Mesozooplankton assemblage in the gulf of cádiz estuaries: Taxonomic and trait-based approaches.

In this study, two different approaches based on taxonomic assemblages and on copepod functional groups were used to investigate the mesozooplankton assemblage structure and its relationship with environmental variables in the main estuaries of the Gulf of Cádiz (Guadalquivir, Guadiana and Tinto-Odiel) during the dry-warm season. In general, the mesozooplankton assemblages were dominated by copepods, especially the calanoid Acartia tonsa, which reached its highest abundance in the inner zones while the adjacent coastal zones were characterized by a mixture of copepods and cladocerans, especially Penilia avirostris. Regarding the trait-based approach, three copepod functional groups were identified, principally sorted by their feeding strategy. Group 1 (composed of omnivorous copepods displaying a mixed feeding strategy and broadcast-spawners) was found mainly in the inner areas, while Groups 2 (omnivorous cyclopoids, sac-spawners that feed via active ambush) and 3 (herbivores-omnivores employing a filter feeding strategy and mostly broadcast-spawners) were predominant in the adjacent coastal zones. The relative abundance of copepod functional groups suggested that Group 1 could be considered the most important contributor to secondary production in the estuarine systems of the Gulf of Cádiz. In relation to environmental factors, salinity was the most influential variable on mesozooplankton assemblages in both approaches. Our results suggest that the studied estuaries, although taxonomically different, have mesozooplankton assemblages that perform similar ecological functions. Both methods provide valuable and complementary information about mesozooplankton assemblage dynamics in the main estuaries of the Gulf of Cádiz.

Sport fishing and vessel pressure on the endangered cetacean Delphinus delphis. Towards an international agreement of micro-sanctuary for its conservation.

Delphinus delphis Linnaeus 1758 is considered an endangered species in the Mediterranean. The species is resident in the Bay of Algeciras - Gibraltar (southern Spain; waters partially shared with Gibraltar, UK). This area is subject to strong anthropogenic pressure, but with an input of renewed waters in its central area. During three consecutive years (March 2017-March 2020), sightings were observed concentrated along the submarine canyon that runs north to south across the bay, forming a "specular S″ with a maximum depth of 460 m. The pods of Dd showed a continuous or semi-continuous spatial distribution along the vertical axis of the submarine canyon, where they feed, mate, breed and rear calves in a well-defined area that constitutes a critical habitat. This area has been cartographically delimited, choosing the area of maximum dolphin frequency as highly vulnerable due to the possibility of collisions with small vessels (<15 m) and interactions with sport fishing activities (popping, ballooning, trolling) which constitute the main threat counting the derived impacts from noise pollution. Spatio-temporal mapping has been developed to visualize the overlapping between the dolphin groups and small vessels. Mapping analysis has shown that an international Spanish-British micro-sanctuary urgently needs to be established in order to create a protected area specifically for the common dolphins, and for other species which inhabit/use the waters between Spain and Gibraltar. Coordinates and a delimited surface area have been proposed in this paper.

Effects of maintenance dredging on the macrofauna of the water column in a turbid estuary.

Many human activities in or near aquatic habitats generate alterations in their environmental conditions, which could affect the organisms that inhabit them. Maintenance dredging of navigation channels in order to allow large ships access to inland ports is one such source of disturbance. In this study, by taking multiple approaches (immediate-, short- and medium term), we analysed the effects of a maintenance dredging operation on physiochemical variables and the early life stages of fish and other macrofauna groups present in two zones of the Guadalquivir estuary with different salinity ranges (poly- and mesohaline). Most physiochemical variables were homogenized in the water column immediately after the water mass passed by the dredger, including sediment resuspension. However, this process seemed to be transient as no significant increments in the depth-averaged levels of turbidity were observed in the short- and medium-terms. Instead, metal concentrations of Cr, Fe and Zn increased in the polyhaline station. Even so, these perturbations did not appear to be severe enough to influence the macrofauna. Still, organisms can suffer direct mechanical impacts of the trailer suction. Hyperbenthic species, like Pomatoshcistus spp. or decapods, tended to decrease slightly, while pelagic species such as Engraulis encrasicolus or mysids did not, indicating that benthic organisms are usually more susceptible to high entrainment. Nonetheless, the possible effects of this disturbance were of the same order or less than those of natural ones; therefore, organisms of the macrofauna could be well adapted to cope with them.

Environmental consequences of dredged-material disposal in a recurrent marine dumping area near to Guadalquivir estuary, Spain.

