Physical and biological factors govern community and population features of sandy beach macrofauna. At the macroscale, species richness decreases from tropical to temperate beaches, and from ...macrotidal dissipative to microtidal reflective beaches. At the species level, life history traits are highly plastic over latitudinal gradients; large-scale variations in environmental variables modulate intraspecific phenotypic differentiation. At the mesoscale, alongshore and across-shore distributions tend to be unimodal, bell-shaped within a beach, with abundance varying from the central region to the boundaries, even though environmental gradients (wave exposure, salinity) can cause asymmetries. Zonation is highly dynamic and not sharply defined. This is attributed to short- (hourly, daily) or medium- (seasonal) term reactions to environmental conditions, passive transport and sorting by the swash (e.g. recruits), active micro-habitat selection (e.g. adults), and intra- and interspecific interactions. Across-shore distribution may become multimodal due to intraspecific segregation by sizes during recruitment. At the microscale (individual neighbourhood or quadrat scale), behavioural factors and intra-/interspecific interactions become more important as density increases. Human induced impacts also generate variability in population demography, structure and dynamics. We identify physical-biological coupling at different temporal and spatial scales, emphasizing the role of life history traits in order to assess alternative regulatory mechanisms and processes. Our synthesis suggests that: (1) biological interactions are more important regulatory agents than previously thought: in benign dissipative beaches or undisturbed sites, intra- and interspecific competition can be more intense than in reflective beaches or disturbed sites, where the populations are physically controlled; (2) supralittoral forms are relatively independent of the swash regime and show no clear response to beach type; (3) marked long-term fluctuations are noticeable in species with planktonic larvae structured as metapopulations, due to environmental disturbances and stochasticity in reproduction and recruitment.
Species richness and abundance of macrofauna on sandy shores increase from microtidal reflective to macrotidal dissipative beach conditions. However, no attempt has been made to deconstruct these ...patterns. Using information on the macrofauna from 63 microtidal sandy beach surveys in South America, we deconstructed the community to discriminate among taxonomic groups, supralittoral and intertidal forms, and groups with different feeding habits and development modes. We also separated the effects of development mode and beach zone (intertidal vs. supralittoral) at the species level and scaled body size to density estimates. Total species richness decreased towards reflective beaches, but this trend was less marked in crustaceans than in molluscs or polychaetes. Supralittoral air-breathing crustaceans increased in richness and abundance from dissipative to reflective conditions, a reverse trend to that seen in intertidal crustaceans. Development modes (species with direct development and with planktonic larvae) showed the same response to beach type as the community as a whole. Filter feeders, scavengers and deposit feeders showed the same trend, but the latter were scarce or absent on reflective beaches. Zone was more important than either development or feeding modes in determining individual species responses to beach type. Body size decreased and density increased from reflective to dissipative beaches, suggesting that smaller forms are more sensitive to harsh conditions where density is lower, and hence there is less scope for biological interactions in reflective beaches. The deconstruction approach provided insights into the relationships between life cycle characteristics and richness and abundance patterns and the relative importance of environmental variables in beach ecology.
Changes in the structure and dynamics of sandy beach macrofaunal populations result from the simultaneous action of local and regional factors acting synergistically. This is particularly noticeable ...in transitional interfaces between freshwater and marine ecosystems, where large-scale gradients affect local beach morphodynamics and resident fauna. The wedge clam
Donax hanleyanus
occurs on beaches with contrasting morphodynamics along the salinity gradient generated by the Rio de la Plata estuary. We conducted sampling surveys to determine a fine-grained comprehensive coverage of the species’ distribution in Uruguay to assess the concurrent effects of large-scale variations in salinity and local beach morphodynamics on wedge clam populations along 400 km (16 sandy beaches) over 2 yr. The main factor controlling wedge clam occurrence was salinity, overriding the effects of local habitat features. On beaches where the species was present, total abundance was higher on oceanic dissipative shores, which also harbored a higher abundance and relative representation of recruits. Recruitment was almost lacking in reflective beaches. However, biomass of adults with larger body sizes prevailed on reflective beaches, suggesting a scaling of abundance to body size and potential density-dependent effects. In this metapopulation, estuarine beaches are sinks, whereas oceanic beaches act as source habitats. We concluded that large-scale gradients generated by salinity variations translated into local population patterns (distribution, abundance and population structure) and processes (recruitment), which were secondarily driven by local morphodynamics. The relative importance of pre- and post-settlement processes across the morphodynamic spectrum from reflective to dissipative beaches has yet to be elucidated.
