Feeding preferences of two seagrass grazing monacanthid fishes

Two seagrass grazing fishes, Meuschenia freycineti and Meuschenia trachylepis (Monacanthidae), were offered three choices of Posidonia australis seagrass blades of different epiphyte coverage and leaf age to determine whether these fishes exhibit a preference for epiphyte-covered seagrass blades. Both species removed significantly more biomass of the epiphyte-covered blades than of the two other blade types in multiple-choice tests. This clear preference for epiphyte-covered seagrass blades results in a preferred removal of older blades within the seagrass shoot of P. australis .     

Epiphytic diatoms of the inshore marine area near Davis Station

Collections of macrophytic algae from the subtidal and lower intertidal regions were processed to observe the diatom epiphytes both by light and scanning electron microscopy. For the purpose of comparison some samples of the sub-ice assemblage were also collected and processed similarly. The standing crop of epiphytes was high throughout the winter as well as the summer but the community composition varied depending upon the collection site and the morphology of the host macrophyte. The genus Cocconeis was ubiquitous achieving densities approaching 10⁵ cells cm⁻² and surpassed only by Nitzchiawith a density of twice that amount on one sample.     

Seasonal changes in the epiphyte community of natural and artificial macrophytes in Lake Memphremagog (Que. & Vt.)

Seasonal changes in the epiphyte biomass, measured both as chlorophyll a and as cell volume, and species composition were compared on Potamogeton richardsonii and on a similar plastic plant grown together in a shallow bay of Lake Memphremagog (46°06'N, 72°16W). Both substrates exhibited two periods of high biomass during the June to September growing season; one in June, when the community was dominated by loosely attached species with a strong planktonic component (up to 37%), and one in September, when the epiphytes were characterized by species tightly attached to the leaves. Although this seasonal trend was similar, the loosely and tightly attached communities were best developed on the natural and artificial plants, respectively. The diversity of the epiphytes was significantly higher on the natural than on the artificial leaves from July on. Both the diversity differences and differences in community structure appear to be the result of the summer accumulation of CaCO₃ observed only on the upper leaf surfaces of the natural plants. Consequently, P. richardsonii appears to affect epiphyte development largely by its precipitation of CaCO₃, with no evidence for either direct inhibition or stimulation of the epiphytes by the natural plants. The reduced epiphyte biomass on growing tips was no different from that on artificial plants of the same age and exposure and is attributable to an insufficient time for colonization rather than to inhibition by the macrophyte.Contribution No. 8, Lake Memphremagog Project, Limnology Research Group     

The growth patterns of some hydroids that are obligate epiphytes of seagrass leaves

The growth patterns of the hydroids Campanularia asymmetrica, Sertularia perpusilla and Algaophenia harpago on the Mediterranean seagrass Posidonia oceanica, and of Laomedea angulata on the temperate seagrass Zostera marina, were examined. The seagrass leaves grow from a basal meristem and have a short life which presents problems for these long-lived obligate epiphytes. Downward growth onto younger leaf tissue, shown by S. perpusilla and C. asymmetrica, reduces the risk of interspecific competition with other epiphytes, and places the hydroids on substrates that survive longer than older distal leaf tissue, close to short young leaves which they can colonize by stolon transfer. S. perpusilla was found only on the basal areas of leaves, possibly because of the progressive degeneration of their most apical tissue. C. asymmetrica showed no such degeneration and was found over most of the length of the leaves. The hydrorhizae of most small A. harpago and L. angulata grew both upward and downward along the leaves. Both species were most abundant on the apical halves of older leaves. This distal distribution is considered to be advantageous for these large branched hydroids which are suited for capturing planktonic prey, and to enhance their probability of colonizing neighbouring plants. Its disadvantages include the reduced probability of maintaining the hydroids on the same plant and an increased risk of being eaten by seagrass grazers.     

