Multi-specific Assemblages Research Articles

Age Readings and Assessment in Coastal Batoid Elasmobranchs from Small-Scale Size-Selective Fishery: The Importance of Data Comparability in Multi-Specific Assemblages

The large variation in vertebral shape and calcification observed among elasmobranch species prevents using a single method for enhancing growth bands and reading age. Further, estimating age and growth parameters can be difficult or impractical when samples are incomplete due to the bycatch of a size-selective fishery. Using a single and rapid method, age readings were obtained on the vertebrae of four batoid species, namely 53 individuals of Dasyatis pastinaca, 51 of Raja asterias, 15 of Torpedo marmorata, and 55 specimens of Torpedo torpedo, from the local small-scale trammel net fishery in the coastal waters (5–20 m depth) of the Central Tyrrhenian Sea during 2019–2021. Based on these data, a statistical routine was developed to obtain multiple estimates of age and growth parameters for incomplete samples due to size-selective fishing. The acceptable agreement between and within readers (intra and inter-reader disagreement < 5%) and the rate of increase in vertebral size with body size (differently ranked across species) demonstrated the consistency of the enhancing method. The parameters estimated by the Von Bertalanffy and Gompertz growth models matched the data available in the Mediterranean Sea for the species studied, with D. pastinaca, T. torpedo, and R. asterias showing the lowest (k = 0.05–0.12), intermediate (k = 0.112–0.19), and highest (k = 0.18–0.23) growth rates, respectively, in line with the life history traits of these species. Overall, the method proved effective both in delineating band pairs in vertebrae of different species and in reliably estimating the age and growth parameters of problematic samples due to size-selective fishing. The proposed method supports the collection of comparable demographic data from other areas where similar multi-specific assemblages are bycatch of size-selective fisheries impacting potential nursery areas and other essential habitats for elasmobranchs.

Microbial community and network responses across strong environmental gradients: How do they compare with macroorganisms?

The way strong environmental gradients shape multispecific assemblages has allowed us to examine a suite of ecological and evolutionary hypotheses about structure, regulation and community responses to fluctuating environments. But whether the highly diverse co-occurring microorganisms are shaped in similar ways as macroscopic organisms across the same gradients has yet to be addressed in most ecosystems. Here, we characterize intertidal biofilm bacteria communities, comparing zonation at both the "species" and community levels, as well as network attributes, with co-occurring macroalgae and invertebrates in the same rocky shore system. The results revealed that the desiccation gradient has a more significant impact on smaller communities, while both desiccation and submersion gradients (surge) affect the larger, macroscopic communities. At the community level, we also confirmed the existence of distinct communities within each intertidal zone for microorganisms, similar to what has been previously described for macroorganisms. But our results indicated that dominant microbial organisms along the same environmental gradient exhibited less differentiation across tidal levels than their macroscopic counterparts. However, despite the substantial differences in richness, size and attributes of co-occurrence networks, both macro- and micro-communities respond to stress gradients, leading to the formation of similar zonation patterns in the intertidal rocky shore.

Evidences of human impact on megabenthic assemblages of bathyal sediments in the Alboran Sea (western Mediterranean)

Megabenthic assemblages in deep-sea sedimentary environments receive far less attention than those occurring on rocky environments, despite they have been widely impacted by destructive trawling activities, mainly due to their association with important commercial species. ROV dives conducted on bathyal muds of the Alboran Sea continental slope (western Mediterranean) were used to characterize megabenthic assemblages, as well as assess their response to trawling and benthic litter. We identified a multispecific assemblage, dominated by the isidid Isidella elongata, and two monospecific assemblages composed by the sea-pens Funiculina quadrangularis and Kophobelemnon stelliferum. These assemblages are defined as vulnerable marine ecosystems by international institutions. Trawled areas exhibit significant low densities of habitat-forming species and a striking impoverishment of habitat complexity and diversity. Plastic debris and lost fishing gears were the most abundant components of the marine litter. This study highlights the destructive effects of human activities on bathyal muds, emphasizing the need for urgent conservation measures.

