共查询到20条相似文献,搜索用时 31 毫秒
1.
The reproductive biology of Antipathes fiordensis Grange, a species endemic to south-western New Zealand, was followed from April 1994 to May 1995. Ten colonies were individually
tagged in Doubtful Sound and sampled on a monthly basis in order to determine their reproductive activity. The fecundity of
each of the five tagged female colonies was determined by estimating the total number of polyps per colony from photographs
of each colony and by planimetry, the proportion of gravid polyps per colony, and the mean number of oocytes per gravid polyp.
In addition, 56 colonies were sampled in March 1995 to estimate the sex ratio, height at sexual maturity, and mean sizes of
females and males. A. fiordensis was found to be a dioecious species which, in the absence of gonads in the polyps, has no obvious external morphological
differences between the sexes. Broadcast spawning of gametes is the likely mode of reproduction. Gametogenesis began in November
1994 and was highly synchronous within and between colonies, with spawning occurring in March 1995. The sex ratio in adults
was 1:1. Colonies reached sexual maturity between the heights of 70 and 105 cm which, based on existing estimates of growth
rate, corresponds to a minimum age for sexual maturity of about 31 yr. The largest oocytes measured ranged from 100 to 140 μm
in size. Female colonies produced between 1.3 and 16.9 million oocytes, with the larger colonies dominating the reproductive
output of the population.
Received: 23 June 1997 / Accepted: 1 August 1997 相似文献
2.
The euryalinid brittle-star (snake star) Astrobrachion constrictum (Farquhar) lives coiled around the branches of black coral (Antipathes fiordensis) colonies. Twenty-two vertical transects, 10 m wide by 30 m deep, were swum in Doubtful Sound over a 2.5 yr period from 1993
to 1995. Numbers, disc diameters and colour morphotypes of brittle-stars inhabiting coral colonies were recorded. 36.3% of
the coral colonies >200 mm tall (n = 292) hosted ≥1 Astrobrachion constrictum (range 0 to 12). Overall, the population was patchily distributed on the available coral habitat. The dark red colour morphotype
of A. constrictum was most common (87%, n = 279) followed by the yellow, striped, and then spotted varieties. The population was comprised mainly of large (≥10 mm
disc diam) individuals, and juveniles were rarely encountered, indicating low rates of recruitment or a high mortality of
recruits. Disc-diameter data gathered from this and previous studies indicated that growth in A. constrictum is initially rapid, with individuals reaching a disc diameter of 15 mm in ≃2.5 yr; growth decreases with age, as in other
deep-sea ophiuroids. Growth rate within years, however, was not constant, with faster growth in the spring/summer. Maximum
size for A. constrictum is reached in ≃8 yr at ˜23 mm disc diam. Anecdotal evidence indicates that A. constrictum may not be confined solely to black coral colonies.
Received: 25 September 1996 / Accepted: 16 October 1996 相似文献
3.
Coral reefs in the northern Gulf of Eilat are exposed to continuous man-made disturbances, resulting in decreased coral coverage
and reduced recruitment at the Nature Reserve of Eilat. The construction of artificial reefs on sandy bottoms is a possible
option to decrease diving pressure on natural reefs. In the present study we tested this hypothesis by submerging an experimental
artificial reef anchored to the bottom at 18 m depth and floated vertically 3 m below water surface. The reef was composed
of PVC plates, attached both vertically and horizontally along a wire. Propagules of two coral species, the stony coral Stylophora pistillata and the soft coral Dendronephthya hemprichi, were transplanted to this artificial reef. Planulae of S. pistillata were obtained during the breeding season, seeded in petri dishes in the laboratory and after 2 wk the dishes were transferred
to the experimental artificial reef. Automized fragments of D. hemprichi which had previously settled on 10 × 10 cm PVC plates were transplanted onto the experimental artificial reef. The survivorship
of the transplanted D. hemprichi colonies was significantly higher on the lower sides of shallower plates. Survivorship of S. pistillata colonies increased with depth when located on the vertical plates, or on the upper sides of the horizontal plates. The highest
survivorship of this coral was on the vertical plates and on the upper sides of the horizontal plates, while very low survivorship
was recorded on the lower sides. The results indicate that vertical artificial surfaces offer the optimal biotic and abiotic
conditions for the survival of the two examined corals. The vertical plates are characterized by low sed imentation rates,
low coverage of turf-algae, minimal grazing by sea urchins and absence of the competitor tunicate Didemnum sp. In addition, the vertical orientation of the experimental plates reduces shading and offers the required light intensity
for zooxanthellate corals such as S. pistillata. Only a few studies to date have tried to implement artificial reefs in a coral reef environment. The results of the present
study indicate the potential of enhancing recruitment of corals by transplantation of juvenile recruits onto appropriate artificial
structures. Maximal survivorship of these recruits is dependent upon the structural features of the artificial reef, which
should offer optimal conditions.
Received: 25 May 1996 / Accepted: 15 July 1996 相似文献
4.
