Tisular and population level responses to habitat harshness in sandy beaches: the reproductive strategy of <Emphasis Type="Italic">Donax hanleyanus</Emphasis>

Microscopic analysis and field sampling procedures were used to compare demographic and reproductive strategies of the intertidal wedge clam Donax hanleyanus (Bivalvia: Donacidae) in two exposed sandy beaches with contrasting morphodynamics (reflective vs. dissipative) during 13 consecutive months. Histological analysis showed that: (1) the reproductive cycle of D. hanleyanus was more extended in the dissipative beach, and this was true for all the three pre-active (beginning of gonadal activity), active (maturation) and spawning stages; and (2) males and females showed significantly smaller sizes at sexual maturity at the reflective beach. Even though successive increments in proportion and mature at size were observed, the sigmoid function was significantly steeper at the reflective Arachania for both sexes, suggesting an abrupt transition to maturity. Field sampling revealed a more extended recruitment period at the dissipative beach, where recruits were also significantly more abundant than at the reflective beach. These results give support for the habitat harshness hypothesis, which predicts that in intertidal species capable of sustaining populations across a wide spectrum of physical conditions, such as D. hanleyanus, abundance, recruitment, size at maturity and extent of reproductive and recruitment seasons increase from reflective to dissipative beaches. However, a recent hypothesis suggests that reflective beaches acting as sink populations were not sustained, because mature and spawning individuals of both sexes were found in the reflective beach throughout the study period. Thus, we suggest that post-settlement processes are critical in modulating population patterns for this bivalve.     

Discarded queen conch (<Emphasis Type="Italic">Strombus gigas</Emphasis>) shells as shelter sites for fish

Within the Caribbean millions of queen conch (Strombus gigas Linnaeus) are harvested each year and shells discarded randomly or as middens. Fish use of discarded conch shells was investigated in four different habitat types: sand, seagrass beds, mangrove forests, and coral reefs. The study was carried out in the waters off South Caicos, Turks and Caicos Islands (TCI), between October 2003 and January 2004. The density of discarded shells was greatest near coral reefs; however, the percentage of shells occupied by adult fish was higher in isolated shells on sand and in mangrove habitats. Juvenile fish also showed a preference for sheltering in conch shells relative to other microhabitat types on sandy plains and in mangrove and seagrass habitats. Differences in use of single shells by fish in different habitats were attributed to differences in piscivore abundance and habitat complexity. Although not all isolated shells were occupied by fish, all conch middens deposited by fishermen had fish inhabitants. Examination of fish use of conch middens in three habitat types and conch piles of one, three, and five shells constructed on sand found both fish diversity and abundance increased on conch middens of increasing size. This study suggests that disposal of conch shells as large middens in habitats of low complexity will increase the amount of shelter present and may enhance fish populations in these habitats.Communicated by J.P. Grassle, New Brunswick     

Habitat harshness and morphodynamics: life history traits of the mole crab Emerita brasiliensis in Uruguayan sandy beaches

The habitat harshness hypothesis (HHH) postulates that in reflective beaches the harsh environment forces organisms to divert more energy towards maintenance and they therefore have lower abundance, fecundity, growth and survival rates than in dissipative beaches. Recent investigations have tested this hypothesis through single comparisons of only two beaches, and thus the observed trends in population level variables cannot be attributed incontestably to the beach state, but only to location. Here, abundance, reproduction, recruitment, population structure and body size of the intertidal mole crab Emerita brasiliensis were compared between populations from eight microtidal exposed sandy beaches with contrasting morphodynamics, sampled bimonthly during 22 months throughout the 180 km Uruguayan Atlantic coast. Physical variables and compound indices of the beach state were used to categorize sandy beaches. The results of this bi-annual large-scale analysis were fully consistent with the predictions of the HHH: abundance (total and population components), duration of the reproduction and recruitment seasons and the individual size of megalops and females of the mole crab E. brasiliensis decreased from dissipative to reflective beaches. This was reflected by linear or, mostly, nonlinear relationships between biological and both physical variables and compound indices of beach state. In conclusion, this multi-beach sampling provides compelling evidence of a consistent response of demographic and life history traits of an intertidal beach species to morphodynamic characteristics.     

