Differences and similarities between spiny lobster’ sexes diet could result from multifactorial environmental influence. We evaluated the trophic spectrum for Panulirus argus, estimated lobster’s selectivity, and corroborated the hypothesis that lobster’ sexes diet is similar between subzones with different benthic community in two fishing subzones of the gulf of Batabano, Cuba. Stomach contents of 52 lobsters from Diego Pérez (DP), and 68 from Aguardiente (AA), were analyzed. Frequency of occurrence (FO), gravimetric (G), and relative importance (IIR) indices were calculated for each food category. Ellenberg Similarity (ISe), Morisita, and Ivlev Selectivity (E) indices were also applied. Different diet descriptors were also related to benthic community attributes also used to compare between subzones and sexes. Trophic spectrum for P. argus consisted of gastropods, bivalves, polyplacophores, sea urchins, stomatopods, brachyurans, anomurans, polychaetes, ophiuroids, sponges, foraminifera, hydrozoans, fish, and plant matter. The E index showed a P. argus positive selectivity for gastropods Costoanachis sp., Diodora sp., Lucapina sp., Rissoina sp., Fasciolaria tulipa, and Gibberula fluctuata, the bivalves Arcopsis sp., Barbatia domingensis, Antillipecten antillarum, and Codakia orbicularis, and crustaceans of the Order Stomatopoda. Selectivity was highest but negative for Pinctada imbricata, Tucetona pectinata, Chione sp., and anomurans. Diet between sexes was similar in DP (ISe = 47.1%) and the same in AA (ISe = 97.6%), both with high trophic level overlap. Lobster’s diet descriptors and the diet for each sex were similar (medium level) between subzones, while the attributes of the benthic community were different. Similarities between diets for each sex were kept despite differences in benthic community-specific composition.
Temporary ponds contribute to the maintenance of freshwater biodiversity. Biotic and abi�otic predictors are known to infuence community assembly patterns in ponds, but the magnitude of these efects on diferent facets of diversity remains poorly investigated. We evaluated the infuence of diferent ecological predictors (climatic and local environmental descriptors, and reproductive modes) on the taxonomic, functional, and phylogenetic diversity of anuran tadpoles in 10 temporary ponds in southern Brazil. We hypothesize that: (i) tadpole diversity will be afected by ecological predictors, particularly climate, known to infuence the diver�sity of anuran reproductive modes; (ii) congruent
responses by the three facets of diversity to the environmental predictors. We used structural equation models to reveal the pathways by which each eco�logical predictor afected tadpole diversity. Models explained over 85% of the variation in tadpole diversity. Water depth and dissolved oxygen positively infuenced all dimensions of tadpole diversity, while pond area, air humidity, evaporation, and maximum and minimum air temperature negatively afected all facets of diversity. The foam nest strategy positively infuenced phylogenetic diversity. Environmental fltering seems to be the driver behind the assembly
patterns of tadpole communities in these temporary ponds, acting mostly through climate and pond area. The reproductive mode of leptodactylids contributes to the resilience of the communities during the dry phase of the ponds. Finally, the congruent responses
of the three components of diversity to the environmental gradients reinforce the idea that tadpole communities are not randomly structured.
Trophic interaction in tropical regions is influenced by factors such as the size of organisms and the presence of intermediate predators. Macrophytes can act directly on predator–prey dynamics through the habitat structure provided by plants. We conducted an in situ mesocosm experiment (100 L) in a Brazilian reservoir to evaluate the top-down and bottom-up control promoted by the fish Astyanax lacustris, and to evaluate the effects of floating and submerged macrophytes’ morphology on trophic interaction. The experiment lasted ten days and consisted of four treatments in triplicate (n = 12): a control (C) without fish, with only the natural plankton community, and treatments with addition of fish (+ F), fish + floating macrophyte (+ FFM) and fish + submerged macrophyte (+ FSM). In treatments with macrophytes, artificial plants were added to serve as shelter for zooplankton and Chaoborus. Our results showed that fish reduced small cladoceran and Chaoborus biomass by top-down control and increased edible phytoplankton biomass by increasing nutrient concentrations by bottom-up control. Chaoborus increased the food chain length to four levels, with negative effects on the biomass of small cladocerans. Submerged macrophytes were more efficient in providing refuge for copepods and Chaoborus. In general, planktivorous fish had a direct effect on zooplankton and an indirect effect on phytoplankton, and the invertebrate Chaoborus interfered with the functioning of trophic networks. Our results show that, in experimental conditions, macrophytes can play a fundamental role in tropical reservoirs by reducing the strength of top-down control in the trophic cascade.
Food quality is known as a major driver of organisms’ performances, but the way it may modulate the response of consumers to environmental stressors now appears as critical issue of trophic ecology. Here we evaluated whether and how food quality mediates the salinity tolerance of the model organism Daphnia magna to assess the resistance of zooplankton populations to salinization, which constitutes a serious threat for freshwater ecosystems worldwide. We showed that diets lacking highly unsaturated fatty acids (HUFA) and sterols reduce the salinity tolerance range of daphnids by more than 30%. Our measurements of individual metabolic rate coupled with the quantification of consumers NaCl body content revealed that this reduction in salinity tolerance arises either from an increased energetic cost of iono-/osmo-regulation when food quality declines or from a lower resistance to NaCl when consumers lack sterols and highly unsaturated fatty acids (HUFA). While improving individual salt tolerance, these two mechanisms may have opposite consequences at ecosystem scale and need to be fully considered when predictions of consumers responses to multifactorial stresses are induced by global change.
Six potential toxic metals (PTMs) in water-sediment-submerged macrophyte systems were investigated in six shallow lakes in Changsha City, Central China. The mean metal concentrations in the surface and interstitial water were in the order of Cu>As>Zn>Cr>Pb>Cd and As>Cu>Zn>Cr>Pb>Cd, respectively. Both surface and interstitial water were not polluted, except the interstitial water of Yue Lake with slight pollution (PN=1.93). The mean metal concentration was in the order of Zn>Cr>As>Cu>Pb>Cd in the sediments. The concentration of As in all urban shallow lakes exceeded 25 mg kg‒1, and Cd in Meixi Lake and Xianjia Lake also exceeded 0.3 mg kg‒1. The sediments were slight to severe pollution in the studied urban shallow lakes. Among the submerged macrophytes, the concentrations of PTMs were decreased in the order of Vallisneria natans (Lour.) Hara > Myriophyllum verticillatum L. > Centella asiatica (L.) Urban > Potamogeton crispus L. Zn was the most accumulated in all the submerged macrophytes, and the highest bioaccumulation factor (BAF) of Zn was 43.0 in V. natans. V. natans also exhibited relatively high BAFs of 4.6, 2.4, and 4.7 for Cu, As, and Pb, compared with other submerged macrophytes. The translocation factor (TF) of As was no more than 0.3 in all submerged macrophytes. The TFs of the other metals were dependent on the plant species. For most studied metals (As, Pb, Zn, and Cd), significant positive correlations were identified between submerged macrophytes and their surrounding water/sediments (P<0.05). These results indicated that the potential use of native submerged macrophytes, especially for V. natans, for PTM removal from urban shallow lakes is worth further exploration.
