Common patterns in the fluctuations of macrozoobenthic species living at different places on tidal flats in the Wadden Sea

During 17 successive years (1969–1985) the macrozoobenthos has been sampled quantitatively in the latewinter/early-spring period at 15 stations scattered over Balgzand (a 50 km² tidal flat area in the western-most part of the Wadden Sea) and at 5 stations located in a small (3 km²) area 150 km away from Balgzand in the eastern part of the Dutch Wadden Sea. In 25 species, numbers per m² were, in most years, sufficiently high at 2 or more of the Balgzand stations to allow between-station comparisons of fluctuation patterns. Comparisons were made by rank correlation. Out of a total of 1003 of such comparisons that could be made with the Balgzand data, 47% yielded significantly positive correlations and less than 1% significantly negative ones. Thus, nearly half of the fluctuation patterns of the populations living at the 15 stations within the Balgzand area showed a high similarity. Synchronization of population fluctuations was augmented particularly by the incidence of severe winters (causing low spring numbers in about a quarter of the species that were sensitive to low temperatures and high reproductive success in several species during the subsequent summer) and further by the increasing trends in numbers in about half of the species, probably as a consequence of eutrophication.Similar results as on Balgzand were obtained within the restricted area Groninger Wad in the eastern part of the Dutch Wadden Sea (Essink & Beukema, this issue). Comparison of the fluctuation patterns between the 2 distant areas also yielded high numbers of significantly positive correlations, though the proportion of the patterns that were similar was lower than these proportions were within the 2 areas.It is concluded that common patterns of fluctuation in numerical densities of macrobenthic species can be assessed over vast areas. Such common patterns will represent the normal or base-line fluctuations that may be used to distinguish (as departures from such patterns) the effects of local disturbing influences.     

Long-term changes in macrozoobenthic abundance on the tidal flats of the western part of the Dutch Wadden Sea

For 20 years (1969–1988), larger bottom animals have been sampled quantitatively once or twice annually at 15 stations scattered over Balgzand (a 50 km² tidal flat area in the westernmost part of the Dutch Wadden Sea). In 29 species, numbers were sufficiently high to allow a statistical evaluation of the fluctuation patterns of their annual densities. The results revealed two main trends: (1) a sensitivity to low winter temperatures in 12 species, causing low densities in these species immediately after a severe winter (1979, 1985, 1986 and 1987) and relatively high densities during a period with some mild winters in succession (1973–1975); (2) an upward long-term trend in 11 (other) species, causing upward trends (viz. roughly a doubling) of total macrozoobenthic biomass and production over the 20-year period of observation, probably as a consequence of increasing eutrophication. By far the major part of the species thus exhibited either of these two patterns, causing total biomass and species number to be governed largely by the above two trends. Results of less frequent sampling (once per 5 or 10 years) of 26 transects scattered over the ≈500 km² of tidal flats of the whole western half of the Dutch Wadden Sea showed that the two trends also represent the changes occurring in a much larger area. Some local departures from the general patterns are discussed and related to specific causes. Presented at the VI International Wadden Sea Symposium (Biologische Anstalt Helgoland, Wattenmeerstation Sylt, D-2282 List, FRG, 1–4 November 1988)     

The effects of mechanical and manual digging for lugworms (Arenicola marina L.) on the benthic fauna of the tidal flats in the Dutch Wadden Sea

Effects of manual bait digging and mechanical cropping ofArenicola marina (L.) on the macrobenthic animals in the Dutch Wadden Sea were investigated. Samples were taken on two tidal flat areas: the Balgzand and the Vlakte van Kerken, from March to November 1981. Only the impacts on major species and on the total biomass are discussed.The numbers of most of the major species are severely reduced immediately after mechanical digging. Some species (e. g. Macoma balthica, Scoloplos armiger) show a fast migration to the depopulated area. Mechanical cropping appears to be more efficient, catching moreArenicola per m². However, manual digging causes less mortality of other benthic animals perArenicola. Recovery of the diminished abundance varies per species; in general the areas harvested show a larger recruitment compared with the non-disturbed areas.     