Variability in the chemical defense of the sponge Chondrilla nucula against predatory reef fishes 总被引:2,自引:0,他引:2
Chondrilla nucula is a common Caribbean demosponge that grows in a range of habitats, from coral reefs to mangrove swamps. On reefs, C. nucula grows as a thinly encrusting sheet, while in mangrove habitats it surrounds submerged mangrove roots as fleshy, lobate clumps.
Previous feeding experiments using predatory reef fish revealed a high degree of variability in the chemical defenses of C. nucula. The present study was undertaken to determine whether a relationship exists between habitat, growth form, and chemical defense
of C. nucula. Both laboratory and field feeding-assays of crude extracts confirmed that C. nucula possesses a chemical defense with high intercolony variability, but there was no significant variation in feeding deterrency
between reef and mangrove habitats at either geographic location (Bahamas and Florida). Extracts of C. nucula collected during September and October 1994 from the Bahamas were significantly more deterrent than those collected during
August 1993, May 1994, and May 1995 from Florida, and extracts of these spring and summer Florida collections were more deterrent
than extracts of C. nucula collected in December 1994 and February 1995 in the same locations. There was no evidence that deterrent compounds were concentrated
in the surface tissues of the sponge, or that chemical defense could be induced by simulated predation. Laboratory and field
assays of the fractionated crude extract revealed that feeding deterrency was confined to the most polar metabolites in the
extract. Field transplants were used to determine whether predation influenced the growth form of C. nucula. Uncaged sponges transplanted from the mangrove to the reef were readily consumed by spongivorous reef fishes. Lobate mangrove
sponges became thinner after being caged on the reef for 3 mo, but encrusting reef sponges did not become thicker after being
caged in the mangroves for the same period of time. Reef sponges that were caged for 3 to 15 mo thickened by only a small
amount (<1 mm) compared to uncaged and open-caged (i.e. in cages lacking tops) sponges. Simulated bite marks on both reef
and mangrove sponges were repaired at a rapid rate (0.8 to 1.6 mm d−1). Fish predation has an important impact on the distribution and abundance of C. nucula, but the thin growth form common to reef environments may be more the result of hydrodynamics than of grazing by spongivorous
fishes.
Received: 6 October 1997 / Accepted: 19 March 1998 相似文献
5.
Reproductive success among clonal taxa is often portrayed as a simple function of clone size, but reproduction in Pseudoplexaura porosa (Houtuyn), a common Caribbean gorgonian, reflects a more complex relationship between size and gamete production. Tagged
colonies were sampled at two reefs in the San Blas Islands, Panama during the 1995 spawning season to determine the colony
size at first reproduction, size-dependent polyp fecundities, and whole colony gonad production, and to follow the gametogenic
cycle. Additional data were obtained during non-spawning months in 1984 and 1985. Of 120 colonies ranging in height from 20
to 250 cm, only colonies taller than 50 cm were reproductive. An average of 4.33 oocytes polyp−1, 560 to 800 μm in diameter, were released during monthly synchronous spawning events from June to September. Oocytes released
each month developed from a group of intermediate size oocytes present at the end of the preceding month. Almost all oocytes
>560 μm were released during each spawning event. Spermatogenesis was a shorter process than oogenesis. During each spawning
month, mature spermaries developed from a group of <125 μm spermaries. Virtually all spermaries >190 μm were released each
month, and most of the spermary volume in mature male polyps was generated anew each month of spawning. Among reproductive
colonies, polyp fecundity increased with colony height from 50 to 200 cm. Per capita fecundity of >200 cm tall female colonies
was lower than for 150 to 200 cm colonies, but whole colony fecundity of large colonies was greater due to the exponential
increase in the number of polyps that occurs with increasing colony height. In male colonies, both polyp and colony reproductive
output increased with colony height. The large amounts of sperm produced by large male colonies probably contributes to the
high rates of in situ fertilization observed in P. porosa. Differences in fecundity as a function of colony size and sex suggest differences in some combination of the cost of reproduction
and/or allocation of resources to reproduction.
Received: 9 September 1998 / Accepted: 7 June 1999 相似文献
6.
S. E. Beaulieu 《Marine Biology》2001,138(4):803-817
Photographs of the deep-sea floor often show organisms attached to biogenic structures that protrude from the soft bottom.