Surma River of Bangladesh is a representative of sub-tropical river system which is complex, dynamic and interacting socio-ecological system. Though land-based activities control the water quality of this river system, no studies have been conducted on the role of land-use patterns on water quality and biotic communities. Therefore, this study aimed to understand the impacts of water quality on the plankton community dynamics of Surma River basin. In addition, the study also examined the impacts of land-use patterns on water quality of river. Land-use patterns were identified by analyzing Landsat-8 imageries of the United State Geological Survey. Data on biotic and abiotic variables were collected from 15 sampling stations during dry season. Unsupervised and supervised classification techniques were used to identify the land-use patterns. Weighted arithmetic method was used to develop water quality index of river system. This study found four types of land-use patterns around Surma River basin (i.e., built-up area, barren land, river, vegetation and agriculture). Water quality index indicates that water quality is good in the rural area, while bad in the urban areas. Our study found that land-use pattern is a good predictor of water quality (R² = 0.97) of Surma River basin. Our study also found that high plankton species diversity coincides with the good water quality of the river. This study will serve as tool for the management of Surma River basin of Bangladesh.
Identifying conservation strategy is essential regarding prioritization, planning, and managing biodiversity. The Eastern Himalayan freshwater reaches contain diverse taxa of fish species. Despite
having several coarse scales of assessment, the information regarding the fine-scale conservation priorities is scanty. The development of indices from multimeric attributes has been proved efficient, aiding conservation planning, in-depth research, exploitation,
policy-making, and public awareness. Therefore, this study aims to provide detailed indexing of conservation values for the freshwater fish species inhabiting the sub-Himalayan Terai–Dooars ecoregion of the Eastern Himalayas. Based on three years of extended sampling in six freshwater reaches, 170 indigenous fish species were identified. Each fish species was assigned a discrete conservation value following their rarity, taxonomic singularity, contribution to β diversity, global threat status, regional importance, and maximal achievable body lengths. Neolissochilus hexagonolepis has the highest
onservation value. In contrast, the lowest values were observed for Pethia gelius, Pethia guganio, and Pethia phutunio. The freshwater habitats of upper and lower elevation harbor essential fish species for conservation, driven by precipitation, topographic, and land cover variability. Such results were accomplished through spatial interpolation and prioritization regarding fish conservation, protection, and vulnerability toward the human footprint for this region of the Eastern Himalayas.
Benthic microalgae (BMA) biomass and community structure in freshwater lotic systems are often limited by inorganic nutrient availability. We examined nutrient limitation of benthic algae biomass and community structure using nutrient diffusing substrates in four rivers along a land use gradient in the Lake Biwa basin, Japan. Ambient in-stream nutrient concentrations were correlated to catchment land use, with the highest nitrogen and phosphorus concentrations being found in rivers draining more forested catchments. Nutrient limitation of primary producer biomass and nutrient-driven changes in community structure were evident in all four rivers, regardless of in-stream nutrient concentrations and surrounding land use. BMA biomass (measured as chlorophyll log-response ratio) exhibited the greatest nutrient limitation in rivers with higher in-stream nutrient concentrations. The relationship to catchment land use was less clear, with the highest nutrient limitation being observed in the catchment with moderate amounts of agricultural and forested land use. Nutrient additions resulted in a shift from dominance by Bacillariophyceae (diatoms) to a mixed Bacillariophyceae-Chlorophyceae (chlorophyte) community in all rivers and this shift was most pronounced in the forested catchments. Changes within the diatom community with nutrient additions were also observed, although the shifts in diatom community within a river in response to nutrient additions were much smaller than the differences in diatom community composition among rivers. Diatom taxa classified as highly motile increased with nutrient additions in all rivers. Our results suggest that primary producer community in rivers may be sensitive to nutrient inputs even in areas with elevated nutrient concentrations and catchments dominated by agricultural land use. There is likely widespread nutrient limitation in rivers of Japan, across both in-stream nutrient and land use gradients and any increases in nutrient loading will likely stimulate benthic algal growth. Our findings highlight the importance of looking at both biomass and species composition to assess ecosystem-level impacts of elevated nutrient levels.
Understanding the effect of different coverage of aquatic plants on the characteristics of the phytoplankton community structure is beneficial for management of lakes and protection of the aquatic ecosystems. In the present study, the effect of aquatic plants coverage on plankton community structure in a shallow macrophytic lake located in the middle reaches of the Yangtze River was investigated by dividing the lake into low, median, and high coverage habitats. Furthermore, the characteristics of phytoplankton and zooplankton community structures, and physicochemical indexes of lake water in the three habitats were analyzed. The results showed that an increase in aquatic plant coverage effectively reduced total phosphorus and total nitrogen in water and reduce the risks posed by phytoplankton blooms. Phytoplankton populations fluctuated slightly, and cyanobacteria density decreased in the medium coverage habitat when compared to those in the low coverage habitat. The phytoplankton species and quantity increased, and the lake water stability was enhanced in low coverage habitat when compared to those in the high coverage habitat. Zooplankton density, biodiversity index, and Pielou’s evenness index of the medium coverage habitat were higher than those of the low and high coverage habitats. Our results suggest that to improve the stability of shallow lake water environment, the coverage of aquatic plants should be maintained at 26.7–33.1% based on the physicochemical properties of water bodies and variations in phytoplankton community structure.
Macrophytes are an integral component of lake communities; therefore, understanding the factors that affect macrophyte community structure is important for conservation and management of lakes. In Sibley County, Minnesota, USA, five of the largest and most recreationally important lakes were surveyed using the point-intercept method. At each point the presence of macrophytes were recorded, water depth was measured, and a sediment sample was collected. Sediment samples were partitioned by determining sand, silt, clay, and organic matter fractions. The richness of macrophytes in all lakes were modeled via generalized linear regression with six explanatory variables: water depth, distance from shore, percent sand, percent silt, percent clay, and percent sediment organic matter. If model residuals were spatially autocorrelated, then a geographically weighted regression was used. Mean species richness (N point⁻¹) was negatively related to depth and distance from shore and either positively or negatively related to silt depending on the lake and which macrophytes were present. All species richness models had pseudo-R² values between 0.25 and 0.40. Curlyleaf pondweed (Potamogeton crispus) was found at 44% of all sampling points in one lake, and its presence was related to water depth, percent silt, and percent sediment organic matter during early season surveys. Results from this study exhibit the inhibitory relationship between water depth and macrophyte growth. The results from these models suggest interactions are complex between macrophytes, environmental factors, and sediment texture; and that these interactions are species and site specific. A single landscape scale model would not be appropriate to capture the in-lake processes driving macrophyte distribution and abundance; and management strategies will need to be developed on a lake-by-lake basis.
Bisphenol A (BPA) and polystyrene (PS) microplastics have attracted much attention because they are widely distributed in the environment, while their combined toxicity to aquatic organisms has rarely been studied. Therefore, this study explored the impact of microplastics on the toxic effects and biodegradation of BPA to the microalgae Chlorella pyrenoidosa. The results indicated that during the 16 days culture, PS (5 mg/L) increased the growth inhibition of BPA (1 mg/L and 10 mg/L) on C. pyrenoidosa compared to without PS. Similarly, PS (5 mg/L and 100 mg/L) also increased the degradation efficiency of BPA (1 mg/L and 10 mg/L) by algae. However, the changes of the chlorophyll content and the Fv/Fm value were opposite due to the hermetic and shading effect. Moreover, this study also found that five intermediates were formed during BPA degradation process because of the presence of oxidoreductase and glycosyltransferase. The results of the study provided vital information on the effect of PS on the toxicity and biodegradation of BPA to microalgal.
