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831.
Spatial and temporal patterns of predation on seeds of the seagrass Phyllospadix torreyi S. Watson were quantified at four sites near Santa Barbara, California, USA. Over a period of four flowering seasons during
1995 to 1998, monthly patterns of seed fall and intensity of seed predation were similar among sites, but were temporally
quite variable. Abundance of dispersed seeds varied greatly both among seasons and years. Within any one year, seeds were
present in the environment every month, but they peaked in abundance during the fall months following the annual flowering
period. Seeds were more abundant during the earlier years of the study. The intensity of predation steadily increased throughout
the study period, from a low of ≤10% seeds consumed during 1995 to ∼50% consumption by 1997, and it was not correlated with
abundance of seeds in the environment. Pre-dispersal seed loss also was estimated in two flowering seasons by counting the
numbers of seeds consumed prior to release from the plant, and was relatively low (<15%). No differences were detected among
the four study sites in patterns of pre-dispersal loss. Field surveys were done at two sites to identify potential seed predators.
Three of the most abundant species identified in these surveys were tested in the laboratory to determine size-specific patterns
of feeding activity and to assess which early life stages of P. torreyi (fruits within spadices, dehisced fruits, seedlings) were most vulnerable to predation. All three of the early life stages
were consumed. The crabs Pugettiaproducta (Randall) and Pachygrapsus crassipes Randall were much more voracious predators than the isopod Idotea resecata Stimpson.
Received: 8 June 1999 / Accepted: 2 February 2000 相似文献
832.
One concept of evolutionary ecology holds that a living fossil is the result of past evolutionary events, and is adapted
to recent selective forces only if they are similar to the selective forces in the past. We describe the present environment
of the living coelacanth Latimeria chalumnae Smith, 1939 at Grande Comore, western Indian Ocean and report depth-dependent cave distribution, temperature, salinity and
oxygen values which are compared to the fish's distribution and its physiological demands. We studied the activity pattern,
feeding behaviour, prey abundance and hunting success to evaluate possible links between environmental conditions, feeding
ecology and evolutionary success of this ancient fish. Transmitter tracking experiments indicate nocturnal activity of the
piscivorous predator which hunts between approximately 200 m below the surface to 500 m depth. Fish and prey density were
measured between 200 and 400 m, both increase with depth. Feeding tracks and feeding strikes of the coelacanth at various
depths were simulated with the help of video and laser techniques. Along a 9447 m video transect a total of 31 potential feeding
strikes occurred. Assuming 100% hunting success, medium-sized individuals would obtain 122 g and large females 299 g of prey.
Estimates of metabolic rates revealed for females 3.7 ml O2 kg−1 h−1 and for males 4.5 ml O2 kg−1 h−1. Today coelacanths are considered to be a specialist deep-water form and to inhabit, with their ancient morphology, a contemporary
environment where they compete with advanced, modern fish.
Received: 5 July 1999 / Accepted: 11 November 1999 相似文献
833.
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
834.
C. T. Achuthankutty Y. Shrivastava G. G. Mahambre S. C. Goswami M. Madhupratap 《Marine Biology》2000,137(1):19-22
Effect of salinity on the feeding rate and parthenogenetic reproduction of asexual females of the cladoceran Diaphanosoma celebensis Stingelin was studied. Short-term (10 h) grazing experiments were conducted using Isochrysis galbana as feed at 5, 17, 25 and 30 psu salinity. Gut pigment concentration showed a significantly higher rate of feeding at lower
salinities. Survival, growth, maturity attainment and neonate production of asexual females reared in the above four test
salinities indicated preference for lower salinities (5 and 17 psu). The mean size of adult females decreased from 909 to
593 μm, mean life span from 24 to 5 d, mean neonate production from 12 to 2 and mean size of neonates from 434 to 400 μm as
the salinity increased from 5 to 30 psu. Salinity variations also affected the size and age of primiparous females. Resting
egg formation and sexual reproduction did not occur at the tested salinities. The results indicate that D. celebensis is adapted to low saline, estuarine environments.
Received: 14 January 2000 / Accepted: 24 March 2000 相似文献
835.
L. Zane L. Ostellari L. Maccatrozzo L. Bargelloni J. Cuzin-Roudy F. Buchholz T. Patarnello 《Marine Biology》2000,136(2):191-199
Meganyctiphanes norvegica (M. Sars)is a pelagic crustacean that plays a key role in marine food webs of North Atlantic Ocean and marginal seas. We
studied eight population samples collected in the European Atlantic and Mediterranean Sea. By means of single strand conformation
polymorphism analysis (SSCP) and direct sequencing, we investigated a segment of 158 base pairs of the mitochondrial gene
coding for the subunit 1 of NADH dehydrogenase. We found 12 sequence variants among the 385 individuals studied. Analysis
of molecular variance (AMOVA) showed that 14.75% of the total genetic variability was explained by differences between populations,
thus indicating absence of panmixia for these populations. Pairwise comparisons revealed three distinct genetic pools: the
first one represented by Cadiz Bay, the second one by the Ligurian Sea, and the third one included all the NE Atlantic samples.
