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1.
Besides diatoms Demospongiae are the most important consumers of dissolved silica in the sea. They can play an important
role for the silica budget especially in the shallow water areas of the Baltic Sea. The dependence of the silica uptake rate
on the silica concentration of the seawater was measured for the sponge Halichondria panicea (Pallas, 1766). The sponges were collected in Kiel Bight. The uptake conformed to Michaelis–Menten kinetics with a half-saturation
constant of 46.41 μM and a saturated uptake rate of 19.33 μmol h−1 g−1 ( p < 0.01). In the red algae zone of Kiel Bight the sponges depend on silica supply from the surrounding waters and may be silica-limited
rather than food-limited in growth. Because of the much faster uptake of silica by diatoms and their lower saturation point,
as well as the difference in spatial distribution of the two main silica consumers, a competition for silica between sponges
and diatoms seems unlikely.
Received: 21 June 1997 / Accepted: 15 July 1997 相似文献
2.
Friederike Hoffmann Hans Røy Kristina Bayer Ute Hentschel Martin Pfannkuchen Franz Brümmer Dirk de Beer 《Marine Biology》2008,153(6):1257-1264
The Mediterranean sponge Aplysina aerophoba kept in aquaria or cultivation tanks can stop pumping for several hours or even days. To investigate changes in the chemical
microenvironments, we measured oxygen profiles over the surface and into the tissue of pumping and non-pumping A. aerophoba specimens with Clark-type oxygen microelectrodes (tip diameters 18–30 μm). Total oxygen consumption rates of whole sponges
were measured in closed chambers. These rates were used to back-calculate the oxygen distribution in a finite-element model.
Combining direct measurements with calculations of diffusive flux and modeling revealed that the tissue of non-pumping sponges
turns anoxic within 15 min, with the exception of a 1 mm surface layer where oxygen intrudes due to molecular diffusion over
the sponge surface. Molecular diffusion is the only transport mechanism for oxygen into non-pumping sponges, which allows
total oxygen consumption rates of 6–12 μmol cm−3 sponge day−1. Sponges of different sizes had similar diffusional uptake rates, which is explained by their similar surface/volume ratios.
In pumping sponges, oxygen consumption rates were between 22 and 37 μmol cm−3 sponge day−1, and the entire tissue was oxygenated. Combining different approaches of direct oxygen measurement in living sponges with
a dynamic model, we can show that tissue anoxia is a direct function of the pumping behavior. The sponge-microbe system of
A. aerophoba thus has the possibility to switch actively between aerobic and anaerobic metabolism by stopping the water flow for more
than 15 min. These periods of anoxia will greatly influence physiological variety and activity of the sponge microbes. Detailed
knowledge about the varying chemical microenvironments in sponges will help to develop protocols to cultivate sponge-associated
microbial lineages and improve our understanding of the sponge-microbe-system. 相似文献
3.
This paper reports on the feeding biology of a predatory and of a facultatively predatory nematode, Enoploides longispiculosus and Adoncholaimus fuscus, respectively. Both species represent genera which are common and abundant in the littoral of the North Sea and in adjacent
estuaries. Observations on the foraging behaviour of both species are given, and for the former species, a range of prey from
its natural habitat is identified. Respiration was determined using a polarographic oxygen electrode technique and compared
to consumption determined as predation rates on the monhysterid nematode Diplolaimelloides meyli. The daily C-loss due to respiration accounted for 15% of the measured C-consumption in E. longispiculosus and for 111% in A. fuscus, proving the observed feeding rates in the latter species to have been inadequate for the maintenance of its aerobic metabolism.
Daily respiration rates at an average environmental temperature were 219 ng C ind−1 d−1 for adults of A. fuscus and 21.9 ng C ind−1 d−1 for adults of E. longispiculosus. Using radiotracer techniques, no uptake of bacterial cells or of organic matter in the dissolved phase was demonstrated
for E. longispiculosus. In A. fuscus, however, a significant drinking of label in the dissolved or volatile fraction occurred; bacterial cells were taken up at
a level insignificant to the nematode's daily C-ration. It is concluded that E. longispiculosus has a fairly strict predatory feeding strategy, while A. fuscus gains a majority of C from additional foraging strategies, among which the uptake of dissolved material and scavenging on
macrofauna carcasses (as reported in the literature) may be of particular importance.
