In situ measurements of hydrodynamic forces imposed on Chondrus crispus Stackhouse

Among the hydrodynamic forces experienced by intertidal organisms, drag and the impingement force are thought to have the greatest effect on macroalgae. These forces are modified by biotic factors such as algal morphology, reconfiguration, and the presence of a canopy. However, much of what is known about the hydrodynamics of macroalgae has been garnered from low-velocity laboratory flume studies. Few field studies have measured drag and none have directly measured the effects of the canopy on force. To examine in situ hydrodynamic forces imposed on the turf forming macroalga Chondrus crispus, compact digital force sensors were developed that measure and record the 3-dimensional force imposed on a macroalga without disturbing the surrounding canopy. Sensors were positioned within natural Chondrus beds and the effects of the canopy, algal morphology, and sea state on in situ hydrodynamic force were examined. Additionally, the predictions of a new model for drag on flexible macroalgae were tested by simultaneously measuring force and water velocity. Digital force recordings indicated that Chondrus only experience drag; lift and impingement force were negligible in all combinations of factors. Canopies significantly reduced drag by 15-65%. Morphology and size also influenced drag, such that lower forces were imposed on small planar algae than large arborescent individuals. Further, planar algae experienced low drag in all combinations of sea and canopy state, indicating that these individuals may not be as susceptible to wave disturbance as arborescent individuals. Overall, these data indicate that the ability for Chondrus to grow large, arborescent individuals is dependent on the drag reducing properties of the canopy, while more hydrodynamically harsh habitats may be accessible to planar morphologies. Additionally, these data suggest that drag models for canopy forming macroalgae must incorporate the effects of the canopy to predict drag accurately in situ.     

EFFECT OF CURRENT VELOCITY ON THE DETACHMENT OF THALLI OF ULVA LACTUCA (CHLOROPHYTA) IN A NEW ZEALAND ESTUARY

Experiments were undertaken in a recirculating flume to determine the relationships among water velocity, thallus area, drag, and the probability of thallus breakage or detachment in the foliose green alga Ulva lactuca L. In all specimens tested to breaking point, thalli detached from their bivalve substrates as a result of stipe breakage rather than in midthallus or by holdfast detachment. There was no relationship between thallus size and drag at which detachment occurred. Rather, the probability of detachment was normally distributed about a mean drag of 0. 70 N (95% confidence limits 0.55–0.85 N). Average breaking stress of stipes was 345 kN.m^-2 (95% cl 250–485 kN.m^-2). Similar results were obtained in field experiments where the horizontal force required to detach thalli was measured directly as 0.93 N (95% cl 0.69–1.15 N). Drag coefficients of plants were not constant with water velocity but increased up to 0.4 m.s^-1, declining exponentially at velocities above this. Empirical relationships were established between coefficient of drag and Reynold's number and, hence, among drag, thallus area and water velocity. These relationships permitted estimation of mean water velocity at which plants of a given area would detach .     

Intermittent aeration affects the bioremediation potential of two red algae cultured in finfish effluent

The high cost of aeration needed to tumble culture macroalgae is a limiting factor for integration with land-based finfish culture. Toward reducing this electricity cost, we compared intermittent aeration (16 h on:8 h off) with continuous aeration (24 h on) on the productivity of two strains of Chondrus crispus (Basin Head and Charlesville) and Palmaria palmata from Atlantic Canada between May and June 2011. Algal fronds were cultured under a 16:8-h light/dark photoperiod in 50-L tanks supplied with finfish effluent (49 μmol L^?1 of ammonium and 11 μmol L^?1 of phosphate) at a mean water flow rate of 0.4 L min^?1. Nitrogen (N) influx was 1.8 gN m^?2 day^?1, and phosphorus (P) influx was 0.9 gP m^?2 day^?1, with uptake rates ranging from 0.02 to 2.4 gN m^?2 day^?1 and ?0.2 to 0.4 gP m^?2 day^?1. On average, the macroalgae culture system (algae and biofilms) removed 1.0 gN m^?2 day^?1 (51.9 %). The growth of macroalgae (pooled across treatment and strain) ranged from 0.5 to 1.6 % day^?1, which accounted for a yield of 2.2 to 5.4 g DW m^?2 day^?1. Switching off aeration at night improved the growth rate of Basin Head Chondrus by 146 % and had no effect on growth rate or nitrogen and carbon removal by P. palmata and Charlesville Chondrus. Growth and yield of Basin Head Chondrus under intermittent aeration were over two times greater than both Charlesville Chondrus treatments.     

