Reflective Beaches Research Articles

Assessing the extreme overwash regime along an embayed urban beach

Coastal overwash is one of the most important hazards affecting the coastal zone and therefore has been the focus of several studies related to the establishment of setback lines. However, studies of extreme overwash (EO) events along urban beaches backed by a seawall or structure are scarce, and reveal the difficulties associated with its assessment, measurement and validation. The Nazaré coastal urban area (located on the west coast of Portugal) is developed adjacent to an embayed reflective beach and is subject to frequent and localized inundation due to EO events capable of overtopping the protection seawall. The current work develops a methodological approach to simulate total water levels (TWL) and seawall overtopping occurrences in time and space, with the ultimate goal of identifying the factors that govern the extreme overwash regime. The method uses multi-decadal time series of site-specific wave and tide, and high-resolution topo-bathymetric data, and recreates the TWL time series for a 36-year period. The model is successfully validated against video imagery and maximum swash line data that provide information on the reach of the water levels measured during modal and extreme TWL conditions along the studied beach. This study establishes the importance of the interaction of the modal and extreme hydrodynamic processes with the beach and backshore morphology. The Nazaré embayment is in equilibrium with the alongshore-varying modal wave conditions, resulting in higher vulnerability of the most sheltered sector during extreme events.

Trophic niche shifts driven by phytoplankton in sandy beach ecosystems

Stable isotopes (δ13C and δ15N) together with chlorophyll a and densities of surf diatoms were used to analyze changes in trophic niches of species in two sandy beaches of Uruguay with contrasting morphodynamics (i.e. dissipative vs. reflective). Consumers and food sources were collected over four seasons, including sediment organic matter (SOM), suspended particulate organic matter (POM) and the surf zone diatom Asterionellopsis guyunusae. Circular statistics and a Bayesian isotope mixing model were used to quantify food web differences between beaches. Consumers changed their trophic niche between beaches in the same direction of the food web space towards higher reliance on surf diatoms in the dissipative beach. Mixing models indicated that A. guyunusae was the primary nutrition source for suspension feeders in the dissipative beach, explaining their change in dietary niche compared to the reflective beach where the proportional contribution of surf diatoms was low. The high C/N ratios in A. guyunusae indicated its high nutritional value and N content, and may help to explain the high assimilation by suspension feeders at the dissipative beach. Furthermore, density of A. guyunusae was higher in the dissipative than in the reflective beach, and cell density was positively correlated with chlorophyll a only in the dissipative beach. Therefore, surf diatoms are important drivers in the dynamics of sandy beach food webs, determining the trophic niche space and productivity. Our study provides valuable insights on shifting foraging behavior by beach fauna in response to changes in resource availability.

Irregular wave runup statistics on plane beaches: Application of a Boussinesq-type model incorporating a generating–absorbing sponge layer and second-order wave generation

Efficient absorption of reflected waves at the offshore boundary is a prerequisite for the accurate physical or theoretical modelling of long-duration irregular wave runup statistics at uniform, gently sloped beaches. This paper presents an implementation of the method suggested by Zhang et al. (2014) to achieve reflected wave absorption and simultaneous generation and propagation of incident waves in an existing numerical wave flume incorporating a moving boundary wavemaker. A generating–absorbing layer is incorporated within this 1DH hybrid Boussinesq-nonlinear shallow water equation model such that inshore-travelling incident waves, encompassing bound-wave structure approximately correct to second order, propagate unhindered while offshore-travelling reflected waves are absorbed. Once validated, the method is used to compile random wave runup statistics on uniform beach slopes broadly representative of dissipative, intermediate, and reflective beaches. Analyses of the individual runup time series, ensemble statistics and comparison to an empirical formula based on experimental runup data suggest that the main aspects of runup observed in the field are properly represented by the model. Existence of an upper limit on maximum runup is investigated using a simple extreme-value statistical analysis. Spectral saturation is examined by considering ensemble-averaged swash spectra for three representative beach slopes subject to incident waves with two different offshore significant wave heights. All spectra show f−4 roll-off at high frequencies in agreement with many previous field studies. The effect is also investigated of the swash motions preceding one particular extreme runup event on the eventual maximum runup elevation.