While the physical characteristics of sandy beaches play a significant role in shaping the macrofaunal community features through morphodynamics, regional environmental factors may also account for ...deviations from the expected patterns. Here, we assess the concurrent effects of local morphodynamic factors and regional variables, such as sea surface temperature (SST), salinity, and chlorophyll-a (chl-a), on species richness and abundance of intertidal macrofaunal assemblages in four sandy beaches located along the estuarine gradient generated by the Río de la Plata (RdlP) in the southwestern Atlantic Ocean. Species richness was higher in dissipative beaches compared to intermediate ones, consistent with the predictions of the Swash Exclusion Hypothesis. However, this trend was not observed for total abundance, which significantly increased with chl-a. Both local and regional-scale environmental factors, such as salinity and chl-a, proved to be significant predictors in the arrangement of these communities. These results further support previous findings that highlight the critical role of the estuarine gradient of the RdlP in shaping life-history traits, population structure, and abundance of the resident intertidal macrofauna at both local and regional scales. The study underscores the importance of integrating environmental factors operating at different spatial scales to decipher community patterns in these physically-controlled environments.
•Species richness was higher in dissipative beaches, consistent with the predictions of the Swash Exclusion Hypothesis.•Trends in total abundance did not follow the Swash Exclusion Hypothesis, but increased significantly with chlorophyll-a.•Salinity and chlorophyll-a proved to be significant predictors in the arrangement of the communities.•The estuarine gradient of the Río de la Plata has a key role in shaping macrofaunal responses at local and regional scales.
The wedge clam Donax hanleyanus Philippi, 1845 is a conspicuous member of the sandy beach macrofauna along hundreds of kilometres in the northern coasts of Argentina. Age, growth, mortality, and ...productivity of this species were assessed in the southernmost limit of its distribution range (Mar del Plata, Buenos Aires province, Argentina). The parameters of the von Bertalanffy growth function were SL
∞
= 23.23 mm, K = 1.62 year
−1
, and t
0
= 0.08 years. The maximum individual production was 7.9 × 10
−7
g shell-free wet mass (SFWM)·year
−1
at a shell length of 14–16 mm. Individuals between 10 and 12 mm contributed the most to the secondary production (P) of 0.01 g SFWM·m
−2
·year
−1
. The mean annual biomass (B) was 0.002 g SFWM·m
−2
·year
−1
. Annual P/B ratio and mortality coefficient (Z) were 4.48 year
−1
and 4.78 year
−1
, respectively. Low production and high mortality could be caused by a sharp decrease in habitat quality, given the suboptimal temperatures at the southernmost edge of the species distribution. These results strongly limit its potential for future commercial exploitation.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Large-scale spatial and temporal variability in environmental conditions may result in differences in life-history traits, population demography, and abundance of sandy-beach species. We analyzed the ...effects of salinity, chlorophyll
a
(chl
a)
, and sea surface temperature (SST) on population parameters of the wedge clam
Donax hanleyanus
from 75 South American sandy beaches covering a 15° latitudinal range. Generalized modeling results showed that between-beach differences in abundance, population structure, growth performance, productivity, mortality, and individual shell mass were mainly explained by salinity fluctuations, with chl
a
and SST as secondary contributors, overriding, in most cases, local habitat features (Dean’s parameter, grain size, slope). Our results provide valuable insights into macroscale ecological processes, setting a basis to delineate conservation guidelines at large spatial scales that respond to the potential effects of climate variability and change on sandy beach populations.
Small-scale fisheries (SSFs) constitute a critical socioeconomic sector by providing a source of income and animal protein for fishing communities worldwide. In Uruguay this sector has traditionally ...been neglected. More recently, the Uruguayan government has shown an increasing interest in readdressing this situation by setting a high-level policy for SSFs. This paper addresses the long-term process from conceptualization to operationalization of the Ecosystem Approach to Fisheries (EAF) in Uruguayan SSFs. An overview of the social-ecological enabling conditions that facilitated EAF operationalization across four pilot sites is also provided. Long-term results showed that the intrinsic characteristics of each fishery conditioned the goals achieved. Fishery systems with more favorable enabling conditions served as starting points for operationalizing an EAF strategy. By contrast, SSFs with historical conflicts of use and a complex relationship between the fisheries management agency and fishing communities are still challenging. These results were used as learning platforms to strength and enhance the normative framework regarding management of SSFs. Progresses in EAF implementation at pilot sites have provided initial building blocks for scaling practices to other Uruguayan SSFs. The translation of processes and results into the long-term fishery policy allowed establishing an appropriate legal basis for further EAF development at a national level. Despite the above, long-term political will is critical for sustaining responsible fishing practices and the involvement of fishers as stewardships of their own activity.
Display omitted
•Definition of functional ecosystem management units (UFMEPs).•Successful implementation in UFMEPs with well-defined boundaries and reduced resource mobility.•Legitimate leaders, clear access rules and community cohesion were critical.•Partnerships between communities, management agency and academy triggered EAF implementation.