Hydrodynamic patterns in lotic intertidal sands and their bioclimatological implications

Water movement is probably the most important factor influencing life in the interstices of sandy beaches. In order to better understand this ecosystem, e.g. the distribution and migration of interstitial fauna and overall energy transfer, measurements of water flow through high energy beaches were made on the Atlantic coast of the USA. Special hot thermistor-probes and associated electronic circuits were built, capable of measuring water-flow velocity down to less than 10 m/sec. These were buried in the sand at various depths and locations in the intertidal zone and the flow velocity recorded continuously for one or more tidal cycles. In addition, an orientation sensor was constructed and used together with the flow probe so that a picture of the flow patterns in the intertidal zone of a beach and their changes during a tidal pattern could be developed and defined quantitatively.     

Geographic mosaic of mutually exclusive dominance of obligate commensals in symbiotic communities associated with a burrowing echiuran worm

Species richness and community composition of symbionts associated with the burrowing echiuran worm, Ochetostoma erythrogrammon Leuckart & Rüppell, 1828, were quantitatively surveyed on subtropical intertidal flats in the Ryukyu Archipelago, Japan. Overall, we recorded seven species of burrow associates, including at least six obligate commensals. According to symbiont community composition, the study sites were largely divided into two groups; one was characterized by the dominance of a snapping shrimp, Alpheus barbatus Coutière, 1897, and the other by the dominance of a scale worm, Lepidonotus sp. Furthermore, a granulometric analysis showed that the sediment characteristics differed significantly between shrimp- and scale worm-dominant sites in terms of median diameter and inclusive graphic standard deviation. These results suggest that these symbionts have different habitat requirements, resulting in the mutually exclusive dominance pattern. Our findings indicate that habitat heterogeneity is important to the evaluation and conservation of the symbiotic diversity in intertidal flats.     

Topographic heterogeneity influences fish use of an experimentally restored tidal marsh.

Ecological theory predicts that incorporating habitat heterogeneity into restoration sites should enhance diversity and key functions, yet research is limited on how topographic heterogeneity affects higher trophic levels. Our large (8-ha) southern California restoration experiment tested effects of tidal creek networks and pools on trophic structure of salt marsh habitat and high-tide use by two regionally dominant fish species, California killifish (Fundulus parvipinnis) and longjaw mudsucker (Gillichthys mirabilis). We expected tidal creeks to function as "conduits" that would enhance connectivity between subtidal and intertidal habitat and pools to serve as microhabitat "oases" for fishes. Pools did provide abundant invertebrate prey and were a preferred microhabitat for F. parvipinnis, even when the entire marsh was inundated (catch rates were 61% higher in pools). However, G. mirabilis showed no preference for pools. At a larger scale, effects of tidal creek networks were also mixed. Areas containing creeks had 12% higher catch rates of G. mirabilis, but lower catch rates and feeding rates of F. parvipinnis. Collectively, the results indicate that restoring multiple forms of heterogeneity is required to provide opportunities for multiple target consumers.     

Zonation of the interstitial polychaeteStygocapitella subterranea (Stygocapitellidae) in European sandy beaches

The zonation ofStygocapitella subterranea Knoellner (Polychaeta, Stygocapitellidae) in sandy beaches is compared for several localities along the European coasts. In tidal beaches the species occupies a zone near average high tide level (AHTL), whereas in non-tidal beaches it is found at a fairly long distance from the water line. The regularities observed inS. subterranea indicate that the interstitial fauna may prove well suited for the establishment of a general scheme of zonation in sandy beaches analogous to that for rocky shores proposed byStephenson andStephenson (1949).     

