Long-term monitoring of the fish community in the Minho Estuary (NW Iberian Peninsula).

Background: The paper presents an extensive fish sampling dataset spanning a long-term period from 2010 to 2019. The data were collected in Lenta Marina, an upstream area in the Minho Estuary of the NW Iberian Peninsula, which belongs to a LTSER (Long-Term Socio-Ecological Research) platform. To capture fish, fyke nets were utilised as the sampling method and deployed at Lenta Marina. This dataset offers valuable insights into the abundance of each collected taxa recorded over time. New information: The dataset reports a comprehensive compilation of data on the abundance of fish species observed in the area during the sampling period (includes zeroes when a given taxonomic entity was absent in a given sampling event). It provides a detailed record of the abundances of the fish community through time in a frequent sampling regime (on average, sampling was done every 6 days). The dataset shows that the amount of fish from invasive taxa exceeds the count of fish from native taxa in the Minho Estuary.

Boom and bust: Simulating the effects of climate change on the population dynamics of a global invader near the edge of its native range.

Despite the increasing awareness of climate change, few studies have used the Intergovernmental Panel on Climate Change (IPCC) scenarios to simulate the effects of climate change on estuarine populations of crustaceans. The objective of this study was to investigate the effects of temperature and salinity fluctuations on the population dynamics of the shore crab Carcinus maenas at the southern edge of its native range. To this end, a population dynamics model was developed based on experimental and literature data on the biology, ecology and physiology of the species. Results showed that the shore crab will be more affected by changes in temperature than in salinity. The parameter sensitivity analysis revealed that the larval phase of the species is the most sensitive stage of the shore crab life cycle. Three IPCC scenarios (SSP1-2.6, SSP2-4.5, and SSP3-8.5) were used to simulate the effects of temperature increase on the population of C. maenas in the near- (2040), mid- (2060), and long-term (2100). Two scenarios of drought conditions accompanied by the estimated salinity change were also simulated (10 % and 40 % drought). Results suggested that slight increases in temperature (up to 2 °C) lead to a strong increase on the density of C. maenas in the mid-term, while further temperature increases lead to a decline or local extinction of the shore crab population at the southern edge of its distribution range. Results indicated that a salinity increase in the estuary had a negative effect on the shore crab population. Given the importance of the species to temperate coastal ecosystems, both population increase and local extinction are likely to have significant impacts on estuarine communities and food webs, with unknown ecological and socioeconomic consequences.

Influence of climate change and extreme weather events on an estuarine fish community.

Extreme weather events are becoming more frequent as a result of climate change, and the increasing frequency of these events may lead to significant changes in fish assemblages. In this sense, this work aimed to study the effects of climate change and extreme weather events on fish assemblages in the Rio Minho estuary (Portugal). Between 2010 and 2019, continuous weekly sampling with fyke nets was carried out to assess the dynamics of fish assemblages in the estuary. In addition, temperature and precipitation data were obtained from satellite information to assess the relationship between climatic variables and fish composition, structure, and diversity. Fish populations changed significantly over time, becoming less diverse and largely dominated by a few, mostly invasive species (e.g., carp, goldfish, pumpkinseed, and tench), while the abundance of most native species declined over the years (e.g., panjorca, stickleback, and shad). High temperatures and low precipitation negatively affected native species, while the invasive species benefited from increased temperatures and extreme weather events (droughts and floods).

Influence of temperature on intraspecific, unbalanced dyadic contests between crabs.

Intraspecific agonistic interactions are widespread across the animal kingdom, with many individual morphological and physiological characteristics playing important roles in the fate of disputes. Additionally, changes to environmental conditions can influence the outcomes of animal contests. The shore crab (Carcinus maenas) is a globally distributed species, present in numerous coastal and estuarine temperate systems around the world. Although shore crabs are highly tolerant to changes in temperature, this parameter has important physiological effects on the species' ecology, while its effects on behavior are not fully understood. Our study aims to investigate how different individual characteristics (such as sex, color morphotype, carapace and chela morphology) and temperature conditions affect the dyadic interactions between shore crabs when disputing food resources. In general, the differences in carapace width between opponents, their sexes, color morphotypes and the temperature conditions interacted and were important predictors of the contest fate. We found that the body size and color morphotype of C. maenas determined the fate of dyadic disputes. However, the higher temperatures disrupted the well-established dominance of the larger red color morphotype individuals. Overall, the agonistic contest results suggest higher plasticity than previously acknowledged.

Potential impacts of the invasive species Corbicula fluminea on the survival of glochidia.

