Physiological responses of Mytilus edulis and Cardium edule to aerial exposure

Physiological responses of two bivalves (Mytilus edulis L. and Cardium edule L.) to intertidal conditions were studied. Specimens were collected from S. W. England in autumn/winter, 1980, and acclimatized to either intertidal or subtidal regimes before measurement of rates of heat dissipation and oxygen uptake during 5 h of air exposure, and rates of , particle clearance, ammonia excretion, and food-absorption efficiency during 7 h of reimmersion. Subtidal individuals were either intermittently or continuously fed in order to distinguish the effects of periodic food supply from the effects of air exposure. Specimens of M. edulis had low aerial rates of (14 to 20% of aquatic rate), and was greater than the energy equivalent of , indicating that they were largely anaerobic. In contrast, C. edule air-gaped and had higher aerial rates of and (50 to 75% of aquatic rate). There were behavioural and metabolic differences in the responses of intertidally and subtidally acclimatized mussels and cockles to air exposure. Intertidal individuals of both species were more quiescent, had lower aerial rates of and , and showed a conditioned response at the expected time of reimmersion. The reduction in aerial rate of was an energy-saving mechanism and the payment of the oxygen-debt within 2 h of reimmersion represented a significant cost. The heat increment associated with feeding and digestion was estimated as 15 to 17% of the oxygen uptake by M. edulis during all stages of recovery. M. edulis adapted to the intertidal regime by reducing its time-averaged aerial and aquatic rates of ammonia excretion. In contrast, C. edule maintained a high aerial and aquatic rate of ammonia excretion. The clearance rates of M. edulis recovered rapidly (0.5 to 1.5 h) following reimmersion, whereas those of C. edule recovered more slowly, particularly for the subtidal individuals following acute exposure (>4 h). There was no evidence of increased clearance rate or absorption efficiency by intertidal individuals to compensate for the loss of feeding time. Intertidally acclimatized individuals of M. edulis and C. edule had more energy available for growth (scope for growth) integrated over a 12 h period and higher growth efficiencies than subtidal individuals subjected to acute air exposure and intermittent feeding regimes. This was the result of reduced aerial and aquatic rates of energy expenditure, a relatively small cost in terms of the payment of oxygen-debt and a rapid recovery of clearance rate following reimmersion.     

Effects of plant size and distribution on the numbers of invertebrate species and individuals inhabiting the brown alga Pelvetia fastigiata

The invertebrates living on specimens of the brown alga Pelvetia fastigiata, growing in the intertidal zone at La Jolla, California (USA) in November 1975 were enumerated. Within 7 collecting sites, larger plants generally shelter more animal species and individuals than smaller plants. The number of species on a given plant can be described as an equilibrium number; numbers of species and individuals can become similar on defaunated and transplanted algae of comparable sizes placed at the same experimental site. Such equilibria are site-specific because the colonization, immigration and loss rates of animals differ among the sites studied. Relationships between plant size and the number of animal species and individuals on P. fastigiata also differ among the collecting sites. The between-site differences are related to tidal level, to habitat diversity and to habitat patch-size. Small isolated plants without epiphytes shelter few species. The faunas of larger isolated plants at mid-tide levels generally include many thallus-dwelling, tubiculous, vagrant and epiphyte-dwelling species, but few such species commonly inhabit plants within aggregations of P. fastigiata. Within aggregations, the plants host relatively few epiphytes and thus lack habitat diversity, and the net emigration rates of many animals including epiphyte-dwellers are relatively high. Plants within aggregations, however, usually shelter more animal indivuduals than isolated plants. Thus, faunal diversity is reduced, not increased within the largest patches of P. fastigiata.     

Space partitioning and interactions in an intertidal sand-burrowing amphipod guild

A nine-year study at a moderately exposed, fine sand intertidal beach at Long Sands, Maine, USA identified marked seasonal changes in the foci of sand-burrowing amphipod activities. These included seasonal population movements, degree of interspecific horizontal overlap, life stage segregation within and between species, and sand depth stratification. Behavioral interactions related to competition for available space are considered important in affecting the distribution and abundance of amphipod species, and community structure. Significant negative correlations were shown between the abundance and upper distributional limits of the smaller, lower shore Acanthohaustorius millsi and the abundance of the larger, higher shore species Haustorius canadensis. Tolerance limits to a variety of prevailing physical factors alone, were not considered a serious obstacle to occupation of higher intertidal level sands by A. millsi. Summer brooding females of both species occupied similar 5 to 10 cm sand depths, but were strongly segregated horizontally. Laboratory coexistence experiments during the reproductive period showed increased mortality of adults and negligible reproductive output of A. millsi when in combination with H. canadensis compared to controls where the former species was alone. A third species, Amphiporeia virginiana, occupied primarily very shallow sand (0 to 2.5 cm), and performed seasonal movements opposite in direction to A. millsi and H. canadensis. The presence, amount, and refinement of biological interactions across the wave exposure gradient requires further study. Until then, we consider as inappropriate the blanket designation of all types of intertidal sand communities as physically controlled.     

