Partition among niche and neutral explanations for metacommunity patterns of fish from Cerrado streams

The Species-Sorting concept, one of the models developed to explain patterns in metacommunity structure, suggests that relationships between biological communities and environmental conditions is the basic means of the species selection processes. A second concept is Neutral Theory, and the idea of neutral dynamics underpinning metacommunity structure, cannot be overlooked. The third mechanism is the Mass-Effect concept, that focuses on the interaction between environmental condition and neutral effects. In the present study, we partitioned fish communities in streams between niche and neutral theory concepts, identifying the best representation of metacommunity structure, and assessed if linear and hydrographic distance were equivalent in the representation of neutral processes. The result points to the importance of species sorting mechanisms in structuring fish communities with neutral processes best represented by the linear distances. These results are important for the fish fauna conservation leading to three considerations: (i) the variation of the landscape and habitat is important for the stream fish, (ii) the natural barriers are an important landscape component to be considered, and (iii) the artificial barriers (dams and impoundments) need to be planned taking in account the catchment basin as the landscape unit.

Underwater Video as a Tool to Quantify Fish Density in Complex Coastal Habitats

Habitat loss is a serious issue threatening biodiversity across the planet, including coastal habitats that support important fish populations. Many coastal areas have been extensively modified by the construction of infrastructure such as ports, seawalls, docks, and armored shorelines. In addition, habitat restoration and enhancement projects often include constructed breakwaters or reefs. Such infrastructure may have incidental or intended habitat values for fish, yet their physical complexity makes quantitatively sampling these habitats with traditional gears challenging. We used a fleet of unbaited underwater video cameras to quantify fish communities across a variety of constructed and natural habitats in Perdido and Pensacola Bays in the central northern Gulf of Mexico. Between 2019 and 2021, we collected almost 350 replicate 10 min point census videos from rock jetty, seawall, commercial, public, and private docks, artificial reef, restored oyster reef, seagrass, and shallow sandy habitats. We extracted standard metrics of Frequency of Occurrence and MaxN, as well as more recently developed MeanCount for each taxon observed. Using a simple method to measure the visibility range at each sampling site, we calculated the area of the field of view to convert MeanCount to density estimates. Our data revealed abundant fish assemblages on constructed habitats, dominated by important fisheries species, including grey snapper Lutjanus griseus and sheepshead Archosargus probatocephalus. Our analyses suggest that density estimates may be obtained for larger fisheries species under suitable conditions. Although video is limited in more turbid estuarine areas, where conditions allow, it offers a tool to quantify fish communities in structurally complex habitats inaccessible to other quantitative gears.

Features of the species composition and structure of fish communities in small anthropogenic reservoirs with different content of dissolved mineral nitrogen

In 22 small anthropogenic reservoirs with an area of 0.4 to 62 ha located in the territory of the Udmurt Republic, individuals of different fish species were captured and water samples were taken in late spring for analysis of NO3–, NO2– and NH4+ content. In many reservoirs, concentrations of ammonium exceed the maximum permissible according to the fishing standards for water quality, and in some this is also the case with nitrites. Ponds with zooplanktophages (bleak Alburnus alburnus (L.) and belica Leucaspius delineates (Heckel)) present in fish communities were statistically significantly different in the increased content of total dissolved mineral nitrogen from reservoirs where these two fish species were not registered. In perch and roach reservoirs, the numerical proportion of river perch Perca fluviatilis was negatively and statistically significantly related to the level of their contamination with nitrogen ionic forms.

Key Drivers Influencing the Presence and Absence of Micropterus salmoides and Their Effect on Native Fish Communities and Biotic Integrity

Invasive alien fish species (IAFS) influence recipient ecosystems in multiple ways, from altered native fish communities to poor ecological health and higher economic losses to control and eradication. We tested key drivers and connections between an IAFS (Micropterus salmoides) presence, absence, geomorphological, hydro-chemical, physical habitat, native fish assemblages, and large river basins biotic integrity during 2016–2019. A total number of 62,121 individuals (TNI) representing 74 fish species were observed, out of which 68 species (45,677 TNI) belonged to the Geum River (GR) basin, while 63 species (16,444 TNI) were from the Mankyong/Dongjin River (MDR) basin. The results illustrated a significant contrast based on stream order, catchment area, altitude, stream gradient, and width among the sites with and without largemouth bass. However, fluctuations in nutrients (nitrogen and phosphorus) were not affected by variations in pH, dissolved oxygen, conductivity, suspended solids, and river flow. The largemouth bass has emerged as the 8th largest fish population in the GR and swiftly occupies the MDR basin with a constancy value of 45.5. Native sensitive (r = −0.38), insectivore (r = −0.252), carnivores (r = −0.085), and TNI (r = −0.512) displayed a negative correlation with increasing largemouth bass abundance. Largemouth bass induced significant regime transformation in the carnivore species. A significant difference (p < 0.01) of biotic integrity was illustrated among the largemouth bass population sites. A conspicuous interplay between ‘poor’ ecological health (r = 0.33, p = 0.038, n = 41) sites and ‘fair–excellent’ (r = −0.38, p < 0.001, n = 622) sites as compared to the overall ecological health linked with largemouth bass abundance (r = −0.397, p < 0.001, n = 663) alluded to stronger impact of the IAFS. In conclusion, the largemouth bass has potentially altered the native fish assemblage and ecological health. Further, we conclude that rapidly shifting flow patterns supported by the expanding anthropogenic interventions (weirs and dam) are the most approving factors of impending fish invasions.