Effects of tree characteristics and substrate condition on critical breaking moment of trees due to heavy flooding

To elucidate tree breakage conditions with different breaking mechanisms, i.e., moment by drag force, local scour, and degradation of the substrate around trees, field surveys were conducted after a flood event (September 2007 flood due to Typhoon 9) in the Tamagawa River, Japan. Trees in a river have two main breaking mechanisms during a flood event, moment by fluid force and erosion of the substrate. Moment by fluid force causes two breaking phenomena, trunk damage (bending, breakage) and overturning. Trunk bending or breakage can be expressed as a function of d ^c , where d is the trunk diameter at breast height and the power c equals 3 for trunk bending or breakage, and approximately 2 for overturning. Smaller diameter trees experienced trunk breakage, but larger trees were overturned. The range for these two breaking patterns changes with the substrate condition. If severe scouring has occurred, the threshold for overturning moment can be quite small. Tree overturning occurred mostly on the bank side of the gravel bar; however, some trees, especially Robinia pseudo acacia and Morus bombycis, were overturned if the substrate was a thin deposited soil or silt layer on gravel. The roots were anchored in the small-particle deposited layer in that case. As for the erosion of the substrate, the tree-breaking patterns can be classified into three types depending on the relationship between the nondimensionalized bed shear stress of d ₅₀ and d ₈₄, the representative grain diameters at which 50 and 84% of the volume of the material, respectively, is finer. The nondimensionalized shear stress of d ₈₄ is an important parameter for discussing the rehabilitation of the gravel bed bar. The boundary region for tree overturning can be changed by the effects of plant cover and debris attachment.     

Estimating maximal force output of cetaceans using axial locomotor muscle morphology

Cetaceans span a large range of body sizes and include species with the largest known locomotor muscles. To date, force output and thrust production have only been directly measured in the common bottlenose dolphin (Tursiops truncatus), although thrust forces have been hydrodynamically modeled for some whales. In this study, two metrics of epaxial muscle size—cross‐sectional area (CSA) and mass—were used to estimate force output for 22 species (n = 83 specimens) ranging in size from bottlenose dolphins to blue whales (Balaenoptera musculus). Relative to total body length (TL), maximum force output estimated based upon both muscle CSA (TL^{1.56 ± 0.05}) and mass (TL^{2.64 ± 0.07}) scaled at rates lower than those predicted by geometric scaling, suggesting relative force output decreases with increasing body size in cetaceans. Estimated maximal force outputs were compared to both published drag forces and to the breaking strengths of commercial fishing lines known to entangle whales. The breaking strengths of these lines are within the same order of magnitude, and in some cases, exceed the estimated maximal force output of whales. These results suggest that while powerful animals, large whales may be unable to break the extremely strong fishing line used today.     

Reproductive phenology and growth rates in two species of Gracilaria from Hawaii

Observations on wild populations of Gracilaria bursapastoris (Gmelin) Silva and G. coronopifolia J. Ag. showed significant differences in gametophyte: tetrasporophyte ratios from the expected 1: 1 ratio. As in many other perennial red algae, the proportion of tetrasporic individuals in a population of these two Gracilaria spp. dominates the combined male and female gametophytc stage. There were significantly more male than female thalli in the G. cornopifolia population whereas the gametophytes of G. bursapastoris occurred in the expected 1: 1 ratio. In addition, there are seasonal changes in the proportions of tetrasporic and gametophytic individuals within the populations. Tetrasporic thalli of G. coronopifolia evinced a biphasic seasonal pattern with high proportions in winter and summer. The tetrasporic phase of G. bursapastoris, on the other hand, showed a low proportion in winter. Maximum biomass does not necessarily correlate with maximum proportion of the tetrasporophyte generation. Seasonal patterns in the proportion of male and female gametophytes differed for each stage as well as for each species. The proportion of male thalli in G. bursapastoris and G. coronopifolia showed high peaks in winter and autumn, respectively. Cystocarpic thalli were most abundant in the former in late winter and summer and in the latter in winter and spring. In both species the female gametophytes grew significantly slower than did the male gametophytic or tetrasporophytic stages. Practical applications regarding seasonal cycles in the various reproductive stages and their differential growth rates are discussed.     

