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991.
992.
The impact of motorcycle traffic on soil and vegetation of stabilized coastal dunes, Israel 总被引:1,自引:0,他引:1
This study aimed to assess the response of soil and annual plant vegetation of stabilized coastal dunes in Israel, to varying
intensities of off-road motorcycle (ORM) traffic, and to assess their resistance and resilience to such a disturbance. A standard
experimental procedure that included 0, 20, 50, 100 and 200 ORM straight passes and 150 ORM turn passes was used. Plant ground
cover, mean plant height, species richness, species diversity, soil penetrable depth, organic matter and moisture contents
were measured on several dates within a period of 372 days after the experiment. Results have shown that: (1) ORM passes had
a significant immediate impact on annual plants that increased with traffic intensity. The impact on the soil was detected
only as an increase of penetrable depth. (2) The maximum impact on annual plants was observed in the wheel ruts and turn areas.
The impact on the area between the wheel ruts and on the margins outside the wheel ruts was indirect and smaller. (3) Annual
plant ground cover and mean plant height were less sensitive parameters than species richness and species diversity for determining
the impact of ORM traffic on the area. (4) One year after the experiment, soil and annual plant vegetation in all passes were
very similar to their pre-experimental condition. This indicates high resilience and recovery potential of the Mediterranean
stabilized coastal dune ecosystem to ORM disturbance. 相似文献
993.
Green sea urchins, Strongylocentrotus droebachiensis OF Müller, collected off the coast of New Hampshire, USA, in late February 1995, were brought into the laboratory and fed
an artificial diet ad libitum, and subjected to a photoperiod advanced by 4 months. During this study, temperatures and salinities
for experimental urchins mirrored those recorded at the collection site. We examined the effects of changes in feeding regime
and photoperiod on gametogenesis and compared the experimental urchins with those from the source population. During the 7-month
period, experimental urchins showed no detectable changes in mean test height or diameter. Experimental urchins had a significantly
higher gonad index (GI) in March, April and May (18 ± 6%) compared with field urchins in March (11 ± 3%). Subsequently, experimental
urchins had a mean monthly GI of 25 to 30%, while the mean GI for field urchins was 11 to 13%. Gonial cell mitosis and gametogenesis
occurred earlier in experimental male and female urchins compared with field urchins. Stereological and histological observations
and stage–frequency data showed that the ovaries of experimental urchins were large because of the accelerated development
of nutritive phagocytes, the volume fraction (V
v) of which was 89 to 90% of the gonad, while new vitellogenic primary oocytes occupied <1% V
v. In males, stereological and histological observations and stage–frequency data suggested a mobilization of materials from
the nutritive phagocytes beginning between June and August, i.e. earlier than in females, and, by September, new gametes occupied
a V
v of 49 ± 3% of the testes. Oocyte size–frequency distributions demonstrated that most primary oocytes were <80 μm in diameter
between March and September, suggesting that cold temperatures may be needed for completion of vitellogenesis. We describe
changes in the two principal cell types in the germinal epithelium of urchin gonads and indicate how knowledge of their population
dynamics may be useful in aquaculture applications.
Received: 21 February 1997 / Accepted: 3 June 1998 相似文献
994.
The predation impact of the two chaetognaths Eukrohnia hamata and Sagitta gazellae on mesozooplankton standing stock were investigated in three depth layers during two 24 h stations occupied in the vicinity
of Marion Island in late austral summer (April/May) 1986. The zooplankton community at both stations was dominated by small
copepods (Oithona spp., Microcalanus spp.), which accounted for >95% of total zooplankton abundance. Chaetognaths comprised <2% of total zooplankton abundance.
E. hamata constituted >95% of the total chaetognath stock. The general trend in both species was decreasing abundance with increasing
depth, which appeared to be correlated to the distribution of copepods (r
2 = 0.45; P <0.05). Gut-content analysis showed that copepods (mainly Oithona spp., Calanus spp. and Rhincalanus gigas) and ostracods were the main prey of both species, accounting for 87 and 61% of the total number of prey in E. hamata and S.␣gazellae stomachs, respectively. In the guts of S.␣gazellae, pteropods (Limacina spp.) and chaetognaths were also well represented. The mean number of prey items (NPC) for E. hamata ranged from 0.02 to 0.06 prey individual−1 which corresponds to an individual feeding rate (Fr) of between 0.05 and 0.12 prey d−1. For S.␣gazellae, the NPC values were higher, varying between 0.04␣and 0.20 prey individual−1, or between 0.15 and 0.76 prey d−1. The daily predation impact of the two chaetognaths was estimated at between 0.3 and 1.2% of the copepod standing stock or
between 7 and 16% of the daily copepod production. Predation by S. gazellae on chaetognaths accounted for up to 1.6% of the chaetognath standing stock per day.
