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Only a few key prey species fuel a temperate coastal fish food web.
Abstract
ABSTRACT: The food web structure of a coastal fish community (western Dutch Wadden Sea) was studied based on stomach content data from samples collected between 2010 and 2018. In total, 54 fish species were caught and 72 different prey items were identified. Fish species consumed from only a few up to >30 different prey species, suggesting the presence of both opportunistic and more specialized feeders. We found no significant differences between years or switches in food source with fish size. The trophic positions of the Wadden Sea fish community ranged from 2.0 to 4.7, with most trophic positions above 3.0. In the past, (near)-resident species were the most abundant guild in spring, and juvenile marine migrants in autumn. At present, all guilds are present in similar but low abundances. The (near)-resident community consisted of about 20 species that fed primarily on amphipod crustaceans, brown shrimps and juvenile herring. There was only a
slight overlap in diet with the group of juvenile marine migrants (5 species of juvenile flatfishes and clupeids), whose preferred prey were copepods, polychaetes and brown shrimps. About 15 species of marine seasonal visitors showed an overlap in diet with both the (near)-resident and the juvenile marine migrants, especially for brown shrimps and to a lesser extent herring and gobies. Our results illustrate (1) the pivotal position of a few key prey species (amphipod crustaceans, brown shrimps, juvenile herring and gobies) for the coastal Wadden Sea fishes and (2) that the substantial prey overlap in the diet of some predators cannot exclude intra- and inter-specific competition among these predators.
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Estuarine food webs are generally considered to be supported by marine pelagic and benthic primary producers and by the import of dead organic matter from the open sea. Although estuaries receive considerable amounts of freshwater phytoplankton and organic compounds from adjacent rivers, the potential contribution of these living and dead matter to estuarine food webs is often assumed to be negligible and, therefore, not examined. Based on stable isotope analyses, we report the importance of freshwater suspended particulate organic matter (FW-SPOM) for fuelling estuarine food webs in comparison to estuarine SPOM and microphytobenthos. This previously neglected food source contributed 50–60% (annual average) of food intake of suspension-feeding bivalves such as cockles (Cerastoderma edule), mussels (Mytilus edulis) and Pacific oysters (Magallana gigas) at the Balgzand tidal flats, an estuarine site in the western Wadden Sea (12–32 psu). For these species, this proportion was particularly high in autumn during strong run-off of SPOM-rich freshwater, whilst estuarine SPOM (20%-25%) and microphytobenthos (15%-30%) were relatively important in summer when the freshwater run-off was very low. These findings have implications for our understanding of the trophic interactions within coastal food webs and for freshwater management of estuarine ecosystems.
Habitat quality of a subarctic nursery ground in northern Norway for 0-group plaice Pleuronectes platessa was investigated by following settlement, mortality and growth during 2005 and 2006. Newly settled individuals were first observed in the end of May to early June and settlement lasted until mid-July. Densities peaked in early July and were comparable to those reported in temperate nursery grounds. Mortality estimates after settlement differed between 0.062 d−1 in 2005 and 0.025 d−1 in 2006. Potential predators appeared to be rather similar as those reported in other areas: the brown shrimp Crangoncrangon, the shore crab Carcinus maenas and demersal fish species (gadoids). Population mean growth indicated linear growth until August leveling-off afterwards. 0-group plaice reached a lower mean size (5–6 cm) at the end of the growing season than in temperate areas probably due to later settlement timing in combination with lower summer–autumn water temperatures. The comparison of observed growth rates with predictions of maximum growth models indicated a similar pattern as observed in temperate nursery grounds: Growth appeared to be maximal except for the period after summer. Whether or not this was related to changes in food quality throughout the season, to interspecies competition or to emigration remains to be elucidated.
Temperate estuaries are indispensable as refuelling areas for long-distance shorebirds, where they depend on intertidal benthic fauna, such as bivalves, as food source. Bivalve recruitment is thought to be, at least partly, top-down regulated by epibenthic predators (the shrimp Crangon crangon and the crab Carcinus maenas) but this interaction is part of a complex predator–prey system since various fish species prey upon the crustaceans.The impact of climate change in temperate estuarine food web will be determined by how the various size-selective interactions are affected by temperature. This will depend on the temperature sensitivity of each species’ growth and on how food conditions allow them to fill in this growth potential. In this paper, the focus is on the first aspect: temperature sensitivity of the epibenthic predators compared with that of the bivalve prey and among the various predator species. Our results show that crustaceans have higher temperature sensitivity and tolerance range compared with their potential predators and with their bivalve prey. It is hypothesized that a temperature increase can potentially lead to an overall higher predation pressure in these systems with negative impacts in bivalve recruitment and hence, in the functioning of temperate estuaries as fuelling stations. However, prevailing food conditions for bivalves and predators will determine to what extent the potential impacts of an increase in temperature will be realized.