Biomechanical properties and holdfast morphology of coenocytic algae (Halimedales, Chlorophyta) in Bocas del Toro, Panama

For attached marine organisms, specific biomechanical properties may result in detachment or in tissue loss, when sufficient tensile force is applied. Algae experience such forces through water movement, which may thus act to limit size, abundance, and species composition, of populations of algae.Coenocytic construction is uncommon in the algae, but it occurs relatively more frequently in green algae found in shallow subtidal sediments associated with coral reefs, e.g., at our study site of Isla Colon, Bocas del Toro, Panama. We studied the biomechanical properties of some tropical coenocytic algae (Udotea flabellum (Ellis et Solander) Lamouroux, Penicillus capitatus Lamarck, P. pyriformis A. and E.S. Gepp, and Halimeda gracilis Harvey) anchored in sediments. We compare our results with published data on other coenocytic algae, as well as with multicellular algae. Our results show that properties of sand-dwelling coenocytes, such as mean force to dislodge (4.9-12.7 N), mean force to break (6.6-22.1 N), and mean strength (1.0-7.0 MN m^− 2), are all within the range reported for temperate, multicellular, algae. In contrast, the coenocytes differed markedly from the temperate non-coenocytes in the consequences of applied tensile force: coenocytes were removed whole, while most temperate algae attached to rocks break within the thallus. Some multicellular algae can regrow from tissue left on the substratum; three of the four coenocytic species we examined had rhizoids connecting closely adjacent (0.1-0.15 m) individuals, and these rhizoids may serve to regrow a new individual. While our experiments indicated that sufficient tensile force results in dislodgment, calculations using the experimentally determined variables led us to conclude that water velocities sufficient to dislodge individuals are unlikely to occur. Since dislodgment is usually fatal for algae, the role of the holdfast is a critical one. All of the species we investigated had similar holdfast morphology, a mass of rhizoids which entrained sand, the entire unit forming a hemispherical to cylindrical mass. Despite the consistency in holdfast form, and the initial prediction that this was an optimal form for anchoring these algae, our data suggest that this is not the case.     

Ecosystem Engineering by Plants on Wave-Exposed Intertidal Flats Is Governed by Relationships between Effect and Response Traits

In hydrodynamically stressful environments, some species—known as ecosystem engineers—are able to modify the environment for their own benefit. Little is known however, about the interaction between functional plant traits and ecosystem engineering. We studied the responses of Scirpus tabernaemontani and Scirpus maritimus to wave impact in full-scale flume experiments. Stem density and biomass were used to predict the ecosystem engineering effect of wave attenuation. Also the drag force on plants, their bending angle after wave impact and the stem biomechanical properties were quantified as both responses of stress experienced and effects on ecosystem engineering. We analyzed lignin, cellulose, and silica contents as traits likely effecting stress resistance (avoidance, tolerance). Stem density and biomass were strong predictors for wave attenuation, S. maritimus showing a higher effect than S. tabernaemontani. The drag force and drag force per wet frontal area both differed significantly between the species at shallow water depths (20 cm). At greater depths (35 cm), drag forces and bending angles were significantly higher for S. maritimus than for S. tabernaemontani. However, they do not differ in drag force per wet frontal area due to the larger plant surface of S. maritimus. Stem resistance to breaking and stem flexibility were significantly higher in S. tabernaemontani, having a higher cellulose concentration and a larger cross-section in its basal stem parts. S. maritimus had clearly more lignin and silica contents in the basal stem parts than S. tabernaemontani. We concluded that the effect of biomass seems more relevant for the engineering effect of emergent macrophytes with leaves than species morphology: S. tabernaemontani has avoiding traits with minor effects on wave attenuation; S. maritimus has tolerating traits with larger effects. This implies that ecosystem engineering effects are directly linked with traits affecting species stress resistance and responding to stress experienced.     