The concurrent role of morphodynamics and estuarine gradients in shaping population patterns in sandy beach macrofauna has not been adequately assessed. Here, we analyze the effects of beach ...morphodynamics, salinity, sea surface temperature, and chlorophyll-a (chl-a) on life-history traits of the wedge clam Donax hanleyanus in four sandy beaches located along the estuarine gradient generated by the Río de la Plata (RdlP, Argentina) over a 13-month period. A general linear model showed that chl-a and salinity were positively correlated with the abundance of D. hanleyanus, whereas between-beach differences in individual size, population structure, and growth performance were mainly explained by salinity fluctuations. These results indicate that the estuarine gradient of the RdlP plays a critical role in shaping life-history traits, population structure, and abundance of D. hanleyanus at local to regional scales, overriding the effects of local characteristics of the habitat. The study highlights the importance of conducting multi-scale studies that integrate environmental factors to elucidate the main physical drivers of population patterns in sandy beach ecosystems.
•Chlorophyll-a and salinity explained between-beach differences in Donax hanleyanus.•The Río de la Plata plays a key role in shaping Donax hanleyanus populations.•Estuarine gradient may override morphodynamics effects at local to regional scales.•Environmental factors are crucial to decipher population patterns in sandy beaches.
The population of wandering albatrosses Diomedea exulans at South Georgia is decreasing because of bycatch in longline fisheries. Until at least the early 1990s, the survival rate of females was ...lower than males, consistent with the adult female‐biased bycatch reported for fisheries operating around the Brazil‐Falklands Confluence (BFC). Here we use extensive tracking data (1990–2012) from breeding birds at South Georgia to investigate overlap with longline fishing effort reported to the International Commission for the Conservation of Atlantic Tunas (ICCAT). Using data from multiple years, we conclude that breeding females are at higher risk than males from all the main pelagic longline fleets in the south‐west Atlantic. Our overlap index (based on fishing effort and bird distributions) correlated positively with numbers of ringed birds reported dead on longliners, indicating that the metric was a good proxy of bycatch risk. The consistent sex bias in overlap across years, and the likely resulting sex‐biased mortality, could account for lower adult female survival rate at the colony. The risk from fisheries changed seasonally; both sexes overlapped with pelagic longline effort during incubation (January–March), and particularly during post‐brood chick‐rearing (May–December), whereas overlap was negligible during brooding (April). The highest percentage of overlap was with the Taiwanese fleet, then vessels flagged to Brazil, Uruguay, Spain, Japan and Portugal. Females were consistently at greatest risk in the BFC region, whereas males showed lower and more variable levels of overlap with fisheries from 35 to 45°S. Our results have important implications for management of ICCAT longline fisheries and conservation of this highly threatened albatross population.
We discuss methodological aspects directed to quantify the across-shore population structure and abundance of sandy beach macroinfauna. The reliability of estimates derived from design-based ...(stratified random sampling) and model-based (geostatistics, kriging) approaches is discussed. Our analysis also addresses potential biases arising from environmentally driven designs that consider a priori fixed strata for sampling macroinfauna, as opposed to species-driven sampling designs, in which the entire range of across-shore distribution is covered. Model-based approaches showed, spatially, highly autocorrelated and persistent structures in two intertidal populations of the Uruguayan coast: the isopod Excirolana armata and the yellow clam Mesodesma mactroides. Both populations presented zonation patterns that ranged from the base of the dunes to upper levels of the subtidal. The Gaussian model consistently explained the spatial distribution of species and population components (clam recruits and adults), with a minor contribution ( less than or equal to 5%) of unresolved, small-scale variability. The consistent structure of spatial dependence in annual data strongly suggests an across-shore-structured process covering close to 35 m. Kriging predictions through cross-validation corroborated the appropriateness of the models fitted through variographic analysis, and the derived abundance estimates were very similar (maximum difference=7%) to those obtained from linear interpolation. Monthly analysis of E. armata data showed marked variations in its zonation and an unstable spatial structure according to the Gaussian model. The clear spatial structure resulting from species-driven sampling was not observed when data was truncated to simulate an environmentally driven sampling design. In this case, the linear semivariogram indicated a spatial gradient, suggesting that sampling was not performed at the appropriate spatial scale. Further, the cross-validation procedure was not significant, and both density and total abundance were underestimated. We conclude that: (1) geostatistics provides useful additional information about population structure and aids in direct abundance estimation; thus we suggest it as a powerful tool for further applications in the study of sandy beach macroinfauna; and that (2) environmentally driven sampling strategies fail to provide conclusive results about population structure and abundance, and should be avoided in studies of sandy beach populations. This is especially true for microtidal beaches, where unpredictable swash strength precludes a priori stratification through environmental reference points. The need to use adaptive sampling designs and avoid snapshot sampling is also stressed. Methodological implications for the detection of macroecological patterns in sandy beach macroinfauna are also discussed.
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