Littorina Irrorata Research Articles

Mercury Exposure and Habitat Fragmentation Affect the Movement, Foraging Behavior, and Search Efficiency of the Marsh Periwinkle (Littorina irrorata).

The interactions between habitat fragmentation and other stressors are considered a key knowledge gap. The present study tested the hypotheses that mercury enhances the effects of fragmentation by (1) reducing the cumulative daily movement of organisms, (2) shifting their foraging behavior, and (3) altering the vertical movement of the marsh periwinkle (Littoraria irrorata) in a field experiment. Random walk simulations were used to access how changes in movement affect the search efficiency of organisms in the long term. Eighteen 1.5 m2 plots were constructed in a salt marsh where landscapes characteristics were manipulated to reach three different levels of habitat cover. Daily movement of 12 marked control and mercury-exposed snails were measured in each plot. Bayesian models were used to analyze the data and evidence ratios were used to test the hypotheses. The results showed that the effects of fragmentation were consistent in both control and exposed treatments, with an increase in the cumulative displacement of organisms. However, mercury significantly reduced the movement of organisms in all levels of fragmentation, shifting their foraging behavior (evidence ratio > 1000). Exposed snails were more likely to be found inactive in comparison with the control treatment (evidence ratio > 1000). Fragmentation also reduced the vertical movement of organisms in both treatments. In contrast, mercury increased the vertical movement of organisms (evidence ratio > 1000). The search efficiency of organisms also increased in a highly fragmentated landscape, suggesting that changes in foraging behavior are likely due to reduced resources and consequently increase in foraging effort. The present study shows that mercury exposure can enhance the effects of habitat fragmentation by changing organisms' movement, foraging behavior, and search efficiency. Environ Toxicol Chem 2023;42:1971-1981. © 2022 SETAC.

Radiocarbon in Marsh Periwinkle (Littorina Irrorata) Conchiolin: Applications for Archaeology

ABSTRACTIn coastal and island archaeology, carbonate mollusk shells are often among the most abundant materials available for radiocarbon (14C) dating. The marsh periwinkle (Littorina irrorata) is one of these such species, ubiquitously found along the Atlantic and Gulf coasts of the United States in both modern and archaeological contexts. This paper presents a novel approach to dating estuarine mollusks where rather than attempting to characterize the size and variability of reservoir effects to “correct” shell carbonate dates, we describe a compound-specific approach that isolates conchiolin, the organic matter bound with the shell matrix of the L. irrorata. Conchiolin typically constitutes <5% of shell weight. In L. irrorata, it is derived from the snail’s terrestrial diet and is thus not strongly influenced by marine, hardwater, or other carbon reservoir effects. We compare the carbon isotopes (δ13C and Δ14C) of L. irrorata shell carbonate, conchiolin, and bulk soft tissue from six modern, live-collected specimens from Apalachicola Bay, Florida, with samples that represent possible sources of carbon within their environment including surface sediments, marsh plant tissues, and dissolved inorganic carbon (DIC) in water. Ultimately, this paper demonstrates that samples obtained from wet chemical oxidation of L. irrorata conchiolin produces accurate 14C dates.

Periwinkle climbing response to water- and airbone predator chemical cues may depend on home-marsh geography.

The salt marsh periwinkle, Littorina irrorata, exhibits a spatial refuge from predation by climbing the stems of Spartina alterniflora in order to avoid benthic predators. Salt marsh periwinkles have a broad geographic distribution, and for many species, responses to predators also varies with biogeography. This study sought to determine if the geographical location of the home marsh influenced the response of periwinkles (climbing height) to blue crab predator cues both via air and water. Snails from Louisiana (LA) climbed higher in general than those from North Carolina (NC), regardless of chemical cue. However, LA snails climbed 11 cm higher in the presence of waterborne predators than control snails with no cue, while NC snails only climbed five cm higher in the same comparisons. Airborne chemical cue tended to have snails climbing at intermediate heights. These responses were significantly enhanced when both populations of snails were housed together. Periwinkle response to predator cues was stronger in LA than NC, and so it is possible that the behavioral response of these snails to predators varies with biogeography of the home marsh. Also interestingly, the results of this study also suggest that cue delivery is probably occurring via mechanisms other than water, and potentially via airborne cues. Therefore, salt marsh periwinkles likely respond to numerous cues that initiate behavioral responses, including airborne cues, and these responses may vary by home-marsh geography.

