Full stomachs at empty tides: tidal cycle affects feeding activity and diet of the sandy beach gastropod Olivella minuta

Olivella minuta is an abundant neogastropod on sandy beaches from Texas (USA) to southern Brazil. This study aimed to characterize and compare the feeding activity and diet of a Brazilian population of O. minuta in different tidal zones (intertidal and subtidall, and different tidal levels (high and low tides), with three combinations of tidal zone and level being studied (intertidal during low tide, intertidal during high tide and subtidal). The results showed that diet composition was generally similar among tidal conditions, with O. minuta being a generalist, feeding on 45 different food items. Feeding activity, however, was higher in the intertidal during low tide, whereas the richness and diversity of food items were higher in the intertidal during high tide. The higher feeding activity of O. minuta during low tide may be linked to a lower risk of predation; at low tide organisms may be able to feed for a longer time, arid this may be particularly true on beaches with fine sand, where water retention is higher than that on beaches with coarse sand. The higher diversity of food items consumed in the intertidal during high tide is likely related to the increased prevalence of planktonic food during high tide. Our results indicate that tidal zone and level may strongly influence the feeding activity of coastal soft-bottom species and that species may show higher feeding activity during low tide. Given the current loss of intertidal habitats due to anthropogenic activity and climate-change associated factors, our study has important implications, highlighting the importance of intertidal areas for the ecology and conservation of sandy beach species.UIDB/04326/2020info:eu-repo/semantics/publishedVersio

Non-linear curve adjustments widen biological interpretation of relative growth analyses of the clam Tivela mactroides (Bivalvia, Veneridae)

Evaluation of relative (allometric) growth provides useful information to understand the development of organisms, as well as to aid in the management of fishery-exploited species. Usually, relative growth analyses use classical models such as the linear equation or the power function (allometric equation). However, these methods do not consider discontinuities in growth and may mask important biological information. As an alternative to overcome poor results and misleading interpretations, recent studies have suggested the use of more complex models, such as non-linear regressions, in conjunction with a model selection approach. Here, we tested differences in the performance of diverse models (simple linear regression, power function, and polynomial models) to assess the relative growth of the trigonal clam Tivela mactroides, an important fishing resource along the South American coast. Regressions were employed to relate parameters of the shell (length (L), width (W), height (H) and weight (SW)) among each other and with soft parts of the organism (dry weight (DW) and ash-free dry weight (ASDW)). Then, model selection was performed using the information theory and multi-model inference approach. The power function was more suitable to describe the relationships involving shell parameters and soft parts weight parameters (i.e., L vs. SW, DW, and AFDW, and SW vs. DW). However, it failed in unveiling changes in the morphometric relationships between shell parameters (i.e., L vs. W and H; W vs. H) over time, which were better described by polynomial functions. Linear models, in turn, were not selected for any relationship. Overall, our results show that more complex models (in this study polynomial functions) can unveil changes in growth related to modifications in environmental features or physiology. Therefore, we suggest that classical and more complex models should be combined in future studies of allometric growth of molluscs

Short-term exposure to antifouling copper paint does not affect a key intertidal grazer

It is well known that grazing gastropods, notably limpets, have a structuring effect on rocky shore ecology. The findings to establish this knowledge came from exclusion experiments, often using fences necessitating complex procedural controls. Barriers of anti-fouling copper paint (AP) have been shown to be an effective way to control densities of species in intertidal rocky shores. This method may produce fewer confounding effects than traditional methods of exclosure such as fences/cages and, consequently, is seen as a better solution for excluding grazing molluscs. Nevertheless, the potential artefacts arising from AP as a barrier system are not fully quantified. To better understand the biological impacts of AP and also determine its applicability in field studies, we first determined if using AP as a fence to enclose limpets led to elevated copper levels in test animals. Then, we tested short-term effects of AP on the tenacity, foraging behaviour, grazing pressure and body mass of the limpet Cellana tramoserica in its natural environment over a representative experimental period. AP barriers increased copper concentrations tenfold in C. tramoserica, but this did not affect any of the response variables measured under natural conditions. Overall, our results showed that AP is not as deleterious to limpets as reported from laboratory studies and this supports its use as an effective cageless method to manipulate densities of species on rocky shores in a short time scale4931419CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQCOORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPES240918/2012-614796/13-