The structure of plankton communities of the Indian Ocean

Species diversity and trophic structure of plankton communities have been considered as most important biological features. The Fisher () and Simpson () indices and the information index H=- pi log₂ pi (Margalef) were used for evaluation of species diversity. The indices have been calculated within the group of filter feeders by numbers ( and H) and biomass ( and H) of the species; the best results were obtained in the latter case. The index H=- pi log₂ pi is proposed for the quantitative evaluation of trophic structure, where a portion of an individual trophic group is taken as pi. The plankton material was collected by the R.V. Vityaz in the northern Indian Ocean in January through February, 1960. Analysis of characteristics of zooplankton distribution, species and trophic diversity in connection with characteristics of the water regime resulted in the definition of 3 types of the plankton communities: (a) those in intensive divergence zones; (b) those in poor divergence zones; (c) those in regions with stable water stratification or with feebly marked convergence, distiguished by different values of biomass, species diversity, and trophic group ratios.     

Ecological effects of intertidal uplifting from nuclear testing

Uplifting of a portion of an intertidal rock bench by the Milrow underground nuclear test at Amchitka Island, Alaska affected algal abundance, species composition, and zonation. Parts of the populations of 8 species died off, primarily in the Hedophyllum sessile zone, and mostly within the first 6 months after the disturbance. The center of abundance of these species shifted seaward. Fucus distichus, a species of the upper intertidal, appeared in the area and recolonized a portion of the H. sessile zone. The observations indicate that intertidal algal communities at Amchitka Island are very sensitive to positive elevation changes.Contribution No. 376 of the College of Fisheries, University of Washinton, USA. This publication is based on work performed under U.S. Atomic Energy Commission Contract AT(26-1)-171 for Battelle Memorial Institute, Columbus Laboratories.     

The role of hatching asynchrony in siblicidal brood reduction of two booby species

Summary Hatching asynchrony (HA) of masked boobies (Sula dactylatra) in the Galápagos Islands differs from that of its sympatric congener, the blue-footed booby (S. nebouxii), in association with differences in brood reduction systems. Masked booby nestlings are obligately siblicidal, have long HA, and the probability and timing of siblicide is strongly influenced by HA. Blue-footed boobies are facultatively siblicidal and have shorter HA. Experimental shortening of masked booby HA demonstrated that this species maintians its HA above an early reduction threshold, below which parents may incur costs of provisioning a brood that they cannot raise to fledging, but that blue-footed booby HA occur above, at, and below the masked booby threshold. Differences in HA alone cannot explain the differences between these two brood reduction systems.     

Salinity tolerance of benthic estuarine diatoms as tested with a rapid polarographic measurement of photosynthesis

Measurements of net photosynthesis of benthic estuarine diatoms were made by polarographic registration of oxygen saturation. A measuring cell was constructed in which media with salinities of 2.0 to 100.7 were pumped over the algae between measurements. Diatoms from unialgal cultures and mixed populations from intertidal flats appeared to be highly tolerant of extreme salinities. During short-term exposures (20 min) the net photosynthesis of the algae did not drop below 70% of the initial values, within the salinity range 4.0 to 60.0. Prolonged exposure (up to 6 h) gave essentially the same results. Populations of benthic diatoms, sampled from field stations with mean salinities of about 30, 12, and below 5, showed only gradual differences in their tolerance of salinities between 2.0 and 33.7. Two species, Navicula arenaria and Nitzschia sigma, were cultured in media ranging in salinity from 8.0 to 45.0 and from 2.0 to 45, respectively. The tolerance to changing salinity was only slightly affected by the salinity of the medium in the preculture. The role of salinity in the production and distribution of intertidal diatoms is discussed.     

