Benthic Nematode assemblages response to seagrass beds spatial heterogeneity in natural recovery process of Zostera Noltii after major colapse

After a seagrass beds (Zostera noltii) colapse in 2008 of the Mira estuary (SW coast of Portugal) symptoms of early recovery were observed. The principal goal of this study is to assess the evolution and resilience of the benthic nematodes assemblages during the natural recovery of the seagrass beds through analysis of the spatial and temporal differences in structural and functional characteristics of the communities. The horizontal macroscale (km) and small scale (m) variability was evaluate. We hypothesize that the new environmental conditions of the early recovery, with sparsely distributed and small-sized seagrass patches, will increase the spatial heterogeneity of nematode communities and significantly affect community diversity, both taxonomic and functional. The sampling design was follows: Samples were collected in five “occasions”, (February, June, September, December 2010 and February 2011), at randomly “stations” located over a distance 50 m, at two “sites”, 2km distance. To test the hypothesis that the composition of nematodes assemblages changes spatially and seasonally a two–way PERMANOVA analysis was performed. Mean nematode densities varied between 1416 ± 107 ind. 10 cm-2 (Site A) and 2611 ± 230 ind. 10 cm-2 (Site B) , and a total of 89 species were identified. The PCO ordination based on abundance and composition of nematode genera do not shown the discrimination of the two sampling sites. However densities and trophic groups showed significant differences across macroscale (sites A and B), the increase of spatial heterogeneity was clear identified in small scale. No significant differences was observed between the temporal variation. The response of the nematode assemblages after the collapse, both in terms of density and diversity, showed a substantial potential of resilience and recovery

Sample acidification effects on carbon and nitrogen stable isotope ratios of macrofauna from a Zostera noltii bed

Acidification treatment has been used in most stable isotope studies to eliminate inorganic non-dietary carbon, allowing d13C measurement of organic carbon needed for trophic studies. Because only limited information about the acidification effects on isotopic ratios exists in the literature, we provide an assessment of such effects for a wide range of benthic macroinvertebrates from estuarine intertidal sediments with sparse Zostera noltii Hornem. vegetation. Our results revealed only few significant d13C shifts for macrobenthos; however, d13C decrease after acidification was substantial for several species. We conclude that acidification is not necessary for removing calcium carbonate in a majority of macrobenthos, but we also suggest preliminary testing before deciding it can be omitted. The magnitude of the d15N shifts was substantial for some species and variability in d15N values of replicate acidified samples exceeded that of nonacidified samples. Therefore, sample acidification should be avoided for d15N determination. Moreover, acidification effects vary considerably among species belonging to a single class, rendering generalisations from single-species information potentially spurious

Recovery of benthic nematode assemblages after a major collapse of Zostera noltii seagrass beds.

During 2008, Zostera noltii seagrass beds of the Mira estuary (SW coast of Portugal) suffered a total collapse, though during 2009 slight symptoms of their recovery were already observed. This association of events, in a short period of time, creates a rare opportunity for obtaining new knowledge concerning natural recovery of ecosystems and habitats. The principal goal is to analyse nematode community responses to the collapse of seagrass beds. Through a comparison of pre- and post-impact data, nematode assemblage recovery and resilience will be assessed. Additionally, the carbon resources utilized by nematodes will be examined, in order to better understand the importance of seagrass detritus as a potential resource for meiobenthic organisms. Significant differences were observed in the community patterns and trophic composition of nematode assemblages before and after the Zostera collapse. The dominant genera of the precollapse community were Terschellingia, Odontophora and Linhomoeus, generally considered microbivorous and/or deposit-feeding nematodes. Immediately after the collapse, they were replaced by Ptycholaimus, Paracomesoma and Metachromodora, all of which are herbivores feeding on diatoms and other microalgae

Recovery of benthic nematode assemblages after a major collapse of Zostera noltii seagrass beds.

During 2008, Zostera noltii seagrass beds of the Mira estuary (SW coast of Portugal) suffered a total collapse, though during 2009 slight symptoms of their recovery were already observed. This association of events, in a short period of time, creates a rare opportunity for obtaining new knowledge concerning natural recovery of ecosystems and habitats. The principal goal is to analyse nematode community responses to the collapse of seagrass beds. Through a comparison of pre- and post-impact data, nematode assemblage recovery and resilience will be assessed. Additionally, the carbon resources utilized by nematodes will be examined, in order to better understand the importance of seagrass detritus as a potential resource for meiobenthic organisms. Significant differences were observed in the community patterns and trophic composition of nematode assemblages before and after the Zostera collapse. The dominant genera of the precollapse community were Terschellingia, Odontophora and Linhomoeus, generally considered microbivorous and/or deposit-feeding nematodes. Immediately after the collapse, they were replaced by Ptycholaimus, Paracomesoma and Metachromodora, all of which are herbivores feeding on diatoms and other microalgae

Unravelling complexities in mangrove meio- and macrofauna benthic food webs using carbon, nitrogen and hydrogen stable isotopes

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