Genetic and environmental effects on the growth rate of Littorina saxatilis

Transfer experiments with two morphs of Littorina saxatilis Olivi (=L. rudis) typically inhabiting exposed and sheltered localities, showed a between-morph difference in shell growth in the same type of habitat, and a withinmorph difference between exposed and sheltered environments. The former indicates a genetic difference between the two morphs, although growth rate has an environmental component as shown by the latter. Juvenile snails of the exposed morph were on average slightly larger than sheltered morph juveniles on hatching, but at 20 wk, when raised in identical environments, the sheltered morph juveniles had grown significantly larger than the exposed ones. A rise in temperature from 5° to 10°C enhanced growth rate for snails raised in the laboratory. Temperature alone could not however explain increased growth during the spring and summer in natural populations.     

Geographic variation in the growth rates of Littorina littorea and L. saxatilis

The two intertidal grazers Littorina littorea and L. saxatilis occupy extensively overlapping distributions on both sides of the Atlantic. Morphological, electrophoretic and physiological evidence suggests that the direct developer L. saxatilis is more geographically differentiated than the planktonic developer L. littorea. This hypothesis was tested by collecting both species in 1980 and 1981 from three geographically separated beaches in Massachusetts, USA, marking them, and releasing them in two of the sites. Individuals from all three L. littorea populations, grown at a common site, tended to grow at similar rates, while L. saxatilis exhibited consistent population differences in individual growth. This study supports the view that L. saxatilis achieves its broad geographic distribution via locally adapted ecotypes, while L. littorea achieves its distribution by individual physiological plasticity.     

Evaluation of the significance of metal-binding proteins in the gastropod Littorina littorea

Measurements of metals in Littorina littorea from clean and contaminated sites in Great Britain confirmed that body concentrations of Ag, Cd and Hg vary according to environmental contamination, while the essential elements Cu and Zn are regulated. Investigation of the cytosolic distribution of metals in L. littorea, using Sephadex G-75 gel-permeation chromatography, revealed important distinctions in the partitioning of elements. In contrast to Ag and Hg, which were mainly associated with high molecular weight ligands, Cd was bound predominantly to an intermediate molecular weight, soluble protein (CdBP-I, apparent mol. wt=20 000). However, although the main function of CdBP-I, both in clean as well as contaminated individuals, was sequestration of Cd, significant quantities of other non-essential metals (Ag, Hg) were similarly bound. Laboratory experiments confirmed the role of CdBP-I in complexing cadmium, and also revealed the induction of a second cadmium-binding protein (CdBP-II) in response to high cadmium levels. The apparent molecular weight (10 000), absorbance characteristics and high (inducible)-SH content of CdBP-II suggest similarities with metallothionein. A dose-related increase in the-SH content of very low molecular weight (>3 000) fractions was also observed in cadmium-exposed L. littorea, although no cadmium was associated with these ligands. A detoxifying role is tentatively proposed for the metal-binding proteins CdBP-I and II in L. littorea. However, some spillover of cadmium to the high molecular weight protein pool was observed in individuals exposed to cadmium in the field and laboratory. The use of L. littorea in biochemical assays of environmental contamination is discussed.     

Sodium regulation in the shore crab Carcinus maenas as related to ambient salinity

