostracods and cyclopoid copepods increased their secondary production in the impacted reach as a result of the nutrient addition.5. Our study demonstrated that moderate nutrient enrichment can affect the biomass and production of stream meiofauna, but it is still unclear whether this effect was because of autotrophic or heterotrophic pathways.

Temporal changes in periphytic meiofauna in lakes of different trophic states

Meiofaunal organisms in the periphyton of stony hard-substrates (epilithon) were studied in three Swedish lakes with different trophic states (oligo-, meso- and eutrophic) with respect to seasonal successions in abundance, biomass, and production. Over a period of 2 years, the meiofaunal population of all three lakes fluctuated greatly, with densities varying up to nine-fold within a season. In the oligotrophic lake, a significant decrease in meiofauna in winter was striking, whereas in the other two lakes, richer in nutrients, there was a pronounced peak in early summer. Although the lakes, on average, did not differ in epilithic organic and inorganic material, the differences in meiofaunal abundance, biomass, and production were significant. Correlation analysis revealed that altogether the meiofaunal biomass was positively related to the lakes’ trophic state (total phosphorus), while the meiofaunal abundance and production along the trophic spectrum displayed a humped-shape distribution, with maximum values measured in the mesotrophic Lake Erken (1324 ind cm-2 and 2249 mg DW cm-2 y-1). Nematodes were the dominant meiofaunal group in the epilithon of all three lakes, accounting for up to 58% in abundance, 33% in biomass and 55% in production of the whole meiofaunal community. However, their relative importance tended to decrease with increasing trophic state. Beside nematodes, rotifers, oligochaetes, copepods and tardigrades were also found in large numbers in the epilithon. Overall, the results demonstrated that, due to their high abundance, biomass, and production, meiofaunal organisms play an important role in epilithic communities.

A Multi-Year Survey of Meiofaunal Abundance From the Northern Gulf of Mexico Continental Shelf and Slope

This 3-yr (2007–09) survey documented meiofauna abundance across the northern Gulf of Mexico on the continental shelf and slope from south Texas to south Florida. Sediment samples were collected from depths ranging from 29 to 509 m (average = 132 m) on the National Oceanic and Atmospheric Administration ship Gordon Gunter during the annual fall small pelagics fish-sampling cruise. A total of 259 sediment samples from 99 Shipek® grabs were analyzed. Meiofauna were isolated from the sediment by sieving (63-μm sieve) and concentrating the organisms via Ludox® centrifugation. Each year the two dominant animal groups were nematodes and copepods, followed by polychaetes, nauplii, kinorhynchs, priapulid loricate larvae, tardigrades, and Acari. Spearman correlations indicated that abundances of nematodes, copepods, polychaetes, and nauplii were positively related, and that all meiofauna groups decreased in abundance with increasing longitude (farther west). Abiotic variables such as salinity, temperature, and depth did not correlate with any meiofauna group. Distribution maps of the animals indicated a clear geographic trend that was supported statistically, in that the animal groups were more concentrated in Florida samples rather than the central and western continental shelf.

Seasonal shifts of meiofauna community structures on sandy beaches along the Chennai coast, India

Meiofauna standing stocks and community structures were studied at five sandy beaches along the Chennai coast of the Bay of Bengal, at the SE coast of India from January 2000 to February 2001. Meiofauna densities ranged from 1341.14 ± 1205.76 ind. 10 cm-2 to 3.73 × 106 ± 4.1 × 105 ind. 10 cm-2. Mean abundance was highest during February 2000 (35 565.85 ± 12 463.03 ind. 10 cm-2) and lowest during March 2000 (11 465.85 ± 4250.26 ind. 10 cm-2). As for individual stations, the highest abundances were found at Neelangarai (67 058.31 ± 7153.43 ind. 10 cm-2) and lowest at Marina (52 517.69 ± 5373.63 ind. m-2), respectively. As for taxa, the mean of the highest and lowest meiofauna abundance was observed in Copepoda and Cladocera during different months (109 372.29 ± 10 906.42 ind. 10 cm-2 and 1341.14 ± 241.15 ind. 10 cm-2) and at different stations (30 6242.40 ± 3905.26 ind. 10 cm-2 and 3755.20 ± 88.90 ind. 10 cm-2), respectively. Cluster analysis and principal component analysis showed that the elements of the meiofauna were separated into three major groups according to their distribution and abundance. Correspondence analysis showed the importance of meiofauna abundance with different months and stations. Ecological indices varied with month, station, and with meiofauna group. Monthly changes in the nematode-copepod index showed that both Ernavoor and Thiruvotriyur were more subjected to pollution, with the highest diversity and evenness values for nematodes among all stations.

