Meiofaunal emergence from intertidal sediment measured in the field: significant contribution to nocturnal planktonic biomass in shallow waters

Field studies on the occurrence of meiobenthos in the water column above intertidal sandflats have been performed near the Island of Sylt in the northern Wadden Sea. Swimming meiobenthos was strongly dominated by harpacticoid copepods. Many of them have a semiplanktonic life-style. They rest in superficial sediment layers at low tide and swin in the water column at high tide. Swimming activity correlated negatively with light. The abundance in the water column was one order of magnitude higher during the night. Strong currents caused by storm tides significantly decreased meiobenthic abundance in the water column. Light and flow being constant, no significant changes of meiobenthic abundance per unit area occurred over a tidal cycle. Since holoplankton and meroplankton abundances correlated positively with the height of the water column, semiplanktonic meiobenthos may dominate the mesozooplankton in shallow waters. On an average, emergence of meiobenthos increased the mesozooplanktonic biomass by about 2% during diurnal high tides over the entire tidal cycle, and by about 50% during nocturnal high tides. Because of seasonal cycles of the dominant harpacticoids, this high contribution to planktonic biomass may be a summer phenomenon.     

Dugong habitat use in relation to seagrass nutrients,tides, and diel cycles

The dugong is the only herbivorous mammal that is strictly marine and a seagrass community specialist. The pasture available to the dugong varies with the tides because seagrass occurs in both intertidal and subtidal areas. We GPS-tracked seven dugongs within a 24 km², intensively used seagrass habitat in subtropical Australia in winter. We modeled resource selection within the habitat by comparing the dugongs’ use of space with the distribution of seagrass in an area defined using the combined space-use of the tracked animals. Selection by dugongs for seagrass quantity (biomass) and quality (nutrients) was analyzed within six time/tide combinations to examine the influences of tidal periodicity and the diel cycle on resource selection. Dugong habitat use was consistently centered over seagrass patches with high nitrogen concentrations, except during the day at low tides when the animals had fewer habitat choices and their space use was centered over high seagrass biomass. The association of dugongs with seagrass high in starch was positive during both day and night high tides when the animals could access the intertidal areas where seagrass biomass was generally low. Associations between dugongs and seagrass species were less definite, reflecting the potential for dugongs to exploit several species. Our model of dugong resource selection suggests that nitrogen is the primary limiting nutrient for dugong populations and also confirms the preference of dugongs for high-energy foods.     

Amphibious behaviour and feeding ecology of the four-eyed blenny (Dialommus fuscus, Labrisomidae) in the intertidal zone of the island of Santa Cruz (Galapagos, Ecuador)

The labrisomid Dialommus fuscus , endemic to the Galapagos archipelago, is a predator of crustaceans, which moves up and down the intertidal zone with the tides. Its divided eye and elongated body permit it to forage in the wet sections of the intertidal habitat during low tide, both on the rocks and below the water line and in tide pools. Compared with other intertidal fishes (e.g. Bathygobius sp.), it was present on the rock flat in significantly smaller tide pools nearer to the water line during low tide.     

Interactive effects of food availability and aerial body temperature on the survival of two intertidal Mytilus species

Intertidal organisms must episodically contend with the rigors of both the terrestrial and the marine environments. While body temperatures during high tide are driven primarily by water temperature, aerial body temperatures are driven by multiple environmental factors such that temperature of an organism during low tide is usually quite different from air temperature. Thus, whereas decades of research have investigated the effects of water temperature on intertidal species, considerably less is known about the physiological impacts of temperature during aerial exposure at low tide, especially with regard to the interaction of aerial body temperature with other stressors. We examined the interactive effects of aerial body temperature and food supply on the survival of two intertidal blue mussels, Mytilus galloprovincialis and Mytilus trossulus. Survival was monitored for nine weeks using a simulated tidal cycle, with two levels of food and three levels of aerial body temperature (30, 25, and 20 °C). Decreased food supply significantly reduced the survival of mussels, but only under the 30 °C treatment. In the other two thermal regimes there were no significant effect of food on survival. When aerial body temperatures are high, food availability may have a greater effect on intertidal organisms. Decreases in ocean productivity have been linked to increased in ocean temperatures, thus intertidal organisms may become more susceptible to thermal stress as climates shift.     