Received: 28 August 1998 / Accepted: 8 March 1999 相似文献
4.
The relative contribution of dissolved nitrogen (ammonium and dissolved free amino acids DFAAs) to the nitrogen budget of
the reef-building coral Pocillopora damicornis was assessed for colonies growing on control and ammonium-enriched reefs at One Tree Island (southern Great Barrier Reef)
during the ENCORE (Enrichment of Nutrient on Coral Reef; 1993 to 1996) project. P. damicornis acquired ammonium at rates of between 5.1 and 91.8 nmol N cm−2 h−1 which were not affected by nutrient treatment except in the case of one morph. In this case, uptake rates decreased from
80.5 to 42.8 nmol cm−2 h−1 (P < 0.05) on exposure to elevated ammonium over 12 mo. The presence or absence of light during measurement did not influence
the uptake of ammonium ions. Nitrogen budgets revealed that the uptake of ammonium from concentrations of 0.11 to 0.13 μM could completely satisfy the demand of growing P. damicornis for new nitrogen. P. damicornis also took up DFAAs at rates ranging from 4.9 to 9.8 nmol N cm−2 h−1. These rates were higher in the dark than in the light (9.0 vs 5.1 nmol m−2 h−1, P < 0.001). Uptake rates were highest for the amino acids serine, arginine and alanine, and lowest for tyrosine. DFAA concentrations
within the ENCORE microatolls that received ammonium were undetectable, whereas they ranged up to 100 nM within the control microatolls. The contribution of DFAAs to the nitrogen budget of P. damicornis constituted only a small fraction of the nitrogen potentially contributed by ammonium under field conditions. Even at the
highest field concentrations measured during this study, DFAAs could contribute only ≃11.3% of the nitrogen demand of P.␣damicornis. This contribution, however, may be an important source of nitrogen when other sources such as ammonium are scarce or during
periods when high concentrations of DFAAs become sporadically available (e.g. cell breakage during fish-grazing).
Received: 22 April 1998 / Accepted: 3 November 1998 相似文献
5.
In situ measurements of photosynthetic irradiance responses of two Red Sea sponges growing under dim light conditions 总被引:6,自引:0,他引:6
Photosynthetic responses to irradiance by the photosymbionts of the two Red Sea sponges Theonella swinhoei (Gray) and Clionavastifica (Hancock) growing under dim light conditions were measured in situ (in September 1997) using a newly developed underwater
pulse amplitude modulated (PAM) fluorometer. Relative rates of photosynthetic electron transport (ETR) were calculated as
the effective quantum yield of photosystem II (Y ) multiplied with the photosynthetic photon flux (PPF). Photosynthesis versus irradiance (P-I ) curves, obtained within minutes, showed that individual specimens of both sponges, growing under very low light conditions,
feature lower light saturation points as well as lower maximal ETRs than individuals growing under higher light. Evaluations
of such curves using low irradiances of the actinic light source (20 to 130 μmol photons m−2 s−1) showed a general decrease in Y, with a shoulder from the lowest irradiance applied till 20 to 30 μmol photons m−2 s−1. Point measurements yielded ETRs close to what could be estimated from the P-I curves. These point measurements also revealed good correlations between the diurnally changing ambient irradiances (1 to
50 μmol photons m−2 s−1) and average ETR values for both species. Further analysis showed that although Y values varied considerably between the different point measurements, they did not decrease significantly with light under
these very low irradiances. Therefore, PPF rather than Y seems to determine the in situ diel photosynthetic performance at the low ambient irradiances experienced by these sponges.
Received: 22 November 1997 / Accepted: 8 April 1998 相似文献
6.
Analysis of the isotope composition of calcareous structures of marine organisms has proved useful in providing biological
data. The present study constitutes the first detailed work undertaken on the isotope composition of coleoid cephalopods.
We analysed the carbon- and oxygen-isotope composition [δ13C (CO2−
3) and δ18O (CO2−
3), respectively] of the cuttlebone aragonite of wild and cultivated specimens of Sepia officinalis Linnaeus, 1758. δ13C (CO2−
3) ranged from −2.94 to 1.00‰, δ18O (CO2−
3) from −0.18 to 2.08‰. The carbon-isotope composition is not in equilibrium with the carbon species of the ambient seawater,
and does not reflect the deposition of CaCO3 in seawater. The potential influence of environmental factors and biological processes on the carbon-isotope composition
of the cuttlebone is discussed. In contrast to δ13C, the oxygen-isotope composition of cuttlebone aragonite appears to be in isotopic equilibrium with the ambient seawater.
