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1.
Avian escape strategy is highly dependent on the ability to fly, and the success rate of raptor attacks is reduced if the
prey gets fully airborne. Therefore, when escaping from predator attacks, the initial take-off is crucial and a rapid take-off,
high velocity, and high angle of ascent maximize the chance of survival. However, due to the laws of gravity, birds face a
trade-off between maximizing its linear acceleration and maximizing its rate of climb when taking off. The optimal policy
between velocity and angle of ascent when a bird escapes from an attacking predator might depend on the detailed nature of
the predator’s attack, the proximity to cover, and the presence of conspecifics. Many small birds rely on a quick dash to
protective cover. In this study, we examine how the availability of protective cover affects take-off strategy in birds. Male
great tits (Parus major) were subjected to a surprise attack by a model predator either in the presence or absence of protective cover. When attacked
by the predator, great tits took off and perched in the cover when it was available. Birds subjected to the predator attack
in the absence of cover took off in 10° higher angle of ascent and flew faster in the start of the take-off, compared to birds
that took off in the presence of cover. Thus, this study for the first time shows that a bird do trade off speed with angle
of ascent in an adaptive way, depending on the presence of protective cover. 相似文献
2.
Nutrients were added separately and combined to an initial concentration of 10 μM (ammonium) and/or 2 μM (phosphate) in a series of experiments carried out with the giant clam Tridacna maxima at 12 microatolls in One Tree Island lagoon, Great Barrier Reef, Australia (ENCORE Project). These nutrient concentrations
remained for 2 to 3 h before returning to natural levels. The additions were made every low tide (twice per day) over 13 and
12 mo periods for the first and second phase of the experiment, respectively. The nutrients did not change the wet tissue
weight of the clams, host C:N ratio, protein content of the mantle, calcification rates or growth rates. However, ammonium
(N) enrichment alone significantly increased the total population density of the algal symbiont (Symbiodinium sp.: C = 3.6 · 108 cell clam−1, N = 6.6 · 108 cell clam−1, P = 5.7 · 108 cell clam−1, N + P = 5.7 · 108 cell clam−1; and C = 4.1 · 108 cell clam−1, N = 5.1 · 108 cell clam−1, P = 4.7 · 108 cell clam−1, N + P = 4.5 · 108 cell clam−1, at the end of the first and second phases of the experiment, respectively), although no differences in the mitotic index
of these populations were detected. The total chlorophyll a (chl a) content per clam but not chlorophyll a per cell also increased with ammonium addition (C = 7.0 mg chl a clam−1, N = 13.1 mg chl a clam−1, P = 12.9 mg chl a clam−1, N + P = 11.8 mg chl a clam−1; and C = 8.8 mg chl a clam−1, N = 12.8 mg chl a clam−1; P = 11.2 mg chl a clam−1, N + P = 11.3 mg chl a clam−1, at the end of the first and second phases of the experiment, respectively). The response of clams to nutrient enrichment
was quantitatively small, but indicated that small changes in inorganic nutrient levels affect the clam–zooxanthellae association.
Received: 2 June 1997 / Accepted: 9 June 1997 相似文献
3.
Carbon consumption and nitrogen requirements were estimated for populations of the sandy beach bivalve Donax serra on nine beaches of the west coast of South Africa. Subtidal populations composed mainly of adult clams were responsible for
the bulk of standing stock (3538 g C m−1), annual carbon consumption (13 444 g C m−1 yr−1), faeces production (6478 g C m−1 yr−1 ) and nitrogen regeneration (2525 g N m−1 yr−1). Kelp detritus, bacteria and kelp consumers' faeces available in the water column surpass several times the carbon and nitrogen
requirements of intertidal and subtidal clam populations. Individual Donax serra pop ulations, in turn, may regenerate up to 3.2% of the total nitrogen requirements of all primary producers from kelp beds
and 14% of the requirements of phytoplankton. These high standing stocks of clams are presumably supported mainly by organic
matter originating from kelp which, in contrast to phytoplankton, is in constant supply and comprises the largest proportion
of the annual production of particulate organic matter on this coast. Wide and shallow continental shelves with gentle slopes
probably limit the penetration of upwelled waters to the nearshore waters, decreasing the influence of external inputs and
increasing the importance of internal flows of nutrients and carbon within the nearshore zone. In this context, sandy beaches,
rocky shores and kelp beds may be more closely interlinked compartments of a larger ecosystem encompassing the whole nearshore
than traditionally thought.
