F. Baldó

Spatial and temporal variation of the nekton and hyperbenthos from a temperate european estuary with regulated freshwater inflow

The aquatic macrofauna of the Guadalquivir estuary were sampled (1 mm mesh persiana net) at 5 sampling sites located along the entire (except the tidal freshwater region) estuarine gradient of salinity (outer 50 km). A total of 134 fish and macroinvertebrate species was collected but only 62 were considered common or regularly present in the estuary. Univariate measures of the community structure showed statistically significant differences among sampling sites: species richness, abundance, and biomass decreased in the upstream direction, being positively correlated with the salinity. Temporal differences of these three variables were also statistically significant. While a clear seasonal pattern (minimum densities in winter and maximum in spring-summer) was observed for abundance and biomass, no such pattern existed for the number of species. Mysids was the most dominant group throughout the estuary (96% to 99% of abundance; 49% to 85% of biomass), although fish biomass was also important at the outer estuary (36% to 38%). Multivariate analyses indicated highly significant spatial variation in the macrofaunal communities observed along the salinity gradient. These analyses suggest that the underlying structure was a continuum with more or less overlapping distributions of the species dependent on their ability to tolerate different physicochemical conditions. There were also significant temporal (intermonthly + interannual) variation of the estuarine community; the relative multivariate dispersion indicated that monthly variation was more considerable (relative multivariate dispersion >1) at the outer part of the estuary during the wet year (last 20 km) and was higher in the inner stations during the dry year (32 to 50 km from the river mouth). Since a clear negative exponential relationship was observed between the freshwater input (from a dam located 110 km upstream) and water salinity at all sampling stations, it is concluded that the human freshwater management is probably affecting the studied estuarine communities. While the higher seasonal (long-term) stability of the salinity gradient, due to the human control of the freshwater input, may facilitate the recruitment of marine species juveniles during the meteorologically unstable early-spring, the additional (short-term) salinity fluctuations during the warm period may negatively affect species that complete their lifecycle within the estuary.

Eco-evolutionary Dynamics of Individual-Based Food Webs

The past decade has seen the rise of high resolution datasets. One of the main surprises of analysing such data has been the discovery of a large genetic, phenotypic and behavioural variation and heterogeneous metabolic rates among individuals within natural populations. A parallel discovery from theory and experiments has shown a strong temporal convergence between evolutionary and ecological dynamics, but a general framework to analyse from individual-level processes the convergence between ecological and evolutionary dynamics and its implications for patterns of biodiversity in food webs has been particularly lacking. Here, as a first approximation to take into account intraspecific variability and the convergence between the ecological and evolutionary dynamics in large food webs, we develop a model from population genomics and microevolutionary processes that uses sexual reproduction, genetic-distance-based speciation and trophic interactions. We confront the model with the prey consumption per individual predator, species-level connectance and prey–predator diversity in several environmental situations using a large food web with approximately 25,000 sampled prey and predator individuals. We show higher than expected diversity of abundant species in heterogeneous environmental conditions and strong deviations from the observed distribution of individual prey consumption (i.e. individual connectivity per predator) in all the environmental conditions. The observed large variance in individual prey consumption regardless of the environmental variability collapsed species-level connectance after small increases in sampling effort. These results suggest (1) intraspecific variance in prey–predator interactions has a strong effect on the macroscopic properties of food webs and (2) intraspecific variance is a potential driver regulating the speed of the convergence between ecological and evolutionary dynamics in species-rich food webs. These results also suggest that genetic–ecological drift driven by sexual reproduction, equal feeding rate among predator individuals, mutations and genetic-distance-based speciation can be used as a neutral food web dynamics test to detect the ecological and microevolutionary processes underlying the observed patterns of individual and species-based food webs at local and macroecological scales.

Effects of the river discharge management on the nursery function of the Guadalquivir river estuary (SW Spain)

Within the Guadalquivir estuary, young recruits of marine species seem to respond to changes in freshwater flow by moving with the mass of estuarine water that is most “suitable” for them. The control of the river flow, from a dam 110 km upstream from the river mouth, has an immediate effect on the estuarine salinity gradient, displacing it either seaward or upstream. Consequently, there is a reduction or enlargement of the estuarine area that is used as nursery grounds. The analysis of the temporal estuarine recruitment and spatial distribution of young stages of marine species, during six annual cycles, provides evidence that the estuarine zone used as nursery grounds is mainly that part situated seaward from an isohaline value of 5. The relationship between the position of that isohaline (D5) and the freshwater discharges from the dam was also examined during high and low tides. It was found that a high percentage of the isohaline position variation (75% and 73% at high and low tides, respectively) can be explained by the freshwater volume discharged from the dam during the previous week. These preliminary results suggest that an accurate model of the relationship between these two variables may be a useful tool for future management strategies of freshwater discharges to the estuary.