Freshwater gastropods occupy relatively low trophic levels in food webs and are frequently consumed as prey items by a wide variety of predators. Many studies have documented these organisms’ abilities to utilize chemical cues to make decisions relating to growth, reproduction, and behavior. Chemical communication in these species has been studied in terms of transmission and detection within only one environmental medium (i.e., water) despite there being some species that regularly cross barriers between media that may be capable of—and benefit from—detecting chemical cues in both aquatic and terrestrial environments. Previous gastropod reviews have focused heavily on mucus trails (Ng et al. in Biol Rev 88:683–700, 2013) and the anatomy and physiology behind gastropod olfactory navigation (Wyeth in J Exp Biol, https://doi.org/10.1242/jeb.185843, 2019). In this review, I discuss how freshwater gastropods respond to a variety of conspecific and heterospecific cues, and the known—or potential—ecological implications of these responses. I present several directions for future research to further explore chemical cue detection in both air and water as well as the ways in which freshwater gastropod communication may interact with the broader ecological community, particularly in the context of predation.
Recurrent blooms of the toxic dinoflagellate Ostreopsis cf. ovata are frequently reported in the Northwestern Mediterranean Sea. The impact of these proliferations on other microalgal species inhabiting the same habitats is of interest from an ecological prospective. In vitro experiments were carried out to investigate the influence of O. cf. ovata on the growth of the co-occurring benthic diatoms Licmophora paradoxa, Navicula arenaria and the benthic dinoflagellates Prorocentrum lima and Coolia monotis. Overall, O. cf. ovata exhibited weak allelopathic effects towards these microalgal species, with a reduction in the cell abundance for L. paradoxa and P. lima only. Interestingly, dead cells of L. paradoxa and N. arenaria were observed embedded in the thick mucus surrounding O. cf. ovata cells, suggesting that the mucous layer could act as a toxic phycosphere, especially for non-motile cells. All competitors were further exposed for 24 h to ovatoxins, the major toxins produced by O. cf. ovata, and the maximum quantum yield efficiency of L. paradoxa, N. arenaria and P. lima was affected at a minimum concentration of 10 µg mL⁻¹. We then hypothesized that the diffusion of solubilized ovatoxins in the culture medium affects only moderately the competitors’ growth, whereas their accumulation in the mucus would yield deleterious effects. More precisely, the competitors’ sensitivity to ovatoxins was enhanced in their stationary phase of growth and resulted from a rapid inhibition of an uncharacterized photosynthetic step downstream photosystem II. Altogether, these results emphasize the predominant role of the O. cf. ovata’s mucus in driving ecological interactions and suggest that it can affect the growth of several benthic microalgae by accumulating the potent ovatoxins.
More has yet to be indicated on the ability of microphyte plants for the removal of heavy metals from contaminated environments. In the present research, the ability of the aquatic macrophyte, Typha domingensis species, for the phytoremediation of heavy metals (Zn, Cd, Ni, Pb, and Cr) in aqueous solution was investigated. Accordingly, 50 plants of T. domingensis species were harvested from Shadegan International Wetland, Iran. The plants were then translocated in the aquariums containing water contaminated with heavy metals (Zn, Cd, Ni, Pb, Cr) at concentrations between 0 (as control) and 20 mg L⁻¹ in two different pHs (4 and 7) for 30 days. Plant absorption of heavy metals, determined for different plant tissues, increased with increase in heavy metal concentration and decrease in water pH. The highest total uptake of heavy metals was in the following order: Zn (77.5%) > Pb (70.2%) > Ni (63.1%) > Cr (47.8%) > Cd (38.2%), with the order tissue of roots > stems > leaves > flowers. Plant roots had the highest values of bioconcentration (BCF) factor for Zn (2.16) > Pb (1.66) > Ni (1.46) > Cr (1.09) > Cd (0.94). However, compared with the leaves and flowers, plant aerial parts indicated the highest TF values, by the following order: Zn (0.95) > Pb (0.94) > Ni (0.90) > Cr (0.85) > Cd (0.79). T. domingensis is a heavy metal hyperaccumulator and can be efficiently used for the phytoremediation of aqueous solutions, contaminated with heavy metals including Zn, Pb, Ni, Cr, and Cd.
Diatoms are eukaryotic microalgae representing one of the major groups in the marine phytoplankton, accounting for up to 40% of annual productivity at sea. They are widely distributed in all aquatic environments, including extreme ones. To adapt and thrive in such different environments, diatoms have evolved several strategies, including the production of secondary metabolites and toxins as defence mechanisms. Despite the great ecological relevance of these organisms, the study of chemical interactions underlying intraspecific and interspecific communication is still an open field of research. To date, the best known example of chemical mediators in diatoms is represented by oxylipins. These compounds have multiple functions such as antipredator, antibacterial, infochemical and allelochemical, influencing the abundance and distribution of other species in the surrounding environments and eventually shaping the ecosystem functioning. Other lipidic compounds involved in chemical signalling in many organisms have been identified in diatoms, but their role in these microalgae is still poorly understood. In this review, we focus on lipidic secondary metabolites produced by diatoms, i.e. oxylipins, prostaglandins and sterols, their biosynthetic pathways and their established or putative role as infochemicals.
Chemical ecology and ecotoxicology are research directions that emerged between the 1950s and 1970s following a rise in awareness for info- or allelochemicals influencing biotic interactions or ecological and ecosystem consequences of anthropogenic pollutants. The aim of this paper, focussing mainly on freshwater systems, is to present already existing links between both disciplines and to outline the potential of a strengthened alliance for a better evaluation of environmental risks. A wide range of anthropogenic or natural contaminants may cause a so-called infodisruption, the disturbance of infochemical-mediated biotic interactions. Metals, pesticides and personal care products are among the most cited pollutants that might interfere with the chemical ecology of organisms. Given the widespread environmental pollution in the current era of the Anthropocene, it seems important to consider disturbances such as “infodisruption” in environmental risk assessment. Chemical ecology can provide new response factors that might help identifying sublethal effects of pollutants. Further, exploring natural, non-toxic alternatives to currently used biocides can help in risk management. The link between both disciplines should be fostered as both are already multi- and interdisciplinary fields, and developing common themes between chemical ecology and ecotoxicology might enhance a deeper understanding of ecological processes. It can also help to achieve the aim of the 2020 European chemicals strategy for sustainability towards a toxic-free environment.