The Balgzand (Dutch Wadden Sea) tidal flats as a source of soluble silicate

Summary The huge numbers of molluscs, worms and bacteria found in the sheltered tidal flats of the Dutch Wadden Sea, decompose large amounts of organic matter. In this process nutrients incorporated in the particulate organic matter are transferred to the dissolved state. The importance of this process for nutrient budgets was first demonstrated by POSTMA (1954) and later by various authors with emphasis on tidal watersheds and sheltered bays (see Neth. J. Sea Res., 8 (2/3). 1974).The nutrient budgets of the Balgzand tidal flats, as a typical example of a sheltered bay, have been studied during one tidal period by TIJSSEN and VAN BENNEKOM (1976) and recently for a longer period in a cooperative project by the Studiedienst Hoorn of Rijkswaterstaat (DE BOER, 1978) and the Netherlands Institute for Sea Research (MANUELS, 1978). A qualitative measure for the high intensity of mineralization are the high concentrations of nutrients in the water on the Balgzand, compared to those in the Marsdiep (Table I).Simple box models can be used to derive the intensity of nutrient production from the concentration differences in which also the water depth and the exchange velocity of the water with adjacent areas contribute. As a first approximation all mineralization is thought to be situated in the surface sediment (VAN BENNEKOM et al., 1974) and the characteristics parameter becomes the nutrient production per m² per day. For reactive silicate this parameter shows a pronounced seasonal cycle. In January, February and Marchin situ production is hardly detectable while in July and August 500 mg SiO₂ m^–2d^–1 is found. For comparison, weathering of soil by rain water gives 4–30 mg SiO₂.m^–2d^–1 with only slight seasonal variations. The difference is at least partially explained by assuming a different source: diatom frustules in the case of the Balgzand and silicate minerals in the case of normal weathering.The scarce data available indicate that the seasonal cycles of in situ production of phosphate, nitrate and ammonia on the Balgzand are less pronounced than for reactive silicate. The picture is further complicated because ammonia is always produced, but sometimes nitrate is consumed, apparently by denitrification.The nutrient ratios change during the year (Table II). Especially in summer the contribution of silicate is relatively large. This is in marked contrast with the nutrient ratios in the coastal sea water where during the summer the amount of silicate is relatively low. The nutrient ratios are probably an important factor in the seasonal and regional species composition of the phytoplankton.     

Increasing southern invasion enhances congruence between endemic and exotic Mediterranean fish fauna

Species movements in relation with global warming may increase the spatial overlap between exotic and endemic species, which is a critical issue for the conservation of biodiversity. The Mediterranean Sea, which is a receptacle for exotic species while being a hotspot for endemism, provides exceptional material for a case study. The aim of our study was to quantify (i) the increasing invasion from southern fish exotic species (Red Sea and Atlantic Ocean) that the Mediterranean biota is experiencing and (ii) the spatial overlap between exotic and endemic Mediterranean fish fauna following the northward movement of exotic species within the Mediterranean Sea in the context of global warming. The historical invasion dynamic of exotic fish species and the sea surface temperature series were reconstructed from 1810 to 2006 in order to estimate the correlation between invasion rate and climate. The geographical distributions of exotic and endemic fish richness before and after the period of global warming were used to assess the dynamic of spatial congruence. The results revealed (i) an acceleration of successful introductions from the Red Sea and (ii) the introduction of Atlantic species from lower latitudes in correlation with the increasing temperature of the Mediterranean Sea. We also showed an increasing overlap between the spatial distributions of endemic and exotic species richness. Taken together, our results suggest that endemic fish species are facing a growing number of exotic species because the Mediterranean Sea is acting as a catchment basin for southern species.     