The contribution of seagrass beds (<Emphasis Type="Italic">Zostera noltii</Emphasis>) to the function of tidal flats as a juvenile habitat for dominant,mobile epibenthos in the Wadden Sea

Since the substantial loss of subtidal eelgrass (Zostera marina L.) in the 1930s, seagrass beds in the Wadden Sea are limited to the intertidal zone and dominated by Z. noltii Hornem. This study deals with the effect of vegetated tidal flats on quantities of mobile epifauna and proves empirically the function of seagrass canopies as a refuge for marine animals remaining in the intertidal zone at ebb tide. Drop-trap samples were taken in the Sylt-Rømø Bight, a shallow tidal basin in the northern Wadden Sea, on vegetated and unvegetated tidal flats during July and August 2002, and during the entire growth period of Z. noltii from May to September in 2003. The species composition in Z. noltii and bare sand flats showed minor differences since only two isopod species (Idotea baltica and I. chelipes) occurred on Z. noltii flats exclusively. Juvenile shore crabs (Carcinus maenas L.), brown shrimps (Crangon crangon L.) and common gobies (Pomatoschistus microps Krøyer) were also found abundantly on bare sand flats. However, the results showed significantly higher abundances and production of these dominant species on vegetated tidal flats. Additionally, the analyses of faunal size classes indicated higher percentages of small individuals in the seagrass bed during the entire sampling period. Despite drastic diurnal fluctuations of dissolved oxygen at low tide, faunal density in the residual water layer remaining in seagrass canopies at ebb tide was found to be consistently higher than that found in artificially created tide-pool units. Although species composition of mobile epifauna did not basically differ between vegetated and unvegetated tidal flats, Z. noltii beds are considered to contribute quantitatively to the function of tidal flats, as an extended juvenile habitat for some of the most important species of the Wadden Sea food web.Communicated by O. Kinne, Oldendorf/Luhe     

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.     

Comparative species composition and relative abundance of decapod crustaceans in marine habitats of Panamá

The community structure of the decapod crustacean fauna of 7 tropical, shallowwater, marine habitats (sandy beaches, mangrove swamps and rocky intertidal habitats on both the Pacific and Caribbean coasts of Panama, and Pocillopora damicornis coral habitat of the Bay of Panama) were examined and analyzed for species composition and relative abundances. Collections from the 7 habitats yielded 4361 individuals, representing 236 species. The number of species per habitat was (Pacific, Caribbean): sandy beach (16, 7); mangrove (20, 17); P. damicornis (53); rocky intertidal (78, 67). There were more species represented by more individuals in the Pacific habitats. An index of faunal similarity was calculated for each pair (Pacific-Caribbean) of habitats. This index is the number of ecologically similar congeneric species which occurred in both habitats expressed as a percentage of the total number of species present in the pair of habitats. For the sandy beach communities there were three Pacific species which were similar to three Caribbean species, a similarity of 6/23 or 26%. The index of similarity for the mangrove communities is 54% and for the rocky intertidal communities it is 37%. The P. damicornis community has affinities with the Pacific rocky intertidal community (18%), with that of the Caribbean rocky intertidal (16%) and with that of Indo-West Pacific pocilloporid corals (20%). A few specialized species dominated each of the communities. The habitats and the number of species accounting for over half of the individuals present are (Pacific, Caribbean): sandy beach (1, 1); mangrove (4, 4); P. damicornis (5); and rocky intertidal (3, 6). Most of the species in each community were represented by one or a few individuals.     

Plasticity of biometrical and mechanical properties of Echinocardium cordatum spines according to environment

We investigated the plasticity of spines of the burrowing heart urchin Echinocardium cordatum inhabiting sandy beaches. This urchin has very specialized spines which play specific roles in feeding and locomotion. Biometrical and mechanical properties of the spine skeleton of individuals from a wave-exposed intertidal site and a protected subtidal site (Brittany, France) were compared and related to sediment grain size, food supply and urchin small-scale distribution and burrowing depth. The intertidal site was characterized by coarser sand; the urchins were more scattered and more deeply buried than in the subtidal site. Intertidal urchins were bigger than subtidal urchins but showed similar resource allocation. Spines of intertidal urchins were longer than those of subtidal urchins, their architecture was reinforced and they presented a higher fracture force and stiffness. These spine differences would be essentially due to passive plasticity, but could also be adaptative at a certain extent.     

