Predation by Callinectes sapidus (Rathbun) within Spartina alterniflora (Loisel) marshes

This study examined predation by the blue crab, Callinectes sapidus Rathbun, within intertidal Spartina alterniflora (Loisel) marshes of Dauphin Island, Alabama. Species and size preferences displayed by the predator when foraging within the marsh were investigated using nektonic, epifaunal, and infaunal prey populations including Fundulus similis Baird and Girard, Littorina irrorata Say, and Geukensia demissa Dillwyn.

Short-term field experiments involving the use of predator inclusion cages, in which the relative abundances of all prey species and the density of macrophyte vegetation were manipulated, indicated that mean mortality differed significantly among species. Blue crabs exhibited a distinct species preference for Littorina, and to a lesser extent, for Fundulus. However, the predator rarely choses infaunal individuals. Within predator inclusion cages, size selection by the crabs among three size classes of each prey was evident for Littorina and Fundulus but not for Geukensia. Blue crabs tended to select intermediate-sized snails and large fish while not exhibiting a size preference for infaunal bivalves.

In the marsh, mean percentage of the Littorina population within the 14–18 mm size class exhibited an increased mortality as compared to two other size classes, which was negatively correlated with increasing tidal height. Such a relationship may have been due to a decreasing gradient of crab predation associated with increasing tidal height. Geukensia size class distributions showed little evidence of differences along the tidal height gradient. No data are available for Fundulus, a mobile species which would not experience such differential predation along a marsh gradient.

In comparing crab predation patterns among prey species, it is apparent that Callinectes utilizes prey species differentially. Such differential utilization may be based on optimization of energy yield and minimization of energy expenditure. Thus, the preference of blue crabs for nektonic and epifaunal prey is hypothesized to be the result of a smaller energy expediture as a result of the crab's visual evaluation of these prey. Infaunal prey species (e.g., Geukensia) require a greater energy investment because of the necessity of excavating the prey item. Such prey also allow little selection by size because of being cryptic.     

Physical and biological processes influencing zonation patterns of a subtidal population of the marine snail, Astraea (Lithopoma) undosa Wood 1828

The population density and size distribution of the marine gastropod, Astraea (Lithopoma) undosa Wood 1828, at Bird Rock, Santa Catalina Island, CA, reveal an inverse relationship between population density and mean individual size, over a depth gradient. This trend may be correlated with physical and biological differences between habitats for parameters such as water motion, competitive interactions, and predation.

The potential effect of hydrodynamic forces on the zonation patterns of Astraea undosa was tested in laboratory and field experiments. Based on theoretical predictions of the relationship between shear force and water velocity on different-sized snails, large snails are subjected to greater shear forces, as a result of water motion, than medium or small snails. Results of dislodgment experiments conducted in the laboratory indicated that for a given force per unit area, all snails dislodged at nearly the same frequency, with 50% of snails predicted to dislodge at about 4 m/s, and 100% of snails predicted to dislodge at about 8 m/s velocity. These results suggest that hydrodynamic forces may be an important factor in the shallowest subtidal zones.

A factorial-designed caging experiment was used to test the effects of snail population density on growth rates of snails of three different size classes. For small and medium size classes, results indicated an inverse relationship between population density and growth rates, which was especially pronounced for smaller snails. These data, in conjunction with long-term patterns of population density and size distribution in the field, suggest that intraspecific competition also plays a role in determining size-specific zonation patterns.

Tethering experiments, used to estimate predation rates in different algal-cover zones, suggest that there are no differences in survival rates among different snail size classes; however, survival rates differ among zones and may contribute further to the observed zonation patterns. Overall, data indicate that a combination of physical and biological processes controls the population density and size-distribution of Astraea undosa over a depth gradient at Santa Catalina Island, California.     