Impact of ocean acidification and warming on the productivity of a rock pool community

This study examined experimentally the combined effect of ocean acidification and warming on the productivity of rock pool multi-specific assemblages, composed of coralline algae, fleshy algae, and grazers. Natural rock pool communities experience high environmental fluctuations. This may confer physiological advantage to rock pool communities when facing predicted acidification and warming. The effect of ocean acidification and warming have been assessed at both individual and assemblage level to examine the importance of species interactions in the response of assemblages. We hypothesized that rock pool assemblages have physiological advantage when facing predicted ocean acidification and warming. Species exhibited species-specific responses to increased temperature and pCO2. Increased temperature and pCO2 have no effect on assemblage photosynthesis, which was mostly influenced by fleshy algal primary production. The response of coralline algae to ocean acidification and warming depended on the season, which evidenced the importance of physiological adaptations to their environment in their response to climate change. We suggest that rock pool assemblages are relatively robust to changes in temperature and pCO2, in terms of primary production.

Trophic structure of frugivorous bats in the Neotropics: emergent patterns in evolutionary history

Abstract Knowing the relative importance of phylogeny in dietary specialisation in frugivorous bats is key to understanding the ecological and evolutionary processes that drove their diversification and to elucidating the mechanisms allowing their coexistence in multispecific assemblages. We evaluate the trophic structure of frugivorous phyllostomids using multiple data sets collected throughout the Neotropics. Then, we investigate the relationship between trophic and phylogenetic structure of phyllostomids, and evaluate the evolutionary mechanisms driving current resource partitioning in phyllostomid assemblages. We compiled a data set of 14500 dietary records from 24 well‐studied bat communities in the Neotropics. We recoded data at the plant genus level and composed two new data sets including tropical sites only, and tropical and subtropical sites pooled (i.e. including sites where diversity is significantly reduced). We performed multivariate analyses on both data sets and estimated phylogenetic effects on the dietary patterns. Dietary structure in both data sets indicated that bat species remained faithful to their core plant taxa. A phylogenetic comparative method selected only a few basal clades from the entire phyllostomid tree that significantly explained the impact of evolutionary history on the observed multivariate patterns. These clades were dated to the middle Miocene, a period of particularly intense geological and environmental changes in the Neotropics. These clades were always younger than the core plant taxa with which they were strongly associated. Accordingly, the core diet of phyllostomid bats has remained remarkably stable since at least the past 15 My (million years), suggesting a bottom‐up control of the evolution of the bat‐plant interactions in the Neotropics.

Coupling suitable prey field to in situ fish larval condition and abundance in a subtropical estuary

Survival of fish larvae is influenced by the suitability of the prey field and its variability in time and space. Relationships among food quality, quantity and recruitment have been explored in temperate ecosystems where spawning and secondary production are strongly seasonal, but for subtropical estuaries the mechanisms responsible for larval survival remain poorly identified. This study evaluated the nutritional condition (feeding incidence and AARS activity) and abundance of a multi-specific assemblage of fish larvae from a subtropical estuary in South America (Solís Grande, Uruguay) during the fish reproductive season; and related both variables to prey abundance, composition, size and fatty acids content. The larval assemblage was composed of 13 species belonging to different functional groups and composition varied seasonally. Contrary to expectations larval condition did not match an increase in prey quality. Food availability was high throughout the study period, although significant changes existed in the size and taxonomic structure of the prey assemblage. The temporal succession of complementary factors - temperature, prey composition, abundance and quality - promoted a wide window of opportunity for larvae, where quality seemed to have compensated quantity. Such combination of factors could allow an extended larval survival along the spawning season. These findings underline the importance of a better understanding of subtropical estuaries as nursery areas.

How to capture fish in a school? Effect of successive predator attacks on seabird feeding success.