Seasonal changes in isotopic temperature revealed by our analyses agreed with changes in the temperature of the ambient seawater.
CaCO3 was deposited all year round. A maximum life span of 2 yr, a year-round spawning season, and variable growth rates among and
within individuals have been inferred from the isotopic temperatures.
Received: 14 April 1998 / Accepted: 26 November 1998 相似文献
7.
Organic nitrogen uptake and growth by the chrysophyte Aureococcus anophagefferens during a brown tide event 总被引:5,自引:0,他引:5
The quantitative importance of light-mediated, dissolved organic nitrogen (DON) utilization in relation to overall nitrogen-assimilation
in Aureococcusanophagefferens Hargraves et Sieburth was assessed during a brown tide event in Shinnecock Bay, Long Island, 24 through 26 July 1995. The
growth response of A. anophagefferens was maximal in organic-rich Bay water and decreased proportional to the organic:inorganic nutrient ratio of the water. Short-term
uptake measurements with six nitrogenous substrates revealed that reduced nitrogen could potentially represent 95% of overall
nitrogen uptake of which 70% was due to organic nitrogen alone. Potential uptake of urea by the A. anophagefferens-dominated bloom was substan tially greater than uptake of the other substrates tested during the study, contributing the
largest percentage of total nitrogen uptake (58 to 64%; ρ′
max(urea) 4.4 μg atom N l−1 h−1), followed by NH4
+ (18 to 26%; ρ′max(NH4+) 2 μg atom N l−1 h−1). The combined rates of uptake of algal extract, lysine and glutamic acid contributed between 11 and 16% of total uptake,
whereas NO3
−contributed 5 to 8%. Based on the kinetic determinations from this study we suggest an ecological framework for the events
leading to the dominance and abundance of A. anophagefferens in coastal bays.
Received: 29 March 1997 / Accepted: 24 April 1997 相似文献
8.
E. Pfeiler 《Marine Biology》1997,127(4):571-578
Bonefish (Albula sp.) larvae (leptocephali) from the Gulf of California complete metamorphosis in ˜10 d in natural seawater (35‰S; Ca2+ conc = 10.5 mM). The increase in ossification that occurs near the end of the non-feeding metamorphic period, in addition to the ability
of larvae to complete metamorphosis in dilute seawater (8‰ S) prompted the present study, where the effects of varying the
external calcium ion concentration, [Ca2+]e, of artificial seawater (ASW) on the survival, development and internal (whole-body) calcium ion content, (Ca2+)i, of unfed metamorphosing larvae were investigated. Early-metamorphosing larvae placed in␣ASW, where [Ca2+]e = 10.1 mM, survived for up to 10 d and developed normally without exogenous nutrients. In shorter-term experiments (4 to 5 d), no differences
in survival were found for larvae in ASW with [Ca2+]e rang-ing from 1.5 to 10.1 mM. However, in Ca2+-free ASW, most larvae died within 27 h and no larvae survived more than 42 h; the median lethal time (LT50), and its 95% confidence limits, were 14.5 (10.0 to 20.9) h. High mortality (81% after 20 h) also occurred in 1.0 mM Ca2+ ASW, but 2 of 16 larvae tested survived for 96 h. The 96 h median tolerance limit (TLM), corrected for control mortality, was 1.2 mM Ca2+. In natural seawater, larval (Ca2+)i remained relatively constant ( = 0.419 mg larva−1)␣in early- and intermediate-metamorphosing larvae, and then increased to a mean value of 0.739 mg larva−1 in advanced larvae, indicating that Ca2+ was␣taken up from the medium at this stage; the increase in (Ca2+)i corresponded to the period of ossification of the vertebral column. Internal (whole-body) magnesium ion content (Mg2+)i showed no significant change during metamorphosis ( = 0.089 mg larva−1). No significant differences in (Ca2+)i were found in advanced larvae in natural seawater and those in ASW, with [Ca2+]e ranging from 2.0 to 10.1 mM. However, clearing and staining revealed that ossification of the vertebral column had not yet occurred in advanced larvae
from 2.0 to 10.1 mM Ca2+ ASW. Also, low [Ca2+]e (1.0 to 2.0 mM) usually produced deformed larvae that swam erratically, at times showing “whirling” behavior.