Crayfish induce a defensive shell shape in a freshwater snail

Abstract. This study was undertaken to determine whether intraspecific variation in shell morphology of the freshwater snail Elimia (= Goniobasis ) livescens is caused by predator-induced morphological changes. Juvenile snails from 3 populations were grown in the presence of effluent from predatory crayfish feeding on conspecific snails or in effluent from conspecific snails only. Snails from one population, Clear Creek, exhibited a predator-induced morphology; they grew a narrow body whorl when exposed to the effluent from crayfish. Experimental feeding trials with crayfish and snails from Clear Creek were conducted to determine whether a narrow body whorl reduced predation in the presence of the crayfish Orconectes propinquus . In the feeding trials, snails with a narrow body whorl were eaten less frequently than snails with wider shells. However, there was no difference in overall size (length) between snails that were eaten and those that were not. Thus, juvenile snails from Clear Creek exposed to the presence of crayfish were induced to develop relatively narrow shells, which reduce the risk of successful attack by these crayfish. Hence the induced shell morphology is probably a defense against predation by crayfish.     

The effects of prey size, predator size, and sediment composition on the rate of predation of the blue crab, Callinectes Sapidus Rathbun, on the hard clam, MercenariaMercenaria (Linné)

Sediment preferences of blue crabs, Callinectes sapidus Rathbun, and predation rates on various size classes of the hard clam, Mercenaria mercenaria (Linné), in a variety of sediment types were studied in the laboratory. Blue crabs of all size classes exhibited a preference for sand, mud, and sand/mud rather than crushed oyster shell or granite gravel. Clams were more vulnerable to predation by crabs in sand and sand/mud than in crushed oyster shell or granite gravel. When crabs were given a choice of clam sizes based on carapace width (CW), small crabs (<75 mm CW) consumed 5- and 10-mm shell length (SL) clams. Medium crabs (75–125 mm CW) preferentially consumed 10-mm SL clams. Large crabs (> 125 mm CW) consumed 10- and 25-mm SL clams equally. Blue crabs did not eat clams that were >40-mm SL.     

Predation induced changes in behavior and growth rate in three populations of the intertidal snail, Littorina sitkana (Philippi)

We investigated the sublethal effects of a predatory crab, Cancer productus (Randall), on the behavior and growth of its snail prey, Littorina sitkana, by setting up controlled rearing and prey-size selection experiments. L. sitkana were collected from three sites on San Juan Island, WA, USA. These sites varied in snail size, abundance, and vertical distribution, and in the abundance of the crab predator C. productus. Snails from all three populations were raised for 34 days under the following treatments: no-crab control, a non-feeding C. productus encased in mesh box, and an encased C. productus feeding on L. sitkana. The non-feeding crab treatment did not affect snail foraging behavior or growth rate in comparison with the no-crab control. In contrast, the presence of a feeding crab elicited escape behavior in the snails, halted grazing, and consequently reduced growth rates. A population difference in escape behavior was observed: upward migration in snails from rocky shores and hiding in crevices in snails from a mud flat. It thus appears that chemicals leaching from crushed conspecific snails, rather than the presence of the crab predator, act as the “alarm substance” to which L. sitkana react. The magnitude of the growth depression in the presence of feeding crabs was 85%, with no difference among the three populations. Once the feeding crab stimulus was removed, snails in all populations resumed normal growth, suggesting that this response to feeding predators is reversible with changing environmental conditions. Laboratory experiments were set up to determine if all size classes of L. sitkana are equally susceptible to C. productus predation. C. productus consistently selected the largest of three size classes of L. sitkana. These results suggest that slow growth rate and small size in L. sitkana may actually be an adaptation for coexisting with high C. productus abundance, rather than simply a cost of escape behavior.     

Predation by the salt marsh killifish Fundulus heteroclitus (L.) in relation to prey size and habitat structure: Consequences for prey distribution and abundance

Laboratory feeding preference experiments show that the maximum size of prey eaten (the snail Melampus bidentatus (Say) and the amphipod Orchestia grillus (Bosc)) increases with increasing size of the predator, Fundulus heteroclitus (L.). Melampus > 7 mm in shell height escape predation by even the largest killifish. In the laboratory, consumption of prey is reduced in high marsh habitat relative to low marsh, particularly in the case of larger fish. Low marsh has few grass stems per unit area, while high marsh is considerably more complex, with dense small stems providing cover for prey and reducing successful fish hunting. The population of Melampus in low marsh within Great Sippewissett salt marsh consists mainly of large snails but this size is rare in high marsh. The size-distribution is inverse for Orchestia, with large amphipods more abundant in high marsh. The construction of fences excluding Fundulus from the marsh surface led to low marsh size-distributions of Melampus and Orchestia resembling those of high marsh, in agreement with the laboratory results. Killifish predation seems to be an important factor regulating the abundance and size-distribution of the two prey species in the two marsh habitats.     

