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221.
The pathway for the flow of salt-marsh grass production into marsh food-webs is still not well defined. We compared the abilities
of three marsh macroinvertebrates [salt marsh periwinkles, Littoraria irrorata (Say) (=Littorina irrorata), salt-marsh coffee-bean snails, Melampus bidentatus (Say); and a talitrid amphipod, Uhlorchestia spartinophila Bounsfield and Heard] to access standing-dead leaves of smooth cordgrass (Spartina alterniflora Loisel). The invertebrates were incubated with naturally-decaying leaves, and the rates of removal of organic matter and
living fungal biomass (ergosterol) were measured. The impact of invertebrate activity upon fungal growth rates was measured
as rates of fungal-membrane synthesis (incorporation of radioacetate into ergosterol). The removal rates of organic leaf biomass
per mg individual biomass were highest for amphipods (700 μg mg−1 d−1) and lowest for periwinkles (90 μg mg−1 d−1), but the relatively large biomass of the snails made their removal rates per individual greater than those of amphipods.
Net removal of ergosterol by all three invertebrates was >50% for yellow-brown (early-decay) leaf blades. For fully-brown
(advanced-decay) blades, >50% removal of ergosterol was found only for periwinkles; exposure to coffee-bean snails and amphipods
resulted in a net ergosterol reduction of ≤20%. The lower net reduction of living fungal biomass by coffee-bean snails and
amphipods may have been due to fungal-growth stimulation (2.3-fold stimulation in coffee-bean snails and 1.5-fold stimulation
in amphipods). Grazing by periwinkles did not stimulate fungal growth, possibly because of its high intensity. Grazing by
these three salt-marsh shredders may affect marsh-grass shoot-decay in different ways. Periwinkles may abbreviate the period
of fungal production, and incorporate the decaying material relatively quickly into snail biomass and fecal-pellet rain to
the sediments. Coffee-bean snails and amphipods may enhance and prolong fungal production, along with the formation of fecal-pellet
rain. All three invertebrates fed preferentially on leaf blades rather than leaf sheaths, and feeding rates of gastropods
were higher during the night than during the day.
Received: 25 November 1998 / Accepted: 4 November 1999 相似文献
222.
Cadmium accumulation in the female shore crab Carcinus maenas during the moult cycle and ovarian maturation 总被引:2,自引:0,他引:2
The influence of moulting and ovarian maturation on cadmium accumulation in the tissues of female shore crabs Carcinus maenas exposed to 1 mg Cd l−1 in the water was investigated. Cadmium accumulation in all tissues examined was markedly increased in crabs in the postmoult
stages (A and B) compared to crabs in all other moult stages. During the moult cycle, average cadmium accumulation in the
midgut gland ranged from 29 μg Cd g−1 dw at premoult stage (D2) to 589 μg Cd g−1 dw at postmoult stage (A). Average cadmium concentrations in the haemolymph ranged from 0.56 μg Cd ml−1 at intermoult stage (C4) to 4.6 μg Cd ml−1 at postmoult stage (A), while the gills accumulated from 103 μg Cd g−1 dw in intermoult stage (C3) to 352 μg Cd g−1 dw in postmoult stage (A). Cadmium concentration in gills and haemolymph was also significantly higher in crabs in late premoult
stage (D3) compared to C4-crabs, while midgut gland cadmium concentration remained elevated in C1- and C3- intermoult stages relative to C4. During ovarian maturation the cadmium accumulation in midgut gland, gills, ovaries and haemolymph decreased. Average cadmium
concentration in the midgut gland decreased from 63 μg g−1 dw in ovarian Stage I to 19 μg g−1 dw in ovarian Stage VI. The same pattern was observed for gills, haemolymph and ovaries. The present study demonstrates that
cadmium accumulation in the female shore crab strongly depends on the physiological status of the animal. A possible association
between physiological calcium requirements and cadmium accumulation during moulting is discussed.
Received: 20 January 2000 / Accepted: 20 July 2000 相似文献
223.
The effects of variable food supply on growth rate and feeding behaviour in two coexisting intertidal gastropods were examined
through field and laboratory experiments involving mark and recapture procedures, growth experiments under controlled food
supply and video observations of feeding. All cohorts of both Japeuthria species grew most in summer, with the highest growth rate being achieved by the youngest cohort of both sexes. In contrast,
almost all cohorts (except the youngest one) showed zero to negative growth in winter. The growth rates of Japeuthria species clearly varied depending on feeding frequencies and the initial size of individuals. Females of both species had
a significantly higher growth rate than males, though the difference became less marked with decreasing food supply. The total
time spent on feeding and the length of the first feeding bout generally increased as the duration of the interval between
meals was increased across treatments. From both the field growth experiment and the observations of feeding behaviour it
is clear that J. ferrea had a higher frequency of feeding than J. cingulata in the field; 1- to 3-d intervals of feeding frequency in the former and 3- to 6-d intervals in the latter. Most notably,
the two species showed a reversal in growth rates with changing conditions of food supply. When food was relatively abundant
J. ferrea achieved better growth than J. cingulata, but J. cingulata grew better than J. ferrea under low food supply. In view of the fact that J. ferrea seems to be competitively superior to J. cingulata under normal levels, the present observation that J. cingulata can perform better than J. ferrea when food availability is low gives an important advantage to the latter in terms of its coexistence with the former.