Received: 21 August 1996 / Accepted: 26 August 1996 相似文献
9.
Zooplankton responses to hypoxia: behavioral patterns and survival of three species of calanoid copepods 总被引:2,自引:0,他引:2
Seasonally recurrent and persistent hypoxic events in semi-enclosed coastal waters are characterized by bottom-water dissolved
oxygen (d.o.) concentrations of < 2.0 ml l−1. Shifts in the distribution patterns of zooplankters in association with these events have been documented, but the mechanisms
responsible for these shifts have not been investigated. This study assessed interspecific differences in responses to hypoxia
by several species of calanoid copepods common off Turkey Point, Florida, USA: Labidocera aestiva (Wheeler) (a summer/fall species), Acartia tonsa (Dana) (a ubiquitous year-round species), and Centropages hamatus (Lilljeborg) (a winter/spring species). Under conditions of moderate to severe hypoxia 24-h survival experiments were conducted
for adults and nauplii of these species from August 1994 to October 1995. Experiments on adults used a flow-through system
to maintain constant d.o. concentrations. Adults of A. tonsa showed no decline in survival with d.o. as low as 1.0 ml l−1, sharp declines in survival at d.o. = 0.9 to 0.6 ml l−1, and 100% mortality with d.o. = 0.5 ml l−1. Adults of L. aestiva and C. hamatus were more sensitive to oxygen depletion: both species experienced significant decreases in survival for d.o. = 1.0 ml l−1. Nauplii of L. aestiva and A. tonsa showed no significant mortality with d.o. = 1.1 to 1.5 ml␣l−1 and d.o. = 0.24 to 0.5 ml l−1, respectively. In addition, experiments investigating behavioral avoidance of moderate to severe hypoxia were carried out
for adults of all three species. None of the three species effectively avoided either severely hypoxic (d.o. < 0.5 ml l−1) or moderately hypoxic (d.o. ≈ 1.0 ml l−1) bottom layers in stratified columns. These results suggest that in␣nearshore areas where development of zones of d.o. < 1.0 ml
l−1 may be sudden, widespread, or unpredictable, patterns of reduced copepod abundance in bottom waters may be due primarily
to mortality rather than avoidance.
Received: 31 August 1996 / Accepted: 24 September 1996 相似文献
10.
Photosynthetic rates of eight seagrass species from Zanzibar were limited by the inorganic carbon composition of natural
seawater (2.1 mM, mostly in the form of HCO3
−), and they exhibited more than three time higher rates at inorganic carbon saturation (>6 mM). The intertidal species that grew most shallowly, Halophila ovalis, Halodule wrightii and Cymodocea rotundata, showed the highest affinity for inorganic carbon (K
1/2 = ca. 2.5 mM), followed by the subtidal species (K
1/2 > 5 mM). Photosynthesis of H. wrightii, C. rotundata, Cymodocea serrulata and Enhalus acoroides was >50% inhibited by acetazolamide, a membrane-impermeable inhibitor of carbonic anhydrase, indicating that extracellular
HCO3
− dehydration is an important part of their inorganic carbon uptake. Photosynthetic rates of H. wrightii, Thalassia hemprichii, Thalassodendron ciliatum, C. serrulata and E. acoroides were strongly reduced by changing the seawater pH from 8.2 to 8.6 in a closed system. In H. ovalis, C. rotundata and Syringodiumisoetifolium, photosynthesis at pH 8.6 was maintained at a higher level than could be caused by the ca. 30% CO2 concentration which remained in the closed experimental systems at that pH, pointing toward HCO3
− uptake in those species. It is suggested that the ability of H. ovalis and C. rotundata to grow in the high, frequently air-exposed, intertidal zone may be related to a capability to take up HCO3
− directly, since this is a more efficient way of HCO3
− utilisation than extracellular HCO3
− dehydration under such conditions. The inability of all species to attain maximal photosynthetic rates under natural conditions
of inorganic carbon supports the notion that seagrasses may respond favourably to any future increases in marine CO2 levels.
Received: 19 March 1997 / Accepted: 31 March 1997 相似文献
11.
