Assessing cockle shells (Anadara granosa) for reconstruction subdaily environmental parameters: Implication for paleoclimate studies

This study aims to investigate the potential of cockle shells as an environmental recorder, examining the environmental factors controlling the shell growth of the intertidal Anadara granosa from west coast of Malaysia. Subdaily environmental factors were recorded from December 2011 to November 2012. A total of 600 individuals were collected on a monthly basis and the shells sectioned from umbo to ventral margin, polished, etched and photographed under a light microscope to observe microgrowth bands and increments. Comparison of correlation matrix between mean increment width and each environmental factor indicated that shell growth had the highest positive correlation with seawater temperature (+0.72) and weak positive correlation with salinity (+0.53). Multiple regression analysis was used to assess independent associations between shell mean increment width and environmental parameters. Study model showed that 60.8% of the variation in shell growth could be explained by temperature, salinity, rainfall and tidal change. Individually, temperature and salinity made the greatest unique contribution to explain shell growth, respectively (p < 0.01). Laboratory results showed shell growth was in a linear trend to optimum temperature and salinity. These findings provide a basis for the interpretation of the temporal changes in shell microgrowth patterns in terms of environmental conditions of cockle shells.     

An environmentally induced tidal periodicity of microgrowth increment formation in subtidal populations of the clam Ruditapes philippinarum

The periodicity of increment formation in the shell of the Manila clam Ruditapes philippinarum was investigated in the subtidal zone of the Auray River estuary (South Brittany, France). Calcein markings were performed at different periods between May and October 2007 using in situ benthic chambers tented by scuba divers. This study shows that shell microgrowth increments were well-defined and deposited with a tidal periodicity in the subtidal zone, providing the calendar base for high-resolution ecological studies and environmental reconstruction from these R. philippinarum shells. Endogenous rhythmicity in shell microgrowth increment formation and oxygen consumption was previously documented in this species from intertidal flats. Our study suggests that, in the subtidal zone, Manila clams' rhythmic activity may be controlled by such an endogenous process, synchronized by tidal cues. As in other bivalves, R. philippinarum is an osmoconformer euryhaline bivalve. The tidal rhythmicity of shell microgrowth increments in subtidal specimens of this species could be explained by a behavioral adaptation of valve closure at low tide to protect the clam from low salinities and/or to synchronize with food availability. Finally, large inter-individual variability in tidally associated growth rates and asynchronous growth breaks were observed, and could be due to genetic variability between individuals, asynchronous partial spawning events or predation.     

TIDALLY PRODUCED GROWTH BANDS IN THE SUBTIDAL BIVALVE SPISULA SUBTRUNCATA (DA COSTA)

Shells of the subtidal bivalve Spisula subtruncata (da Costa)were marked by treatment with cold shock and allowed to growunder different environmental conditions. In animals kept inthe intertida] zone at low water of spring tides (LWST) theshell banding showed a pattern related to the spring and neaptides. During spring tides when the animals were emersed distinctsemi-diurnal bands were laid down in the shell. However duringneap tides the bands were weaker and ill-defined with an approximatecirca-tidal periodicity. Similarly, animals grown in the laboratoryin a simulated semi-diurnal tidal règime of 11 hourshigh tide, 1 hour low tide and under different light règimes,deposited a number of growth bands which coincided with thenumber of tidal emersions. Individuals continuously immersedin the laboratory and in subtidal boxes in the natural environmentshowed ill-defined growth bands which approximate to a semi-diurnalfrequency. In the laboratory the number of bands deposited wasindependent of any change in the light règimes. Thereis a possibility that an endogenous rhythm of band productionexists which persists when the animals are kept continuouslyimmersed in the laboratory (Received 21 May 1987;     

The mud flat anemone-cockle association: mutualism in the intertidal zone?