Vertically-oriented trace fossil Macaronichnus segregatis from Neogene of Santa Maria Island (Azores; NE Atlantic) records vertical fluctuations of the coastal groundwater mixing zone on a small oceanic island

The trace fossil Macaronichnus segregatis is interpreted to be produced by opheliid polychaetes that feed on epigranular microbes and organic matter commonly abundant in shallow-marine foreshore sands. Resulting traces are horizontal and typically random in orientation, but sometimes perpendicular to the shoreline. However, M. segregatis in Neogene sandy sediments from Santa Maria Island in the Azores shows a vertical or sub-vertical orientation. This is explained by vertical flow of pore waters and oxygenation fluctuations within the mixing zone between interstitial marine and freshwater aquifers–where epigranular microbes and organic matter are most enriched. On reefless volcanic oceanic islands like the Azores, insular shelves are invariably steep, narrow, and exposed to strong swell. Aquifers in this setting respond rapidly to small changes on account of limited shelf space and a high potential differential that stimulates a vertical shift in habitats. Freshwater aquifers on small, low-relief oceanic islands form a thin lens, the edges of which are wedged against marine interstitial waters and migrate up and down in response to changes caused by tides, storm surges and precipitation. During the Late Miocene–Early Pliocene, Santa Maria was an island fitting this description. Due to a waning volcanism, intense marine erosion and gradual submersion, the island developed a wide shallow platform covered by sandy shoals, as exemplified by the Malbusca section with vertical Macaronichnus. The process, however, is more acute on small, reflective beaches perched on rocky island coasts. Here, sand blankets cover small ramps cut in the basaltic bedrock, resulting in very limited freshwater aquifers subject to strong changes due to the low permeability of basalts. The mixing zone is therefore forced to migrate chiefly up and down, mostly due to tides. The same response is dramatic in sandy fillings trapped in basalt fissures. As a consequence, the producer of Macaronichnus was tightly constrained in movement. Both situations occur in the “Pedra-que-pica” section on Santa Maria.

Effects of beach morphodynamic features on production and P/B ratio of the crab Emerita brasiliensis Schmitt, 1935 (Decapoda: Hippidae) in sandy beaches of South America

The mole crab Emerita brasiliensis inhabits exposed sandy beaches, both reflective and dissipative, along the Atlantic coast of South America, where it usually attains high biomass and production. We assessed the effects of physical characteristics of beaches (mean grain size, beach width and slope) on production and turnover rate (P/B ratio) of E. brasiliensis. Six production and P/B ratio datasets, estimated with cohort-based and size-based methods, were gathered from studies carried out on subtropical (~25°S) and temperate beaches (~32°S). Based on the estimates available, general trends were identified. Production was positively related to the intermediate/dissipative conditions of wider beaches with finer sand grains and gentler slopes. P/B ratio was negatively related to grain size (mm) and positively related to beach width. These results suggest that P/B ratios also increase towards intermediate/dissipative features due to higher growth rate, as indicated by higher values of the curvature parameter of the von Bertalanffy growth function (K) in more benign conditions (wider beaches with finer grains). In addition, the recurrent pattern of size structure on intermediate/dissipative beaches, with high frequency of recruits, leads to higher P/B ratio estimates on these beaches than on reflective beaches. The relationship of production and P/B ratio with physical features, such as mean grain size, beach width and slope indicates that a ‘short-cut’ approach to estimate Emerita brasiliensis production is a promising prospect and, therefore, more data on the production of this species should be provided.