During commercial handling of Nephropsnorvegicus (L.) there are a number of situations when the prawns may be exposed to very high ambient ammonia levels. These experiments
evaluated the effects of increased levels of ambient total ammonia (TA = NH3 + NH4
+) on␣blood ammonia, ammonia efflux rates and on the cardio-ventilatory performance of N. norvegicus. When prawns were taken from <1 to 2000 μmol TA l−1 medium, blood TA concentrations increased rapidly for the first 2 h but tended to drop thereafter. Original blood TA levels
were restored 6 h after the prawns were transferred back from seawater containing 2000 to <1 μmol TA l−1. Sudden exposure to 500, 1000, 2000 or 4000 μmol TA l−1 medium induced blood TA concentrations to increase respectively to 50, 30, 33 and 36% of external concentrations (normally,
internal TA values are much higher than external levels). Immediately after transfer back to seawater with low ammonia concentration
( <1 μmol TA l−1), excretion rates were higher than those of control prawns, and the absolute amounts of TA excreted were considerably higher
than those calculated to have accumulated in the haemolymph. Heart rate (HR) and scaphognathite rate (SR) were not altered
when prawns were subjected to sudden alterations in ambient ammonia ( <1 to 2000 to <1 μmol TA l−1). When water ammonia concentrations were altered more gradually, both rates increased, but only at 4000 μmol TA l−1. These results show that N. norvegicus is able to remove ammonia from the haemolymph and/or transform ammonia into some other substance when subjected to increased
levels of ambient ammonia. Possible mechanisms involved (e.g. active transport across the gills; storage in some other tissue;
glutamate synthe sis) are discussed.
Received: 20 May 1996 / Accepted: 1 July 1996 相似文献
12.
The toxicity of fenitrothion was determined in larvae (nauplii, Zoeae 1 to 3, Mysis 1 to 3), postlarvae (PL stages) and juvenile
shrimp (Penaeus japonicus Bate), in two media, seawater (SW) and diluted seawater (DSW) (1100 and 550 mosM kg−1, ≃ 37 and 19‰ S). The effects of fenitrothion on the osmoregulatory capacities (OC) of juveniles were recorded. A gill and
epipodite histopathological study was also conducted. For larvae in seawater, 24 and 48 h LC50s ranged from 32.9 μg l−1 (Zoeae 2) to 10.7 μg l−1 (Mysis 3), and from 3.9 μg l−1 (Zoeae 3) to 2.0 μg l−1 (Mysis 3), respectively; 48 and 96 h LC50s in postlarvae (PL) at the same salinity ranged from 1.8 μg l−1 (PL1) to 0.6 μg l−1 (PL5), and from 0.3 μg l−1 (PL7) to 0.4 μg l−1 (PL15). In juveniles, 96 h LC50s were 0.8 μg l−1 in seawater and 1.5 μg l−1 in diluted seawater. From hatching to juvenile stages, the overall trend was a rapid decrease (from nauplii to PL5–PL7) followed
by a slight increase (from PL7 to PL15 and juveniles) in the shrimp's ability to tolerate the insecticide. In juveniles kept
in seawater and in diluted seawater, fenitrothion decreased the osmoregulatory capacity (OC = difference between the hemolymph
osmotic pressure and the osmotic pressure of the medium) at both lethal and sublethal concentrations. This effect was time-
and dose-dependent. In SW, the decrease in hypo-OC was ˜ 25% at sublethal concentrations and ˜ 35% at the 96 h LC50. In DSW, the decrease in hyper-OC was ˜ 10 to 15% at sublethal concentrations. In SW, shrimp were able to recover their OC
in less than 48 h when transferred to water free of pesticide. In DSW, recovery at 48 h was only possible after exposure to
the lowest tested sublethal concentration. Haemocytic congestions (thrombosis) of the gills, lamellae necrosis and other alterations
of gills and epipodites (breakage of the cuticle, reduction of the hemolymph lacunae) were noted in juveniles exposed to lethal
and sublethal concentrations of fenitrothion.
Received: 7 October 1996 / Accepted: 13 November 1996 相似文献
13.
Ammonium concentrations of ∼1 M are commonly cited as being the threshold for inhibition of NO3
− uptake, but the applicability of this threshold to phytoplankton from different taxonomic classes has rarely been examined.