Composition and distribution of vascular epiphytes in a tropical semideciduous forest,Ghana

The composition and distribution of vascular epiphytes were studied in two 1‐ha plots in the KNUST Botanic garden, Ghana. One‐hectare plot each was randomly set up in secondary and cultivated forests for the identification and enumeration of trees and shrubs (≥10 cm dbh), and epiphytes. Each tree was carefully examined, noting the presence, positions and life‐forms of all epiphytes. Twenty‐nine epiphyte (29) species belonging to fourteen genera and eleven families were identified in the study. These were hosted by 48 tree species and occurred in three life‐forms: hemi‐epiphytes (45%), casual epiphytes (45%) and true epiphytes (10%). The vascular epiphyte species made up 25.7% of all the identified plant species (excluding herbs and climbers) encountered. Host species (P < 0.001), habitat (P = 0.001) and their interaction (P < 0.001) had strong effects on epiphyte composition in the forests. Moraceae was the most dominant family (44.8%), while Nephrolepis undulata J. Sm. and N. biserrata (Sw.) Scott. were the commonest species of epiphytes. In terms of vertical distribution, most epiphytes were located on the trunk, while a few occurred in the canopy.     

Drought resistance does not explain epiphytic abundance of accidental epiphytes

ABSTRACT

Background

Accidental epiphytism is common among vascular plants in forest ecosystems around the globe. A frequent observation in surveys of accidental epiphytes is the occurrence of few species with high epiphytic abundance, while most co-occurring terrestrial species are rarely found as epiphytes.     

Production of <Emphasis Type="Italic">Cocconeis neothumensis</Emphasis> (Bacillariophyceae) biomass in batch cultures and bioreactors for biotechnological applications: light and nutrient requirements

Cocconeis neothumensis, a benthic diatom living as epiphyte on Posidonia oceanica leaves, was hypothesised to synthesize secondary metabolites inducing apoptosis in the androgenic gland of the protandric shrimp Hippolyte inermis. The optimization of C. neothumensis cultures is a primary aim in order to identify and characterise the active compounds produced by this diatom. Light intensity and concentration of nutrients, such as silicates and selenium, are of major importance in determining the growth rate of diatoms and the maximum produced biomass. Thus, we evaluated the growth performances of C. neothumensis cultures at different light intensities, corresponding to those recorded in Posidonia oceanica meadows in April, when the induction of sexual reversal in Hippolyte inermis occurs; the growth performances were also determined in relation to different selenium and silicate availability in the culture medium and the possible interactions between these two micronutrients were evaluated. Two methods of cultivations were compared: batch cultures in Petri dishes and cultures in a bioreactor with a continuous medium flow in the system. C. neothumensis showed a faster growth at low light intensities, although with a good acclimation capacity in the range from 60 to 140 μmol photons m⁻² s⁻¹. The presence of selenium in the medium improved both the exponential growth rate and the maximum cell density. The same results were evidenced for a silicate concentration double that in Guillard f/2 medium. On the other hand, a simultaneous increase of silicate concentration and the presence of selenium led to a loss of the positive effects detected with single nutrients. This result suggests either a possible antagonism in selenium and silicate uptake or a negative interaction between these two micronutrients in Cocconeis. The yields of the two tested cultivation methods calculated in terms of diethyl ether extract dry weight per unit of substrate area were highest for the bioreactor.     