Assessing sandy beach macrofaunal patterns along large-scale environmental gradients: A Fuzzy Naïve Bayes approach

A Fuzzy Naïve Bayes (FNB) classifier was developed to assess large-scale variations in abundance, species richness and diversity of the macrofauna inhabiting fifteen Uruguayan sandy beaches affected by the effects of beach morphodynamics and the estuarine gradient generated by Rio de la Plata. Information from six beaches was used to estimate FNB parameters, while abiotic data of the remaining nine beaches were used to forecast abundance, species richness and diversity. FNB simulations reproduced the general increasing trend of target variables from inner estuarine reflective beaches to marine dissipative ones. The FNB model also identified a threshold value of salinity range beyond which diversity markedly increased towards marine beaches. Salinity range is suggested as an ecological master factor governing distributional patterns in sandy beach macrofauna. However, the model: 1) underestimated abundance and species richness at the innermost estuarine beach, with the lowest salinity, and 2) overestimated species richness in marine beaches with a reflective morphodynamic state, which is strongly linked to low abundance, species richness and diversity. Therefore, future modeling efforts should be refined by giving a dissimilar weigh to the gradients defined by estuarine (estuarine beaches) and morphodynamic (marine beaches) variables, which could improve predictions of target variables. Our modeling approach could be applied to a wide spectrum of issues, ranging from basic ecology to social-ecological systems. This approach seems relevant, given the current challenge to develop predictive methodologies to assess the simultaneous and nonlinear effects of anthropogenic and natural impacts in coastal ecosystems.

Surfzone-Beach-Dune interactions: Flow and Sediment Transport across the Intertidal Beach and Backshore

ABSTRACT Hesp, Patrick A. and Smyth, T.A.G., 2016. Surfzone-Beach-Dune interactions: Review; and flow and sediment transport across the intertidal beach and backshore. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp.8–12. Coconut Creek (Florida), ISSN 0749-0208. The original wave-beach-dune model (Hesp, 1982) stated that in the medium to long term, modal dissipative beaches display maximum onshore wave driven sediment transport, maximum aeolian transport off beaches, the largest foredune heights and volumes, and the largest Holocene dunefields. Modal reflective beaches display the opposite, while modal intermediate beaches display a trend in these from relatively high to relatively low sediment transport, foredune volumes, and Holocene barrier volumes with a trend from dissipative to reflective. New Computational Fluid Dynamic (CFD) modelling of fl...

BEACH-FACE MORPHODYNAMICS OF DIFFERENT MORPHOLOGICAL SETTING ALONG TELUK CHEMPEDAK TO KUALA PAHANG, MALAYSIA

The present study on beach morphology and its profile dynamics was carried out to categorize the morphodynamic classification of selected beaches in Pahang, comprising the areas from Teluk Chempedak to Kuala Pahang. Beach stations were monitored monthly for a complete 1-year cycle; beginning from February 2012 to February 2013 at 12 corresponding stations established at random morphological intervals. Based on the results obtained, which include the granulometric analysis and beach surface topography, three main beach classes have been differentiated: reflective, intermediate and dissipative beaches. The reflective beaches exhibits rather high degree beach slopes and coarse-grain sand sizes compared to intermediate and dissipative classes.

Vertical distribution of meiofauna on reflective sandy beaches

Abstract Extreme physical conditions usually limit the meiofauna occurrence and distribution in highly hydrodynamic environments such as reflective beaches. Despite sediment grains of the upper layers being constantly resuspended and deposited, the high energy of the swash zone besides depositing coarse sediments allows an ample vertical distribution of meiofaunal organisms. The effect of physical, chemical and sediment variables on the vertical distribution of meiofaunal organims and nematodes was analysed on two reflective exposed beaches. Sampling was conducted at three sampling points on each beach in the swash zone. The sediment collected was divided into four 10-cm strata (0-10 cm, 10-20 cm, 20-30 cm, 30-40 cm). The statistical differences between strata due to factors previously established (i.e. meiofaunal composition, density of most abundant taxa) were tested using a hierarchical PERMANOVA applied under similarity and euclidian distances. An inverse relation among average grain size, content of organic matter and sediment sorting was evident. Coarser sediment characterized the upper layers, while at deeper layers the sediment was very poorly sorted and presented a higher content of organic matter. A similar pattern in the vertical distribution of meiofaunal and nematofaunal composition and density was detected. The lowest densities were associated with the first stratum (0-10 cm), highly affected by hydrodynamics. The vertical distribution of organisms was statistically different only when the interaction among factors was considered. This result suggests that zonation and vertical distribution of meiofaunal organisms are determined by the within-beach variability.