Time and tide wait for no fish: intertidal fishes out of water

Synopsis Hypoxic conditions are rare in the open ocean, but may occur during low tides in tidepools. Intertidal fishes respond to low tides in a variety of ways, including avoiding the intertidal zone during low tides, respiring in the well-oxygenated layer at the surface of the water, or simply tolerating hypoxic water. A number of intertidal fish species have the ability to leave the water and survive terrestrially for a period of time while breathing air. This paper reviews the literature on ecomorphology of amphibious intertidal fishes, suggests ecomorphological and ecophysiological approaches to clarifying the adaptations of intertidal fishes for emergence from water, and considers differences in the types of emergence behavior and activities seen in three broadly defined behavioral types. These types include the skippers, fishes that actively emerge at all phases of the tidal cycle and engage in routine terrestrial activity, the remainers, that emerge passively under cover such as rocks or vegetation by remaining in place as the tide recedes, and the tidepool emergers, that typically spend low tides in tidepools but may emerge from hypoxic water. Portioning of gas exchange between the gills and the skin, the release of CO₂ into air, the effect of emergence on metabolic rate, and vertical zonation in distribution of fishes in the intertidal zone are compared for fishes in each of these behavioral styles.     

Thermal tolerance,evaporative water loss,air-water oxygen consumption and zonation of intertidal prosobranchs: a new synthesis

Duration of emergence increases with tidal height on rocky shores therefore, emergence adaptations in intertidal species such as littorine and other prosobranch gastropods have been considered correlated with zonation patterns; temperature tolerance, desiccation resistance and aerial respiration rate all commonly assumed to increase progressively with increasing zonation level. Such direct correlations are rarely observed in nature. Maximal aerial gas exchange occurs in mid-shore, not high shore species. Temperature tolerance and desiccation resistance do not increase directly with shore height. Thus, hypotheses regarding physiological correlates of zonation require revaluation. A new hypothesis is presented that the high tide mark presents a single major physiological barrier on rocky shores. Above it, snails experience prolonged emergence and extensive desiccation; below it, predictable submergence and rehydration with each tidal cycle. Thus, desiccation stress is minimal below the high tide mark and maximal above it. Therefore, species restricted below high tide (the eulittoral zone) should display markedly different adaptive strategies to emergence than those above it (the eulittoral fringe). A review of the literature indicated that adaptations in eulittoral species are dominated by those allowing maintenance of activity and foraging in air including: evaporative cooling; low thermal tolerance; elevated aerial O₂ uptake rates; and high capacity for radiant heat absorption. Such adaptations exacerbate evaporative water loss. In contrast, species restricted to the eulittoral fringe display adaptive strategies that minimize desiccation and prolong survival of emergence including: foot withdrawal, preventing heat conduction from the substratum; aestivation in air; elevated thermal tolerance reducing necessity for evaporative cooling; position maintenance by cementation to the substratum and increased capacity for heat dissipation. In order to test of this hypothesis the upper thermal limits, tissue and substratum temperatures on emergence in direct sunlight and evaporative water loss and tissue temperatures on emergence in 40 °C were evaluated for specimens of six species of eulittoral and eulittoral fringe gastropods from a granite shore on Princess Royal Harbour near Albany, Western Australia. The results were consistant with adaptation to the proposed desiccation barrier at high tide. The eulittoral species, Austrocochlea constricta, Austrocochlea concamerata, Nerita atramentosa and Lepsiella vinosa, displayed adaptations dominated by maintenance of activity and foraging during emergence while the eulittoral fringe littorine species, Bembicium vittatum and Nodilittorina unifasciata displayed adaptations dominated by minization of activity and evaporative water loss during emergence. The evolution of adaptations allowing tolerance of prolonged desiccation have allowed littorine species to dominate high intertidal rocky shore gastropod faunas throughout the world's oceans.     

