Tidal rhythms in activity in the intertidal gastropodPolinices incei (Philippi)

When removed into the laboratory, the intertidal snailPolinices incei, retains a tidal rhythm in activity for several days when maintained under conditions of constant light. There is, in addition, a gradual decline in activity following collection and a batch to batch effect of some note. When a 12∶12 light regime is maintained there is apparent also a c. 24 h rhythm in activity which may supercede the tidal one under some circumstances. The simplest explanation of the results is that there exist both tidal and diel rhythms. These results are compared with those observed by others for a variety of marine organisms, the adaptiveness of the behaviour pattern is discussed, and the implications of the work for further behavioural studies is explored.     

Short-term changes of meiofaunal abundance in intertidal sediments

Some species of various meiofaunal taxa may actively emerge from the sediment and swim in the water column, preferably at night. In the water column they get dispersed by tital currents. The hypothesis that this drift may cause significant short-term changes in the abundance of these species was tested. Such changes were verified for harpacticoid copepods and plathelminths. Depending on the hydrographic conditions, abundance changes may be unpredictable or show regularly alternating patterns. In the light of these results, small-scale spatial estimates of abundance become generally very difficult to make in the taxa containing emergent species. It is suggested that reliable averages can only be obtained by repeated or large-scale spatial sampling.     

Structural features associated with respiration in some intertidal Uropodina (Acarina: Mesostigmata)

The present study suggests that the peritremes of both Phaulodinychus repleta (Berlese) (Uropo-didae) and Thinozercon michaeli Halbert (Thinozerconidae) are incapable of forming peritreme plastrons in the same manner as the Gamasina or Phaulodinychus mitis (Leonardi) (Uropodidae) described in previous studies. However, it is proposed that extra-peritrematic plastrons may be formed by other structures, for example the pedofossae and legs in P. repleta and the coarse sculpturing on the dorsal surface of the peritrematic shield in T. michaeli , which may trap an airfilm during inundation.     

Activity rhythms and cyclical changes of microhabitat preferences in the intertidal pipefish Nerophis lumbriciformis (Pisces: Syngnathidae)

As an inhabitant of the intertidal zone, Nerophis lumbriciformis predictably should show a clear rhythmic activity, with its maximum closely correlated with the high tide period, as observed in several other rocky intertidal fish species. We investigated the rhythmic activity patterns of N. lumbriciformis and analysed to what extent specific substratum preferences may be linked to water level and, ultimately, to the particular activity rhythm patterns of the fish. To determine N. lumbriciformis substratum preferences, two different experiments were conducted. The first evaluated substratum preferences from among a group of the four most common substrates found in the sample area. The second experiment evaluated the fish's maintenance of that substratum preference, after alteration of the water level in a simulated ebb tide. From the available substrata, N. lumbriciformis displayed a clear preference for algae until the water level began to decrease. Then, the preference radically shifted from algae to boulders. N. lumbriciformis showed a clear rhythmic activity, affected by both tidal and circadian periodicity, producing asymmetrical activity peaks. Unlike the rhythms of other rocky intertidal fish species, the maximum activity peaks were not centred at the expected high tide period. The adaptive explanation for the apparently peculiar activity peaks appears to be related to the particular substratum preferences of N. lumbriciformis. The detected circatidal period seems, consequently, closely related to small migrations between substrata, whilst the observed increase in diurnal activity, independent of the tidal cycle, may be related to predatory activity, since N. lumbriciformis is a visual feeder. Electronic Publication     

The structure and probable function of the peritreme in intertidal Gamasina (Acarina: Mesostigmata)

The peritremes of the British intertidal Gamasina are structurally similar to those described for species occurring in soil and leaf litter, the highly elaborate peritreme plastrons present in species occurring in low oxygen tension environments are not typical of the fauna. It is shown that elaborate peritremes can form effective gas gills if an airfilm is supported by the peritrematic slit; however, if the airfilm is supported by the micropapillae on the floor of the peritreme, then the respiratory efficiency of the gas gilhbecomes comparable with that of elaborate peritreme plastrons. Evidence is presented reinforcing the theory that the plastron is supported by the micropapillae. The absence of elaborate respiratory peritreme plastrons among the intertidal Gamasina suggests that these mites are preadapted to respiration during tidal inundation. Other preadaptations include the distal parabolic shape of the micropapillae, however in the plastron forming species the micropapillae are shorter and basally thicker to prevent bending under pressure Developmental trends within the peritremes, with respect to plastron formation are discussed.     

Tidal activity rhythms and depth distribution of rocky shore fish in an altered intertidal environment

In this note we report on changes of activity level of littoral fish and their use of different microhabitats in an altered intertidal environment, where intertidal fish are never emersed and turbulence is confined to high tides. Despite these atypical conditions, the structure of the assemblage is basically the same found in a typical rocky-shore situation. Two intertidal fish known to possess internal tidal rhythms, Lipophrys pholis and Coryphoblennius galerita, retain those rhythms in these altered conditions, and the associated social changes in L. pholis are also retained. These observations support the studies of Gibson (1971), who showed that changes in hydrostatic pressure were of prime importance in keeping the tidal rhythm entrained. The subtidal Parablennius pilicornis, on the contrary, is more active during low tide than at high tide. The hypothesis that some subtidal species are excluded from the intertidal by a turbulence-avoiding mechanism is discussed.     