Macrobenthic community structure in estuarine pollution assessment on the Gulf of Cádiz (SW Spain): Is the Phylum-level Meta-analysis approach applicable?

Abstract Macrobenthic species abundances and biomasses were determined at twelve stations from three estuarine areas of the Gulf of Cadiz (SW Spain). They are subject to different sources of pollution: urban effluents (Bay of Cadiz), agricultural/urban sewages (Barbate River Estuary) and mining/industrial sewages (Odiel River Estuary). Different univariate and multivariate techniques were used in the assessment of the community disturbance status. At the Species-level, inferences from Gray and Pearson’s graphics together with multivariate MDS ordinations provided a reliable picture of the severity of the community disturbance at the twelve sampling sites. At the Phylum-level, the meta-analysis of “production” also gave a reliable disturbance status for all the stations when new samples were introduced in the MDS analysis one by one. These results suggest a more general applicability of the Phylum-level meta-analysis, provided that the original NE Atlantic data ordination remains unmodified.

Initial effects of the toxic waste spill (Aznalcóllar mine accident) on the aquatic macrofauna of the Guadalquivir Estuary

The initial effects of the toxic waste spill in April 1998 at the Aznalcóllar mine (SW Spain) on the nektonic community of the Guadalquivir Estuary were examined at three sampling sites using univariate and multivariate techniques. Since studied communities showed a considerable seasonal trend, only seasonally homogenous periods were compared to analyse effects of the spill: May-August 1997 (before spill) and May-August 1998 (after spill). Results of both techniques (two-way nested ANOVA and ANOSIM tests, P > 0.05) indicated that there was no significant difference between the nektonic community of the estuary before and after the spill (monthly number of species, abundance, biomass and similarity among samples). Conversely, an unusually high density was observed at the outer sampling site immediately after the spill for species typical of more stagnant estuarine habitats. This feature seems to indicate that the fauna in the estuarine area through which the untreated water penetrated into the main course may have been disturbed. Results also suggest that this initial sudden input of fresh water to the estuary could have enhanced the effects of an increased river flow (a drop in the salinity). Nevertheless, longer temporal series of data, especially for permanent estuarine inhabitants, are recommended before conclusions can be drawn on the effects of the toxic waste spill on estuarine communities.

Freshwater scarcity effects on the aquatic macrofauna of a European Mediterranean-climate estuary

In the Mediterranean-climate zone, recurrent drought events and increasing water demand generally lead to a decrease in freshwater input to estuaries. This water scarcity may alter the proper function of estuaries as nursery areas for marine species and as permanent habitat for estuarine species. A 12-year data set of the aquatic macrofauna (fish, decapod and mysid crustaceans) in a Mediterranean estuary (Guadalquivir estuary, South Spain) was analysed to test if water scarcity favours the nursery function of regional estuaries to the detriment of permanent estuarine inhabitants. Target species typically displayed a salinity-related distribution and estuarine salinisation in dry years resulted in a general upstream community displacement. However, annual densities of marine species were neither consistently higher in dry years nor estuarine species during wet years. Exceptions included the estuarine mysid Neomysis integer and the marine shrimp Crangon crangon, which were more abundant in wet and dry years, respectively. High and persistent turbidity, a collateral effect of water scarcity, altered both the structural (salinity-related pattern) and functional (key prey species and predator density) community characteristics, chiefly after the second drought period of the analysis. The observed high inter-year environmental variability, as well as species-specific effects of water scarcity, suggests that exhaustive and long-term sampling programmes will be required for rigorously monitoring the estuarine communities of the Mediterranean-climate region.

Nekton response to freshwater inputs in a temperate European Estuary with regulated riverine inflow

The aim of this 12-year study was to assess the nekton (fish, decapod crustaceans) response to freshwater inputs (rainfall, dam discharges) in a temperate estuary with regulated riverine inflow. Although interannual variability in river discharges to the Guadalquivir estuary has been extremely high since the construction of a dam in 1930, a significant decreasing trend in the dams discharges has been observed in the last 80 years. During this study, an alternation of wet, standard and dry years occurred in the estuarine area but no significant long-term trend was observed. River discharge, in turn, showed a considerable interannual variability and a significantly decreasing long-term trend. Freshwater inputs had an immediate effect on estuarine salinity and turbidity, and consequently on prey availability (mysids). Although 124 nektonic species were collected, only 47 of them (adding up to 99.7% of total abundance) were regularly present in the estuary: 32 marine migrants, 13 estuarine species and 2 diadromous species. Well-defined temporal changes in species composition and abundance yielded clear seasonal patterns in the estuarine nektonic community. Considerable intermonth and interannual changes were occasionally observed relating to freshwater inputs, mainly in winter/autumn of wet years. Thus, within each two-month period, some significant interannual differences in the nektonic community were also observed, with marine migrants tending to be more abundant in dry years. However, changes in the studied nektonic community did not show long-term trends. In conclusion, natural and human-controlled freshwater inputs currently play a significant role in determining the physicochemical conditions and the biota of the Guadalquivir estuary. However, although freshwater input seemed to transitorily affect the estuarine nekton, either directly (flushing out) or indirectly (through changes in salinity, turbidity and prey availability), a quick reestablishment of the estuarine nekton (strong resilience) was observed following freshwater inputs together with the recovery of environmental conditions within the estuary.

