盐城自然保护区射阳河口潮间带大型底栖动物空间分布与季节变化

2008年11月—2009年10月,在盐城自然保护区射阳河口潮间带按月份对大型底栖动物群落进行取样。共得到大型底栖动物16种,隶属3门4纲15科,为软体动物、节肢动物甲壳类和环节动物多毛类,其中,潮间带米草丛6种,高潮带光滩7种,中潮带光滩13种,低潮带光滩7种。对潮间带各样点的物种数、密度、生物量以及不同样点的生物多样性指数Margalef指数(S)、Shannon指数(H)、Pielou指数(J)和Simpson指数(D)进行样点-季节间无重复双因素方差分析,发现样点间物种数、密度和生物量差异极显著(所有P<0.01),三者季节间差异均不显著;样点间H、D和S差异显著(所有P<0.05),季节间差异均不显著;而季节间和样点间J差异均不显著。对四季4个样点的群落进行聚类和排序分析发现,中、高潮带光滩界限不明显,潮间带米草丛和低潮带光滩界限明显。结果表明:生境条件的不同是潮间带大型底栖动物群落组成差异的主要原因,同一生境大型底栖动物群落季节间差异不显著。     

Untersuchungen über die Auswirkung kommunaler Abwässer auf das benthische Ökosystem mariner Watten

The influence of domestic sewage on intertidal sand and mud flat benthic communities has been studied at three minor outfalls around the North Sea island of Sylt (F. R. Germany) and at the main outfall of Vancouver, B. C. (Canada). During high tide, domestic waste water was found at the water surface due to its lower specific gravity. Consequently, O₂ depletion and salinity decrease occured mainly in surface waters. Oxygen deficiency prevailed in the sediment-water layer, when settled sewage particles were re-suspended by strong tidal currents. This resulted in anaerobic conditions at the sediment surface for up to 40% of the day. Substantial pH decrease and increase in seston load of the water were observed only along the sewage channels and around the outlets when large quantities of sewage were discharged. The amount of particulate organic material increased up to 10% and more in muddy sediments due to sedimentation of sewage sludge. Considerable eutrophication of the mud flats resulted from nutrient load of the sewage and from decomposition of faecal material deposited on the sediments. The vertical distribution of microalgae in the sediment was not influenced by sewage. Primary productivity of microalgae on the sediment surface was positively correlated with the degree of pollution. In heavily and mediumly polluted zones, heterotrophic bacterial production exceeded primary production rates at the sediment surface. Compared with unpolluted intertidal flats the number of macrobenthic species was not reduced in polluted mud flats. In regard to overall species abundance, the macrofauna associations of the disposal area showed three distinct zones: (1) Heavy pollution around the outfall resulted in a degradation zone either without benthic invertebrates or with a very low density of individuals; (2) medium polluted areas were characterized by a zone of maximum density; (3) with decreasing or diminishing pollution the number of individuals returned to normal values (background values). The distribution of species within these zones indicated a significant difference between the response of the channel fauna and the flat fauna to pollution: while the number of species increased continously inside the channels with decreasing pollution, the species variety of the tidal flats was positively correlated with the number of individuals. The diversity of the benthos inside the channels was negatively correlated with the degree of pollution, whereas the diversity indices for the fauna on the tidal flats increased quickly from the centre of pollution, remained at a high level in the medium polluted zone, and decreased again to the area of diminishing pollution. The number of dominating species in the sewage channel increased from the outlet towards the low-tide level, with ratios of 0.9 to 0.33; on the flats the number remained constant throughout the three zones, with maximum ratios of 0.5, demonstrating that no qualitative changes for the macrobenthos of intertidal flats result from domestic sewage disposals. In polluted intertidal flats the macrobenthos is dominated by muddy-sand species whose adaptability to varying sedimentary factors, such as grain size distribution and content of organic material (coefficients of variability: 50.7 and 45.7%, respectively), is relatively high compared with mud and sand species. A special indicator community for polluted intertidal areas does not exist. Intensified waste-water treatment prior to discharge reduced the size of the degradation zone around the outfalls while it simultaneously caused a lower density of the macrobenthos in the medium polluted zone.

---

---

Dissertation aus dem Fachbereich Biologie der Universität Hamburg.     