Responses of Amblyseius ovalis (Evans) (Acarina: Phytoseiidae) to natural food resouces and two artificial diets

Six phytophagous mites, maize pollen, and two artificial diets were fed to Amblyseius ovalis to evaluate their food suitability for the predator. The parafilm diet-chip of Hager and Tassan was adopted for artificial diet studies. The floating leaf method was the best among all tested methods, producing high survival, developmental, and reproductive rates of the predator. Offspring of A. ovalis fecding on artificial diets did not complete their life cycles. A. ovalis feeding on E. orientalis, O. mangiferus, ad O. taiwanicus developed into adult form faster than those feeding on other food resources. Predators feeding on the natural food, except those feeding on T. kanzawai, had much higher immatural survival rates, lower escape rates, and shorter developmental durations than those feeding on the artificial diets.All A. ovalis laid an average of two eggs per female per day after 2 days of preoviposition, except for those feeding on T. kanzawai which produced none. A. ovalis feeding on artificial diets showed a shorter oviposition period, lower daily and total reproductive rates, and shorter longevity. The complicated webbing life type of T. kanzawai inhibited the activities of A. ovalis, indicating that the predators may require nutrients other than T. kanzawai eggs to molt into adults and to reproduce. The functions varying the phytoseiid-tetranychid relationship during the predator's approach to the microhabitat of the prey were postulated from the predator's structures and the prey's life type. Most predator eggs were laid by 2–18 day-old females feeding on natural food resources. A. ovalis retained its high activity on the low webbing habitats of O. mangiferus and E. orientalis, and on maize pollen. The intrinsic rate of increase, mean generation time, and net reproductive rate of A. ovalis on each of nine tested food resources were evaluated from its life tables. The predator showed the highest intrinsic rates of increase when feeding on the prey of E. orientalis, O. mangiferus, and on maize pollen, and the lowest rates when feeding on the artificial diet even when the immatures had fed on the O. mangiferus and maize pollen. Consequently, the optimal food resources for A. ovalis appear to be O. mangiferus or O. oriintalis with supplements of maize pollen. When fed on these food resources, the predators demonstrated the highest rates of survival, longevity, fecundity, and intrinsic increase.     

Carrageenans from chilean samples of Stenogramme interrupta (Phyllophoraceae): structural analysis and biological activity

Carrageenans extracted from cystocarpic and tetrasporic Stenogramme interrupta were analysed by chemical and spectroscopic methods. The carrageenan from cystocarpic plants is composed predominantly of 0.5 M KCl-insoluble and 1 M KCl-soluble fractions. The insoluble fraction contained iota-carrageenan as the major component with alpha-carrageenan and pyruvated carrageenan as minor components. The soluble fraction is highly heterogeneous and did not contain the precursors mu- and nu-carrageenans. The polysaccharide from tetrasporic plants is composed of zeta- and lambda-carrageenans, and low sulfated galactans. It is soluble in KCl and partly cyclized by alkaline treatment. The antiviral and anticoagulant properties of the insoluble polysaccharide fraction from cystocarpic S. interrupta and the polysaccharide from tetrasporic S. interrupta are reported the results of which suggest promising antiherpetic activity.     

Circadian and circatidal locomotory rhythms in the intertidal beetle Thalassotrechus barbarae (Horn): Carabidae

Thalassotrechus barbarae (Horn) is a member of the intertidal crevice fauna. It forages and mates at night outside the crevice but only during periods of low water. Exogenous stimuli probably inhibit emergence and activity when conditions are not favourable but the main timing of activity is endogenously controlled. Under a LD 15:9 regime (270 lux, tungsten light) the insects were active only during the dark period. Under constant conditions (15–16 °C, 0.05 lux) the beetles showed a circatidal and circadian rhythm of locomotory activity. The circadian rhythm, which has an estimated period of 23.9 h, is quite stable, persisting for at least 7 days. The circatidal rhythm persists for 3 days suggesting that it is subordinate to the dominant circadian rhythm; it probably modifies the latter by inhibiting activity during periods of nocturnal high tides. A possible Zeitgeber for the circatidal rhythm is water movement which, like the probable stimulus entraining the circadian rhythm (light), is capable of being perceived by the eyes of this insect.     

