Habitat associations of imperilled fishes after conservation intervention in the Cape Fold Ecoregion, South Africa.

The aim of this study was to examine the habitat associations of a native cyprinid community of the recovering Rondegat River in the Cape Fold Ecoregion of South Africa as part of a long-term native fish abundance monitoring project. Relative abundance data were extracted from underwater video camera footage across the longitudinal gradient of the river in three sampling instances. Using multivariate methods the authors assessed community composition with respect to habitat, its overlap with a protected area and species-specific abiotic predictors of relative abundance. Distance from the uppermost site in the river was the most significant predictor of species abundance, indicating spatial segregation and varying overlap between species. The protected status of sites in the upper reaches, vegetated substrates and the size of individual sites were the most impactful on the relative abundance of the endangered fiery redfin Pseudobarbus phlegethon. The results of this study indicate that underwater video monitoring is an effective and low-cost approach that can inform conservation recommendations. Reducing agricultural runoff and sedimentation in the lower reaches may be useful further interventions to maintain key habitats of submerged vegetation.

Checklist of the fish fauna of the Munim River Basin, Maranhão, north-eastern Brazil.

Background: The Maranhão State harbours great fish diversity, but some areas are still undersampled or little known, such as the Munim River Basin in the northeast of the State. This lack of knowledge is critical when considering anthropogenic impacts on riverine systems especially in the face of major habitat destruction. These pressing threats mean that a comprehensive understanding of diversity is critical and fish checklists extremely relevant. Therefore, the present study provides a checklist of the fish species found in the Munim River Basin, Maranhão State, north-eastern Brazil, based on collected specimens. New information: A total of 123 species were recorded for the Munim River Basin, with only two non-native species, Oreochromisniloticus and Colossomamacropomum, showing that the fish assemblage has relatively high ecological integrity. In addition, 29 species could not be identified at the species level, indicating the presence of species that are probably new to science in the Basin. A predominance of species belonging to the fish orders Characiformes and Siluriformes, with Characidae being recovered as the most species-rich family (21 species) agrees with the general pattern for river basins in the Neotropical Region. The total fish diversity was estimated by extensive fieldwork, including several sampling gears, carried out in different seasons (dry and rainy) and exploring different environments with both daily and nocturnal sampling, from the Basin's source to its mouth. A total of 84 sites were sampled between 2010 and 2022, resulting in 12 years of fieldwork. Fish assemblages were distinct in the Estuary and Upper river basin sections and more similar in the Lower and Middle sections indicating environmental filtering processes. Species were weakly nested across basin sections, but unique species were found in each section (per Simpsons Index). High variability of species richness in the Middle river basin section is likely due to microhabitat heterogeneity supporting specialist fish communities.

Identifying economic costs and knowledge gaps of invasive aquatic crustaceans.

Despite voluminous literature identifying the impacts of invasive species, summaries of monetary costs for some taxonomic groups remain limited. Invasive alien crustaceans often have profound impacts on recipient ecosystems, but there may be great unknowns related to their economic costs. Using the InvaCost database, we quantify and analyse reported costs associated with invasive crustaceans globally across taxonomic, spatial, and temporal descriptors. Specifically, we quantify the costs of prominent aquatic crustaceans - crayfish, crabs, amphipods, and lobsters. Between 2000 and 2020, crayfish caused US$ 120.5 million in reported costs; the vast majority (99%) being attributed to representatives of Astacidae and Cambaridae. Crayfish-related costs were unevenly distributed across countries, with a strong bias towards European economies (US$ 116.4 million; mainly due to the signal crayfish in Sweden), followed by costs reported from North America and Asia. The costs were also largely predicted or extrapolated, and thus not based on empirical observations. Despite these limitations, the costs of invasive crayfish have increased considerably over the past two decades, averaging US$ 5.7 million per year. Invasive crabs have caused costs of US$ 150.2 million since 1960 and the ratios were again uneven (57% in North America and 42% in Europe). Damage-related costs dominated for both crayfish (80%) and crabs (99%), with management costs lacking or even more under-reported. Reported costs for invasive amphipods (US$ 178.8 thousand) and lobsters (US$ 44.6 thousand) were considerably lower, suggesting a lack of effort in reporting costs for these groups or effects that are largely non-monetised. Despite the well-known damage caused by invasive crustaceans, we identify data limitations that prevent a full accounting of the economic costs of these invasive groups, while highlighting the increasing costs at several scales based on the available literature. Further cost reports are needed to better assess the true magnitude of monetary costs caused by invasive aquatic crustaceans.