In this study we assessed the effects of the recurrent disposal of dredged material from the Guadalquivir estuary (south-western Spain) in a marine disposal area. We analysed shifts in sediment characteristics as well as bioaccumulation and biomagnification of heavy metals through the benthic food web. Results showed that the significant increase in concentration of some heavy metals observed in the marine disposal area after the latest disposal event could be attributed to the deposition of river-dredged sediments. This increase could also explain the decreased amphipod survival in the ecotoxicology analysis. Heavy metal concentrations in organisms indicated some bioaccumulation in deposit feeders and predators but with no clear patterns nor biomagnification through the food web. Hence, combining studies that monitor shifts in sediment characteristics and their possible consequences for the food web seems to be an interesting approach that should be assessed further in this type of studies.

Environmental factors affecting the nursery function for fish in the main estuaries of the Gulf of Cadiz (south-west Iberian Peninsula).

Hydrological, geomorphological, physicochemical and biological factors influence the nursery function of estuaries. Our study compared the environmental conditions and the assemblages of early life stages of fish in the main four estuaries of the Gulf of Cadiz (Cadiz Bay, Guadalquivir, Odiel-Tinto and Guadiana). Samples were taken within each estuary and on their adjacent coast, during the dry-warm seasons of 2016, 2017 and 2018. Results showed that rivers with smaller basins had a very low freshwater input and their estuaries, Odiel-Tinto and Cadiz Bay, were essentially sea extensions into the land, containing similar physicochemical conditions to nearshore zones, as well as similar assemblages and densities of early life stages of fish. Open water masses of these estuaries do not have important nursery functions. In contrast, inner zones of estuaries with bigger basins and higher freshwater discharges, Guadalquivir and Guadiana, have different environmental characteristics and a long transition zone with a well-defined salinity gradient. Their assemblages and densities of early life stages of fish were different between them and with other estuaries. The Guadalquivir estuary held the highest abundance of larval and early juvenile fish, as well as macrozooplankton biomass. The most abundant fish species in all zones of every estuary was the anchovy Engraulis encrasicolus; the Guadalquivir inner zone had the highest density. High concentration of suspended organic matter, provided by freshwater input and correlated with total suspended solid, suspended inorganic matter and turbidity, was the physicochemical characteristic more typical of the Guadalquivir. This characteristic, in addition to the salinity gradient, could explain the highest densities of macrozooplankton found in this estuary, and consequently, of early fish stages. Recurrent jellyfish blooms were observed in Cadiz Bay and the inner zone of Guadiana, affecting their nursery functions. Odiel-Tinto showed altered physicochemical and biological characteristics, which may need further specific research.

Human pressures on two estuaries of the Iberian Peninsula are reflected in food web structure.

As a result of the increased urban and agricultural development in coastal environments, estuaries are among the most modified and threatened aquatic ecosystems. This study used stable isotopes to examine the effects of human impacts by contrasting the food web structures of two Iberian estuaries exposed to different degrees of human pressure. More complex feeding pathways were found in the more altered estuary (Guadalquivir). Greater spread among species along the carbon axis suggests that the primary consumers exploit organic matter with various origins, whereas different nitrogen signals of the secondary consumers suggest that they feed on different suites of prey. In contrast, the similar isotopic signals of secondary consumers in the relatively little influenced estuary (Guadiana) suggests similarity in diet composition and feeding on the same organic matter sources. Understanding trophic interactions in estuaries is vital for defining proper management and conservation, and the preliminary data provided here are one step in this direction.

Maintenance dredging impacts on a highly stressed estuary (Guadalquivir estuary): A BACI approach through oligohaline and polyhaline habitats.

Understanding the effects of dredging in estuaries is a hard task due to the difficulty of implementing an adequate environmental diagnosis, as a consequence of the salinity gradient and anthropogenic disturbances. To assess the effects of maintenance dredging work on the Guadalquivir estuary (southwestern Spain), we used a Before-After-Control-Impact (BACI) approach to determine both direct and indirect effects in two salinity ranges. No effects were found on water and sediment physicochemical characteristics. The small impacts on dredged areas were followed by a rapid recovery of opportunistic species. The poor status of the benthos does not permit the detection of significant effects on macrofaunal community structure. The use of stable isotopes analysis to determine impacts on food web structure showed that changes over time seem to be explained by natural temporal variation rather than the dredging works. This paper emphasises the need to define proper management and conservation plans to improve the status of the benthic communities of the Guadalquivir estuary.

