Habitat-specific size structure variations in periwinkle populations (<Emphasis Type="Italic">Littorina littorea)</Emphasis> caused by biotic factors

Shell size distribution patterns of marine gastropod populations may vary considerably across different environments. We investigated the size and density structure of genetically continuous periwinkle populations (Littorina littorea) on an exposed rocky and a sheltered sedimentary environment on two nearby islands in the south-eastern North Sea (German Bight). On the sedimentary shore, periwinkle density (917 ± 722 individuals m⁻²) was about three times higher than on the rocky shore (296 ± 168 individuals m⁻²). Mean (9.8 ± 3.9 mm) and maximum (22 mm) shell size of L. littorea on the sedimentary shore were smaller than on the rocky shore (21.5 ± 4.2 and 32 mm, respectively), where only few small snails were found. Additionally, periwinkle shells were thicker and stronger on the rocky than on the sedimentary shore. To ascertain mechanisms responsible for differences in population structures, we examined periwinkles in both environments for growth rate, predation pressure, infection with a shell boring polychaete (Polydora ciliata) and parasitic infestation by trematodes. A crosswise transplantation experiment revealed better growth conditions on the sedimentary than on the rocky shore. However, crab abundance and prevalence of parasites and P. ciliata in adult snails were higher on the sedimentary shore. Previous investigations showed that crabs prefer large periwinkles infested with P. ciliata. Thus, we suggest that parasites and shell boring P. ciliata in conjunction with an increased crab predation pressure are responsible for low abundances of large periwinkles on the sedimentary shore while high wave exposure may explain low densities of juvenile L. littorea on the rocky shore. We conclude that biotic factors may strongly contribute to observed differences in size structure of the L. littorea populations studied on rocky and sedimentary shores.     

Enemy-free space and habitat-specific host specialization in a butterfly

The majority of herbivorous insects have relatively specialized food habits. This suggests that specialization has some advantage(s) over generalization. Traditionally, feeding specialization has been thought to be linked to digestive or other food-related physiological advantages, but recent theory suggests that generalist natural enemies of herbivorous insects can also provide a major selective pressure for restricted host plant range. The European swallowtail butterfly Papilio machaon utilizes various plants in the Apiaceae family as hosts, but is an ecological specialist being monophagous on Angelica archangelica in southern Sweden. This perennial monocarp grows in three seaside habitat types: (1) on the barren rocky shore in the absence of any surrounding vegetation, (2) on the rocky shore with some surrounding vegetation, and (3) on species-rich meadows. The rocky shore habitat harbors few invertebrate generalist predators, whereas a number of invertebrate predators abound in the meadowland habitat. Here, we test the importance of enemy-free space for feeding specialization in Papilio machaon by assessing survival of larvae placed by hand on A. archangelica in each of the three habitat types, and by assessing the habitat-specificity of adult female egg-laying behavior by recording the distribution of eggs laid by free-flying adult females among the three habitat types. Larval survival was substantially higher in the rocky shore habitat than in the meadowland and significantly higher on host plants without surrounding vegetation on the rocky shore. Eggs laid by free-flying females were found in all three habitat types, but were significantly more frequent in the rocky shore habitat, suggesting that females prefer to lay eggs in the habitat type where offspring survival is highest. These results show that larval survivorship on the same host plant species can be strongly habitat-specific, and suggest that enemy-free space is an underlying factor that drives feeding specialization in Papilio machaon.     

Patterns of growth and energy allocation in northern California populations of Littorina (Gastropoda: Prosobranchia)

Seasonal patterns in shell growth rates, tissue weights, and female reproductive efforts were monitored for three species of western North American rocky shore gastropods, Littorina keenae Rosewater (supralittoral), L. scutulata Gould (high intertidal), and L. plena Gould (high intertidal). Growth rates conformed to the Von Bertalanffy growth model. Relative to male snails, female L. keenae appeared to sacrifice shell growth to expend more energy on the production of large quantities of gametes during the spring; growth rates of females and large males were highest during autumn when microalgal food supplies were seasonally abundant. In contrast, spring tended to be the best season for shell growth of L. scutulata and L. plena; however, reproductive output was poor and sporadic for these two species, and growth rates in the field during all seasons were low compared to growth rates of snails held under laboratory conditions with abundant food. High population densities of snails at shore levels occupied by L. scutulata and L. plena may greatly reduce food levels upon which individual snails rely for growth and reproduction.     