珠江口水域夏季小型底栖生物群落结构

Meiofauna,a fundamental component of terrestrial and marine benthic ecosystems,form an integral element of food webs and play a critical role in nutrient recycling.To clarify the composition and ecological roles of meiobenthic communities within sediments of the Pearl River Estuary,Southern China,meiofauna composition,abundance,biomass and distribution were reported together with abiotic parameters(temperature and salinity of water,organic matter content organic and particle size of sediment) based on samples conducted at 16 stations(from 22.10° N to 22.80°N,113.50° E to 114.00° E) in summer,2010. A total of 16 meiofaunal groups were identified in the whole sampling study.Free living marine nematodes were the most dominant group,with an abundance of(115±115) ind./10cm2,accounting for 62.61% of the total meiofauna,followed by Bivalvia larvae(22.62%),crustacean nauplii(5.02%),and harpacticoid copepods(3.28%).The remaining groups accounted for less than 2% of total meiofauna,and included Polychaeta,Nemerteana,Echiurida,Ostracoda,Kinorhyncha,Oligochaeta,Turbellaria,Tanaidacea,Cnidaria,Acarina,Tardigrada and unidentified taxa.The average abundance,biomass and production of the meiobenthos was(183±174) ind./10cm2,(345±334)μg dwt/10cm2 and(3104±3008)μg dwt/10cm2 respectively.Based on the meiobenthic biomass,the main dominant groups were bivalves(50.57% of total meiobenthos biomass),followed by nematodes(13.33% of total) and polychaetes(12.47% of total).Most meiobenthos(81.15%) were found distributed in the 0—5 cm layer of sediment.Vertical distribution was different for the dominant groups of the meiobenthos;bivalves and nematodes were in the 0—5 cm layer of sediment,most copepods were in the 0—2 cm layer,and polychaetes were in the 2—5 cm layer.Analysis of abiotic parameters showed that the average organic matter content of the sediment was 6.90%,which showed an increase from the west to the east of the estuary,and from the upper reaches to the lower.The dominant sediment type was poor sorted silt-clay,representing 84.39%—97.29% of total sediment and with median diameter(MDФ) from 6.56—7.18.This sediment type was found throughout most areas of the estuary.In the top 8 cm of sediment,average Chl-a concentration was 0.80 μg/g and the average organic matter was 6.90%. The correlation analysis between meiobenthos and abiotic parameters indicated that the abundance of meiobenthos correlated positively with salinity,and negatively with temperature near the bottom,silt-clay content,median diameter(MDФ) and organic matter of sediment.The abundance of polychaetes and nematodes was also found to correlate negatively with bottom water temperature and positively with water salinity.The results of hierarchical clustering and multidimensional scaling(MDS) analysis of the sampling showed that all sites could be divided into three groups at the similarity level of 50%.The structure and diversity of the sampling sites were expressed using the Shannon-Wiener index,the Margalef index and the dominance index.Values of the Shannon-Wiener index ranged from 0.667—1.653,while the dominance index ranged 0.314—0.784.The mean nematode/copepod-ratio(N/C-ratio) showed an increasing trend from upper to lower reaches and from west to east of the estuary,which could correspond to the organic pollution of the Pearl River Estuary.

Effects of Endosulfan (Thiodan 35 EC®) on Meiofauna Community Through a Microcosm Approach

A microcosm experiment with natural community of meiofauna was performed to test the effects of the organochlorine pesticide Thiodan 35 EC (35% endosulfan) at concentrations more likely to reach the estuaries by the sugar cane crops runoff. A methodological proposal for microcosms was tested for tropical estuaries. The nominal concentrations (0.001, 0.005, 0.01, 0.05, 0.10, 0.20, 0.35 and 0.55 μg.g-1 + control) and experimental times (0, 1, 4, 8 and 16 days) were adopted. Nominal and measured endosulfan concentrations in Thiodan showed highly significant correlation with losses below 60%. Significant differences were detected for meiofauna structure between experimental days and concentrations tested. The organochlorine Thiodan measured as endosulfan concentrations had affected the Kinorhyncha group on Day 8 and the Simple Linear Regression explained part of densities variation. There were no significant concentration effects on microphytobenthos and its concentration was not related to groups’ feeding. Despite the moderate to high volatilization rate of the endosufan observed in the end of the experiment, it is suggested the absence of mortality patterns due to pesticide bioavailability related to both sedimentary factors and the presence of microalgae. Possible replacement of sensitive by tolerant species or predominance of resistant species in each meiofauna group throughout the experiment is another hypothesis to be discussed.

Cryptic Species in Tropic Sands - Interactive 3D Anatomy, Molecular Phylogeny and Evolution of Meiofaunal Pseudunelidae (Gastropoda, Acochlidia)

BackgroundTowards realistic estimations of the diversity of marine animals, tiny meiofaunal species usually are underrepresented. Since the biological species concept is hardly applicable on exotic and elusive animals, it is even more important to apply a morphospecies concept on the best level of information possible, using accurate and efficient methodology such as 3D modelling from histological sections. Molecular approaches such as sequence analyses may reveal further, cryptic species. This is the first case study on meiofaunal gastropods to test diversity estimations from traditional taxonomy against results from modern microanatomical methodology and molecular systematics.ResultsThe examined meiofaunal Pseudunela specimens from several Indo-Pacific islands cannot be distinguished by external features. Their 3D microanatomy shows differences in the organ systems and allows for taxonomic separation in some cases. Additional molecular analyses based on partial mitochondrial cytochrome c oxidase subunit I (COI) and 16S rRNA markers revealed considerable genetic structure that is largely congruent with anatomical or geographical patterns. Two new species (Pseudunela viatoris and P. marteli spp. nov.) are formally described integrating morphological and genetic analyses. Phylogenetic analysis using partial 16S rRNA, COI and the nuclear 18S rRNA markers shows a clade of Pseudunelidae species as the sister group to limnic Acochlidiidae. Within Pseudunela, two subtypes of complex excretory systems occur. A complex kidney already evolved in the ancestor of Hedylopsacea. Several habitat shifts occurred during hedylopsacean evolution.ConclusionsCryptic species occur in tropical meiofaunal Pseudunela gastropods, and likely in other meiofaunal groups with poor dispersal abilities, boosting current diversity estimations. Only a combined 3D microanatomical and molecular approach revealed actual species diversity within Pseudunela reliably. Such integrative methods are recommended for all taxonomic approaches and biodiversity surveys on soft-bodied and small-sized invertebrates. With increasing taxon sampling and details studied, the evolution of acochlidian panpulmonates is even more complex than expected.