Meiobenthic Diversity Research Articles

Metabarcoding analysis of meiobenthic biodiversity along the Gulf of Mexico continental shelf

This study explores how diverse the meiobenthic (meiofauna and other benthic micro-eukaryotes) community is throughout the United States Gulf of Mexico (GOM) continental shelf. In late 2010 and 2011, 51 sediment samples were collected along GOM from Texas through Florida at a range of depths (40m–496m). An additional six deep-sea slope sediment cores were collected in December 2010 near the Deepwater Horizon platform (1370–1385m and 1865m). Metabarcoding of the 18S hypervariable V9 region was conducted to assess biodiversity. Within continental shelf samples, there was greater meiobenthic diversity off the Eastern GOM coast in comparison to both Central and Western GOM coast locations. The Eastern GOM coast has known sediment differences from Western GOM sites. These sediment differences along with influences from the Gulf of Mexico Loop Current may account for observed variations in GOM meiobenthic diversity.

Functional impact and trophic morphology of small, sand‐sifting fishes on coral reefs

Abstract Oligotrophic tropical coral reefs are built on efficient internal energy and nutrient cycling, facilitated by tight trophic interactions. In the competition for available prey, some small fishes have evolved to feed on apparently barren sand patches that connect hard‐substratum patches in many reef habitats. One strategy for obtaining prey from a particulate matrix is to sift out small prey items from the sediment (often called ‘winnowing’). Yet, the trophic link between small winnowing consumers and their prey are poorly resolved, let alone the morphological specialisations that enable this foraging behaviour. We used aquarium‐based feeding experiments to quantify the impact of winnowing by two sand‐dwelling goby species (Valenciennea sexguttata and Valenciennea strigata) on meiobenthos abundance and diversity and examined their actual ingestion of meiobenthos using gut content analysis. To identify potential morphological structures involved in winnowing, we investigated the gobies' feeding apparatus with electron microscopy (SEM) and micro‐computed tomography (micro‐CT). After 4 days of sifting through the sand matrix, the two species significantly reduced meiobenthic prey abundance by 30.7% ± 9.2 SE (V. sexguttata) and 46.1% ± 5.1 SE (V. strigata), but had little impact on the meiobenthic diversity. The most abundant prey groups (copepods and annelids) experienced the greatest reduction in number, suggesting selection by size, shape and density of prey items. Furthermore, gut content analysis confirmed that winnowing gobies can efficiently separate meiobenthic prey from heavier inorganic particles (sand), likely facilitated by a specialised epibranchial lobe, pharyngeal jaws and highly abundant papillose taste buds in the oropharyngeal cavity. Our results provide important background on the trophic link between the meiobenthos and winnowing gobies on coral reefs. The revealed specialisations of the goby feeding apparatus facilitate sand‐sifting foraging behaviour and access to an otherwise inaccessible trophic niche of microscopic prey. By having evolved a specialised strategy to obtain nutritious and highly abundant prey from seemingly barren sand, we suggest that winnowing gobies act as an important conduit for sand‐derived energy to higher trophic levels. Read the free Plain Language Summary for this article on the Journal blog.

Meiobenthic assemblages as ecological indicator of natural variability induced by ecosystem engineers

Indonesia is biologically one of the most diverse areas in the world. Nevertheless, its biodiversity is underestimated, and this is particularly evident for meiobenthic assemblages. Seagrass meadows are known to be ecosystem engineers that can significantly modify the habitat heterogeneity and, thereby, increase the meiobenthic diversity. Therefore, a study on the meiobenthic distribution and biodiversity was conducted in two seagrass meadows around Siladen Island (Bunaken Marine National Park): Barat and Lagoon, characterized by different sedimentary regimes, as well as by different anthropogenic impact. An overall high level of diversity indices and richness were recorded (H′: 1.19–1.69; J: 0.46–0.67; number of taxa: 9–14), with meiobenthic abundances ranging between 770 and 2529 ind. 10 cm −2. The lowest meiobenthic abundance and diversity (i.e. Shannon-diversity, number of taxa) were reported at Barat meadow, probably in response to sedimentological modifications and higher anthropogenic pressure at this site. Differences in meiobenthic assemblage structures were particularly evident when only rare taxa were considered (i.e taxa found in low abundances and characterized by a sporadic distribution in the study area). This result underlines the role of rare species as possible indicators of spatial variability generated by engineer species and different environmental conditions.