Sphagnum mosses are considered peatland engineers because of their ability to create conditions inducing carbon accumulation. Here, we report on a review of the effects of four environmental variables (elevated temperature, N and CO2 and reduced moisture) on the capitulum biomass, length increment, respiration, photosynthetic capability, N and P exchange and content of the 3 most studied Sphagnum subgenera (Acutifolia, Cuspidata, Sphagnum). Overall, we observe that, when compared to in situ experiments, laboratory experiments tend to exacerbate length increments and underestimate maximum photosynthesis in most of the studies inventoried. This review underscores some differences among results that can be associated with the used of different protocols (e.g. exposure time, instrumental analysis). Studies that investigated the impact of elevated temperature (2–5 °C) on Sphagnum reveal an increase in length, respiration and photosynthesis regardless of the experimental conditions and subgenus. Elevated N (3–23 g Nm⁻²y⁻¹) on the other hand appears to reduce the length increment but had contrasting effects on photosynthesis. Some divergent responses are found with Cuspidata species because of their tolerance to high doses of N. Low moisture reduces the length increment and photosynthesis of species of the Cuspidata and Sphagnum subgenera but has different effects on species of the Acutifolia subgenus, which are relatively tolerant to water fluctuations. Responses to elevated CO2 have no clear trends reported. Allelochemical interactions between Sphagnum, their microbiome or surrounding mosses or other plants were found to be determinant to Sphagnum responses under those variables and reinforce the interest of such investigations.
We hypothesized that cyclopoids, being predators, have a stronger allelopathic influence than calanoids on life-history variables of herbivorous rotifers. To test this hypothesis, we quantified the allelopathic effects of conditioned medium obtained separately from males and females of a calanoid (Arctodiaptomus dorsalis) and a cyclopoid (Mesocyclops longisetus) on the life table demography of the rotifer Brachionus havanaensis. The conditioned medium of the male and female A. dorsalis and male M. longisetus caused a significant reduction (14–18%) in the life expectancy at birth of B. havanaensis. Gross and net reproductive rates of rotifers reduced significantly on the conditioned medium of male or female A. dorsalis; however, the conditioned medium from either sex of M. longisetus had no significant effect on these variables. The population growth rate, r, varied from 0.53 to 0.64 d⁻¹ depending on the treatment; the r was significantly lower when cultured on the conditioned medium from A. dorsalis (males or females) and female M. longisetus Contrary to our hypothesis, calanoid allelochemicals adversely affected the life history variables of rotifers more than those produced by the cyclopoids.
The reproduction of many brachyuran crustaceans involves the formation of mating pairs often around the time of the female moult with attraction of a sexual partner and mating behaviour controlled by sex pheromones. In shore crabs, Carcinus maenas , females produce sex pheromones that are released in the urine. High Performance Liquid Chromatography analysis (HPLC) of female urine shows that the pheromone, identified as the nucleotide uridine diphosphate (UDP), elutes as an unresolved peak with structurally related nucleotides. We examined female urine samples over the moult cycle and detected UDP as well as uridine triphosphate (UTP). Bioassays were conducted to establish the possibility of a blend of nucleotides forming a sex pheromone bouquet in C. maenas . Whilst UDP induced the male mate guarding behaviour (cradling), a mixture of the two nucleotides at a ratio of 4:1 UDP:UTP elicited an even stronger mating response than either UDP or UTP individually. The urine concentration and composition of these nucleotides changes over the moult period pre and post ecdysis, providing evidence that a pheromone bouquet composition is not always constant. The change of the bouquet is related to the physiological state of the sender, here the moult cycle. Our study unravels the functionality of reaction-specific molecules in a pheromone bouquet. Whilst UDP is the mating signal, UTP acts as an attractant and combined they maximise the reproductive response. The use of bouquets provides species-specificity, potentially enabling reproductive isolation of sympatric species, and contains valuable information on the physiological state of the sender.
Marine invasive species and their bioactive metabolites have become critical ecological issues in the Mediterranean Sea. In particular, the highly invasive green algae Caulerpa taxifolia and Caulerpa cylindracea are known to contain the bioactive sesquiterpene caulerpenyne (1) and the bisindolic alkaloid caulerpin (2), potentially acting as chemical stressors for native species. The recent spread of a variety of C. taxifolia, Caulerpa taxifolia var. distichophylla, also raises urgent questions about its chemical composition. Indeed, the only chemical data available for this alga are limited to the seasonal variations of caulerpenyne (1) in samples collected in the Eastern Mediterranean. In this study, we confirmed the presence of 1 also in C. taxifolia var. distichophylla collected along the Sicilian coast, while 2 was not detected in the alga. However, caulerpin (2) was found both in a Mediterranean specimen of C. taxifolia, and at a much higher level in the congeneric C. cylindracea. This suggests that C. taxifolia var. distichophylla differs from C. taxifolia in its secondary metabolism, potentially exerting dissimilar chemically mediated impacts on native biota. Further chemical investigations on the terpenoidic content of C. taxifolia var. distichophylla led to isolate and identify squalene 2,3 oxide (3), phytol (4), and plastoquinone (5), along with the two unreported sesquiterpene lactones 6 and 7. Finally, chemoecological assays clarified that caulerpenyne (1) at its natural concentration in C. taxifolia var. distichophylla elicits avoidance responses in native shrimp, although sensitization was a prerequisite to significantly induce food rejection.
Arguably climate change is one of the biggest challenges faced by many organisms. One of the more significant of these is the decreasing pH level of the ocean, a consequence of the increasing amount of atmospheric CO 2 being absorbed. With the current open ocean pH level of 8.15 projected to fall to just over 7.6 in 2100, the impacts could be devastating for marine species reliant upon olfaction to survive. Here, we show that Carcinus maenas (shore crab) can detect and respond to the presence of odour cues from predatory species with no significant change between both current and projected pH conditions. In contrast, C. maenas ability to detect and respond to prey cues is altered in the projected climate change conditions, with a delayed response being observed at pH 7.6. A difference can be seen between males and females, with males detecting prey cues faster than females in reduced pH, suggesting the potential for males to be better acclimated to future climate change conditions. The change in ocean chemistry is postulated to have a fundamental impact on chemical communication systems in aquatic species. Here, we show such negative impacts of altered pH on feeding responses in Carcinus maenas , a typically robust keystone intertidal species and confirm that not all behaviours are affected equally with potentially significant implications for such functional traits and species interactions.
Marine and freshwater ecosystems differ in persistence, size, population connectivity, and the variance in physical and biotic conditions they experience. These differences may select for differing reproductive modes, life histories, dispersal strategies, and chemically cued recruitment behaviors. In marine systems, adults are commonly less mobile, while larvae spend hours to weeks to months dispersing in the plankton and may move over great distances. It is these immature larval stages that must select appropriate recruitment sites in marine environments. In freshwater systems, the fully developed adults more commonly disperse over greater distances, and it is usually adults that determine juvenile recruitment sites via their placement of larvae or fertilized eggs. Thus, in terms of large-scale habitat choices involving chemical cuing, adult stages should be selected to detect and react to habitat cues among most freshwater species, while juveniles should play this role among most marine species. Few studies assess this hypothesis, but adults of freshwater organisms as different as mosquitoes and frogs do key on chemical cues to select sites for depositing eggs or larvae, while chemical cuing of recruitment in marine systems occurs primarily among the larval stages of the numerous fishes and marine invertebrates investigated to date. Cues to general habitat features, to predators or competitors, and to specific prey or hosts have all been shown to affect recruitment. Here, we review chemically mediated recruitment in marine versus freshwater systems, summarizing what is known and suggesting unknowns that may be productive to investigate.