The distribution, age and growth of wrasse (Labridae) in inshore waters of west Scotland

Wrasse were widely distributed in inshore waters of west Scotland in rocky and algal habitats. Ctenolabrus rupestris and Centrolabrus exoletus dominated commercial and experimental catches using creels, traps and fyke nets, but Crenilabrus melops, Labrus bergylta and L. mixtus were infrequent. Maximum age of sampled fish was 16yr in C. rupestris , 9 yr in C. exolefus , 5 yr in C. melops , 15 yr in L. bergylta , and 11 yr in L. mixtus . Growth was more rapid prior to maturation in all species. The von Bertalanffy growth model fitted data for C. rupestris and C. exoletus . Male C. rupestris and C. exoletus were significantly longer than females in most age groups and growth of all species captured in mid–Scottish areas was more rapid than in northern localities. Mortality (Z) of C. rupestris was 0–1861 per year and 0·4185 in C exoletus .     

Differences in the activity rhythms of juvenile gobiid fish,Chasmichthys gulosus,from different tidal localities

Activity patterns of intertidal gobiid fish,Chasmichthys gulosus, collected from different tidal localities, were recorded in a constant environment. Gobies collected from a rocky shore with a large tidal range and a regular tidal regime displayed a ca. 12 hour rhythm in their activity pattern. Gobies from a rocky shore with a small tidal range and an irregular tidal regime, however, did not clearly display any such rhythm. The ecological implications of such activity rhythms are discussed from the viewpoints of feeding and avoidance of predators.     

Effects of acid wastes from titanium dioxide production on biomass and species richness of benthic algae

Titanium dioxide wastes are suspected to be toxic to rocky shore communities in an estuary in southeast Norway. An experimental project lasting two years examined whether titanium dioxide wastes affected recolonization by rocky shore organisms. The experiments were performed in situ in six tanks (each with 9 m³ brackish water) at two different levels of salinity. Three different concentrations of industrial waste water were used. The growth season in 1986 was dry and sunny compared to 1987, causing reduction of growth on exposed granite chips compared to controls. At the two highest waste concentrations in the tanks, Fucus serratus was observed with necrotic tissue both years, and in 1986 benthic diatoms were scarce.     

Variability in the reproductive effort of the limpet,Cellana tramoserica

Summary The reproductive effort of the limpet, Cellana tramoserica was investigated in high, mid, and low intertidal areas of the rocky shore as well as in a subtidal population. The reproductive effort of individuals within a population was independent of age. There was, however, a noticeable difference among populations with respect to the relative amount of gonad material spawned per year. The individuals from the subtidal population had the greatest reproductive effort, spawning the equivalent of 101% of their somatic weight per year, while the low, mid and high intertidal populations spawned the equivalent of 66%, 20%, 51%, respectively.Experimental transplants showed that individuals from all three intertidal populations increased their reproductive effort to match that of subtidal individuals. It was unlikely, therefore, that the observed patterns were the result of genetic differences among the populations. The reproductive effort of the populations was also not correlated with the rate of mortality of the adults in the four populations. The observed differences could be explained by a combination of the availability of food and intraspecific competition. The flexibility in the reproductive pattern of Cellana is hypothesised to be a result of this species having a dispersive larval stage, which may result in selection for plasticity of reproductive allocation, depending upon the environmental conditions at the site of settlement and growth to adult size.     