Short-term fluctuations in benthic diatom numbers on an intertidal sandflat in the Westerschelde estuary (Zeeland,The Netherlands)

During the period March–May 1991, sediment samples were taken every two or three days at one intertidal station in the brackish part of the Westerschelde estuary. Quantitative cell counts were made in order to investigate the short-term temporal changes in diatom numbers and assemblage structure.Throughout the whole sampling period, the diatom assemblage was dominated by epipsammic diatoms. Three species, Achnanthes delicatula, Opephora cf. perminuta and Catenula adhaerens on average accounted for almost 67% of all valves counted. The epipsammic diatom fraction showed no significant changes in absolute numbers; its species composition appeared relatively stable. In contrast, epipelic diatom densities significantly increased towards the end of the study period. Species composition within this fraction was less stable. Multivariate analysis (Principal Components Analysis), in combination with multiple regression, indicated that total sky irradiance (on the second and third day preceding sampling) and percentage organic matter were related to the short-term fluctuations of the epipelic diatom fraction.     

Swimming activity rhythms in solea vulgaris (Q) juveniles

The locomotory activity of juvenile flatfish (Solea vulgaris) was studied in actotaxigraphs at constant temperature and under different conditions of illumination.

The juveniles were swimming in cylindrical transparent vertical tanks and were detected by infrared barriers. In constant darkness, they exhibited a rhythmic circadian activity which was synchronized by light variations.     

3,4-Dihydroxyphenylalanine (dopa) decarboxylase activity in the arthropod nervous system

1. When homogenates of brains from mature adult locusts (Locusta migratoria) were incubated with l-3-(3,4-dihydroxyphenyl)[3-(14)C]alanine the major radioactive metabolite was dopamine, suggesting the presence of a dopa (3,4-dihydroxyphenylalanine) decarboxylase. 2. Decarboxylation of l-dopa by this tissue, measured under optimum conditions by a radiochemical method, was 21mumol of CO(2)/h per g wet wt. Apparent decarboxylation of l-tyrosine proceeded at 0.34mumol of CO(2)/h per g wet wt. There was no detectable decarboxylation of l-tryptophan, l-histidine or l-phenylalanine. 3. Dopa decarboxylase activity was found in all major regions of the ventral nerve cord of the mature locust (range: 4-7mumol of CO(2)/h per g wet wt.) but was low or absent in thoracic peripheral nerve. 4. Marked decarboxylation of l-dopa was found in homogenates of brains of four other species of insects, and in brain and ventral nerve cord, but not in the claw nerve, of the crayfish. 5. The activity of the locust brain enzyme may be slightly lower at the time of imaginal ecdysis than during the mature period. By contrast, the dopa decarboxylase that produces dopamine as an intermediate in cuticle biosynthesis is known to be high in activity at the time of ecdysis and low in activity during the intermoult stages.     

Circadian activity rhythms in the crayfish Paranephrops zealandicus (Crustacea)

The diel activity rhythm shown by Paranephrops is usually unimodal with most activity occurring at night. In constant darkness, locomotor activity is expressed for up to 60 days as a free-running circadian rhythm. The period varies from 18 to 38 hours following a seasonal cycle (summer mean period 24 hours, winter mean 30 hours). No adaptive significance can be attached to either seasonal or individual variations in period and it is suggested that such variations are a consequence of the way in which the clock mechanism operates, the period being linked to the overall activity level following Aschoff's ( 1960 ) "Circadian Rule". Activity levels will inevitably vary individually and seasonally.     

Daily rhythms of locomotor activity in some Carabidae (Coleoptera)

The daily cycle of activity was investigated in a number of species of Carabidae. Most were either nocturnal or diurnal, but some were plastic and responded to environmental conditions.

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Résumé Le cycle quotidien de l'activité des mouvements fut étudié chez plusieurs espèces de Carabidae par observations d'élevage en insectarium.L'auteur a trouvé que la majorité des espèces pourraient être classées strictement comme nocturnes ou diurnes.Certaines espèces furent classées comme indifférentes, le cycle journalier de leur activité variant en fonction des modifications naturelles du milieu externe.

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This work formed part of a thesis submitted for the degree of Doctor of Philosophy in the University of London.     

Seasonal changes in arthropod diversity patterns along an Alpine elevation gradient

1. Deciphering patterns in species distributions and species interactions along ecological gradients are fundamental topics in ecology. Theory holds that species diversity is greater and interactions are stronger under warmer and more stable environments, such as low elevations and latitudes. However, recent findings have shown conflicting evidence, potentially due to seasonal effects.
2. We aimed to address this gap by studying seasonal changes in arthropod communities over an elevation gradient in the Swiss Alps, as well as herbivore-predator interactions and their resulting consequences on plant herbivory levels.
3. Overall, we found hump-shaped patterns in arthropod abundance, richness and diversity with increasing elevation, with all factors peaking below the tree line. However, these patterns varied seasonally, with strong mid-elevation peaks at the beginning of the summer, shifting to a pattern of linear decrease at the beginning of the fall. In searching for mechanisms explaining these changes, we found that shifts in arthropod communities over elevation and seasons usually followed shifts in vegetation productivity estimates. Other factors, such as top-down control by natural enemies, which was generally stronger at low elevations, and plant species-specific resistance rates along elevation gradients were also implicated as drivers of diversity and herbivory rates.
4. These results highlight the complexity of arthropod communities' responses to environmental gradients, which vary during the season in response to relative changes in both bottom-up and top-down forces.