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.     

Patterns and processes of larval emergence in an estuarine parasite system

Trematode parasites in intertidal estuaries experience constantly varying conditions, with the presence or absence of water potentially limiting larval transport between hosts. Given the short life spans (< or =24 h) of cercariae, emergence timing should be optimized to enhance the probability of successful transmission. In the present study, field measurements and laboratory experiments identified processes that regulate the emergence of cercariae from their first intermediate snail hosts in an intertidal marsh. Larvae emerged over species-specific temperature ranges, exclusively during daylight hours, and only when snails were submerged. The three factors operate over different temporal scales: temperature monthly, light diurnally (24-h period), and water depth tidally (12-h period). Each stimulus creates a necessary condition for the next, forming a hierarchy of environmental cues. Emergence as the tide floods would favor transport within the estuary, and light may trigger direct (downward or upward) swimming toward host habitats. Abbreviated dispersal would retain asexually reproduced cercariae within the marsh, and local mixing would diversify the gene pool of larvae encysting on subsequent hosts. In contrast to the timing of cercarial release, emergence duration was under endogenous control. Duration of emergence decreased from sunrise to sunset, perhaps in response to the diminishing lighted interval as the day progresses. Circadian rhythms that control cercarial emergence of freshwater species (including schistosomes) are often set by the activity patterns of subsequent hosts. In this estuary, however, the synchronizing agent is the tides. Together, exogenous and endogenous factors control emergence of trematode cercariae, mitigating the vagaries of an intertidal environment.     

Entrainment of the activity rhythm of the mole crab Emerita talpoida

The mole crab Emerita talpoida migrates with the tide in the swash zone of sand beaches. A circatidal rhythm in vertical swimming underlies movement, in which mature male crabs show peak swimming activity 1-2 h after the time of high tides at the collection site. In addition, there is a secondary rhythm in activity amplitude, in which crabs are maximally active following low amplitude high tides and minimally active following high amplitude high tides. The present study determined the phase response relationship for entrainment of the circatidal rhythm with mechanical agitation and whether the cycle in activity related to tidal amplitude could be entrained by a cycle in the duration of mechanical agitation at the times of consecutive high tides. After entrainment with mechanical agitation on an orbital shaker, activity of individual crabs was monitored in constant conditions with a video system and quantified as the number of ascents from the sand each 0.5 h. Mechanical agitation at the times of high tide, mid-ebb and low tide reset the timing of the circatidal rhythm according to the timing relationship to high tide. However, mechanical agitation during flood tide had no entrainment effect. In addition, a cycle in duration of mechanical agitation entrained the rhythm in activity amplitude associated with tidal amplitude. Both rhythms and entrainment effectiveness over the tidal cycle may function to reduce the likelihood of stranding above the swash zone.     

Endogenous rhythms and entrainment cues of larval activity in the horseshoe crab Limulus polyphemus

The American horseshoe crab, Limulus polyphemus (Linnaeus), typically inhabits estuaries and coastal areas with pronounced semi-diurnal and diurnal tides that are used to synchronize the timing of spawning, larval hatching, and emergence. Horseshoe crabs spawn in the intertidal zone of sandy beaches and larval emergence occurs when the larvae exit the sediments and enter the plankton. However, L. polyphemus populations also occur in areas that lack significant tidal changes and associated synchronization cues. Endogenous activity rhythms that match predictable environmental cycles may enable larval horseshoe crabs to time swimming activity to prevent stranding on the beach. To determine if L. polyphemus larvae possess a circatidal rhythm in vertical swimming, larvae collected from beach nests and the plankton were placed under constant conditions and their activity monitored for 72 h. Time-series analyses of the activity records revealed a circatidal rhythm with a free-running period of ≈ 12.5 h. Maximum swimming activity consistently occurred during the time of expected falling tides, which may serve to reduce the chance of larvae being stranded on the beach and aid in seaward transport by ebb currents (i.e., ebb-tide transport). To determine if agitation serves as the entrainment cue, larvae were shaken on a 12.4 h cycle to simulate conditions during high tide in areas with semi-diurnal tides. When placed under constant conditions, larval swimming increased near the expected times of agitation. Thus, endogenous rhythms of swimming activity of L. polyphemus larvae in both tidal and nontidal systems may help synchronize swimming activity with periods of high water and inundation.     