Tank bromeliad transplants as an enrichment strategy in southern Costa Rica

Epiphytes represent up to 50% of all vascular plant species in neotropical forests but they are among the slowest plants to recolonize regenerating ecosystems. This discrepancy underlines the need for restoration ecologists to learn how to assist the colonization of organisms in this key functional group. Transplanting tank bromeliads (i.e. bromeliads featuring overlapping leaves that form a water impounding rosette) could be a good approach in the neotropics, where abundant, fallen bromeliads can be sustainably collected from the forest floor. Moreover, tank bromeliads could accelerate restoration processes by providing relatively stable microenvironments for invertebrates, thus helping them resist severe drought and high temperatures, such as predicted in light of many climate change models. We transplanted 60 individuals of the tank bromeliad Werauhia gladioliflora onto trunks and branches of comparable size and orientation on three host tree species. The study took place in three long‐term restoration plantations located in a tropical premontane rainforest zone in southern Costa Rica. Transplant survivorship after 9 months varied among sites, from 65 to 95%. Transplants hosted twice as many arthropod orders as untreated control branches, and they buffered microclimates during the driest (+1.7 to 19.7% relative humidity) and warmest (?0.5 to 5.0°C) times of the day. Our results suggest that bromeliad transplantation is a cost‐effective (circa Epiphytes represent up to 50% of all vascular plant species in neotropical forests but they are among the slowest plants to recolonize regenerating ecosystems. This discrepancy underlines the need for restoration ecologists to learn how to assist the colonization of organisms in this key functional group. Transplanting tank bromeliads (i.e. bromeliads featuring overlapping leaves that form a water impounding rosette) could be a good approach in the neotropics, where abundant, fallen bromeliads can be sustainably collected from the forest floor. Moreover, tank bromeliads could accelerate restoration processes by providing relatively stable microenvironments for invertebrates, thus helping them resist severe drought and high temperatures, such as predicted in light of many climate change models. We transplanted 60 individuals of the tank bromeliad Werauhia gladioliflora onto trunks and branches of comparable size and orientation on three host tree species. The study took place in three long‐term restoration plantations located in a tropical premontane rainforest zone in southern Costa Rica. Transplant survivorship after 9 months varied among sites, from 65 to 95%. Transplants hosted twice as many arthropod orders as untreated control branches, and they buffered microclimates during the driest (+1.7 to 19.7% relative humidity) and warmest (?0.5 to 5.0°C) times of the day. Our results suggest that bromeliad transplantation is a cost‐effective (circa $0.5 USD/successful transplant) strategy to assist the recovery of epiphyte diversity in forest restoration sites with minimal impact on source populations. Longer‐term studies are needed to test this strategy for other epiphyte families or for mixed‐taxa assemblages found on fallen branches.     

Differential expression of genes of Pseudomonas syringae on leaves and in culture evaluated with random genomic lux fusions

Differential expression of genes of Pseudomonas syringae strain B728a on plants and in culture was assessed by measuring light production by a large collection of mutant strains containing random genomic insertions of a promoterless lux operon. Reporter gene fusions were made using Tn4431 containing lux CDABE from Vibrio fisheri. Light production reproducibly increased seven-fold when n-decanal was added to cells harvested from plant surfaces, to over 800-fold when added to cells cultured on a solidified culture medium, thus increasing the sensitivity of this reporter gene system. One of the 173 mutants tested exhibited significantly higher light production on plants than on solidified culture media compared to other mutants, while one lux fusion-containing strain produced significantly more light on culture media than on plants relative to the other mutants. The plant-inducible genes identified were not required for pathogenicity of this strain. Approximately 2% of the genes of P. syringae are apparently transcribed more actively in cells growing epiphytically on plants than in common culture media indicating that bacterial cells on plants may have substantially different behaviours than that of cultured cells.     

The Seasonal Succession of Epiphytic Communities within an Equisetum fluviatile L. Stand in Lake Pääjärvi,Southern Finland

The seasonal succession of epiphytic communities on Equisetum fluviatile was controlled both directly and indirectly by the macrophyte. Decaying macrophytic material supported rich algal growth and biomass accumulation in spring and early summer. Emergence of the macrophytes severely reduced underwater light availability, and the epiphytic algal biomass declined rapidly as a result of both lower photosynthetic activity of the epiphytic algae, and more intensive grazing by invertebrate herbivores. Epiphytic N: P ratios were lower than those in the water around suggesting that either the water was not the only source of phosphorus for the epiphytic algae or the algae took phosphorus up selectively from the water. Low epiphytic C: N ratios suggested a high potential nutritional value for herbivores.     

Assessing the effects of forest management on epiphytic lichens in coppiced forests using different indicators

Abstract

Epiphytic lichens are one of the taxonomic groups most sensitive to forest management. Nevertheless, they have not yet been exhaustively included in the assessment of Sustainable Forest Management. This work aimed at evaluating the effects of forest management on epiphytic lichens in coppiced forests, exploring the spatial patterns of diversity and the composition of communities. Moreover, the goal was to compare the performance of four potential indicators for monitoring the effects of forest management on epiphytic lichens: total lichen diversity, species associated with intensive management, species associated with aged coppiced woodlands and Indicator Species Ratio (ISR). In humid Mediterranean Liguria, 50 sampling units were chosen in Castanea sativa and deciduous Quercus spp. forests subjected to different forest management practices: intensively managed coppice and aged coppice/high forest. The effect of forest management was evident in terms of species composition, since it was possible to find significantly associated species for each of the two management types. At each sampling site, the four indicators were calculated using Indicator Value Analysis and compared through correspondence analysis. The ISR was shown to be a more effective indicator, being independent of floristic composition and the occurrence of rare species.     