The intertidal cockle Austrovenus stutchburyi exists in a symbiotic relationship with the mud flat anemone Anthopleura aureoradiata, the latter using the shell of buried cockles as the only available hard substrate for attachment. The cockles are also host to a detrimental larval trematode Curtuteria australis that invades the bivalves through the filtration current, and here we demonstrate that the anemones significantly depress the rate by which cockles accumulate parasites in the field. Along the tidal gradient, the relative parasite load of cockles was lowest where anemones were most abundant, and the area occupied by anemones per square meter sediment surface explained 30% of the spatial variation in infection intensity. At a smaller spatial scale, parasite loads were significantly lower (34%) in cockles from patches with than without anemones at the same tidal height. A field experiment manipulating the density of anemones showed that the rate of parasite accumulation in cockles decreased with increasing anemone density, and that the generally positive relationship between infection intensity and cockle size tended to disappear in the presence of anemones. The results suggest that the anemone-cockle symbiosis is a non-obligate mutualistic relationship in which the former is provided with a suitable substrate for attachment whereas the latter obtains protection against parasitic infections.     

Parasite Induced Summer Mortality in the Cockle Cerastoderma edule by the Trematode Gymnophallus choledochus

In late summer 2004, a conspicuous cockle (Cerastoderma edule) mortality event was observed on a tidal flat in the northern Wadden Sea (North Sea, Germany) with many fresh valves and still living cockles lying on the sediment surface. To investigate whether trematode parasites utilizing the cockle as first or second intermediate host were involved in this mortality, buried and surfaced cockles were sampled and analyzed, and a laboratory experiment conducted. The field survey showed no statistical difference in intensity of parasites encysted in the foot of cockles. Three species of Himasthla utilizing the cockle as second intermediate host and known to impair the cockle’s burrowing ability were found in buried cockles with 148.4±111.1 metacercariae/foot and in surfaced cockles with 164.2±84.4. There was also no difference in infection levels of parasites utilizing the cockles as second intermediate host in other cockle tissues between buried and surfaced cockles. In contrast, surfaced cockles showed a ten times higher prevalence (71.0%) than buried cockles (7.4%) of the trematode Gymnophallus choledochus – a parasite utilizing the cockle as first (and second) intermediate host – filling almost the entire body cavity and eliminating gonad structures. In an aquarium experiment of 14 days, all cockles found buried on the tidal flat survived compared to only 23.3% found on the surface. This suggests G. choledochus to be a castrating agent and a serious mortality factor in adult cockle populations.     

Estuaries as Filters: The Role of Tidal Marshes in Trace Metal Removal

Flux calculations demonstrate that many estuaries are natural filters for trace metals. Yet, the underlying processes are poorly investigated. In the present study, it was hypothesized that intertidal marshes contribute significantly to the contaminant filter function of estuaries. Trace metal concentrations and sediment characteristics were measured along a transect from the subtidal, over an intertidal flat and marsh to a restored marsh with controlled reduced tide. Metal concentrations in the intertidal and restored marsh were found to be a factor two to five higher than values in the subtidal and intertidal flat sediments. High metal concentrations and high accretion rates indicate a high metal accumulation capacity of the intertidal marshes. Overbank sedimentation in the tidal marshes of the entire estuary was calculated to remove 25% to 50% of the riverine metal influx, even though marshes comprise less than 8% of the total surface of the estuary. In addition, the large-scale implementation of planned tidal marsh restoration projects was estimated to almost double the trace metal storage capacity of the present natural tidal marshes in the estuary.     

Larval and juvenile fishes occurring with flood tides on an intertidal mudflat in the Tama River estuary, central Japan

Intertidal movements of fish larvae and juveniles on a mudflat in the Tama River estuary, central Japan, were investigated by comparing the abundance and sizes of fishes caught in the intertidal zone during flood tides with those in the subtidal zone during low tides. A total of 28465 individuals, belonging to 9 families and 20 species, were collected by small purse seine. Among the abundant species, planktonic larvae and juveniles of gobiids and Konosirus punctatus were more abundant in the intertidal zone at flood tide than the subtidal zone at low tide. Similar occurrence patterns were found in juvenile Plecoglossus altivelis altivelis and Lateolabrax japonicus, having fully developed swimming abilities. In contrast to these species, much higher abundances of epibenthic juveniles of 2 gobiids (Acanthogobius flavimanus and Gymnogobius macrognathos) were found in the subtidal zone at low tide, although they also utilized the intertidal zone at flood tide.     