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.     

Spring-neap cycle as a major driver of temporal variations in feeding of intertidal fishes: Evidence from the sea catfish Sciades herzbergii (Ariidae) of equatorial west Atlantic mangrove creeks

On macrotidal coasts, short- to medium term variations in feeding of intertidal fishes are influenced by several interacting time scales. To identify the driver of major variations in the feeding habits of intertidal fish, we used the pemecou sea catfish Sciades herzbergii (Ariidae), an abundant intertidal benthic second order consumer, as a model species. We analyzed the influence of the spring-neap and the day-night cycle on intertidal abundance, stomach fullness, diet composition and food consumption of S. herzbergii using block nets set at slack high tides in two mangrove creeks in north Brazil. At spring tides, intertidal abundance, stomach fullness, and total daily consumption of S. herzbergii were on average 8.8, 1.9, and 3.8 times higher than at neap tides, respectively. At spring tides, Uca spp. and Grapsidae (mostly Pachygrapsus gracilis) dominated the diet, irrespective of the time of day. Other important food items were Insecta and the semiterrestrial crab Ucides cordatus. At neap tides, Capitellidae contributed to the diet of nightly inundations while no specimens were caught at daytime. Creek location had no effect on any variable. Results from our study area and evidence from other studies suggest that the spring-neap tide pulse is likely the major driver of short- to medium term variations in feeding of intertidal fishes. This has important implications for feeding-related issues on macro- and probably also on mesotidal coasts: (i) juvenile fishes may have fortnightly growth spurts, (ii) intertidal prey populations may suffer regular fluctuations in mortality, (iii) studies of the feeding ecology of intertidal fishes should cover the combined effects of the tidal, diel, lunar and seasonal cycles, and (iv) the modeling of food webs should consider the differences between highly dynamic spring tide and quieter neap tide conditions.     

Tidal movements of the macrofauna on an exposed sandy beach in South Africa

All epifaunal and shallow-burrowing, intertidal macrofauna on an exposed sandy beach appear to undergo tidal migrations which vary in extent but are all upshore on the incoming tide and downshore on the outgoing tide during day and night. In the crustaceans this is probably endogenous rhythmic behaviour and they show increased activity at night. In the molluscs this movement is not synchronised by an intrinsic mechanism but results from behavioural responses to changing physical conditions. The large wedge clam, Donax serra, shows no tidal migrations but does show a semilunar rhythm of movement from just above mean tide level (MTL) during springs to the low tide level during neap tides.     

Aerial release of CO2 and respiratory exchange ratio in intertidal fishes out of water

Synopsis Many fishes in the marine intertidal zone have the ability to exchange respiratory gases in air during brief periods out of water. Previous studies on marine amphibious fishes such as mudskippers and rockskippers have shown that they release CO₂ in air at a rate consistent with its release in aquatic respiration. Respiratory Exchange Ratios (RER, CO₂ released per O₂ consumed) are between 0.7 and 1.0, similar to Respiratory Quotients (CO₂ produced metabolically per O₂ consumed). However, previous studies of temperate intertidal fishes emerged only at low tides have been less consistent, with two species reported similar in ability to the amphibious skipper fishes, and two others reported with much lower RERs in air. This study examines 12 species of fishes, from six families (Batrachoididae, Cottidae, Gobiesocidae, Kyphosidae, Pholididae, and Stichaeidae), present in the intertidal zone of California. All 12 species exchanged O₂ and CO₂ in air. Like the amphibious skipper fishes of marine tropical waters, many intertidal fishes of the temperate zone release CO₂ during low tide emergence in quantities sufficient to match its metabolic production. These results indicate that CO₂ release is not hampered by the change in respiratory medium from water to air.     