Impact of dredged-material disposal on soft-bottom communities in a recurrent marine dumping area near to Guadalquivir estuary, Spain.

This study assesses the effects of dredged material disposal in a recurrent marine dump near the Guadalquivir Estuary (south-western Spain). We compared the changes observed with two reference areas combining a classical ecological approach with new stable isotope techniques to analyse trophic structure. We detected permanent changes in the macrofaunal community structure as well as in the diversity and biotic indices applied, which showed higher values in the disposal area. The community in the marine dump had lost the natural temporal variations observed in the reference areas. These effects could be due to the last disposal event carried out in the summer of 2015 or to the recurrent disposals since 2010. Despite the structural changes shown by the benthic community, these impacts were not reflected in the food web structure of the marine dump. Our results confirm the high variability of disposal disturbances. Hence, we recommend performing studies in every disposal event, merging different functional and structural approaches.

BENFES, a new biotic index for assessing ecological status of soft-bottom communities. Towards a lower taxonomic complexity, greater reliability and less effort.

The new biotic index BENFES (Benthic Families Ecological Status Index) for assessing the ecological status of soft-bottom communities based on presence/absence at the taxonomic family level, is described. BENFES was primarily developed for the communities from the Guadalquivir estuary (South-western Spain), but the aim of the present work was to evaluate the reliability and validity of this index for its application in the Water Framework Directive (WFD), especially as a preliminary and rapid assessment method for monitoring the ecological status of transitional and coastal waters. BENFES was compared with five widely used indices (BOPA, BO2A, BENTIX; AMBI and M-AMBI) in several studies from Southwestern Spain. In addition, we have also established comparisons between these indices and the most commonly used Shannon-Wiener diversity. M-AMBI and BENFES showed the best agreement in ecological status assignation and were the most useful and discriminant between the studied areas. BENTIX was a good discriminant in coastal areas but was severe with the environmental condition from estuaries; BOPA/BO2A did not show clear trends in most of the zones; and AMBI tended to provide overestimations of the ecological status. In conclusion, BENFES shows several advantages such as lower taxonomic resolution, greater reliability and only requiring presence/absence. All this implies a huge possibility to perform a simplified monitoring routine for the control of the ecological quality of water bodies.

Effect of γ-amino butyric acid on limpet populations: towards the future management and conservation of endangered patellid species.

Many neurotransmitters, such as γ-amino butyric acid (GABA), can act as chemical cues influencing settlement and metamorphosis in benthic marine invertebrates. This effect has been described especially in mollusks, such as mussels, clams, or haliotids. This study describes the first record of the effect of GABA on patellogastropod populations. Special attention was paid to the effect of the compound on recruitment processes. The experiment was carried out using 10 × 10 cm artificial limestone plates that were drilled into intertidal rocks at different inclinations, and periodically treated with a 1 mM GABA solution. A total of five limpet species was considered (four patellid limpet species and the pulmonate Siphonaria pectinata). Each individual recorded on the plates as well as within a 20 × 20 cm quadrant was measured, identified to species level, and its straight-line distance to the application point was registered. Treated surfaces were the first to possess both adults and recruits. Individuals also were found in a higher number around GABA-treated plates than around controls. The results indicated that the compound may not only enhance recruitment, but also might accelerate it. Recruits were located at higher distances from GABA treated plates than from control surfaces. This supports the hypothesis that this is the life history stage most sensitive to the compound. The behavior shown by the individuals belonging to the two endangered patellid species present in the study area (Patella ferruginea and Cymbula nigra) also were analyzed. For the former, the results indicated that the use of GABA may have similar effects on recruitment similar to the presence of adult conspecifics. This is the first report of the effect of GABA on patellid limpet recruitment and population dynamics. Conservational implications of the results are discussed.

Assessing a quick monitoring method using rocky intertidal communities as a bioindicator: a multivariate approach in Algeciras Bay.