Distribution in relation to life history in the directdeveloping gastropod Batillaria cumingi (Batillariidae) on two shores of contrasting substrata

Population structure and spatial distribution with growth ofthe direct-developing gastropod, Batillaria cumingi, were investigatedon two shores of differing substrata. Sand-mud shore and rockyshore populations differed in size structure; first-year snailswere ca. 7 mm in shell length (SL) in both populations, whereassecond-year snails, merging with older cohorts, measured 15–25mm SL in the sand-mud shore population and ca. 15 mm SL in therocky shore population. Egg distribution matched adult distributionin the sand-mud shore population, but was more restricted thanthat of adults in the rocky shore population. The distributionof newly-hatched juveniles (0–1 mm SL) was restricted inboth populations, but the growth stage at which snails extendedtheir distribution differed between the two populations; 1–2.5mm SL on the sand-mud shore and 5 mm SL on the rocky shore. Floatingachieved by early juveniles (ca. 2 mm SL), was commonly observedin the sand-mud population, but rarely in the rocky shore population.The sudden expansion in distribution of the 1–2.5 mm SLgrowth stage in the sand-mud shore population is consideredto have been caused by floating, while expansion of the distributionof older growth stages (>5 mm SL) in the rocky shore populationprobably occurs by crawling. (Received 13 May 1998; accepted 25 August 1998)     

Seasonal and regional variations in the feeding habits of the harbour seal, Phoca vitulina, in the Skagerrak and the Kattegat

Studies of the feeding of harbour seals have been carried out at the Tjärnö Marine Biological Laboratory since 1977. The studies are based on fish otoliths found in faeces at seal haulouts. The present paper compares feeding habitats at two different localities. Three families of fish, gadoids, pleuronectids and clupeoids were predominant in the seals' diet at a rocky shore habitat. Pleuronectids made up 75% of the diet at a sandy shore habitat. Temporal variations in feeding habits are also examined. The results indicate that harbour seals are opportunists in their choice of prey species, but some locally abundant species do not appear in their diet.     

Diet composition influences the fitness of the herbivorous crab Grapsus albolineatus

The tropical rocky shore crab Grapsus albolineatus feeds primarily on filamentous algae but eats animal matter whenever it is available. During the summer the crab's diet switches to encrusting algae due to a die-off of filamentous algae. As a result of the switch the nutrients in the diet of the crab vary seasonally and may influence the fitness of the crab. Maintenance, growth, reproductive performance and nutrient storage of crabs were examined under four dietary regimes of increasing nutritional value ranging from low organic to high protein content. The nutritional quality of these diets significantly affected crab survival and moulting. Crabs fed on the nutritionally superior diet of algae and meat exhibited enhanced growth, higher levels of energy in the reproductive organs and stored more energy in the hepatopancreas than did individuals on the shore and crabs fed only on algal diets in the laboratory. Filamentous algae were a better food source than other algae, resulting in fewer deaths and superior levels of maintenance and growth. Growth and maintenance can occur on a pure algal diet, but reproductive performance and nutrient storage require some degree of added nutrients in the form of animal matter in the diet. Crabs fed coralline or foliose algae had higher mortality and fewer successful moults than crabs fed the other two diets. The fitness of G. albolineatus appears to be limited by the amount of extra nutrients obtained from animal matter. The opportunistic consumption of animal material in the form of carrion, or of animals associated with dietary algae, could be a key factor in the reproductive success of this crab.     

Maintenance of zonation patterns in two species of flat periwinkle,Littorina obtusata and L. mariae

The zonation patterns of Littorina obtusata (L.) and Littorina mariae Sacchi et Rastelli were shown to be quite distinct on a sheltered rocky shore. L. obtusata was found at all the heights sampled; it reached peak numbers at mid shore on the alga Ascophyllum nodosum L. (Le Jol). There was no difference in the tidal height occupied by adults or juveniles; or in the mean size of L. obtusata along the vertical gradient of the shore. In contrast L. mariae occurred exclusively low on the shore, on Fucus serratus L. Translocation of the two species within their respective levels resulted in random movement after 4 days, although initial movements after 1 and 2 days were sometimes directional. Animals transplanted to the normal level of the other species showed directional movement towards their home zone; this was most pronounced after 4 days. There was no difference in the distance moved by the two species, although the distance moved did vary with tidal height, both species moving further at mid shore than low shore. Distances moved by littorinids at replicate areas in the low shore were similar but those at mid shore did vary. There was an interaction between the species and the different tidal heights which revealed that transplanted species moved further than translocated species at the same tidal level. However, this was only significant in the case of L. mariae. It is suggested that the close relationship between the winkles and their host algae may direct the homing behaviour of displaced individuals.     