Blooms of freshwater toxic cyanobacteria are a growing environmental health problem, enhanced by anthropogenic eutrophication and climate change. A variety of techniques were tested for their remediation, from physical methods using artificial mixing or flocculation, to chemical methods employing synthetic and natural compounds, as well as constructed wetlands. In this work, we conducted an evaluation at microcosm scale of the usefulness of the allelochemicals produced by a strain of the filamentous cyanobacteria Phormidium sp. for the bioremediation of proliferations of four strains of toxic freshwater cyanobacteria (Cylindrospermopsis raciborskii, Chrysosporum ovalisporum, Anabaena sp. and Nodularia sp.). Allelochemicals produced by this strain of Phormidium sp. belong to the portoamides compounds family. Their effect was tested in bioassays using cell-free filtrate, the results showing that all the four strains were sensitive. In addition, we performed phosphate-limited long-term competition experiments in continuous cultures, in which Phormidium sp. was co-cultured with each of the toxic cyanobacterial strains. The purpose of these later experiments was to demonstrate that allelopathy and not resource competition was responsible for the ecological exclusion of the toxic cyanobacteria strains, and also to employ higher population abundances to test the effectiveness of the allelochemicals. Before that, we needed to estimate the competitive ability of each species to limit the resource that we employed (phosphate). Phormidium sp. were clearly a better competitor for phosphate than Anabaena sp., worse than Nodularia sp., and very similar to C. raciborskii and C. ovalisporum. Only in the case of Nodularia sp. could we demonstrate that the ecological exclusion of the toxic cyanobacteria was caused by allelopathy. However, the rapid exclusion shown in our experiments suggests that allelopathy was the main cause in all cases. An inter-specific competition model including only competition for phosphate and an allelopathic interaction was able to accurately describe the patterns of population dynamics observed in our experiments.
Efficacious monitoring of fish stocks is critical for efficient management. Multibeam acoustic cameras, that use sound-reflectance to generate moving pictures, provide an important alternative to traditional video-based methods that are inoperable in turbid waters. However, acoustic cameras, like standard video monitoring methods, produce large volumes of imagery from which it is time consuming and costly to extract data manually. Deep learning, a form of machine learning, can be used to automate the processing and analysis of acoustic data. We used convolutional neural networks (CNNs) to detect and count fish in a publicly available dual-frequency identification sonar (DIDSON) dataset. We compared three types of detections, direct acoustic, acoustic shadows, and a combination of direct and shadows. The deep learning model was highly reliable at detecting fish to obtain abundance data using acoustic data. Model accuracy for counts-per-image was improved by the inclusion of shadows (F1 scores, a measure of the model accuracy: direct 0.79, shadow 0.88, combined 0.90). Model accuracy for MaxN per video was high for all three types of detections (F1 scores: direct 0.90, shadow 0.90, combined 0.91). Our results demonstrate that CNNs are a powerful tool for automating underwater acoustic data analysis. Given this promise, we suggest broadening the scope of testing to include a wider range of fish shapes, sizes, and abundances, with a view to automating species (or ‘morphospecies’) identification and counts.
Between 2014 and 2019, Central Europe was subject to unusually high temperatures and periods of drought due to climate change, with a subsequent occurrence of low and zero flows. As aquatic organisms have shaped their life strategies in direct relation to natural hydrological regimes, any changes to these regimes necessarily lead to a cascade of responses in biota species composition in the ecosystem concerned. Here, we examine changes in aquatic macroinvertebrates assemblage composition and diversity in a small fishless headwater brook in a highland area of the Czech Republic that took place between 2010 and 2019. While flow rates were relatively constant prior to 2014, the hydrological regime was significantly influenced by periods of severe drought between 2017 and 2019, with periods of zero discharge and dry riverbed. The shift from a perennial to an intermittent stream led to an increase in generalist taxa abundance and a decline in lotic taxa, while the abundance of lentic and semi-aquatic taxa was subjected to fluctuations non-related to the hydrological regime (drought occurrence). During the period of droughts, the abundance of taxa recognised as indicators of good quality water declined, while the numbers of those indicating moderately to heavily polluted environments increased.
The time and space dynamics of phytoplankton and its driving factors were studied in Hongfeng Reservoir, southwestern China, from March 2016 to December 2019 to explore the spatiotemporal dynamics and driving factors of the phytoplankton community structure. The structural equation model (SEM) was used to analyze the relationship between abundance of phytoplankton and environmental factors in order to determine the main environmental factors that affect changes in phytoplankton. A total of 110 phytoplankton taxa were obtained from six sites. They were members of seven phyla and 68 genera with 12 dominant species or genera. The SEM showed that the main environmental factors that affected the cyanobacteria and diatoms were the temperature (WT), total nitrogen (TN), nitrite nitrogen, nitrate nitrogen, dissolved oxygen, and transparency (SD). Those that affected the Chlorophyta were the pH, TN, ammonia nitrogen (NH4⁺–N), and orthophosphate phosphorus (PO4³⁻–P). We concluded that changes in the WT, SD, and the concentration of nutrients significantly affected the abundance of phytoplankton and the dominance of Cyanobacteria and diatoms, whereas these factors had insignificant effects on green algae. The WT, SD, TN and NH4⁺–N were found to be important environmental factors that affect the structure, growth, and reproduction of the phytoplankton community in Hongfeng Reservoir. This study should provide a scientific reference for the reservoir phytoplankton community ecology and a database on the changes in water quality.
This study elucidates the responses of bloom-forming benthic dinoflagellates, Amphidinium carterae and Bysmatrum gregarium (formerly known as B. caponii) to salinity changes and prolonged darkness. Both dinoflagellates are known to inhabit rock pools that experiences significant variations in environmental conditions. In both dinoflagellates, salinity changes did not trigger cyst formation but morphological responses were different under prolonged darkness. B. gregarium underwent encystment while A. carterae showed cell shrinkage and flagella movement (up to 9 days) without cell division. This study documents cyst formation in B. gregarium for the first time. However, both dinoflagellates showed reduced growth and photosynthetic efficiency under lower salinity (< 5) and prolonged darkness. Interestingly, both dinoflagellates did not show a maximum photosynthetic efficiency of 0.65 under optimal growth conditions which could be due to the prevalence of carotenoid-chlorophyll protein complex and diatoxanthin (fluorescence quencher). This study proposes that seasonal rainfall (e.g., Southwest monsoon along the Indian coast) can control the proliferation of both dinoflagellates in rock pools (i.e., just before the onset of monsoonal rainfall) as it hampers cell growth, inhibits photosynthesis, and does not induce cyst formation as adaptive survival strategies. Further findings on their dark survival for several days will have implications in the studies related to the transportation to different locations through the ship’s ballast water discharge or to deeper sediments in the intertidal regions.