泉州湾蟳埔潮间带大型底栖动物群落的时空分布

为了比较泉州湾蟳埔潮间带沙滩、互花米草滩和牡蛎石泥滩3种生境(3个潮层)的大型底栖动物群落,2011年4月至2012年1月对3种生境的大型底栖动物进行了季度定量取样。在3种生境共获得85种大型底栖动物,其中环节动物39种,软体动物20种,节肢动物21种,刺胞动物、扁形动物、纽虫动物、星虫动物和脊索动物各1种。多维标度排序(MDS)分析表明,春季和冬季泉州湾蟳埔潮间带3种生境的大型底栖动物群落相似性较低;夏季和秋季互花米草滩与牡蛎石泥滩的大型底栖动物群落相似性较高,而与沙滩的大型底栖动物群落相似性较低。沙滩大型底栖动物群落的季节变化较明显,其次是牡蛎石泥滩,而互花米草滩大型底栖动物群落的季节变化较不明显。大型底栖动物栖息密度和生物量随着潮层降低而增加。单变量双因素方差分析(Two-way ANOVA)表明,不同生境之间的大型底栖动物物种数、栖息密度、多样性指数、均匀度指数和丰度指数有显著差异,但生物量无显著差异,这是因为沙滩的物种数较少,栖息密度较低,但优势种弧边招潮蟹(Uca arcuata)个体较大,互花米草滩和牡蛎石泥滩的优势种为加州中蚓虫(Mediomastus californiensis),个体相对弧边招潮蟹小。不同季节之间大型底栖动物物种数、栖息密度、生物量和丰度指数有显著差异,但多样性指数和均匀度指数元显著差异,这是因为沙滩物种数少,但个体分布比较均匀,而互花米草滩和牡蛎石泥滩物种数较多,个体分布较不均匀。以上结果表明,潮汐、沉积物粒径和生境是影响潮间带大型底栖动物群落的主要因素。潮汐导致潮间带的空间异质性,空间异质性导致大型底栖动物群落的差异。     

中街山列岛岩相潮间带大型底栖动物的群落格局

于2006年9月和2007年7月在中街山列岛4个有居民海岛岩相潮间带设立8个断面,对大型底栖动物的群落结构进行了调查。共获得大型底栖动物34种,其中腔肠动物1种,环节动物3种,甲壳动物10种,软体动物20种。优势种有日本笠藤壶(Tetraclita japonica)、紫贻贝(Mytilus edulis)和节蝾螺(Turb articulatus)等4种。以季节和站位为因子对多样性指数进行双因素方差分析,结果表明只有夏、秋季丰富度指数(P=0.028)存在显著差异,其他指数的方差分析没有显著差异(P>0.05)。3个潮带4个岛屿共12个站位的聚类分析和MDS标序分析表明,12个群落可分为3组(Ⅰ、Ⅱ和Ⅲ组)。大型底栖动物ABC曲线分析表明底栖动物群落尚未受到干扰。     

南麂列岛潮间带大型底栖动物群落优势种生态位

为了解南麂列岛潮间带大型底栖动物的群落特征及其物种间相互作用情况,于2012年5月至2013年2月对南麂列岛保护区内的12个资源位点(潮间带3个潮区的4个季节采样)进行了调查。共采集和鉴定出大型底栖动物354种,其中,18个优势种分别隶属于3门5纲12科。通过对优势种生态位的宽度、重叠度和相似比例的分析,发现:1)带偏顶蛤Modiolus comptus、条纹隔贻贝Septifer virgatus和异须沙蚕Nereis heterocirrata的生态位宽度较宽,均大于0.9;白条地藤壶Euraphia withersi和白脊藤壶Fistulobalanus albicostatus的生态位宽度则较窄,均小于0.5。2)各优势种群的生态位重叠度较低而生态位相似比例较高,生态位宽度值较高的物种对其他物种的生态位重叠值和生态位相似比例也较高,反之则较低。3)Bray-Curtis相似性聚类分析和非度量多维尺度排序(NMDS)结果表明,这些优势种基本属于同一生态类群,没有表现出明显的群落差异。经分析,潮间带大型底栖动物各优势种生态位宽度的分化是由于其对环境的适应能力和迁移能力的不同所导致的,而生态位重叠度较低情况的出现主要是由于各物种占据潮间带上不同的潮区,减小了种间竞争的压力。     