Organic biomarkers and Meiofauna diversity reflect distinct carbon sources to sediments transecting the Mackenzie continental shelf

During the Arctic spring freshet, the Mackenzie River delivers large amounts of dissolved and particulate terrestrial organic carbon to the Canadian Beaufort Sea shelf. This pulse of material and nutrients fuels phytoplankton blooms in late spring and summer and together with under ice primary production contributes to the organic carbon reservoir of the coastal shelf sediments. As a component of the Marine Arctic Ecosystem Study (MARES), samples transecting the Canadian Mackenzie Trough were collected in fall before ice cover to examine the balance of marine and terrestrial carbon in sediments and its relationship with sediment meiobenthic diversity and abundance. Organic biomarker analysis of lipid proxies together with total hydrolyzable amino acids (THAA) defined organic matter sources and potential lability. Across the shelf transect, consistent values observed in sedimentary total organic carbon (1.09%–1.62%) belied a shift in the balance of terrestrial and marine carbon sources. Predominately terrestrial inputs at the shallow site near the delta outflow appeared to constrain meiofaunal populations while the deepest location off shelf reflected lower labile marine organic carbon reaching the sediments that limited benthic production. Surface sediments at the mid-shelf, however, showed a near 3-fold increase (to 1.16 mg C OC-1) in contributions by diatoms and dinoflagellates markers plus a peak in total amino acids (9.53 mg g OC-1) which corresponded with higher meiofauna abundance. The combination of detailed organic analysis together with meiofaunal community measures suggest that mid-shelf sediments receive higher contributions of labile marine carbon which drive increased meiofauna diversity and abundance despite the large background of terrestrial organic material exiting the Mackenzie River outflow.

Above-below surface interactions mediate effects of seagrass disturbance on meiobenthic diversity, nematode and polychaete trophic structure

Ecological interactions between aquatic plants and sediment communities can shape the structure and function of natural systems. Currently, we do not fully understand how seagrass habitat degradation impacts the biodiversity of belowground sediment communities. Here, we evaluated indirect effects of disturbance of seagrass meadows on meiobenthic community composition, with a five-month in situ experiment in a tropical seagrass meadow. Disturbance was created by reducing light availability (two levels of shading), and by mimicking grazing events (two levels) to assess impacts on meiobenthic diversity using high-throughput sequencing of 18S rRNA amplicons. Both shading and simulated grazing had an effect on meiobenthic community structure, mediated by seagrass-associated biotic drivers and sediment abiotic variables. Additionally, shading substantially altered the trophic structure of the nematode community. Our findings show that degradation of seagrass meadows can alter benthic community structure in coastal areas with potential impacts to ecosystem functions mediated by meiobenthos in marine sediments.

Meiobenthic diversity off Pudimadaka, Bay of Bengal with special reference to free-living marine nematodes

Meiobenthic diversity off Pudimadaka, Bay of Bengal with special reference to free-living marine nematodes

Meiobenthic diversity and abundance along Arthunkal coast in Kerala, southwest coast of India

Meiobenthic diversity and abundance along Arthunkal coast in Kerala, southwest coast of India

Meiobenthic diversity in space and time: The case of harpacticoid copepods in two Mediterranean microtidal sandy beaches

Meiobenthic data from two microtidal sandy beaches of the eastern Mediterranean (Crete, Greece) were used to investigate patterns of both alpha and beta diversity in space and time. Copepod assemblages and environmental variables related to sediment characteristics, morphodynamics and food were studied over a year at four distinct habitats at each beach; the retention, resurgence and saturation zones of Salvat's intertidal scheme (midlittoral zone), and the surf zone of the sublittoral. Αlpha diversity analysis indicated similar species richness at both beaches when the whole 13-month data set was considered but was higher at the sheltered site when each sampling period was examined separately. Both beaches supported higher diversity in the sublittoral zone. Species richness increased seawards at the midlittoral zone of the sheltered site whereas, no pattern was evident at the exposed site, where the intense hydrodynamic conditions homogenized the sediments. Beta diversity increased markedly towards the sublittoral, indicating greater differences in alpha diversity between the sublittoral and the midlittoral zone. Species turnover was more variable at the exposed beach and at the most landward stations, where environmental conditions change often between extremes. A proportion of the variation in alpha diversity was explained by food availability at both beaches and additionally by grain size at the sheltered site. However, no environmental variable explained beta diversity patterns. Although the results of our study support the hypothesis of Multicausal Environmental Severity proposed for sandy beach macrofauna, we believe the classic Intermediate Disturbance Hypothesis is a more appropriate framework for the meiofauna communities of the studied sites.