The early stages of fish during their life cycle, including larvae and juveniles, are sensitive to the environment. Determining the occurrences of fish larvae and juvenile relative to their associated environments is essential for conservation and fisheries management. Computer-based modeling has rarely been applied for forecasting the distribution patterns of the early fish stages in dynamic systems such as estuaries. In the present study, we applied novel modeling techniques to fish larval and juvenile samples collected in May, September, November, and December during 2019 along the Ba Lat estuary of the Red River, northern Vietnam. The results showed that the occurrences of freshwater and marine fish larvae and juveniles were inversely related to environmental factors (electrical conductivity, temperature, pH, depth, shore distance and turbidity) with a high square of multiple correlation coefficients. The occurrences of the two fish groups were strongly related to temporal and spatial changes in the estuary, and these correlations could be utilized for machine learning processing. Linear regression, Gaussian process models, ensemble regression, and artificial neural network (ANN) models were applied to elucidate the distributions of fish larvae and juveniles. It shows that ANN models obtained the highest R² (> 0.63). In addition, the spatial distribution prediction of fish larvae and juveniles using ANN models was similar to the field measurement. Thus, we suggest utilizing ANN models to predict the occurrences of early fish stages in estuaries in tropical regions such as Vietnam. Recommendations for further applications of ANN models are also given in this study.
Microorganisms play a central role in the structure and function of marine ecosystems. Its vast diversity makes the disentangling of the microbial taxonomic composition an essential task. Engaño Bay, a highly productive temperate region on the Patagonian Atlantic Coast, constitutes a remote uncharted area. Here, metabarcoding analyses revealed that the microbiome community (cells < 5 µm) of surface water is dominated by a few bacterial taxa along with diverse low frequency groups. A substantial number of sequences of photosynthetic picoeukaryotes (PPE) were also evidenced, yet no cyanobacterial sequences could be observed. Specific PCR-detection of cyanobacteria, monitoring of viruses specific for cyanobacteria and PPE, microbiological isolation, and molecular diet analyses confirmed these findings. Cyanobacteria were PCR detected in three out of thirteen samples, while virological monitoring indicated the presence of PPE viruses and the absence of cyanobacteria phages. Traditional culture methods allowed the isolation of Ostreococcus and Micromonas spp. from samples belonging to warm and cold seasons, respectively. Molecular diet analyses showed that PPE were grazed by nanoplankters and that grazing pressure on PPE was stronger than on bacteria. Phylogenetic characterization of viral sequences indicated the presence of Ostreococcus virus, four Micromonas virus lineages and a divergent clade of Phycodnavirus belonging to no known viral species, pointing out a complex scenario of its hosts. This work characterizes the marine microbiome from a temperate uncharted region at the Southern Hemisphere, demonstrating the prevalence of PPE as primary producers with a complex scenario which warrant further studies.
Multiple fish-based indices of biotic integrity (FIBI) exist to estimate stream health using fish community structure. Yet, these metrics require different amounts of data and may result in different interpretations of stream health. We compared functionality of “low-metric” (5 metrics) and “metric-rich” (12 metrics) coldwater FIBIs for estimating stream health in 138 coldwater streams of northeastern Iowa, USA. Then, we investigated associations between FIBI scores and environmental factors at local and catchment scales using mixed effects linear regression. FIBI scores from both protocols were positively correlated (R² = 0.77); the majority of streams scored fair (n = 31, mean = 45; fair) using the metric-rich index but scored very poor using the low-metric index (n = 35, mean score = 25; poor). FIBI scores were higher (mean = good) when Brook Trout Salvelinus fontinalis were present with both indices. When Brook Trout were absent, scores were lower and less variable with the low-metric index (mean = 19.63; poor) compared to the metric-rich index (mean = 40.38; fair). Local habitat was more related to both FIBI scores than catchment-scale habitat: maximum daily stream temperature and bare bank severity index were negatively correlated with both FIBI scores whereas canopy coverage correlated positively with metric-rich FIBI scores. Brook Trout presence was indicative of coldwater stream health for both indices. Our results suggest the metric-rich FIBI index has improved ability to differentiate lower quality sites due to increased sensitivity. Our results can be used to improve stream health estimates and restoration prioritizations.
The desmids constitute a highly diverse group with potential as a bioindicator of the conservation status of freshwater environments. We evaluated the changes in the desmid community on macrophytes with different structural complexities within mixed stands in a floodplain shallow lake in the Brazilian semi-arid region. Our main question was whether the environmental variables that best predict desmid structure among macrophyte species in mixed stands. Samplings were performed at each two months at four fixed stations during one year in a shallow tropical lake. To assess the changes in community structure, we sampled the periphyton on three macrophytes species (Cabomba caroliniana, Nymphaea amazonum, and Utricularia foliosa) with different complexity levels, which were quantified by their fractal dimension. Multivariate analysis showed that the structure and composition of the periphytic desmids were influenced by fractal dimension, nutrient availability, and temperature. The richness, density, and diversity of desmids differed between macrophytes with complex structure (U. foliosa and C. caroliniana) and simple structure (N. amazonum). We also observed that more complex macrophytes have a greatest contribution of desmids with small cell (< 40 μm) in the community, suggesting that the substrate complexity affects the use of habitat. Our results suggest that the substantial fractal differences between host macrophytes are a major determining factor in the structure of periphytic desmid communities.
Seamounts and oceanic currents are important oceanographic features that influence genetic diversity of a species along its distribution, acting both as barriers or pathways for species dispersal. There are two important seamount chains in the Tropical Western Atlantic (TWA): the Fernando de Noronha Chain in northeastern Brazil and the Vitória-Trindade Chain in southeastern Brazil. This region is influenced by the North and South branches of the Southern Equatorial Current (SEC), which flow from the east to west. In order to evaluate how these oceanographic characteristics influence the genetic diversity and population structure of O. insularis along its broad distribution area, we analyzed specimens from sampling sites of the Brazilian coast and oceanic islands, Ascension and Saint Helena archipelago, Mexican Caribbean, and San Blas, Panama. The analyses performed using fragments of 659 bp of the mitochondrial gene (cox1) showed the occurrence of four distinct populations: one from Caribbean to Fernando de Noronha archipelago (Central-North), another from east coast of Brazil to Trindade archipelago (South), and the others restricted to Ascension and Saint Helena, and São Pedro and São Paulo archipelagos, respectively. Both the seamounts and ocean currents contributed to the genetic structure observed along O. insularis distribution. The bifurcation of the SEC seems to separate Center-North and South populations, while the gene flow within oceanic islands and the coast in each population is explained by the existence of seamounts. Since O. insularis has a broad distribution (mainly the Center-North population) divided into four genetically distinct fisheries, the species fishery needs to be managed accordingly, which might depend on the international policies agreements.
Shelters are crucial for intertidal organisms as a way to protect from environmental stress. The present study examines whether the shelter selection of the amphipod Ampithoe valida is influenced by ultraviolet radiation (UVR) and whether this selection depends on the amount of photoprotective compounds (UV-absorbing compounds, UVAC) that the amphipods acquire through the diet. Amphipods were exposed to radiation (photosynthetically active radiation and UVR) and offered a choice of UVR-transparent versus UVR-shielded shelters. Experiments were carried out (1) in the short term (i.e., hours) and (2) in the middle term (i.e., days), with individuals feeding on diets with different amounts of UVAC either prior to or during the exposure, respectively. In the short term, both sexes preferentially selected UVR-shielded shelters. In the middle term, the preference for this shelter type was only observed after 5 days of exposure in females and in males just partially; however, no shelter preferences could be detected during the first two days of exposure in either sex. In the case of the experiment with females, this latter was possibly related to lower irradiances due to cloudy conditions, whereas males may have traded shelter for higher mobility. UVAC acquired through the diet did not alter A. valida’s shelter selection, indicating that seeking shelter remains an important strategy to protect from deleterious levels of UVR even when other mechanisms of photoprotection are available.
