A diatom assemblage living below the surface of intertidal sand flats

The assemblages of species living on and in intertidal sand flats at Barnstable Harbor, Massachusetts (USA) are briefly described. An endopsammic assemblage of diatoms, mainly Amphora species, living below the surface is described for the first time in such a marine situation. Some aspects of its ecology and relationship to the other diatom assemblages living on the sediments are discussed.     

Parasitism as a determinant of community structure on intertidal flats

The burrowing and movement ability of the New Zealand cockle Austrovenus stutchburyi is reduced when infected by echinostome trematodes. Previous experimental evidence from a single site suggests that this parasite-induced behavioural change of a key bivalve can affect the structure of the surrounding benthic community. By using multiple regression analyses on data collected from 17 intertidal flats, we here show that cockle parasitism is associated with macrozoobenthic community structure on a larger spatial scale. Regressions were performed for animal abundance, biomass, species diversity and species richness separately, entering cockle parasitism (infection intensity), presence/absence of ghost shrimps (Callianassa filholi), cockle density, primary producer abundance and organic content, particle size, sorting coefficient and gravel content of the substrate as predictors. Next to ghost shrimps, cockle parasitism was the best predictor of animal abundance by affecting (mainly positively) 8 of the 49 most widespread species significantly. Cockle parasitism was also associated with the biomass of anthozoans (positively), nemerteans (negatively) and bivalves (positively), whereas overall animal biomass was positively related to the sorting coefficient of the substrate. Species diversity was positively associated with cockle parasitism and gravel content of the substrate. Species richness was significantly associated with cockle parasitism (positively), ghost shrimps (negatively) and abundance of primary producers (positively) in combination. The impact of cockle parasitism on benthic community structure is believed governed directly or indirectly by (1) reduced sediment disturbance, (2) increased surface structural complexity and (3) availability of larval trematodes as an additional food source.     

The distribution of intertidal phytopsammon in an Oregon estuary

The sediments of two tidal flats in Yaquina Bay, Oregon, USA, were studied to determine the distribution and abundance of the interstitial microalgal communities. The hydrography of the bay, as well as fluetuations in various physical and chemical parameters appear to regulate the biomass and the vertical and intertidal distribution of these organisms.     

Hydrocarbon metabolism in the intertidal fiddler crab Uca pugnax

The fiddler crab Uca pugnax was examined for its ability to metabolize foreign hydrocarbons. The microsomal mixed function oxidase system was identified in U. pugnax tissues using Aldrin epoxidation rates as the assay. Rates were slow: 96 pM Dieldrin per mg microsomal protein per hour in the hepatopancreas, 438 pM mg^-1 h^-1 in the gill, and 228 pM mg^-1 h^-1 in claw-muscle microsomes. Using standard methods, no difference in rates could be detected between crabs living in clean areas and those living in environments highly contaminated with foreign hydrocarbons. In vivo rates of naphthalene oxidation were measured and used to calculate a clearance time for U. pugnax body tissues based on the aromatic hydrocarbon content of crabs collected from an oil-polluted salt marsh. Calculated clearance time was beyond the life span of the crab. It is concluded that this minimal ability of U. pugnax to metabolize foreign hydrocarbons partially accounts for its sensitivity to oil pollution in the environment.     

Temperature sensitivity of metabolism in offshore and intertidal onuphid polychaetes

Acclimated metabolism-temperature curves have been constructed for 4 populations of the intertidal onuphid Diopatra cuprea, and for the 2 offshore species Hyalinoecia tubicola and H. artifex. The intertidal species shows greater temperature sensitivity than its offshore relative, despite its presumed adaptation to thermally unstable habitats. Temperature changes considerably in excess of natural fluctuations do not greatly alter metabolic rates in Hyalinoecia. However, the range of thermal tolerance in these two species is considerably reduced.     

