1,721,026 research outputs found
Larval microhabitat associations of the non-native gastropod Crepidula fornicata and effects on recruitment success in the intertidal zone
No full textHabitat-specific distributions of marine benthic invertebrates can be caused by several processes acting prior to, during or after settlement, including differential settlement and varying levels ofmortality between habitat types following adaptation of the benthicmode. The non-native gastropod Crepidula fornicata is known for its gregarious settlement patterns, yet associations with other shellfish species are also common. In the present study, a series of no-choice and choice laboratory assays were undertaken in which larvae were offered different settlement substrata, separately and simultaneously, to investigate whether differential settlement of C. fornicata larvae occurs in favour of specific microhabitat types. A field experiment was also conducted to test if recruitment success in the intertidal differed between microhabitat types, by comparing densitiesof young (b2 weeks) andolder (b8 weeks) settlers. The laboratory studies indicated that settlement occurs in larger numbers in association with certain habitats. However, settlement in association with specific microhabitat types was not observed in the intertidal. Instead, the distribution of C. fornicata recruits is established after settlement, as the distribution of older recruits, but not younger ones, differed between microhabitat types. Our findings show that the availability of certain complex structures in the intertidal zone is highly important in determining survival success of C. fornicata, due to varying levels of post-settlement mortality
The importance of larval supply, larval habitat selection and post-settlement mortality in determining intertidal adult abundance of the invasive gastropod Crepidula fornicata
No full textUnderstanding the processes that drive the recruitment of invasive non-native species is of critical importance in evaluating their potential to colonise previously unoccupied habitats. The slipper limpet Crepidula fornicata has spread rapidly into most European waters since its first introduction from the North West Atlantic in the late 19th century. Its invasion success is thought to have been aided by its long larval phase and its tolerance towards a wide range of environmental conditions. The Milford Haven Waterway in Wales, U.K. supports a population with highly variable densities in the intertidal as well as the subtidal zone. In the present study, we tested a series of existing models to investigate the roles of larval supply, larval habitat selection and post-settlement mortality in determining the final distribution of C. fornicata in the intertidal zone of the Milford Haven Waterway. During the main reproductive season of 2011, data on total settlement rates and recruitment were collected by deploying slate panels for varying durations in the low intertidal zone, and data on larval abundances were obtained by taking frequent plankton samples at two sites with contrasting adult densities: Beggars Reach (~ 15 ± 13 ind m? 2) and Pennar (~ 343 ± 360 ind m? 2). Total larval densities were much higher at Pennar, but densities of late-stage larvae (i.e. larval supply) were similar at both sites, indicating that local hydrodynamics may have resulted in the spatial homogenisation of supply of late-stage, metamorphically competent larvae, despite the higher larval production at the high adult abundance site. Settlement rates also did not differ between sites. Seasonal recruitment was overall low, indicating that post-settlement mortality, likely as a consequence of exposure to intertidal conditions, is very high. The lack of a relationship between adult abundance and settlement rates indicates that the final distribution of C. fornicata in the intertidal may be a result of differential post-settlement mortality. Understanding recruitment patterns in non-native species is essential for developing management strategies for potentially harmful invaders such as C. fornicata
The influence of mussel-modified habitat on Fucus serratus L. a rocky intertidal canopy-forming macroalga
Full text linkThe influence of habitat modification by Mytilus edulis L. on the settlement and development of Fucus serratus populations was investigated on rocky shores of the Isle of Anglesey, North Wales. Settlement of fucoids was higher inside mussel habitat than outside on one of two shores studied. The effect of microhabitat on survival of fucoid germlings was examined by transplanting the germlings into and outside mussel habitats, each with and without the exclusion of grazers. Observation showed that periwinkles and top shells were abundant in mussel habitat, while limpets dominated bare rock. Exclusion of grazers greatly enhanced the survival of fucoid germlings in both habitats, indicating that while mussel habitat supports a different grazer assemblage to bare rock, both assemblages are important in limiting fucoid recruitment. The risk of dislodgement was assessed and compared between fucoids growing on mussel shells and bare rock. In situ pull-tests showed that less force was required to detach large fertile thalli growing on mussel shells than those growing on the rock. Adhesion was generally broken between the mussel and the rock rather than between the holdfast and the mussel. These observations indicate that mussels provide an unstable substrate for mature fucoids. Overall results suggest that a negative effect of mussel-modified habitat on fucoids is profound in adults; but the effect is context-dependent in juveniles and can be positive at settlement. Results from a survey on population structure of fucoids across two shores showed that there were greater numbers of large fertile fucoids growing directly attached to rock than on mussel shells, while there was no difference for juvenile fucoids confirming the experimental results. Moreover thalli larger than 60 cm were found only on the rock but not on shells. This finding suggests that a mussel dominated habitat may have a significant impact on reproductive output in fucoid populations
Interaction between a fucoid canopy and limpet grazing in structuring a low shore intertidal community
