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  • 1
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The prokaryotic green alga Prochloron sp. (Prochlorophyta) is found in symbiotic association with colonial didemnid ascidians that inhabit warm tropical waters in a broad range of light environments. We sought to determine the light-adaptation features of this alga in relation to the natural light environments in which the symbioses are found, and to characterize the temperature sensitivity of photosynthesis and respiration of Prochloron sp. in order to assess its physiological role in the productivity and distribution of the symbiosis. Colonies of the host ascidian Lissoclinum patella were collected from exposed and shaded habitats in a shallow lagoon in Palau, West Caroline Islands, during February and March, 1983. Some colonies from the two light habitats were maintained under conditions of high light (2 200 μE m−2 s−1) and low light (400 μE m−2 s−1) in running seawater tanks. The environments were characterized in terms of daily light quantum fluxes, daily periods of light-saturated photosynthesis (Hsat), and photon flux density levels. Prochloron sp. cells were isolated from the hosts and examined for their photosynthesis vs irradiance relationships, respiration, pigment content and photosynthetic unit features. In addition, daily P:R ratios, photosynthetic quotients, carbon balances and photosynthetic carbon release were also characterized. It was found that Prochloron sp. cells from low-light colonies possessed lower chlorophyll a/b ratios, larger photosynthetic units sizes based on both reaction I and reaction II, similar numbers of reaction center I and reaction center II per cell, lower respiration levels, and lower Pmax values than cells from high-light colonies. Cells isolated from low-light colonies showed photoinhibition of Pmax at photon flux densities above 800 μE m−2 s−1. However, because the host tissue attenuates about 60 to 80% of the incident irradiance, it is unlikely that these cells are normally photoinhibited in hospite. Collectively, the light-adaptation features of Prochloron sp. were more similar to those of eukaryotic algae and vascular plant chloroplasts than to those of cyanobacteria, and the responses were more sensitive to the daily flux of photosynthetic quantum than to photon flux density per se. Calculation of daily minimum carbon balances indicated that, though high-light cells had daily P:R ratios of 1.0 compared to 4.6 for low-light cells, the cells from the two different light environments showed nearly identical daily carbon gains. Cells isolated from high-light colonies released between 15 and 20% of their photosynthetically-fixed carbon, levels sufficient to be important in the nutrition of the host. Q10 responses of photosynthesis and respiration in Prochloron sp. cells exposed briefly (15–45 min) to temperatures between 15° and 45°C revealed a discontinuity in the photosynthetic response at the ambient growth temperatures. The photosynthetic rates were found to be more than twice as sensitive to temperatures below ambient (Q10=3.47) than to temperatures above ambient (Q10=1.47). The Q10 for respiration was constant (Q10=1.66) over the temperature range examined. It appears that the photosynthetic temperature sensitivity of Prochloron sp. may restrict its distribution to warmer tropical waters. The ecological implications of these findings are discussed in relation to published data on other symbiotic systems and free-living algae.
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  • 2
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The gonads of sea urchins undergo large changes in mass during their gametogenic cycle. In addition, they have relatively low aerobic capacities and are poorly perfused by the circulatory system and thus are continually hypoxic or anoxic. The present study of Strongylocentrotus droebachiensis investigates seasonal changes in the relationships among mass of the ovaries, pH and PO2 of the perivisceral coelomic fluid which bathes the ovaries, and partitioning of ovary energy metabolism into its anaerobic and aerobic components. S. droebachiensis were collected at Blue Hill Falls, Maine, USA, from August 1982 to March 1984. We found that from 76 to 92% of the heat dissipated by isolated ovaries of the sea urchin S. droebachiensis derives from anaerobic energy metabolism at partial pressures of oxygen prevailing in vivo. Ovaries from S. droebachiensis have the capacity to produce large amounts of lactate under imposed anoxia, but lactate accounts for only 37% of the total anoxic heat dissipation, which suggests that other end products of anaerobiosis are present. Seasonal changes in pH and PO2 of the perivisceral coelomic fluid can be explained by a complex relationship among changes in temperature, reproductive condition, and anaerobic and aerobic metabolism in the ovaries, gut and body wall. Seasonal changes in the buffering capacity of the perivisceral coelomic fluid must be determined before the effects of respiratory and metabolic acid production on the acid-base status of the coelomic fluid can be fully understood.