Food limitation of a Delaware salt marsh population of the mummichog,Fundulus heteroclitus (L.)

Summary The relationship of the mummichog, Fundulus heteroclitus, to its food supply was examined using 8 m x 20 m enclosures under field conditions. Density effects were examined by stocking these enclosures with fish at densities ranging from 1/8 to four times the natural population density. Mean growth rate in each pen was estimated from measurements on individually marked fish. Fish enclosed at normal density grew at the same rate as fish from the natural population, indicating that caging had minimal effects on growth rate. When enclosed below natural density, mummichogs had a growth rate that was 2–3 times higher than that of the natural population. Fish enclosed at four times normal density had a negative mean growth rate, a higher mortality rate than fish enclosed at natural density, and no egg production.In further experiments, food was added to the same type of enclosure at fish densities ranging from one-half to four times natural density. Food additions had a positive effect on growth rate at all densities. Food additions also caused egg production of fish enclosed at the highest density to increase to a rate equivalent with the natural population. We conclude that the total food supply may regulate the maximum size of the Canary Creek mummichog population by affecting the individual growth rate, mortality rate, and fecundity.     

Crab: snail size-structured interactions and salt marsh predation gradients

We studied size-structured predator-prey interactions between blue crabs (Callinectes sapidus) and marsh periwinkles (Littoraria irrorata) with a combination of field studies, laboratory experiments and individual-based modeling. Size distributions of Littoraria differed among years at the same sites in a salt marsh and could largely be explained by dominance of strong cohorts in the population. At a given site, abundance increased with elevation above tidal datum. Size-selective predation by blue crabs does not appear to be an important regulator of snail size distributions but may have a major effect on local abundance. Laboratory studies indicated that predator-prey interactions between Callinectes and Littoraria are strongly size-dependent. Crabs were generally effective at feeding on periwinkles at size ratios greater than approximately 6 (crab width: snail length). At lower size ratios crabs were far less effective at manipulating the snails, which often survived but with damaged shells. An individual-based model which incorporated information about incidence of snail shell scarring (resulting from non-lethal interactions) and snail density, predicted reduced predation rates and smaller average crab size with distance from the low tide refugium for crabs.     

The importance of crevices to the intertidal snail Littoraria articulata (Philippi) in a tropical mangrove forest

The intertidal gastropod, Littoraria articulata (Philippi), is common on the trunks of mangroves at Coorooman Creek, Central Queensland. Individuals of shell length less than 3 mm were only found in empty tests of the barnacle Hexaminius popeiana (Foster). Larger snails were exposed on the trunk or occasionally in crevices such as knot holes. The relationship between shell length and shell strength differed between barnacle dwelling and larger L. articulata: in both cases it was linear, but the rate of increase of strength with increasing length was significantly greater for barnacle dwelling snails than for exposed ones. In contrast, there was an exponential relationship between shell strength and length for the weaker shelled Littoraria filosa (Sowerby), which occurs higher on the tree and does not inhabit barnacles. The survival of L. articulata was affected by the presence of crevices: significantly fewer disappeared from posts with artificial crivices than from those which lacked them, and some snails testhered to posts appeared to have been eaten by fish. The importance of crevices is discussed in relation to predation pressure, growth and habitat selection by larval L. articulata. This revised version was published online in July 2006 with corrections to the Cover Date.     

Biomechanical limits to ecological performance: mollusc-crushing by the Caribbean hogfish, Lachnolaimus maximus (Labridae)

Functional limitations on feeding ability were investigated in the mollusc-crushing Caribbean hogfish, Lachnolaimus maximus (Labridae). Two constraints were proposed to limit the maximum size prey L. maximus can eat: pharyngeal jaw gape and crushing force. These factors yield diflferent quantitative expectations for the relationship between fish size and maximum prey size. Their relative importance for predation on a frequently consumed gastropod ( Cerithium litteratum ) was investigated in laboratory performance tests designed to determine the largest snails fish could eat. Cerithium predation was found to be force limited rather than gape limited. The importance of this functional constraint in determining the largest Cerithium consumed by wild fish was examined by comparing hogfish feeding capability, as determined by the performance tests, to the maximum size snails found in the stomach contents of field-collected fish. Crushing ability appears to limit Cerithium predation in natural fish populations. The utility of performance testing for determining the functional and ecological importance of morphology is discussed.     