Walking with worms: coral‐associated epifaunal nematodes

AbstractAims To study the community structure and habitat preferences of the Epsilonematidae and Draconematidae in coral degradation zones. To assess the contribution of different localities and microhabitats to meiobenthic diversity in such ecosystems. To discuss dispersive capacities and the occurrence of cryptic species in meiobenthic organisms.Location Porcupine Seabight (north‐east Atlantic Ocean; continental slope) and a transect along the Kenyan coast (Indian Ocean; shallow lagoon).Methods In the north‐east Atlantic, dead coral fragments, sponge skeletons and sediment were collected with a boxcorer. Along the Kenyan coast, dead coral fragments and coral gravel were collected during snorkelling and skin diving. Only nematodes belonging to the families Epsilonematidae and Draconematidae were considered. Community structure was analysed using multivariate techniques. Biodiversity was represented via rarefaction curves. Additive partitioning of species diversity was conducted. Turnover between microhabitats within locations and between locations within microhabitats were compared in a ternary plot.Results Twelve epsilonematid and five draconematid species were found in the Porcupine Seabight. In Kenya, 39 epsilonematid and 20 draconematid species were distinguished. Three species were found at both sampling locations. A table with the known distribution of all currently described species encountered in our study area is provided. At both sampling locations, the communities on coral fragments were significantly different from those in the other microhabitats, and were most diverse. In Kenya, species richness was mainly determined by local diversity and by turnover between localities. The contribution of β‐diversity decreased when abundance data were analysed. Turnover between microhabitats and between coral samples from different localities was higher than turnover between locations for gravel samples.Main conclusions Coral fragments were recognized as favourable substrata for typically epifaunal nematodes. Species‐specific habitat preferences were explained by finely tuned morphological adaptations. Our results suggest that cosmopolitan species could well be cryptic species, and this explanation for the existence of morphologically identical nematodes in geographically distant areas is weighed up against other plausible explanations. Coral degradation zones are an important source for new species of Epsilonematidae and Draconematidae. The addition of sampling locations contributed to the total number of species, although the added species were generally rare.

Meiobenthos at the Arctic Håkon Mosby Mud Volcano, with a parental-caring nematode thriving in sulphide-rich sediments

Hakon Mosby Mud Volcano (HMMV, SW Barents Sea slope, 1280 m) is one of the numerous cold methane-venting seeps existing along the continental margins. Analyses of video- guided core samples revealed extreme differences in the diversity and density of the metazoan meiobenthic communities associated with the different sub-habitats (centre, microbial mats, Pogonophora field, outer rim) of this mud volcano. Diversity was lowest in the sulphidic, microbial mat sediments that supported the highest standing stock, with unusually high densities (11 000 ind. 10 cm -2 ) of 1 nematode species related to Geomonhystera disjuncta. Stable carbon isotope analyses revealed that this nematode species was thriving on chemosynthetically derived food sources in these sediments. Ovoviviparous reproduction has been identified as an important adaptation of parents securing the survival and development of their brood in this toxic environment. The proliferation of this single species in exclusive association with free-living, sulphide-oxidising bacteria (Beggiatoa) indicates that its dominance is strongly related to trophic specialisation, evidently uncommon among the meiofauna. This chemoautotrophic association was replaced by copepods in the bare, sulphide- free sediments of the volcano's centre, dominated by aerobic methane oxidation as the chemosyn- thetic process. Copepods and nauplii reached maximum densities and dominance in the volcano's centre (500 ind. 10 cm -2 ). Their strongly depleted carbon isotope signatures indicated a trophic link with methane-derived carbon. This proliferation of only selected meiobenthic species supported by chemosynthetically derived carbon suggests that, in addition to the sediment geochemistry, the asso- ciated reduced meiobenthic diversity may equally be related to the trophic resource specificity in HMMV sub-habitats.