Prey aggregations, such as fish schools, attract numerous predators. This typically leads to the formation of multispecific groups of predators. These aggregations can be seen both as a place of increased competition and as a place of possible facilitation between predators. Consequently, the functional role of such predator-prey aggregation is uncertain, and its effect on individual feeding success is virtually unknown. Using underwater film footage of different predators feeding on fish schools during the sardine run in South Africa, we directly measured the insitu feeding success of individual Cape gannets Morus capensis in different foraging situations. We determined the types of Cape gannet attacks (direct plunge dive or plunge dive followed by underwater pursuit) and we measured the occurrences and timing of attacks from the different species (mostly Cape gannets and long-beaked common dolphins Delphinus capensis). We also estimated the size of the targeted fish schools. These observations were complemented with a simulation model to evaluate the cumulative effect of successive predator attacks on the prey aggregation structure. The probability to capture a fish in one feeding attempt by Cape gannets averaged 0·28. It was lower when gannets engaged in underwater prey pursuit after the plunge compared to direct plunge (0·13 vs. 0·36). We found no effect of the number of prey on gannets' feeding success. However, the timing and frequency of attacks influenced strongly and positively the feeding success of individuals. The probability to capture a fish was the lowest (0·16) when no attack occurred in the few seconds (1-15s) prior to a dive and the highest (˜0·4, i.e. more than twice) when one or two attacks occurred during this time window. The simulation model showed that a prey aggregation disorganized just after an attack and that the maximum of disturbance was obtained a few seconds after the initiation of the successive attacks. Our study suggests that, in multispecies predator assemblages, the cumulative effect (through disorganization of school cohesiveness) of the multiple species attacking a prey aggregation may increase the feeding success of each individual. Therefore, facilitationbetween predators is likely to overcome competition in these multispecific assemblages.

Hydroid gardens of Nemertesia ramosa (Lamarck, 1816) in the central North Atlantic

Nemertesia ramosa (Lamarck, 1816) is a large eurybathic hydrozoan species. Its habitat and spatial distribution in the Azores archipelago (central North Atlantic) are described based on 22 new records collected in situ by scuba diving and by observations using a drop-down camera and remote operated vehicles (ROVs) between 2004 and 2011. N. ramosa grows on hard substrates in mono and multi-specific assemblages. In the Azores it is well known in the sublittoral at 15–158 m depth in the central group of islands, but historical records exist from seamounts down to bathyal grounds of nearly 1000 m. Scuba diving surveys generally reveal N. ramosa as an occasionally occurring and rare species in the infralittoral (1–9 colonies 10−3 m−2), although it may also be common and even abundant at some sites. A circalittoral aggregation was assessed in detail exhibiting densities of up to 2.82 colonies m−2 on rocky substrate and one order of magnitude lower on mixed bottom (0.25–0.55 colonies m−2). An aggregated spatial distribution is described, with aggregations being considered hydroid gardens (>1–9 10−1 m−2). Colonies measured on ROV imagery averaged 23.5 cm in height (STD = 4.1). Taller colonies (max = 36.7 cm) were registered on rocky outcrops protruding more than 15 cm. N. ramosa co-occurred mainly with brown and red algae, bryozoans, polychaetes, and other hydroids. A diverse ichthyofauna was associated to these habitats. Circalittoral communities of N. ramosa included hydrozoans, sponges, and fish.

Identifying coral reef fish larvae through DNA barcoding: A test case with the families Acanthuridae and Holocentridae

A reference collection of COI barcode (650 bp) for the Pacific Society Islands has been constituted for 22 species of Acanthuridae and 16 species of Holocentridae. Divergence between congeneric species was on average 20-fold to 87-fold higher than divergence between conspecific sequences and this set of DNA-identifiers was used to identify 40 larvae of both families. All larvae sequenced could be identified to species using DNA-barcodes. Pools of larvae constitute multi-specific assemblages and no additional species compared to adult reef communities were sampled in larval pools, suggesting that the larval assemblages originated from adult communities on neighboring reefs.