The activity of Na–K-ATPase was measured in crude homogenates prepared from various organs (leg muscle, pincer muscle, heart, testes, digestive gland, hypodermis, gills 1–9) of shore crabs, Carcinus maenas L., acclimated to salinities ranging between 10 and 50 S (in steps of 10 S). In all salinities tested, Na–K-ATPase activity was highest in posterior gills 7–9 (10–12 mol P_i mg protein^-1 h^-1), followed by anterior gills 1–6 (ca. 2.5 mol P_i mg protein^-1 h^-1) and the other organs (in most cases far below 2mol P_i mg protein^-1 h^-1). In gills only, Na–K-ATPase activity was salinity-dependent, with the highest values in the lowest salinities and vice versa. In gills 7–9, Na–K-ATPase activity was increased more than threefold following a reduction in salinity from 50 to 10 S. Na–K-ATPase activity, expressed as percentage of total ATPase activity, amounted to 60–80% in gills, about 60% in hypodermis and 20–40% in the other organs. Ouabain, a specific inhibitor of Na–K-ATPase activity, reduced serum osmolalities in crabs kept at 9–10 S only when injected into the hemolymph (1 and 5 · 10^-5 M), but had no effect when dissolved in ambient water (10^-4 M). The results obtained underline that crustacean gills are the main organs for ionic regulation, and confirm the hypothesis of the central role of the Na–K-ATPase in active Na uptake as the basic mechanism of hyperregulation in dilute media. Reduction of serum osmolalities following injection of ouabain into the hemolymph confirms previous reports on localization of the sodium pump in the basolateral parts of epithelial cells.     

Rhythmic vertical migration of the gastropod Cerithidea decollata in a Kenyan mangrove forest

In Mida Creek, Kenya (3°20′S, 40°5′E), at high water, the snail Cerithidea decollata dwells on the trunks of mangrove trees (Avicennia marina), while during low water it migrates to the ground, foraging at various distances from the trunk, where it aggregates again well before the incoming tide. Snails from the upper shore level are 150–200 m distant from those living at the lower shore level and they cluster at lower heights on trunks. In any case, sufficient height is usually attained to avoid being submersed. An experiment was designed (February and October 2005), exchanging individuals from different shore levels subject to different tide regimes, in order to test whether snails rely on internal information or on external, direct cues, to adapt their behaviour to local conditions. Results show that C. decollata mostly rely on internal information, presumably based on an internal clock. When individuals from upper and lower shore levels were exchanged, their internal clocks continued to govern when to ascend the home trunk and how high to climb for five to six successive tides, after which the behaviour was reset to the new local conditions.     

Carbon emission associated with respiration and calcification of nine gastropod species from the intertidal rocky shore of Western Europe

Intertidal rocky shores are characterized by vertical zonation that results from the interplay between environmental conditions, organism physiology, and species interactions. Metabolism of intertidal organisms is highly variable between species and it changes with vertical position along the intertidal gradient. The present study aimed to quantify the carbon metabolism of nine intertidal rocky shore gastropods, in order to clarify their respective roles in carbon production during emersion and immersion. The influences of monthly temperature variation and tidal level were tested for each species. Analyses were performed in the laboratory using the infrared gas analyzer method for measuring aerial respiration rates, and the dissolved inorganic carbon and total alkalinity technique for measuring aquatic respiration rate and calcification. Hourly carbon fluxes were calculated for the mean annual temperature of 13 °C measured in both air and underwater in the study area. Respiration rates were similar for emersion (8–25 μmol CO₂ g AFDW^?1 h^?1) and immersion (10–23 μmol DIC g AFDW^?1 h^?1). For all species, underwater respiration fluxes were more influenced by monthly temperature variation than by air fluxes, probably as an adaptation to the rapid changes occurring during emersion. Calcification was an important factor influencing annual carbon fluxes for all studied species; every species showed different calcification rates according to its size and position on the intertidal zone. Annual carbon emissions were calculated using the mean immersion/emersion time of each species. Intertidal gastropod carbon emission was primarily influenced by body biomass and their vertical position within the intertidal zone.     