Additionally, little is known about the influence of environmental variables (e.g. growth temperature) on the interaction
between ambient NH4
+ and NO3
− uptake. Four species of estuarine phytoplankton, two diatom [Chaetoceros sp., and Thalassiosira weissflogii (Grunow) Fryxell et Hasle] and two dinoflagellate [Prorocentrum minimum (Pavillard) Schiller, and Gyrodinium uncatenum Hulburt], were grown on NO3
− at several different temperatures (4, 10, 15, or 20 °C), and the impact of NH4
+ additions on NO3
− uptake/assimilation (non-TCA-extracted) and assimilation (TCA-extracted) was assessed. For all species at all temperatures,
NO3
− uptake/assimilation and assimilation rates decreased in a roughly exponential manner with increasing NH4
+ concentrations but were not completely inhibited even at elevated NH4
+ concentrations of 200 μM. Estimated half-inhibition concentrations (K
i) were significantly greater in the diatom species (mean ± SE; 2.70 ± 0.67 μM) than in the dinoflagellate species (1.26 ± 0.55 μM). Half-inhibition constants were positively related to temperature-limited relative growth rate although not significantly.
The observed inhibition of NO3
− uptake and assimilation, as a percentage of NO3
− uptake in the absence of NH4
+, averaged about 80% and ranged from 49 to 100%. For all species, a significant (P < 0.001) positive correlation was found between percent inhibition of NO3
− assimilation and temperature-limited relative growth rate. Two experiments on Chesapeake Bay phytoplankton during an April
1998 diatom bloom showed that in short-term (∼1 h) temperature manipulation experiments, percent inhibition of NO3
− uptake/assimilation was also positively related (P = 0.05) to experimental temperature. The observed relationships between temperature-limited relative growth rate and percent
inhibition of NO3
− assimilation rates for the species tested suggest that at the enzyme level, the inhibitory mechanism of NO3
− assimilation is similar among species, but at the whole cell level may be regulated by species-specific differences in the
accumulation of internal metabolites. These findings add not only to our understanding of species-specific variability and
the role of growth temperature, but also provide additional data with which to evaluate current models of NH4
+ and NO3
− interactions.
Received: 31 August 1998 / Accepted: 7 December 1998 相似文献
14.
Halichondria panicea (Pallas) is a marine sponge, abundantly occurring in the Adriatic Sea, North Sea, and Baltic Sea. It was the aim of the present
study to investigate if this sponge species harbors bacteria. Cross sections through H. panicea were taken and inspected by electron microscopy. The micrographs showed that this sponge species is colonized by bacteria
in its mesohyl compartment. To identify the bacteria, polymerase chain reaction (PCR) analysis of the 16S rRNA gene segment,
typical for bacteria, was performed. DNA was isolated from sponge material that had been collected near Rovinj (Adriatic Sea),
Helgoland (North Sea), and Kiel (Baltic Sea) and was amplified with bacterial primers by PCR. The data gathered indicate that
in all samples bacteria belonging to the genus Rhodobacter (Proteobacteria, subdivision α) are dominant, suggesting that these bacteria live in symbiotic relationship with the sponge.
In addition, the results show that the different samples taken contain further bacterial species, some of them belonging to
the same genus even though found in sponges from different locations. The possibility of the presence of toxic bacteria was
supported by the finding that organic extracts prepared from sponge samples displayed toxicity, when analyzed in vitro using
leukemia cells.
Received: 7 March 1997 / Accepted: 2 October 1997 相似文献
15.
Redwood of the reef: growth and age of the giant barrel sponge Xestospongia muta in the Florida Keys 总被引:1,自引:0,他引:1
The growth of animals in most taxa has long been well described, but the phylum Porifera has remained a notable exception.