Scale Effects between Body Size and Limb Design in Quadrupedal Mammals

Recently the metabolic cost of swinging the limbs has been found to be much greater than previously thought, raising the possibility that limb rotational inertia influences the energetics of locomotion. Larger mammals have a lower mass-specific cost of transport than smaller mammals. The scaling of the mass-specific cost of transport is partly explained by decreasing stride frequency with increasing body size; however, it is unknown if limb rotational inertia also influences the mass-specific cost of transport. Limb length and inertial properties – limb mass, center of mass (COM) position, moment of inertia, radius of gyration, and natural frequency – were measured in 44 species of terrestrial mammals, spanning eight taxonomic orders. Limb length increases disproportionately with body mass via positive allometry (length ∝ body mass^0.40); the positive allometry of limb length may help explain the scaling of the metabolic cost of transport. When scaled against body mass, forelimb inertial properties, apart from mass, scale with positive allometry. Fore- and hindlimb mass scale according to geometric similarity (limb mass ∝ body mass^1.0), as do the remaining hindlimb inertial properties. The positive allometry of limb length is largely the result of absolute differences in limb inertial properties between mammalian subgroups. Though likely detrimental to locomotor costs in large mammals, scale effects in limb inertial properties appear to be concomitant with scale effects in sensorimotor control and locomotor ability in terrestrial mammals. Across mammals, the forelimb''s potential for angular acceleration scales according to geometric similarity, whereas the hindlimb''s potential for angular acceleration scales with positive allometry.     

Biomass variation and reproductive phenology of Gracilaria gracilis in a Patagonian natural bed (Chubut, Argentina)

The biomass variation and the reproduction of the natural Gracilaria gracilis bed in Bahía Bustamante (Patagonia, Argentina) were analyzed for 2 years, with the aim of determining the present situation of the population for an updated status overview; establishing the relevant features of the temporal variation in both biomass and reproductive states in relation to environmental factors, epiphytes and associated algae; and assessing carpospore availability for future spore-culture development. Field measurements and sampling were performed monthly between March 2006 and February 2008. In both years, G. gracilis biomass presented marked seasonal variations, with a minimum in winter and a maximum in late spring and in summer. During both years, coexistence of the three life-cycle phases was found, with dominance of tetrasporophytes. Two data sets from individuals originated from sexual reproduction (tetraspores and carpospores) and from asexual reproduction by thallus fragmentation were analyzed separately. In the fragmentation fraction, tetrasporophyte frequencies remained higher than those for gametophytes. However, in the spore-originated fraction, a generation ratio close to 0.5 was observed. Female gametophytes bearing cystocarps were always present, with a maximum in summer and autumn. Biological data were related to environmental factors by means of canonical correspondence analysis (CCA). The first year was characterized by higher biomass values of G. gracilis and Undaria pinnatifida, lower epiphytism, larger Gracilaria thalli and greater proportion of mature tetrasporophytes and gametophytes. The second year was characterized by a high proportion of Gracilaria vegetative thalli and high epiphyte density. The best time to obtain spores from cystocarpic thalli would be in summer and early autumn.     

Complanate Scytosiphon lomentaria (Lyngbye) J. Agardh (Scytosiphonales: Phaeophyta) from Southern Australia: The effects of season,temperature, and daylength on the life history

Cultures of the complanate form of Scytosiphon lomentaria (Lyngbye) J. Agardh were initiated at different times of year, maintained in several temperature daylength regimes, and grown through at least three generations. The composition of the F₁ generation varied on a seasonal basis, with a greater proportion of complanate individuals in winter and a predominance of ralfsioid and and cylindrical individuals in spring-summer.In culture, complanate thalli were only initiated from zooids derived from thalli (complanate or ralfsioid) grown in short days; ralfsioid progeny developed in long days. Some kinds of ralfsioid thalli and the cylindrical thalli developed and reproduced in long and short day conditions. The effects of temperatures between 11° and 20°C were subtle, and principally related to the rate of growth of cultured plants and not to the determination of particular stages in the life history.The relationship between the seasonal occurrence of complanate S. lomentaria, its seasonal pattern of reproduction, and the effects of daylength on the life history are discussed.     