Most of our knowledge of biodiversity and its causes in the deep-sea benthos derives from regional-scale sampling studies of the macrofauna. Improved sampling methods and the expansion of investigations into a wide variety of habitats have revolutionized our understanding of the deep sea. Local species diversity shows clear geographic variation on spatial scales of 100–1000 km. Recent sampling programs have revealed unexpected complexity in community structure at the landscape level that is associated with large-scale oceanographic processes and their environmental conse-quences. We review the relationships between variation in local species diversity and the regional-scale phenomena of boundary constraints, gradients of productivity, sediment heterogeneity, oxygen availability, hydrodynamic regimes, and catastrophic physical disturbance. We present a conceptual model of how these interdependent environmen-tal factors shape regional-scale variation in local diversity. Local communities in the deep sea may be composed of species that exist as metapopulations whose regional distribution depends on a balance among global-scale, landscape-scale, and small-scale dynamics. Environmental gradients may form geographic patterns of diversity by influ-encing local processes such as predation, resource partitioning, competitive exclusion, * The US Government has the right to retain a nonexclusive, royalty-free license in and to any copyright covering this paper.
The Wadden Sea is the world's largest intertidal ecosystem and one of the most productive coastal areas worldwide. People have fished and hunted marine resources in the Wadden Sea since its origin ∼7500 years ago, but have since depleted the majority of formerly important species and their supporting habitats. Most of these changes have been lost from memory. Here, I reconstructed the history of fishing and marine resource use in the Wadden Sea using a multi-disciplinary approach that combines archaeological, historical, fisheries, and ecological records.
Annual development of density and mean weight of juvenile plaice Pleuronectes platessa was examined at 2 nursery grounds (Port Erin Bay, Isle of Man, Irish Sea and Admucknish Bay, Firth of Lorne, west coast of Scotland) over a number of years. In both cases there was evidence of 'self-thinning' in the populations when the density was high, although in Port Erin Bay the slope suggested a relationship different from the standard (4/3) rule proposed for animal populations. The site specific dynamic thinning lines (dynamic carrying capacities) were consistent with the dynamic thinning line (-(4/3) rule) for both populations. The 2 nursery grounds were different, with growth rates and densities generally higher on the Ardmucknish Bay nursery ground compared with Port Erin Bay. Similarly, the estimated total biomass of plaice was higher in Ardmucknish Bay than Port Erin Bay, but there was considerable inter-annual variation. Maximum plaice biomass generally occurred from August to September for both sites. In Port Erin Bay this coincided with the maximum consumption rates. The size structure was described using the Gini coefficient (G) and the timing of size structure development by the centre of gravity (CG). The size structure of the populations differed and in both cases varied during the season in response to settlement and mortality. Over the study periods, population density was only occasionally high enough to reach the site specific self-thinning line. This suggests that these populations rarely approached the carrying capacity of the nursery grounds.
Traditionally, marine ecosystem structure was thought to be determined by phytoplankton dynamics. However, an integrated view on the relative roles of top-down (consumer-driven) and bottom-up (resource-driven) forcing in large-scale, exploited marine ecosystems is emerging. Long time series of scientific survey data, underpinning the management of commercially exploited species such as cod, are being used to diagnose mechanisms that could affect the composition and relative abundance of species in marine food webs. By assembling published data from studies in exploited North Atlantic ecosystems, we found pronounced geographical variation in top-down and bottom-up trophic forcing. The data suggest that ecosystem susceptibility to top-down control and their resiliency to exploitation are related to species richness and oceanic temperature conditions. Such knowledge could be used to produce ecosystem guidelines to regulate and manage fisheries in a sustainable fashion.