In situ variation in heart rate of the shore crab Carcinus maenas in relation to environmental factors and physiological condition

Heart rate of Carcinus maenas was recorded continuously for two days in situ, together with water temperature, salinity, depth and light intensity. Of each sex, 25 crabs were used and assigned to groups on the basis of size and colour (the carapace changes colour with prolongation of the intermoult phase). Wet weight:dry weight ratios of midgut gland, muscle, gonads and whole body were examined together with midgut gland lipid content and haemolymph protein concentration. Heart rates and wet wt:dry wt ratios for all the tissues examined were higher in early intermoult than in late intermoult stages of the adult C. maenas (P<0.05). Heart rate, lipid content and haemolymph protein concentrations were higher and wet wt:dry wt ratios of midgut gland, gonads and whole body were lower in juvenile crabs than in adults (P<0.05). The relationship between heart rate and wet wt:dry wt of whole body differed among C. maenas in early and late intermoutl. Heart rate was positively correlated with midgut gland lipid content (a Darwinian fitness parameter) in crabs that were in late intermoult. Physico-chemical environmental parameters, sex and colour accounted for 12% of the variation in heart rate of C. maenas recorded in situ. Temperature and prolonged intermoult were the most important factors influencing heart rate. The findings are discussed in relation to laboratory studies of cardiac activity and observed behaviour of C. maenas in the field.     

Huddling up in a dry environment: the physiological benefits of aggregation in an intertidal gastropod

In many intertidal gastropods, the formation of aggregations and closing of the opercular opening are behaviors commonly assumed to be associated with water conservation and maintenance of body temperature during tidal emersion periods. In the laboratory, we quantified the relationship between these two behaviors in a littorinid snail common to the north-central shores of Chile, Echinolittorina peruviana, and evaluated any benefit of these behaviors during desiccating conditions. We predicted that solitary individuals would maintain their opercula open for less time than aggregated snails when exposed to drier conditions due, at least in part, to differences in evaporative water loss. In laboratory trials, where relative humidity was manipulated, we observed that aggregated snails maintained their opercula open for longer periods of time than solitary snails under increasingly drier conditions. These results, together with observations of body temperature, suggest that aggregated animals may able to maintain gaseous exchange with their environment for longer periods of time than solitary individuals in response to desiccation stress. Our results suggest an interactive effect of two behaviors that confer physiological benefits when confronted with extreme physical conditions experienced during periods of emersion.     

Interindividual variability in metal status in the shore crab<Emphasis Type="Italic"> Carcinus maenas</Emphasis>: the role of physiological condition and genetic variation

The relations between genetic variation, physiological condition, size and metal status in the shore crab Carcinus maenas (L.) were investigated. Shore crabs were collected at three sites around the island of Funen, Denmark, and carapace width, colour, moulting stage and major ions and protein in the haemolymph were determined. Concentrations of water, cadmium, copper and zinc in midgut glands, muscles and gills were measured, and allozyme variation at 15 loci was studied. Generally, tissue water content and copper, zinc and cadmium concentrations decreased from the moulting stages C₃ over C₄ to D crabs, whereas the opposite was true for copper and zinc concentrations in gills and muscle. However, the water content of the tissues increased with the size of the crabs. Since tissue water contents changed consistently over moulting stages, conclusions on changes in metal concentrations sometimes diverged when expressed on a dry versus wet weight basis. Regarding allozymes, esterase, malate dehydrogenase and phosphoglucomutase were polymorphic. The crabs showed a low level of genetic variability for both polymorphism (0.14) and for heterozygosity (0.07) at the three sites. Allelic frequencies showed very low levels of differentiation among the samples, no evidence of inbreeding and no population subdivision. Multilocus heterozygosity was positively correlated with size. Concentrations of copper and zinc in midgut gland, muscle tissue and gill were not correlated with genotype, whereas a weak correlation between phosphoglucomutase genotypes and concentrations of cadmium in the midgut gland was found.Communicated by M. Kühl, Helsingør     

Diets of four deep-water scaphopod species (Mollusca) in the North Atlantic and the Nordic Seas

