Swash Climate Research Articles

Spatiotemporal patterns of macrophyte subsidies to sandy beaches of Yucatán, Mexico

The spatial and temporal patterns of macrophyte wrack in six sandy beach localities of the northern Yucatán Peninsula were described to answer three main questions: (1) Is the composition and biomass of stranded macrophyte homogeneous along the coast and independent of climatic events?; (2) Which environmental features of beaches are the main predictors of macrophyte biomass deposition and retention?; and (3) Is there a significant relationship between deposited, retained, and buried wrack and the content of organic matter in sediments? To this end, the macrophyte wrack was collected in five random replicated quadrats along the recent drift line (representing the deposited wrack). The same operation was repeated along the aging strandline (representing the retained wrack). All material was washed and weighed. Macrophytes of each sample were separated into nine categories to determine variations in their composition. Macrophyte wrack patterns of species composition were primarily explained by large spatial scales (localities), separating the west side (Celestún and Sisal) from the rest of the Yucatán coast. The composition of macrophytes was consistent, although their temporal dynamics varied between sites and localities. Biomass patterns showed a more complex spatial and temporal pattern with a significant relation of the arrived and retained wrack biomass. The main environmental predictors of wrack biomass deposition and retention were longitude coordinates, shoreline orientation, grain size, and swash climate. However, the beach state did not correlate with the deposited and retained wrack biomass. The amount of buried wrack was significantly related to the amount of retained wrack, and the former significantly contributed to explaining the amount of organic carbon in sediments. In general, we hypothesized that the nearshore and heterogeneous habitats could be responsible for the complex spatiotemporal patterns of wrack variation found in the sandy beaches of Yucatán.

Richness, abundance and microhabitat use by Ardeidae (Aves: Pelecaniformes) during one seasonal cycle in the floodplain lakesof the lower Amazon River

The role of morphodynamic features such as grain size, swash climate and wave action on the macrofauna of beaches are well-known. However, few studies have investigated natural disturbances as potential drivers of temporal community variations. In southeastern Brazil, we sampled the intertidal macrofauna of two sandy beaches to test whether seasonal disturbances as the frequency of storm wave events (SWE) and rainfall have significant influence on their composition and abundance. The macrofauna assemblage differed significantly between the rainy and the dry seasons, but rainfall was not the main driver of community changes, although both beaches are in the vicinity of extensive river plumes. Actually, SWE explained most macrofauna richness overtime, with positive effects. Our results point to the importance of learning more about the effects of poorly studied disturbances on macrofaunal communities, and based on them we strongly recommend including these seasonal phenomena when monitoring sandy beaches.

Do natural disturbances have significant effects on sandy beach macrofauna of Southeastern Brazil?

The role of morphodynamic features such as grain size, swash climate and wave action on the macrofauna of beaches are well-known. However, few studies have investigated natural disturbances as potential drivers of temporal community variations. In southeastern Brazil, we sampled the intertidal macrofauna of two sandy beaches to test whether seasonal disturbances as the frequency of storm wave events (SWE) and rainfall have significant influence on their composition and abundance. The macrofauna assemblage differed significantly between the rainy and the dry seasons, but rainfall was not the main driver of community changes, although both beaches are in the vicinity of extensive river plumes. Actually, SWE explained most macrofauna richness overtime, with positive effects. Our results point to the importance of learning more about the effects of poorly studied disturbances on macrofaunal communities, and based on them we strongly recommend including these seasonal phenomena when monitoring sandy beaches.

Across-shore distribution of Ocypode quadrata burrows in relation to beach features and human disturbance

ABSTRACTSpatial distribution patterns of the ghost crab Ocypode quadrata were analysed using different approaches at one disturbed and two preserved reflective sandy beaches of the Mexican Caribbean. We used spatial correlation analysis to describe the across-shore distribution of O. quadrata and their patch dynamics by beach and sampling time. In addition, we analysed the across-shore variability of habitat extent of O. quadrata (habitat envelope) and its relation to human disturbance and beach features. The spatial structure of burrow density was consistent through time, showing a bimodal distribution with very low abundance in the mid distribution range and a discrete increment of burrows to landward. Nonetheless, the size of patches varied temporally for the three beaches. Burrow size increased from seaward to landward. The location of the first burrow and the habitat envelope varied among sampling times and beaches. The location of the first burrow is mostly mediated by the swash climate, while the habitat envelope is mainly controlled by the level of human disturbance. Despite the low number of disturbed and control beaches, our results suggest that the habitat envelope could be included in future studies when using ghost crabs as indicators of human disturbance. Polynomial models and variographic analysis proved to be useful tools to describe the across-shore distribution and patch dynamics of the ghost crab.