Utilization of selected non-vertebrate wildlife species in Niger delta, Nigeria

Non vertebrate wildlife resources are the priority means of survival for most rural households in developing countries due to their abundance and free accessibility, but factors militating against their availability and utilisation in the Niger Delta of Nigeria are yet to be known. The study was therefore conducted to investigate both consumptive and non-consumptive utilisation of Crab Callinectes spp; Oyster, Ostrea edulis; Periwinkle, Littorina irrorata; and the Raphia palm weevil Larvae, Rhynchophorus phoenicis and the factors militating against utilisation of the species in the study area. Bassambiri and Ogbolomabiri in Bayelsa State and Isaka and Okrika Communities of Rivers State were selected at random from other communities in Niger Delta with abundance of these selected species. Data for the study were obtained through a set of structured questionnaires, in-depth interview and personal observation. A set of questionnaires were administered systematically to 4% of household representatives in the four selected communities. In all, a total of 301 households were sampled in the four communities. Data obtained were analysed using descriptive statistics such as frequencies and percentages; while Chi-square was used to test significance of associations. Utilisation of Crab, Periwinkle, Oyster and Raphia palm beetle (Edible maggot) is not significantly associated with age, occupation, level of education, and gender but household size (X2 = 158.457a) and knowledge of the species (X2 = 166.699a). The species are used for various consumptive and non consumptive purposes in the communities. Most respondents utilise Crab (71.9%), Oyster (72.2%) and Periwinkle (78.5%) as food while some respondents sell them for income generation. Crab is sold at 4 individuals for N200.00K (1.29 USD) only. Among the four species studied the Edible maggot is the least used as food (28.7%) and the least known by respondents (63.0%).The flesh of these species are used in preparing cultural delicacies such as Crab soup and Periwinkle soup in Nembe community. In Nembe, Shells of Periwinkle and Oyster are used by respondents in checking erosion, elevating frontages, solidifying marshy grounds, as substitutes for gravel during construction and as source of calcium in feed meals. The factors militating against utilisation of these non vertebrate wildlife species were identified as skin irritation after consumption, cultural belief, religious belief and limited knowledge of respondents about the species. Households in Okrika and Isaka do not utilise the edible mag- got, as they lack knowledge of the species. These non-vertebrate species are of utmost importance to the rural people of the Niger Delta. Their decline and depletion could result in loss of income. Tropical Agricultural Research and Extension 15(4): 2012: page 108-114

Availability and Nutritional Values of Selected Non Vertebrate Wildlife Species in Niger Delta, Nigeria

The study investigated the sources, availability, and nutritional values of Crab (Callinectes spp); Oyster (Ostrea edulis); Periwinkle (Littorina irrorata); and the Raphia palm weevil larvae (Rhynchophorus phoenicis) in the study area. Bassambiri and Ogbolomabiri in Bayelsa State and Isaka and Okrika Communities of Rivers State were selected at random from other communities in Niger Delta with abundance of these selected species. Data for the study were obtained through administration of structured questionnaire, in-depth-interview and personal observation. A set of questionnaires was administered systematically to 4% of household representatives in the four selected communities. In all, a total of 301 households were sampled in the four communities. Data obtained were analysed using descriptive statistics. The species are harvested manually or with local traps. According to many respondents (54.46%) Crabs are more abundant in the rainy season while the Oyster, Periwinkle and Edible maggot are more abundant during the dry season. Although Periwinkle, Oyster, Crab and Raphia palm weevil larvae contain Sodium, Phosphorus, Potassium, Magnesium, Calcium and Iron, Crab is relatively the best source of Calcium among the species, while Oyster is the least since the shells are entirely removed during extraction. Harvesting of these species is done by most members of households. Boiling is the most preferred method for processing these species because it makes them tasty (64.03%). However, majority (83.33%) of respondents from Ogbolomabiri community in Bayelsa State prefer smoking the species because it increases their shelf life. These non-vertebrate wildlife species are of utmost importance to the rural people of the Niger Delta thus their decline and depletion subsequently could result in loss of income, malnourishment and overall poverty.