Usnea lichen community biomass estimation on volcanic mesas, James Ross Island, Antarctica

Ground macrolichens dominated by several species of fruticose Usnea spp. with foliose Leptogium puberulum constitute an important component of the terrestrial ecosystem of James Ross Island. Long-term monitoring of lichen communities in respect to their reaction to ongoing climatic changes in this part of Antarctica became a research task for scientists in recent years. The non-destructive estimation of lichen biomass provides data necessary for the management and protection of Antarctica. We have developed and tested the methodology of non-destructive estimation of biomass of fruticose Usnea species, which predominate in the ice-free tertiary basalt outcrop areas on James Ross Island. In 38 experimental squares (non-destructive measurements), the density and height of lichen thalli were measured and digital photography with ground cover evaluation was performed. Lichen biomass was harvested from 14 experimental squares and analysed for dry mass, chlorophyll a, b content, and thalli surface area (TSA). Predictive linear models were constructed from available non-destructively measured variables with the aim to maximize predictive accuracy for the destructively measured attributes. A total of 82.3?% of variability in the TSA values was explained (87.5?% for biomass determination). Cross-validated prediction error for lichen TSA estimation was 423?cm² (11.5?% of the average TSA). In the case of lichen dry mass determination, cross-validated prediction error was 4.53?g?m^?2 (7.3?% of the average dry mass). This study proves that macrolichens in maritime Antarctica can be monitored non-destructively by simple field methods combining digital photography and measurements of lichen thalli in botanical squares.     

Feeding biomechanics and theoretical calculations of bite force in bull sharks (Carcharhinus leucas) during ontogeny

Evaluations of bite force, either measured directly or calculated theoretically, have been used to investigate the maximum feeding performance of a wide variety of vertebrates. However, bite force studies of fishes have focused primarily on small species due to the intractable nature of large apex predators. More massive muscles can generate higher forces and many of these fishes attain immense sizes; it is unclear how much of their biting performance is driven purely by dramatic ontogenetic increases in body size versus size-specific selection for enhanced feeding performance. In this study, we investigated biting performance and feeding biomechanics of immature and mature individuals from an ontogenetic series of an apex predator, the bull shark, Carcharhinus leucas (73–285 cm total length). Theoretical bite force ranged from 36 to 2128 N at the most anterior bite point, and 170 to 5914 N at the most posterior bite point over the ontogenetic series. Scaling patterns differed among the two age groups investigated; immature bull shark bite force scaled with positive allometry, whereas adult bite force scaled isometrically. When the bite force of C. leucas was compared to those of 12 other cartilaginous fishes, bull sharks presented the highest mass-specific bite force, greater than that of the white shark or the great hammerhead shark. A phylogenetic independent contrast analysis of anatomical and dietary variables as determinants of bite force in these 13 species indicated that the evolution of large adult bite forces in cartilaginous fishes is linked predominantly to the evolution of large body size. Multiple regressions based on mass-specific standardized contrasts suggest that the evolution of high bite forces in Chondrichthyes is further correlated with hypertrophication of the jaw adductors, increased leverage for anterior biting, and widening of the head. Lastly, we discuss the ecological significance of positive allometry in bite force as a possible “performance gain” early in the life history of C. leucas.     

Prey size, prey nutrition, and food handling by shrews of different body sizes

We tested some predictions relating metabolic constraints offoraging behavior and prey selection by comparing food handlingand utilization in four sympatric shrew species: Sorex minutus(mean body mass = 3.0 g), S. araneus (8.0 g), Neomys anomalus(10.0 g), and N. fodiens (14.4 g). Live fly larvae, mealwormlarvae, and aquatic arthropods were offered to shrews as smallprey (body mass <0.1 g). Live earthworms, snails, and smallfish were offered as large prey (>0.3 g). The larvae werethe high-nutrition food (>8 kJ/g), and the other prey werethe low-nutrition food (<4 kJ/g). The smallest shrew, S.minutus, utilized (ate + hoarded) <30% of offered food,and the other species utilized >48% of food. The largerthe shrew, the more prey it ate per capita. However, highlyenergetic insect larvae composed 75% of food utilized by S.minutus and only >40% of the food utilized by the other species. Thus, inverse relationships appeared between shrewbody mass and mass-specific food mass utilization and betweenshrew body mass and mass-specific food energy utilization:the largest shrew, N. fodiens, utilized the least food massand the least energy quantity per 1 g of its body mass. Also,the proportion of food hoarded by shrews decreased with increase in size of shrew. With the exception of S. araneus, the sizeof prey hoarded by the shrews was significantly larger thanthe size of prey eaten. Tiny S. minutus hoarded and ate smallerprey items than the other shrews, and large N. fodiens hoardedlarger prey than the other shrews.     