Gas Exchange and Water Vapor Uptake in the Atmospheric CAM Bromeliad Tillandsia recurvata L.: The Influence of Trichomes

Tillandsia recurvata is an epiphytic atmospheric CAM bromeliad without functional roots. As an adaptation to very exposed and often dry habitats T. recurvata takes up liquid water via trichomes, which cover the plant. Gas exchange measurements also show an absorption of water vapor at the trichomes simultaneously with an increase in relative humidity at the beginning of the dark period. A similar amount of water is lost again when the relative humidity is decreased. Experiments with heat-killed plants show that this was due exclusively to physical equilibration of the hygroscopic walls of the dead trichome cells. This effect would have prevented an accurate calculation of transpiration and conductance, but can be accounted for by substracting water vapor exchange of heat-killed plants from that of the living tissue which yields the true water vapor conductance of the tissue. This is found to be rather low (3.37 mmol H₂O kg^?1 s^?1) in comparison to other plants, and the proportion of total conductance due to trichomes is relatively high (0.53 mmol H₂O kg^?1 s^?1). This explains the slow rates of photosynthesis and growth found in this plant.     

Effect of epiphytes on the extent of necrotic injuries of resistant and susceptible poplar clones infected with Dothichiza populea.

Poplar cuttings of a resistant clone, Populus ‘Grandis’, and susceptible clones, Populus nigra ‘Italica’ and Populus ‘Robusta’, were infected with the pathogenic fungus Dothichiza populea alone, or with the pathogen and one of five strains of epiphytes antagonistic towards it (in vitro), isolated from poplar bark. The extent of injury was examined for 28 days after infection by determining the length of necrotic patches and their area as expressed in per cent of the total area of a cutting or the area of necrotic injuries caused by the pathogen alone.

All the poplar cuttings of both the resistant and susceptible clones became diseased when infected with the pathogen alone. Surprisingly enough, however, the least affected clone was the susceptible P. ‘Robusta’, in which necrotic injuries covered 28% of the total area, as against 40% and 70% in the resistant P. ‘Grandis’ and the susceptible P. nigra ‘Italica’, respectively.

When the cuttings were infected simultaneously with Dothichiza populea and its antagonistic epiphytes, the diseased area in the resistant clone diminished by as much as two-thirds, and in the susceptible P. nigra ‘Italica’, by one-third in comparison with the area affected by the pathogen alone. In turn, in the susceptible P. ‘Robusta’ the introduction of three out of five epiphytes stimulated the growth of the pathogenic fungus producing on average a double increase in the necrotic area. The differences in the response of the pathogen to the presence of epiphytes recorded in the susceptible clones indicate a marked influence of the plant on the nature of interactions between its epiphytic microflora and the pathogen.     

Photosynthetic Capacity Increases with Plant Size

The photosynthetic capacity of mature leaves of the epiphytic orchid, Dimerandra emarginata, was studied in plants of different size. There was a linear increase of both area-based and dry weight-based rates of O₂-evolution with size by more than 100% from the smallest (1 cm tall) to the largest (50 cm tall) individual. Similar size-related changes were observed in the leaf nitrogen content but not in the chlorophyll content. The results are discussed in the context of the optimal partitioning theory.     

Nitrogen-fixation in the littoral benthos of an oligotrophic lake

Blue-green algae are common in the benthos of Mirror Lake, New Hampshire (U. S. A.) — on macrophytes and on the lake bottom-and are probably responsible for the variable, sometimes high rates of N-fixation that detected by a series of acetylene-reduction assays during September and October.     

