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Ana A.

on 19 June 2013

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Transcript of Nemas2

a priori defined estuarine stretches
11 sampling stations
Subtidal sediments
Extraction from the sediment
(cc) image by jantik on Flickr
" If all the matter in the universe except the nematodes were swept away, our world would still be dimly recognizable..." -N.A. Cobb, 1914
Sex differentiation
Trophic structure
Feeding groups by Wieser (1953)
1A. Selective deposit feeders
1B. Non-selective deposit feeders
2A. Epigrowth-feeders
2B. Predators (Wieser, 1953).

Predatory nematode feeding on a phytonematode (plant-parasitic worm) (100x)
Biological trait approach add relevant information to species pattern regarding relationships between diversity patterns and the abiotic environment
Application of nematodes' features in spatial and temporal studies in estuaries
The Mondego estuary as study case
Southern European estuary
Venice salinity classes:
Environmental parameters
Environmental variables - PCA
Meiofauna communities can also suitably reflect the ecological conditions present in a particular system
Macrofauna communities have traditionally been used to assess and evaluate ecological integrity
What if the best characteristics of meiofauna and macrofauna could be taken advantage of to obtain complementary information allowing a more precise environmental monitoring?
Main Goal
Determine whether subtidal nematode and macrofauna assemblages provide a comparable assessment of ecological conditions, using specific tools and approaches of each benthic compartment .
Do nematode and macrofauna assemblages provide similar ecological assessment information?
Chromadora sp.
Sabatieiria sp.
Cuticle pattern
Chromadorita sp.
Doliolaimus sp.
Buccal cavity (shape, absence/presence of teeth)
Terschellingia sp.
Praeacanthocus sp.
Antomicron sp.
Amphid (presence and shape)
Metachromadora sp.
Tail shape
Dichromadora sp.
Cuticle: type and pattern
Buccal cavity
Males are more usefull in species identification
nMDS nematodes community
Investigate changes in patterns of nematodes assemblage composition and diversity, trophic composition and life strategies between different estuarine locations and sampling occasions.
Diversity indices
Functional indices
Trophic index:

Maturity Index:
The density contribution of each trophic group to total nematode density.
Ranges from 0.25 (highest trophic diversity) to 1 (lowest trophic diversity)
Significant differences: distinct stretches (R=0.804; p=0.001)

nMDS plot
Reflects the spatial distribution

92% : mean sand%, NO3-,NO2-, NH4+
Distinct assemblages (R= 0.694; p=0.001)

nMDS plot
Reflects the estuarine gradient

83% : salinity and dissolved oxygen
Index Trophic Diversity: discriminates between assemblages of nematodes belonging to each estuarine stretch

Maturity Index: difficult to distinguish between stations. Upstream stretch distinct from the remaining ones (high values: undisturbed conditions)
Benthic Assessment Tool (H’, d, AMBI): the Ecological Quality Status ranged from “Poor” to “Moderate”
Same “picture” of the estuary

Closely followed the estuarine gradient

Distinction between stretches more evident as represented by the nematode community

The transition from freshwater fauna to typical estuarine assemblages and then to marine communities has been observed for both benthic groups
Both macrofauna and meiobenthic nematodes may provide different but complementary types of information, depending on the indices used and the different “response-to-stress” times of each benthic group. Since they reveal different aspects of the benthic ecossystem, optimally, both groups should be used in marine pollution monitoring programs.
Differences in the results of the structural and functional attributes
Consistent with the stretches defined a priori
Ecological indicators focusing on the same group gave divergent information (ITD ≠ MI)
Answering to our main question is not straightforward

Both invertebrate groups were characterized by distinctive assemblages
There is the need to develop a multimetric index that takes into account abundance, composition and taxon sensitivity to stress, in order to provide clearer information regarding the ecosystem status in accordance to the WFD requisites.