Freshwater mussels (Bivalvia, Unionida) are one of the most imperilled faunal groups globally, being the introduction of invasive species a possible major mechanism of threat. The Asian clam Corbicula fluminea is a problematic invasive species in aquatic ecosystems and can impair the survival of parasitic larvae (glochidia) of native freshwater mussels. However, this possible mechanism of threat remains speculative and to date very few studies addressed quantitatively this issue. In order to cover this gap, we have performed a series of manipulative laboratory studies to assess how distinct densities of C. fluminea can affect the survival of glochidia after 6, 12, 24 and 48 h of exposure, using larvae of the native freshwater mussel Anodonta anatina. Our results suggest an increase in mortality of A. anatina glochidia with an increase in density of C. fluminea. Two main mechanisms may possibly explain our results: 1) the high filtration capacity of C. fluminea that can contribute to the mortality of glochidia due to the mechanical damage of their fragile shells when passing by siphons and/or digestive tract of C. fluminea and 2) the high excretion capacity of C. fluminea that can lead to mortality of glochidia due to increase in ammonia concentration. Mortality of glochidia was also time dependent with higher values registered after 48 h. This work is one of the first showing the influence of C. fluminea density on the survival of glochidia, being filtration (and consequent passage in the digestive tract) and biodeposition the main potential mechanisms explaining overall mortality. These results also suggest that sites with high densities of C. fluminea may be highly detrimental for the conservation of freshwater mussels, potentially impairing the survival of glochidia and negatively affecting the recruitment of juveniles.

Assessing the effects of temperature and salinity oscillations on a key mesopredator fish from European coastal systems.

A population dynamics model was developed to assess the short and long-term effects of temperature and salinity variations in the common goby Pomatoschistus microps in a Portuguese estuary (Minho estuary, NW Portugal). The population was divided into juveniles, females and males, which constituted the model's state variables. Linear regressions between the observed and the predicted density of juveniles, females and the total population were significant. Parameter's sensitivity and uncertainty analysis were estimated. The model was able to satisfactory describe the P. microps population dynamics, and thus was used to simulate the effects of climatic changes on the fish population. Simulations indicated that the common goby population is sensitive to both temperature and salinity changes. Overall, scenarios of more than 3 °C increase caused significant population decreases. Similarly, increased salinities led to a population shrinkage, whereas scenarios of salinity decrease generated an opposite variation on the population. According to the IPCC predictions for climatic tendencies, the population of the common goby will tend to decrease in the near future, experiencing marked oscillations (decrease or increase) during climatic extremes, namely droughts and floods, respectively. These results may be a useful for future planning and management of estuarine systems given that the common goby is an important species of estuarine food webs in many temperate ecosystems.

Physical legacy of freshwater bivalves: Effects of habitat complexity on the taxonomical and functional diversity of invertebrates.

Bivalves may play a major role in structuring aquatic communities. This may be especially relevant in aquatic communities dominated by non-native invasive bivalves, which can contribute to the increase of habitat homogenization. In this study, we assess how habitat homogenization, through the reduction of empty bivalve shells identities, influences the macroinvertebrate assemblages. Towards this end, a manipulative experiment with the empty shells of two native (Potomida littoralis and Unio delphinus) and one non-native (Corbicula fluminea) species was performed. Seven treatments were prepared, three of them consisting of homogeneous substrates using shells of one species, and four of them consisting in heterogeneous substrates using more than one species. The associated fauna colonizing different treatments was analyzed through taxonomic and trait-based approaches. Our results showed that the substrate complexity influenced the density of macroinvertebrates, with the heterogeneous treatments significantly yielding more dense assemblages. Also, the trait patterns differed among the levels of habitat heterogeneity, influencing mainly organisms that feed on microphytes of both small and big sizes, that inhabit areas with slow to moderate water flow, and that have short and long live cycles. Further, the functional diversity was not influenced by the substrate heterogeneity. Therefore, the habitat homogenization, through the accumulation of non-native C. fluminea empty shells in the river bottom, did not affect the functional diversity of the macroinvertebrate assemblages.

Effects of the invasive clam Corbicula fluminea (Müller, 1774) on an estuarine microbial community.