SEQUENTIAL CONFLICTING SELECTION DUE TO MULTISPECIFIC INTERACTIONS TRIGGERS EVOLUTIONARY TRADE-OFFS IN A MONOCARPIC HERB

Trade-offs are crucial in understanding phenotypic evolution of organisms. A main source of trade-offs is conflicting selection, a phenomenon very likely in complex multispecific scenarios in which many potential selective agents coexist. The main goal of this study is to investigate the selective trade-offs arising due to conflicting selection on female-fitness components in Erysimum mediohispanicum. I quantified the selection exerted on 10 plant traits by a mutualistic (pollinators) and antagonistic (gall-makers, predispersal and postdispersal seed predators, mammalian herbivores) multispecific assemblage acting sequentially throughout eight selective episodes of the plant, from floral bud to juvenile production. Variation in lifetime female fitness (quantified as number of juveniles) was related mostly to variation in number of flowers, fruit initiation, and seedling establishment. The direction of selection changed among different selective episode for many traits. Most importantly, conflicting selection was frequent in the study system, with half of the phenotypic traits experiencing opposing selection in different selective episodes. Selection at individual life-cycle stages diverged remarkably from selection based on total fitness. Consequently, the evolution of many traits is determined by the relative importance of each episode of selection, with conflicting selection inevitably yielding evolutionary compromises.

Linking seed fate to natural dispersal patterns: factors affecting predation and scatter-hoarding of Virola calophylla seeds in Peru

Natural seed deposition patterns and their effects on post-dispersal seed fate are critical in tropical tree recruitment. Previous research showed that the key dispersal agent of the neotropical tree, Virola calophylla, is the spider monkey (Ateles paniscus). Spider monkeys generate a heterogeneous seed deposition pattern because they scatter-disperse seeds diurnally, whereas they clump-disperse seeds at their sleeping sites. The recruitment consequences of this pattern were investigated using manipulative experiments and observations. Scatter-hoarding by spiny rats (Proechimys spp.) caused little rearrangement of the initial seed deposition pattern because they moved seeds only short distances. Seed survival to the seedling stage depended negatively on conspecific seed density and positively on the distance from the nearest adult V. calophylla female. These effects were likely mediated by two important seed predators, spiny rats and beetles (Scolytidae). Furthermore, spider monkeys' seed deposition patterns influenced seed survival. Scatter-dispersed and experimentally dispersed seeds had the highest survival. Conversely, clump-dispersed seeds at sleeping sites, which are far from V. calophylla females, and non-dispersed seeds had equally low survival, suggesting that conspecific density- and distance-dependence acted independently and did not explain all variation in seed survival. Instead, other characteristics of the seed deposition pattern, such as the multi-specific assemblage of seeds at sleeping sites, also affected post-dispersal seed fates.Resumen: La conexión entre el patrón natural de dispersión de semillas con el destino después de la dispersión es clave para el reclutamiento de árboles tropicales. Mediante experimentos y observaciones se investigó esta conexión utilizando el árbol neotropical Virola calophylla (Myristicaceae). Ateles paniscus (maquisapa), el principal dispersor de sus semillas, genera un patrón de deposición heterogéneo. Durante el día las semillas son depositadas de manera esparcida mientras que en los dormitorios las semillas son depositadas de manera agregada. En este estudio se encontró que los roedores espinosos (Proechimys spp.) almacenaron semillas individuales debajo de la hojarasca, sin embargo estos no alteraron el patrón de dispersión ya que las semillas fueron transportadas distancias cortas y la tasa de predación fue alta. Se encontró que la tasa de sobrevivencia hasta la etapa de plántula tuve una relación negativa con la densidad de las semillas y una relación positiva con la distancia al árbol hembra de V. calophylla mas cercano. Estos efectos sucedieron por medio de roedores espinosos y coleópteros (Scolytidae), predadores importantes de las semillas de V. callophylla. Adicionalemente, el patrón de deposición de los maquisapas influenció la sobrevivencia de las semillas. Tanto las semillas dispersadas por los maquisapas como las dispersadas experimentalmente tuvieron la tasa de sobrevivencia más alta. Por el contrario, tanto las semillas depositadas en los dormitorios, usualmente lejos de hembras de V. calophylla, como las semillas que cayeron debajo del árbol hembra tuvieron bajos niveles de sobrevivencia. Estos reultados sugieren que tanto la densidad como la distancia tuvieron efectos independientes y no explicaron toda la variación observada en la sobrevivencia de semillas. Por el contrario, otras características de la deposición de semillas tales como la riqueza de especies de la comunidad de semillas en los dormitorios también afectaron el destino de las semillas después de dispersadas.