Tidal activity rhythms and depth distribution of rocky shore fish in an altered intertidal environment

In this note we report on changes of activity level of littoral fish and their use of different microhabitats in an altered intertidal environment, where intertidal fish are never emersed and turbulence is confined to high tides. Despite these atypical conditions, the structure of the assemblage is basically the same found in a typical rocky-shore situation. Two intertidal fish known to possess internal tidal rhythms, Lipophrys pholis and Coryphoblennius galerita, retain those rhythms in these altered conditions, and the associated social changes in L. pholis are also retained. These observations support the studies of Gibson (1971), who showed that changes in hydrostatic pressure were of prime importance in keeping the tidal rhythm entrained. The subtidal Parablennius pilicornis, on the contrary, is more active during low tide than at high tide. The hypothesis that some subtidal species are excluded from the intertidal by a turbulence-avoiding mechanism is discussed.     

Phylogenetic study and barcoding of the blood cockle, Tegillarca granosa, found on the west coast of peninsular Malaysia using the COI gene

Blood cockles are among the most economically important brackish water invertebrates found in Malaysia. However, our knowledge of blood cockle phylogeny and systematics is rudimentary, especially for the species Tegillarca granosa. It is unclear, for instance, whether the cockles occurring on the west coast of peninsular Malaysia constitute a single species, or multiple, phylogenetically distinct species. We performed the first DNA molecular phylogenetic analysis of T. granosa to distinguish it from other related species found in other parts of the world and to create a DNA database for the species. An approximately 585-nucleotide fragment of the mitochondrial DNA (cytochrome oxidase I, COI) was sequenced for 150 individual cockles, representing 10 populations: three from the north, four from the central part and three from the southern part of peninsular Malaysia. Phylogenetic analyses of the resulting dataset yielded tree topologies that not only showed the relationship between T. granosa and its closest relatives but its position in the evolutionary tree. Three mitochondrial clades were evident, each containing an individual genus. Using the mutation rate of the COI gene, the divergence time between T. granosa and its closest related species was estimated to be 460 thousand years ago. This study provides a phylogenetic framework for this ecologically prominent and commercially important cockle species.     

The intertidal zoning of cockles (<Emphasis Type="Italic">Cerastoderma edule</Emphasis>) in the Wadden Sea,or why cockle fishery disturbed areas of relatively high biodiversity

Recently, Kraan et al. (ICES J Mar Sci 64:1735–1742, 2007) reported that areas in the Wadden Sea selected by mechanical cockle dredgers were of greater zoobenthic diversity than areas that remained undredged. The present paper attempts to explain this observation, focussing on the elevation-related zoning of the macrobenthic fauna on tidal flats. Dense beds of cockles Cerastoderma edule occur in a specific intermediate intertidal-height zone where more species are present (and reach their maximal abundance) than in either lower or higher zones. This coincidence of preferred intertidal zones in many species, including cockles, may cause the higher species richness (and higher total macrozoobenthic biomass) of the fisher-chosen dredging areas as compared to other nearby non-dredged tidal-flat areas.     

Tidal effects on the organic carbon mineralization rate under aerobic conditions in sediments of an intertidal estuary

Laboratory experiments and field measurements were conducted to examine the effect of tide on the organic carbon mineralization rate in sediments under aerobic conditions of an intertidal estuary. Core samples of surface sediments were collected from an intertidal estuary of the Kurose River, Hiroshima, Japan. To mimic low and high tide in the intertidal estuary, organic carbon mineralization rates in the samples were measured in the laboratory under both air-exposed and submerged conditions. Mineralization rates under air-exposed conditions were two to five times higher than those under submerged conditions. Field measurements of the rate of CO₂ emission from the sediment surface revealed a rapid increase in the rate as the sea level fell during ebb tide. The estimated amount of daily organic carbon mineralization assuming a constantly submerged condition was 30% less than that estimated when considering the semi-diurnal fluctuation in sea level. These results indicate that tide has a marked impact on the organic carbon mineralization rate in sediments under aerobic conditions on an intertidal estuary, and tidal effects need to be considered when the amount of mineralized organic carbon is estimated.     