Received: 9 March 1999 / Accepted: 8 October 1999 相似文献
224.
Arm damage is a widely reported but superficially investigated aspect of the biology of the starfish Asterias rubens L. In the present study, the incidence of arm damage was surveyed in populations of A.
rubens at two sites in the Firth of Clyde, Scotland, and three sites in Gullmarsfjorden, Sweden. The mean (±SD) incidence across
all sites of individuals with basal arm damage (resulting from detachment at the basal autotomy plane) was 19.69 ± 8.86%,
the incidence of those with distal arm damage (resulting from amputation at more distal levels) was 7.74 ± 10.01%. The mean
incidence of arms with basal damage was 5.28 ± 4.12%, of those with distal damage 1.83 ± 2.45%. There was a significant negative
correlation between size and the incidence of basal damage at all but one site, but no significant correlation between size
and distal damage at any site. Mechanical tests on specimens of the aboral body wall from the basal region of the arm (which
included the autotomy plane) and from a more distal region revealed that with increasing body size there was a significant
increase in yield stress, ultimate stress and Young's modulus (stiffness) but no significant change in yield strain and ultimate
strain. There was no significant difference between the relationships for basal and distal specimens. It is hypothesised that
in larger individuals increased mechanical toughness replaces autotomy as an effective antipredator strategy. Using two methods
to induce autotomy, a significant positive correlation between size and the delay between the onset of stimulation and arm
detachment was found; this may represent a size-related decline in the efficiency of the autotomy mechanism through the relaxation
of selection pressure. Since size is an unreliable indicator of age in A.
rubens, the trends identified herein can be interpreted only tentatively as age-associated phenomena.
Received: 4 September 1999 / Accepted: 17 February 2000 相似文献
225.
Early development of the Antarctic sea urchin Sterechinus neumayeri was examined under two differ-ent culture regimes: one to simulate development near-bottom (“demersal development”) and the
other to simulate the development of embryos in the water column (“pelagic development”). When embryos of both treatments
reached the hatching blastula stage at 5 d post-fertilization (−1.5 °C), the blastulae that had undergone demersal development
evidenced significant differences (by ANOVA or suitable non-parametric comparison) in the following: a thicker blastoderm
layer (12%, P < 0.001), higher ash-free dry weights (19%, P < 0.01), lower mass-specific respiration rates (50%, P < 0.001), higher incorporation rates of 35S-methionine into protein (23%, P < 0.003), and a differential pattern of protein synthesis. When embryos developed demersally, they remained in the jelly-coat
material released with the eggs at spawning. Quantitative isolation of this jelly-coat material in S. neumayeri demonstrated that it contained a significant amount of organic matter, 115 ng ash-free dry mass per egg, equivalent to 17%
of the egg's initial organic mass. Uptake of external nutrients during embryogenesis may be a significant component of the
physiological energetics of this polar invertebrate by allowing the utilization of jelly-coat material released by a female
during spawning.
Received: 21 April 1999 / Accepted: 5 June 2000 相似文献
226.
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
227.
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
228.
The sibling species, Pseudocalanus moultoni (Frost, 1989) and P. newmani (Frost, 1989), occur sympatrically on Georges Bank. Taxonomic discrimination of the species relies on subtle morphological
characteristics, making routine identification of the species very difficult. DNA sequence variation of two mitochondrial
genes, 16S rRNA and cytochrome oxidase I (COI), reliably discriminated P. moultoni and P.␣newmani. Levels of DNA sequence variation for both genes were consistent with those between species of calanoid copepods. A molecular
systematic protocol (based on allele-specific PCR amplification) was designed from the COI sequences and used to discriminate
females of the two species. The distributions and relative abundances of the two species were mapped for April 1996 based
on samples of 15 to 30 females from 12 collections across Georges Bank. The results of this study indicated that P. moultoni females predominated along the northern flank of Georges Bank, while P. newmani females were common on the southern flank, deeper than the 60-m isobath.
Received: 16 May 1997 / Accepted: 26 April 1998 相似文献
229.
Recovery of benthic communities at Macquarie Island (sub-Antarctic) following a small oil spill 总被引:5,自引:0,他引:5
Intertidal communities at Macquarie Island (sub-Antarctic) were re-evaluated seven years after a small oil spill resulting
from the grounding of the “Nella Dan”, and six years after the first assessment of biological impact. Sampling was conducted
to evaluate community structure in three zones of the exposed rocky shore (upper red, kelp, and lower red) and in samples
of Durvillaea antarctica holdfasts. There were no significant differences between the community structure in oiled and control locations in any of
the three shore zones, but holdfast macrofaunal communities at oiled sites still showed evidence of impact. Holdfast community-structure
in samples from heavily oiled sites showed moderate levels of recovery, with increased abundances of species which were considered
sensitive to the oiling in the first post-impact studies and decreased abundances of opportunistic polychaete and oligochaete
worms. In contrast, samples collected from the moderately oiled location at Secluded Bay showed little evidence of recovery.
Holdfasts at this site were filled with sediment containing traces of diesel oil, and the macrofaunal community was dominated
by opportunistic worms. This study clearly indicates that even small incidents of anthropogenic perturbation can have long-lasting
consequences for marine communities at Macquarie Island.
Received: 23 July 1997 / Accepted: 5 February 1998 相似文献
230.
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