Seasonal thermoregulatory responses in mammals

This study examined the proportional seasonal winter adjustments of total and mass-specific basal power (watts and watts g^–1, respectively), thermal conductance (watts g^–1 °C^–1), non-shivering thermogenesis capacity (ratio of NST/basal power), body temperature (°C), and body mass (g) of mammals. The responses are best summarized for three different body size classes; small mammals (<100 g), intermediate-sized mammals (0.1–10 kg), and large mammals (>10 kg). The principal adjustments of the small mammals center on energy conservation, especially the Dehnel Effect, the winter reduction in body size of as much as 50%, accompanied by reductions in mass-specific basal power. On average, these reductions reduce the total basal power approximately in direct proportion to the mass reductions. Reductions in mass-specific basal power are matched by concomitant reductions in conductance to maintain the setpoint body temperature during winter. The overall thermoregulatory adjustments in small mammals serve to (a) lower overall winter power consumption, (b) maintain the setpoint body temperature, and (c) lower the lower critical limit of thermoneutrality and hence thermoregulatory costs. In intermediate-size mammals, the seasonal response is centered more on increasing thermogenic capacity by increasing basal power and NST capacity, accompanied by predictable and large reductions in conductance. The Dehnel effect is negligible. Very large mammals undergo the largest reductions in total and mass-specific basal power and conductance. However, there are too few data to resolve whether the reductions in total basal power can be attributed to the Dehnel effect, because the moderate decreases in body mass may also be caused by nutritional stress. Apart from the seasonal changes in basal power, these observations are consistent with the predictions of Heldmaiers seasonal acclimatization model.     

Temporal variations of vegetative features, sex ratios and reproductive phenology in a Dictyota dichotoma (Dictyotales, Phaeophyceae) population of Argentina

This paper addresses the phenology of a Dictyota dichotoma population from the North Patagonian coasts of Argentina. The morphology of the individuals was characterized, and analyses of the temporal variations of vegetative features, diploid and haploid life cycle generations and sex ratios are provided. Individuals, represented by growing sporophytes and gametophytes, occurred simultaneously throughout the year. Morphological variables showed temporal variation, except the width and height of medullary cells, which did not vary between seasons. All vegetative variables were significantly correlated with daylength. Besides, frond length, frond dry mass and apical and basal branching angles were significantly correlated with seawater temperatures. Vegetative thalli were less abundant than haploid and diploid thalli. Sporophytes were less abundant than male and female gametophytes. Male gametophytes dominated in May, August, October and January, and female gametophytes were more abundant in September, November, December, February and March. The formation of female gametangia showed a significant correlation with daylength, and the highest number of gametangia was registered in spring. In general, the male/female sex ratio varied between 1:2 and 1:1. Apical regions were more fertile than basal regions. Our data about frequency in the formation of reproductive structures and male/female ratios are the first recorded in the Dictyota genus and thus could not be compared with populations from other regions of the world. Significant morphological variation was observed in thalli of both life cycle generations, regarding length and dry mass, number of primary branches and branching basal angle. In general, all variables analyzed varied seasonally except cortical cell width.     

Mycotoxins and usnic acid and their distribution in lichens belonging to the genera Cetraria,Flavocetraria, and Cladonia

The content and the pattern of distribution of mycotoxins and usnic acid in thalli of lichens belonging to the genera Cladonia (four species), Cetraria (two species), and Flavocetraria (two species) have been studied using the method of immunoenzymatic analysis. Statistically significant differences have been estimated between the upper and the lower parts of the thalli. The levels of the mycotoxins in the lower, older parts of the thalli have been higher than in the upper, younger ones. The comparison of lichen specimens belonging to the same species and collected in the same location at different years did not reveal statistically significant differences in the content of mycotoxins both in the upper and the lower parts of the thalli. Statistically significant differences in the usnic acid content have been revealed only in the case of C. stellaris. In the upper part of the podetia of this species, the usnic acid content has been higher than in the lower one.     