Macrozoobenthic community structure in the Ría de Foz,an intertidal estuary (Galicia,Northwest Spain)

The community structure of the macrobenthic (>1 mm) fauna of an intertidal soft-bottom estuary, the Ría de Foz (Galicia, Northwest Spain) was investigated on 99 occasions during June, September and December 1984 and March 1985. The infaunal data were subjected to classification and ordination techniques. The analyses indicated that sediment characteristics (grain size, percentage silt-clay and organic-matter content) and tidal height are the most important factors governing the distribution and abundance of the intertidal communities. Three faunal assemblages were identified and examined in terms of species dominance, constancy and fidelity. In the clean sands of the outer estuary two main assemblages were distinguished; one, corresponding to the boreal LusitanianTellina community, inhabited the middle and lower tidal levels; the other, typical of a biocoenosis of sands and slightly muddy mediolittoral sands, inhabited the upper tidal level. The third benthic assemblage occupied the muddy sands and mud of the inner estuary and displayed some features in common with theCardium edule-Scrobicularia community described by Thorson.     

Seasonal variability of intertidal bacterial metabolism and growth efficiency in an exposed sandy beach during low tide

Benthic gross primary production (GPP) and community respiration (BCR) were regularly measured on sandy beach sediment during low tide in a megatidal ecosystem. These measurements were assessed during 2 years in situ within a benthic chamber simultaneously with bacterial production (BP). Results suggested that community respiration in Wimereux sandy beach sediments was probably dominated by bacterial respiration and that the estimated benthic bacterial growth efficiency (BGE) was highly variable. Although temperature significantly controlled both BP and BCR during low tide at the annual scale, the temperature effect on BGE was not significant. The instability and sediment erosion caused by the wave action and the tidal cycle were thus thought to influence the BGE. Since the sampling site is regularly affected by Phaeocystis foam deposit (enhancing the BCR and decreasing the BGE), and since GPP rates were highly variable and supported by high assimilation numbers (i.e., >1 mgC mgChla ⁻¹ h⁻¹), phytoplankton organic matter deposit following the immersion of the study site was thought to explain the BGE variability.     

Interactions between two introduced species: Zostera japonica (dwarf eelgrass) facilitates itself and reduces condition of Ruditapes philippinarum (Manila clam) on intertidal flats

Dwarf eelgrass (duckgrass; Zostera japonica) and Manila clams (Ruditapes philippinarum) are two introduced species that co-occur on intertidal flats of the northeast Pacific. Through factorial manipulation of clam (0, 62.5, 125 clams m⁻²) and eelgrass density (present, removed by hand, harrowed), we examined intra- and interspecific effects on performance, as well as modification of the physical environment. The presence of eelgrass reduced water flow by up to 40% and was also observed to retain water at low tide, which may ameliorate desiccation and explain why eelgrass grew faster in the presence of conspecifics (positive feedback). Although shell growth of small (20–50 mm) clams was not consistently affected by either treatment in this 2-month experiment, clam condition improved when eelgrass was removed. Reciprocally, clams at aquaculture densities had no effect on eelgrass growth, clam growth and condition, or porewater nutrients. Overall, only Z. japonica demonstrated strong population-level interactions. Interspecific results support an emerging paradigm that invasive marine ecosystem engineers often negatively affect infauna. Positive feedbacks for Z. japonica may characterize its intraspecific effects particularly at the stressful intertidal elevation of this study (+1 m above mean lower low water).     

Motile cryptofauna of Tuléar reef flats

A study of the calcareous tube-building polychaete Hydroides dianthus (Verrill) in a temperate estuary (Delaware Bay, USA) revealed an assemblage that was strongly associated with the serpulid. This polychaete species provided numerous microhabitats by means of its tubes and sediment enriched with tube fragments. Quantitative associations for winter and summer tube heads showed that 17 and 12 species, respectively, were statistically dependent on H. dianthus. There were significant associations between number of species, number of individuals, mean number of animals, standard deviation, the size of the tube clump for both seasons (winter and summer), and for scaled standard deviation (SDN) and species diversity (H) during the winter. Successional development of the serpulid assemblage starts with the settling of H. dianthus, progresses through growth, maturation, mortality, and the interaction of associates and predators, resulting in a highly diverse benthic assemblage in this temperate estuary.     