Sexual Dimorphism and Feeding Ecology of Diamond-backed Terrapins (Malaclemys terrapin)

Natural and sexual selection are frequently invoked as causes of sexual size dimorphism in animals. Many species of turtles, including the Diamond-backed Terrapin (Malaclemys terrapin), exhibit sexual dimorphism in body size, possibly enabling the sexes to exploit different resources and reduce intraspecific competition. Female terrapins not only have larger body sizes but also disproportionately larger skulls and jaws relative to males. To better understand the relationship between skull morphology and terrapin feeding ecology, we measured the in-lever to out-lever ratios of 27 male and 33 female terrapin jaws to evaluate biomechanics of the trophic apparatus. In addition, we measured prey handling times by feeding Fiddler Crabs (Uca pugnax), a natural prey item, to 24 terrapins in the laboratory. Our results indicate that although females have disproportionately larger heads, they have similar in:out lever ratios to males, suggesting that differences in adductor muscle mass are more important in determining bite force than jaw in:out lever ratios. Females also had considerably reduced prey handling times. Understanding the factors affecting terrapin feeding ecology can illuminate the potential roles male and female terrapins play as top-down predators that regulate grazing of Periwinkle Snails (Littorina irrorata) on Cord Grass (Spartina alterniflora).

Diet of the Carolina Diamondback Terrapin (Malaclemys terrapin centrata) in Northeastern Florida

Abstract We evaluated the diets of 81 Carolina diamondback terrapins (Malaclemys terrapin centrata) from northeastern Florida by analyzing fecal samples. Female diets were significantly different from male diets (p < 0.01); fecal samples from females contained crabs, marsh periwinkles (Littorina irrorata), and dwarf surf clams (Mulinia lateralis) in that order of occurrence, whereas fecal samples from males had dwarf surf clams and crabs in that order. We suggest that head-size dimorphism is advantageous to females during nesting forays when they experience a shift in prey availability.

Shell use by juvenile fiddler crabs Uca pugnax and U. pugilator

The present study documents for the first time shell use by juvenile fiddler crabs in the salt marsh. Twenty visits were made to six salt marsh sites at Tybee Island, Georgia between 2007 and 2009. One hundred empty Littorina irrorata shells were collected at each site on each field trip. Juvenile carapace width was measured, crabs sexed, and species identification completed using RFLP analysis. Shell use of up to 79% was observed. Two species of fiddler crabs were found in empty shells, Uca pugnax and U. pugilator. U. pugnax was the dominant species at all sites representing 62–84% of the juvenile fiddler crab population. Juvenile sex ratios were female-biased (1.7:1) at all six sites. Juvenile size did not vary significantly between species but males of both species were significantly larger than females. Size frequency distribution of carapace width revealed that shell use varied with size and sex. In the 3 to 4 mm size class, juvenile females outnumbered juvenile males in empty L. irrorata shells while in the 5 to 6 mm size class and greater, juvenile males outnumbered juvenile females in shells. Significantly more juvenile fiddler crabs were found in empty shells during flood than ebb tide at 3 of the sites. This discovery illuminates the resourcefulness of juvenile fiddler crabs and provides another mechanism that might enhance survival.

