The choice between keeping out chronic pollution versus acute mortality due to emersion: the case of the <i>Tricolor</i> oil pollution prevention in the Zwin nature reserve (Belgium)

As a result of the impending Tricolor oil pollution in the Southern Bight of the North Sea the Zwin nature reserve was blocked from the North Sea by use of a sandbarrier. This method of protection has an important consequence for tidal flat ecosystems: the absence of the tide. The effects on the ecological very important bottom-life of the tidal flats could not be estimated beforehand. All species that were present before the damming up were still present afterwards. During the emersion period Talitrus saltator and Orchestia gammarellus were found in high densities while these species were absent before and after the emersion. Strikingly was the strong decline in abundance of all species which were present in high densities in a sampling station and the abundance of Aphelochaeta marioni and Pygospio elegans declining in all sampling stations during the period of emersion

Does medium-term emersion cause a mass extinction of tidal flat macrobenthos? The case of the <i>Tricolor</i> oil pollution prevention in the Zwin nature reserve (Belgium and The Netherlands)

As a result of the Tricolor oil pollution in the Southern Bight of the North Sea (winter 2003) the Zwin nature reserve, consisting of tidal flats and salt marshes, was blocked from the North Sea by use of a sand barrier. Hence, macrobenthic tidal flat organisms, by nature strongly dependent on the cyclic incoming seawater, were emersed during a period of 27 days. Because the effect of medium-term emersion on the ecologically important benthic life could not be assessed beforehand, the damming was taken as an opportunity to examine these effects. This study demonstrated that: (1) no species vanished due to emersion, (2) although the emersion might have caused some mortality, a mass mortality within the macrobenthos did not occur, and (3) the supra-littoral amphipods Talitrus saltator and Orchestia gammarellus performed a strong, though ephemeral immigration into the intertidal zone during the period of emersion. In view of both its minor impacts on the macrobenthos and its effectiveness in preventing oil pollution in the Zwin nature reserve, damming as a measure against oil pollution may be considered effective protection, especially during winter

An outbreak of sheep-associated malignant catarrhal fever in sows

his paper describes a case of malignant catarrhal fever in a sow herd in Belgium caused by infection with ovine herpesvirus-2 (OHV-2). The 11 affected sows had high fever and 10 of them died within 3 days after the onset of clinical disease. The most prominent macroscopic lesion was a hemorrhagic to pseudo-membranous gastritis. Histopathology revealed severe infiltration and necrosis of the gastric mucosa. Neither antimicrobial treatment nor injection with anti-inflammatory drugs ameliorated the severity of the disease. As the sows and sheep were housed in the same building with the possibility of having direct nose-to-nose contact, and as PCR testing showed that the virus found in the sows was identical to that found in the sheep, it is very likely that the infection was transmitted from the subclinically infected sheep to the sows. The present case showed that OHV-2 infection should be included in the differential diagnosis when facing problems of fever followed by death, especially when pigs are housed in close contact with sheep

The early life history of the clam <i>Macoma balthica</i> in a high CO₂ world

This study investigated the effects of experimentally manipulated seawater carbonate chemistry on several early life history processes of the Baltic tellin (Macoma balthica), a widely distributed bivalve that plays a critical role in the functioning of many coastal habitats. We demonstrate that ocean acidification significantly depresses fertilization, embryogenesis, larval development and survival during the pelagic phase. Fertilization and the formation of a D-shaped shell during embryogenesis were severely diminished: successful fertilization was reduced by 11% at a 0.6 pH unit decrease from present (pH 8.1) conditions, while hatching success was depressed by 34 and 87%, respectively at a 0.3 and 0.6 pH unit decrease. Under acidified conditions, larvae were still able to develop a shell during the post-embryonic phase, but higher larval mortality rates indicate that fewer larvae may metamorphose and settle in an acidified ocean. The cumulative impact of decreasing seawater pH on fertilization, embryogenesis and survival to the benthic stage is estimated to reduce the number of competent settlers by 38% for a 0.3 pH unit decrease, and by 89% for a 0.6 pH unit decrease from present conditions. Additionally, slower growth rates and a delayed metamorphosis at a smaller size were indicative for larvae developed under acidified conditions. This may further decline the recruit population size due to a longer subjection to perturbations, such as predation, during the pelagic phase. In general, early life history processes were most severely compromised at ,pH 7.5, which corresponds to seawater undersaturated with respect to aragonite. Since recent models predict a comparable decrease in pH in coastal waters in the near future, this study indicates that future populations of Macoma balthica are likely to decline as a consequence of ongoing ocean acidification

Settlement of Macoma balthica larvae in response to benthic diatom films

The role of multi-species benthic diatom films (BDF) in the settlement of late pediveliger larvae of the bivalve Macoma balthica was investigated in still-water bioassays and multiple choice flume experiments. Axenic diatom cultures that were isolated from a tidal mudflat inhabited by M. balthica were selected to develop BDF sediment treatments characterized by a different community structure, biomass, and amount of extracellular polymeric substances (EPS). Control sediments had no added diatoms. Although all larvae settled and initiated burrowing within the first minute after their addition in still water, regardless of treatment, only 48-52% had completely penetrated the high diatom biomass treatments after 5 min, while on average 80 and 69% of the larvae had settled and burrowed into the control sediments and BDF with a low diatom biomass (<3.5 mu g Chl a g(-1) dry sediment), respectively. The percentage of larvae settling and burrowing into the sediment was negatively correlated with the concentration of Chl a and EPS of the BDF. This suggests higher physical resistance to bivalve penetration by the BDF with higher diatom biomass and more associated sugar and protein compounds. The larval settlement rate in annular flume experiments at flow velocities of 5 and 15 cm s(-1) was distinctly lower compared to the still-water assays. Only 4.6-5.8% of the larvae were recovered from BDF and control sediments after 3 h. Nonetheless, a clear settlement preference was observed for BDF in the flume experiments; i.e., larvae settled significantly more in BDF compared to control sediments irrespective of flow speed. Comparison with the settlement of polystyrene mimics and freeze-killed larvae led to the conclusion that active selection, active secondary dispersal and, at low flow velocities (5 cm s(-1)), passive adhesion to the sediment are important mechanisms determining the settlement of M. balthica larvae in estuarine biofilms

Nematode assemblages in a nature reserve with historical pollution

Nematodes, and especially nematode communities, have significant potential as bio-indicators. The present studyaimed to assess the nematode community structure of several sites with different historical pollution. Long-term polluted municipal waste-, tar- and sludge- sites were compared with less disturbed annex sites. At each site heavy metal and PAHs concentrations were measured together with soil texture classes, pH and total organic matter. Identification of three hundred nematodes at each location resulted in the discrimination of 63 genera from 32 different families of which the Cephalobidae, Belonolaimidae, Tylenchidae, Hoplolaimidae, Belonolaimidae and Plectidae were the most abundant families. The sampling sites harbour significantly different nematode communities and significant differences of life-strategy-related parameters (cp-groups, MI indexes) wereobserved. The significant augmentation of the proportion of the cp 2 nematodes in historically-polluted sites was especially informative. Omitting the cp 1 group from the MI (=MI2-5) better reflects putative historical pollution-induced community changes. However, the current study did not reveal significant relationships between historical pollution and the feeding type composition, or the Shannon-Wiener diversity. The observed results are critically assessed in the light of possible flaws such as sampling and analyzing limitations