Desde microorganismos a la macrofauna: un estudio comparativo de las comunidades bentónicas profundas y su respuesta a las variables ambientales a lo largo del talud de Malta (mar Jónico)

A comparative study for abundance, biomass and diversity was carried out for the prokaryote, meiofauna and macrofauna communities at three depth stations (1200, 1800 and 2100 m) along the Malta Escarpment (Mediterranean Sea). Our investigation showed a two-fold increase with depth in prokaryote abundance; the contribution of prokaryote biomass to the total benthic biomass was predominant at all depths. Bacteria were the dominant prokaryote component and Archaea formed a considerable fraction (20%-30%) of the prokaryote assemblages. The meio- and macrofauna abundances and meiofauna biomass did not decrease significantly with depth but macrofauna biomass did. The α diversity did not follow a clear bathymetric trend for both nematode and macrofauna species. Probably because of the large number of eurybathic nematode genera, nor did the turnover diversity in nematode composition change down the depth gradient. Conversely, for the macrofauna there was a perceptible change in community composition between the shallowest station and the two deeper stations. Food availability affected only the macrobenthic component. The increase in the prokaryote organisms with depth and the dominance of nematodes and macrofauna deposit feeders suggest active grazing by the two benthic components on microbes. This would transfer energy to the higher trophic levels through the microbial compartment.Se llevó a cabo un estudio comparativo de las comunidades de procariotas, meiofauna y macrofauna sobre la abundancia, biomasa y diversidad. Fue realizado en tres estaciones en varias profundidades (1200, 1800 y 2100 m) a lo largo del talud de Malta (mar Mediterráneo). Nuestra investigación muestra que, aumentando la profundidad, la abundancia de procariotas se duplica. La contribución de la biomasa procariota al total de la biomasa bentónica predominó en todas las profundidades. Las bacterias eran la fracción procariota dominante y junto con los Archaea representaban al 20-30% del total de procariotas. Por otra parte la abundancia de la meiofauna y macrofauna y la biomasa de la meiofauna no disminuían significativamente con la profundidad, mientras que la biomasa de la macrofauna sí lo hacía. La diversidad α no siguió una tendencia batimétrica muy clara para las especies de los nematodos y macrofauna. Probablemente debido a la gran abundancia de géneros de nematodos eurybatiales, la tasa derenovación de la diversidad en la composición de nematodos tampoco cambió por el gradiente de profundidad. En cambio, para la macrofauna hubo un cambio apreciable en la composición de la comunidad entre la estación más superficial y las dos estaciones más profundas. La disponibilidad de alimentos afectó sólo al componente macrobentónico. El aumento con la profundidad de los organismos procariotas, el dominio de los nematodos y la macrofauna que se alimenta de los materiales depositados sugieren un medio activo para los dos componentes bentónicos microbianos. Esto daría lugar a una transferencia de energía a niveles tróficos superiores a través del compartimento microbiano

Mangrove-mudflat connectivity shapes benthic communities in a tropical intertidal system

Understanding the connectivity among seascape habitats is an important emerging topic in marine ecology and coastal management. Mangroves are known to provide many ecosystem services such as coastal protection and carbon cycling, but their functional relationships with adjacent benthic intertidal communities are less clear. We examined how spatial adjacency to mangroves affects macrobenthic communities of intertidal mudflats in a tropical estuarine ecosystem. In the Bijagós Archipelago, Guinea-Bissau, benthic macrofauna assemblages were compared among sampling locations with different connectivities between intertidal mudflats and mangrove stands. We explored how a single mangrove connectivity index (MCI), combining mangrove tidal basin size and the distance to the mangrove edge, affected macrobenthic composition, and compared this effect to sediment properties. In addition, we used structural equation modelling (SEM) and ordination to determine how different environmental predictors directly and indirectly affected macrobenthic communities. MCI strongly affected macrobenthic composition and species abundance, and SEM revealed that this effect contained both a direct component and an indirect component through mudflat NDVI (normalized difference vegetation index, an indicator for microphytobenthos). Sediment properties (grain size, organic matter) affected macrobenthos independently from MCI, nevertheless sediment properties were also affected by MCI. We show the importance of accounting for the seascape structure of tidal basins when investigating the connectivity between mangroves and macrobenthic communities of intertidal mudflats. As benthic macrofauna is a key food source for endangered fish and waders in these systems, our findings provide strong arguments for the integrative conservation of intertidal mudflats and mangroves at the seascape scale

