1,721,019 research outputs found
Interplay of encrusting coralline algae and sea urchins in maintaining alternative habitats
No full textIn proximity of shelters, grazing by sea urchins plays a fundamental role in establishing and maintaining areas dominated by encrusting corallines. Much attention has been given to the effects of urchins on algal assemblages in shallow subtidal reefs, but few studies attempted to clarify the role played by encrusting coralline algae in this system. It has been shown that encrusting corallines are able to reduce settlement of potential competitors, suggesting that they do not rely on grazing by herbivores to prevent swamping by erect algal species. In shallow subtidal reefs of the Mediterranean Sea, the sea urchins Paracentrotus lividus and Arbacia lixula are the main herbivores, whose grazing commonly leads to a mosaic of areas dominated alternatively by encrusting corallines and turf-forming algae. This study aims to separate the effects of urchins and encrusting corallines on the re-colonisation of encrusting coralline-dominated patches (barren habitat) by surrounding erect algal species (turf-forming algae). Different hypotheses were tested by means of multivariate and univariate analyses. The multivariate hypothesis was that the algal assemblage developing when encrusting corallines and urchins are simultaneously removed would be more similar to that establishing in stands of turf-forming algae, than that developing when none or only 1 of the 2 factors is manipulated. The univariate hypotheses tested were: (1) that there is a negative effect of sea urchins and encrusting corallines on the re-colonisation of barren areas by surrounding turf-forming algal species and (2) that the effects of encrusting corallines are weaker than those of urchins, but that they operate in the same direction. These hypotheses were tested by means of an orthogonal manipulation of urchins and encrusting corallines. At each of 3 study sites, 2 replicate barren patches were assigned to each of these treatments: (1) +corallines+urchins; (2) +corallines-urchins; (3) -corallines+urchins; (4) -corallines-urchins. The results suggest that the occurrence of areas dominated by encrusting corallines on shallow subtidal reefs in the northwest Mediterranean is not simply the result of grazing by sea urchins on turf-forming species. The removal of encrusting corallines also affected the abundance of dominant algal species and determined the development of an algal assemblage resembling those occurring within stands of algal turfs. The effects of the removal of urchins on turf-forming species were generally positive, while those of encrusting corallines varied from negative (Padina pavonica) to positive (Acetabularia acetabulum and filamentous algae). Therefore, the role played by encrusting corallines in maintaining alternative habitats on shallow subtidal reefs should be taken into account, thus avoiding the overestimation of the effects of grazing by sea urchins
FIGURE 2 in Apseudes talpa revisited (Crustacea; Tanaidacea). The impact on apseudidaen systematics
No full textFIGURE 2. Apseudes talpa, Portugal (reg # MMF41156-3). A, non-ovigerous female/juvenile, B–E, ovigerous simultaneous hermaphrodite. A, lateral view, Scale bar = 1 mm; B, lateral shield of pleonites, dorsal view; C, antennae; D, pleopod; E, uropod. Scale bars = 1 mm.Published as part of Larsen, Kim, Bertocci, Iacopo & Froufe, Elsa, 2011, Apseudes talpa revisited (Crustacea; Tanaidacea). The impact on apseudidaen systematics, pp. 19-30 in Zootaxa 2886 on page 24, DOI: 10.5281/zenodo.27760
Integrating spatial and temporal patterns of free‐living nematodes with physical and chemical environmental traits: implications for coastal ecological monitoring
No full textRelating biological patterns to the physical environment is increasingly explored in current period of global biodiversity crisis and attempts to identify ecological status. Free-living marine nematodes (FMN) were proposed as ecological indicators, although often under approaches based on developing synthetic indexes of environmental quality, contextually neglecting the crucial issue of their spatial and temporal variability in abundance and diversity, and its relationship with environmental drivers. This study, carried out on the north-eastern coast of India as a region subject to various anthropogenic activities, assessed the patterns of FMN structure, richness, equitability, trophic guilds, life strategy and morphological traits at three sites, three times over 1 year, two beach levels and three sediment layers upto 15 cm deep. Nematode patterns were then related to the amount of sand, silt and clay, organic carbon, and salinity. Each FMN characteristic was largely variable in time and space, being organic carbon and salinity the environmental variables most correlated to such patterns. Monitoring designs suited to capture such variability are recommended to improve the use of FMN as bioindicators. Just relying on unidirectional data to define environmental status is questioned, while it is proposed to consider the Effect of Positional Constraints when assessing ecosystem health
Effects of enhanced loads of nutrients on epiphytes on leaves and rhizomes of Posidonia oceanica