Animal associations with the dominant species of shallow water macrophytes along the coastline of the Vestfold Hills,Antarctica

Benthic grab samples, taken through core holes in sea-ice 1983, returned eight species of marine macrophytes which had associated fauna on at least one sample. A total of 24 animal taxa were found on these eight macrophytes. Phyllophora antarctica had a significantly greater biomass of attached fauna per unit of macrophyte biomass than any of the other seven species. It also had the greatest variety of epiphytic fauna (21 taxa). Phyllophora antarctica was the only macrophyte collected from comparatively protected Ellis Fjord, apart from filamentous algae, including Cladophora subsimplex and Geminocarpus austrogeorgiae, which were found in the most landward basin. It therefore played an important role in the ecology of the fjord. Palmaria decipiens was commonly collected at more exposed coastal sites and was dominant in Long Fjord, characterized here as intermediate in terms of water movement. Sixteen animal taxa were collected from this macrophyte with the greatest numbers being found in July and August. Only four animal taxa were collected from Iridaea cordata. The other five macrophyte species from which epiphytic animals were collected (Porphyra endiviifolium, Plocamium cartilagineum, Desmarestia menziesii, Himantothallus grandifolius and Cladophora subsimplex had animals associated with them on less than half the occasions when they were found.     

The role of flow velocity combined with habitat complexity as a top–down regulator in seagrass meadows

Large‐scale losses of seagrass areas have been associated with eutrophication events, which have led to an overproduction of photosynthetic organisms including epiphytes. Grazers that feed on epiphytes can exert a significant top–down control in the system, but the effects of physical factors on grazing activity and feeding behaviour have been rarely examined. We addressed the combination of hydrodynamic regime and seagrass shoot density can alter the feeding and foraging behaviours of mesograzers. A full factorial experiment, with flow velocity (high, medium and low) and shoot density (high versus low) as main factors, was conducted in a racetrack flume using artificial seagrass plots. The results showed that when high flow velocity conditions were combined with low shoot density, consumption of epiphytes by mesograzers was strongly reduced. In contrast, when flow velocity was low or shoot density was high, mesograzers exhibited high feeding rates and vigorous swimming behaviour. These results clearly indicate that hydrodynamic stress reduces the time that mesograzers can spend feeding, since it inhibits their swimming behaviour, and thus indirectly affecting to the density of epiphytes. Therefore, the triggering of trophic cascade effects in seagrass communities under these experimental conditions depended on the interrelationship and feedbacks among shoot density, abiotic (flow velocity) and biotic (epiphytes and mesograzers) compartments, with flow velocity exerting a top–down control on seagrass ecosystems.     

Protozoan communities in chalk streams

This study assessed the individual effects of three mayflies (Paraleptophlebia sp., Ephemerella subvaria McDunnough and Epeorus sp.) and one caddisfly (Psilotreta sp.) on periphyton communities associated with clay tiles and leaves. Algal densities were estimated for leaf discs and tiles from experimental chambers (with individual grazers) and control chambers (i.e., no grazers). Scanning electron micrographs (SEM) of leaf discs and tiles also were taken for all mayfly grazing experiments. Densities of algae on leaf discs were two to five times lower than on tiles. Mouthpart morphology influenced how different insects grazed the periphyton community. Paraleptophlebia had typical collector-gatherer mouthparts and had no effect on diatom densities associated with leaves whereas diatom densities on grazed tiles were higher than densities on tiles from control chambers. Epeorus had brusher mouthparts and had little impact on diatom densities regardless of substratum type. The other two grazers had the blade-like mandibles of a scraper. Psilotreta did not reduce the numerical abundance of diatoms on either substratum, but did alter community structure by significantly reducing densities of stalked Gomphonema olivaceum and large species of Navicula and Nitzschia; densities of smaller diatoms (Achnanthes spp) increased. However, E. subvaria reduced densities of most algal species regardless of size on both substrata and also significantly altered community structure. SEMs of substrata grazed by mayflies showed reductions in fungal hyphae on all grazed leaf discs, decreases in filamentous algal forms on grazed tiles, and greatly shortened stalks of G. olivaceum (Paraleptophlebia only). Thus, periphyton communities are different on leaves versus tiles and grazers with different mouthpart morphologies have varying effects on both algal and heterotrophic microbial community structure.