Received: 26 November 1996 / Accepted: 31 October 1997 相似文献
995.
The Norway lobster Nephrops norvegicus (L.) inhabits burrows in muddy clay sediments (e.g. on the Swedish west coast), where an autumnal oxygen deficiency in the
bottom water can occur. Our experiments investigated whether the irrigation of the burrows would reflect a behavioural adaptation
to hypoxia, and whether any gender differences of such behaviour exist. Irrigation is performed by the pleopods which may
compensate for a decreasing oxygen tension. Pleopod activity (total number of strokes per sampling time), associated with
oxygen concentration and gender, was studied in N. norvegicus kept in artificial burrows resembling their natural habitat. Male and female lobsters were separately exposed to either normoxia
(70% oxygen saturation) or hypoxia (30% oxygen saturation). A sexual difference in behaviour was found, where females irrigated
the burrow less than males during normoxia. Females showed a significant increase of pleopod activity in hypoxia compared
with normoxic conditions, which was not displayed by the males probably due to the degree of individual variation found. However,
when only males were studied during progressive hypoxia (from 60 to 5% oxygen saturation), following any changes of irrigational
behaviour, a significant increase of accumulated pleopod activity occurred. A major increase of pleopod activity appeared
between 60 and 50% oxygen saturation, below which the activity remained high until a critical point (<10% saturation, 11 °C,
33 psu) where irrigation dropped to a level close to that of normoxic values. Activity sessions during hypoxia were longer
and had a higher stroke rate than during normoxia.
Received: 22 October 1997 / Accepted: 26 February 1998 相似文献
996.
The relationship between sperm characteristics and reproductive success was examined in male herring, Clupea harengus L. Males were categorised as being first-time or repeat spawners on the basis of their age; they were also grouped according
to whether their sperm were immediately active and exhibited forward motion on contact with seawater (FM) or had little or
only vibratory motion (VM). Unlike the Pacific herring C. pallasii Valencienes, Atlantic herring sperm is usually motile on contact with seawater. The age, weight and gonadosomatic index (testes
mass as a percentage of somatic mass = GSI) were measured and used as characteristics for individual fish. Sperm traits measured
were (1) adenosine triphosphate (ATP) concentration, (2) sperm count, (3) duration of sperm motility. Reproductive success
for each male was estimated from the fertilisation rate and from the length of larvae at hatching. Fertilisation rates for
all fish were generally >80%. The ATP concentration of non-activated spermatozoa was negatively correlated with fertilisation
rate. Among repeat spawners, fish with higher GSIs produced larvae that were larger at hatching. Although VM sperm fertilised
eggs at rates equivalent to fertilisation by FM sperm, the larvae produced by VM sperm were significantly smaller at hatching.
Larval length tended to increase in parallel with the duration of sperm motility, but the relationship was not significant
in these tests. The results did not indicate any age or size pattern to spawning readiness in male herring. Sperm that are
not yet ready to be shed are not fully motile on contact with seawater, but are still capable of fertilising eggs that hatch
successfully. There is likely to be a progression of males which come into spawning readiness within a spawning shoal; therefore
it is possible that paternal influences would result in a progressive decrease in larval size over the spawning period in
winter-spawning Celtic Sea herring.
Received: 22 November 1997 / Accepted: 8 June 1998 相似文献
997.