Contrôle de la dynamique à court terme du microphytobenthos intertidal par le cycle exondation-submersion

We test herein the hypothesis that the succession of low tides — during which biomass increases — and high tides — during which biomass decreases — controls the dynamic behaviour of the microphytobenthic compartment. Results indeed show that during a complete lunar cycle (14 d) biomass exhibits a series of oscillations due to biomass increases during low tides and decreases during high tides. Moreover, the datasets show that the production level is in the range of previously recorded values and they indicate that the major part of the photosynthetically produced biomass during low tide can be exported into the water column during high tide. This clearly suggests that microphytobenthos is the major autochtonous source of organic matter production in the littoral zone and that it directly supplies the associated pelagic trophic web.     

VERTICAL MIGRATION OF A MIXED‐SPECIES EUGLENA (EUGLENOPHYTA) ASSEMBLAGE INHABITING THE HIGH‐INTERTIDAL SANDS OF NYE BEACH,OREGON1

Comparatively little is known about the vertical migration of the microphytobenthic community forming visible patches on high‐energy beaches. We collected surface and cored samples to evaluate the timing and extent of downward migration of a multispecies Euglena assemblage inhabiting Nye Beach, Oregon. Euglena density at the surface was highly variable and was not correlated with the time of low tide or instantaneous irradiance measurements; however, triplicate cores collected at low and high tides revealed a tidal rhythm in mean depth. On average, 95% of the assemblage occurred within 1 cm of the surface during low tide, but 54% of the assemblage was collected between 1 and 8 cm below the surface during high tide. A midday shading experiment revealed that short‐term changes in irradiance levels altered the Euglena density at the sediment surface by inducing vertical migration. This response to short‐term fluctuations in light may explain the weak correlation between cell density at the surface and time of day. The high‐intertidal location of these patches prevented the removal of nonmigrating cells by daily high tides, which increased the variability in surface samples and obscured the tidal migration rhythm detected in the core samples. Due in part to the semidiurnal nature of Oregon tides, this study provides in situ confirmation of past mesocosm research indicating that sediment disturbance during daily submersed periods is an important process in maintaining the quasi‐tidal rhythm in the appearance and disappearance of Euglena spp. from the surface of beaches and intertidal sandflats.     

Tolerance of forced air emergence by a fish with a broad vertical distribution, the rockpool blenny, Hypsoblennius gilberti (Blenniidae)

Many intertidal fishes, particularly among the Blenniidae and Cottidae, possess amphibious adaptations, including the ability to breathe in air and to avoid desiccation in terrestrial conditions. These traits are absent in subtidal species of blennies and cottids. Hypsoblennius gilberti, the rockpool blenny, is found in shallow rockpools in the mid to high intertidal areas of Southern California, and deeper to 18 m in the subtidal zone. This broad vertical distribution could indicate that this blenny is adapted for tidal air emergence, although H. gilberti has not been observed out of water in its natural habitat. H. gilberti does not emerge voluntarily from hypoxic sea water in the laboratory, but it easily withstands 3 h out of water. The aerial respiratory exchange ratio (CO2 released compared to O2 consumed) is 0.70, similar to that of amphibious intertidal fishes in air, indicating sufficient release of metabolically produced CO2 while emerged. There is no increase in aquatic respiration following emergence. However, unlike other amphibious fishes that maintain aerial oxygen consumption at a level similar to aquatic oxygen consumption, H. gilberti has an aerial oxygen consumption rate one-third that in water. H. gilberti can recover rapidly from terrestrial water loss, and shows no change in evaporative water loss rates at 93% and 77% relative humidities. The amphibious capabilities in H. gilberti, even if rarely used, permit survival in air during tidal emergence. These findings suggest that H. gilberti may demonstrate an intermediate condition between the amphibious species of intertidal fishes that regularly emerge from water, and the subtidal fishes that do not survive air emergence and are completely restricted to an aquatic habitat.     