Analysis of the effects of zinc pollution on the macro-invertebrate populations of the Afon Crafnant,North Wales

The study of the input draining from mine-waste into the Afon Crafnant, N. Wales, revealed that the most significant pollutant was zinc. The concentrations of zinc were monitored during 1978 and 1979, and spot samples were concentrated and analysed for lead, copper, cadmium, iron, cobalt, manganese and nickel. Analysis was by flame atomic absorption specto-scopy. The total zinc concentration of the input was about 4 mg Zn/l which was diluted by the Afon Crafnant to give mean annual concentrations of 213 g Zn/l and 146 g Zn/l for 1978 and 1979 respectively at a site 60 metres downstream of the input. The numbers of individuals and number of taxa in the macro-invertebrate community were reduced at these concentrations. The taxa affected werePhagocata vitta,Erpobdella octoculata, Oligochaeta,Ithytrichia lamellaris, Simuliidae,Ancylus fluviatilis andRithrogena semicolorata. Several commonly used diversity indices failed to show differences between the macro- invertebrate communities at the affected and control sites whereas a modified version of Chandler's Biotic Score (detailed in this paper) revealed both the acute effects at higher concentrations and the chronic effects at lower concentrations.     

Migrational orientation in two species of littoral gastropods (Littorina angulifera and Nerita senegalensis)

Littorina angulifera (Lamark) and Nerita senegalensis Gmelin, both intertidal gastropods, appear to have a preference for specific levels of the shore. In some experiments conducted both in the laboratory and in the field, displaced snails exhibited a general homing behaviour when displaced upshore or downshore. Cues involved in this migrational behaviour have not clearly been identified.     

Comparison of three techniques for administering radiolabeled substrates to sediments for trophic studies: uptake of label by harpacticoid copepods

Microbial grazing by two species of meiofaunal harpacticoid copepods (Heteropsyllus nunni and Thompsonula hyaenae) was determined by uptake of radioactive labels following their introduction into natural sediments from a low-energy intertidal site in Florida (29°5440N; 84°3130W) in May 1986. Grazing was related to three methods of radioactive-label introduction: injection, porewater replacement, and slurry. Uptake of label by harpacticoids was examined using two dual-label combinations, ³H-thymidine/¹⁴C-bicarbonate and ³H-thymidine/¹⁴C-acetate. The injection and porewater-replacement methods yielded statistically indistinguishable results. Results obtained by the slurry method differed significantly from the other two methods. We suggest that the unique results obtained in the slurry method were a consequence of the disruption of microbial-meiofaunal spatial relationships.     

Photosynthetic response to temperature and desiccation of the intertidal alga Mastocarpus papillatus

When exposed to air during low tide, intertidal macroalgae experience a terrestrial environment and often encounter extreme levels of heating and desiccation. Two aspects of photosynthesis may be influenced by this increase in temperature and decrease in water content during exposure to air: (1) the rate of aerial photosynthesis itself, and (2) the rate at which aquatic photosynthesis recovers upon immersion in water at high tide. This laboratory study examines the effect of air temperature and desiccation on photosynthesis of the intertidal macroalga Mastocarpus papillatus Kützing. Plants were collected at Hopkins Marine Station, California, USA (36°37N; 121°54W) between July and December 1990. When apical tips were exposed to 15 to 25°C air for 2 h, photosynthesis was rapidly recovered upon reimmersion in seawater. Recovery was delayed, but complete, when tissue was exposed to 30°C air, but did not occur after exposure to 35°C air. Desiccation did not influence either the rate or the ultimate level of recovery upon reimmersion. Photosynthesis in air generally decreased with increasing desication, with no net photosynthesis occurring below 25% relative water content. Net photosynthesis of hydrated thalli increased with air temperature from 15 to 30°C, then decreased at 35°C. Dark respiration of hydrated thalli increased over the entire temperature range. This study indicates that thallus heating and desiccation during periods of exposure to air can potentially influence the total carbon budget of M. papillatus.     

Dietary constraints on reproductive periodicity in two sympatric deep-sea astropectinid seastars

Examination of the diet of two sympatric species of seastar, Bathybiaster vexillifer and Plutonaster bifrons from 2200 m depth in the Rockall Trough, NE Atlantic Ocean (57°18'N; 10°28'W), suggested that diet may determine the different reproductive patterns found between these two species. In the non-seasonally breeding B. vexillifier, the diet showed a high Shannon-Wiener prey diversity index, the dominant prey being the irregular echinoid Hemiaster expergitus together with a variety of prosobranch gastropods and protobranch bivalves. By contrast, the prey diversity in the seasonally breeding P. bifrons was significantly lower than that of B. vexillifer. In addition, organic carbon content in the sediment residue in the stomachs of P. bifrons displayed a seasonal cycle, while no such seasonality was detected in B. vexillifer. The stomachs of P. bifrons also contained a higher proportion of scavenged material, including the seasonally available remains of mesopelagic blue whiting. These data, together with Bathysnap (time-lapse camera) observations of feeding behaviour in both species, suggest that B. vexillifer is a predator feeding deep in the sediment, whereas P. bifrons feeds close to the sediment surface where it is affected by the seasonal availability of phytodetritus and fish carcasses.     