No full textThe relative roles of a macroalgal canopy, Fucus serratus L., and a grazer, Patella vulgata L., in structuring a low shore community of a sheltered, rocky intertidal site were examined using a factorial experimental design. Canopy removal and grazer exclusion treatments were used to determine the effects of both factors on the understorey community. Re-establishment of the canopy was studied in relation to grazing pressure and substrate type in order to determine how this macroalga maintains its spatial and temporal dominance on the low shore. In addition, the size of canopy clearances were varied to determine the effect of gap size on community structure. Removal of the F. serratus canopy alone resulted in little change to the understorey community. Few understorey species were adversely affected by exposure to increased light levels and the grazing pressure of limpets was sufficient to prevent large scale recruitment of algae. Removal of limpets alone resulted in little change except for a greatly enhanced recruitment of F. serratus juveniles, indicating that grazing pressure rather than the canopy was inhibiting recruitment of the canopy species. Large changes in community structure only occurred following removal of both the canopy and grazers together since either the canopy or limpet grazing alone was sufficient to prevent large scale recruitment of algae. Limpet grazing did not prevent the re-establishment of a F. serratus canopy, although recovery was delayed in comparison to plots where limpets were removed. The size of gaps in the canopy had no discernible effect on the species composition or rate of succession in experimental treatments
Population resistance to climate change: modelling the effects of low recruitment in open populations
No full textIsolated populations or those at the edge of their distribution are usually more sensitive to changes in the environment, such as climate change. For the barnacle Semibalanus balanoides (L.), one possible effect of climate change is that unpredictable spring weather could lead to the mismatching of larval release with spring phytoplankton bloom, hence reducing the recruitment. In this paper, model simulations of a variable open population with space limited recruitment were used to investigate the effects of low and zero recruitment on population abundance in S. balanoides. Data for model parameters was taken from an isolated population in the Isle of Man, British Isles. Model simulations with observed frequencies of years with low recruitment showed only small changes in population dynamics. Increased frequencies of low recruitment had large effects on the variation in population growth rate and free space and on population structure. Furthermore, populations with intermediate to high frequencies of low recruitment appeared more sensitive to additional changes in recruitment. Exchanging low recruitment with zero recruitment severely increased the risk of local extinctions. Simulations with consecutive years of low recruitment showed a substantial increase in free space and an increase in the time taken to recover to normal densities. In conclusion, model simulations indicate that variable populations can be well buffered to changes in the demography caused by introduced environmental noise, but also, that intermediate to high frequencies of disturbance can lead to a swift change in population dynamics, which in turn, may affect the dynamics of whole communities
Extirpation-resistant species do not always compensate for the decline in ecosystem processes associated with biodiversity loss
No full textAccelerating rates of biodiversity loss may result in a rapid decline in important ecosystem processes such as carbon capture. Whether extirpation-resistant species compensate for the decline in ecosystem processes associated with the loss of extirpation-prone species is poorly understood.We apply a novel approach to answer this question using an assemblage of salt marsh plants. First, manipulations were performed to simulate a realistic sequence of species loss, based on observed sensitivity to disturbance. Then, changes in biomass and primary production of extirpation-resistant species were monitored over three consecutive growing seasons.Extirpation-resistant species did not compensate for the loss of either biomass or primary production associated with the removal of extirpation-prone species. Factors that determine the potential for compensation within ecosystems are discussed. These include resource-regulated compensation rates, the level of functional redundancy within an assemblage and the extirpation resistance of species which possess good compensation traits. Synthesis. These results suggest that we cannot assume extirpation-resistant species will compensate for the decline in ecosystem processes associated with biodiversity loss across all ecosystems. Understanding those factors that influence the ability of ecosystems to compensate for declines in ecosystem processes associated with biodiversity loss constitutes a significant challenge
Grazing dynamics in intertidal rockpools: Connectivity of microhabitats
No full textDifferences between rockpool and emergent rock communities are often attributed to their contrasting physical conditions. However, differences in grazing pressure between rockpools and open rock could also exert an important structuring role. Greater densities and/or the lack of tidal constraints on foraging may allow grazing intensity to be greater in rockpools. Here, wax discs were deployed to compare grazing intensity between rockpool and emergent rock habitats at each of three tidal heights on a moderately exposed shore in SW England. Grazing intensity was then examined in relation to herbivore density. Grazing intensity in pools was twice that on emergent rock, despite a lower density of herbivores in the rockpools. Of these herbivores, patellid limpets are the dominant grazers on rocky shores throughout the NE Atlantic and are recognised to have a major role in structuring intertidal communities. Thus, subsequent experiments focussed on the influence of limpets in determining the differences in consumer pressure between rockpools and emergent rock. Three alternative explanations were considered: (1) the effect of