Received: 28 August 1996 / Accepted: 7 October 1996 相似文献
4.
In many species, the ability to evade predators is known to be periodically impaired by increased weight loads due to feeding
and reproduction. Not only may extra weight reduce escape speed, but feeding and mating can also make the prey more noticeable
to visually hunting predators. A number of butterfly species mate for hours, and if a mating couple is disturbed, one of the
butterflies is responsible for flying, whereas its partner remains still. This study investigated the ability of male Pieris napi butterflies to fly while mating, with the prediction that mate carrying impairs flight ability compared to single flying
males and that males with relatively high flight muscle ratios (FMR; male thorax mass/male + female body mass) will have better
flight performance in copula. Our results clearly show that whereas single males always take off at steep angles and fly upwards,
couples invariably have a negative take-off angle and rarely gain height. Moreover, landing height of the couples is positively
associated with higher FMR. Hence, male flight ability when in copula is positively associated with a high relative thorax
mass. Butterfly pairs may thus be at greater risk of predation as a consequence of their impaired flight ability, especially
couples with critically low FMRs (<16%). 相似文献
5.
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
6.
Fluoride in Antarctic marine crustaceans 总被引:2,自引:0,他引:2
The concentration of fluoride in the body parts of a range of Antarctic crustaceans from a variety of habits was examined
with the aim of determining whether fluoride concentration is related to lifestyle or phylogenetic grouping. Euphausiids had
the highest overall fluoride concentrations of a range of Antarctic marine crustaceans examined; levels of up to 5477 μg g−1 were found in the exoskeleton of Euphausia crystallorophias. Copepods had the lowest fluoride levels (0.87 μg g−1 whole-body); some amphipods and mysids also exhibited relatively high fluoride levels. There was no apparent relationship
between the lifestyle of the crustaceans and their fluoride level; benthic and pelagic species exhibited both high and low
fluoride levels. Fluoride was concentrated in the exoskeleton, but not evenly distributed through it; the exoskeleton of the
head, carapace and abdomen contained the highest concentrations of fluoride, followed by the feeding basket and pleopods,
and the eyes. The mouthparts of E.␣superba contained almost 13 000 μg F g−1 dry wt. Antarctic krill tail muscle had low levels of fluoride. After long-term (1 to 5 yr) storage in formalin, fluoride
was almost completely lost from whole euphausiids.
Received: 1 April 1998 / Accepted: 29 July 1998 相似文献
7.
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
8.
The benthic crustacean Saduria entomon occurs frequently in deeper parts of the Gulf of Gdańsk. It is one of a few species able to survive oxygen deficiencies in
its natural environment. The anaerobic heat production of S. entomon during 40 h of anoxia was determined. Additionally, the effects of size, sex and activity of the organism on its heat production
were investigated. Average heat production of S. entomon was 0.25 ± 0.16 mJ g−1 wet wt s−1 (n=55, avg. length 39 ± 6 mm). The amount of heat produced decreased with increasing body size. The heat production of S. entomon males was greater than that of females ( p<0.05). Specimens kept in chambers with glass beads and water were less active and had lower metabolic rates than those placed
in chambers containing water only (more active). During 40 h of anoxia S. entomon gradually decreased its heat production to 5–16% of aerobic level, demonstrating the high adaptation of this species to changeable
oxygen conditions in the Baltic Sea.
Received: 31 July 1997 / Accepted: 21 January 1998 相似文献
9.
Benthic mucilage, whether native or artificially fragmented to microscopic dimensions by ultrasonic treatment, was mixed
with cytochrome c, which was used as a 12 000 Da polycationic model compound. Cytochrome c binding profiles proved to depend on the aggregation state of the mucilage. The native mucus matrix binds cytochrome c quasi hyperbolically with an apparent affinity constant K = 1 × 106
M
−1. As shown by chemical modification of both the mucilage and cytochrome c, the binding expression is dependent on the availability of both the positive charges on the cytochrome c surface and the negative charges within the mucus matrix. The extent of binding is sensitive to the ionic strength of the
medium. The ultrasonic-stabilized mucus fragments display a peculiar binding profile, with an apparent low affinity, abruptly
entering into a high affinity binding region. The results suggest that, depending on the mucus to polycation ratio, a polymeric
reticulus builds up. This reticulus can accommodate molecules of at least 12 000 Da molecular weight. The results are also
discussed with respect to biological implications.