Body shape and burial behavior of the sand crab Emerita analoga (Stimpson 1857) in a reflective to intermediate morphodynamic range of sandy beaches

Sand crabs belonging to the genus Emerita are the dominant species on sandy beaches of the Pacific and Atlantic coasts of America. The success of this genus has been attributed to the great phenotypic plasticity of life history traits that enables them to cope with swash climate variability from beach to beach. The burrowing rate and variation in carapace shape of Emerita analoga from south-central Chile were studied on a series of five sandy beaches with contrasting reflective-intermediate swash conditions (harsher swash to benign swash). Environmental sampling was carried out monthly from September 2009 to November 2010, while biological experiments were conducted in September and October 2010. A combination of field experiments, geometric morphometric tools and multivariate analysis was used to assess the relationship between burrowing behavior and carapace shape with variables of swash climate. Our results showed that (1) body shape of E. analoga is directly affected by the frequency of effluent line crossing, (2) burrowing rate of E. analoga is affected directly by shape variability, (3) burrowing rate is affected directly and indirectly by the swash climate variables: frequency of effluent line crossing and mean grain size of sediment. Thus, the physical conditions in the intertidal zone may be the main environmental constraints determining cephalothorax shape, with a wider cephalothorax on beaches with finer sand and more benign physical dynamics, and a narrower shape on beaches with coarser sand and harsher physical dynamics. The latter phenotype (narrower shape) probably allows compensating the high difficulty of burying in coarser sediments.

Effect of swash climate and food availability on sandy beach macrofauna along the NW coast of the Iberian Peninsula

The swash exclusion hypothesis (SEH) is widely used in explaining the abundance and diversity of macrofauna in sandy beaches. This hypothesis predicts a reduction in richness, abun- dance and biomass of macrofaunal assemblages from flat slope beaches to steep slope ones due to the swash climate. Nevertheless, flat slope beaches are characterised by greater food availability than steep slope beaches; thus, food supply may also explain macrofaunal trends in exposed sandy beaches. This paper investigates the relative importance of food availability (expressed as biopoly- meric carbon and chlorophyll a) and swash climate within this macrofauna impoverishment. Macro- faunal assemblages and sediment food availability were studied at 3 levels on the shore, 2 intertidal and 1 supratidal, at each of 11 sandy beaches located on the NW coast of the Iberian Peninsula. Results indicated that: (1) the beach slope had a stronger effect on richness, density and biomass of macrofaunal assemblages at the intertidal than at the supratidal level; (2) steep slope beaches pre- sented a higher percentage of active burrower species than flat slope beaches; and (3) species rich- ness, density and biomass of macrofauna were not related to food availability, measured as bio- polymeric carbon and chlorophyll a in the sediment. Overall, our results strongly support the idea that the harsh swash climate of steep slope beaches may exclude some species without active and rapid burrowing abilities, and is probably one of the mechanisms responsible for the observed decrease of macrofauna in this habitat.

Behavioural strategies and surface activity of the sandhopper Pseudorchestoidea brasiliensis (Amphipoda: Talitridae) on a Brazilian beach

The behaviour and surface activity of Pseudorchestoidea brasiliensis (Dana, 1853) was studied at the Boqueirao Beach, southeast Brazil. In May 1995, sampling was performed in two periods of 24 h, the first at neap tide (6–7 May) and the second at spring tide (27–28 May). Sampling was carried out along a transect from the upper limit of swash zone to the base of the dune vegetation. This transect was divided systematically into strata 3 m apart, which varied in number (15 high tide to 19 low tide); three circular pitfalls traps (3.5 cm2) were placed at each stratum along a transect. The animals caught were removed hourly. Surface activity pattern, total and hourly mean zonations were calculated in daily hours at spring and neap tides. Correlation analysis was used to compare the patterns of activity of the age and sex classes in relation to hourly mean zonation, temperature, and tidal height. The results indicate the existence of three peaks of surface activity. The activity peaks were registered at sunrise, at sunset and around midnight. Differences in the activity patterns between juveniles and adults were observed. Adults had nocturnal activity, whereas most juveniles were active at sunset and at sunrise. Hourly mean zonations varied between the two synodic phases, with a probably landward shift at spring tide. During the day, the amphipods occupied 18 m of the intertidal zone, on average, whereas at night this extension was wider (mean 27 m). Activity rhythms of the adults were correlated with sediment temperature. However, the activity rhythms of the juveniles were not correlated with the sediment temperature and they showed a higher activity during the day. The surface activity of the adults and of juveniles were generally not correlated with tidal range. The results provide evidence of the behaviour plasticity of talitrids in which the behaviour and the activity patterns of juveniles and adults enable them to adapt to different sandy beach conditions (morphodynamic states, exposure index, beach slope and swash climate).