continuous immersion on grazing intensity in rockpools; (2) differences in limpet species abundance between the two habitats; (3) movement of limpets from emergent rock into pools to feed. The level of grazing pressure exerted by Patella ulyssiponensis (Gmelin), the predominant species living constantly immersed in rockpools, was similar to that of P. vulgata (Linnaeus) which is predominantly found on emergent rock. P. vulgata were observed moving from emergent rock into rockpools during high tide. Manipulative experiments confirmed that these foraging excursions resulted in a 2-fold increase in grazing intensity in the pools. Grazing activity of P. vulgata in rockpools was not consistent between sites and may be influenced by differences in wave exposure and/or the abundance of microbial resources. Elevated consumer pressure in rockpools may be an important factor influencing algal assemblages and probably explains the predominance of grazer resistant-species in these pools
Rocky shores as tractable test systems for experimental ecology
No full textRocky shore ecology has been studied for a long time, starting with qualitative descriptions and becoming more quantitative and experimental over time. Some of the earliest manipulative experimental ecological studies were undertaken on rocky shores. Many, over time, have made considerable contributions to ecological theory, especially highlighting the importance of biological interactions at the community level. The suitability of rocky shores as convenient test systems for ecological experimentation is outlined. Here we consider contributions from rocky shores to the emerging concepts of supply-side ecology, the roles of competition, predation and grazing, disturbance and succession and positive interactions in structuring communities along environmental gradients. We then address alternative stable states, relationships between biodiversity and ecosystem functioning, and bottom-up and top-down control of ecosystems. We briefly consider the feedback and synergies between ecological concepts and experimental work on rocky shores, whilst still emphasizing the traditional values of marine natural history upheld in JMBA since its first publication. The importance of rigorous experimental designs championed by Underwood and co-workers is emphasized. Recent progress taking advantage of new technologies and emerging approaches is considered. We illustrate how experimental studies have shown the importance of biological interactions in modulating species and assemblage-level responses to climate change and informed conservation and management of coastal ecosystems
Patterns of reproductive traits of fucoid species in core and marginal populations
No full textFucoid macroalgae are important primary producers and habitat modifiers on North Atlantic intertidal rocky shores. With decreasing latitude, western European fucoid populations display reduced levels of abundance, biomass and recruitment, while experiencing higher levels of physical environmental stress during summer months. We hypothesized that such reduction in the south is accompanied by a detectable decline in fucoid reproductive capacity. To test this hypothesis, morphological and reproductive traits of core (Welsh) and marginal (Portuguese) populations of two common fucoid species, Fucus vesiculosus and F. spiralis (Ochrophyta, Fucales), were examined. Morphological measurements showed that for a given thallus length, both fucoid species had smaller thallus volume and lower biomass in the southerly marginal part of the range. Significantly lower biomass of reproductive tissue of F. vesiculosus and a smaller number of receptacles per individual on specimens of both species indicate that levels of reproductive output are probably lower in southern populations. Despite the differences in reproductive traits observed between regions, reproductive effort (measured as the percentage of total dry biomass represented by reproductive tissue) of both species remained similar, as algae from both regions made similar investments in reproduction. The results indicate that stressful conditions reduced growth and number of receptacles of both species and amount of reproductive biomass of F. vesiculosus in the south but do not seem to change the way these algal species invest their energy. The decline in mass and reproductive biomass of specimens from southern shores found in this study, when combined with the lower abundance of adults and lower recruitment levels previously observed, is a strong indication of fucoid populations with lower levels of propagule output. This is an important factor when considering responses of these populations to a changing environment
Spatial heterogeneity increases the importance of species richness for an ecosystem process
No full textThe role of biodiversity in mediating ecosystem processes has been the subject of focused theoretical and empirical attention since the mid-1990s. Theory predicts that the balance between species richness and identity effects will critically depend on the degree of environmental heterogeneity, which dictates the extent to which differences between species in patterns of resource use can be expressed. We conducted a mesocosm experiment to explicitly test this hypothesis. We manipulated the richness and identity of intertidal molluscan grazers, as well as the spatial heterogeneity of the substrate upon which they grazed. The magnitude of algal consumption was used as our focal ecosystem process. The grazer treatments consisted of three monocultures and a single polyculture including all three species; heterogeneity was represented as the proportion of topographically complex and flat substrate. Species identity had strong effects on homogeneous substrates, with the identity of the best-performing species dependent on the substrate. On the heterogeneous substrate, suitable conditions for all three species were represented, allowing the expression of spatial complementarity of resource use and the enhancement of total algal consumption. Our findings provide the first explicit experimental evidence that spatial heterogeneity of the physical environment can play a key role in mediating effects of species diversity
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