Motor pattern control for increasing crushing force in the striped burrfish ( Chilomycterus schoepfi)

The relationship between muscular force modulation and the underlying nervous system control signals has been difficult to quantify for in vivo animal systems. Our goal was to understand how animals alter muscle activation patterns to increase bite forces and to evaluate how accurate these patterns are in predicting crushing forces. We examined the relationship between commonly used measures of cranial muscle activity and force production during feeding events of the striped burrfish ( Chilomycterus schoepfi), a mollusc crushing specialist. We quantified the force required to crush a common gastropod prey item ( Littorina irrorata) of burrfish using a materials testing device. Burrfish were fed these calibrated prey items while we recorded electromyograms (EMGs) from the main jaw closing muscles (adductor mandibulae A1 β, A2 α, and A2 β). We quantified EMG activity by measuring the burst duration, rectified integrated area, and then calculated the intensity of activity from these two variables. Least squares regressions relating force to crush ( F crush ) and all EMG variables were calculated for each fish. Multiple regression analyses were used to determine how much of the variation in F crush could be explained by muscle activation patterns. We found that 20 cm burrfish are capable of generating extremely high crushing forces (380 N peak force) primarily by increasing the duration of muscle activity. EMG variables explained 71% of the total variation in force production. After accounting for the inherent variation in F crush of snails, EMGs do a very good job of predicting bite forces for these fish.

Grazing rates of organic matter and living fungal biomass of decaying Spartina alterniflora by three species of salt-marsh invertebrates

The pathway for the flow of salt-marsh grass production into marsh food-webs is still not well defined. We compared the abilities of three marsh macroinvertebrates [salt marsh periwinkles, Littoraria irrorata (Say) (=Littorina irrorata), salt-marsh coffee-bean snails, Melampus bidentatus (Say); and a talitrid amphipod, Uhlorchestia spartinophila Bounsfield and Heard] to access standing-dead leaves of smooth cordgrass (Spartina alterniflora Loisel). The invertebrates were incubated with naturally-decaying leaves, and the rates of removal of organic matter and living fungal biomass (ergosterol) were measured. The impact of invertebrate activity upon fungal growth rates was measured as rates of fungal-membrane synthesis (incorporation of radioacetate into ergosterol). The removal rates of organic leaf biomass per mg individual biomass were highest for amphipods (700 μg mg−1 d−1) and lowest for periwinkles (90 μg mg−1 d−1), but the relatively large biomass of the snails made their removal rates per individual greater than those of amphipods. Net removal of ergosterol by all three invertebrates was >50% for yellow-brown (early-decay) leaf blades. For fully-brown (advanced-decay) blades, >50% removal of ergosterol was found only for periwinkles; exposure to coffee-bean snails and amphipods resulted in a net ergosterol reduction of ≤20%. The lower net reduction of living fungal biomass by coffee-bean snails and amphipods may have been due to fungal-growth stimulation (2.3-fold stimulation in coffee-bean snails and 1.5-fold stimulation in amphipods). Grazing by periwinkles did not stimulate fungal growth, possibly because of its high intensity. Grazing by these three salt-marsh shredders may affect marsh-grass shoot-decay in different ways. Periwinkles may abbreviate the period of fungal production, and incorporate the decaying material relatively quickly into snail biomass and fecal-pellet rain to the sediments. Coffee-bean snails and amphipods may enhance and prolong fungal production, along with the formation of fecal-pellet rain. All three invertebrates fed preferentially on leaf blades rather than leaf sheaths, and feeding rates of gastropods were higher during the night than during the day.

The effects of polycyclic aromatic hydrocarbon contamination and grazing on the abundance and composition of microphytobenthos in salt marsh sediments (Pass Fourchon, LA)