Empty habitat in coastal sediments for populations of macrozoobenthos

Species with wide dispersal are expected to have little empty habitat. This was tested by analysing habitat use in the Wadden Sea near the island of Sylt (North Sea). Sampling covered 222 intertidal sites spread across the K?nigshafen tidal flats (4.5 km², mapping approach conducted once) and 270 subtidal sites along 12 km of a tidal channel system (stratified random sampling in spring and autumn). For any single species, 'suitable habitat' was extrapolated from the ranges of water depth and sediment composition present at the ten sites with the highest frequency or abundance of the species. On average, macrobenthic species actually used less than half of the suitable sites within the scale of local populations; this was far less than expected from a lognormal distribution. In the subtidal, abundance of most species changed between the two sampling seasons. A 50% increase in overall abundance was accompanied by a decrease in empty habitat of only about 25%. Thus, a doubling of abundances would not fill the empty space but just of half of it. The polychaete Scoloplos armiger was an exception in occupying almost all of its suitable habitat in the intertidal and subtidal sediments. A distinct patch of high species richness occurred where flood waters persistently form a large gyre which may enhance larval settlement. We suggest that limitations to larval settlement and/or juvenile survival primarily cause the extent of the observed habitat emptiness. Electronic Publication     

Zonation of intertidal macrobenthos in the estuaries of Schelde and Ems

Based on data, collected in 1980–1990, the intertidal benthic macrofauna of the Schelde and Ems estuaries was compared. The spatial occurrence of the benthic macrofauna along the salinity gradient, including the freshwater tidal area was emphasized. Both estuaries appeared to have a very similar species composition, especially at genus level. The higher number of species observed in the Schelde estuary was probably due to a greater habitat diversity. In both estuaries species diversity decreased with distance upstream. The total density did not vary along the estuarine gradient, whereas biomass is highest in the polyhaline zone.In both estuaries distinct intertidal benthic communities were observed along the salinity gradient: a marine community in the polyhaline zone, a brackish community in the mesohaline zone, and a third community in the oligohaline and freshwater tidal zones of the estuary. These three communities were very similar between both estuaries. Their main characteristics were discussed together with the occurrence and distribution of the dominant species.For the Schelde estuary and to a lesser extent also for the Ems estuary, there was evidence that anthropogenic stress had a negative effect on the intertidal macrobenthic communities of the oligohaline/freshwater tidal zone. Only Oligochaeta were dominating, whereas the very euryhaline and/or true limnetic species were missing. In the mesohaline zone, the Schelde estuary was dominated by large numbers of short-living, opportunistic species, whereas in the Ems estuary relatively more stable macrobenthic communities were observed. A comparison with some other European estuaries showed in general similar trends as those observed for the Schelde and Ems estuaries.     

Sediment-benthos relationships as a tool to assist in conservation practices in a coastal lagoon subjected to sediment change

This study explores the relation between sediment composition and intertidal macrobenthos populations in the Zwin nature reserve (Belgium and The Netherlands), a tidal lagoon that is included in the Ramsar list of wetlands of international importance and has been designated as Natura 2000 area, among others due to its function as wintering habitat for shorebirds that feed upon macrobenthic invertebrates. Species response models show highest biomass of these prey species in organically enriched cohesive sediments and a distinct decline in probability of occurrence for most species in coarse sediments. Further, the biomass of macrobenthos declined between 2003 and 2010 in the extensive low intertidal inlet channel concurrent with the coarsening of the sediment over time in this hydrodynamically stressed habitat. In contrast, macrobenthos biomass increased in a sheltered shallow intertidal habitat that acted as a catchment area for finer sediments, therefore facilitating the succession towards a higher elevated habitat with salt marsh vegetation establishment. Hence, spatio-temporal sediment dynamics decreased site quality for intertidal predators due to a reduction in feeding areas over time, and a change in physical sediment properties that alter the macrobenthos species occurrence and population biomass. This study thus illustrates that sediment transport dynamics may affect the functioning of coastal shallow soft-sediment habitats, like coastal lagoons. The presented macrobenthos species response models provide a tool to assist in management actions that enable the conservation of cohesive low intertidal habitats that provide a high food supply to shorebirds, fish and macrocrustaceans.     