Habitat choice in the intertidal snail Tegula funebralis

Intraspecific variation in habitat preference was studied in the black turban snail Tegula funebralis (Adams, 1854), at two locations on the northern U.S. Pacific Coast. Studies in 1977 using a mass-marking technique showed that most snails found either above or in permanent tidepools at low tide return to their original habitats within a few days after experimental habitat reversal. This return is not due to homing behavior, but is apparently based on the recognition of ecological characteristics of the two habitats. Experiments in 1978 with individually-marked snails suggest that they prefer specific intertidal levels, and not merely above-pool or in-pool habitats. Theoretical models predict that this behavior could play a major role in the maintenance of genetic polymorphism in a species like T. funebralis, whose intertidal environment is characterized by extreme spatial heterogeneity.     

Seasonal changes in the structure of an intertidal community

Quantitative (0.25 m²) samples of macrofaunal (>1.0 mm) invertebrates were taken in each season from one habitat of an intertidal sandbar in the North Inlet estuary near Georgetown, South Carolina, USA. During all seasons the community inhabiting the sample site was numerically dominated by two species of haustoriid amphipods (Acanthohaustorius millsi and Pseudohaustorius caroliniensis). Seasonal changes at the community level were clearly controlled by the population dynamics of the numerically dominant species, and qualitative information on life histories was important to the interpretation of analyses' results.This work was supported by the Environmental Technology Center of Martin Marietta Corporation and the Belle W. Baruch Institute for Marine Biology and Coastal Research. It is Contribution No. 138 of the Belle W. Baruch Institute for Marine Biology and Coastal research.     

Orientation in the intertidal salt-marsh collembolan Anurida maritima

We investigated the cues used by the intertidal insect Anurida maritima (Apterygota: Collembola) to orient to the appropriate zone in which to seek shelter during high tide. Our experiments clearly ruled out any significant role for magnetic, local topographic, slope or celestial cues. Instead, we suggest that the difference between the appearance of the up-shore and the down-shore horizon is the major cue used by the collembolans. When a mirror was used to duplicate either of the two horizons, the insects were not able to orient. The insects moved towards an artificially dark horizon (the reverse of the mirror) placed down-shore, the opposite of their usual direction of movement. The insects had an endogenous circatidal rhythm of phototactic behaviour: most of the population was always negatively phototactic, but between 2 and 7 h after low tide, a significant proportion of the population became positively phototactic. This is the first demonstration of an endogenous tidal rhythm of orientation in an insect. Received: 31 May 1999 / Received in revised form: 1 February 2000 / Accepted: 19 February 2000     

Intertidal hyperbenthic populations in the Nanaimo estuary

Samples were pumped from within 5 and 30 cm of the sediment surface in a tidal channel of the Nanaimo estuary and filtered through 100-m mesh plankton nets. Despite homogeneity of the water at these levels, as indicated by salinity and oxygen, there were large persistent differences in population density of small crustaceans. The density at the 5 cm level always exceeds the density at the 30 cm level by a factor of 2 to 20. These results are discussed in relation to Beyer's concept of hyperbenthic plankton populations which is extended to include intertidal areas. It is concluded that hyperbenthic populations are real phenomena and are of considerable importance in trophodynamics. A model for formation and maintenance of hyperbenthic populations is proposed.     

Desiccation as a factor in the intertidal zonation of barnacles

Four species of balanomorph barnacles, Balanus crenatus Brugière, B. balanoides (L.), Elminius modestus Darwin and Chthamalus stellatus (Poli), were studied to assess the susceptibility of intertidal barnacle species to desiccation. Known sized samples of barnacles were exposed to controlled desiccating conditions and subsequent survival and water loss were determined. It is clear that the ability to live high on the shore is dependent on a reduction of the overall permeability to water loss. Because of greater surface area to volume ratios, small stages are particularly prone to desiccation. In normal intertidal emersion periods, small stages of B. crenatus particularly, and also of B. balanoides and E. modestus which are similar in their desiccation resistance, would be susceptible to desiccation at normal temperatures and low humidities. Large barnacles would be more prone to death from high temperatures when the tide is out. The spat of C. stellatus, although surviving much longer than spat of larger dimensions of the other species, must also be prone to prolonged emersion conditions at high shore levels.     