The Response of Experimental Rocky Shore Communities to Nutrient Additions

The aim of this study was to determine whether the experimental nutrient enrichment of littoral rocky shore communities would be followed by a predicted accumulation of fast-growing opportunistic algae and a subsequent loss of perennial benthic vegetation. Inorganic nitrogen (N) and potassium (P) was added to eight concrete mesocosms inhabited by established littoral communities dominated by fucoids. The response to nutrient enrichment was followed for almost 2 1/2 years. Fast-growing opportunistic algae (periphyton and ephemeral green algae) grew significantly faster in response to nutrient enrichment, but the growth of red filamentous algae and large perennial brown algae was unaffected. However, these changes were not followed by comparable changes in the biomass and composition of the macroalgae. The biomass of opportunistic algae was stimulated only marginally by the nutrient enrichment, and perennial brown algae (fucoids) remained dominant in the mesocosm regardless of nutrient treatment level. Established rocky shore communities thus seem able to resist the effects of heavy nutrient loading. We found that the combined effects of the heavy competition for space and light imposed by canopy-forming algae, preferential grazing on opportunistic algae by herbivores, and physical disturbance, succeeded by a marked export of detached opportunistic algae, prevented the fast-growing algae from becoming dominant. However, recruitment studies showed that the opportunistic algae would become dominant when free space was available under conditions of high nutrient loading and low grazing pressure. These results show that established communities of perennial algae and associated fauna in rocky shore environments can prevent or delay the accumulation of bloom-forming opportunistic algae and that the replacement of long-lived macroalgae by opportunistic species at high nutrient loading may be a slow process. Nutrient enrichment may not, in itself, be enough to stimulate structural changes in rocky shore communities.     

Notes on Guayana mosses with new information of Sphagnum ornatum

Mosses restricted to tepui summits in the Guayana Highland are relatively few.Sphagnum ornatum Crum, though, only recently described from Brazil, has been found subsequently in a number of localities in nearby Venezuela and Guyana. These additional collections make for a better understanding of the diagnostic features of a species characteristically found on the tops of the sandstone mesas of southern Venezuela and adjacent areas.     

Vertical distribution of chitons (Mollusca: Polyplacophora) in the rocky intertidal zone of central Chile

The patterns of vertical distribution of chitons in various exposed rocky shore habitats of central Chile are described. The density and size of the individuals were determined at different levels on intertidal rock walls, in pools and on boulders. A group of four species was found on rock walls while another group of four species was found in tidal pools and on boulders. The species showed vertical separation on rock walls and segregation according to a range of increasing frequency of water movement in pools and on boulders. Only the two species with largest adult individuals (Acanthopleura echinata (Barnes) and Chitonlatus Sowerby) showed vertical segregation in size. Small-sized species and small individuals of large-sized species were found higher on rock walls or in zones where water movement is less; large chitons occur in zones of greatest water impact. This suggests that water movement may be a significant factor in setting the lower limits of distribution of these herbivores. Some of the species examined were extremely abundant (600·m^-2) with densities of one to two orders of magnitude greater than for other chiton species elsewhere.     