Consumption of benthic fauna by carnivorous birds in the Wadden Sea

Consumption by carnivorous birds was estimated for the Sylt-Rømø tidal inlet in the northern part of the Wadden Sea, as well as the subarea Königshafen, a small, tidal bay. The bird community of the Sylt-Rømø Wadden Sea was dominated by Dunlin (35% of all birds counted), Eider (9%), Oystercatcher (8%), Knot (8%), and Shelduck (7%). The community in the Königshafen was dominated by Eider (20%), Knot (17%), Bar-tailed Godwit (17%), Dunlin (13%), and Oystercatcher (8%). Annual consumption was estimated at 3.4 g AFDW · m^?2 · year^?1 for the entire Sylt-Rømø Wadden Sea and 19.2 g AFDW · m^?2 · year^?1 for the Königshafen. Restricting the calculations to the intertidal area resulted in a consumption of 8.7 g AFDW · m^?2 · year^?1 for the Sylt-Rømø Wadden Sea and 17.6 g AFDW · m^?2 · year^?1 for the Königshafen. In the two areas, consumption was dominated by the Eider with 37% and 60% of the total consumption, respectively. In comparison to the western parts of the Wadden Sea the seasonal pattern of consumption as well as species composition differed, most probably as an effect of different climatic conditions, whereas annual consumption on intertidal flats seems to be in the same order of magnitude. On average, 15–25% of the mean annual macrozoobenthic biomass seems to be taken by carnivorous birds in the Wadden Sea, which is in the same order of magnitude as in other northern temperate estuarine areas.     

Epibenthic fauna dredged from tidal channels in the Wadden Sea of Schleswig-Holstein: spatial patterns and a long-term decline

The epibenthic fauna dredged in the channels of the Wadden Sea of Schleswig-Holstein is dominated by crustaceans. Mean species richness is lower in a southern region (7.6±2.2 species haul⁻¹) which is part of the Elbe estuary and lacks protective barrier islands. A northern region is more marine and is protected by a seaward barrier of high sands. Here mean species richness is 10.9±2.8. Within channels, there is no significant inshore-offshore gradient, and species number does not increase with depth. Stratified sampling near the island of Sylt revealed that abundance and diversity are high along the gentle upper slope (5 m depth) of channels when mussels are present, but low in the absence of mussels. Abundance and diversity are also low along the steeper slope below (at 10 and 15 m depth). In a channel with scattered stones and boulders, highest diversity (16.0±5.1) and dense epibenthic assemblages were encountered along the upper and middle slopes (5 and 10 m). Comparisons with historical surveys suggest that a decline of nearly fifty percent of all epifaunal species within the last hundred years may be attributed to fishery disturbances.     

Shrubs as ecosystem engineers across an environmental gradient: effects on species richness and exotic plant invasion

Ecosystem-engineering plants modify the physical environment and can increase species diversity and exotic species invasion. At the individual level, the effects of ecosystem engineers on other plants often become more positive in stressful environments. In this study, we investigated whether the community-level effects of ecosystem engineers also become stronger in more stressful environments. Using comparative and experimental approaches, we assessed the ability of a native shrub (Ericameria ericoides) to act as an ecosystem engineer across a stress gradient in a coastal dune in northern California, USA. We found increased coarse organic matter and lower wind speeds within shrub patches. Growth of a dominant invasive grass (Bromus diandrus) was facilitated both by aboveground shrub biomass and by growing in soil taken from shrub patches. Experimental removal of shrubs negatively affected species most associated with shrubs and positively affected species most often found outside of shrubs. Counter to the stress-gradient hypothesis, the effects of shrubs on the physical environment and individual plant growth did not increase across the established stress gradient at this site. At the community level, shrub patches increased beta diversity, and contained greater rarified richness and exotic plant cover than shrub-free patches. Shrub effects on rarified richness increased with environmental stress, but effects on exotic cover and beta diversity did not. Our study provides evidence for the community-level effects of shrubs as ecosystem engineers in this system, but shows that these effects do not necessarily become stronger in more stressful environments.     

Relative influence of regional species richness vs local climate on local species richness in China's forests

Disentangling the relative effects of local and regional processes on local species richness (LSR) is critical for understanding the mechanisms underlying large‐scale biodiversity patterns. In this study we used 1098 forest plots from 41 mountains across China, together with regional flora data, to examine the relative influence of local climate vs regional species richness (RSR) on LSR patterns. Both RSR and LSR for woody species and all species combined decreased with increasing latitude, while richness of herbaceous species exhibited a hump‐shaped pattern. The major climatic orrelates of species richness differed across spatial scales. At the regional scale, winter coldness was the best predictor of RSR patterns for both woody and herbaceous species. At the local scale, however, productivity‐related climatic indices were the best predictors of LSR patterns. Local climate and RSR together explained 48, 54 and 23% of the variation in LSR, for overall, woody and herbaceous species, respectively. Both local climate and RSR independently influenced LSR in addition to their joint effects, suggesting that LSR patterns were shaped by local and regional processes together. Local climate and RSR affected LSR of woody species mainly through their joint effects, while there were few shared effects of climate and RSR on the LSR of herbaceous species. Our findings suggest that while geographic RSR patterns are mainly determined by winter coldness, the ecological processes driven by productivity may be critical to the filtering of regional flora into local communities. We also demonstrate that biogeographic region is not a good surrogate for regional richness, at least for our dataset. Consequently, whether biogeographic region can effectively reflect regional effects needs further examination.     