The intertidal zoning of cockles (<Emphasis Type="Italic">Cerastoderma edule</Emphasis>) in the Wadden Sea,or why cockle fishery disturbed areas of relatively high biodiversity

Recently, Kraan et al. (ICES J Mar Sci 64:1735–1742, 2007) reported that areas in the Wadden Sea selected by mechanical cockle dredgers were of greater zoobenthic diversity than areas that remained undredged. The present paper attempts to explain this observation, focussing on the elevation-related zoning of the macrobenthic fauna on tidal flats. Dense beds of cockles Cerastoderma edule occur in a specific intermediate intertidal-height zone where more species are present (and reach their maximal abundance) than in either lower or higher zones. This coincidence of preferred intertidal zones in many species, including cockles, may cause the higher species richness (and higher total macrozoobenthic biomass) of the fisher-chosen dredging areas as compared to other nearby non-dredged tidal-flat areas.     

胶州湾潮间带大型底栖动物的群落生态

潮间带是沿岸带位于最大高潮水面到最小低潮水面之间的区域,处于陆海过渡带,生物资源非常丰富,也是受各种理化环境因子以及人类活动影响最大的区域。我国近年来对各地不同类型的潮间带进行了一些生态调查研究,包括对胶州湾也进行了数次生态调查,如劭晓阳等(2001)研究了浙江省岛     

灵昆岛东滩潮间带大型底栖动物功能群及营养等级构成

2003年11月至2004年8月,在温州湾的灵昆岛东滩针对大型底栖动物群落进行了取样调查,利用调查数据进行功能群和营养等级构成研究。共得到大型底栖动物33种,隶属7门8纲21科,主要为软体动物、节肢动物甲壳类和环节动物多毛类。其中,高潮带25种,中潮带30种,低潮带14种。Margalef物种丰富度指数和Shannon—Weiner多样性指数均表现为：高潮带〉中潮带〉低潮带;Pielou均匀度指数和Simpson优势度指数表现为：高潮带〈中潮带〈低潮带。定性取样得到的浮游生物食者4种,植食者12种,肉食者8种,杂食者7种,碎屑食者2种,定量取样得到的分别为：3,8,5,3种和2种。定量取样获得数据中各个功能群种类数和密度季节间差异均不显著,不考虑季节变化因素肉食者和植食者密度在潮带间存在差异,杂食者和植食者种类数在潮带间存在差异,其他功能群密度和种类数数据在潮带间的差异不显著。研究显示了功能群的生境梯度变化,高潮带主导的功能群为肉食者,植食者和浮游生物食者;中潮带主导的功能群为肉食者和浮游生物食者;低潮带主导的功能群为肉食者,这些变化反映了不同潮带营养等级构成和食物来源的差异,由于生境中能提供的植物沿着高潮带,中潮带和低潮带方向递减,至低潮带未发现植食者;且由于中潮带的生境最为复杂,其功能群的构成也最为复杂;3个潮带的碎屑食者数量比较稳定。大型底栖动物群落与其食物来源一起共有4个营养等级,其中大型底栖动物占据了第2、3、4级,第1级主要碎屑、浮游生物和植物,第2级包括了碎屑食者、浮游生物食者和植食者,第3级主要是杂食者,第4级是肉食者,各个营养级、食物来源之间构成一张复杂的食物网。     

Trophic functional groups and trophic levels of the macrobenthic community at the eastern tidal flat of Lingkun Island, China

A total of 33 taxa, including 21 families, 8 classes and 7 phyla, were found at the eastern tidal flat of Lingkun Island, Wenzhou Bay. Most of them were mollusks, crustaceans and polychaetes. The species numbers found at 3 tidal flats (high, middle and low) were 25, 30 and 14, respectively. It was shown that the high tidal flat had the highest value of diversity indices, followed by middle and low tidal flats. The species belonged to 5 different trophic functional groups: Phytophagous, Camivorous, Omnivorous, Planktophagous and Detritivorous in qualitative samplings. Then 3, 8, 5, 3 and 2 species belonged to Planktophagous, Phytophagous, Camivorous, Omnivorous and Detritivorous groups, respectively, in quantitative samplings. The density and species number of each functional group did not display seasonal variation by the two-way ANOVA method. Regardless of seasonal variation, density of the Phytophagous group and Camivorous group had distinct difference among different zones of tidal flats, and the species number of the Phytophagous group and Omnivorous group had obvious difference among different zones of tidal flats. Results show that there was variation of functional groups among habitats. Change in components of the macrobenthic community reflected different food sources in different zones of tidal flats.     