Endogenous swimming rhythms of juvenile blue crabs, Callinectes sapidus, as related to horizontal transport

The blue crab Callinectes sapidus settles and metamorphoses in areas of aquatic vegetation in estuaries. Crabs in the first-fifth instar stages (J1-5) then emigrate from these areas by walking on the bottom or pelagic dispersal throughout estuaries. The present study was designed to characterize the timing of this migration pattern relative to the light-dark and tidal cycles. Field sampling in Pamlico Sound, NC, USA indicated that J4-5 juveniles were most abundant in the water column during the night. J4-5 juveniles were collected from Pamlico Sound in an area near Oregon Inlet that has semi-diurnal tides, a Mid-Sound area where tides are weak, and on the West side where regular tides do not occur. Crabs from all three sites had a circadian rhythm in which they swam up in the water column during the time of darkness in the field. Peak swimming consistently occurred at about 0300 h, but was not related to the timing of the tidal cycle. Similar results were obtained for juvenile crabs from an adjacent estuary having semi-diurnal tides. Dispersal at night reduces predation by visual predators, and allows early juvenile blue crabs to disperse planktonically from initial settlement sites.     

An estimate of the sustainable rate of shell extraction from the Dutch Wadden Sea

1. Shell production by cockles Cerastoderma edule was studied to examine whether or not the present licensed rate of shell extraction in the Dutch Wadden Sea exceeds the current rate of shell addition to the exploitable stocks.
2. Long-term data on numbers of cockles and weights of their shells were used to estimate their annual production on Balgzand, a 50-km² tidal flat area in the western-most part of the Wadden Sea. During the 1969–97 period, it amounted to an average of 125 g m^–2, including 107 g m^–2 of shells large enough to be exploitable for shell-lime fishery.
3. The very irregular annual recruitment of cockles was the main cause of the wide 95% confidence limits (74 and 140 g m^–2 year^–1) of this 28-year estimate. Moreover, high mortality rates in severe winters substantially reduced production per recruit in some year classes.
4. About one-third of the estimated production does not reach exploitable stocks, because it is fragmented by birds (particularly eider ducks), permanently buried in the sediment, or removed by the fishery for live cockles.
5. During the last few decades, the estimated mean amount added annually to the exploitable stocks was 88 million kg or 132 000 m³ of large cockle shells. This amount compares favourably with the current annual level of removal of 134 000 m³ of shells, three-quarters of which are cockles.
6. Even at temporarily lower production rates, the exploitation of shell stocks at its present rate is not expected to lead to a rapid exhaustion of the existing stocks in the tidal inlets of the Dutch Wadden Sea, as these stocks will be in the order of a few million m³.     

The climbing behaviour of Cerithidea anticipata (Mollusca: Gastropoda): The roles of physical and biological factors

Abstract Many molluscs in tidal wetlands climb trees as the tide rises, a behaviour usually assumed to be a means of avoiding subtidal predators. Some species are more active during neap tides, when the access of subtidal predators to the forest is limited, but rest on trees during spring tides. Cerithidea anticipata, which inhabits the mangrove forests around Darwin Harbour (Northern Territory, Australia), displayed almost exactly the opposite pattern. This species climbed higher, and was less active, during neap tides that did not flood the forest than during spring tides. In experiments with tethered snails, individuals prevented from climbing died during neap tides, apparently from physiological stress. Further, individuals resting on trees around clearings, usually selected shaded sites. These results suggest that the major reason C. anticipata climbed was to avoid physiological stress during neap tides, not subtidal predators during spring tides. There was some evidence of predation under the canopy, but the rate was relatively low and the species responsible appeared to be resident in the forest.     