We also investigated one population from the Alboran Sea (within the Mediterranean basin, east of the Strait of Gibraltar).
This population was found to be genetically intermediate between the NE Atlantic samples and the Ligurian sample, suggesting
that the restriction to the gene flow is not associated with the Strait of Gibraltar, but possibly with the Oran–Almeria oceanographic
front. The present work indicates that M. norvegica, although endowed with a high dispersal capacity because of its pelagic habit, can develop separate breeding units inside
the same oceanic basin (the Atlantic). Furthermore, the Ligurian sample should be considered as a distinct evolutionary entity,
separated from the Atlantic population.
Received: 2 May 1999 / Accepted: 26 November 1999 相似文献
836.
Population structure and reproductive ecology of the burrowing ghost shrimp Callianassa filholi Milne-Edwards, 1878 were studied in populations along a latitudinal gradient throughout New Zealand during the breeding season.
Size-frequency distributions revealed unimodal populations, with predominantly sexually mature shrimp. All populations showed
an unbiased sex-ratio, and there appeared to be no significant difference in size (carapace length, CL) between sexes. At
the same time, CL and size at maturity differed significantly between populations; however, a general increase in sizes from
north to south was not consistent throughout the latitudinal range studied. The timing of the breeding cycle differed significantly
between populations, and breeding started earlier in southern populations. Number of embryos (fecundity) increased linearly
with female CL at each location, but rates differed significantly between populations. Embryo size was not related to number
of embryos, and the former increased significantly with latitude. With the exception of embryo size, observed differences
in body size/size at maturity and reproductive timing between C. filholi populations are thought to be determined by food availability rather than temperature. Thus, further study is suggested on
these aspects of thalassinid reproductive biology.
Received: 17 June 1999 / Accepted: 8 January 2000 相似文献
837.
Effects of dissolved ammonium addition and host feeding with Artemia salina on photoacclimation of the hermatypic coral Stylophora pistillata 总被引:6,自引:0,他引:6
E. Titlyanov K. Bil' I. Fomina T. Titlyanova V. Leletkin N. Eden A. Malkin Z. Dubinsky 《Marine Biology》2000,137(3):463-472
Effects of nutrient treatments on photoacclimation of the hermatypic coral Stylophora pistillata (Esper) were studied. Studies on photoacclimation of colonies from different light regimes in the field were evaluated and
used to design laboratory experiments. Coral colonies were collected in the Gulf of Eilat (Israel) from January to March 1993.
Exterior branches of colonies from different depths (1 to 40 m) displayed different trends in production characteristics at
reduced and very low levels of illumination. From 24 ± 3% to 12 ± 2% of incident surface photosynthetic active radiation (PARo), zooxanthella population density and chlorophyll a+c per 106 zooxanthellae increased, a trend seen in the range of light levels optimal for coral growth (90 to 30% PARo). The P
max of CO2 per 106 zooxanthellae decreased, while P
max of CO2 per 103 polyps increased, indicating an increase in zooxanthella population density at low light levels. Proliferous zooxanthella
frequency (PZF, a measure of zooxanthella division) declined significantly at light levels <18 ± 3% PARo. At the lowest levels of illumination (<5% PARo), zooxanthella population density decreased, as did the PZF; chl a+c per 106 zooxanthellae was unchanged. In 28-d experiments, exterior coral branches from the upper surfaces of colonies from 3 m depth
(65 ± 4% PARo) were incubated in aquaria under bright (80 to 90% PARo), reduced (20 to 30% PARo), and extremely low (2 to 4% PARo) light intensities. At each light intensity, the corals were maintained in three feeding treatments: sea water (SW); ammonium
enriched SW (SW + N); SW with Artemia salina nauplii (SW + A). An increase in P
max of CO2 per 103 polyps was found in corals acclimated to reduced light (20 to 30% PARo) in nutrient-enriched SW, while in SW, where the increase in zooxanthella population density was smaller, it did not occur.
Nutrient enrichments (SW + N at 2 to 4% PARo and SW + A at 20 to 30% PARo) increased zooxanthella population density, but had no effect on chl a+c per 106 zooxanthellae. Acclimation for 14 d to reduced (10 to 20% PARo) and extremely low (1 to 3% PARo) light intensities shifted 14C photoassimilation into glycerol and other compounds (probably glycerides), rather than sugars. Both ammonium addition and
feeding with Artemia salina nauplii resulted in an increase in photosynthetic assimilation of 14C into amino acids. We conclude that acclimation to reduced light consists of two processes: an increase in photosynthetic
pigments and in zooxanthella population density. Both processes require nitrogen, the increase in zooxanthella population
density needing more; this adaptation is therefore limited in nitrogen-poor sea water.