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  • 3
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Suspension feeding by a stalkless crinoid (Oligometra serripinna) was studied at Lizard Island, Australia, in 1985. The crinoids were placed in a laboratory flume with a slow, unidirectional current of seawater. Nutritive and non-nutritive particles (15 to 180 μm) were introduced upstream from the crinoid, and feeding behavior was recorded at high magnifications on videotape for frame analysis. These direct observations showed that each intercepted particle (whether a dejellied clam egg, Sephadex bead or latex sphere) contacts a single, evidently adhesive tube foot and is rapidly transferred to the pinnular food groove by a bend of the tube foot. The tube foot bends in about 0.1 s and returns to its extended position in 1 to 2 s. Spheres less than 20 μm in diameter cause only the intercepting tube foot to bend. In contrast, larger spheres cause the coordinated bending of the intercepting tube foot plus many of the neighboring tube feet: the stimulus spreads through the reacting group of tube feet at about 1 cm s-1. After transfer to the pinnular food groove, the nutritive particles (dejellied clam eggs) travel at about 1 cm min-1 to the arm axis and thence down the arm food groove at about 4 cm min-1 to the mouth; in contrast, non-nutritive particles (Sephadex beads and latex spheres) are discarded from the pinnular food groove between 1 and 30 s after capture. Tube-foot bending is presumably triggered when arriving particles (whether nutritive or non-nutritive) are detected by sensory cells in the tubefoot epithelium: mechanoreception by itself appears sufficient to initiate bending, although chemoreception may modify the reaction. Then, soon after captured particles have been transferred to the pinnular food groove, the crinoid discards those judged unsuitable (probably by contact chemoreceptors in the food-groove epithelium). Clam eggs with intact jelly layers temporarily hang up on tube feet they contact and then float away in the curent: the jelly evidently interferes with mechanoreception and/or chemoreception by the tube-foot epithelium. Some previous studies of crinoid feeding have suggested that particles are trapped in extensive nets or strands of mucus: we found no evidence for this in O. serripinna, which captures particles predominantly be the direct interception method of the aerosol filtration model.
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  • 4
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The toxicity of copper and zinc to the estuarine copepod Acartia tonsa and to the two diatom food species Thalassiosira pseudonana and T. weissflogii was measured in nitrilotriacetate-trace metal ion buffer systems at 25‰ S. Overall, A. tonsa appeared to be more sensitive to cupric and zinc ion activity than either of the diatoms; however, its sensitivity varied among the different life stages examined. Adult survival was not affected within the zinc ion activity range 10-11 to 10-8 M and cupric ion activity range 10-13 to 10-11 M over a 96-h period, but a cupric ion activity of 10-10 M caused total mortality of adults within 72 h. Egg-laying rate was most sensitive to zinc, and was reduced at zinc ion activities ≧10-10 M. Naupliar survival after 96 h was reduced by zinc ion activities ≧10-8 M and by cupric ion activities ≧10-11 M, and was reduced to zero at a zinc ion activity of 10-7 M and at a cupric ion activity of 10-10.5 M. In an interspecies comparison of 96-h adult survival, Centropages typicus was more sensitive to copper and zinc than A. tonsa and the survival of Labidocera aestiva was dependent on the ratio of cupric to zinc ion activity. A comparison of our results with estimates of zinc and cupric ion activities in estuaries suggests that ionic activities of these metals are high enough in some polluted estuaries to affect the survival and reproduction of copepods.
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  • 5
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Frequencies of electromorphs encoded by 14 polymorphic loci were used to estimate genetic distances among samples of the rabbitfishes Siganus argenteus, S. doliatus, S. fuscescens, S. guttatus, S. javus, S. punctatus, S. randalli, S. spinus, S. vermiculatus, and S. (Lo) vulpinus. Samples of the surgeonfish Naso lituratus (Acanthuridae) were included in the electrophoretic survey for the purpose of outgroup comparison. A matrix of genetic-distance estimates was used for construction of dendrograms by neighbor-joining, complete-linkage and single-linkage procedures, and the unweighted pair-group method of arithmetic averages (UPGMA). Cluster analysis revealed interspecific relationships that are concordant with several predictions intimated in the most recent taxonomic revision of this assemblage of fishes. S. randalli and S. vermiculatus, the pair postulated to be sibling species on the basis of strikingly similar external morphology, were found to exhibit the lowest levels of genetic divergence relative to all other pairs of study species. S. randalli, S. guttatus, and S. vermiculatus comprised one of three clusters discerned in all resultant topologies (i.e., “ball clusters”). S. argenteus, S. fuscescens, and S. spinus, three fusiform-bodied species, formed a second ball cluster that was clearly separable from the remainder of the siganids studied (which are all relatively deep-bodied). A third ball cluster contained S. punctatus and S. vulpinus: S. doliatus was depicted as being allied with S. punctatus and S. vulpinus in the neighbor-joining and complete-linkage topologies but not in topologies generated by UPGMA and single linkage. It is noteworthy that S. punctatus, S. vulpinus, and S. doliatus are the only three species included in the present study which purportedly school when young but form pair-bonds as adults. In all topologies, S. javus occupied branches stemming from furcation points between fusiform-bodied and deep-bodied species. Of all the siganids studied, S. argenteus was found to be least divergent genetically from N. lituratus. S. argenteus is the only siganid known to spawn pelagic eggs and undergo a specialized pelagic stage (features typical within the Acanthuridae). Hence, genetic relationships within the Siganidae and among the Siganidae and a representative acanthurid coincide with a host of predictions stemming from morphologic and life-history studies of the Acanthuroidei.