Macrofauna on flood delta shoals in the Wadden Sea with an underground association between the lugwormArenicola marina and the amphipodUrothoe poseidonis

Living conditions for macrofauna on flood delta shoals are determined by surf, strong currents and sediment mobility. Thus, a unique assemblage of invertebrate species colonize these far off-shore, low intertidal flats. We here describe the macrobenthic fauna of emerging shoals in the Wadden Sea between the islands of Römö and Sylt. Besides ubiquitous macroinvertebrates of the intertidal zone and species which attain their main distribution in the subtidal zone, the flood delta shoals are characterized by organisms adapted to live in these highly unstable sediments, like the polychaetesSpio martinensis, Streptosyllis websteri, Magelona mirabilis, Psammodrilus balanoglossoides, the pericarid crustaceansCumopsis goodsiri, Tanaissus lilljeborgi, Bathyporeia sarsi and a few others. Average abundance (1440 m^?2 of ind >1 mm) and biomass (12.9 g AFDW m^?2) were low compared to other intertidal habitats in the Wadden Sea. Biomass was dominated by largesized individuals of the lugwormArenicola marina. The U-shaped burrows of these polychaetes were inhabited by high numbers ofUrothoe poseidonis. Maximum densities of these amphipods occurred in the deepest parts of the burrows. Sampling at approximately montly intervals revealed no apparent seasonality ofU. poseidonis abundance. Together with smallCapitella capitata, these amphipods constitute a deep-dwelling component of the macrofauna associated with lugworms, which is separated from all other macrofauna living at the sediment surface. As a response to rising sea level and increasing tidal ranges, we expect the unstable sandy shoals, inhabited by numerousSpio martinensis andUrothoe poseidonis, to expand within the Wadden Sea at the cost of stable sandy flats with abundant macrofauna.     

Historical changes and inventory of macroalgae from Königshafen Bay in the northern Wadden Sea

Knowledge on the distribution, abundance and species richness of intertidal macroalgae occurring on sandy and muddy flats of the German Wadden Sea is still incomplete. We summarize published and unpublished information available on the presence of macroalgae on the tidal flats of Königshafen Bay (island of Sylt, North Sea), one of the more extensively studied areas of the Wadden Sea. A total of 46 green algal species, 36 brown algal species and 26 red algal species has been recorded within the last 120 years on soft and hard substrata of Königshafen Bay (disregarding species found unattached or drifting). Several of these species were only temporarily resident on the tidal flats. Today, at least 35 green, 15 brown and 12 red algal species occur within or close to Königshafen Bay. Significant long-term changes in species abundances have occurred in all three major groups of algae: Since the late 1970s, dense green algal mats dominated byEnteromorpha flexuosa, E. radiata andE. prolifera have occurred regularly on the intertidal flats, whereas a general decrease of brown and red algae has been documented. Two red algal species,Gracilaria verrucosa and its epiphyteCallithamnion corymbosum, were conspicuous members of the macroflora until the middle of this century. Although still present in the 1980s, they have now disappeared completely. On the other hand, the brown algaSargassum muticum has begun to colonize mussel beds. The causal background of long-term changes in the macroalgal flora of Königshafen Bay is discussed. Owing to substantial nomenclatural changes during the last 120 years, a revised species list with authors’ names and synonyms is included.     

Recruitment of shore crabsCarcinus maenas on tidal flats: Mussel clumps as an important refuge for juveniles

During the late summer and early fall, juvenile shore crabs (Carcinus maenas L.) occurred in high abundances in mussel clumps scattered on tidal flats of the Wadden Sea. Abundances were much lower on bare tidal flats without mussel clumps and decreased substantially from July to November, whereas numbers in mussel clumps remained high. Large crabs left the tidal flats in early fall, whereas juveniles undertook tidal migrations only in the late fall. In March very few shore crabs were found in the intertidal area. The size of juvenile shore crabs living between mussels did not increase significantly during fall. On the bare tidal flats surrounding the mussels, a size increase was observed. Mussel beds and mussel clumps serve as a spatial refuge for the early benthic phases of juvenile shore crabs. Between mussels they can hide effectively from their epibenthic predators. Juvenile shore crabs do not leave the intertidal area and the mussel habitats before their major predators have left the area. Mussel clumps scattered over the tidal flats may be a critical refuge for juvenile shore crabs settling on tidal flats. Intensified efforts in mussel culturing in the European Wadden Sea during recent decades may have caused an increased abundance of mussel clumps on tidal flats, thus enhancing habitat availability for some mussel-clump inhabitants.     