Despite their importance for species conservation and sound management of exploited living resources, the density-dependent mechanisms that regulate wild populations are among the least understood process in ecology. In many marine fish species, there is strong evidence that regulation occurs at the juvenile stage, when individuals concentrate in spatially restricted nurseries. However, little is known about the underlying mechanisms. Whether competition for food resources determines fish growth and survival is particularly controversial. We investigated whether food supply may have limited juvenile fish production (integrating both growth and survival) in a coastal and estuarine nursery in western Europe. Using a recent bioenergetics-based approach, we calculated annual macrobenthic food production (FP) and annual food consumption (FC) by juvenile fish and predatory invertebrates for three consecutive years (2008–2010). We also calculated exploitation efficiency (FC:FP) and used it as an index of food limitation. Results revealed substantial interannual variations in FP (FP ∼2–3 times higher in 2008 and 2010 than in 2009). FC by young-of-the-year fish followed a fairly similar pattern. In addition, predatory invertebrates consumed as much food as juvenile fish, highlighting the need to consider all dominant epibenthic predators when estimating the overall predation pressure on macrobenthic prey. Lastly, exploitation efficiency of the entire epibenthic predator community reached ∼30% in 2009, which is relatively high despite the conservative modeling approach. Overall, these results suggest that food supply may have limited juvenile fish production during the study period, at least in 2009. Nonetheless, further studies based on longer time-series and/or other study sites are required to strengthen these findings.
Fluctuations in species composition can have major effects on the functionality of an ecosystem; however, studying such impacts is often complicated because fluctuations coincide with changes in other parts of the ecosystem. In this study, we explored long-term (1975 to 2014) changes in predator-prey interactions following concurrent changes in predatory epibenthic fish and crustaceans as well as their prey, macrozoobenthic bivalves and polychaetes, in the western Wadden Sea. Historical and recent invasions have resulted in an increase in relatively large and long-lived bivalves (Mya arenaria, Ensis directus, Crassostrea gigas) which have found a size refuge from epibenthic predators in the Wadden Sea. While bivalves dominated the macrozoobenthic biomass, polychaetes were the main food source of epibenthic predators, with the invasive polychaete Marenzelleria viridis probably becoming an important food source during the early 2000s. Food requirements of epibenthic crustaceans, mainly Crangon crangon, almost doubled from 5 to 10 g ash-free dry mass (AFDM) m⁻² yr⁻¹, and requirements of epibenthic fish decreased by more than 80%, mainly due to the local disappearance of Pleuronectes platessa. While the overall food requirements of the epibenthic predators stayed more or less constant, the edible fraction of the macrozoobenthic biomass increased from 5 to 20 g AFDM m⁻² until the 2000s and decreased to 10 g AFDM m⁻² thereafter. This was the result of changes in native (Nereis diversicolor and Heteromastus filiformis) and invasive (M. viridis) polychaetes. These findings illustrate that coinciding species-specific changes and interactions of both predators and prey should be taken into account to determine the impact of invasions on the food web structure and functioning of coastal systems.
Long-term patterns in fish phenology in the western Dutch Wadden Sea were studied using a 53 year (1960–2013) high resolution time series of daily kom-fyke catches in spring and autumn. Trends in first appearance, last occurrence and peak abundance were analysed for the most common species in relation to mode of life (pelagic, demersal, benthopelagic) and biogeographic guild (northern or southern distribution). Climate change in the western Wadden Sea involved an increase in water temperature from 1980 onwards. The main pattern in first day of occurrence, peak occurrence and last day of occurrence was similar: a positive trend over time and a correlation with spring and summer water temperature. This is counterintuitive; with increasing temperature, an advanced immigration of fish species would be expected. An explanation might be that water temperatures have increased offshore as well and hence fish remain longer there, delaying their immigration to the Wadden Sea. The main trend towards later date of peak occurrence and last day of occurrence was in line with our expectations: a forward shift in immigration into the Wadden Sea implies also that peak abundance is delayed. As a consequence of the increased water temperature, autumn water temperature remains favourable longer than before. For most of the species present, the Wadden Sea is not near the edge of their distributional range. The most striking phenological shifts occurred in those individual species for which the Wadden Sea is near the southern or northern edge of their distribution.