Received: 23 April 1997 / Accepted: 24 November 1997 相似文献
10.
The aim of our investigations was to determine, via oxygen and carbon-dioxide respirometry, how much energy dolphins (Tursiops truncatus) require when swimming at different speeds. Experiments were conducted on two female bottlenose dolphins (mean mass 162 kg)
in the dolphinarium in Nuremberg Zoo, Germany, between March and August 1997. Animals were stationed in a respiration chamber
for a minimum of 90 s after performing a variety of activities. We measured respiration frequency and oxygen requirements
during (1) resting, (2) swimming at various velocities and (3) leaping to various heights. Resting metabolic rate of our bottlenose
dolphins (2.15 W kg−1) was comparable to previously published data. Metabolic rate in swimming dolphins increased to 2.47 W kg−1 at 2 m s−1, while leaps to 2.2 and 3 m height required a power input of 3.5 and 4 W kg−1, respectively. Transport costs of swimming dolphins were lowest (1.16 J kg−1 m−1, corresponding to 0.12 J N−1 m−1) at a speed of 2.5 m s−1, yielding an optimal range speed of between 1.9 and 3.2 m s−1 (corresponding to minimum cost of transport ±10%). Breathing rates during all experiments correlated very well with oxygen
consumption (r
2 > 0.89) and could be used to derive metabolic rates in unencumbered dolphins at sea.
Received: 18 December 1998 / Accepted: 27 April 1999 相似文献
11.
Frederico P. Brandini Eduardo T. da Silva Franciane M. Pellizzari Alessandra L. O. Fonseca Luciano F. Fernandes 《Marine Biology》2001,138(1):163-171
Production rates, chlorophyll concentrations and general composition of periphytic diatom communities growing on glass slides
were studied in relation to environmental parameters during one seasonal cycle in the Bay of Paranaguá, southern Brazil. Slides
were routinely submersed at 1, 2 and 3 m depth and recovered weekly for microscopic examinations, analyses of chlorophyll,
cell counts and in situ photosynthetic incubations using the Winkler titration method. Water samples were also collected at
surface and bottom layers for determinations of temperature, salinity, nutrients and chlorophyll in the water. The periphytic
community was mainly formed by epipelic and epipsammic species, dominated by Navicula phyllepta, Cylindrotheca closterium, Navicula spp. and Amphora sp. Weekly chlorophyll a and cell accumulations on slides varied from <1–32 mg m−2 and up to 31 × 108 cells m−2, respectively. Photosynthetic rates varied from <1 to 35 mg oxygen mg chlorophyll a
−1 h−1, with higher values in summer. Daily production varied from 5 to 3,600 mg oxygen m−2 day−1 (<0.01–1.4 g carbon m−2 day−1). Multiple regression analysis revealed that vertical differences in light conditions and grazing pressure jointly affected
the influence of temperature on the seasonal patterns of cell densities and chlorophyll concentrations according to depth.
Received: 27 April 2000 / Accepted: 16 August 2000 相似文献
12.
Effect of amino acids on the swimming activity of newly hatched turbot larvae (Scophthalmus maximus)
The swimming behaviour of newly hatched turbot (Scophthalmus maximus L.) larvae was observed in artificial seawater (ASW) and in solutions of 21 l-amino acids at a concentration of 10−5
M. The behaviour of 20 larvae was analysed in each solution. Each larva was observed for 1 min. Individual movements were recorded
on video and analysed using a computer-assisted program. The larvae swam in convoluted, randomised three-dimensional paths,
rested and started swimming again. There were large variations in the swimming behaviour of turbot larvae during ontogeny.