生态因子对红螯相手蟹捕食毛蚶苗种的影响

敌害生物的捕食在控制海洋底栖生物群落的丰度和组成中起着关键性的作用。以红螯相手蟹(Sesarma haematocheir)和毛蚶(Scapharca subcrenata)为试验对象,研究了红螯相手蟹的密度、规格、性别,以及毛蚶的密度、规格、海水温度和底质条件对毛蚶苗种存活的影响。结果表明,蟹表现出了第二种类型的功能反应,高密度底播毛蚶苗种可以显著提高成活率;当毛蚶苗种壳长达到20mm以上时,蟹的摄食速率显著下降;随着蟹个体的增大,其摄食速率显著增加,毛蚶的存活率下降;当蟹的密度逐渐增加的时候,同种个体之间的干扰竞争显著提高了毛蚶存活率;雄蟹凭借强有力的螯导致了更多毛蚶苗种的死亡;海水温度较低的春季和秋季底播毛蚶苗种可以显著提高成活率;底质条件的复杂性和异质性为毛蚶的存活提供了"庇护空间",从而减少了敌害生物捕食所带来的损失。     

Early development and pathogenesis of Lobatostoma manteri Rohde (Trematoda: Aspidogastrea)

The prosobranch Planaxis sulcatus is reported as a new natural host of Lobatostoma manteri at Heron Island, Great Barrier Reef. Planaxis sulcatus and Cerithium moniliferum were experimentally infected with large numbers of eggs. The larvae hatch in the stomach and migrate immediately along the ducts of the digestive gland into the digestive follicles. The larvae feed on the secretion and probably epithelial cells of the follicles. The acetabulum is used for adhesion to the epithelium and contributes to its erosion. In heavily infected snails, the digestive follicles disappear gradually and the larvae live in cavities lined by a flattened epithelium, parts of which show secretory activity. In snails dissected 47–49 and 65–66 days after infection, the cavities are fused, forming several large spaces which communicate with each other; only small parts of the epithelium are still secretory. Concentrations of amoebocytes occur in the walls of the digestive gland and in the wall between digestive gland and stomach of infected Planaxis. Some young worms were found in the stomach of Planaxis. No tissue reactions were seen around the stomach except in the wall between digestive gland and stomach. In Cerithium with 65–67 days old infection, the cavities contain much detritus and disintegrating cells, the epithelium is practically non-secretory and surrounded by loose connective tissue. In larvae with a body length of approximately 0·5–0·6 mm, the acetabulum begins to divide into alveoli and its anterior end grows forward; the anterior alveoli gradually increase in size and new alveoli are formed in the posterior undivided zone. In two specimens of approximately 1·3 mm body length, the whole adhesive disk was divided into half the number of alveoli usually found in adults. Allometric shifts during growth of the worms are analysed.     

The effect of calcium and pH on Florida apple snail, Pomacea paludosa (Gastropoda: Ampullariidae), shell growth and crush weight

Pomacea (Ampullariidae) snails, commonly referred to as apple snails, serve as prey for many freshwater-dependent predators, and some species are highly invasive. Identifying limits to apple snail distribution and abundance are pertinent to understanding their ecology. Calcium (Ca²⁺) availability and pH generally influences freshwater snail populations, yet scant data exist for Pomacea snails. We measured 6-week change in shell length (ΔSL) in P. paludosa in two laboratory experiments with varying Ca²⁺ and pH levels. ΔSL was significantly higher in ≥28 mg Ca²⁺/l compared with treatments ≤14 mg/l. Snails from populations living in low Ca²⁺/pH waters did not appear genetically predisposed at growing faster in these conditions. Smallest ΔSL was in snails treated with 3.6 mg Ca²⁺/l and pH < 6.5 water; these snails had signs of shell erosion. Shell crush weights (CWs) were lowest for snails grown in the lowest Ca²⁺/pH treatment. Smaller shells and lower CWs have implications for predation vulnerability and reproductive success. Our results are consistent with reports associating relatively low snail densities with relatively low Ca²⁺/pH waters, and they are consistent with the geographic distribution of P. paludosa as related to the underlying water chemistry as influenced by geology.     