Received: 19 June 1998 / Accepted: 13 June 2000 相似文献
838.
We investigated the effect of different densities of the burrowing deposit-feeding amphipod Monoporeia affinis on the potential for recruitment of zooplankton from benthic resting eggs. Hatching of resting eggs was induced in the laboratory
on sliced and resuspended 1-cm depth-sections of sediment cores, collected at six stations in an archipelago area of the Gulf
of Bothnia, Baltic Sea. The uppermost 5 cm of the sediment was studied. The most common species that hatched was Eurytemora affinis (Copepoda). Individuals from another copepod genus, Acartia, hatched in significant numbers only in the cores from two stations with low amphipod abundance. Cores from stations with
high amphipod densities showed a deeper distribution of emerging E. affinis nauplii compared with stations with few amphipods; the oxidised sediment layer was also deeper at high M. affinis densities than at low. Total (0 to 5 cm strata pooled) number of hatched E. affinis nauplii was independent of amphipod density. This indicates that the effect of M. affinis on E. affinis eggs involves deeper burial due to bioturbation, rather than predation. Decreased benthic recruitment of zooplankton at localities
with high M. affinis density is suggested, since more deeply positioned eggs are less likely to hatch. When hatching was induced in intact, non-sliced
cores from one station, the number of E. affinis nauplii that hatched was on average 43% of the number that hatched in the upper centimetre of the sliced cores from the same
station. This fraction (43%), if applied to the other stations, implied a potential for benthic recruitment of up to 80 000 ind
m−2 for E. affinis. Due to its high abundance, M. affinis is likely to greatly reduce benthic recruitment of zooplankton in this system.
Received: 17 September 1999 / Accepted: 23 February 2000 相似文献
839.
The reproductive biology of female Penaeus japonicus Bate was investigated in the Ariake Sea and Tachibana Bay (located outside the Ariake Sea), Japan from 1994 to 1996. Interannual,
seasonal, individual female body size and spatial influences on the incidence of spawning were examined. The proportion of
inseminated females, increased with increasing body size up to 170 mm body length (BL) and decreased thereafter. The minimum
size at maturity was similar between years; 130 to 140 mm BL. The minimum size of individuals with developing ovaries or spermatophores
differed from that of ripe females by 20 to 25 mm. Spawning occurred in the central part of the Ariake Sea and Tachibana Bay
but rarely in the inner part. P. japonicus had a clear reproductive cycle. Spawning started earlier and ended later, occurring from mid-May to mid-October, in the eastern
central part of and outside of the Ariake Sea compared with the western central part, where spawning occurred from mid-June
to mid-September. Spawning dynamics differed across seasons, body sizes and areas but not across years. The seasonal peak
in the proportion of ripe females varied with body size. In small individuals (130 to 169 mm BL), no peak was observed, whereas
in large individuals (>170 mm BL) the proportion of ripe individuals peaked in June. The proportion of ripe individuals increased
with increasing body size and was high outside the Ariake Sea. Factors causing the variation in spawning dynamics are discussed.
Received: 30 November 1998 / Accepted: 12 October 1999 相似文献
840.
Western sandpiper (Calidris mauri) predation was examined by concurrent experiments and direct observations of foraging behaviour on high intertidal mudflats
of the Fraser River estuary, British Columbia. Western sandpipers foraged by either “pecking” on the surface (64% of observational
time) or probing into sediment (29%). The first experiment (probe-mark method) consisted of collecting small-volume cores
(21.2 cm3) of probed (experimental) and non-probed (control) sediment on the tidal flat, following a 22.5-min feeding period. The second
experiment (exclosure method) involved deploying exclosures immediately prior to the feeding period and subsequent collection
of cores from inside (control) and outside (experimental) the exclosures. Sediment cores were analysed for both macrofaunal
and meiofaunal size fractions. Comparisons between macro- and meiofaunal invertebrate densities in experimental and control
sediments revealed significant differences, attributed to shorebird predation, for both experiments. The probe-mark experiment
detected the removal of large infaunal polychaetes (∼ 20 mm), while the exclosure experiment showed depletion of epifaunal
harpacticoid copepods (0.063–0.5 mm). Predation on macrofaunal cumaceans was detected in both experiments. Invertebrates selected
by western sandpipers neither fell within traditional infaunal size classifications (macro- vs. meiofauna; 500 μm delineation)
nor corresponded to the highest densities of taxa. Rather, inference from experimental results and observations is that western
sandpipers forage in two modes, by: (1) surface gleaning of epibenthic copepods and cumaceans in the macro- and meiofaunal
size ranges and (2) selective probing for larger infauna, such as polychaetes. These findings were facilitated by the combination
of methodologies employed.
Received: 29 December 1999 / Accepted: 11 September 2000 相似文献