Predicting the competitive interactions and trophic niche consequences of a globally invasive fish with threatened native species.

Novel trophic interactions between invasive and native species potentially increase levels of interspecific competition in the receiving environment. However, theory on the trophic impacts of invasive fauna on native competitors is ambiguous, as while increased interspecific competition can result in the species having constricted and diverged trophic niches, the species might instead increase their niche sizes, especially in omnivorous species. The competitive interactions between an omnivorous invasive fish, common carp Cyprinus carpio, and a tropically analogous native and threatened fish, crucian carp Carassius carassius, were tested using comparative functional responses (CFRs). A natural pond experiment then presented the species in allopatry and sympatry, determining the changes in their trophic (isotopic) niche sizes and positions over 4 years. These predictive approaches were complemented by assessing their trophic relationships in wild populations. Comparative functional responses revealed that compared to crucian carp, carp had a significantly higher maximum consumption rate. Coupled with a previous cohabitation growth study, these results predicted that competition between the species is asymmetric, with carp the superior competitor. The pond experiment used stable isotope metrics to quantify shifts in the trophic (isotopic) niche sizes of the fishes. In allopatry, the isotopic niches of the two species were similar sized and diverged. Conversely, in sympatry, carp isotopic niches were always considerably larger than those of crucian carp and were strongly partitioned. Sympatric crucian carp had larger isotopic niches than allopatric conspecifics, a likely response to asymmetric competition from carp. However, carp isotopic niches were also larger in sympatry than allopatry. In the wild populations, the carp isotopic niches were always larger than crucian carp niches, and were highly divergent. The superior competitive abilities of carp predicted in aquaria experiments were considered to be a process involved in sympatric crucian carp having larger isotopic niches than in allopatry. However, as sympatric carp also had larger niches than in allopatry, this suggests other ecological processes were also likely to be involved, such as those relating to fish prey resources. These results highlight the inherent complexity in determining how omnivorous invasive species integrate into food webs and alter their structure.

Ichthyofauna of the Mata de Itamacaoca, an urban protected area from the upper Munim River basin, Northern Brazilian Cerrado / Ictiofauna da Mata de Itamacaoca, uma area de proteção urbana da bacia do alto Rio Munim, Cerrado norte brasileiro

Abstract: The Munim River basin is one of the main river drainages of the Hydrological unit Maranhão, but there are few published studies which focus on ichthyological surveys and taxonomic work within this basin. The present study aims to provide a fish species inventory of the Mata da Itamacaoca, one of the few urban protected areas from the upper Munim River basin, comparing the ichthyofauna with other lists by conducted at the upper Munim River basin. A total of 42 collection expeditions were conducted, the sampling was conducted at five collecting sites distributed within the boundaries of Mata de Itamacaoca, upper Munim River basin. Diversity indices were calculated and generalised linear models (GLMs) were employed to assess differences in species richness, diversity and evenness depending on season and location in relation to the reservoir dam wall. In order to visualize fish community differences, non-metric multidimensional scaling (nMDS) and a one-way PERMANOVA was used to understand whether factors of site, season and location to the dam wall had an effect on fish community compositions. A total of six orders, 13 families, and 23 fish species were found, and the order with the highest species richness, considering all reaches, was Characiformes followed by Cichliformes. The most abundant species was Nannostomus beckfordi, while Pimelodella parnahybae and Hoplerythrinus unitaeniatus were the rarer species sampled. There were no alien invasive species collected within the study area. Species richness was significantly higher below the dam wall, but there were no other significant differences in diversity indices with regards to season or location. Fish community composition was significantly different above and below the dam wall and was significantly affected by sampling site. Season did not have an effect on fish community. This study corroborates other studies conducted in the Unidade Hidrológica Maranhão sensu Hubbert and Renno (2006), that the ichthyofaunal composition and taxonomy of species within this region face major data deficits, anthropogenic impacts, this study may be a baseline for comparing similar environments throughout the region.