No full textThe increase of anthropogenic activities has severely altered both terrestrial and aquatic systems. Urbanisation, excessive use of agricultural fertilisers, organic runoff and climate change have caused an increase of nutrients in coastal waters, altering the diversity and food-web structure of benthic assemblages. The aims of the present paper were to text if an experimentally increased availability of nutrients, primarily nitrogen and phosphorous, in an oligotrophic basin, would affect epiphytic assemblages on leaves and rhizomes of P. oceanica and whether this could change rates of consumption of the plant by herbivores. In particular, we tested the hypothesis i) that changes to species composition and abundance of epiphytic assemblages generated by nutrients enrichment would vary between leaves and rhizomes and that ii) alterations to epiphytic assemblages on leaves might, in turn, modify feeding rates of herbivorous fish. After two years, the structure of both leaf and rhizome epiphytic assemblages responded to changes in nutrient concentrations before the occurrence of drastic alterations to the host plant, but only the former showed significant changes in terms of species composition. Moreover, a larger intensity of grazing on P. oceanica leaves was documented in experimentally enriched areas than in controls. The present findings and conclusions are applicable to other systems where patterns of biodiversity depend on changes in the availability of nutrients due to natural or anthropogenic events, likely interacting with biological processes, such as competition and grazing
Competitive ability of macroalgal canopies overwhelms the effects of variable regimes of disturbance
No full textPredicting the response of natural systems to climate change is key for maintaining their functioning and the services they deliver to humans. Along with variations in the mean intensity of environmental and meteorological events, climate change is expected to generate a substantial increase in their temporal variance, the ecological impact of which has been largely
overlooked. In the marine environment, these changes may result in altered natural regimes of disturbance that, interacting with the current decline of species playing key ecological roles, could influence the structure of natural communities. The aim of this study was to experimentally investigate the compounded effects of changes in the mean intensity and temporal variance of storms and loss of canopy-forming macroalgae on the abundance and diversity of benthic assemblages in temperate rockpools. Our results showed that competitive effects of Cystoseira spp. on the cover and diversity of assemblages were more important than changes in intensity or temporal
variance of events of disturbance per se. As a consequence, predicted changes in the regime of disturbance due to storms do not have the potential to counteract community shifts towards the dominance by algal turfs, once Cystoseira spp. are lost
Apseudes Leach 1814
No full textGenus Apseudes Leach, 1814 Diagnosis. Simultaneous hermaphroditism present. Body more or less dorsoventrally flattened. Carapace about as long as wide, without lateral spines anterior to the respiratory chamber but with anterolateral plumose setae. Rostrum ventrally curved and pointed. Ocular lobes conspicuous, separated from carapace by a groove, visual elements usually present. Pereonite 1 without lateral projections; pereonite 2 with or without lateral prolongation; pereonites 3–6 with lateral prolongation in anterior half (prolongations usually pointed but not necessarily acute). Pleon with five pleonites. Pleotelson as long as width of the last pereonite, with many circumplumose setae. Antennule biramous, with a row of small denticles on inner margin of the first article; inner flagellum with at least four articles (excluding the common article). Antenna peduncle article 3 much shorter than 4 and 5. Mandible with three-articulate palp, mandibular body with prominent denticulate ridge running on the outer side, from the palp insertion to beyond the molar insertion. Maxillule with bi-articulate palp. Maxilliped with one to three spiniform seta on the outer corner of the second palp article; endite without leaf-shaped seta. Cheliped and pereopod 1 with exopodite. Cheliped basis with strong ventromedial spiniform seta or spine. Pereopod 1 larger than the following pereopods, merus with dorsodistal spiniform seta. Pereopod 4 dactylus slightly reduced, with ventral spines; propodus with distal, transverse, row of short, serrated, spiniform setae. Pereopods 5–6 with row of short spiniform setae on the ventral or ventrodistal margin. Pereopod 6 with plumose setae on both margins of basis, ischium, merus, and carpus. Pleopods biramous, well developed. Uropod biramous, exopodite at least with four articles and often with pseudo-articulations. Dimorphism. Large specimens either male (non-ovigerous) or simultaneous hermaphrodites (ovigerous). Pereonite 6 with genital cone. Cheliped carpus somewhat shorter and stouter and with two ventral spines; fixed finger with inner process. Ovigerous specimen with five pairs of oostegites, on cheliped and pereopods 1–4. Smaller specimens non-ovigerous, either females or juveniles. Pereonite 6 without genital cone. Chelipeds with female characteristics (carpus somewhat longer and thinner and without spiniform projections; slightly longer propodus, no process on fixed finger). Remarks. The main modifications to the diagnosis of Apseudes as constructed by Guţu (2006: 54) are: the presence of the denticulate ridge running on the side of the palp, down past the molar on the mandibular body; the presence of simultaneous hermaphrodites; the reduction of the pereopod 4 dactylus and the propodus with transverse row of modified setae.Published as part of Larsen, Kim, Bertocci, Iacopo & Froufe, Elsa, 2011, Apseudes talpa revisited (Crustacea; Tanaidacea). The impact on apseudidaen systematics, pp. 19-30 in Zootaxa 2886 on page 20, DOI: 10.5281/zenodo.27760
Modularity buffers the spread of spatial perturbations in macroalgal networks