The Wadden Sea bordering the Dutch, German and Danish coast, is traditionally a region with important functions for many fish species: as a nursery area for juveniles (marine juveniles), as a feeding area, as a transit to and from fresh water, and resident species complete their whole life cycle there. Because of indications that the importance of the Dutch Wadden Sea has changed drastically for many species during the past decades, we analysed and classified trends of 24 common fish species in the last 45 years, which were assigned to 5 different ecological guilds. Trends were examined for three Wadden Sea regions and compared to trends in the adjacent two North Sea coastal regions. For these analyses we made a combined use of two longterm time series: an annual beamtrawl survey, the Demeral Fish Survey (DFS) with a high spatial but poor seasonal resolution and a fyke series with a high seasonal but poor spatial resolution. We investigated for which species the DFS survey was appropriate for trend analysis, and we evaluated whether a change in timing may contribute to patterns in DFS time trends.
1. The various commonly used methods of assessing, on the basis of gut contents, the food of those fishes which have a generalized diet are listed and discussed. Both during the present investigation and by re-examination of published data it is shown that, when a large number of fish are examined, and when the results are expressed comparably, i.e. each food item is shown as a percentage of the total food eaten, all methods give substantially the same results. Reasons are, however, given for rejection of the method based on the number of organisms eaten, and also of the practice of comparing data so obtained with counts of the organisms found in samples of small areas of the substratum. Such comparisons have in the past been used to give numerical expression to the availability of food organisms; but it is suggested that this would be better accomplished by using an arbitrary method of allocation of points on the basis of estimated volume of each food item present (a) in the fish guts, and (b) in general faunal collections from the habitat. The number of points, expressed as a percentage of the total, gained by any food item in the fish guts and in the general collections could then be compared. 2. The food of Gasterosteus aculeatus is studied, and it is shown that the diet, consisting chiefly of Crustacea and insects, changes slightly with season and with increase in size of fish. During the winter the fish eat less than at other times, and both sexes feed more sporadically than usual during the breeding season. It is suggested that the two biological races, A and B of Heuts, have different diets. 3. The food of Pygosteus pungitius is shown to be similar to that of Gasterosteus aculeatus, and to vary similarly. The data for the winter are, however, incomplete, and it appears that feeding in this species is more affected during the breeding season. 4. The food relations of three species of fish (G. aculeatus, Pygosteus pungitius and Rutilus rutilus) in a a small muddy Cheshire stream are discussed. It is shown that R. rutilus does not compete with the two other species, but that the diets of the two stickleback species are almost identical. It is suggested that differences in breeding habits enable these two species to live together as they nest in different areas, and that the number of each species is regulated by the fact that during the breeding season the males defend a definite territory round their nests. There is therefore only room for a certain number of nests of each species.
There is a need in the marine research and management communities for a clear operational definition of the term, eutrophication. I propose the following: eutrophication (noun) - an increase in the rate of supply of organic matter to an ecosystem. This definition is consistent with historical usage and emphasizes that eutrophication is a process, not a trophic state. A simple trophic classification for marine systems is also proposed: [GRAPHICS] Various factors may increase the supply of organic matter to coastal systems, but the most common is clearly nutrient enrichment. The major causes of nutrient enrichment in coastal areas are associated directly or indirectly with meeting the requirements and desires of human nutrition and diet. The deposition of reactive nitrogen emitted to the atmosphere as a consequence of fossil fuel combustion is also an important anthropogenic factor. The intensity of nitrogen emission from fertilizer, livestock waste, and fossil fuel combustion varies widely among the countries of the world. It is strongest in Europe, the northeastern United States, India/Pakistan, Japan/Korea, and the Caribbean. This geographical distribution corresponds with many areas where coastal marine eutrophication has become a recent concern. Demographic and social trends suggest that past practices leading to coastal nutrient enrichment are likely to be repeated in the coming decades in the developing countries of Asia, Africa, and Latin America.