长江口低盐淡水区潮间带鱼类群落结构季节及半月相变化

基于2006年春（5月）、夏（7月）、秋（9月下旬）和冬季（2月）对长江口低盐淡水区水域进行的潮间带鱼类调查结果,分析了鱼类种类及丰度的半月相及其季节变化. 结果表明：长江口低盐淡水区水域潮间带鱼类共有53种;其中鲤科鱼类最多,虾虎鱼科次之,其他科较少. 2顶网具渔获物的鱼类种类和丰度均以春、夏、秋季较高,冬季最低.各个季节的平均种类数和平均丰度均为小潮期小于大潮期. Shannon-Weaver指数（H′）在一个潮周期内的波动幅度较大,且小潮期H′值略低于大潮期. 对鱼类种类丰度进行聚类分析发现,冬季鱼类聚成一组,春、夏和秋季聚成一组. 从整年的情况来看,潮间带鱼类的丰度变化与水温的相关性最高;与潮高的相关性次之;而与盐度的相关性最小.     

Effects of Tidal and Diel Cycles on Dugong Habitat Use

ABSTRACT Quantifying the factors influencing behaviors of aquatic mammalian grazers may enhance the generic understanding of grazer ecology. We investigated diel and tidal patterns in movements of the dugong (Dugong dugon) by Global Positioning System—tracking 12 animals in 5 inshore—intertidal and 3 offshore—subtidal habitats along the coast of Queensland, Australia. We examined effects of tide height and time of day on the dugong's distance from 1) the nearest coast, 2) water >3 m deep, 3) actual water depth (bathymetry + tide ht) experienced, and 4) distribution of the directions of movements. Both tidal and diel cycles influenced dugong movement. Tracked dugongs tended to be closer to shore at high tide than at low tide and closer to shore at night than during the day. Onshore movement was more prevalent on incoming tides and in the afternoon and evening. Offshore movement was more prevalent on outgoing tides and from midnight through the morning until midday. Tidal and diel variation in water depths used by the inshore—intertidal dugongs was small, but probably underestimated, hidden by a sampling bias in the telemetry equipment. Onshore movement at high tide allowed dugongs to exploit intertidal seagrass beds. Dugongs are closer to shore in afternoons and evenings than in mornings. This behavior may be related to the avoidance of predators or watercraft. Our findings can be used to predict spatial patterns of dugongs within areas of conservation management significance and to assess, avoid, and mitigate adverse effects of anthropogenic disturbance.     

Alternation between attachment mechanisms by limpets in the field

The attachment mechanism used by limpets in the rocky, wave-swept intertidal zone of California was determined during high tide and low tide. The two mechanisms that limpets are known to use, suction and glue-like adhesion, were distinguished by measuring the limpets' attachment forces in shear and by staining for glue-like residues where the limpets had been attached. The results show that ≈ 73% of limpets at high tide use suction, while the rest use glue-like adhesion. Conversely, ≈ 75% of limpets at low tide use glue-like adhesion, while the rest use suction. The normal tenacity of limpets was also measured at high and low tide. The mean tenacity at high tide was significantly less than that at low tide. From these data it was estimated that the mean tenacity of glue-like adhesion is ≈ 0.23 MN·m⁻² and the mean tenacity of suction adhesion is ≈ 0.09 MN·m⁻². It is hypothesized that the cycle of alternating attachment mechanisms is linked to the limpets foraging cycles.