Resumo: A bacia do rio Munim é uma das principais drenagens da unidade Hidrológica do Maranhão, mas existem poucos estudos publicados que enfoquem levantamentos ictiológicos e trabalhos taxonômicos dentro desta bacia. O presente estudo tem como objetivo fornecer um inventário de espécies de peixes da Mata da Itamacaoca, uma das poucas áreas protegidas urbanas da bacia do alto rio Munim, comparando a ictiofauna com outras listas realizadas na bacia do alto rio Munim. Foram realizadas 42 expedições de coleta, a amostragem foi conduzida em cinco locais de coleta distribuídos dentro dos limites da Mata de Itamacaoca, bacia do alto rio Munim. Índices de diversidade foram calculados e modelos lineares generalizados (GLMs) foram empregados para avaliar diferenças na riqueza de espécies, diversidade e equitabilidade dependendo da estação e localização em relação à parede da barragem do reservatório. A fim de visualizar as diferenças da comunidade de peixes, escalonamento multidimensional não métrico (nMDS) e um PERMANOVA unilateral foi usado para entender se os fatores de local, estação e localização da parede da barragem afetavam a composição da comunidade de peixes. Um total de seis ordens, 13 famílias e 23 espécies de peixes foram encontradas, sendo que a ordem com maior riqueza de espécies, considerando todos os trechos, foi Characiformes seguida por Cichliformes. A espécie mais abundante foi Nannostomus beckfordi, enquanto Pimelodella parnahybae e Hoplerythrinus unitaeniatus foram as espécies mais raras amostradas. Não houve espécies exóticas invasoras coletadas na área de estudo. A riqueza de espécies foi significativamente maior abaixo da parede da barragem, mas não houve outras diferenças significativas nos índices de diversidade em relação à estação do ano ou localização. A composição da comunidade de peixes foi significativamente diferente acima e abaixo da parede da barragem, e foi significativamente afetada pelo local de amostragem. A estação do ano não afetou a comunidade de peixes. Este estudo corrobora outros estudos realizados na Unidade Hidrológica Maranhão sensu Hubbert and Renno (2006), que a composição ictiofaunística e taxonomia das espécies desta região enfrentam grandes déficits de dados. Impactos antropogênicos, este estudo pode ser uma linha de base para comparar ambientes semelhantes em toda a região.

Assessing predator-prey interactions in a chemically altered aquatic environment: the effects of DDT on Xenopus laevis and Culex sp. larvae interactions and behaviour.

Behavioural assays are used as a tool to understand ecotoxicological effects on organisms, but are often not applied in an ecologically relevant context. Assessment of the effect of chemical contaminants on behaviours relating to fitness and trophic interactions for example, requires incorporating predator-prey interactions to create impact assessments. Dichlorodiphenyltrichloroethane (DDT) is a controlled substance but is still regularly used as a form of mosquito control. There is little explicit information on the effect of DDT on animal behaviour and the consequent effects upon trophic interactions. This study uses a 3 × 2 factorial design to assess the feeding behaviour of Xenopus laevis toward Culex sp. larvae when supplied with different prey cues. We also assess the behavioural responses of mosquito larvae when supplied with no threat cue and predator threat cues when exposed to 0 µg/L, 2 µg/L and 20 µg/L DDT. There was a significant "DDT exposure" x "prey cue" interaction whereby DDT significantly decreased the foraging behaviour of X. laevis towards live prey cues, however there was no effect of DDT on X. laevis response to olfactory prey cues. Dichlorodiphenyltrichloroethane exposure caused mosquito larvae to appear hyperactive regardless of DDT concentration. Mosquito larvae anti-predator response was significantly dampened when exposed to 2 µg/L DDT, however when exposed to 20 µg/L the anti-predator responses were not impaired. Our results indicate a complex interplay in trophic interactions under DDT exposure, wherein effects are mediated depending on species and concentration. There are possible implications regarding reduced anti-predator behaviour in the prey species but also reduced foraging capacity in the predator, which could drive changes in ecosystem energy pathways. We demonstrate that in order to quantify effects of pesticides upon trophic interactions it is necessary to consider ecologically relevant behaviours of both predator and prey species.