狙击生物入侵的对策探讨

我国加入 WTO后 ,随着世界经济贸易自由化进程和改革开放步伐的加快 ,国际生物水平的科技成果或产品将渗透进入我国生物界中 ,外来生物在丰富我们生物物种的同时 ,也会带来负面影响。近期生物界出现一个新的名词——生物入侵 ,是指生物由原生地经自然或人为的途径侵入到另一个新环境 ,对入侵地的生物多样性 ,农林牧渔业生产以及人类健康造成经济损失或生态灾难。通俗地说 ,就是外来物种“入侵并打败”当地物种 ,“反客为主”,导致当地生态失衡 ,进而引发一系列的问题。近年来 ,随着全球经济一体化步伐的加快 ,国内外贸易往来越来越频繁 ,…     

The distribution of 0-group flatfish in relation to abiotic factors on the tidal flats in the brackish Dollard (Ems Estuary, Wadden Sea)

The distribution of 0-group flatfish was investigated in 1992 in the Dollard (Ems–Dollard estuary, Wadden Sea). 0-Group plaice, flounder and sole were not evenly distributed over the sampled locations. The spatial distribution pattern of 0-group flatfish in the Dollard changed during the investigation period. In the first week of sole presence, when the mean length of sole was 24–30 mm, salinity correlated significantly with sole density. The distribution of juvenile sole larger than 40 mm total length was affected by the elevation of the location: 0-group sole was restricted to the sampled site with the lowest elevation. The distribution of 0-group plaice was related to sediment: no juvenile plaice were caught at locations with more than 10% mud fraction in the sediment. The distribution of 0-group flounder was also correlated with sediment. Later in the year, salinity correlated negatively with the distribution of 0-group flounder. The influence of sediment composition is probably indirect and linked to the abundance of preferred food items, such as Corophium volutator . Abiotic conditions were suitable to 0-group plaice, flounder and sole.     

Macroparasite community in molluscs of a tidal basin in the Wadden Sea

We provide a quantitative inventory of macroparasites in intertidal molluscs from a tidal basin in the Wadden Sea (eastern North Sea). Gastropods and bivalves contained a species rich macroparasite community consisting of trematodes (26 species), turbellarians (1), nematodes (1), copepods (2) and polychaetes (1) in 3,800 host individuals from 10 host species. Highest parasite burdens were observed in the gastropods Hydrobia ulvae and Littorina littorea and in the bivalves Cerastoderma edule and Mytilus edulis. In contrast, only one parasite species and no trematodes were found in Crepidula fornicata. The parasite community in the molluscs was similar to other Western European localities but some parasite species showed obvious differences, related to the large-scale distribution of intermediate and final hosts. Parasitism seems to be a common phenomenon in molluscs of the Wadden Sea and hence the detrimental effects observed in experiments can be expected to frequently happen in the field.     

Comparative taphonomy of three bivalve species from a mass shell accumulation in the intertidal regime of North Sea tidal flats

This study comprises a comparative taphonomic analysis of three endobenthic bivalves (Mya arenaria, Cerastoderma edule, and Macoma balthica) derived from a mass accumulation of mainly vertically packed shells from the “Wurster Watt” in Lower Saxony’s Wadden Sea, German Bight. Bulk samples from two transects were analyzed with respect to taxonomic composition, left/right valve presence, counts and weight percentages of taxa, and size-frequency distributions. Taphonomic features including abrasion, fragmentation, encrustation and bioerosion were subjected to a semi-quantitative analysis. Taphonomic results show significant differences with respect to bivalve taxa as well as between transects. Mya arenaria, a large endobenthic bivalve, shows the greatest amount of fragmentation and is often encrusted by balanids and bryozoans. The smaller and more robust Cerastoderma edule has the greatest values for bioerosion especially by the polychaete Polydora ciliata. Macoma balthica, which has the thinnest valves, shows the highest values for abrasion, but low values for the rest of the measured taphonomic features. Taphonomic differences between the taxa, samples and transects are related to (1) the origin of the bivalves (from living populations or exposed colonization horizons), (2) the different size and morphology of the valves (themselves related to mode of life), (3) the taphonomic trajectories of the different bivalves, as well as (4) the varying depositional environment of the two transects.     