In ASW the mean frequency of trajectories longer than a body length of 4 mm larva−1 min−1 increased from 1.2 at Day 1, to 10 at Day 4. Analysing the data (Dunnett's method) revealed that the frequency of swimming
trajectories increased in the presence of glycine, histidine and glutamine, and decreased in the presence of proline. The
total distance swum increased for glycine but decreased for proline. The threshold concentration for glycine detected by turbot
larvae was 10−5
M. The straightness index did not change in the presence of the amino acids. The possible role of these changes in behaviour
is discussed.
Received: 12 June 1997 / Accepted: 13 January 1998 相似文献
13.
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
14.
We analysed growth of the Antarctic bryozoan Melicerita obliqua (Thornely, 1924) by x-ray photography and stable isotope analysis. M. obliqua colonies form one segment per year, thus attaining maximum length of about 200 mm within 50 years. In the Weddell and Lazarev
Seas, annual production/biomass ratio of M. obliqua is 0.1 yr−1, which is in the range of other Antarctic benthic invertebrate populations. Production amounts to 3.34 mg Corg m−2 yr−1 and 90.6 mg ash m−2 yr−1 on the shelf (100 to 600 m water depth), and to 0.13 mg Corg m−2 yr−1 and 36.8 mg ash m−2 yr−1 on the slope (600 to 1250 m water depth).
Received: 27 February 1998 / Accepted: 8 May 1998 相似文献
15.
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
16.
The talitrid amphipod Uhlorchestia spartinophila lives in close association with standing-dead leaves of the smooth cordgrass Spartina alterniflora Loisel in salt marshes along the Atlantic coast of North America. This study probed the strength of the trophic link between
the amphipod population and the decomposition process in this detrital-based ecosystem. We measured survival, growth and reproductive
output in groups of amphipods reared for 6 wk on five diets derived from sheath and blade portions of S. alterniflora leaves just prior to (senescent) and during (dead) decomposition. In unfed treatments, the daily specific mortality rate
was 0.391 and starved amphipods survived no longer than 11 d. Among the fed treatments, a diet of senescent sheaths resulted
in the lowest survival (20%) and yielded no offspring. Groups fed senescent blades, dead sheaths, dead blades and unwashed
dead sheaths had survival rates of 56 to 84% and produced 5.0 to 12.5 offspring replicate−1. Sex ratio usually favored females, but approached unity in treatments with high overall survival, suggesting that quality
of available food resources may influence sex ratio in this species. Mean specific growth rates (mm mm−1 d−1) ranged from 0.013 to 0.016, and matched previous estimates of growth from field populations. Overall ecological performance
(survival + growth + reproduction) was similar for all food treatments, except senescent sheaths, which yielded a final mean
(±SD) dry biomass (0.4 ± 0.42 mg replicate−1) of amphipods significantly lower than that of other diets (1.7 ± 0.81 to 2.6 ± 0.69 mg replicate−1). Natural diets derived from decomposing cordgrass leaves can fulfill the nutritional requirements of U. spartinophila populations, but variation in initial amounts of living fungal biomass among the five experimental diets only partially explained
the responses of amphipods in our experiment. Structural characteristics and variation in rates of fungal occupation within
different portions of cordgrass leaves may affect the amphipod's ability to access plant production made available by decomposers.
Received: 12 December 1996 / Accepted: 18 December 1996 相似文献
17.
Phosphorylated ATPases may be involved in the effective pH regulation seen in the hydrothermal vent tubeworm Riftia pachyptila. R. pachyptila appears not only to have a large concentration of ATPases, but the main function of these ATPases seems to have shifted from
other types of transport, such as Na+ and K+ movement, to the facilitation of H+ elimination. Plume and trophosome ATPase activity for R. pachyptila measured 646.2 ± 29.5 and 481.4 ± 32.0 μmol Pi (inorganic phosphate) g−1 wet wt h−1, respectively. Plume tissue ATPase activity (both mass-specific and protein-specific) in R. pachyptila was higher (between 7% and 55%) than the activity measured in any tissue for 7 other shallow- and deep-living species, in
this study. This supports the hypothesis that R. pachyptila regulates acid/base balance via high concentrations of H+-ATPases, including Na+/H+ and K+/H+ exchangers and possibly electrogenic H+-ATPases, as evidenced by a higher total ATPase concentration (646 μmol Pi g−1 wet wt h−1), lesser Na+/K+-ATPase activity (13% of the total, as compared to 20−40% found in other animals), and higher H+-ATPase activity (226–264 μmol Pi g−1wet wt h−1). Overall, R. pachyptila appears to demonstrate elevated ATPase activity, with a greater fraction of the enzymes devoted to proton elimination, in
order to effectively control its extracellular pH in the face of processes acting to acidify the internal environment.