Diatoms of the microphytobenthic community in a tropical intertidal sand flat influenced by monsoons: spatial and temporal variations

Seasonal variations in the microphytobenthic diatom community were investigated in an intertidal sand flat of a tropical marine environment influenced by monsoons. Cores of sediments were collected along the beach gradient: low tide, mid tide and high tide zone up to a depth of 15 cm.. Diatom abundance was lowest during the monsoons and highest during the post-monsoons and the early pre-monsoon season throughout the intertidal transect. Diatom diversity was highest at the mid tide, followed by the high and low tide zones. Diatoms were viable up to a depth of 15 cm throughout the intertidal transect. The diatom community included the pennates, the permanent residents of this area, centric genera, which lead an attached mode of life and also some planktonic genera, brought in from ambient waters. Among the pennates, Navicula and Amphora were the dominant genera whereas in the case of centrics, Thalassiosira dominated the community throughout the intertidal transect down to a 15 cm depth. . Grain size fractions, which served as predictors of some diatom genera changed with tidal zones. The effect of winds on the resuspension of the pennate diatoms was evident only at the low tide zone down to a depth of 5 cm . Chlorophyll a concentration proved to be a good predictor of both pennate and centric diatom abundance at the low tide zone down to a depth of 10 cm and at the mid tide zone down to a depth of 5 cm.. However, even though chlorophyll a concentrations failed to reveal any positive correlation with the diatom abundance at both the deeper sediment layers and the high tide zone, the fact that viable cells were present at these areas reveal that the diatoms adopt survival strategies, contributing significantly to the carbon budgets of such unstable habitats.     

Analysis of lipid components for determining the condition of anchovy larvae,Engraulis mordax

It has been presumed that intertidal spawning by Limulus polyphemus minimizes the loss of egges to subtidal predators; however, this strategy involves considerable risks. Massive beach strandings of adults accompany seasonal spawning migrations of crabs along Cape May in Delaware Bay, (USA). At least 190000 horseshoe crabs, approximating 10% of the adult population, died from beach stranding along the New Jersey shore of Delaware Bay during the 1986 (May to June) spawning season. Abnormalities of the telson (which is used in righting behavior) were significantly more common among stranded crabs than among individuals actively spawning on the intertidal beach. The number of stranded crabs per day was not correlated with tidal height or environmental variables (wind speed, wave height) which characterized the conditions at spawning. A complex suite of factors, including the size of the available spawning population, tidal and weather conditions, and beach slope, influence the number stranded during the breeding season. Horseshoe crab stranding results in a large loss of gravid females from the population, and may represent a major input of organic matter to intertidal sandy beaches in certain regions of Delaware Bay.     

Geographical patterns in reproductive biology of the Pan-American sandy beach isopod<Emphasis Type="Italic"> Excirolana braziliensis</Emphasis>

Eleven populations of the Pan-American sandy beach isopod Excirolana braziliensis, distributed from tropical (9°N) to temperate (39°S) sandy beaches in Atlantic and Pacific Oceans, were analyzed to determine latitudinal variations in: breeding and recruitment patterns, sex ratios, size of ovigerous females and of juveniles and length–fecundity relationships. E. braziliensis exhibited strong latitudinal patterns in all reproductive traits throughout its distribution range. Breeding and recruitment shifted from continuous to seasonal from tropical to temperate beaches, having a predominance of females at higher latitudes. In agreement with the latitudinal gradient hypothesis, ovigerous females inhabiting tropical sandy beaches (low latitudes) were smaller, became sexually mature at smaller sizes and had lower individual fecundity than on temperate beaches. Juveniles were also smallest at low latitudes. Between-ocean comparisons showed very similar reproductive characteristics for roughly the same latitude. These linked reproductive parameters suggest that the intensity of breeding effort is associated with the duration of the breeding season and geographically size-related characteristics of the species. Geographic variations in the breeding and recruitment seasons, as well as in individual fecundity, size structure of mature females and sex ratios, are proposed to have major consequences in explaining local variations in population demography. Our paper also reinforces the notion that sandy beach animals are highly plastic.Communicated by O. Kinne, Oldendorf/Luhe     