The buccal pouch contents of four deep-water scaphopod (Mollusca) species, Pulsellum affine, Pulsellum teres, Siphonodentalium lobatum and Polyschides olivi, collected in the North Atlantic and the Nordic Seas, were examined. The buccal pouches of the examined scaphopod species contained almost exclusively foraminifers, which agrees with previous studies on shallow and deep-water scaphopods. The scaphopods seemed to be engulfing at least some of the most common foraminifer species, which are distributed in the cold waters of the Nordic Seas or the temperate waters in the northernmost part of the North Atlantic. About half of the food species (30 foraminifer species) occurred in only one scaphopod species, nearly always in very low numbers, and seemed to be an unimportant food source. The remaining and more frequent food species occurred in two or more scaphopod species. A similarity tree was calculated with parsimony and presence–absence coding of the food species in the scaphopods. This resulted in the similarity tree: 100%{P. teres 79%[P. affine 70%(P. olivi and P. lobatum)]}, when branch support was measured with percentage jackknife stability. A general trend was found towards larger food items being consumed by larger scaphopod species, indicated by the positive correlation between the size of the scaphopods and the food species. It is suggested that microdistribution of the foraminifers and the large individual size of the foraminifers may be important factors in avoiding predation by scaphopods.     

Growth and reproductive rates of Littorina rudis from three contrasted shores in North Wales,UK

Data are presented on growth and reproductive rates of Littorina rudis Maton from 3 contrasted habitats: a sheltered saltmarsh, a moderately sheltered boulder shore and an exposed cliff face. Growth was fastest in L. rudis from the moderately sheltered boulder shore, followed closely by snails from the sheltered saltmarsh. Growth was much slower and the asymptotic size much less in L. rudis from the exposed cliff face, this being attributed to the reduced time available for foraging caused by longer and more erratic periods when the substratum dries out. Eggs extracted from the brood chambers of the saltmarsh L. rudis took about 72 d to hatch in the laboratory at 10°C. No seasonal trend was detected in the percentage of sexually mature snails, which fluctuated erratically round about 54 to 99% in each population. Similarly, the ratio of females: males fluctuated erratically about 1.0. The number of eggs and embryos held in the brood chamber peaked in May–June and birth rates (release of young from the brood chamber) peaked in July-August. Following a lull in August, the brood chamber contents were maintained at moderately high levels throughout the winter, whereas the birth rates declined to very low levels. These differences in the seasonal cycle of brood chamber contents and birth rates were probably caused by seasonal differences in embryological development rate and in the propensity of the young to leave the brood chamber. Fecundity increased with parental size and, because of this, the smaller, slower growing exposed-shore L. rudis had much lower potential fecundities than L. rudis from the other shores. However, the size-specific fecundity of the exposedshore L. rudis was about 1.7 times that of L. rudis on the more sheltered shores. This difference was apparently not attributable to smaller young or to a greater capacity of the brood chamber in the exposedshore L. rudis, and must therefore have been caused by higher rates of egg production. 18% of mature females from the boulder shore and 5% of those from the cliff face were oviparous, having a jelly gland in place of the brood chamber.     

Biochemical composition and energy reserves in the larvae and adults of the four british periwinkles Littorina littorea,L. littoralis,L. saxatilis and L. neritoides

The biochemical composition of the adult body tissue is similar in Littorina littorea, L. littoralis, L. saxatilis and L. neritoides. In the newly crawling metamorphosed young of L. littoralis and L. saxatilis, the biochemical composition is similar to that of the mature adults. The newly released planktonic veliger larvae of L. littorea and L. neritoides, which represent and earlier stage of development than the newly crawling young, have a neutral lipid level (mean, 16.5% of ash-free dry flesh weight) approximately three times the level (5.4%) in the newly crawling young of L. littoralis and L. saxatilis. Otherwise the biochemical composition of free-swimming larvae is similar to that of newly crawling young and adults. Neutral lipid is apparently utilised by L. littoralis and L. saxatilis larvae during larval development and metamorphosis. It is suggested that neutral lipid is the major energy reserve of Littorina veliger larvae whereas in the adults, as exemplified by L. littorea, both lipid and carbohydrate are important as energy reserves.     