Hypoxic events have always naturally occurred in freshwater ecosystems but are worsening due to anthropogenic activities. Hypoxia tolerance greatly varies among fish species and is difficult to quantify in nature in large fish species. We analysed the movements of 40 subadult and adult European catfish Silurus glanis [(727; 2150) mm] exposed to a natural summer hypoxic event in a shallow lake of southeastern France. Catfish could withstand very low dissolved oxygen concentrations (DOC), down to 1.3 mg/L in the upper half of the water column (corresponding to a mean dissolved oxygen saturation rate of 16%), when their preferred benthic habitats were anoxic. While hypoxia was becoming more severe, individuals significantly increased their activity and the surface area they visited, whatever their size. This led them to a refuge zone where they aggregated or stayed in close vicinity, very little mobile, over one and a half day during the overall anoxia of the lake. This zone, located very close to the well oxygenated water inflow, was probably one of the most oxygenated accessible zone. However, during this aggregation, the smallest individuals were more active than the largest ones. This was probably because they more often needed to move to better-oxygenated places within the gathering area, compared to larger dominant fish that occupied the best places. The ability of catfish to withstand very low DOC, along with its high optimum temperature range, could give it a competitive advantage over other predatory species in the context of global change.
In the present study, we evaluated the trophic role of Octopus insularis Leite and Haimovici 2008 in the food web of Rocas Atoll, a preserved insular territory in the Southwest Atlantic. Using stable isotope analysis of C and N, we showed that the local trophic web comprises at least four trophic levels, where the octopus occupies a trophic position (TP) between the second and third trophic levels (mean ± SD TP additive = 3.08 ± 0.36; TP Bayesian-= 3.12 ± 0.17). Among other benthic/reef-associated consumers, this cephalopod stood out for its much wider isotopic niche, pointing to a diet diversified in carbon sources, but focussed on prey in lower TPs. This finding was in accordance with the time-minimizing feeding strategy described for the species, which seemed almost permanent throughout the life cycle of the octopus, given the great niche overlap between octopuses in different maturity stages and their very similar trophic positions. Also, as a prey, octopuses composed up to almost 23% of the diet of some benthic/demersal predators. Overall, O. insu-laris represented an important mesopredator for the local food web, principally for bottom-associated organisms, while also serving as a substantial energy input to the next trophic levels.
Worldwide trade of the carnivorous snail Anentome helena may result in its chance dispersal from aquaria to the natural habitats. In course of consuming the invasive snail Physella acuta and the native snail Racesina luteola, selectively, A. helena can weaken the competitive interactions and elicit non-consumptive effects (NCEs) as well. To determine the NCEs on R. luteola and P. acuta, induced by the exotic A. helena, we observed the life-history trait variations due to competition, presence of A. helena and its cues. Since the prey snails were not exposed to such exotic predators, the resultant response will help to evaluate the prospective differences in the evasion and vulnerability of the interacting native and exotic snails. We initiated the experiment using freshly hatched R. luteola and P. acuta by placing them into intra and interspecific competitions. Furthermore, the experimental containers were divided into three treatment levels: control, presence of predator cues and A. helena. We did not find any alteration in the number of days required to attain the sexual maturity of both prey snails due to competition or predator treatments. Although R. luteola had no effects of competition; the body mass and fecundity were negatively affected by the presence of A. helena and its cues. However, the strong effect of intraspecific competition on P. acuta was weakened through increased length, body mass, and fecundity under the presence of A. helena. Therefore, the probable introduction of A. helena may indirectly affect the life-history parameters of both prey and favour P. acuta over R. luteola in the freshwater habitats of West Bengal, India.
Island biogeography is based on the idea that the larger an island, and the less it is isolated from other areas, the higher the biodiversity it contains. The premise of island size contributing to diversity is based on the fundamental ecological concept—the species area relationship (SAR). Wetlands and, in particular, arid zone spring wetlands can be considered islands as they are wetted habitat surrounded by a harsh and dry landscape—“girt by dirt”—forming an ideal setting to study island biogeography. While studies in spring wetlands have identified SARs that conform to the concept, others identified conflicting information. The aim of our study was to assess the relationship between spring wetland wetted area and its aquatic invertebrate taxonomic richness across three of Australia’s Great Artesian Basin spring complexes. Wetted area and aquatic invertebrates were recorded for 32 individual spring wetlands. The constraint that wetted area has on invertebrate taxonomic richness was analysed using quantile regression. ANOSIM was used to compare differences in the invertebrate community between spring complexes. No significant relationship between wetted area and taxonomic richness was identified across all springs, but the aquatic invertebrate community and taxonomic richness was significantly different across the three spring complexes. Analyses were repeated for one spring complex. Increasing wetland size was found to constrain invertebrate taxonomic richness at Edgbaston Springs. These results contrast with the basic SAR concept but can potentially be the result of a “small island effect” where the relationship is overridden by anthropogenic disturbance.
The biometry and seasonal size distribution of the medusae, Crambionella annandalei and Chrysaora spp. were investigated from fortnightly gillnet landings between January 2017 and December 2018 along the West coast of the Bay of Bengal. Although both taxa exhibited strong patterns of seasonality in abundance and growth, being commonest and smallest in summer, C. annandalei were largely absent in the monsoon and post-monsoon seasons, while Chrysaora spp. could be recorded throughout the year in a variety of size groups. There was a strong cohesion in pattern between years, suggesting that the monsoon impacts populations of both species, albeit in slightly different ways. We provide rare, field-based measurements of growth for both species that are in broad agreement with the data published for similar taxa elsewhere: our length–weight data provide useful contributions to baseline information.
Loss of submerged macrophytes resulting from high turbidity has become a global environmental problem in shallow lakes, associated with eutrophication. To help macrophyte recovery, application of artificial light-emitting diodes (LEDs) has been proposed to complement nutrient load reductions. We set up a mesocosm experiment to test if LEDs could compensate for shading effects from phytoplankton. We incubated three submerged macrophytes (Vallisneria natans, Myriophyllum spicatum and Ceratophyllum demersum) in 12 tanks of 1000 L under three artificial LED light treatments (red, blue and white) for 94 days in summer. The results showed that 1) growth of V. natans and M. spicatum was stimulated in all the LED light treatments, while C. demersum died in the end of the experiment in all treatments. The growth variables (MLShoot, DMShoot) of V. natans in blue, red and white treatments were 1.8–4.5 times greater than those in the control treatment. For M. spicatum, all plants only survived in the treatments with artificial light supplement. 2) Growing status of V. natans was similar among the treatments of different light colors, while M. spicatum grew best in the red light treatment. The results suggest that artificial light, particularly red light, can promote the recovery of submerged macrophytes in waters where impaired light climate would prevent or delay growth of macrophytes and recovery from eutrophication. Further large-scale field studies are, however, needed to fully elucidate the potential of using artificial light to stimulate growth and recovery of submerged macrophytes in shallow lakes.