HABITAT DIFFERENCES IN THE TIMING OF REPRODUCTION OF THE INVASIVE ALGA SARGASSUM MUTICUM (PHAEOPHYTA,SARGASSACEAE) OVER TIDAL AND LUNAR CYCLES1

Sargassum muticum (Yendo) Fensholt is an invasive species that is firmly established on intertidal and subtidal rocky shores of Europe and the Pacific coast of North America. Local success and spread of S. muticum is thought to rely on its reproductive potential that seems dependent on exogenous factors like tidal and lunar cycles. This study is the first to compare the reproductive patterns (periodicity of egg expulsion and embryo settlement) of this invader in two different habitats: the middle and low intertidal. The combination of monthly, daily, and tidal samples at triplicate sites within each habitat showed a semilunar periodicity of egg expulsion and embryo settlement coincident with increasing tidal amplitude just before full and new moons. In both habitats, duration of each egg expulsion event was ～1 week, and embryo settlement occurred during the first daily low tide and with the incoming high tide during spring tides. However, both expulsion and settlement started 1–2 d earlier, expulsion saturation was faster, and settlement was higher in the mid‐ compared to the low intertidal. Our results suggest that the exact timing of gamete expulsion and embryo release of S. muticum responds to local factors, including tidal cues, which result in differences between mid‐ and low‐intertidal habitats.     

Macrozoobenthos on an intertidal mudflat in the Danish Wadden Sea: Comparisons of surveys made in the 1930s, 1940s and 1980s

To assess whether long-term faunal changes have occurred on intertidal flats in the Danish Wadden Sea, results of faunal surveys in the Skallingen area during the 1930s, 1940s and 1980s were compared. Since the earlier studies, two species have disappeared (Scrobicularia plana andPetricola pholadiformis) and two have invaded the area (Tharyx killariensis andEnsis americanus). This is, however, not a local event as species changes have occurred on a larger scale (Wadden Sea region). Comparison of abundance data did not provide evidence of changes from the 1930s until the 1980s. Spatio-temporal fluctuations in two dominant species, the mudsnailHydrobia ulvae and the cockleCerastoderma edule chosen for closer examination, could be explained by natural processes. Growth data on cockles from the 1930s and the 1980s matched perfectly. During both periods, cockles showed a much lower growth rate than generally reported from the Wadden Sea, while at the same time they occurred at high densities (>2000 ind·m⁻²). Intraspecific competition among cockles is suspected as being a major cause of the low growth rates. Estimates of secondary production and P/B-ratios of cockles were also in general agreement during the 1930s and the 1980s when corrected for differences in the age structure of the cockle populations. With the possible exception ofMytilus edulis, which according to some observations has extended its range along the low-water line, the present comparison failed to demonstrate long-term faunal changes caused by increased eutrophication. This results is expected to be representative for intertidal flats not exposed to direct impacts from terrestrial run-offs and waste-water discharges.     

Heat-shock response and antioxidant defense during air exposure in Patagonian shallow-water limpets from different climatic habitats

Climate warming involves not only a rise of air temperature means, but also more frequent heat waves in many regions on earth, and is predicted to intensify physiological stress especially in extremely changeable habitats like the intertidal. We investigated the heat-shock response (HSR) and enzymatic antioxidant defense levels of Patagonian shallow-water limpets, adapted to distinct tidal exposure conditions in the sub- and intertidal. Limpets were sampled in the temperate Northern Patagonia and the subpolar Magellan region. Expression levels of two Hsp70 genes and activities of the antioxidants superoxide dismutase (SOD) and catalase (CAT) were measured in submerged and 2- and 12-h air-exposed specimens. Air-exposed Patagonian limpets showed a tiered HSR increasing from South to North on the latitudinal gradient and from high to low shore levels on a tidal gradient. SOD activities in the Magellan region correlated with the tidal rhythm and were higher after 2 and 12 h when the tide was low at the experimental site compared to the 6 h value taken at high tide. This pattern was observed in intertidal and subtidal specimens, although subtidal individuals are little affected by tides. Our study shows that long-term thermal adaptation shapes the HSR in limpets, while the oxidative stress response is linked to the tidal rhythm. Close to the warm border of their distribution range, energy expenses to cope with stress might become overwhelming and represent one cause why the limpets are unable to colonize the shallow intertidal zone.     