The giant barrel sponge Xestospongia muta dominates Caribbean coral reef communities, where it is an important spatial competitor, increases habitat complexity, and
filters seawater. It has been called the ‘redwood of the reef’ because of its size (often >1 m height and diameter) and presumed
long life, but very little is known about its demography. Since 1997, we have established and monitored 12 permanent 16 m
diameter circular transects on the reef slope off Key Largo, Florida, to study this important species. Over a 4.5-year interval,
we measured the volume of 104 tagged sponges using digital images to determine growth rates of X. muta. Five models were fit to the cubed root of initial and final volume estimates to determine which best described growth. Additional
measurements of 33 sponges were taken over 6-month intervals to examine the relationship between the spongocoel, or inner-osculum
space, and sponge size, and to examine short-term growth dynamics. Sponge volumes ranged from 24.05 to 80,281.67 cm3. Growth was variable, and specific growth rates decreased with increasing sponge size. The mean specific growth rate was
0.52 ± 0.65 year−1, but sponges grew as fast or slow as 404 or 2% year−1. Negative growth rates occurred over short temporal scales and growth varied seasonally, significantly faster during the
summer. No differences in specific growth rate were found between transects at three different depths (15, 20, 30 m) or at
two different reef sites. Spongocoel volume was positively allometric with increasing sponge size and scaling between the
vertical and horizontal dimensions of the sponge indicated that morphology changes from a frustum of a cone to cylindrical
as volume increases. Growth of X. muta was best described by the general von Bertalanffy and Tanaka growth curves. The largest sponge within our transects (1.23 × 0.98 m
height × diameter) was estimated to be 127 years old. Although age extrapolations for very large sponges are subject to more
error, the largest sponges on Caribbean reefs may be in excess of 2,300 years, placing X. muta among the longest-lived animals on earth. 相似文献
16.
Microsensor studies of photosynthesis and respiration in the symbiotic foraminifer Orbulina universa 总被引:1,自引:0,他引:1
Oxygen and pH microelectrodes were used to investigate the microenvironment of the planktonic foraminifer Orbulina universa and its dinoflagellate endosymbionts. A diffusive boundary layer surrounds the foraminiferal shell and limits the O2 and proton transport from the shell to the ambient seawater and vice versa. Due to symbiont photosynthesis, high O2 concentrations of up to 206% air saturation and a pH of up to 8.8, i.e. 0.5 pH units above ambient seawater, were measured
at the shell surface of the foraminifer at saturating irradiances. The respiration of the host–symbiont system in darkness
decreased the O2 concentration at the shell surface to <70% of the oxygen content in the surrounding air-saturated water. The pH at the shell
surface dropped to 7.9 in darkness. We measured a mean gross photosynthetic rate of 8.5 ± 4.0 nmol O2 h−1 foraminifer−1. The net photosynthesis averaged 5.3 ± 2.7 nmol O2 h−1. In the light, the calculated respiration rates reached 3.9 ± 1.9 nmol O2 h−1, whereas the dark respiration rates were significantly lower (1.7 ± 0.7 nmol O2 h−1). Experimental light–dark cycles demonstrated a very dynamic response of the symbionts to changing light conditions. Gross
photosynthesis versus scalar irradiance curves (P vs E
o curves) showed light saturation irradiances (E
k) of 75 and 137 μmol photons m−2 s−1 in two O. universa specimens, respectively. No inhibition of photosynthesis was observed at irradiance levels up to 700 μmol photons m−2 s−1. The light compensation point of the symbiotic association was 50 μmol photons m−2 s−1. Radial profile measurements of scalar irradiance (E
o) inside the foraminifera showed a slight increase at the shell surface up to 105% of the incident irradiance (E
d).
Received: 26 January 1998 / Accepted: 11 April 1998 相似文献
17.
The physico-chemical microenvironment of larger benthic foraminifera was studied with microsensors for O2, CO2, pH, Ca2+ and scalar irradiance. Under saturating light conditions, the photosynthetic activity of the endosymbiotic algae increased
the O2 up to 183% air saturation and a pH of up to 8.6 was measured at the foraminiferal shell surface. The photosynthetic CO2 fixation decreased the CO2 at the shell down to 4.7 μM. In the dark, the respiration of host and symbionts decreased the O2 level to 91% air saturation and the CO2 concentration reached up to 12 μM. pH was lowered relative to the ambient seawater pH of 8.2. The endosymbionts responded immediately to changing light conditions,
resulting in dynamic changes of O2, CO2 and pH at the foraminiferal shell surface during experimentally imposed light–dark cycles. The dynamic concentration changes
demonstrated for the first time a fast exchange of metabolic gases through the perforate, hyaline shell of Amphistegina lobifera. A diffusive boundary layer (DBL) limited the solute exchange between the foraminifera and the surrounding water. The DBL
reached a thickness of 400–700 μm in stagnant water and was reduced to 100–300 μm under flow conditions. Gross photosynthesis
rates were significantly higher under flow conditions (4.7 nmol O2 cm−3 s−1) than in stagnant water (1.6 nmol O2 cm −3 s−1), whereas net photosynthesis rates were unaffected by flow conditions. The Ca2+ microprofiles demonstrated a spatial variation in sites of calcium uptake over the foraminiferal shells. Ca2+ gradients at the shell surface showed total Ca2+ uptake rates of 0.6 to 4.2 nmol cm−2 h−1 in A. lobifera and 1.7 to 3.6 nmol cm−2 h−1 in Marginopora vertebralis. The scattering and reflection of the foraminiferal calcite shell increased the scalar irradiance at the surface up to 205%
of the incident irradiance. Transmittance measurements across the calcite shell suggest that the symbionts are shielded from
higher light levels, receiving approximately 30% of the incident light for photosynthesis.