Home range and habitat utilization of adult California sheephead,<Emphasis Type="Italic"> Semicossyphus pulcher</Emphasis> (Labridae), in a temperate no-take marine reserve

The California sheephead, Semicossyphus pulcher Ayres (Labridae), is a carnivorous, temperate, rocky-reef/kelp-bed species that is highly sought in recreational and commercial fisheries. Fine-scale acoustic telemetry tracking was used to ascertain the home range and habitat utilization of S. pulcher. Sixteen adult S. pulcher (26–38 cm SL) were surgically fitted with small acoustic transmitters and manually tracked for up to 144 h during multiple, 24-h periods between March 2001 and August 2002 within the Catalina Marine Science Center Marine Life Reserve (33°26N; 118°29W). A geographic information system was used to calculate home range sizes (95% kernel utilization distributions) and habitat use. Tracking of the first five fish over 24 h confirmed that S. pulcher were strictly diurnal, so the remaining 11 fish were tracked from 1 h before sunrise to 1 h after sunset. Home ranges varied greatly, from 938 to 82,070 m², with a mean (±SD) of 15,134±26,007 m². Variability in home range sizes among fish was attributed to differences in habitat shape (embayment vs. contiguous coastline) and to natural habitat boundaries (deep, sandy expanses) in adjacent areas within the reserve. There was a significant relationship between fish length and proportion of time spent in different habitats (sand vs. reef). S. pulcher were found within rocky-reef areas 54% of the time, and, within these areas, a greater percentage of daytime was spent in high-relief areas. Based on the relatively small size and persistence of home ranges of adult S. pulcher, no-take reserves, if they contain appropriate habitat, would provide adequate protection for their stocks.Electronic Supplementary Material Supplementary material is available in the online version of this article at http://dx.doi.org/10.1007/s00227-005-1573-1.Communicated by J.P. Grassle, New Brunswick     

Active swimming in meiobenthic copepods of seagrass beds: geographic comparisons of abundances and reproductive characteristics

The entry of meiobenthic copepods from sediments or seagrass blades into the water column and reproductive characteristics of actively migrating fauna were investigated from 1981–1986 in a temperate intertidal Zostera capricorni seagrass bed in Pautahanui Inlet, New Zealand and in a subtidal Thalassia testudinum bed in Tampa Bay, Florida, USA. Emergence of copepods in New Zealand varied over a tidalcycle, while in Florida a distinct diel periodicity was displayed. Selected copepod species in New Zealand had similar numbers emerging from sediments and/or blades over a 6 h period as the common copepods actively migrating from sediments in Florida. Daily abundances of emerging copepods (24 h) in Tampa Bay, Florida, were substantially greater than those in New Zealand, where migration is linked to tidal cover. In Z. capricorni meadows in New Zealand, sex ratios of copepods in sediments and on blades were dominated by females; males dominated water-column samples. In T. testudinum meadows in Tampa Bay, sex ratios of males to females, although of a lowermagnitude than in Z. capricorni beds, were higher in trap than in sediment samples. Differences in sex ratios, the availability in emergence traps of females of appropriate stage for mating, and observations on clasping in live samples from traps suggest that swimming behavior in copepods may be partly linked to prenuptial courtship. Meiobenthic copepods may use the water column as an important habitat for reproductive behavior.     