Species composition, abundance, feeding relationships and guild structure of the fish assemblage in the Sylt-Rømø bight, a tidal basin in the northern Wadden Sea, were investigated to show seasonal differences and the importance of functional groups in this area. The tidal flats and in shallow subtidal areas were sampled using a beach seine and a bottom trawl net was used for deeper subtidal areas and tidal gullies. Species richness of fish was highest in summer where 26 species were caught, while the lowest richness was recorded in winter (17 species). Clear differences in species richness and abundance were found between shallow areas and deeper parts of the bight. Clupea harengus and Ammodytes tobianus were the most abundant species in deeper areas, while Pomatoschistus microps and Pomatoschistus minutus dominated shallower waters. Gut contents of 27 fish species were identified and the guild structure analyzed by UPGMA clustering of niche overlaps. Calanoid copepods (19.9%), Crangon crangon (18.2%) and mysid shrimps (8.4%) were the most abundant prey items of all fish species combined. Seven feeding guilds were present in the fall and winter, and eight and six in spring and summer, respectively. Fish feeding on calanoid copepods and C. crangon were present year round, whereas the occurrence of other guilds varied between seasons. Species composition of prey changed through seasons and, for some fish species, even the feeding mode itself varied with season. Most noticeable, 11 fish species changed guilds between seasons. We found a convergence in summer towards abundant prey items, whereas in winter diet overlap was lower. This is the first investigation of guild structure of almost all fish species present in a Wadden Sea area, and shows that consideration of seasonal differences is essential when determining feeding relationships of fish in temperate areas.
Etude de la preference et de la consommation alimentaires de: Crangon crangon, Carcinus maenas, Potamoschistus microps, P. minutus, Pleuronectes platessa dans les eaux peu profondes de la cote ouest de la Suede, en 1977 et 78. Discussion sur le chevauchement de la niche ecologique de ces especes
This paper examines the implications of the hypotheses that (a) before exploitation by man, the size of a fish population
was mainly determined in the long term by resource limitation and that (b) populations have adapted to fluctuations in recruitment
by density-dependent responses at the juvenile and adult stages. It is not possible to prove or disprove these views rigorously.
What can be done, however, is to argue that this theory satisfies the necessary condition that it is consistent with the known
facts, and can provide explanations for fundamental ecological questions.
The stomach contents of 5762 herring caught during North Sea trawl surveys in February 1983, February 1984 and February, May and August 1986 were analysed. The principal prey organisms were the copepods Calanus finmarchicus and Temora longicaudata, but Euphausiacea and the post-larval stages of Ammodytes spp. and clupeoids contributed a large percentage of the weight. Fish eggs were eaten, chiefly those of plaice, Pleuronectes platessa, but not in large numbers.
The various causes of extirpation of marine and estuarine species were investigated for the Dutch Wadden Sea to gain an impression of their relative importance. I obtained data from geological, archaeological, historical, and biological publications. At least 10 species of algae, 10 invertebrates, 13 fishes, 5 birds, and 4 marine mammals became extinct during the past 2000 years. Habitat destruction played a part in at least 26 cases, overexploitation in at least 17, and pollution in at least 3. Causes of the disappearance of two species are unknown. Introduction of exotic marine species was not involved in any of the extirpations. I compared this pattern of extinction to that of worldwide extinctions of marine and estuarine species, which have been attributed to overexploitation, habitat destruction, and in two cases to the introduction of terrestrial predators to the breeding habitats of marine birds. The results imply that conservation of marine species should address overexploitation and habitat destruction as the main causes of extinction.
The ecology of juvenile plaice, Pleuronectes platessa L., of the O-, I- and II-group in the western Wadden Sea has been studied on the Balgzand intertidal flats during the years 1972 through 1975. The present paper deals especially with density, growth and food-intake on 4 representative sampling squares, intensively sampled from March to October 1973.The O-group arrived as new settlers in the intertidal zone in April and reached maximum densities in June; the I- and II-group repopulated the area as early as March, reaching peak densities in May. In June and July densities of all age groups decreased rapidly, on the one hand as the result of mortality (the O-group) and on the other through emigration (I- and II-group). Since mortality in O-group decreased abruptly in July, from this age group relatively large numbers remained in the intertidal zone until October (end of observation period).Growth of O-group plaice on the Balgzand was relatively high as compared to that of the German Wadden Sea and British coastal waters. In I-group and particularly in II-group plaice, growth may be under-estimated due to gradual emigration of larger individuals.Study of the length-weight relation showed isometric growth in I- and II-group, and an allometric growth in the O-group; the smallest plaice were “too heavy” for their length.From density and growth data the productivity of the plaice populations was followed in the course of the seasons. Top values were found in April–May (II-group), May–June (I-group) and in June–July (O-group). Total production of plaice tissue was estimated at about 5 grammes wet-weight per m2 in the growing period (March through October).Data on stomach contents and gastric digestion led to a description of the food composition, and to estimates on individual feeding rates, food conversion and population food-intake. When individual feeding rate is expressed relatively to weight of the fish, feeding appeared to be most intensive in spring. The same applies to the conversion of food into body tissues. Superimposed on this seasonal effect, both feeding rate per gramme fish and food conversion are negatively related to the age (or size) of the plaice.From data on population density and the individual feeding rate, population food-intake—predation pressure—was followed in the course of the season. Total food-intake in grammes ashfree dry-weight per m2 from March to October amounted to 0.25 g (O-group), 0.43 g (I-group) and 4.35 g (II-group); in total to about 5 grammes. Predation on the benthic invertebrate populations appeared to be most intensive from April to June. The biomass of the macro-benthos, however, showed in the same period an increase from 80% to 120% of the yearly average. Apparently maximum predation coincides with maximum productivity of the benthic invertebrates.Since survival and growth conditions seem to be very favourable on the Balgzand, the importance of the Wadden Sea as a nursery for the North Sea plaice was discussed.
