Tropical herbivores provide resilience to a climate‐mediated phase shift on temperate reefs

Climate‐mediated changes to biotic interactions have the potential to fundamentally alter global ecosystems. However, the capacity for novel interactions to drive or maintain transitions in ecosystem states remains unresolved. We examined temperate reefs that recently underwent complete seaweed canopy loss and tested whether a concurrent increase in tropical herbivores could be maintaining the current canopy‐free state. Turf‐grazing herbivorous fishes increased in biomass and diversity, and displayed feeding rates comparable to global coral reefs. Canopy‐browsing herbivores displayed high (~ 10 000 g 100 m^?2) and stable biomass between 2006 and 2013. Tropical browsers had the highest abundance in 2013 and displayed feeding rates approximately three times higher than previously observed on coral reefs. These observations suggest that tropical herbivores are maintaining previously kelp‐dominated temperate reefs in an alternate canopy‐free state by grazing turfs and preventing kelp reestablishment. This remarkable ecosystem highlights the sensitivity of biotic interactions and ecosystem stability to warming and extreme disturbance events.     

Characterizing coal and mineral mines as a regional source of stress to stream fish assemblages

Mining impacts on stream systems have historically been studied over small spatial scales, yet investigations over large areas may be useful for characterizing mining as a regional source of stress to stream fishes. The associations between co-occurring stream fish assemblages and densities of various “classes” of mining occurring in the same catchments were tested using threshold analysis. Threshold analysis identifies the point at which fish assemblages change substantially from best available habitat conditions with increasing disturbance. As this occurred over large regions, species comprising fish assemblages were represented by various functional traits as well as other measures of interest to management (characterizing reproductive ecology and life history, habitat preferences, trophic ecology, assemblage diversity and evenness, tolerance to anthropogenic disturbance and state-recognized game species). We used two threshold detection methods: change-point analysis with indicator analysis and piecewise linear regression. We accepted only those thresholds that were highly statistically significant (p ≤ 0.01) for both techniques and overlapped within ≤5% error. We found consistent, wedge-shaped declines in multiple fish metrics with increasing levels of mining in catchments, suggesting mines are a regional source of disturbance. Threshold responses were consistent across the three ecoregions occurring at low mine densities. For 47.2% of the significant thresholds, a density of only ≤0.01 mines/km² caused a threshold response. In fact, at least 25% of streams in each of our three study ecoregions have mine densities in their catchments with the potential to affect fish assemblages. Compared to other anthropogenic impacts assessed over large areas (agriculture, impervious surface or urban land use), mining had a more pronounced and consistent impact on fish assemblages.     

A comparison of modeling techniques to predict juvenile 0+ fish species occurrences in a large river system

Even if European river management and restoration are largely supported by the use of reliable tools, these tools are most often “generalist” and provide only initial leads of alteration sources. Acknowledging that young-of-the-year (YOY) fish assemblages are highly dependent on riverine habitat conditions, the development of a YOY-based tool might be very useful or even essential in the design and implementation of conservation or restoration plan of large rivers, in measuring more straight-forward the losses and gains of hydro-ecological functionalities. In the past 20 years, new modeling techniques have emerged from a growing sophistication of statistical model applied to ecology. “Machine learning methods” (ML) are now recognized as holding great promise for the advancement of understanding and prediction of ecological phenomena. The aim of this work was to select the appropriate statistical technique to model YOY assemblages according to different meso-scale habitat variables that are meaningful to planners. To do this, two “Machine Learning” methods, Classification and Regression Trees (CART) and Boosted Regression Trees (BRT), were compared to Generalized Linear Models (GLM). We modeled the occurrence of 9 species from the Seine River basin (France) in order to compare models abilities to accurately predict the presence and absence of each species. BRT appeared to be the best technique for modeling 0+ fish occurrences in our dataset.     

Parsimony Analysis of Endemicity (PAE) of Mexican hydrological basins based on helminth parasites of freshwater fishes

Aim The distributional patterns of helminthological fauna of freshwater fishes were analysed to postulate a general hypothesis on the relationships of some Mexican hydrological systems. Location Eight hydrological systems of central and eastern Mexico were studied and compared with records from Nicaragua. Methods A Parsimony Analysis of Endemicity (PAE) was applied to the presence/absence of ninety‐two helminth parasite taxa (Monogeneans, Digeneans, Cestodes, Acanthocephalans and Nematodes) of freshwater fishes, from eight Mexican hydrological systems, using the Hennig86 program. Results The results represent the first attempt for a biogeographical analysis through application of the PAE method to the distributional patterns of helminth parasites of freshwater fishes in Mexico. A single most parsimonious cladogram was obtained, which grouped all the Neotropical systems in accordance with previous proposals based on other plant and animal taxa. Main conclusions The most basal systems were Santiago and Lerma basins, which exhibited Nearctic affinities. The remaining areas of the cladogram showed Neotropical affinities. All the southeastern systems were grouped in a clade with the Nicaragua system, providing support for a ‘Mesoamerican province’ based on helminth parasites of cichlids. The cladogram also suggests that the treatment of the Lerma‐Santiago basin as a single biogeographical unit is inaccurate and that they should be treated as separate systems.     