Maintenance of the shore-level size gradient in the marine snail Tegula funebralis (A. Adams): Importance of behavioral responses to light and sea star predators

The intertidal gastropod, Tegula funebralis (A. Adams) exhibits a shore-level size gradient with mean shell size increasing in a down-shore direction. Snails transferred to zones where they do not usually occur migrated back towards their original zone, thus re-establishing a size gradient and implying differential movement among size classes. Both large (≥2.1 cm shell width) and small (≤ 1.77 cm) snails were photonegative on a horizontal surface and geonegative in the laboratory; there were no statistical differences between size classes. Light, however, inhibited upward, or caused downward, movement of large snails on vertical surfaces. Small snails were unaffected, ranging higher on illuminated vertical surfaces than large snails. Both sizes exhibited similar distributions in the dark. In an experimental chamber providing both emersed and immersed surfaces, T. funebralis established vertical size gradients when the chamber was illuminated from above. It is suggested that light is an important factor in the formation and maintenance of Tegula's shore-level size gradient.In response to water-borne chemicals derived from the sea star Pisaster ochraceus (Brandt), large snails moved up vertical surfaces in greater proportion than small. In response to contact with the predator, large snails moved away faster than small and individuals collected from crevices in the field moved away slower than those collected from open rock faces. Although predation may select for a size gradient in Tegulafunebralis, it is unlikely that responses to predatory sea stars directly and proximally cause or maintain them over the short term.     

Predator-induced morphological plasticity across local populations of a freshwater snail

The expression of anti-predator adaptations may vary on a spatial scale, favouring traits that are advantageous in a given predation regime. Besides, evolution of different developmental strategies depends to a large extent on the grain of the environment and may result in locally canalized adaptations or, alternatively, the evolution of phenotypic plasticity as different predation regimes may vary across habitats. We investigated the potential for predator-driven variability in shell morphology in a freshwater snail, Radix balthica, and whether found differences were a specialized ecotype adaptation or a result of phenotypic plasticity. Shell shape was quantified in snails from geographically separated pond populations with and without molluscivorous fish. Subsequently, in a common garden experiment we investigated reaction norms of snails from populations' with/without fish when exposed to chemical cues from tench (Tinca tinca), a molluscivorous fish. We found that snails from fish-free ponds had a narrow shell with a well developed spire, whereas snails that coexisted with fish had more rotund shells with a low spire, a shell morphology known to increase survival rate from shell-crushing predators. The common garden experiment mirrored the results from the field survey and showed that snails had similar reaction norms in response to chemical predator cues, i.e. the expression of shell shape was independent of population origin. Finally, we found significant differences for the trait means among populations, within each pond category (fish/fish free), suggesting a genetic component in the determination of shell morphology that has evolved independently across ponds.     

Differential susceptibility of marine invertebrate larvae: Laboratory predation of sand dollar, Dendrasterexcentricus (Eschscholtz), embryos and larvae by zoeae of the red crab, Cancer productus Randall

Predation on eggs, embryos, and larvae of the sand dollar, Dendraster excentricus (Eschscholtz) was investigated in a series of laboratory feeding experiments. Dendraster susceptibility to predation by zoea larvae of the red crab, Cancer productus Randall was strongly dependent on developmental stage and ontogenetic differences in motility. Clearance rates by C. productus were highest for eggs and averaged 0.551·zoea⁻¹·day⁻¹. Embryos and prism larvae of Dendraster were consumed at an intermediate rate, while pluteus larvae were captured at a relatively low rate. Clearance rates decreased from 0.18 to 0.031·zoea⁻¹·day⁻¹ during the transition of prism larvae into echinoplutei. Differences in Dendraster susceptibility to predation cannot be attributed to increasing prey body size because dwarf plutei were captured at the same rate as normal plutei. Reduced capture rates by Cancer productus zoeae are dependent on the development of Dendraster swimming behavior. Periodic reversals in the direction of ciliary beating and backwards swimming effectively remove Dendraster plutei from the immediate capture sphere of Cancer productus. Reversed swimming appears to function as a post-contact encounter response that reduces the mortality rates of Dendraster plutei.     

