Ecological status evaluation of the quality element macro-invertebrates for the Belgian coast (2007-2009)
Van Hoey, G.; Derweduwen, J.; Hillewaert, H.; Hostens, K.; Pecceu, E.; Wittoeck, J. (2010). Ecological status evaluation of the quality element macro-invertebrates for the Belgian coast (2007-2009). Report ILVO-Animal Sciences-Fisheries, 6. ILVO: Oostende. 65 pp.
Part of: Report ILVO-Animal Sciences-Fisheries. ILVO
The Water Framework Directive (WFD; 2000/60/EG) aims to achieve a good ecological and chemical quality status of the European waters (Rivers, Lakes, coastal- and transitional waters). The quality status is determined based on the evaluation of different quality elements, e.g. macro-invertebrates. Macro-invertebrates are good indicators for detecting anthropogenic impacts and ecological degradation. The Belgian Coastal water body (< 1 nautical mile) is a small area, but this environment is highly influenced by the inputs from 4 harbors and 2 rivers (Ijzer, Scheldt), coastal defense works (dredging, sand suppletion) and fisheries. To evaluate the ecological quality status of this area, a WFD monitoring program was implemented in 2007 and the BEQI (Benthic Ecosystem Quality Index) (www.beqi.eu) is used as macro-invertebrate indicator tool. The ecological quality status has to be reported in the River Basin Management Plan of a water body, which is characterised by a reporting cycle of six years (2009-2015). The current WFD monitoring program for macro-invertebrates is designed to evaluate its ecological quality status with a good confidence on an adequate spatial and temporal scale. A good spatial coverage of the samples per habitat in a water body is very important for a water basin assessment (habitat approach), due to the small scale spatial variation of the benthic characteristics. Therefore, samples were randomly taken at 9 or 11 locations, representative for one or more habitat types (Abra alba, Nephtys cirrosa and Macoma balthica habitat), in the water body Belgian Coast. A temporal coverage of the samples is important due to the fact that the benthic characteristics show strong year-to-year variations. Therefore, a yearly monitoring is executed instead of monitoring once over the evaluation period of 6 years. Currently, we are halfway of the first monitoring cycle (2007-2012). Finally to obtain a good confidence, a high number of samples has to be taken to reduce the chance of misclassification in the ecological quality status. Therefore, the number of samples is determined based on the observed variance in benthic characteristics in the reference dataset of each habitat type. In this report, the monitoring results of the third year (2009) are outlined, together with an ecological quality status evaluation over the first part (2007-2009) of the first monitoring cycle. Beside it, a profound analysis on the habitat approach and a confidence analysis of the assessment of the macro-invertebrate monitoring program is made. The most obvious pattern in the benthic data of the year 2009 is the massive recruitment of the bivalve Ensis directus, an invasive alien species, along the entire coastline. The linking of the samples to a certain habitat type is less obvious than in the previous years, partly due to the presence of Ensis directus. There are also more samples taken in sandy sediments (Nephtys cirrosa habitat). The BEQI level 3 shows that the Abra alba and Nephtys cirrosa habitat are in moderate status compared to the reference situation, which is mainly due to Ensis directus and a lower species richness. The Macoma balthica habitat is in a good status, mainly due to the high status of the parameter density. The ecological quality status assessment over the period 2007-2009 shows an overall moderate status of the water body Belgian Coast for the quality element macro-invertebrates, due to the moderate status of all habitats. The Abra alba habitat shows a moderate status for most parameters, due to lower densities compared to the reference situation, mainly of the species Spisula subtruncata, Magelona johnstoni and Lanice conchilega. The poor to moderate status of the habitat.Nephtys cirrosa is due to the unusual high benthic densities (Ensis directus) in this sandy environment. The Macoma balthica habitat at the west coast is in a good status, but moderate in the central and eastern coast. This moderate status is mainly due to the nearly absence of Petricola pholadiformis, Barnea candida and Polydora spp. The number of species expected in this habitat type is also lower compared to the reference situation. It seems that the moderate benthic status of the Belgian Coastal waters is mainly caused by the lower densities and presence of certain key species in each habitat or the introduction and success of an alien species (Ensis directus). This ecological degradation of the macro-invertebrate fauna in the Belgian coastal area cannot directly be linked to one anthropogenic pressure, but is probably the result of the combined acting of the present anthropogenic impacts. Two aspects, which are of importance in the benthic monitoring design, are the habitat approach and the confidence analysis on the assessment and this is investigated in more detail in this report. Currently, the determination of the habitat type of each sample is based on a biological analysis of the data, funded with sedimentological sample information. This approach may lead to the assignation of some poor benthic samples, qua diversity and density, to the wrong benthic habitat type. In other words, this approach can mask the real habitat potential of some locations. Secondly, the assigned habitat type of some parts of the locations does not correspond with the habitat suitability map. Therefore, it can be advisable to re-run the habitat suitability model in the Belgian Coastal area, based on the recent gathered monitoring information. A different procedure for habitat assignation of the samples has an effect on the EQR score’s of the habitat, as tested in this report. Therefore, we concluded that one approach has to be selected, based on the visions of the benthic experts in Belgium. The confidence of the ecological quality assessment, coupled to the sampling effort, is judged with a statistical power analysis in the BEQI approach. An estimate of the sampling effort depends on the wanted power, the effect size and the variance in the benthic habitat characteristics (number of species, density). Currently, confidence classes are defined based on the effect size that can be measured with a power of 75%. Setting the power on 75% should lead to an acceptable sample effort. For obtaining a good confidence, the sampling effort in the assessed habitat has to be of that size to detect an effect size of factor 2 (halving or double) with a power of 75%. Due to difference in variance in benthic parameters, the sampling effort needs to be much higher for the parameter density compared to number of species and varies also between the three habitat types. By this kind of analysis, the government and scientists can investigate the sampling effort to obtain a certain confidence over the effect size they want to judge. There can be concluded that, regarding the quality element macro-invertebrates, the ecological status assessment over the period 2007-2009 assigns the Belgian coast as moderate. Therefore, the operational monitoring program needs to be continued. Adaptations or reductions in the program are possible, whereof some suggestions were tested and reported in this report, but the aspects regarding the habitat approach and confidence may not be neglected.
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