A geomorphological response of beaches to Typhoon Meari in the eastern Shandong Peninsula in China

Eight representative beach profiles on the eastern coast of the Shandong Peninsula are observed and measured in 2011 and 2012 to determine the coastal processes under the lower tropical wind speed condition and the beach response to and recovery from the tropical storm Meari in a rare typhoon region. The results show that it is the enhancement and directional change of cross-shore and longshore sediment transports caused by Meari that leads to the beach morphological changes, and most of the sediment transports occur during the pre-Meari landing phase. The erosional scarp formation and the berm or beach face erosion are the main geomorphological responses of the beaches to the storm. The storm characteristics are more important than the beach shapes in the storm response process of the beaches on Shandong Peninsula. The typhoon is a fortuitous strong dynamic event, and the effect on the dissipative beach is more obvious than it is on the reflective beach in the study region. Furthermore, the beach trend is the main factor that controlls the storm effect intensity, and it is also closely related to the recovery of the beach profiles.

Potential application of oil-suspended particulate matter aggregates (OSA) on the remediation of reflective beaches impacted by petroleum: a mesocosm simulation.

This paper presents the oil-suspended particulate matter aggregate (OSA) resulted from the interaction of droplets of dispersed oil in a water column and particulate matter. This structure reduces the adhesion of oil on solid surfaces, promotes dispersion, and may accelerate degradation processes. The effects of the addition of fine sediments (clay + silt) on the formation of OSA, their impact on the dispersion and degradation of the oil, and their potential use in recovering reflective sandy beaches were evaluated in a mesoscale simulation model. Two simulations were performed (21days), in the absence and presence of fine sediments, with four units in each simulation using oil from the Recôncavo Basin. The results showed that the use of fine sediment increased the dispersion of the oil in the water column up to four times in relation to the sandy sediment. There was no evidence of the transport of hydrocarbons in bottom sediments associated with fine sediments that would have accelerated the dispersion and degradation rates of the oil. Most of the OSA that formed in this process remained in the water column, where the degradation processes were more effective. Over the 21days of simulation, we observed a 40% reduction on average of the levels of saturated hydrocarbons staining the surface oil.

Beach morphology and coastline evolution in the southern Bohai Strait

The beach studied in this paper spans a length of 51 km and is one of several long sandy beaches in the southern Bohai Strait. Due to the obstruction of islands in the northeast and the influence of the underwater topography, the wave environment in the offshore area is complex; beach types and sediment transport characteristics vary along different coasts. The coastlines extracted from six aerial photographs in different years were compared to demonstrate the evolving features. Seven typical beach profiles were selected to study the lateral beach variation characteristics. Continuous wind and wave observation data from Beihuangcheng ocean station during 2009 were employed for the hindcast of the local wave environment using a regional spectral wave model. Then the results of the wave hindcast were incorporated into the LITDRIFT model to compute the sediment transport rates and directions along the coasts and analyze the longshore sand movement. The results show that the coastline evolution of sand beaches in the southern Bohai Strait has spatial and temporal variations and the coast can be divided into four typical regions. Region (I), the north coast of Qimudao, is a slightly eroded and dissipative beach with a large sediment transport rate; Region (II), the southwest coast of Gangluan Port, is a slightly deposited and dissipative beach with moderate sediment transport rate; Region (III), in the central area, is a beach that is gradually transformed from a slightly eroded dissipative beach to a moderately or slightly strong eroded bar-trough beach from west to east with a relatively moderate sediment transport rate. Region (IV), on the east coast, is a strongly eroded and reflective beach with a weak sediment transport rate. The wave conditions exhibit an increasing trend from west to east in the offshore area. The distribution of the wave-induced current inside the wave breaking region and the littoral sediment transport in the nearshore region exhibit a gradual weakening tendency from west to east, which is opposite to the trend of the wave conditions outside the breaking region. The presence of submerged shoal (Dengzhou Shoal), deep trough (Dengzhou Channel), islands and irregular topography influnces the wave climate, beach types, wave-induced current features, littoral sediment transport trends and coastline evolution patterns in the southern Bohai Strait. Human activities, such as the sand exploitation of Dengzhou Shoal and other coastal engineering projects, also influence the beach morphology and coastline evolution.