Biological control of Biomphalaria tenagophila (Mollusca, Planorbidae), a schistosomiasis vector, using the fish Geophagus brasiliensis (Pisces, Cichlidae) in the laboratory or in a seminatural environment

In order to investigate a possible method of biological control of schistosomiasis, we used the fish Geophagus brasiliensis (Quoy & Gaimard, 1824) which is widely distributed throughout Brazil, to interrupt the life cycle of the snail Biomphalaria tenagophila (Orbigny, 1835), an intermediate host of Schistosoma mansoni. In the laboratory, predation eliminated 97.6% of the smaller snails (3-8 mm shell diameter) and 9.2% of the larger ones (12-14 mm shell diameter). Very promising results were also obtained in a seminatural environment. Studies of this fish in natural snail habitats should be further encouraged.     

Demography of a population of Moina micrura kurz (Crustacea: Cladocera) in a temporary pond,peninsula of paraguaná, Venezuela

A population of M. micrura Kurz from a shallow, muddy and temporary pond, located in Peninsula of Paraguaná, western Venezuela, was studied from filling to drying phase. Population density, age structure, fecundity, and length of females, were determined. This population showed a low population density (< 50 ind/1), a low and density-dependent fecundity (mean eggs/adults = 1.3; mean clutch size = 2.1 eggs + embryos), and low juveniles to adults ratio (0.71). No significant correlation was detected between mean clutch size and mean body length of ovigerous females. Our results suggest effects of food limitations, and fish predation on demographic parameters of this population. Still, in unfavourable conditions, some demographics features associated to opportunistic species were evident.     

基于碳、氮稳定同位素研究胶州湾普氏栉虾虎鱼的摄食习性

普氏栉虾虎鱼属于小型暖温性底层鱼类,是胶州湾鱼类群落中的优势种之一,在胶州湾食物网和生态系统中发挥着重要作用.本文应用碳、氮稳定同位素技术,基于胶州湾渔业资源底拖网调查采集的样品,对普氏栉虾虎鱼的摄食习性进行了研究.结果表明: 胶州湾普氏栉虾虎鱼的δ¹⁵N值范围为11.24‰～13.99‰,平均值为(12.70±0.70)‰,δ¹³C值范围为-20.67‰～-18.46‰,平均值为(-19.08±0.36)‰;各体长组的营养级范围为3.49～3.76,平均营养级为(3.62±0.21),其δ¹⁵N值和营养级与体长呈显著负相关,δ¹³C值与体长无显著相关性.普氏栉虾虎鱼摄食的主要饵料生物类群为多毛类、虾类和软体动物,浮游动物和颗粒有机物(POM)的饵料贡献率较小.聚类分析结果表明,普氏栉虾虎鱼各体长组食物组成的相似性均在92%以上,相似性较高,说明其摄食习性随体长变化无明显差异.普氏栉虾虎鱼在胶州湾生态系统中属于中级消费者,其摄食各饵料生物类群比例的变化可能是其营养级与体长呈负相关关系的主要原因.     

红树林恢复初期莱氏锥滨螺分布动态

树栖腹足类动物是红树林底栖动物的重要组成部分,其组成和分布受到红树植被的影响。因此,在红树林生态修复中,腹足类动物的恢复依赖于植被的发育。滨螺科(Littorinidae)锥滨螺属(Mainwaringia)动物是亚洲红树林的广布种,但针对其在红树林中的分布及种群特征的研究较少,对红树林植被恢复过程中锥滨螺属动物的恢复动态更是鲜有研究。调查了厦门下潭尾湿地秋茄(Kandelia obovata)红树林恢复初期,新记录种莱氏锥滨螺(Mainwaringia leithii)种群恢复的时间动态,并分析其与植被参数的关系。研究发现,红树林恢复初期,秋茄植被生长迅速,株高、冠幅、基径和覆盖度分别由0.5年生幼林的41.3 cm、25.0 cm、1.04 cm和25%增长为8年生样地的179.2 cm、76.7 cm、5.96 cm和95%。在秋茄胚轴种植6个月左右开始记录到莱氏锥滨螺的个体,其密度和生物量在1.5 a后达到最大(分别为136个/m²和1.86 g/m²),而后逐渐降低,种植3 a后秋茄林内莱氏锥滨螺仅零星分布。除8年生的样地,莱氏锥滨...