Density-dependent recruitment after winter disturbance on tidal flats by the lugworm Arenicola marina

The polychaete Arenicola marina is abundant and widespread on intertidal sand flats in K?nigshafen (island of Sylt, North Sea). Juveniles overwinter in subtidal channels and then colonize the upper tidal zone above the range of the adults. In the summers of 1995 and 1997, after a mild and a moderate winter, a distinct nursery belt fringing the shoreline was apparent. The severe winter of 1995/96 changed this pattern. Population size of the adults was halved, and in summer 1996 the juveniles were no longer restricted to an upper intertidal belt and settled over a wide range of tidal flats where adults were diminished. This spatial expansion of recruits is assumed to be a density-dependent response. An overcompensation by one-third of the previous population size did not carry over into the next year. Compared to some other species of the tidal-flat fauna, the disturbance effect by the severe winter on the lugworm population was small and brief. Received in revised form: 7 May 2001 Electronic Publication     

Macrobenthic–mud relations strengthen the foundation for benthic index development: A case study from shallow,temperate New Zealand estuaries

Globally the input of sediment to coastal systems, in particular to estuaries, is predicted to increase due to anthropogenic activities. Sediment mud content is a powerful driver of ecologically important, macrobenthic taxa in estuarine intertidal flats. Accordingly, forecasting species responses to increased sedimentation is fundamental for effective ecosystem management, particularly for productive, geologically young, and sand-dominated estuaries that characterise many countries, including New Zealand (NZ). Modelling studies have highlighted the non-linear, highly variable responses of taxa to mud concentration. However, existing taxon-specific models have not adequately accounted for the full mud gradient, the influence of potentially confounding variables (e.g. organic enrichment, heavy metal concentrations), or regional differences in species responses. Furthermore, such models are often based on qualitative expert consensus of the membership of taxa in ecological groups that characterise their sensitivity to mud content. In this study, data from 25 unmodified to highly disturbed, shallow NZ estuaries, were used to develop an ecologically relevant model to relate the responses of 39 taxa to sediment mud content for use in the intertidal flats of shallow, temperate estuaries. Preliminary analyses indicated that sediment mud content was the dominant driver of macroinvertebrate community composition among sites, total organic carbon was of secondary importance and heavy metals did not explain significant variation in composition. Regression analysis revealed a significant linear relationship between sediment mud and total organic carbon content, which permitted subsequent analyses to be based on mud content alone. Generalised additive models were used to develop taxon-specific models that, according to k-fold cross validation, accurately predicted both probability of presence (up to 79% deviance explained) and maximum density (up to 96% deviance explained) along the sediment mud gradient (0.1–92.3%). Estimates of “optimal mud range” and “distribution mud range” were quantitatively-derived for each taxon and used to categorise taxa into one of five ecological groups (identical to those used in existing biotic indices), based on their individual sensitivities to increasing mud content. By removing expert consensus from the grouping process, the classification methods established herein provide strong support for the use of quantitative indices for the assessment and management of estuarine condition in response to increasing sediment mud content. The findings indicate that NZ estuarine sediments (2–25% mud) support a more diverse and abundant macroinvertebrate assemblage and exhibit low organic enrichment (<1% total organic carbon) compared to estuaries with >25% mud content.     

Some results of a survey of the macrobenthic fauna of the Ems-Dollard estuary (Eastern Dutch Wadden sea)