Die verbreitung der uferwanzen (Heteroptera: Saldidae) im brackigen und marinen litoral der nordamerikanischen pazifikküste

Shore bugs (Heteroptera: Saldidae) were collected during summer 1973 along the Pacific Coast of North America between the arctic and the subtropical regions. The field studies were aimed at determining the species-specific upper and lower limits of distribution in the littoral, and the distribution range of these species in estuaries. The saldids inhabiting the littoral zones can be divided into two groups: those species which live mainly along the coast (coastal species), and those which live mainly inland (inland species). Species found in the supralittoral occur at inland localities as well, and thus can either tolerate limnetic-oligohaline conditions (Salda littoralis, S. provancheri, Saldula coxalis) or are confined to habitats along salt lakes (Pentacora signoreti). Inhabitants of the eulittoral can either occur in the supralittoral and inland localities as well and are holeuryhaline (Saldula palustris, S. pallipes), or have disconnected inland populations (S. nigrita), or they live exclusively in the intertidal zones. In the subarctic, coastal species are distributed from the intertidal zones to inland limnetic habitats. The increasing aridity of southern climatic zones may act as a limiting factor confining the distribution of coastal species to the coast. On the other hand, the distribution of inland species may be influenced by competition with the coastal forms.

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Mit dankenswerter Unterstützung der Deutschen Forschungsgemeinschaft.     

Genetic variation and biochemical systematics in the marine bryozoan Alcyonidium mytili

For many years the taxonomic position of the marine ctenostome bryozoan Alcyonidium mytili Dalyell (1848) has been in doubt, with some authorities regarding it as being conspecific with A. polyoum (Hassall). We have set out to resolve this problem using enzyme electrophoresis to examine the genetics of the population structure in the two species. The results show beyond reasonable doubt that sympatric populations of the two species are indeed from quite separate and non-interbreeding gene pools. An examination of various allopatric populations shows a new species of A. mytili to exist sympatrically with the other at Langstone Harbour, Hampshire, England. This species can be readily distinguished on morphological as well as genetic ground. Samples of A. mytili from Guernsey also show substantial genetic differences from other populations examined. It is tentatively concluded that this population also represents a separate gene pool and consequently should be recognised as a third species of A. mytili.     

Potential effects of a resuspension event on the vertical distribution of copepod eggs in the sea bed: a laboratory simulation

Adult female Acartia tonsa and Labidocera aestiva were obtained from inshore marine waters near Turkey Point, Florida (29°54.5N;84°31W) during April and May 1991. For each species, eggs spawned overnight in the laboratory were collected, mixed with sediment, and added to a plastic tube (26 to 29 cm longx5 cm diam) to yield a 2 cm-thick layer. This tube was connected to a 245 cm-long tube, seawater was added and the contents were thoroughly mixed by turning the assembly end-over-end several times. The vertical distribution of eggs in the sediments following resuspension varied according to the grain size of the sediments. For sediments of 125 m particle-diameter, 68 to 72%, and 70 to 73% of the eggs of A. tonsa and L. aestiva, respectively, occurred in the upper 4 mm.For sediments 63 to <125 m particle-diameter, 34 to 36% of the eggs of A. tonsa and L. aestiva, respectively, occurred in the upper 4 mm. For sediments of <63 m particle-diameter, egg distribution was uniform for both species throughout the 2 cm layer. The results indicate that the vertical distribution of eggs in the sea bed following a resuspension event should be highly dependent upon the grain-size composition of the sediments.     

Accumulation of 14C-1-naphthalene by an oceanic and an estuarine copepod during long-term exposure to low-level concentrations