Temperature and salinity adaptation in the purple shore crab Hemigrapsus nudus: An in vitro physiological study with excised gills

The alkali-soluble polysaccharides of the cell wall from 7 different marine diatoms were shown to contain the monosaccharides rhamnose, fucose, galactose, mannose and xylose. The relative amounts of rhamnose and fucose varied widely from one species to another, from the very rhamnose-rich Chaetoceros affinis to Thalassiosira gravida, where no rhamnose was found. All Chaetoceros species were found to have a high content of rhamnose. Also the proportion of mannose to galactose varied widely from species to species. The observed change in monomer composition from the logarithmic to the stationary growth phase is explained by assuming the alkali-soluble fraction to be a mixture of polysaccharides. The soluble, extracellular polysaccharides from 4 of the diatoms were also investigated. The products from C. affinis and C. curvisetus were homogeneous and composed of only 3 monomers: rhamnose, fucose and galactose. The extracellular polysaccharide composition in all species investigated was quite different from the composition of the cellular alkali-soluble fraction. The ecological aspects of these soluble polysaccharides may prove of considerable interest.     

Attraction to prey and stimulus to attack in the predatory gastropod Urosalpinx cinerea

Urosalpinx cinerea (Say), accustomed to feeding on Balanus balanoides, were strongly attracted in a choice chamber by the effluents of B. balanoides and B. eburneus, were indifferent to the effluents of Crassostrea virginica, Crepidula fornicata and Mytilus edulis, and responded negatively to the effluent of their own species. Oyster drills from a population feeding on Crassostrea virginica were attracted to oyster effluent; when these snails were offered a choice between Crassostrea virginica and B. balanoides effluents, they responded in equal numbers to the two effluents. Concentrations of NH₄Cl-ammonia in the range 18.2 to 73.3 mol did not attract the snails, and their responses to animal effluents were not correlated with the ammonia and amino-acid concentrations of the effluents, which ranged from 11.8 to 21.0 mol. It is argued that these results deny ammonia the role of a nonspecific distance attractant. Confined separately with various potential prey species, Urosalpinx drilled Balanus balanoides, B. eburneus, Crassostrea virginica, Crepidula fornicata, C. plana, Mercenaria mercenaria, Modiolus demissus, Mya arenaria, Mytilus edulis, Spisula solidissima, and Yoldia limatula, but not Anomia simplex. The prey species that were the least attractive in running water were generally rendered attractive and subject to attack in standing water. Freshly shucked Crepidula fornicata shells were scarcely drilled unless continuously perfused by C. fornicata effluent, and then only in small numbers. Altering the texture of living C. fornicata shells by wrapping them in nylon netting, by polishing, or by roughening, did not make them immune to drilling. Oyster drills in contact with C. fornicata attacked only if they received the effluent of the living prey, proving that tactile stimuli alone are not adequate to induce drilling.     

Observations of copepod feeding and vertical distribution under natural turbulent conditions in the North Sea

We present results of simultaneous measurements of turbulent-dissipation rate, zooplankton vertical distribution and copepod gut pigments in the northern North Sea. Analysis shows that some, but not all, copepods (by species, sex and stage) exhibit significant dependence on turbulence in respect to vertical distribution and feeding rate. Oithona similis (female and copepodite stages) exhibits an avoidance of the surface layer when turbulence is strong there. For the range of turbulence (10⁻⁷ to 10⁻³m² s⁻³) and ambient chlorophyll concentration (0.5–0.8 μg l⁻¹) encountered, Calanus spp. and Metridia lucens exhibited a significant negative response in feeding-rate index with increasing turbulence. Centropages typicus and Pseudocalanus spp. also exhibited a negative response but of less significance. Received: 12 October 2000 / Accepted: 11 December 2000     

Electrophoretic and biometric variability in the abyssal grenadier Coryphaenoides armatus of the western North Atlantic,eastern South Pacific and eastern North Pacific Oceans