Individual Trait Variation and Diversity in Food Webs

In recent years, there has been a renewed interest in the ecological consequences of individual trait variation within populations. Given that individual variability arises from evolutionary dynamics, to fully understand eco-evolutionary feedback loops, we need to pay special attention to how standing trait variability affects ecological dynamics. There is mounting empirical evidence that intra-specific phenotypic variation can exceed species-level means, but theoretical models of multi-trophic species coexistence typically neglect individual-level trait variability. What is needed are multispecies datasets that are resolved at the individual level that can be used to discriminate among alternative models of resource selection and species coexistence in food webs. Here, using one the largest individual-based datasets of a food web compiled to date, along with an individual trait-based stochastic model that incorporates Approximate Bayesian computation methods, we document intra-population variation in the strength of prey selection by different classes or predator phenotypes which could potentially alter the diversity and coexistence patterns of food webs. In particular, we found that strongly connected individual predators preferentially consumed common prey, whereas weakly connected predators preferentially selected rare prey. Such patterns suggest that food web diversity may be governed by the distribution of predator connectivity and individual trait variation in prey selection. We discuss the consequences of intra-specific variation in prey selection to assess fitness differences among predator classes (or phenotypes) and track longer term food web patterns of coexistence accounting for several phenotypes within each prey and predator species.

Diet of bottlenose dolphins (Tursiops truncatus) from the Gulf of Cadiz: Insights from stomach content and stable isotope analyses

The ecological role of species can vary among populations depending on local and regional differences in diet. This is particularly true for top predators such as the bottlenose dolphin (Tursiops truncatus), which exhibits a highly varied diet throughout its distribution range. Local dietary assessments are therefore critical to fully understand the role of this species within marine ecosystems, as well as its interaction with important ecosystem services such as fisheries. Here, we combined stomach content analyses (SCA) and stable isotope analyses (SIA) to describe bottlenose dolphins diet in the Gulf of Cadiz (North Atlantic Ocean). Prey items identified using SCA included European conger (Conger conger) and European hake (Merluccius merluccius) as the most important ingested prey. However, mass-balance isotopic mixing model (MixSIAR), using δ13C and δ15N, indicated that the assimilated diet consisted mainly on Sparidae species (e.g. seabream, Diplodus annularis and D. bellottii, rubberlip grunt, Plectorhinchus mediterraneus, and common pandora, Pagellus erythrinus) and a mixture of other species including European hake, mackerels (Scomber colias, S. japonicus and S. scombrus), European conger, red bandfish (Cepola macrophthalma) and European pilchard (Sardina pilchardus). These contrasting results highlight differences in the temporal and taxonomic resolution of each approach, but also point to potential differences between ingested (SCA) and assimilated (SIA) diets. Both approaches provide different insights, e.g. determination of consumed fish biomass for the management of fish stocks (SCA) or identification of important assimilated prey species to the consumer (SIA).

Sources and coastal distribution of dissolved organic matter in the Gulf of Cadiz

Dissolved organic matter (DOM) is a major component of the organic matter pool, playing a key role in the global ocean functioning. However, studies on DOM in waters of many ocean regions, such as the Gulf of Cadiz (GoC), are poorly known. Advanced aquatic sensors enable autonomous for long-term deployments in situ collection of high frequency DOM data using fluorescent dissolved organic matter (FDOM) as a proxy. The present study evaluates the relevance of FDOM, the estuarine influence and the environmental factors that determine its spatial distribution in the GoC. Our results suggest that the GoC water mass, under the estuarine influence of three main rivers, is receiving large amounts of DOM transported mainly by Guadalquivir and Guadiana rivers and much less from Tinto-Odiel. Salinity is the main factor explaining the FDOM variability within the Guadalquivir and Guadiana rivers and in the inner shelf of the GoC. In the outer shelf of the GoC, plankton-produced DOM could explain the persistent spatial pattern of FDOM, playing an important role in the dynamics of FDOM from the North area of the GoC through the persistent low-salinity Eastern North Atlantic Central Water. The oceanographic dynamics and the spatial pattern of FDOM concentration in the continental shelf of the GoC suggest a net transport of FDOM through the GCC (Gulf of Cadiz Current) to the Mediterranean Sea.