Similarity of rocky intertidal assemblages along the Pacific coast of Japan: effects of spatial scales and geographic distance

Factors and processes affecting community structures operate at various spatial and temporal scales. We analyzed how similarities of rocky intertidal assemblages vary at different spatial scales using a nested, hierarchical sampling design. Intertidal assemblages consisting of algae, sessile animals, and mobile animals were censused on five rock walls at each of five shores chosen within each of six regions along the Pacific coast of Japan, encompassing 1,800 km of coastlines. Based on this sampling design, similarities in assemblages were calculated using both qualitative (presence/absence) and quantitative (percent cover and density) data, and compared at three spatial levels: (1) rock level (the finest spatial scale, encompassing several to hundreds of meters), (2) shore level (the intermediate spatial scale, encompassing several to tens of kilometers), and (3) region level (the broadest spatial scale, encompassing hundreds to thousands of kilometers). Cluster analysis showed that assemblages were categorized into distinct regional groups except for the two southern regions, but they did not separate clearly from each shore. A nested analysis of similarities revealed significant variation in similarities among regions and among shores within each region, with the former showing greater variation. Similarity was negatively correlated with geographic distance at the regional level but not at the shore or the rock levels. At the regional level, similarity decreased more rapidly with distance for mobile animals than sessile organisms. The analyses highlighted the importance of broad-scale abiotic/biotic factors such as oceanic current conditions and biogeographic factors in determining observed patterns in similarity of rocky intertidal assemblages.     

栝楼雌雄植株的光合作用和蒸腾作用特性

对栝楼雌雄植株生长发育关键时期的光合作用和蒸腾作用进行研究.结果表明:在营养生长阶段,栝楼雄株的光合速率、蒸腾速率、气孔导度和水分利用效率均大于雌株;雄株比雌株提前22 d进入生殖生长阶段,当雄株进入生殖生长阶段后,其光合速率、蒸腾速率和气孔导度均大于雌株,但水分利用效率略小于雌株;当雌株进入生殖生长阶段后,其蒸腾速率和气孔导度大于雄株,而光合速率和水分利用效率显著小于雄株.气候因子对栝楼生长发育的影响主要是在营养生长和生殖生长初期,栝楼生长发育后期对气候因子的响应程度减弱.较高的温度和较低的湿度有利干栝楼的生长发育,光照可提高栝楼尤其是雄株的光合速率.进入生殖生长后,雄株的光合速率随光照的增强显著增加,而雌株的光合速率增加不显著;随气温的升高,雄株的蒸腾速率显著提高,雌株的光合速率极显著提高.     

Infection of the mollusc Littorina saxatilis with parthenites of trematodes and their impact on a shell form: analysis of populations inhabiting the littoral coast of the White Sea

12 rocky shore populations of Littorina saxatilis from three islands of Chupa Inlet (Kandalaksha Bay, White Sea) were examined for infection with trematodes. Morphometric characters (6 indexes of the shell and aperture shape) of molluscs were investigated for all these populations. Exposed and sheltered sites were considered at every island and high and low littoral samples were fulfilled at every site. Seven species of trematodes, Podocotyle atomon, Cryptocotyle lingua, Renicola sp., Himasthla sp., Microphallus piriformes, M. pygmaeus, M. pseudopygmaeus, were found. Uneven distribution of trematodes was confirmed by log-linear analysis. Sheltered populations of L. saxatilis have the greater infection prevalence than exposed ones. This is due to the heavy infection with M. piriformes and M. pygmaeus. The prevalences by these trematodes are up to 52.97% and 27.16% respectively in sheltered populations of the host. The prevalence of M. piriformes tend to be higher at the upper shore level of sheltered sites. In a contrast, the prevalence of M. pygmaeus is significantly higher at the low part of such sites. Factor analysis shows a significant association of the indices of L. saxatilis shell shape with three factors. The first one is associated with the "elongation" of a shell and reveals L. saxatilis from the exposed rocky shore to be more elongated than the molluscs from sheltered sites. The second one is connected with the "aperture shape" index. There is an association of this factor with the shore level position of samples. The third factor reflects the affect of trematodes on the shell shape. The molluscs infected with M. piriformes show "elongated" shell shape and relatively smaller aperture. Shall peculiarities of the hosts infected with M. piriformes and M. pygmaeus are somewhat different. The results of the factor analysis is justified by the series of analysis of variances on the values of shell indices (MANOVA) according to the factors "exposure", "shore level" and "infection".     