The effects of the major factors contributing to habitat quality (food, predators, temperatures, salinity, oxygen, habitat structure, water depth and hydrodynamics) on the growth and survival of flatfishes during their juveniles stages are described. It is concluded that the first three of these factors are the most important. The impact of habitat quantity on recruitment is also examined and found to play a major role in determining overall population size. Neither habitat quality nor quantity act independently and growth, survival and subsequent recruitment levels of juvenile flatfishes from their nursery grounds must be seen as a result of the interplay between both habitat quality and quantity. The general conclusion is that habitat-related processes on nursery grounds probably serve to dampen rather than generate recruitment variability.
The energy flow through the epibenthic community on a shallow soft bottom in Gullmar Fjord, Sweden, is evaluated. The interaction between the dominant epibenthic predators: brown shrimp Crangon crangon L., juvenile plaice Pleuronectes platessa L. and sand goby Pomatoschistus minutus (Pallas), and their food supply is examined, and the fate of the biomass produced within the shallow water ecosystem is described. A steady state model is presented which describes the amounts, pathways and annual rates of energy flowing through the shallow water community. Field and laboratory studies are performed in order to validate the consumption rates of the fish and shrimp species. The brown shrimp occupies a key position in this ecosystem. It represents food, consisting of newly settled juveniles, both to its conspecifics and to other epibenthic species in shallow water. Sixty to eighty per cent of the annual production of shrimps in shallow water is consumed by the epibenthic predators. The brown shrimp constitutes a main predator on other epibenthic species and, by providing such feedback loops, the shrimp constitutes a highly significant regulator of epibenthic carnivores in shallow water. A loss from the benthic community will occur due to predation, maximally amounting to 24–34% of the annual production, which is a high value compared to similar areas. A dynamic simulation is also performed in order to calculate the seasonal change of energy in the epibenthic community in shallow water. Based on mortality calculations, the total output from the shallow nursery should amount to 0·6 g m−2 year−1 (dry wt).
Shallow waters along the North Sea coast provide nursery areas for juveniles of commercially exploited species and natural habitat for resident species and seasonal visitors. The areas have gone through major changes in the last decades due to climate change and human activities such as fishing and eutrophication and changes in abundance of apex predators. Using a long-term dataset we present trends from 1970 to 2006 in 34 fish species in three coastal areas in the Netherlands: the Dutch Wadden Sea, the Westerschelde and the Dutch coastal zone. The patterns varied widely among individual species as well as between the three areas. Total fish biomass showed a dome shape pattern with an increase from 1970 to 1985 and a subsequent decline until the early 2000s. Based on multivariate and time series analyses we explore possible correlations of fish density with a predefined set of three categories of environmental variables: abiotic, biotic and fisheries related variables. Dynamic factor analysis (DFA) identified one common trend for every area: for the Wadden Sea and Westerschelde increasing from the 1970s to the early 1980s followed by a steep decrease until the mid 1990s, a temporary period (until 2002) of increase for the Wadden Sea, and a continuing increase for the Westerschelde. The common trend in the Dutch coastal zone shows a similar increase but a time lag compared to the estuarine areas, while the distinct decline was absent here. The species that showed the strongest correlation with this common trend differed between the areas, and explains the difference between the common trend in the coastal zone with that in the estuarine areas. Common trends were best described by models containing variables from all categories of environmental variables (only maximum 2 tested at a time).
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