Transport of larvae and detritus across the surf zone of a steep reflective pocket beach

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 528:71-86 (2015) - DOI: https://doi.org/10.3354/meps11223 Transport of larvae and detritus across the surf zone of a steep reflective pocket beach Alan L. Shanks1,*, Jamie MacMahan2, Steven G. Morgan3, Ad J. H. M Reniers4, Marley Jarvis1, Jenna Brown2, Atsushi Fujimura4, Chris Griesemer3 1Oregon Institute of Marine Biology, University of Oregon, PO Box 5389, Charleston, Oregon 97420, USA 2Department of Oceanography, Naval Postgraduate School, 327c Spanagel Hall, Monterey, California 93943, USA 3Bodega Marine Laboratory, Department of Environmental Science and Policy, University of California Davis, 2099 Westside Dr., Bodega Bay, California 94923-0247, USA 4Department of Hydraulic Engineering, Delft University of Technology, Civil Engineering and Geosciences, Stevinweg 1, 2628CN Delft, The Netherlands *Corresponding author: ashanks@uoregon.edu ABSTRACT: Larvae of many intertidal species develop offshore and must cross the surf zone to complete their onshore migration to adult habitats. Depending on hydrodynamics, the surf zone may limit this migration, especially on reflective rocky shores. As a logistically tractable analog of a rocky shore environment, we carried out a comprehensive biological and physical study of the hydrodynamics of a steep reflective sandy beach. Holoplankton and precompetent larval invertebrates were much less abundant within the surf zone than offshore, and their concentrations inside and outside the surf zone were not significantly correlated, suggesting that they were not entering the surf zone. Persistent offshore flow throughout the water column at the outer edge of the surf zone may prevent these organisms from entering the surf zone. In contrast, the concentrations of detritus and a competent larval invertebrate (i.e. cyprids), while also not significantly correlated with concentrations offshore, were frequently more concentrated in the surf zone than offshore. Within the surf zone, the concentration of detritus was significantly correlated with concentrations of competent larval invertebrates (barnacles, gastropods, polychaetes, and bopyrid amphipod) and organisms that may be associated with detritus (amphipods and harpacticoid copepods). These concentrations were significantly negatively correlated with average daily wave height. We hypothesize that detritus and larvae enter the surf zone near the bottom during calm wave conditions by a process of near-bottom streaming. Near-bottom streaming is associated with all surf zones and may be a general mechanism for onshore transport of larvae close to the coast. KEY WORDS: Streaming · Cyprids · Competent larvae · Precompetent larvae · Detritus · Reflective beach · Cross-shore exchange Full text in pdf format PreviousNextCite this article as: Shanks AL, MacMahan J, Morgan SG, Reniers AJHM and others (2015) Transport of larvae and detritus across the surf zone of a steep reflective pocket beach. Mar Ecol Prog Ser 528:71-86. https://doi.org/10.3354/meps11223 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 528. Online publication date: May 28, 2015 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2015 Inter-Research.