Received: 9 May 2000 / Accepted: 4 October 2000 相似文献
18.
Spatial and temporal pattern in seagrass community composition and productivity in south Florida 总被引:4,自引:1,他引:3
We document the distribution and abundance of seagrasses, as well as the intra-annual temporal patterns in the abundance
of seagrasses and the productivity of the nearshore dominant seagrass (Thalassia testudinum) in the south Florida region. At least one species of seagrass was present at 80.8% of 874 randomly chosen mapping sites,
delimiting 12,800 km2 of seagrass beds in the 17,000-km2 survey area. Halophila decipiens had the greatest range in the study area; it was found to occur over 7,500 km2. The range of T. testudinum was almost as extensive (6,400 km2), followed by Syringodium filiforme (4,400 km2), Halodule wrightii (3,000 km2) and Halophila engelmanni (50 km2 ). The seasonal maxima of standing crop was about 32% higher than the yearly mean. The productivity of T. testudinum was both temporally and spatially variable. Yearly mean areal productivity averaged 0.70 g m−2day−1, with a range of 0.05–3.29 g m−2 day−1. Specific productivity ranged between 3.2 and 34.2 mg g−1 day−1, with a mean of 18.3 mg g−1 day−1. Annual peaks in specific productivity occurred in August, and minima in February. Integrating the standing crop for the
study area gives an estimate of 1.4 × 1011 g T. testudinum and 3.6 × 1010 g S. filiforme, which translate to a yearly production of 9.4 × 1011 g T. testudinum leaves and 2.4 × 1011 g S. filiforme leaves. We assessed the efficacy of rapid visual surveys for estimating abundance of seagrasses in south Florida by comparing
these results to measures of leaf biomass for T. testudinum and S. filiforme. Our rapid visual surveys proved useful for quantifying seagrass abundance, and the data presented in this paper serve as
a benchmark against which future change in the system can be quantified.
Received: 30 January 2000 / Accepted: 24 July 2000 相似文献
19.
The sea urchin Lytechinus variegatus is capable of surviving chronic exposure to sodium phosphate (inorganic phosphate) concentrations as high as 3.2 mg l−1, and triethyl phosphate (organic phosphate) concentrations of 1,000 mg l−1. However, chronic exposure to low (0.8 mg l−1 inorganic and 10 mg l−1 organic phosphate), medium (1.6 mg l−1 inorganic and 100 mg l−1 organic phosphate) or high (3.2 mg l−1 inorganic and 1,000 mg l−1 organic phosphate) sublethal concentrations of these phosphates inhibits feeding, fecal production, nutrient absorption and
allocation, growth and righting behavior. Food consumption and fecal production declined significantly in individuals exposed
to medium and high concentrations of inorganic phosphates and all levels of organic phosphates. Feeding absorption efficiencies
for total organics and carbohydrates decreased significantly in individuals held in the highest concentration of organic phosphate.
Feeding absorption efficiencies for lipids were significantly reduced in the highest inorganic phosphate concentration only,
while they decreased significantly for protein with increasing phosphate exposure. Carbohydrate and lipid levels in gonad
and gut tissues decreased significantly with exposure to increasing phosphate concentrations, potentially impairing both gametogenesis
and nutrient storage in the gut. Moreover, gonad indices significantly decreased in individuals exposed to the highest concentrations
of either phosphate. Growth rates decreased significantly under the influence of all phosphate concentrations, while increasing
in seawater alone. Individuals exposed to increasing phosphate concentrations showed reduced righting responses (a measure
of stress) and no acclimation in righting times during chronic exposure to phosphates over a 4 week period. These findings
indicate that shallow-water populations of L. variegatus subjected to inorganic and organic phosphate pollutants will exhibit stress and be inhibited in their growth and performance
due to reductions in feeding, nutrient absorption and allocation of nutrients to key somatic and reproductive tissues.
Received: 10 April 2000 / Accepted: 2 October 2000 相似文献
20.
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