Specimens of the abyssal grenadier Coryphaenoides armatus (Hector, 1875), from the western North Atlantic and eastern North Pacific Oceans were compared electrophoretically at 27 presumptive gene loci. At 6 of the 7 polymorphic loci there were only minor differences in allelic frequencies but a nearly fixed difference was found at one locus, phosphogluconate dehydrogenase. Eastern North Pacific grenadiers typically have a narrower interorbital space, a shorter dorsal interspace, more soft rays in the 1st dorsal fin (9–10 versus 8–9) and more pelvic fin rays (21–23 versus 18–21) than grenadiers from the western North Atlantic (as well as grenadiers from the eastern South Pacific, which were included in the biometric analysis). There is an apparent disjunction in the distribution of C. armatus in the eastern Pacific at the Gulf of Panamá which coincides with the change of morphology. It is suggested that North Pacific grenadiers comprise a subspecies, C. armatus variabilis Günther, 1878, which is morphologically distinct from the subspecies C. armatus armatus (Hector, 1875) of the other areas.     

Quantitative alterations in the structure of the digestive cell of Littorina littorea on exposure to cadmium

The effects of sublethal concentrations of cadmium (Cd) on the morphology of the digestive gland of the periwinkle Littorina littorea have been investigated using a planimetric procedure. Five planimetric parameters were recorded (mean epithelial thickness: MET; mean diverticular radius: MDR; mean luminal radius: MLR; MLR/MET and MET/MDR) and tested by diverse statistical methods. The results indicate that MET is depressed after long exposures at high Cd concentrations whilst MLR increases. Variations in MDR have been attributed to different conditions in the tissues surrounding digestive tubules, and are not-significant in relation to the treatment. However, certain increases might be significant due to the presence of parasites or hemocyte proliferation. The ratios MLR/MET and MET/MDR are highly sensitive, and can be expressed as statistical functions of metal concentration and exposure time. Combination of these five planimetric parameters is reliably indicative of the structural changes occurring in the digestive gland of molluscs under conditions of environmental stress.     

Variability in dry weight and vertical distributions of decapod larvae in the Irish Sea and North Sea during the spring

Accumulation of waterborne cadmium in Littorina littorea, Mytilus edulis and Carcinus maenas (collected in 1988 and 1989 around the island of Funen, Denmark) was investigated in a matrix of salinities (10 to 30) and calcium concentrations (2.9 to 8.9 mM Ca⁺⁺). Cadmium accumulation rates in soft parts of L. littorina, soft parts and shells of M. edulis and whole bodies and exoskeletons of C. maenas decreased with increasing salinity. Changes in the calcium concentrations accounted for 72% of the salinity effect on cadmium accumulation rates in L. littorina, whereas calcium concentrations had little or no effect on cadmium accumulation in M. edulis. Cadmium accumulation in the whole body of C. maenas was affected equally by calcium concentrations and total salinity, whereas accumulation in the exoskeleton was mainly affected by changes in total salinity. Individual variability in cadmium accumulation in the organs of C. maenas was greater than the variation attributable either to changes in ambient calcium concentrations or total salinity. An appreciable amount of the inter-individual variability in the cadmium accumulation in all three species was correlated with wet:dry weight ratios of the tissues and size of the organisms.     

Vocalizations of the North Atlantic pilot whale (Globicephala melas) as related to behavioral contexts

Summary Vocalizations of free-ranging North Atlantic pilot whales were studied in different behavioral contexts to gain insight into the function and biological significance of different sound types. Simple whistles (with no frequency inflections) were heard more frequently when whales were milling, a restful behavior type. During surface active behavior, energetic, often coordinated activity probably representing feeding, many sound types, especially complex whistles (with more frequency inflections) and pulsed sounds, occurred with greater frequency than when this behavior was absent. Greater numbers of most whistle types were produced when whales were spread over a larger area and when more subgroups were present. Thus, in pilot whales, there is a significant relationship between their sounds and their behavior, with vocalizations possibly serving to maintain contact and coordinate movements of the herd. Offprint requests to: L.S. Weilgart at the current address