Spatial structure of an intertidal molluscan assemblage on a sheltered sandy beach

The intertidal molluscan fauna on a sandy-mud beach in Newport Bay, California, USA, is divisible into two vertically distinct species assemblages which correspond to the midlittoral zone and sublittoral fringe observed on rocky coastlines and exposed sandy beaches. The species assemblage comprising the midlittoral zone is unusual, however, in that the numerically dominant species are not confined to this zone but range downward through the sublittoral fringe. The two species assemblages are vertically separated at +0.5 to +1.0 ft (+0.15 to +0.30 m; relative to 0.0 tidal datum at mean lower low water), which is higher than previously observed for the separation between the midlittoral zone and sublittoral fringe on rocky shores and exposed sandy beaches. The species composition of some of the samples at +0.5 and +1.0 ft (+0.15 and +0.30 m) was intermediate between samples higher and lower on the beach, while several samples were devoid of molluscs altogether. Additionally, the surface sedimentary environment changes in terms of an increased percent silt-clay fraction and higher sorting coefficients below +0.5 ft (+0.15 m). Since infaunal zonation is correlated with tidal height at the substrate surface, environmental factors operative at the surface are probably most important in influencing the zonation on this beach.     

Behaviour and distribution of the sand-beach amphipod Orchestoidea corniculata

The field distribution of Orchestoidea corniculata Stont a talitrid amphipod inhabiting the upper intertidal zone of sandy beaches, was measured by pitfall trap and subsurface core transects. Variations in the distribution of juveniles and adults were recorded. At Coal Oil Point (Goleta, California, USA), the population was concentrated on the leeward side of the Point and, with increasing distance from the Point, both the number and size of beachhoppers decreased. The amphipods burrowed in a 5 to 7 m wide band during the day, and were active over a 15 to 25 m area at night. When they emerged from their burrows, a net seaward movement of 3 m was observed for the population. Behavioural tests suggested that sand penetrability is an important factor determining the location of burrow sites. Diurnal orientation was investigated, and it was found that the amphipods oriented in a landward direction despite overcast sky conditions, beach slope, moisture gradients, or displacement to a new beach.     

Foraging impact on zooplankton by age-0 walleye pollock (<Emphasis Type="Italic">Theragra chalcogramma</Emphasis>) around a front in the southeast Bering Sea

The waters around the Pribilof Islands in the southeast Bering Sea are a center of abundance for age-0 walleye pollock (Theragra chalcogramma). Each spring and summer a tidal front is formed around the islands separating a well-mixed inshore habitat from a stratified offshore habitat. The objective of this study was to assess the foraging impact on zooplankton by age-0 pollock in the vicinity of this frontal structure. A bioenergetic model was used to estimate age-0 pollock food consumption from field estimates of water temperature, age-0 pollock density, diet and growth. Sampling of field variables took place over three hydrographic habitats along an inshore–offshore transect located north of the islands. The bioenergetics analysis was applied for a 2-week period during the late summer of four consecutive years, 1994–1997. Model results of age-0 pollock food consumption indicated variable levels of food depletion, changing with prey type, year and habitat. The foraging impact of age-0 pollock on copepods and euphausiids (most common prey) ranged from about 3% to 77% of the biomass available at the start of the simulation. Copepod depletion was typically greater than euphausiid depletion. Consequently, juvenile pollock <60 mm in standard length were more likely to experience food limitation due to the greater proportion of copepods in their diet. We present evidence of severe foraging impact during 1996, when one of the primary prey items of juvenile pollock (i.e. large copepods) was scarcely represented both in their diet and in the water column. In all years, most instances of prey depletion were found at the inshore and front habitats; age-0 pollock densities were too low relative to their prey to severely impact the offshore zooplankton populations. We discuss these results with respect to modeling assumptions and in the context of previously acquired knowledge of fish behavior around frontal regions.Communicated by T. Ikeda, Hakodate