A multivariate approach was used to test the value of intertidal communities as a bioindicator of environmental conditions at Algeciras Bay, southern Spain. The study area is located in the Strait of Gibraltar and it is subjected to a variety of anthropic impacts. Eight localities (5 inside and 3 outside the bay) were selected, and four transects were undertaken in each locality to characterise the fauna and flora. The spatial distribution of the intertidal species reflected the physico-chemical conditions of Algeciras Bay. The stations located outside the bay, characterised by high hydrodynamism and dissolved oxygen and low sedimentation and turbidity, had a higher diversity and species richness than the inner stations. According to the BIO-ENV procedure and CCA, water turbidity was the factor which best correlated with the intertidal assemblages. SIMPER showed that the molluscs Chtamalus stellatus, Mytilus cf edulis, Littorina neritoides and Balanus perforatus, and the algae Gelidium pusillum, Corallina elongata, Asparagopsis armata, Colpomenia sinuosa and Fucus spiralis were the species that most contributed to the dissimilarity between internal and external sites. The present study, based on the spatial distribution of intertidal taxa, yielded similar results to those previously obtained in the area with costly physico-chemical analysis based on complex matrices of subtidal epifaunal communities. Consequently, the intertidal sampling method proposed in this study is presented here as a quick, effective alternative strategy, and can be useful in environmental monitoring programs, since these communities are easily accessible and amenable to sample, and the sessile nature of the majority of the species makes future, long-term monitoring relatively simple.

Oxygen levels versus chemical pollutants: do they have similar influence on macrofaunal assemblages? A case study in a harbour with two opposing entrances.

Generally, harbours are polluted zones characterised by low values of hydrodynamism and oxygen in the water column and high concentrations of pollutants in sediments. The harbour of Ceuta, North Africa, has an unusual structure; it is located between two bays connected by a channel, which increases the water movement and exchange in the harbour, maintaining moderate oxygen levels in the water-sediment interface. Nevertheless, high concentration of organic matter, nutrients and heavy metals were measured in sediments from this harbour. Under these unusual conditions (high levels of pollution but total saturation of oxygen in the water column) we studied the responses of soft-bottom macrobenthic communities using uni and multivariate analyses. The number of species was similar inside and outside the harbour but the species composition differed between internal and external stations; oxygen levels seem to control the "quantity" of species whereas pollutants control the "quality" of them.

THE DIET OF PLATYDORIS ARGO (GASTROPODA: NUDIBRANCHIA) AND THE DIETARY SPECIALIZATION OF SPONGE EATING DORIDS.

The diet of the dorid nudibranch Platydoris argo was studied in relation to prey availability, and under different environmental conditions to evaluate richness, evenness, and plasticity of its diet. In order to assess the availability of possible prey, the sponge assemblage at two different habitats was characterized. The results showed that P. argo is a relatively specialized benthic carnivore, feeding exclusively on spiculated demosponges. However, it has a relatively polyphagous diet (16 prey-species) and adapts well to contrasting patterns of prey availability at different sites. At the location with lower sponge diversity, the diet of P. argo included more prey categories, was more diverse, and less selective (lower dietary evenness), foraging preferentially on the most frequent resource, Stylopus dujardini. In contrast, at a station with a clearly more diverse and abundant sponge assemblage, the diet was more selective, and Phorbas tenacior was its principal component. Despite its trophic plasticity, P. argo displayed a specialized pattern of resource exploitation in terms of niche breadth within a given habitat. Foraging was focussed on one preferred prey (which changed from one habitat to another) as indicated by the significant positive selection indexes (S. dujardini = +0.29, P. tenacior = +0.74). The revision of quantitative data on the diet of so-called 'sponge eating dorids' indicates the existence of a more specialized guild of 'spiculated demosponge eating dorids'. Most species revised are 'non-stereotyped specialist', which indicates that they have a polyphagous and plastic diet but only exploit one or few main prey species in each habitat. However, obligate specialists, with a monophagous (or rather oligophagous) diet also seem to be present.

Ultrastructure of the gametolytic gland and seminal receptacle in Hypselodoris messinensis (Gastropoda, Opisthobranchia).

The gametolytic gland of Hypselodoris messinensis is a voluminous globular structure that encloses a large mass of degenerative gametes, especially waste exogenous sperm. The epithelial cells of this organ show some features characteristic of secretory cells and probably release hydrolytic enzymes into the lumen. The amorphous material accumulated in the gametolytic gland does not appear to be reabsorbed by the lining epithelium. The seminal receptacle stores exogenous sperm received during copulation. The spermatozoa are oriented radially: their heads are embedded in the epithelium and their tails are directed toward the center of the lumen. The epithelial cells of the seminal receptacle may synthesize certain substances that induce sperm activation and maintain them in adequate physiological conditions. However, they apparently do not perform an important function of sperm nourishment. The nuclear chromatin of spermatozoa stored in the seminal receptacle is not homogeneously condensed, but forms longitudinal filaments. The significance of this phenomenon, which also occurs in other nudibranchs, remains to be understod.