Substrate size mediates thermal stress in the rocky intertidal

Variation in physical factors, such as slope, orientation, and wind exposure, shapes thermal conditions. Variation in substrate size is common in many habitats, but its thermal consequences for organisms are not well characterized. Larger substrates should remain more thermally stable and act as thermal refuges for associated organisms during short, thermally stressful periods such as midday temperature peaks or tidal exposure. In observations and a transplant and thermal integration experiment, we found that larger rock substrates stayed cooler and facilitated greater survival of the barnacle Semibalanus balanoides in the high intertidal relative to small substrates during the hot summer months in southern New England, USA. However, in thermally benign northern New England, rock substrate size had no effect on barnacle distributions, indicating that the thermal effects of substrate size are mediated by regional climate.     

Factors influencing clustering in the intertidal snail Cerithium moniliferum

The snail Cerithium moniliferum Kiener at Heron Island (southern end of the Great Barrier Reef) clusters at outgoing tide and disperses at incoming tide. In containers with a constant water level, but exposed to the normal day and night rhythm, the snails cluster and disperse rhythmically for up to several days. Graphical simulation and spectral analysis, preceded by first difference filtering, showed two components, one corresponding to the tidal, and the other to the diurnal rhythm. Snails kept under continuous light also exhibit a two-component rhythm of clustering and dispersal. In containers with high (40 cm) water level and under continuous light or normal day and night rhythm, the two-component rhythm may—for some unknown reason—be replaced by long fluctuations of dispersal, with clustering occurring in the afternoon only in snails kept under normal alternation of day and night. Snails kept for 24 h in dryness prior to putting them into containers with water, remain clustered (sometimes with an initial dispersal “shock”) for a long time, with subsequent slow fluctuations of clustering and dispersal, probably induced by the light conditions. Factors contributing to clustering and dispersal are: (1) increased rate of dropping from container walls at outgoing tide; (2) lack of locomotory activity at low tide; (3) negative geotaxis at incoming tide; (4) positive geotaxis at outgoing tide; (5) attraction of snails by other snails (positive chemotaxis) throughout the rhythm. Sudden exposure to light increases the rate of dropping from the container walls and may be a contributing factor to stronger clustering during the day. Factors 1–4 show endogenous periodicities.     

Mating system of the intertidal copepod Tigriopus californicus

Male Tigriopus californicus clasp immature females (copepodid stages II–V) for a period of up to a week prior to the female's terminal molt; upon maturation (stage VI) the female is inseminated and released. While females can mate anytime after their terminal molt, experiments using electrophoretically-detected genetic markers indicate that each mates only once in her lifetime. No evidence of sperm displacement was observed. Hence, male mating behavior can be interpreted as pre-copulatory mate guarding, a strategy employed to assure that a potential mate has not been previously inseminated. Males minimize the time investment required to insemiate a single female successfully by preferentially choosing to clasp more developmentally-advanced females; males clasped to stage III females will release them in order to clasp stage V females if the latter are present. Since males are capable of multiple mating, under most conditions of population sex ratio, this mating system results in low availability of unclasped, developmentally-advanced females; consequently, males must clasp successively younger (i.e. developmentally less-advanced) females in order to obtain a successful insemination.     

Microdistribution of the marine copepodOithona davisae in the shallow waters of Ariake-kai mud flats,Japan

The microdistribution ofOithona davisae Ferrari and Orsi inhabiting shallow waters of Ariake-kai, western Kyushu, Japan, was investigated in 1980–1981 by means of a pumping method. Water samples (10 l) were repeatedly collected from the surface to the bottom at intervals of 0.5 m. This species was dispersed when the tidal current ran fast (more than 20 cm s^–1), but aggregated in the upper layer during the period of slow current. Their density was highest when the current stopped. Aggregation ofO. davisae presumably induced the continuous flat swarm near the surface. It is to be expected that the shallow waters in Ariake-kai would be favorable as nursery grounds for the fish larvae and juveniles which depend on the presence of such swarms.Contribution no. 51 from the Aitsu Marine Biological Station     

Population energetics of the intertidal isopod Cirolana harfordi

Laboratory experiments and field measurements generated a population energy-budget estimate for the isopod Cirolana harfordi (Lockington). Assimilation of food energy averaged 88% on a diet of fish. About 35% of assimilated energy is allocated for growth and reproduction, while the bulk of the remainder is used for maintenance and activity (respiration). The high growth efficiency of C. harfordi is discussed with respect to ecological efficiency and energy transfer in marine systems.