Summary The macrobenthic fauna of the Ems-Dollard estuary has been sampled in the tidal channels as well as on the tidal flats, by a method ensuring quantitative reliability. The size of the samples was such, that at least several specimens of the most abundant species would be cought. As far as possible, the sampling stations were laid out following a stratified random design.After treatment of the samples the following data were available: the species composition at every sampling station; the number of individuals of a certain species per unit area per sampling station and the ash-free dry weight of a certain species per unit area per sampling station.At the sampling stations in the southern and the western Dollard 8 parameters regarding the sediment were measured.To determine the structure of the macrobenthic fauna of the estuary three different cluster analyses were carried out. The first the presence/absence of species (all species being equally important); the second the number of individuals of a species per unit area, in which the abundant species play an dominant role, and the third using the ash-free dry weight of a species per unit area in which large animals play a dominant role as an input for the analyses.In general there was a good agreement between the structures resulting from the three analyses. The results of a factor analysis (used as a different grouping technique) carried out for sampling stations in the Dollard, confirmed the results of the cluster analyses.The overall structure of the macrobenthic fauna can be derived from maps in which the distribution of separate species is plotted. The estuary can be divided in two parts: a northern part, characterized by the occurrence of animals normally found in a more saline environment, and a southern part characterized by the occurrence of animals normally found in the more brackish parts of estuaries. The transitional zone lies between 53° 20 and 53° 25.The distribution pattern of several species permitted more detailed conclusions about the faunistic structure. These agreed well with the results of cluster and factor analysis. The two approaches to evaluate the data (plotting maps of distribution and pattern recognition analyses) appeared to confirm as well as to supplement each other.The almost completely absence of macrobenthic fauna in the S-E part of the Dollard could not be related to one or a combination of the 8 parameters measured, regarding the sediment. It was concluded that it is caused by factors related to the water, presumably by the waste water entering the estuary at Nieuw Statenzijl.A preliminary comparison with other estuaries reveals that the number of species and the actual species that were found during this investigation are normal for an estuary. The mean ash-free dry weight per unit area on the tidal flats in the northern part is low. This may be caused by the degree of exposition. In the middle part extremely low values occur, but the overall mean value (ca. 14 g/m²) is within the range of values normally to be expected. The mean value for the Dollard (ca. 5 g/m²) is lower than could be expected for this estuary.These conclusions are only preliminary and the items mentioned will have to be investigated more closely in future.     

Predation on 0-group and older year classes of the bivalve Macoma balthica: interaction of size selection and intertidal distribution of epibenthic predators

The bivalve Macoma balthica is a common species in the Wadden Sea and North Sea. Juveniles temporarily use nurseries in the high intertidal. To explain this nursery use, predation pressure was examined for both juvenile and adult Macoma at low and high tidal flats. The study was carried out in the eastern Dutch Wadden Sea.Shrimps Crangon crangon, adult crabs Carcinus maenas, gobies Pomatoschistus and juvenile flatfish were more abundant and larger on low than on high tidal flats, but 0-group Carcinus was more abundant on the high tidal flats. Crangon and 0-group Carcinus stomachs frequently contained Macoma remains. These predators selectively preyed on small 0-group Macoma, both in the field and in laboratory experiments. The effect of predation by epibenthic animals and birds, on the low and high tidal flats, was examined in exclosure experiments (2 mm mesh). There was no effect of epibenthos exclosure on adult Macoma. For 0-group Macoma, densities were higher in exclosures than in the controls where predators had normal access. The density reduction by epibenthic predators was much larger in the low than in the high intertidal. We found no effect of bird predation on densities of 0- and 1+group Macoma.Thus, 0-group Macoma is under high predation pressure by epibenthos in the low intertidal, especially by shrimps, while they are relatively safe in the high intertidal. However, most of the shellfish outgrow their epibenthic predators during their first summer. Therefore, it becomes safe for the bivalves to redistribute to locations where epibenthic predators are abundant, during their first winter. On the other hand, it did not become clear from this study why many of the larger Macoma leave the high intertidal. Concluding, the nursery use of Macoma-spat in the high intertidal is probably, at least partly, an adaptation to avoid epibenthic predation.     

Major Changes in the Ecology of the Wadden Sea: Human Impacts, Ecosystem Engineering and Sediment Dynamics

Shallow soft-sediment systems are mostly dominated by species that, by strongly affecting sediment dynamics, modify their local environment. Such ecosystem engineering species can have either sediment-stabilizing or sediment-destabilizing effects on tidal flats. They interplay with abiotic forcing conditions (wind, tide, nutrient inputs) in driving the community structure and generating spatial heterogeneity, determining the composition of different communities of associated species, and thereby affecting the channelling of energy through different compartments in the food web. This suggests that, depending on local species composition, tidal flats may have conspicuously different geomorphology and biological functions under similar external conditions. Here we use a historical reconstruction of benthic production in the Wadden Sea to construct a framework for the relationships between human impacts, ecosystem engineering and sediment dynamics. We propose that increased sediment disturbances by human exploitation interfere with biological controls of sediment dynamics, and thereby have shifted the dominant compartments of both primary and secondary production in the Wadden Sea, transforming the intertidal from an internally regulated and spatially heterogeneous, to an externally regulated and spatially homogenous system. This framework contributes to the general understanding of the interaction between biological and environmental control of ecosystem functioning, and suggests a general framework for predicting effects of human impacts on soft-bottom ecosystems.