Polyandry by wood mice in natural populations

The microhabitat used by the garden dormouse Eliomys quercinus during its nocturnal activity was examined. Twenty-three variables describing habitat structure were measured at 100 trapping points. Logistic regression models were utilized to select the variables that discriminate between used and avoided trapping points and, in a series of pairwise contrasts, between trap sites used by different sexes, age classes and animals in different reproductive periods. Used sites were characterized by a higher (>40%) rock cover, a thicker shrub layer and a younger understory with trees of smaller trunk diameter. These variables describe areas with rockfalls from the upper slope, where trees were younger and smaller, the canopy closure reduced and the shrub layer more developed than in other parts of the forest. Dense shrubby vegetation provided protection from aerial predators and, in conjunction with rocks and stones, might have made hunting by birds and mammals more difficult. Garden dormice may also have been attracted by rocky areas acting as a heat source during the night. The selection of rocky areas was more important in the first months of the active period, when animals emerged from hibernation and started the mating season. At the end of summer, the animals used areas richer in herbs, where insects and other food resources were probably more abundant.     

Predatory behaviour of juvenile shore crab Carcinus maenas (L.)

Juvenile shore crabs Carcinus maenas (L.) were observed feeding on rock barnacles Semibalanus balanoides (L.) on a Bay of Fundy rocky shore. This previously unreported predatory behaviour was further investigated in the laboratory. When given a choice of three common and abundant gastropods, Nucella lapillus (L.), Littorina littorea (L.), and Littorina obtusata (L.), and the rock barnacle Semibalanus balanoides, juvenile shore crabs of both sexes ate mainly barnacles and consumed proportionately more barnacles than gastropods compared with adults, which ate mainly gastropods. The rock barnacle is an abundant and readily available food source which may be important in sustaining the juvenile crab through periods of moults and rapid growth. As the shore crab attains a certain age (size), it must forage lower on the shore as gastropods become more important in its diet.     

Nocturnal courtship,copulation, and egg-laying in the western grebe (<Emphasis Type="Italic">Aechmophorus occidentalis</Emphasis>) and Clark’s grebe (<Emphasis Type="Italic">Aechmophorus clarkii</Emphasis>)

Grebes (Podicipedidae) are primarily diurnal although migration occurs at night and some species forage opportunistically at night. We used motion-activated cameras to study nocturnal reproductive activities of the western grebe, Aechmophorus occidentalis, and Clark’s grebe, Aechmophorus clarkii, at Clear Lake, California, USA, during 2014–2016. During 9283 h of monitoring, 19.4% of rushing displays (n = 75) and 8.4% of copulations (n = 435), plus two weed dancing displays and four instances of egg-laying, occurred at night. Nocturnal copulation and egg-laying often occurred on empty, recently abandoned nests, but some incubating pairs of grebes also copulated at night. Nocturnal reproductive activities occurred more frequently at nests attached to submergent vegetation in open water far from shore when water levels were low than on nests attached to emergent vegetation close to shore when water levels were high, probably due to a reduced risk of predation by nocturnal mammals farther from shore. Nocturnal reproductive activities were not in response to elevated light levels at night, daylight disturbances, diurnal predation, high temperatures on hot days, or sexual interference during daylight. Instead, grebes attempted to increase mating investment and minimize parental investment by exploiting recently abandoned nests at night, and perhaps by undertaking extrapair copulations under the cover of darkness, but some pairs of grebes may simply extended routine reproductive activities into the night. Reproductive activities are probably limited at night by the need to feed during daylight and sleep at night, and by the increased risk of predation by mammals at night. Given the high costs of construction and maintenance of floating nests and the obvious benefit of quickly exploiting abandoned nests, nocturnal reproductive activities may occur more frequently in grebes and other waterbirds using floating nests than in other groups of birds whose reproductive activities occur mostly during daylight.