Abstract A microcosm experiment was conducted to examine the effects of polycyclic aromatic hydrocarbon (PAHs) contamination on the abundance and composition of microphytobenthos in surface (0–10 cm) sediments collected from a salt marsh in Pass Fourchon, LA. Plant pigment biomarkers were used to monitor changes in the microphytobenthos in sediments (over 60 days) with treatments containing high and low concentrations of PAHs. Grazing pressure on microphytobenthos by the periwinkle snail Littorina irrorata as well as its responses to PAH contamination were also examined. Concentrations of total PAHs declined in sediments over the duration of the experiment in all microcosms. There was a pattern of increasing relative abundance of high-molecular-weight PAHs in High-PAH sediments (5.5–16 ppm). Microphytobenthic biomass, estimated by chlorophyll- a concentrations, did not significantly change in the treatments with Low-PAH sediments (0.04–0.33 ppm); however, biomass decreased significantly in all treatments after 4 days from 64 μg to 2–8 μg g dry sed. −1 . Concentrations of the carotenoids fucoxanthin (a biomarker for diatoms) and zeaxanthin (a biomarker for cyanobacteria) were consistent with chlorophyll- a, showing little change in Low-PAH treatments; sediments from the High-PAH treatments showed significantly higher concentrations of fucoxanthin and zeaxanthin (1.8 and 1.2 μg g dry sed. −1 , respectively) than the Low-PAH treatments during the initial phase of the microcosm experiment. However, concentrations of fucoxanthin and zeaxanthin decreased dramatically after 4 days to 0.1–0.3 μg g dry sed. −1 and 0.01–0.15 μg g dry sed. −1 , respectively. Increased total phaeophorbide concentrations (a biomarker for metazoan grazing) over the first 12 days of the experiment in treatments with and without L . irrorata additions indicated that meiobenthos may have been important in grazing-down microphytobenthos. High-Exposure snails (from High-PAH field sites) gained more weight during the initial phase of the experiment when microphytobenthic abundance was decreasing but eventually lost more weight than did Low-Exposure snails (from Low-PAH field sites) by the end of the experiment. Although there was considerable variability in the snail growth values, we speculate that the High-Exposure snails were more active in feeding during this experiment and, after the initial decline in microphytobenthos, became resource-limited throughout the remainder of the experiment.

Shell Strength of Mud Snails (Ilyanassa obsoleta) May Deter Foraging by Diamondback Terrapins (Malaclemys terrapin)

Diamondback terrapins (Malaclemys terrapin) do not eat the common and abundant mud snail (Ilyanassa obsoleta) even though terrapin diets are dominated by similarly sized gastropods. To resolve this paradox, we tested a structural defense hypothesis as the potential deterrent against predation. We compared resistance to compressive force of Ilyanassa and three invertebrates (Littorina irrorata,) Uca spp, and Callinectes sapidus) that terrapins commonly eat. Ilyanassa shells were 2-3 times more resistant to crushing than the other prey. High processing costs for mud snails (in terms of structural resistance to crushing) may deter predation by terrapins despite the low search costs and equivalent energetic returns relative to alternative prey items.

Effects of pipeline construction on the vegetation and macrofauna of two South Carolina, USA salt marshes

We examined the recovery of vegetation and salt marsh macrofauna in a pipeline construction corridor at two locations where it intersected intertidal salt marshes near Charleston, SC. The impacts of construction were evaluated prior to construction and for subsequent periods of 34 and 46 months at the two sites using aerial photography and three field sampling methods. Quadrats were used to estimate densities of selected salt marsh invertebrates, as well as stem densities and aboveground wet-weight biomass ofSpartina alterniflora; pit traps were employed to simulate natural tidal pools for sampling small, motile epibenthic macrofauna that remained on the marsh surface at low tide; and flume nets were used to sample the natant macrofauna that used the marsh edge at high tide. The analyses of vegetation by quadrat and aerial imagery clearly showed that the recovery ofSpartina was more rapid and complete at the Ashley River site (88%) than at Wappoo Creek (48%). In contrast to this apparent, if partial, vegetative recovery, several salt marsh invertebrates, including,Littorina irrorata andGeukensia demissa, were eliminated from the corridor during construction and showed scant recovery by the end of our study. Differences in species composition and abundance of natant organisms in the flume net collections also supported the conclusion that faunal recovery was incomplete after 3–4 years at these sites. The recovery of functional equivalency of the excavations, compared with natural marshes, was not evaluated during our study, but we speculate that their functioning may equilibrate over time, since preexisting hydrologic conditions are more or less intact, seedstock forSpartina revegetation is nearby, and macrofauna will probably eventually reestablish themselves from adjacent areas.