Timing of hatching and release of larvae by brachyuran crabs: patterns, adaptive significance and control

Most semiterrestrial, intertidal and shallow subtidal brachyuran crabs that live in tropical and warm temperate estuaries, bays and protected coasts world-wide release their planktonic larvae near the times of nocturnal high tides on the larger amplitude tides in the biweekly or monthly cycles of tidal amplitude. Crab larvae usually emigrate quickly to the sea where they develop to return as postlarvae to settle in habitats suitable for their survival. Predators of larvae are more abundant where larvae are released than where they develop, suggesting that this migration from estuaries to the sea reduces predation on larvae. Crabs with larvae that are relatively well-protected by spines and cryptic colors do not emigrate and often lack strong reproductive cycles, lending support to this explanation. Adults control the timing of the release of larvae with respect to the biweekly and monthly cycles of tidal amplitude by controlling when they court and mate and females control when development begins by controlling when they ovulate and allow their eggs to be fertilized by stored sperm. By changing the time they breed, fiddler crabs (Uca terpsichores) compensate for the effects of spatial and temporal variation in incubation temperature on development rates so that embryos are ready to hatch at the appropriate time. Control of the diel and tidal timing of hatching and of release of larvae varies with where adults live. Females of the more terrestrial species often move from protected incubation sites, sometimes far from water, and they largely control the precise time, both, of hatching and of release of larvae. Females of intertidal species also may influence when embryos begin to hatch. Upon hatching, a chemical cue is released that stimulates the female to pump her abdomen, causing rapid hatching and release of all larvae in her clutch. Embryos, rather than females, largely control hatching in subtidal species, perhaps because females incubate their eggs where they release their larvae. Topics for further study include the mechanism whereby adults regulate the timing of breeding, the mechanisms by which females control development rates of embryos, the nature of communication between females and embryos that leads to precise and synchronous hatching by the number (often thousands) of embryos in a clutch, and the causes of selection for such precision. The timing of hatching and of release of larvae by cold-temperate, Arctic, and Antarctic species and by fully terrestrial and freshwater tropical species has received little attention.     

THE USE OF MOLLUSCAN SHELL GROWTH PATTERNS IN ECOLOGY AND PALEOECOLOGY

The influence of substratum, depth of water, turbidity, and temperature on daily growth patterns has been studied by transplanting juvenile Mercenaria mercenaria (Linnaeus) from the laboratory to intertidal and subtidal environments.
The study of seasonal growth variations in a population of Gemma gemma Totten from Long Island Sound shows that shell growth patterns may be used to determine the season of death and age of dead shells.
Deep-water species (e.g. Nucula cancellata Jeffreys, Malletia sp., and Calyptogena ponderosa Boss) exhibit growth increments that are more uniform in thickness and less sharply defined than those in shallow-water species.     

Spatial heterogeneity in parasite infections at different spatial scales in an intertidal bivalve

Spatial heterogeneities in the abundance of free-living organisms as well as in infection levels of their parasites are a common phenomenon, but knowledge on parasitism in invertebrate intermediate hosts in this respect is scarce. We investigated the spatial pattern of four dominant trematode species which utilize a common intertidal bivalve, the cockle Cerastoderma edule, as second intermediate host in their life cycles. Sampling of cockles from the same cohort at 15 sites in the northern Wadden Sea (North Sea) over a distance of 50 km revealed a conspicuous spatial heterogeneity in infection levels in all four species over the total sample as well as among and within sampling sites. Whereas multiple regression analyses indicated the density of first intermediate upstream hosts to be the strongest determinant of infection levels in cockles, the situation within sites was more complex with no single strong predictor variable. However, host size was positively and host density negatively correlated with infection levels and there was an indication of differential susceptibility of cockle hosts. Small-scale differences in physical properties of the habitat in the form of residual water at low tide resulted in increased infection levels of cockles which we experimentally transferred into pools. A complex interplay of these factors may be responsible for within-site heterogeneities. At larger spatial scales, these factors may be overridden by the strong effect of upstream hosts. In contrast to first intermediate trematode hosts, there was no indication for inter-specific interactions. In other terms, the recruitment of trematodes in second intermediate hosts seems to be largely controlled by pre-settlement processes both among and within host populations.