Carbohydrate production in relation to microphytobenthic biofilm development: an integrated approach in a tidal mesocosm.

Experiments were performed to evaluate short-term changes in sediment extracellular carbohydrates for a multispecific assemblage of benthic diatoms in relation to physiological status, endogenous migratory rhythms, and environmental conditions. For this purpose, a mesocosm was used, which simulated both tidal and dark: light alternating cycles under controlled conditions. Scanning electronic microscopy in combination with picture analyses indicated that natural diatom migration patterns were reproduced in the mesocosm. Two EPS fractions were operationally separated in colloidal carbohydrate measurements: alcohol-soluble EPS (termed "soluble EPS") and alcohol-insoluble EPS (termed "bound EPS"). Microphytobenthic biomass followed a logistic-type curve and converged toward a maximal value termed the "biotic capacity of the local environment." Both EPS fractions showed oscillations with production during photosynthetic periods and sharp decreases during night immersion periods. Productions of both EPS fractions increased with Chl a production during light periods suggesting a light dependence in relation to migratory patterns. The decreases in both EPS fractions, which occurred during night immersion periods suggest that carbohydrate hydrolysis and/or washaway affected both EPS fractions similarly in benthic environments. Our results confirm the theory according to which the two distinct fractions are under different metabolic controls. No change in soluble EPS release was obtained during the transition from logarithmic to stationary phase. On the other hand, a metabolism modification of microalgae, probably related to ammonium depletion, occurred when cells entered the stationary phase, since there was a high enhancement in bound EPS production. Mesocosm results can serve as a system of reference useful to characterize biofilm development in field investigations and to revisit the effective implication of each EPS fraction in sediment stability.

Composition of biofouling communities on suspended oyster cultures: an in situ study of their interactions with the water column

This study was based on in situ experiments conducted in a shellfish lagoon (Thau, France) to determine the interactions between suspended oyster Crassostrea gigas Thunberg cul- tures and their environment at a seasonal scale. Three groups of descriptors were considered simul- taneously during the course of the study: the taxonomic composition of an oyster culture unit (OCU), the nutrient and oxygen exchanges at the OCU-water interface (fluxes) and the water-column char- acteristics (water). We used a multiple factorial analysis (MFA) to assess in a single reference frame: (1) the seasonal organisation of the taxonomic groups which compose the OCU and (2) the interac- tions between this multispecific assemblage and the water column. We found strong seasonal vari- ability in the OCU composition and the OCU interactions with the water column. Taxonomic richness of the biofouling was at a maximum in spring and minimum in August after a bottom anoxia. Among biofouling species, ascidians always constituted the dominant group. The annual pattern of coexis- tence observed between ascidians and oysters might be explained by resource partitioning, and also by a beneficial trophic interaction between these 2 groups. The structure of the OCU was based on a complex system of interactions, particularly in spring. During this season, the development on the OCU of macrofauna of soft substratum such as polychaetes reflected the presence of a suspended sediment compartment. The influence of the OCU on the water column was maximum in summer and minimum in winter. In the shellfish zone, the OCU plays a central role in nutrient renewal, particu- larly in summer when benthic fluxes are insufficient to satisfy phytoplankton nitrogen requirements. We estimate that the multispecific assemblages occurring on the oyster ropes (oysters and biofouling) have a potential annual DIN production of 2 × 10 7 mol yr -1 , and thus oyster cultures could have a determining influence on nitrogen recycling in the water column in the Thau lagoon.