Meiofauna densities and gastrotrich community composition in a Mediterranean sea cave

During the past 5 decades, the large-sized biota inhabiting dark marine caves has attracted the attention of many marine biologists; in contrast, studies concerning the meiofaunal organisms of these peculiar biotopes remain scanty and mostly with a taxonomic aim. In this study, the nature and abundance of meiofaunal taxa living in a Mediterranean, semi-submerged sea cave was surveyed in relation to distance from the entrance and over two different seasonal periods. Particular attention was paid to the Gastrotricha taxocene. Research was carried out in a cave along the Ionian coast of Apulia (southern Italy), the “Grotta Piccola del Ciolo” which opens for approximately 120 m on the north-eastern side of a shallow fjord and has a bottom blanketed by fine to very fine sand, occasionally rich in detritus. Quantitative samples in four replicates were collected by SCUBA diving, in November 2000 and June 2001, coring the sediment with a hand-held piston corer in three light-free sites (stations 1–3) located at increasing distances from the entrance. At each site, two additional 500-ml sediment samples were collected for an in vivo study of the Gastrotricha. Faunistic analysis found a fairly high meiobenthic diversity, identifying representatives of more than 12 major groups, with total abundances ranging from 656 ind./10 cm2 (10 cm2) in November to 1,069 ind./10 cm2 in June. Station 1, the closest to the entrance invariably hosted the most abundant meiofaunal community (851 ind./10 cm2 in November and 1932 ind./10 cm2 in June), followed by station 2 or 3 depending on the season. While nematodes and harpacticoids appear as the most abundant taxa when the cave is considered as a whole, other taxa may prevail numerically in selected stations, e.g. priapulids, which are the second most abundant taxon at station 1 (30 ind./10 cm2 in November and 83 ind./10 cm2 in June). Although the density of total meiofauna and that of the single groups may not be very high, the cave is interesting by virtue of the peculiarity of the hosted fauna, e.g., species and genera new to science or new to the Mediterranean Sea. Regarding the Gastrotricha, we found 16 species, accounting for 1.3–2.6% of the total meiobenthos (density = 8.4 ind./10 cm2 in November and 27.4 ind./10 cm2 in June). Analysis of the gastrotrich community found, particularly in June, an assemblage of taxa quite different from those found in open habitats, even at the family level; differences that are probably due to the exploitation of different food resources by animals populating the two environments, i.e. algae in the open sea versus bacteria in the caves. Results indicate that for meiofauna, as happens for macrofauna, the marine caves may represent hotspots of biodiversity and endemism; the driving forces at the base of the trophic depletion hypothesis seem to be responsible for structuring the meiofauna community inside the cave.

The influence of Atrina zelandica Gray on meiobenthic nematode diversity and community structure

The influence of the large suspension feeding horse mussel Atrina zelandica Gray on meiobenthic diversity and community structure has been studied at two sites in New Zealand where Atrina beds form discrete patches. Community attributes inside (IN samples) and outside the beds (OUT samples) in the bare sediment have been compared. At both a sheltered muddy harbour site and a more exposed coastal sandy site, significant effects were found. These were stronger, however, at the sheltered site: The presence of Atrina resulted in (i) a greater reduction in several univariate measures (including Shannon diversity), (ii) more pronounced changes in the form of k-dominance curves, (iii) greater differences in species composition as revealed by the R-statistic of ANOSIM, (iv) a higher value for average Bray Curtis dissimilarity between IN and OUT samples and, finally, (v) greater variability among the IN samples compared with the OUT samples as measured by the Index of Multivariate Dispersion. Variations in density of different nematode functional groups indicate that the detrimental effects of Atrina on meiobenthic biodiversity may be attributed to its activity (production of biodeposits) and physical presence, resulting in reduced oxygen concentrations in the sediment. At the exposed coastal sandy site, the mussels were older and probably produced less biodeposits per unit biomass, and also the wave-induced flows over the bed are more likely to result in sediment mixing, which will tend to blur local effects.

Is the Determination of Meiobenthic Diversity Affected by the Sampling Method in Sandy Beaches?

Abstract. Meiobenthic samples were collected by two different methods from the microtidal coralline sand beach at Gosier, Guadeloupe, West Indies: (I) vertical cores and (2) the Karaman/Chappuis (KC) technique of digging a hole and filtering the seepage water from the bottom. Nematode species diversity was unaffected by the sampling method, but nematode species composition differed. There was no evidence from statistical analysis to suggest differences in diversity or composition of higher taxa between sampling methods, although gastrotrichs appeared to be underrepresented by the KC technique.