Biogeographic Patterns of Intertidal Macroinvertebrates and their Association with Macroalgae Distribution along the Portuguese Coast

Geographical patterns in the distribution of epifaunal crustaceans (Amphipoda, Isopoda and Tanaidacea) occurring with dominant macroalgal species were investigated along the Portuguese rocky coast. Three regions, each encompassing six shores, were studied. Algal species were selected according to their geographical distribution: Mastocarpusstellatus and Chondrus crispus (north); Bifurcariabifurcata (north-centre); Plocamiumcartilagineum and Cystoseiratamariscifolia (centre-south); Corallina spp. and Codiumtomentosum (entire coast). Multivariate techniques were used to test for differences in crustacean assemblage composition between sub-regions and host algal species. A clear gradient of species substitution was observed from north to south. Differences in abundance and diversity of epifaunal crustaceans were observed between southern locations and the remaining sites. Four species were recorded for the first time in the Portuguese coast. Among the 57 taxa identified, southern distribution limits were observed for three species and northern distribution limits were observed for four species. Interestingly, the observed geographical patterns in epifaunal abundance and diversity were not related with geographical changes in the indentity of the dominant algal species.     

The effects of clipping and soil moisture on leaf and root morphology and root respiration in two temperate and two tropical grasses

Numerous studies have explored the effect of environmental conditions on a number of plant physiological and structural traits, such as photosynthetic rate, shoot versus root biomass allocation, and leaf and root morphology. In contrast, there have been a few investigations of how those conditions may influence root respiration, even though this flux can represent a major component of carbon (C) pathway in plants. In this study, we examined the response of mass-specific root respiration (μmol CO₂ g⁻¹ s⁻¹), shoot and root biomass, and leaf photosynthesis to clipping and variable soil moisture in two C₃ (Festuca idahoensis Elmer., Poa pratensis L.) and two C₄ (Andropogon greenwayi Napper, and Sporobolus kentrophyllus K. Schum.) grass species. The C₃ and C₄ grasses were collected in Yellowstone National Park, USA and the Serengeti ecosystem, Africa, respectively, where they evolved under temporally variable soil moisture conditions and were exposed to frequent, often intense grazing. We also measured the influence of clipping and soil moisture on specific leaf area (SLA), a trait associated with moisture conservation, and specific root length (SRL), a trait associated with efficiency per unit mass of soil resource uptake. Clipping did not influence any plant trait, with the exception that it reduced the root to shoot ratio (R:S) and increased SRL in P. pratensis. In contrast to the null effect of clipping on specific root respiration, reduced soil moisture lowered specific root respiration in all four species. In addition, species differed in how leaf and root structural traits responded to lower available soil moisture. P. pratensis and A. greenwayi increased SLA, by 23% and 33%, respectively, and did not alter SRL. Conversely, S. kentrophyllus increased SRL by 42% and did not alter SLA. F. idahoensis responded to lower available soil moisture by increasing both SLA and SRL by 38% and 33%, respectively. These responses were species-specific strategies that did not coincide with photosynthetic pathway (C₃/C₄) or growth form. Thus, mass-specific root respiration responded uniformly among these four grass species to clipping (no effect) and increased soil moisture stress (decline), whereas the responses of other traits (i.e., R:S ratio, SLA, SRL) to the treatments, especially moisture availability, were species-specific. Consequently, the effects of either clipping or variation in soil moisture on the C budget of these four different grasses species were driven primarily by the plasticity of R:S ratios and the structural leaf and root traits of individual species, rather than variation in the response of mass-specific root respiration.     

Local dispersal dynamics determine the occupied niche of the red-listed lichen Seirophora villosa (Ach.) Frödén in a Mediterranean Juniperus shrubland

The red-listed lichen Seirophora villosa is associated with undisturbed coastal dune systems dominated by Juniperus spp. The clustered distribution of this species suggests that propagative traits may be responsible for its conservation status. We tested whether the local distribution of an S. villosa population under undisturbed conditions is limited by habitat filtering or by low dispersal fitness. Using Strip Adaptive Cluster Sampling, we estimated the size of one of the largest undisturbed Italian populations of S. villosa. We considered the abundance of both mature and juvenile thalli in relation to geographical and environmental spaces. Multiple regression on distance matrices models were in accordance with the hypothesis that S. villosa is occupying only a small portion of its colonizable niche because of a very limited propagation ability. Apart from the co-occurrence of mature thalli, the presence of juvenile thalli was independent of pure spatial and environmental factors.