Determination of Composition and Vertical Structure of Fish Communities Using in situ Measurements of Acoustic Target Strength

A split-beam echo-sounder was used to estimate in situ acoustic target strengths (TS) of fish from a number of different fish communities on the South African continental shelf. The TS and size distributions (obtained by aimed trawling) were used to describe the size structure and vertical distribution of these communities. TS distributions obtained from several monospecific populations of juvenile Cape hake (Merluccius capensis), the dominant species present, were self-consistent, and there was good correspondence between modes in the TS and length distributions of juvenile hake, adult round herring (Etrumeus whiteheadi), anchovy (Engraulis capensis) recruits, pelagic goby (Sufflogobius bibarbatus), horse mackerel (Trachurus trachurus capensis), and ribbon fish (Lepidopus caudatus). Average TS values for all these species, both per individual and normalized by weight, are presented and compared with published values. The use of TS information in studies of the small-scale community structure and dynamics of fish populations is discussed. It is concluded that the method can be effective on low-density, multispecific assemblages such as those in our study, avoiding many of the pitfalls of conventional net sampling.

Feeding Relationships among Species of Notropis (Pisces: Cyprinidae) in a Wisconsin Stream

The relationship between spatial preference and diet in four species of the genus Notropis (Pisces: Cyprinidae) was investigated in Roxbury Creek, a small stream in southern Wisconsin. Characteristic spatial distributions for each species were determined from frequency of catch in unbaited minnow traps set at varying heights and locations in the pools of the stream. Data for the year 1966—67 indicate that two species, Notropis atherinoides and N. spilopterus are common in midwater. Notropis dorsalis is most frequently found near the bottom and shows a strong preference for the upstream edge of pools Notropis stramineus is also found most often near the bottom but within the pools themselves. The spatial distributions of aquatic invertebrates, the major prey of Notropis in the pools of Roxbury Creek, were also investigated. Data gathered from drift and bottom samples taken in eight sampling periods during 1970—71 suggest a separation between the relatively sedentary bottom fauna, composed of oligochaetes, isopods, several genera of chironomids, tipulids, and trichopterans; and the drift fauna, composed of copepods, chironomids of the subfamily Orthocladiinae, ephemeropterans, and terrestrial anthropods. Certain genera, including the ubiquitous Gammarus were found commonly in both drift and benthic samples. Indices of similarity between pool benthos and drift ranged between 7% and 59%. Data on food habits of Notropis gathered from stomach content analysis of fishes collected over the same period indicate that 73% of the invertebrate genera present are utilized by Notropis species in Roxbury Creek. Considerable overlap exists in the invertebrate genera chosen by the four species (69%—84%), and strong overall correlations between species are found in the importance of various orders of aquatic invertebrates in the diet. Differences in food habits relate principally to differences in space utilization. Midwater species tend to feed on drifting chironomids, copepods, terrestrials, and other animals found in the water column. Bottom—dwelling fishes feed on benthic genera of chironomids, tipulids, oligochaetes, and other organisms found commonly in pool substrates. It is concluded that spatial rather than taxonomic considerations are the chief determinants of prey selection in these four species, and that this pattern of resource subdivision acts to reduce competition in sympatric, syntopic populations of these fishes. Data from other Wisconsin Streams, from aquarium observations, and from literature review suggest that multispecific assemblages of mutually responsive species like the ones in Roxbury Creek are common in Notropis.