Ghost crab populations respond to changing morphodynamic and habitat properties on sandy beaches

The morphodynamic state and habitat properties of microtidal sandy beaches largely account for variations in macrofauna structure. In ecological theory, the habitat harshness hypothesis and the habitat safety hypothesis explain variations in macrofauna populations of the intertidal and supratidal zones of sandy beaches. The former hypothesis states that intertidal macrofauna should increase from reflective to dissipative beaches. The latter hypothesis supports the idea that supratidal species are more successful on reflective beaches, given their relative independence from the swash. However, trends in abundance of supratidal species, particularly crustaceans, have been unclear and further investigation is therefore needed. This study tested the two hypotheses on the largest invertebrate intertidal-to-supratidal crustacean on sandy beaches, namely the ghost crab (genus Ocypode). Variations in ghost crab burrow density, abundance, size and across-shore distribution were measured on four warm-temperate microtidal sandy beaches in KwaZulu-Natal, South Africa. Burrow numbers increased with beach morphodynamic state, while average burrow size decreased. The steepest, narrowest and most inundation-prone beach represented the least hospitable environment for the ghost crabs. The results that are reported here tend to support the habitat harshness hypothesis. However, the relevance of i) individual physical variables, ii) tidal action, and iii) the ecology of various species, in shaping ghost crab population dynamics, is also discussed. The results contribute to the knowledge regarding population dynamics of intertidal and supratidal crustaceans across beach types.

HIGH FREQUENCY MONITORING OF SWASH HYDRO-MORPHODYNAMICS ON A REFLECTIVE BEACH (GRAND POPO, BENIN): A NEW METHOD

A new remote sensing video-based method for measuring rapid variations of the bed elevation and free-surface in the swash zone is tested on a steep reflective beach at Grand Popo. The key assumption is that the free-surface has a distinguishable optical signature with respect to the bed level. This new set up enables a high frequency description of the wave transformation, dissipation and reflection in the swash zone as well as the variations of the bed evolution at the wave-by-wave scale. At a more integrated scale, a good correlation is found between the offshore reflected energy measured by an ADCP, the incident offshore wave characteristics and the swash local morphology, suggesting the importance of the swash dynamics on the energy reflection mechanism.

Saccocirridae (Annelida) from the southern and southeastern Brazilian coasts

Pharyngocirrus gabriellae (Du Bois-Reymond Marcus 1946) and Saccocirrus pussicus Du Bois-Reymond Marcus 1948 are redescribed based on newly collected material from the south and southeastern Brazilian coasts. Neotypes are designated, since no type material was formally indicated in the original descriptions. New morphological information on the muscular ventral pharynx, ciliation, chaetae and pygidium is provided. Pharyngocirrus gabriellae is additionally characterised by the presence of mouth ciliary patches, capillary lyrate chaetae with a single median tooth and equally bifid medium chaetae with denticulate prongs. The novel diagnostic characters of Saccocirrus pussicus include the absence of a pharynx and the presence of 1–3 pygidial, adhesive ridges and 20 fertile segments. The two species live in very distinct interstitial habitats, with varying hydrodynamics. Pharyngocirrus gabriellae is found at sheltered intertidal and shallow areas in sediments with a redox layer, whereas Saccocirrus pussicus prefers the swash zone of exposed, oxygenated, reflective beaches. Morphology and habitat preferences of P. gabriellae and S. pussicus are consistent with other Saccocirridae species from the ‘Pharyngocirrus’ and ‘Saccocirrus’ genera, respectively.

Response of the meiofaunal annelid Saccocirrus pussicus (Saccocirridae) to sandy beach morphodynamics

Interstitial annelids in the family Saccocirridae live in the extremely turbulent and dynamic swash zone of exposed sandy beaches. We examine herein the relationship between distribution patterns of Saccocirrus pussicus du Bois-Reymond Marcus 1948 and morphodynamics, hydrodynamic zones, and environmental variables at beaches sampled along the Brazilian Atlantic coast. The occurrence and the abundance of S. pussicus at regional scale were positively correlated with the presence of a steep slope, large waves and coarse sand, which are characteristic of reflective beaches. On a local scale, S. pussicus occurred at the swash zone and breaking surf zone of reflective beaches. On a microscale, it preferred the upper 20 cm of the swash zone sediment. Saccocirrus pussicus prefers hydrodynamic zones, which change temporally, suggesting dependence with the dynamics of the surging and plunging waves. The coupling of morphological and behavioral adaptations of S. pussicus to beach morphodynamics is crucial for understanding its surfing life strategies within turbulent environments.