Diversity of Wadden Sea macrofauna and meiofauna communities highest in DNA from extractions preceded by cell lysis

Metabarcoding of genetic material in environmental samples has increasingly been employed as a means to assess biodiversity, also of marine benthic communities. Current protocols employed to extract DNA from benthic samples and subsequent bioinformatics pipelines differ considerably. The present study compares three commonly deployed metabarcoding approaches against a morphological approach to assess benthic biodiversity in an intertidal bay in the Dutch Wadden Sea. Environmental DNA was extracted using three different approaches; extraction of extracellular DNA, extraction preceded by cell lysis of a sieved fraction of the sediment, and extraction of DNA directly from small amounts of sediment. DNA extractions after lysis of sieved sediment fractions best recovered the macrofauna diversity whereas direct DNA extraction of small amounts of sediment best recovered the meiofauna diversity. Extractions of extracellular DNA yielded the lowest number of OTUs per sample and hence an incomplete view of benthic biodiversity. An assessment of different bioinformatic pipelines and parameters was conducted using a mock sample with a known species composition. The RDP classifier performed better than BLAST for taxonomic assignment of the samples in this study. Novel metabarcodes obtained from local specimens were added to the SILVA 18S rRNA database to improve taxonomic assignment. This study provides recommendations for a general metabarcoding protocol for marine benthic surveys in the Wadden Sea

In this Issue

Aim: Molluscivorous shorebirds supposedly developed their present wintering distribution after the last ice age. Currently, molluscivorous shorebirds are abundant on almost all shores of the world, except for those in the Indo-West Pacific (IWP). Long before shorebirds arrived on the scene, molluscan prey in the IWP evolved strong anti-predation traits in a prolonged evolutionary arms race with durophagous predators including brachyuran crabs. Here, we investigate whether the absence of molluscivorous shorebirds from a site in Oman can be explained by the molluscan community being too well-defended. Location: The intertidal mudflats of Barr Al Hikman, Oman. Methods: Based on samples from 282 locations across the intertidal area the standing stock of the macrozoobenthic community was investigated. By measuring anti-predation traits (burrowing depth, size and strength of armour), the fraction of molluscs available to molluscivorous shorebirds was calculated. Results: Molluscs dominated the macrozoobenthic community at Barr Al Hikman. However, less than 17% of the total molluscan biomass was available to shorebirds. Most molluscs were unavailable either because of their hard-to-crush shells, or because they lived too deeply in the sediment. Repair scars and direct observations confirmed crab predation on molluscs. Although standing stock densities of the Barr Al Hikman molluscs were of the same order of magnitude as at intertidal mudflat areas where molluscivorous shorebirds are abundant, the molluscan biomass available to shorebirds was distinctly lower at Barr Al Hikman. Main conclusions: The established strong molluscan anti-predation traits against crabs precludes molluscan exploitation by shorebirds at Barr Al Hikman. This study exemplifies that dispersal of "novel" predators is hampered in areas where native predators and prey exhibit strongly developed attack and defence mechanisms, and highlights that evolutionary arms races can have consequences for the global distribution of species

Erratum: Impact of an artificial structure on the benthic community composition in the southern North Sea: Assessed by a morphological and molecular approach

The following affiliation for Lise Klunder was not included in the earlier version of this article. This has now been added: Marine Evolution and Conservation, Groningen Institute of Evolutionary Life Sciences, University of Groningen, Nijenborgh 7, 9747 AG Groningen, The Netherlands.</p

Impact of an artificial structure on the benthic community composition in the southern North Sea:Assessed by a morphological and molecular approach

Man-made structures in the North Sea are known to act as artificial reefs by providing a habitat for sessile epifauna in a predominantly soft sediment environment. This epifauna is hypothesized to cast a so-called "shadow"over the soft sediment ecosystem by altering the nutrient composition in the overlying water column. In addition, the structure itself could alter currents and thereby influence the deposition and erosion of the sediments in the wake of the platform. This study aims to assess the long-Term effects of a gas platform in the southern North Sea on the surrounding benthic community by both morphological and molecular identification of benthic species. The species composition and a set of abiotic factors of the sediment around a gas platform were assessed along four transects. Differences for the abiotic factors were found in the closer vicinity of the platform in the direction corresponding to the predominant currents. The number of benthic fauna families found in the molecular approach were on average three times higher than for the morphological approach. Both approaches showed that small differences occurred primarily due to changes in sedimentary organic matter content. Differences in species composition were more pronounced between transects rather than between distances from the platform.</p