Multiple Mechanisms of Resource Acquisition in Hermit Crabs: Scrums and Odor-Induced Grasping (Decapoda, Diogenidae)

Two behavioral mechanisms shown by hermit crabs (brief grasps of shells and scrum formation) which increase their chances of obtaining new gastropod shells were examined. Individuals of Clibanarius vittatus which smell odors from the snail Littorina irrorata show brief grasps of L. irrorata shells occupied by hermit crabs but long grasps of empty shells. The brief grasp allows identification of the species of shell and whether or not it is occupied. Hermit crabs which are attracted to and closely attend a pair of crabs engaged in shell exchange behavior (scrummage formation) sometimes obtain a shell vacated by the initiating crab as it moves into the shell vacated by the non-initiating crab. These behaviors minimize the time spent by crabs on shells that are not available for easy occupation.

Behavioral thermoregulation inlittorina irrorataby climbing

Littorina irrorata exhibit a positive relationship between substratum temperature and the probability of climbing Spartina alterniflora stems in coastal salt marshes. In August, 1988, at Dauphin Island, Ala., we examined whether or not relationships existed between snail internal temperatures and mud substratum temperature, air temperature, height of snails on vegetation, and plant stem temperatures within low and mid‐intertidal zones. Snails observed at >2cm height on Spartina stems exhibited significantly lower internal temperatures than those found close to the substratum. Snails close to the substratum exhibited a positive relationship between internal temperature and mud temperature, while a negative relationship existed between snail temperature and height on stems for snails elevated above 2 cm. Immobilized snails heated artificially in the laboratory did not reduce their internal temperatures. Therefore, we conclude that climbing behavior enables snails to thermoregulate, avoid mortality due to th...

Behavior and respiration of the salt marsh periwinkle,Littorina irrorata(Say), during winter

The response of the salt marsh periwinkle (Littorina irrorata) to changing environmental conditions was studied in the field and under controlled laboratory conditions. Similar results were obtained in both studies and showed that maximum daily air temperature was the single most important factor controlling snail activity. With declining (23°C to 13°C) temperatures, snail movement was significantly reduced from more than 40% of the sample at temperatures >15°C to 12% at 14°C. Under an increasing regime (0°C to 18°C) dormancy was broken near 11°C in some trials and at 14°C in others. Oxygen consumption rates of warm‐adapted (23°C) and cold‐adapted (0°C) snails were tested at 6, 16 and 26°C. At 6°C, cold‐adapted snails consumed less oxygen than did warm‐adapted snails, but the reverse was true at 26°C. These results suggest that temperature plays a major role in the activity and dormancy of L. irrorata and that the observed dormancy can be classified as true hibernation. In the temperate extension of L. ir...

Digestion of Spartina alterniflora Loisel material with and without fungal constituents by the periwinkle Littorina irrorata Say (Mollusca:Gastropoda)

Visceral hump extracts of the saltmarsh periwinkle Littorina irrorata released more sugars but less amino acids from freshly collected cordgrass leaves ( Spartina alterniflora) than from fungal mycelium ( Phaeosphaeria typharum). When S. alterniflora leaves were first conditioned by the fungus P. typharum, periwinkle enzymes released 19% more amino acids and 11% more sugars. When a lignocellulose preparation or NaOH-extracted S. alterniflora were used, enzymatic sugar release did not change or declined after fungal conditioning. Amino acid release increased in both cases. Culture filtrates of P. typharum growing on S. altemiflora leaves formed insoluble particles when mixed with S. altemiflora leachate, or vanillic acid, or coumaric acid. Periwinkle extracts were able to release amino acids from these phenol-protein particles.