Hydrological disconnection in intermittent rivers is known to increase β-diversity by limiting the dispersal of species and decreasing environmental similarity between sites. Knowledge of the mechanisms driving variation within and between local communities helps elucidate the role of environmental and spatial processes responsible for community composition at multiple scales in intermittent rivers. In this study, we investigated the spatial and environmental patterns of zooplankton β-diversity in an intermittent river in a semiarid region in Brazil. We hypothesized that (1) the zooplankton metacommunity is determined primarily by turnover, and (2) the structure of the zooplankton metacommunity is more heavily influenced by environmental than spatial factors. Our samples yielded 46 taxa of rotifers and cladocerans. β-taxonomic diversity was high, with a predominance of turnover compared with nestedness. The partitioning analysis showed that environmental and spatial processes had a significant influence on the distribution of zooplankton species, but the former had the greatest explanatory power. In the redundancy analysis, high values of temperature, oxygen and submersed macrophytes were significantly correlated with species variation. The observed β-diversity values closely reflected the turnover pattern, whereas Cladocera and Rotifera diverged between predictive processes. Our results highlight the importance of adopting appropriate conservation measures for intermittent river networks as a whole.
Trophic niche width and individual specialization among marine predators are often subjected to seasonal constraints. Differences are expected to arise for sexually dimorphic species exposed to distinct ecological opportunities, as well as intrinsic differences in physiological abilities or energetic requirements. We assess seasonal and sexual differences in isotopic niche overlap and width and analyze inter-individual foraging variation throughout the year of the South American fur seal (Arctocephalus australis). We obtained chronologically ordered δ¹³C and δ¹⁵N data from vibrissae of 25 males and 24 females from southern Brazil and Uruguay. There were significant differences between sexes for both isotopes with males showing higher values (δ¹³C = − 14.5 ± 0.5‰; δ¹⁵N = 18.9 ± 1.2‰) than females (δ¹³C = − 15.2 ± 0.5‰; δ¹⁵N = 17.8 ± 1.2‰), but not among seasons or years. A very small isotopic niche overlap found between sexes (1.1–9.5%), with limited seasonal variation, likely resulted from differences in prey consumption and foraging habitats. Compared to other seasons, females had a wider isotopic niche in spring. While males showed seasonal stability in the foraging niche, females showed some small variation, which is probably influenced by central place foraging. Both sexes had considerable interindividual variation in estimated dietary composition and had different proportions of potential prey contribution at the population level. These findings enlighten the knowledge of South American fur seal trophic ecology, and how they may seasonally and spatially shift their foraging strategies according to their distinct life histories. It ultimately reflects in a small niche partitioning and possibly low intraspecific competition at the species northernmost area of occurrence in the western South Atlantic.
Metacommunity models describe species occupancy frequency distribution (hereinafter ‘SOFD’). Our goal is to present how the differences in eight macroinvertebrate orders dispersal ability affect SOFD patterns. A total of 293 species from eight macroinvertebrate orders were observed in 14 eutrophic lakes in southern Finland. Species occupancy ranged from 1 to 14. About 30% (89 out of 293) of the species were found in only one lake, yielding a surprisingly high number of rare species. So, there were few widely distributed common species and numerous rare species with a restricted distribution. Combined data from eight macroinvertebrate orders supported the bimodal truncated SOFD pattern. Similarly, the low dispersal ability orders, watermites and mayflies, fitted the bimodal truncated SOFD pattern. However, bimodal symmetric SOFD pattern also fitted relatively well to the dragonflies and damselflies with high dispersal ability. It seems that differences in dispersal ability among different macroinvertebrate orders may partly explain observed differences. Moreover, our results supported slightly more a niche-based model rather than a metapopulation dynamics model in eutrophic lakes littoral macroinvertebrate metacommunities. Our results highlight that the dispersal ability is important trait for species conservation in patchily distributed habitat.
Despite the obvious negative effects caused by invasive species, some recent studies have shown that the impacts at local scale are diverse and not necessarily negative. Arborescent benthic organisms such as octocorals form three-dimensional structures capable of increasing the amount of substrate available and providing shelter for epibiont species. We investigated the role of the alien octocoral Carijoa riisei on the diversity of benthic communities in three shipwrecks on the north-eastern coast of Brazil. We expected that (a) the fauna associated with the octocoral are richer and more diverse compared to the adjacent; (b) some species are exclusively associated with C. riisei; (c) the species that are present both in the areas with and without C. riisei have a greater abundance when associated with the octocoral. For this, we compared the macrobenthic communities associated with C. riisei to those found in adjacent areas where the octocoral was absent. Our study showed that the communities associated with the octocoral were 1.5 times richer and 10 times more abundant than adjacent communities, with 29 exclusive taxa. The dominant taxa were the amphipods Ericthonius brasiliensis and Podocerus brasiliensis and polychaetes of the family Syllidae. These taxa were present in areas with presence and absence of C. riisei, but their abundance was significantly greater where the octocoral was present. Our results reinforce the idea that Carijoa riisei acts as an ecosystem engineer in coastal reefs, creating new habitats and increasing diversity at a local scale, even though it is an alien species.
Dead animals may be an important or the only source of tissues to analyze for stable isotopes, with the goal of making inferences about an animal’s past ecological history. However, in nature, stable isotope values may be affected by myriad decomposition processes, such as abiotic environmental conditions and bacterial and fungal decay, potentially reducing the accuracy of derived ecological conclusions. We used Pacific salmon carcasses left in air or submerged under water to test whether stable isotope values of metabolically active (skin, muscle, and adipose fin) and inactive (scale) tissues changed over time. We found that the δ13C values of active tissues were all affected by decomposition but not in a predictable direction, and hard scale tissue was not. In contrast, there was no effect on δ15N values for any tissue up to 4 days under water or 8 days in air. This suggests that tissues can be analyzed for nitrogen stable isotope values even after several days in water and even if covered in fungus on the surface. For populations within which dead animals are frequently encountered, e.g., salmonid carcass surveys, hard tissues of fish (scales, otoliths) and other animals (baleen, bone, hair, feathers) will likely yield relevant biological information even if soft tissue is rotting, providing another avenue to collect important data about the life history of those animals.
The Amazon rainforest has experienced rapid land-use changes, including extensive deforestation of riparian areas, putting at risk among the most diverse freshwater fish assemblages on the planet. At nine study reaches distributed among three Colombian blackwater streams, we described and quantified how variability in riparian vegetation structure—during both dry and rainy seasons—influenced the taxonomic and functional diversity of fish assemblages. We observed 117 species across our study reaches, but taxonomic measures such as species richness and evenness were not different among low, intermediate, or high levels of riparian vegetation coverage. Fish assemblage composition was also not different by riparian vegetation, although we observed significant seasonal shifts—only 16% of species were observed in both rainy and dry seasons. Evenness and effective number of species derived from Simpson’s Index were 7 and 38% greater in the dry season than in the rainy season, respectively. Diet varied by riparian zone condition: 56% of fish stomach contents were of allochthonous origin in stream reaches with intact vegetation versus 37% in streams with altered riparian vegetation. We also observed that the relative proportion of detritivorous fishes was 13% greater in the rainy season, while the proportion of invertivores was 26% greater in the dry season. Both functional divergence and dispersion—measures of the variability of species’ traits—were higher in reaches with more intact vegetation during the rainy season. Our findings highlight the importance of the interaction of riparian vegetation and seasonality, and both longitudinal and lateral hydrological connectivity, for fish functional diversity of Amazonian streams.