Swimming ability and burrowing time of two cirolanid isopods from different levels of exposed sandy beaches

Most of the macroinfauna from sandy beaches is highly mobile, emerging out of the sediment when the tide rises, and using the swash to migrate up and down the beach face or feed (searching for prey or carrion). After swash excursions, they usually burrow back into the sediment, maintaining zonation at low tide. Therefore, the different species abilities to emerge, move around and burrow under different swash climates and sediment conditions are expected to influence observed distribution patterns. Nonetheless, few attempts have been made to understand behavioral mechanisms of these organisms in moving fluids. In this study, we used a flume tunnel to investigate the orientation, swimming ability and burrowing time of two similar species of cirolanid isopods, Excirolana armata Dana and Excirolana braziliensis Richardson, under current velocities ranging from 5 to 30 cm·s −1. E. armata inhabits middle levels of dissipative to intermediate beaches, while E. braziliensis is found towards the upper level of a wider range of beach states. Both species oriented countercurrent above a threshold velocity, which turned out to be significantly lower for E. armata than for E. braziliensis. E. armata proved to be a stronger swimmer as shown by the higher velocities surmounted, and the less drags experienced at the highest current velocity. E. armata also burrowed faster than E. braziliensis. Burrowing time was affected by sediment grain size and water content, but not by water flow. Once organisms managed to begin burrowing under different flow conditions, they were not affected by current velocity. Nonsaturated sand precluded burial, while coarse sand retarded it. Differences in the observed patterns of across-beach distribution may thus be the result of species-specific behavioral responses to swash climate, manifested in swimming ability, burying and orientation in directional flows.

Testing the swash exclusion hypothesis in sandy beach populations: the mole crab Emerita brasiliensis in Uruguay

Exposed marine beaches are physically rigorous habitats in which macrofauna commu- nity patterns have been well correlated with physical factors such as grain size, beach slope and wave/swash processes. In this context, the swash exclusion hypothesis (SEH) gained wide accept- ability in explaining the control of species abundance and diversity of the sandy beach macrofauna by swash climate, determined by wave height and beach face slope. This hypothesis predicts a con- sistent increase in species richness, abundance and biomass from reflective to dissipative conditions. However, predictions of the SEH have not been adequately tested at a population level. Here, demo- graphic and life history characteristics of the intertidal mole crab Emerita brasiliensis were compared between populations of 2 microtidal exposed sandy beaches with contrasting morphodynamics dur- ing 22 consecutive months. The major prediction of the paradigm does not hold for the mole crab: total abundance, as well as that of males, females, males with spermatophores and megalops did not differ between beaches. Moreover, the reflective beach population presented higher male growth rates in size and lower natural mortality. Other population processes and life history traits gave support for the SEH: the dissipative beach population presented (1) higher abundance of ovigerous females, female growth rates, fecundity, egg production potential, size at maturity, as well as weight at size; and (2) lower female mortality and burrowing rates (for both sexes). The SEH seems to be particularly useful in explaining female somatic growth and reproductive features, which could be related to a major amount of food availability in dissipative beaches. However, other competing, but not exclusive, hypotheses are needed to explain variations in population abundance and other pro- cesses such as male growth and survivorship. The empirical evidence from several recent studies on the Uruguayan coast showed that sandy beach populations that co-occur in contrasting environments are less sensitive to variations in beach morphodynamics, which should not be considered the primary factor affecting the abundance and some life history traits. The importance of alternative population regulation processes and mechanisms are stressed.

Cusps and pipis on a sandy ocean beach in New South Wales

The effect of small-scale variation in beach morphology has been largely ignored in studies of beach macrofauna. This study examined the distribution and abundance of the large bivalve, Donax deltoides (commonly known as the ‘pipi’) in relation to beach cusps (rhythmically spaced undulations of the beachface consisting of scalloped bays and flanking horns on a scale of tens of metres). No differences were found in the abundance of pipis downshore of cusp horns versus cusp bays at any of three sites. In contrast, previous work on a relatively low-energy (reflective) beach reported greater abundances of bivalves below cusp bays than below cusp horns. Results suggest that the swash climate on the higher-energy (more dissipative) beach studied here produces weaker cusping and weaker patterns in the active or passive redistribution of beach fauna by swash action. Wider more dissipative beaches also allow beach macrofauna to remain on flatter parts of the beach, further below cusps than on reflective beaches. The more rigorous study design used here may also contribute to the difference in results between this study and previous studies. However, populations of pipis below cusp bays did contain a greater proportion of small individuals (≤20 mm length) than populations on cusp horns, suggesting some effect related to beach cusps. Small pipis live closer to the beach surface as they have shorter siphons and are subject to larger rates of dislodgement and movement from cusp horns to cusp bays by swash action than are large pipis. Future ecological studies of beaches with cusps should take beach cusps and the processes producing them into account as they may affect the distribution, abundance and the size distribution of beach invertebrates.

Estado morfodinâmico praial no instante da observação: uma alternativa de identificação

Determinations of the morphodynamic state of beach and surf zone were made on four beaches in Rio de Janeiro state, with two beaches located northward and two westward of Cabo Frio. Twenty four monthly measurements of beach and surf zone profiles associated to measurements of wave height and period, sediment settling velocity as well as swash climate were made during low spring tide. The beaches were classified by their modal morphodynamic state, a differentiation due to different wave climate and sediment characteristics. With exception for the reflective state, low correlation between the predicted and observed Morphodynamic State were obtained using Dean's parameter (Ω). This is a consequence of the low correlation between the grain size (and settling velocity) of the beach face sediments and the topographic gradient, when applied to a single beach. A new approach for the identification of the Morphodynamic State is proposed by inferring the beach and nearshore morphology through the comparison of the wave height and period in the outer breaker zone to the height and semi-period of wave in the swash zone.