Impact of trematode parasitism on the fauna of a North Sea tidal flat

The impact of larval trematodes on the fauna of a North Sea tidal flat is considered at the individual and at the population level, depicting the digenean parasites of the common periwinkle,Littorina littorea, and their life cycles, as an example. On the German North Sea coast,L. littorea is first intermediate host for 6 larval trematodes representing 6 digenean families —Cryptocotyle lingua (Heterophyidae),Himasthla elongata (Echinostomatidae),Renicola roscovita (Renicolidae),Microphallus pygmaeus (Microphallidae),Podocotyle atomon (Opecoelidae) andCercaria lebouri (Notocotylidae). All exceptP. atomon utilize shore birds as final hosts; adultP. atomon parasitize in the intestine of teleosts, mainly pleuronectid flatfish. Second intermediate hosts ofC. lingua are various species of fish; the cercariae ofH. elongata encyst in molluscs and polychaetes, those ofR. roscovita in molluscs;M. pygmaeus has an abbreviated life cycle;C. lebouri encysts free on solid surfaces; and the fish trematodeP. atomon utilizes benthic crustaceans, mainly amphipods, as second intermediate hosts. On the tidal flats of the Königshafen (Sylt), up to 77% of the periwinkles have been found to be infested by larval trematodes. Maximum infestations in individual samples were 23% forC. lingua, 47% forH. elongata and 44% forR. roscovita. The digeneans cause complete parasitic castration of their carriers and hence exclude a considerable proportion of the snails from the breeding population. Infestation reduces the longevity of affected hosts, and size-related, trematode-induced differential mortality causes changes in the normal size-frequency distribution of individual snail-age classes. Young flatfishPleuronectes platessa from the Königshafen are 100% infested with metacercariae ofC. lingua. Heavy infestation of the gills causes obstruction of blood vessels and respiratory impairment; metacercariae in the eyes and optic nerves cause visual and neurological disturbances. A single metacercaria is sufficient to kill a larval fish.Mytilus edulis andCardium (Cerastoderma) edule are 100% infested with metacercariae ofH. elongata. Heavy infestation impairs the byssus-thread production in mussels and affects the burrowing ability of cockles. Longevity and resistance to environmental — particularly thermal — stress are reduced in bivalves infested withH. elongata andR. roscovita. There is evidence that, in the study area, population size and age composition of the molluscs discussed are (indirectly) controlled by trematode parasites employing sea birds as final hosts, rather than directly by the predatory activities of these birds.     

The invasive herb Lupinus polyphyllus can reduce plant species richness independently of local invasion age

Biological Invasions - The ecological impacts of invasive species may change or accumulate with time since local invasion, potentially inducing further changes in communities and the abiotic...     

Calcium carbonate precipitation in cyanobacterial mats from sandy tidal flats of the North Sea

Precipitated calcium carbonate was found in annual cyanobacterial mats developing on the beaches of the North Sea barrier island Schiermonnikoog (the Netherlands). A variety of different calcium carbonate morphs were found in the cyanobacterial mucous secretions and identified by light- and scanning electron microscopy and X-ray diffraction. Most of the calcium carbonate seemed to be associated with degrading extracellular polymer. It is conceived that supersaturation of calcium carbonate resulted from the periodic evaporation of the mats and from the release of calcium from the cyanobacterial mucous as a result of its degradation. The analysis of the carbon stable isotopic composition of the calcium carbonate showed only a slight depletion of ¹³C, indicating that it did not in major part originated from the decomposition of organic matter. The δ¹⁸O values of the calcium carbonate confirmed the temperature differences between spring and summer but excluded the possibility that excessive evaporative events controlled precipitation. The precipitation of calcium carbonate could represent a potential factor enhancing the stabilization of intertidal siliciclastic sediments through cementing the sand. The discovery of massive calcium carbonate precipitation in these cyanobacterial mats was unexpected and hitherto unknown.