Skin toxins and external parasitism of coral-dwelling gobies

Toxic ( Gobiodon spp.) and non-toxic ( Paragobiodon xanthosomus ) gobies became infected with external parasites (gnathiid isopods) at equal rates in a laboratory experiment. Parasites were evenly distributed over the body of P. xanthosomus but were mostly confined to the fins of Gobiodon spp., where toxin glands are less abundant. Skin toxins were not associated with the rate of infection but their distribution did appear to influence the site of parasite attachment.     

Temperate Utah chub form valid otolith annuli in the absence of fluctuating water temperature

Utah chub Gila atraria , a temperate freshwater minnow, formed valid otolith annuli (annual growth rings), even when raised in a constant‐temperature desert spring environment. This suggests that factors other than seasonal variation in water temperature control annual otolith marking.     

Longitudinal changes and indicator species of the fish fauna in the subtropical Sinos River, Brazil

This study investigated the fish fauna in the subtropical Sinos River, considering species addition and replacement and the occurrence of indicator species along a longitudinal gradient. Patterns in fish assemblage ordination evaluated by correspondence analysis reflected the headwater and lowland river reaches. Uppermost sampling stations were characterized by species with restricted occurrence and medium abundance, whereas in the lowland most species were captured only once during the surveyed period and in low abundance. Species addition prevailed between the headwater sampling stations and both addition and replacement occurred between the lowland sampling stations. Nine species were characteristic for the headwater reach and 14 species for the lowland reach.     

Structure of the seminal pathway in the European chub, Leuciscus cephalus (Cyprinidae); Teleostei

The testicular efferent duct system of Leuciscus cephalus (Cyprinidae), is described for three phases of testicular development. Testicular main ducts were analyzed by means of conventional histology and transmission electron microscopy. Additional techniques were applied for lectin histochemistry to determine secretory activity, as well as immunohistochemistry for cell proliferation activity and for muscle actin to demonstrate the distribution and amount of contractile cells. The contribution of the main ducts' epithelia and of degenerating spermatocytes to seminal fluid composition was confirmed, with the former being a source of carbohydrates and the latter that of phospholipids. The apical glycocalyx of epithelial cells, which is important in cell recognition and potentially involved in sperm storage, was marked by RCA I, LCA, and WGA lectin. Higher numbers of proliferating epithelial cells were ascertained during spawning phase compared to pre- and postspawning phases. In the ducts' stroma, a large number of cells expressed muscle actin and tropomyosin, indicating the ducts' contractile potential for the transport of seminal fluid towards release. Adjacent to these contractile cells, numerous nerves were found, indicating neuronal control of sperm fluid flow.     

Diversity of pectoral fin structure and function in fishes with labriform propulsion

Aquatic propulsion generated by the pectoral fins occurs in many groups of perciform fishes, including numerous coral reef families. This study presents a detailed survey of pectoral fin musculoskeletal structure in fishes that use labriform propulsion as the primary mode of swimming over a wide range of speeds. Pectoral fin morphological diversity was surveyed in 12 species that are primarily pectoral swimmers, including members of all labroid families (Labridae, Scaridae, Cichlidae, Pomacentridae, and Embiotocidae) and five additional coral reef fish families. The anatomy of the pectoral fin musculature is described, including muscle origins, insertions, tendons, and muscle masses. Skeletal structures are also described, including fin shape, fin ray morphology, and the structure of the radials and pectoral girdle. Three novel muscle subdivisions, including subdivisions of the abductor superficialis, abductor profundus, and adductor medialis were discovered and are described here. Specific functional roles in fin control are proposed for each of the novel muscle subdivisions. Pectoral muscle masses show broad variation among species, particularly in the adductor profundus, abductor profundus, arrector dorsalis, and abductor superficialis. A previously undescribed system of intraradial ligaments was also discovered in all taxa studied. The morphology of these ligaments and functional ramifications of variation in this connective tissue system are described. Musculoskeletal patterns are interpreted in light of recent analyses of fin behavior and motor control during labriform swimming. Labriform propulsion has apparently evolved independently multiple times in coral reef fishes, providing an excellent system in which to study the evolution of pectoral fin propulsion.