Accumulation of the bi-cyclic aromatic hydrocarbon ¹⁴C-1-naphthalene in adult female Calanus helgolandicus Claus and adult female Eurytemora affinis Poppe in sea water concentrations of hydrocarbon ranging from 0.2 to 992 g/l was studied during exposure periods of up to 15 days as part of an investigation of the possible effects on marine zooplankton of persistent exposure to low levels of petroleum hydrocarbons. With both species the body levels of radioactivity increased rapidly during the first few days of the exposure period, but after exposure for 7 to 8 days to sea water containing 50 g hydrocarbon/l an equilibrium condition was approached; in some experiments where E. affinis was exposed to 1.0 and 10 g hydrocarbon/l for 15 days there was no further increase in body levels of radioactivity after 7 to 8 days. Using a low concentration of hydrocarbon (1 g/l), the quantity of radioactivity accumulated after 10 days was found to be nearly fifty times greater in the smaller species, E. affinis, than in C. helgolandicus, when expressed in terms of body weight. After they had been exposed to the hydrocarbon for several days the copepods contained a considerable proportion of radioactivity that was no longer identifiable as naphthalene and was presumably present as metabolites. Radioactivity accumulated in the copepods after several days was rapidly lost after they were transferred to uncontaminated sea water: e.g. C. helgolandicus lost nearly 90% of its body level of radioactivity in 24 h. Thereafter the rate of loss was greatly reduced, and 5% of the original body level of radioactivity still remained in the copepods at the end of 11 days. Experiments on the breakdown of naphthalene added at low concentrations to sea water samples containing natural microbial populations indicated degradation rates of 0.1 to 0.2 g/l/24 h in oceanic water, and 2.6 g/l/24 h in inshore water samples. The results are discussed in terms of the possible transfer of hydrocarbon to a higher trophic level in areas subjected to constant low-level inputs of petroleum hydrocarbons.     

“Free space-photosynthesis” in the algae Fucus virsoides and Laminaria saccharina

This paper deals with the role of bicarbonates in the apparent free space (AFS) and their importance for the photosynthetic process. Both the littoral alga Fucus virsoides (Mediterranean Sea) and the sublittoral alga Laminaria saccharina (Baltic Sea) show the same response. Unloading of Clions and subsequent reloading of HCO₃-ions result in a positive photosynthetic rate in distilled water (free of CO₂). Time of exposure of an algal thallus to bicarbonate solutions, as well as the concentration of these solutions, influences AFS-assimilation of the ions.     

Alkaline phosphatase activity in marine macrophytes: histochemical localization in some widespread species in southern Spain

Alkaline phosphatase activity (APA) was determined in 44 species of marine macrophytes collected throughout 1991 and 1992 along the southern coast of Spain. Activity varied between 0.83 mol paranitrophenol (pNP) released g^-1 dry wt h^-1 in Ulva rigida var. gigantea and 238.8 mol pNP g^-1 dry wt h^-1 in Bangia fuscopurpurea. Using a histochemical method, APA sites were located in five of these species: Corallina elongata Ellis et Soland, Gelidium latifolium (Grev.) Thur. et Born., G. sesquipedale (Clem.) Born. et Thur., Porphyra umbilicalis (L.) Kützing and Zostera noltii Hornem. Enzymatic activity was found in the outer part of the thallus, either on the cell wall or in the cortical cells. In the marine phanerogam Z. noltii activity was also located in the vascular bundle. The results suggest that APA is present in many, if not all, marine macrophytes from southern Spain, and plays a relevant role in the utilization of dissolved organic phosphorus compounds.     

The enantiomeric composition of monoterpene hydrocarbons in the defensive secretions ofNasutitermes termites (Isoptera): Inter- and intraspecific variations

Summary Frontal gland secretions of termite soldiers of the speciesNasutitermes costalis, N. ephratae, N. nigriceps, N. rippertii, andN. hubbardii were analyzed. The chiral compositions of the monoterpene hydrocarbons were investigated by means of two-dimensional gas chromatography. Two of them, 3-carene and-pinene were present in the form of (–)-enantiomers of high purity in the majority of the samples. The other monoterpenes,-pinene, camphene, sabinene, limonene, and-phellandrene, exhibited a great variation in the enantiopurity between different species.-Pinene and limonene varied significantly even between different colonies within the species.N. costalis was the only species with an invariable composition of the secretion, independent of the locality or origin.     

Macrozoobenthic community structure in the Ría de Foz,an intertidal estuary (Galicia,Northwest Spain)

The community structure of the macrobenthic (>1 mm) fauna of an intertidal soft-bottom estuary, the Ría de Foz (Galicia, Northwest Spain) was investigated on 99 occasions during June, September and December 1984 and March 1985. The infaunal data were subjected to classification and ordination techniques. The analyses indicated that sediment characteristics (grain size, percentage silt-clay and organic-matter content) and tidal height are the most important factors governing the distribution and abundance of the intertidal communities. Three faunal assemblages were identified and examined in terms of species dominance, constancy and fidelity. In the clean sands of the outer estuary two main assemblages were distinguished; one, corresponding to the boreal LusitanianTellina community, inhabited the middle and lower tidal levels; the other, typical of a biocoenosis of sands and slightly muddy mediolittoral sands, inhabited the upper tidal level. The third benthic assemblage occupied the muddy sands and mud of the inner estuary and displayed some features in common with theCardium edule-Scrobicularia community described by Thorson.