The effect of trail‐following on the locomotion of the marsh periwinkleLittorina irrorata(mesogastropoda: Littorinidae)1

The marsh periwinkle, Littorina irrorata, like many gastropods, can detect conspecific mucous trails and often follows them with polarity. Although trail‐following is a common component of L. irrorata's behavioral repertoire, the adaptive significance of this behavior is not evident. This study examined some of the biomechanical and energetic advantages of tracking in L. irrorata. Mean crawling speeds of L. irrorata on artificial and natural substrata ranged from 0.615 to 1.74 mm/sec and tended to decrease with increasing substratum particle size. The presence of a conspecific's mucus did not affect snail speed over the substrata tested. Similarly, analysis of the foot morphology of marker and tracker snails revealed no significant differences between foot area, perimeter, maximum width, or shape (foot length/foot width). The maximum foot length of markers’ feet were significantly greater than those of trackers. Laboratory tests showed that tracking over the trail of a conspecific required between 15% and...

Decomposition and microbial dynamics for standing, naturally positioned leaves of the salt-marsh grass Spartina alterniflora

Decomposition of leaves of smooth cordgrass (Spartina alterniflora Loisel.) was monitored for two cohorts of leaves from September 1984 to May 1985 (autumn and winterspring) at Sapelo Island (31°23′ N; 81°17′ W). The leaves were tagged in plance at the ligule, rather than cut and placed in litterbags. Dead leaves were not abscised from shoots. Loss of organic mass from the attached leaves was at least 60 to 68% of the orginal values. Fungal mass, as measured by an enzyme-linked immunosorbent assay, formed > 98% of the microbial standing crops in two of three autumn samples, and in all samples for the colder, drier, winterspring cohort. Fungal mass was probably mostly in the form of the mycelium and pseudothecia of an ascomycete, Phaeosphaeria typharum (Desm.) Holm. Fungal dominance of microbial standing crops declined when autumn leaves bent downward and acquired a large sediment content (ash=35% of dry matter); the bacterial crop then rose to 7% of the total microbial crop. Microphotoautotrophic mass was always measurable, but was never more than 2% of the microbial crop. Carbon-dioxide fixation was much lower than carbon-dioxide release, and a substantial portion of the fixation may have been anaplerotic fungal fixation. Threeto 8 wk net fungal productivity (average per day) was much greater (16 to 26 times) than measured instantaneous bacterial productivity (extrapolated to per-day values) early in each decay period. Fungal productivity was negative late in the decay period. Fungal productivity was negative late in the decay period for autumn leaves, and was approximately equal to bacterial productivity late for winter-spring leaves. Net nitrogen immobilization was observed only late in the decay period for autumn leaves, implying that nearly all dead-leaf nitrogen was scavenged into fungal mass after the first sampling interval. Flux estimates for dead-leaf carbon indicated a flow of 11–15% of the original to fungal mass, 2% to bacterial mass, 15–21% to carbon dioxide, 10–12% to dissolved leachage, and 34–36% to small particles; 32–39% remained attached as shreds at the end of the study periods. Salt-marsh periwinkles (Littorina irrorata Say) appeared to be the major shredders of dead leaves and conveyors of leaf-particulate material to the marsh sediment, at least in those parts of the marsh where the snails are densely concentrated (usually areas of short- and intermediateheight cordgrass shoots).

Effects of temperature on climbing behavior ofLittorina irrorata: On avoiding a hot foot

Intertidal salt marsh inhabitants, such as the snail, Littorina irrorata, often exhibit vertical migration between the mud substratum and stems of Spartina altemiflora in synchrony with the tidal cycle. However, this behavior, which has been characterized as a predator avoidance mechanism, also occurs at low tide when aquatic predators are absent. Previous studies may have underestimated the contribution of physical factors in selecting for a behavior which reduces mortality in such a population. A positive relationship between substratum temperature and climbing behavior was demonstrated in the laboratory as well as in the marsh habitat. Temperatures exceeding 35°C in the laboratory resulted in either climbing or inactivity. At a substratum temperature of 40°C, snails exhibited a preference for climbing stems of lower temperatures (e.g., stems of ≤25°C exhibited an 0.80 probability of eliciting climbing behavior). In the marsh, a positive relationship between substratum temperatures ≥29°C and snail climb...