The Asian clam Corbicula fluminea (Müller, 1774) is well recognized for its invasive behavior and high ecological and economic impacts, being classified as one of the 100 worst invasive alien species (IAS) in Europe. In this study, we performed a manipulative experiment under natural conditions to assess the effects of C. fluminea on sediments biochemistry and on the structure of an estuarine microbial (fungi and bacteria) community. We placed 5 treatments (control, rock, closed, live and open) for 2months in the Minho estuary (NW Iberian Peninsula). No differences were detected between treatments regarding the values of carbon (C), nitrite (NO2(-)), ammonium (NH4(+)), phosphate (PO4(3-)) and calcium (Ca) in the sediments; however, potassium (K) had higher values in the open treatment. Furthermore, we found that the presence of live C. fluminea stimulated fungal biomass (but not diversity) and bacterial diversity. Bioturbation activities by C. fluminea are possibly the main mechanism explaining these results; however, other factors such as the presence of other macroinvertebrate species and/or production of feces and pseudofeces by C. fluminea cannot be excluded. To our knowledge, this is the first manipulative experiment under natural conditions that clearly shows the effects of C. fluminea on an estuarine microbial community. Given the widespread distribution of this IAS and the paucity of quantitative assessments of invasive bivalves' effects on microbial communities, it will be important that future studies further investigate these processes.

From water to land: How an invasive clam may function as a resource pulse to terrestrial invertebrates.

Resource pulses are episodes of low frequency, large magnitude and short duration that result in increased resource availability in space and time, with consequences for food web dynamics. Studies assessing the importance of resource pulses by invasive alien species in the interface between terrestrial and aquatic ecosystems are rare, especially those in the direction from water to land. This study assessed the importance of massive die-offs of the Asian clam Corbicula fluminea (Müller, 1774) as a resource pulse to the terrestrial invertebrate community after an extreme climatic event using a manipulative experiment. We used 5 levels of C. fluminea density (0, 100, 500, 1000 and 2000ind·m(-2)), with terrestrial invertebrates being censused 7, 30 and 90days after C. fluminea addition. We also assessed the possible effect of plots position, where plots that delimited the experiment were assigned as edge plots and the remaining as core plots. Clear differences were detected in abundance, biomass, richness and diversity of terrestrial invertebrates depending on the C. fluminea density, time and position. Interestingly, the highest abundance of adult Diptera was observed 7days after C. fluminea addition, whereas that of the other terrestrial invertebrates was on day 30, both with C. fluminea densities higher than 500ind·m(-2) located on the edge of the experimental design. This study highlights the importance of major resource pulses after massive die-offs of invasive bivalves, contributing with remarkable amounts of carrion for adjacent terrestrial systems. Part of this carrion can be consumed directly by a great number of invertebrate species while the remainder can enter the detrital food web. Given the high density and biomass attained by several invasive bivalves worldwide and the predicted increase in the number, intensity and magnitude of extreme climatic events, the ecological importance of this phenomenon should be further investigated.

Effects of tourist visitation and supplementary feeding on fish assemblage composition on a tropical reef in the Southwestern Atlantic

The effects of tourist visitation and food provisioning on fish assemblages were assessed by visual censuses (stationary technique) carried out in a tropical reef in Northeastern Brazil. Comparisons of species abundance, richness, equitability, and trophic structure in the presence (PT) and absence (AT) of tourists suggest that tourist visitation and supplementary food influenced the structure of the fish assemblage, as follows: (a) diversity, equitability and species richness were significantly higher on the AT period, while the abundance of a particular species was significantly higher during PT; (b) trophic structure differed between the AT and PT periods, omnivores being more abundant during the latter period, while mobile invertivores, piscivores, roving herbivores and territorial herbivores were significantly more abundant on AT. Reef tourism is increasingly being regarded as an alternative to generate income for human coastal communities in the tropics. Therefore, closer examination of the consequences of the various components of this activity to reef system is a necessary step to assist conservation and management initiatives.

Os efeitos da visitação turística e da alimentação suplementar sobre a ictiocenose foram avaliados por meio de censos visuais (técnica estacionária) em um recife tropical no nordeste do Brasil. Comparações entre a abundância das espécies, riqueza, equitabilidade e estrutura trófica na presença (PT) e na ausência (AT) de turistas sugerem que a visitação turística e a alimentação suplementar influenciam a estrutura da ictiocenose, como segue: (a) diversidade, equitabilidade e riqueza de espécies foram significativamente maiores no período AT, enquanto a abundância de uma única espécie foi significativamente maior durante o período PT; (b) a estrutura trófica foi diferente entre os períodos AT e PT, com os onívoros sendo mais abundantes no último período, enquanto invertívoros móveis, piscívoros, herbívoros errantes e herbívoros territoriais foram significativamente mais abundantes no período AT. O turismo em ambientes recifais é cada vez mais uma opção na geração de renda para diversas comunidades costeiras nos trópicos. Conseqüentemente, investigações mais detalhadas sobre as conseqüências dos vários componentes desta atividade sobre o sistema recifal são necessárias para subsidiar iniciativas de manejo e conservação.