The absence of differences in the nematodes communities between both arms of the Mondego estuary emphasizes the prime importance of salinity in defining and limiting species distribution in estuaries.

Nematode assemblages were different between areas and sampling occasions. Maximum dissimilarities were observed between the Oligohaline and both the Polyhaline and Euhaline areas.

Nematodes communities comprised a high number of genera but with few dominant ones.
Species that tolerate the highly variable conditions in estuaries tend to be abundant, taking advantage of the resources.
Functional diversity is important for interpreting distribution patterns of the communities. The MI and ITD, based on different ecological principles (life strategy and trophic composition, respectively) behaved differently:

- ITD only differentiated “extreme” conditions: good ecological conditions in the mouth of the estuary (lower values) and lower ecological status upstream;
- MI suggested a high stress level in both the polyhaline and euhaline areas (low values) and a better ecological status in the oligohaline area.

The integration of both taxonomic and functional attributes of nematodes must be taken into consideration when assessing the ecological status of estuaries.

Online identification through Nemys
Identification steps
Nematodes: estuarine story tellers
Ana Sofia Alves
6 September 2012
On a
methodological basis meiofauna is defined as all metazoans that pass t
hrough a sieve with 500 µm or 1mm (upper limit) mesh and are retained on a sieve of 31(deep sea), 38, 42 or 63µm mesh (lower limit).
On a methodological basis meiofauna is defined as all metazoans that pass through a sieve with 500 µm or 1mm (upper limit) mesh and are retained on a sieve of 31(deep sea), 38, 42 or 63µm mesh (lower limit).
The term meiobenthos

(Mare, 1942) was used to describe benthic metazoans of intermediate size: smaller than macrobenthos and larger than the microbenthos (bacteria, diatoms and most protozoa).
Heterogenous group, high abundance, high diversity, short generation times and high productivity.
Ubiquitous in estuaries worldwide, with average densities of of 10^5 inds/m^2.
Microscope fitted with a 100x oil immersion objective
Identification books with pictorial keys
Pedro Barbosa
Indices application
Nematodes are assigned accordingly their ability for colonizing or persisting in a certain habitat, from "colonizers" (high tolerance to disturbance events) to "persisters" (low tolerance).
Mondego estuary
Clear separation of areas: variations in salinity, sediment grain size and nutrient concentrations were the most responsible for the observed estuarine gradient, structuring nematode assemblages.
Highest densities were reached in the Euhaline and Polyhaline areas and lowest in Oligohaline area, regardless of the sampling occasion.
Margalef and Shannon-Wiener index values followed the trend shown by the number of genera, indicating a lower diversity in the Polyhaline areas.
Ecological quality status assessment
Macroalgae, macrophytes
Benthic invertebrate fauna
Meiofauna communities have been only recently considered to be
good indicators of ecological quality
, exhibiting several
over macrofauna, such as their small size, high abundance, rapid generation times and absence of a planktonic phase
Extraction and identification
Drawing tube
Ecologically important for the structuring of biogeochemical cycles in aquatic systems and their food webs.

Useful biological tool to detect anthropogenic pressures.
Four of every five multicellular animals on the planet are nematodes.
Study area
Number of genera
This study allowed a full description of nematode communities along the estuarine gradient, making available information on the ecological conditions of the system and initiating a baseline for long-term monitoring studies
Some genera are indicative of disturbances
The transition between areas was characterized by different assemblages
Coupled with the taxonomic diversity, functional diversity is important for interpreting distribution patterns of the communities
In conclusion...
Nematodes are highly suitable and sensitive biological organisms through which our comprehension of marine and transitional environments can be further explored.

Some studies have proposed the inclusion of nematodes in the biological compartment of the WFD since they represent a synthetic and direct measure, summarizing different and complex aspects of an ecosystem.

It was expected that thse two components of the benthos respond differently to disturbances of their communities, and that these responses provide an interesting and useful basis of comparison.
PC2 (23.8%)
Full transcript