Received: 6 July 1999 / Accepted: 28 April 2000 相似文献
18.
The assessment of relevant spatial scales at which ecological processes occur is of special importance for a thorough understanding
of ecosystem functioning. In coastal ecosystems, the variability of trophic interactions has been studied at different spatial
scales, but never at scales from centimetres to metres. In the present study, we investigated the link between habitat structure
and small-scale variability of food web functioning on intertidal boulder field ecosystems. Two microhabitats, boulder-top
and boulder-bottom, were considered, and the trophic ecology of invertebrate consumers was studied using stable isotope tracers.
We found for two of the main suspension feeders of northern Atlantic rocky shores (the sponges Halichondria panicea and Hymeniacidon sanguinea) consistent 15N enrichment for individuals sampled under boulders, suggesting that these consumers relied on different trophic resource
according to the microhabitat inhabited, at a centimetre scale. The high δ15N signatures found underneath boulders suggested higher use of highly decomposed organic matter in this microhabitat. The
isotopic difference between the two microhabitats decreased in higher trophic level consumers, which likely foraged at a spatial
scale including both microhabitats. Finally, our results reveal that in highly heterogeneous habitats such as boulder fields,
trophic interactions are likely to vary strongly in space, which should be considered in future researches. The link between
habitat physical structure and food web variability might also contribute to the high biological diversity characterizing
heterogeneous ecosystems. 相似文献
19.
The marine planktonic diatom Chaetoceros anastomosans, which was isolated from Sagami Bay, was used for a study of resting spore formation mechanisms in batch culture experiments.
Vegetative cells could grow at salinities ranging from 20.7 to 45.5‰, and resting spore formation was enhanced significantly
in nitrate-depleted, high salinity media (40.0 to 45.5‰). The rate of resting spore formation (1.9 d−1) was comparable to the specific growth rate (1.8 d−1) of vegetative cells in the exponential growth phase in normal salinity medium. The size of resting spores formed under high
salinity conditions was smaller than that of spores formed in normal salinity media. Unlike vegetative cells, resting spores
seemed to possess some mechanisms to survive over a wider range of salinities by resisting bacterial attacks on their cell
walls.
Received: 4 August 1996 / Accepted: 27 August 1996 相似文献
20.
Kinetics of glucose and amino acid uptake by attached and free-living marine bacteria in oligotrophic waters 总被引:1,自引:0,他引:1
Kinetics of glucose and amino acid uptake by attached and free-living bacteria were compared in the upper 70 m of the oligotrophic
north-western Mediterranean Sea. Potential uptake rates of amino acids were higher than those of glucose in all the samples
analysed. Cell-specific potential uptake rates of attached bacteria were up to two orders of magnitude higher than those of
total bacteria, both for amino acids and glucose (0.72–153 amol amino acids cell−1 h−1 and 0.05–58.42 amol glucose cell−1 h−1 for attached bacteria and 0.34–1.37 amol amino acids cell−1 h−1 and 0.07–0.22 amol glucose cell−1 h−1 for total bacteria). The apparent K
m values were also higher in attached bacteria than in total bacteria, both for amino acids and glucose. These results would
reflect the presence of different uptake systems in attached and free-living bacteria, which is in accordance with the different
nutrient characteristics of their microenvironments, ambient water and particles. Attached bacteria show transport systems
with low affinity, which characterise a bacterial community adapted to high concentration of substrates.
Received: 13 June 2000 / Accepted: 6 December 2000 相似文献