The effects of blooms of the cyanobacterium Trichodesmium spp. on penaeid prawn larvae were examined using in situ and laboratory rearing experiments and plankton surveys in Albatross
Bay, Gulf of Carpentaria, Australia. The in situ experiments demonstrated that, during a bloom of Trichodesmium spp., larvae of the prawn Penaeus merguiensis did not develop beyond the first protozoea stage, and survival was low compared with times when diatoms were dominant in
the same study area. Laboratory experiments confirmed the in situ results. None of the prawn larvae fed Trichodesmium sp. in laboratory experiments developed beyond the first protozoeal stage. In contrast, 94% of prawn larvae fed the green
flagellate Tetraselmis suecica successfully developed to the second protozoea stage. Electron microscopy of larvae gut-contents revealed that Trichodesmium spp. were ingested by larvae but were of no nutritional value, resulting in starvation. A 7 yr plankton survey, from 1985
to 1992, showed that minimum abundance of prawn larvae occurs during the annual summer blooms of Trichodesmium spp. and that maximum abundance of prawn larvae generally occurs just after the bloom. There was a negative correlation between
the abundance of larvae and the abundance of Trichodesmium at individual sites, one offshore and one inshore, indicating that the blooms affect the survival of larvae. We conclude that
variations in both timing and magnitude of Trichodesmium blooms are important determinants of prawn larvae abundance in Albatross Bay.
Received: 28 April 1997 / Accepted: 2 April 1998 相似文献
998.
Previously published mtDNA cytochrome b sequences for Xyrichtys novacula (Linnaeus) and two morphologically distinct types of Xyrichtys larvae (Pisces: Labridae) included human cytochrome b sequence, presumably due to sample contamination and/or poor preservation of sample DNA. Those sequences had been used to
identify the two types of Xyrichtys larvae as X. novacula, but owing to the contamination, the identifications are invalid. Fresh specimens were collected: X.␣martinicensis (Cuvier and Valenciennes), X. novacula, X. splendens (Castelnau), and Xyrichtys sp. larvae of each of the two morphotypes (dorsal-forward eye and ventral-forward eye). The cytochrome b fragment was amplified from each specimen using the polymerase chain reaction. Comparison of the sequences with human cytochrome b sequence confirmed that the new sequences were not contaminated. The interspecific differences in Xyrichtys sequences were less than previously reported, but still greater than observed in many fish genera. Distance and parsimony
analyses indicated that X. novacula and X. martinicensis were more closely related to each other than to X. splendens. This conclusion differs from our previous conclusion that X. martinicensis and X. splendens were more closely related to each other than to X. novacula. Distance and parsimony analyses also demonstrated that both larval morphotypes were X. novacula and, thus, our previous conclusions regarding larval ecology and oceanographic transport remain unchanged.
Received: 12 March 1997 / Accepted: 24 October 1997 相似文献
999.
Effect of female molt stage and sex ratio on courtship behavior of the blue crab Callinectes sapidus
In many species, males and females actively participate in courtship, and the outcome of pre-mating interactions influences
the mating success of both sexes. Female blue crabs, Callinectes sapidus, mate soon after their final molt to maturity; thus female molt stage dictates the timing of mating. In a field experiment,
we manipulated female molt stage and sex ratio to test their effects on the courtship behavior of both sexes, if female behavior
influences the behavior and pairing success of males, and if male courtship influences male pairing-success. Early-molt-stage
females avoided males during courtship, whereas late-molt-stage females sought out males. As a result, males had to pursue
and capture early-molt-stage females whereas males displayed to late-molt-stage females and more easily physically controlled
them. Males sometimes abandoned late-molt-stage females, but this occurred more often when females were abundant. The rate
at which females avoided males was positively correlated with that of males abandoning females, and males that were unsuccessful
at pairing met with higher rates of female resistance than successful males, suggesting that female behavior influences male
pairing-success. Unlike unsuccessful males, successful males more often made the transition between display and maintaining
physical control of the female. At high male sex ratios, males initiated courtship more readily; thus both sexual competition
and female behavior influence male courtship in this species.
Received: 7 July 1996 / Accepted: 10 January 1998 相似文献
1000.
R. Wilson G. Peters J. Regel D. Grémillet K. Pütz M. Kierspel H. Weimerskirch J. Cooper 《Marine Biology》1998,130(4):559-566
Stomach temperature loggers have proved useful for the study of feeding activity in free-living seabirds, but their usage
has been restricted because they are frequently dislodged and lost during the seabirds' regular regurgitation of indigestible
prey remains. In the present study we examine the incidence of spontaneous regurgitation (pellet production) in free-living
seabirds, consider the effect this has on the likely retrieval of stomach temperature loggers and present a structural modification
of the logger housings which leads to a much lower incidence of regurgitation. Systems were tested on albatrosses, cormorants,
gannets and penguins.
Received: 15 July 1997 / Accepted: 31 October 1997 相似文献