Spatial and temporal variation in the diet of the sandy beach gastropod olivella minuta

Marine gastropods exert a strong influence on the structure of marine ecosystems through their foraging activities, yet little is known about how environmental differences in space and time may affect their feeding behavior. To enhance the knowledge about the trophic ecology of coastal benthic species, we investigated temporal and spatial variations in the diet of the sandy beach gastropod Olivella minuta. We collected individuals of O. minuta seasonally, over 1 year, at two sandy beaches with different morphodynamic characteristics (Araca Bay, an ultra-dissipative tidal flat, and Barequecaba Beach, a dissipative beach) and analyzed the stomach contents of specimens of O. minuta. We identified approximately 15,000 food items, which we grouped into 14 categories. Thirteen food categories were found at each area, but significant differences in diet were observed between sites and sampling periods. Individuals from Araca consumed an overall larger quantity and diversity of food items, which consisted mainly of foraminiferans, polychaetes, and crustaceans. At Barequecaba, diatoms were the most important item, followed by crustaceans and polychaetes. Temporal variation depended on sites: the number of food items in the stomachs of individuals of O. minuta and dietary composition was roughly constant over time at Araca, whereas larger variations were observed at Barequecaba. Although O. minuta has been previously characterized as a carnivore/scavenger, our results show that the diet of this species varies in space and time and comprises a large variety of food resources. The species thus plays a role in the cycling of both vegetal and animal organic matter. This generalist behavior may allow individuals to shift their diet according to habitat alterations and food availability, thereby enhancing the persistence and resilience of O. minuta in different environments or future climate change scenarios1384CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP309697/2015-8; 484475/2011-8; 150316/2018-6; 150473/2010-92009/17585-6; 2015/03804-9; 2017/17071-9; 2009/15893-

Nestedness patterns and the role of morphodynamics and spatial distance on sandy beach fauna: ecological hypotheses and conservation strategies

Abstract Sandy beach fauna is hypothesized to be mainly structured by environmental variables. As such, it is expected that morphodynamic characteristics are limiting factors, and the species pool inhabiting harsher reflective beaches would be a subset of (i.e., nested in) the fauna of nearby dissipative beaches. We investigated the existence of a nestedness pattern in sandy beach assemblages, as well as the contribution of environmental and spatial variables (i.e., factors that potentially affect an assemblage regardless of environmental conditions - typically related to distance between sites and dispersal of organisms) on sandy beach macrobenthic fauna. Dissipative beaches had higher species richness than reflective beaches but we found no nestedness pattern. Furthermore, almost every beach showed exclusive species. Spatial variables exerted stronger influence on macrobenthic assemblages than local environmental variables. Our results therefore suggest that local and small-scale recruitment is the predominant process structuring macrobenthic assemblages. These results bring important implications for sandy beach conservation: given that spatial distance is an important factor structuring macrobenthic fauna and different sandy beaches harbor different pools of species, conservation programs need to focus on sandy beaches across large spatial scales and with varied morphodynamic characteristics in order to preserve coastal biodiversity

Night underwater rides: the activity of a sandy beach gastropod is affected by interactive effects of light availability and water level

Olivella minuta is an abundant gastropod and important consumer on beach food webs, whose feeding activity was recently demonstrated to be reduced when submerged. Our study aimed to test the interactive effects of water level and light in the activity of O. minuta. Experiments were conducted in the laboratory simulating four conditions: (1) Light, emerged (LE); (2) Dark, emerged (DE); (3) Light, immersed (LI); and (4) Dark, immersed (DI). Our results showed a significant interaction between water level and light variation. During conditions of light availability, the results corroborated our expectations and individuals were less active when immersed. However, individuals showed the highest activity when immersed during lightless conditions. This enhanced activity on dark immersed periods can be explained by optimization of feeding strategy, to benefit from the input of food resources brought by the tide. This could also be an adaptation to avoid predation by visual predators, which needs to be further evaluated. Our results show that patterns of activity of O. minuta may be susceptible to impacts of light pollution and coastal squeezing, and that the interacting effects of light and water level need to be considered in further studies on the behaviour of beach organisms.info:eu-repo/semantics/publishedVersio