Fish assemblages along a morphodynamic continuum on three tropical beaches

A comparative study involving three mesotidal beaches from reflective to estuarine states was conducted between October 2010 and September 2011 in the estuary of Mamanguape River, northeastern Brazil. The aim was to test for differences in fish assemblages along a morphodynamic continuum, particularly the effects of wave action. In total, 3,732 fish from 71 species were examined; Rhinosardinia bahiensisand Atherinella brasiliensisdominated the estuarine beach, whereas Trachinotus carolinus dominated the reflective beach. Fish assemblages were structured by spatial differences among the sites, and overall abundance, richness and biomass demonstrated a clear increasing trend from the reflective to the estuarine beaches, indicating a primary influence of wave exposure in the measured parameters. The Mamanguape River estuary plays a crucial ecological role as a nursery for several species that depend on its resources and have adapted to the high variability of its physical and chemical factors and the diversity of its habitats.

Effects of morphodynamics and across-shore physical gradients on benthic macroinfauna on two sandy beaches in south-eastern Brazil

We examined the benthic macroinfauna at three strata during two seasons (winter and summer) on two sandy beaches (dissipative and reflective) in south-eastern Brazil. The hypothesis raised is that effects of morphodynamics and zonation determine the structure of macroinfauna, with dissipative beaches having comparatively higher species richness and density than the reflective beaches. Flamengo beach (dissipative) had higher species richness but lower density compared to Grumari beach (reflective). A high dissimilarity in assemblage structure (91.75%) was detected between the two beaches. Zonation in the occurrence of macroinfauna was detected for the two beaches in the two examined seasons. At Grumari beach, Emerita brasiliensis occurred mainly in stratum 1 (intertidal swept zone) while Saccocirus sp. occurred in stratum 2 (infralittoral at 0.5 m depth), whereas at Flamengo beach E. brasiliensis and Enoploides sp. had the highest density in stratum 1 (intertidal swept zone) whereas Scolelepis goodbodyi and Donax uncinata dominated in stratum 3 (infralittoral at 1.0 m depth). Scolelepis goodbodyi, Dispio uncinata, Enoploides sp., Nematoda and Trileptium sp. were associated with higher a Dean parameter and content of organic matter at Flamengo beach. In contrast, Hastula sp., Donax sp., Pisionidens indica, Hemipodus californiensis, Saccocirus sp. and Phyllodocidae were associated with the higher wave period and grain size of Grumari beach. The hypothesis that macroinfauna structure differs between the beaches and strata was confirmed, with the dissipative beaches having comparatively higher richness but lower density than the reflective beaches.

An attempt to extend the Habitat Harshness Hypothesis to tidal flats: A case study of Anomalocardia brasiliana (Bivalvia: Veneridae) reproductive biology

The Habitat Harshness Hypothesis (HHH) predicts that populations inhabiting the intertidal area of a dissipative beach should produce more gametes and have a longer reproductive cycle than those inhabiting an intermediate or reflective beach. This hypothesis was proposed for the exposed morphodynamic continuum between the reflective and dissipative states; however, no attempt has been made thus far to verify whether the HHH is valid for tidal flats. In this study, we analysed the reproductive cycle of Anomalocardia brasiliana in an intermediate beach and in a tidal flat and compared the results to determine whether the reproductive cycles of A. brasiliana were in agreement with the predictions of the HHH and to examine the possibility of extending this hypothesis to tidal flats. A continuous spawning season and synchrony between sexes were observed at both sites, although the reproductive effort was higher in the intermediate beach. The results of this first attempt did not support the extension of the HHH to tidal flats. It is possible that hypotheses that take into account only physical variables may not be the most adequate for describing environments with such a high species richness and high abundance as tidal flats. Nevertheless, other studies are necessary to confidently expand or refute the HHH with regard to tidal flats, and this topic should be considered as a priority in future investigations in sandy beach ecology.