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  • 6
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Diffusional permeabilities and drinking rates of 24 h-old Artemia sp. metanauplii incubated at 20 °C were studied at five temperatures: 15, 20, 25, 30, and 35 °C over a period of 6 h. Departures from the incubation temperature resulted in changes in both permeability and drinking rates which both reached their highest values at 35 °C. Metanaupliar permeability and drinking were more elevated than previously reported for adults.
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  • 7
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Restriction enzyme analysis of mitochondrial DNA (mtDNA) was used to test for genetic homogeneity of orange roughy (Hoplostethus atlanticus) in the southern hemisphere. Two hundred and eighty-six orange roughy specimens were collected from seven general localities: the Great Australian Bight; South Australia (off southeastern Kangaroo Island); the west coast of Tasmania; the east coast of Tasmania; New South Wales; New Zealand and South Africa. Mitochondrial DNA was extracted from developing ovary tissue and analysed with 10 six-base enzymes and 3 four-base enzymes. Both forms of analysis revealed a low level of genetic diversity in this species. The six-base enzyme study found no evidence of reproductively isolated populations of orange roughy in southeastern Australian waters. However, an analysis of 107 fish with 3 four-base enzymes identified at least partial genetic separation of the New South Wales (NSW) sample of orange roughy from South Australian (off southeastern Kangaroo Island) and Tasmanian samples. This finding supports biological evidence for the presence of a distinct subpopulation of orange roughy in NSW waters. The four-base study also provided evidence of the presence of genetically distinct samples of orange roughy occurring in the same localities off southeastern Kangaroo Island from consecutive years. Additional sampling and the use of a greater number of four-base enzymes may be needed to determine if any genetic structuring exists among orange roughy south of New South Wales.
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  • 8
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A series of observations, using a dual-frequency calibrated echosounder operating at 38 and 120 kHz, of a patch of Euphausia superba close to South Georgia in 1986 is described. Sea state is shown to cause significant noise close to the surface, but to cause no significant signal attenuation. There is a consistent difference of ∼5 dB between the signal levels at the two frequencies which is in line with the difference noted from independent observations, theoretical models and in studies on encaged aggregations of krill.
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  • 9
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Growth, reproduction and gross biochemical composition of the Manila clam Ruditapes philippinarum were studied for one oceanic and two inner stations in the Bay of Arcachon, France, from March 1989 to March 1991. During this period, sea-water temperature, salinity and chlorophyll a were also recorded. A marked increase in length occurred during the first year in all areas, after which growth rates decreased. In contrast, weight increased more steadily. The Manila clam exhibited best development in the oceanic area, but there was no difference in growth of clams between the two inner stations. Differences in growth between oceanic and inner stations may result from differences in fluctuations of environmental conditions such as temperature and salinity. Except for higher carbohydrate contents in clams recovered in autumn from the oceanic station “Le Ferret”, biochemical components differed little between stations. During the second winter, glycogen levels were relatively low, but no mortalities were recorded. On the other hand, sowing spat in autumn instead of spring or sowing larger-sized spat did not reduce the time required for culture of R. philippinarum.
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  • 10
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Paired flat plates of the hermatypic coral Montipora verrucosa from Kaneohe Bay, Oahu, Hawaii, were acclimated to photosynthetically active radiation (PAR) only and to full sunlight (PAR+UV) for several weeks in the summer of 1990. After the acclimation period, photosynthesis, both in PAR-only and PAR+UV as well as dark respiration were measured. Levels of the UV-absorbing compounds, “S320”, density of zooxanthellae, and chlorophyll a concentration were determined. Corals acclimated in PAR+UV had higher levels of the UV-protective compounds and lower areal zooxanthellae densities than corals acclimated in PAR-only. Chlorophyll a per unit volume of coral host and per algal cell did not differ between corals from the two acclimation treatments. Corals acclimated to PAR+UV displayed higher photosynthesis in full sunlight than corals acclimated to PAR-only, but when photosynthesis was measured in the light regime to which the corals had been acclimated, there were no differences in photosynthesis. Dark respiration was the same for corals from the two acclimation treatments regardless of the light quality immediately preceding the dark period.
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