No full textTheory predicts that spatial modular networks contain the propagation of local disturbances, but field experimental tests of this hypothesis are lacking. We combined a field experiment with a metacommunity model to assess the role of modularity in buffering the spatial spread of algal turfs in three replicated canopy-dominated macroalgal networks. Experimental networks included three modules where plots with intact canopy cover (nodes) were connected through canopy-thinned corridors. The local perturbation consisted of removal of the canopy and understory species from four nodes within a single module to enable the establishment of algal turfs, which could then spread vegetatively to other untouched nodes through the canopy-thinned links. Results show that algal turfs invade mainly untouched nodes in the perturbed module, in agreement with the hypothesis that modularity can effectively constrain the spread of a spatial perturbation. The metacommunity model supports the empirical findings, illustrating greater resistance to perturbations of modular than random macroalgal canopy networks and making alternative explanations for the observed results unlikely. Evidence that the buffering effect of modularity can operate in natural environmental conditions has important implications for designing more robust networks of protected areas and less-fragile human-dominated fragmented landscapes
Subtle differences in growth rate drive contrasting responses of ephemeral primary producers to recurrent disturbances
Full text linkAlthough the importance of time after disturbance is well established in the ecological literature, studies examining how differences in growth rate affect species recovery and persistence in relation to the interval between recurrent perturbations are rare. We examined the response of two ephemeral primary producers inhabiting high-shore rock pools, epilithic microphytobenthos (EMPB), and green filamentous algae, to disturbance regimes varying for the time interval between consecutive events. Informed from an empirically parametrized growth model's outcomes, we tested the hypothesis that EMPB would be able to recover from more frequent disturbance compared with filamentous algae in a field experiment involving three physical disturbance patterns differing for the clustering degree: high, moderate, and low (20, 40, and 80 days between disturbances). We predicted that: high clustering would prevent the recovery of both taxa; moderate clustering would prevent the recovery of the slower growing taxon only (filamentous algae); both taxa would recover under low clustering. Results showed that EMPB persisted independently of the clustering degree, whereas filamentous algae did not withstand any disturbance regime. Dramatically different effects of disturbance on organisms with subtle differences in their growth rate indicate that even stronger responses may be expected from taxa with more markedly contrasting life histories
The seaweed Caulerpa racemosa on Mediterranean rocky reefs: from passenger to driver of ecological change
Full text linkDisentangling the ecological effects of biological invasions from those of other human disturbances is crucial to understanding the mechanisms underlying ongoing biotic homogenization. We evaluated whether the exotic seaweed, Caulerpa racemosa, is the primary cause of degradation (i.e., responsible for the loss of canopy-formers and dominance by algal turfs) on Mediterranean rocky reefs, by experimentally removing the invader alone or the entire invaded assemblage. In addition, we assessed the effects of enhanced sedimentation on the survival and recovery of canopy-forming macroalgae at a relatively pristine location and how their loss affects the ability of C. racemosa to conquer space. C. racemosa did not invade dense canopy stands or influence their recovery in cleared plots. Competition with C. racemosa could not explain the rarity of canopy-forming species at degraded sites. Removing the assemblages invaded by C. racemosa and preventing reinvasion did not trigger the transition from algal turfs to canopies, but it enhanced the cover of morphologically complex erect macroalgae under some circumstances. Once established, C. racemosa, enhancing sediment accumulation, favors algal turfs over erect algal forms and enables them to monopolize space. Our results show that introduced species that rely on disturbance to establish can subsequently become the main drivers of ecological change
Reddened seascapes: experimentally induced shifts in 1/f spectra of spatial variability in rocky intertidal assemblages
No full textEcological tests of 1/f-noise models have advanced our understanding of how environmental fluctuations affect population abundance and species distributions. Most empirical studies have been conducted under controlled laboratory conditions and have focused on individual drivers. We present the results of a four-year field experiment in which canopy presence/absence and the availability of primary space were manipulated as red-noise and white-noise spatial processes, respectively, to evaluate their separate and compounded effects on algal turf distribution in a rocky intertidal community. Algal turfs closely tracked spatial variation in canopy distribution, displaying a reddened spectrum of spatial variation. Surprisingly, white-noise clearings also induced a red-shift in turf distribution, a pattern that was related to a nonlinear relation between gap size and turf colonization. The two disturbances interacted antagonistically, dampening the red-shift of turf distribution. Our results provide evidence of experimentally induced shifts in the spectrum of a spatial variable under natural environmental conditions
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