In particular, the stalks of glass sponges (hexactinellids) provide hard substrata and act as habitat islands for deep-sea
fauna. The primary objectives of this study were to determine the abundance of glass sponge “stalks” at an abyssal station
in the NE Pacific, to identify the fauna associated with stalks, and to compare the distribution patterns of epifaunal taxa
both horizontally and vertically. Densities of stalks and large epifauna were estimated from analysis of ∼9 km of photographic
transects taken in 1994–1995 at station M (34°45′N; 123°00′W; 4,100 m depth) off California, USA. At least 87% of the stalks
were the spicule columns of live or dead hexactinellids in the genus Hyalonema (Gray, 1832). Stalks appeared to be distributed randomly across the sea floor (density: 0.13 stalks m−2). A colonial zoanthid, Epizoanthus stellaris (Hertwig, 1888), inhabited 20% of the stalks and was the most commonly observed epifaunal organism, followed by other suspension
feeders that generally were situated at the top of the structures. Thirty-five stalk communities were collected in tube cores
in 1994–1995 using the submersible “Alvin”. A total of 139 taxa was associated with these hard-substratum habitats (another
five species were observed only in photographs). Although taxon richness was high, the species diversity of these communities
was relatively low due to the dominance in percentage abundance of a foraminiferan, Cibicides lobatulus (Walker and Jakob, 1798), and a serpulid polychaete, Bathyvermilia sp. (Zibrowius, 1973). The relationship between number of taxa and surface area of the stalks yielded a slope (z-value) typical of islands with a low rate of immigration. Three-dimensional complexity created by branching epifauna on the
stalks provided more surface area and a variety of cryptic microhabitats. Vertical zonation on the stalks appeared to be controlled
by biological interactions among species, with solitary fauna and certain functional groups of colonial organisms restricted
by sheet-like colonial organisms that appeared to be dominant space competitors.
Received: 13 April 2000 / Accepted: 9 November 2000 相似文献
7.
Genetic differentiation among populations of a broadcast spawning soft coral, Sinularia flexibilis, on the Great Barrier Reef 总被引:2,自引:0,他引:2
The genetic structure of 12 reef populations of the soft coral Sinularia flexibilis (Octocorallia, Alcyoniidae) was studied along the Great Barrier Reef (GBR) at a maximum separation of 1,300 km to investigate
the relative importance of sexual and asexual reproduction, genetic differentiation and gene flow among these populations.
S. flexibilis is a widely distributed Indo-Pacific species and a gamete broadcaster that can form large aggregations of colonies on near-shore
reefs of the GBR. Up to 60 individuals per reef were collected at a minimum sampling scale of 5 m at two sites per reef, from
December 1998 to February 2000. Electrophoretic analyses of nine polymorphic allozymes indicated that genotypic frequencies
in most populations and loci did not differ significantly from those expected from Hardy–Weinberg predictions. Analysis of
multi-locus genotypes indicated a high number of unique genotypes (N
go) relative to the number of individuals sampled (N) in each reef population (range of 0.69–0.95). The maximum number of individuals likely to have been produced sexually (N*) was similar to the number of individuals sampled (i.e. N*:N ˜ 1), suggesting that even repeated genotypes may have been produced sexually. These results demonstrated a dominant role
of sexual reproduction in these populations at the scale sampled. Significant genetic differentiation between some populations
indicated that gene flow is restricted between some reefs (F
ST=0.026, 95% CI= 0.011 − 0.045) and even between sites within reefs (F
ST=0.041, 95% CI=0.027 − 0.055). Nevertheless, there was no relationship between geographic separation and genetic differentiation.
Analyses comparing groups of populations showed no significant differentiation on a north-south gradient in the GBR. The pattern
in the number of significant differences in gene frequencies in pairwise population comparisons, however, suggested that gene
flow may be more restricted among inner-shelf reef populations near to the coast than among mid/outer-shelf populations further
from the coast.
Received: 10 July 2000 / Accepted: 5 October 2000 相似文献
8.
Male reproductive success of the broadcast-spawning gorgonian, Plexaura kuna Lasker, Kim and Coffroth, 1996, was measured in June 1994 and June and July 1995 at two sites in the San Blas Islands, Panamá
in order to determine the environmental and biotic factors affecting individual reproductive success. Developing embryos were
collected in the field during natural spawning events, and paternity determined using randomly amplified polymorphic DNA markers.
Analyses of F1 progeny from defined laboratory matings established that the markers were inherited in Mendelian fashion, and allowed the
determination of the zygosities of the markers. P. kuna is clonal, but male reproductive success was not strictly proportional to clone size. Proximity to females appeared to have
a greater effect on male reproductive success than clone size, and on both reefs the most successful male clone was the one
closest to the spawning female clone. Current direction and transport of gametes by eddies explained variation in paternity
assignments between nights. Clonal propagation allows clones to grow and spread toward each other, and may enhance male reproductive
success.
Received: 1 April 1997 / Accepted: 11 February 1998 相似文献
9.
Late larvae of the serranid coral trout Plectropomus leopardus (Lacepède), captured in light traps, were released during the day both in open water and adjacent to two reefs, and their
behaviour was observed by divers at Lizard Island, northern Great Barrier Reef. Coral trout larvae (n = 110) were present in light-trap catches from 18 November to 3 December 1997, including new moon (30 November). The swimming
speed of larvae in open water or when swimming away from reefs was significantly greater (mean 17.9 cm s−1) than the speed of larvae swimming towards or over reefs (mean 7.2 cm s−1). Near reefs, larvae swam at average depths of 2.7 to 4.2 m, avoiding 0 to 2 m. In open water, swimming depth varied with
location: larvae >1 km east of Lizard Island swam steeply downward to >20 m in 2 to 4 min; larvae >1 km west oscillated between
2.6 and 13 m; larvae 100 to 200 m east of Lizard Island oscillated between 0.8 and 15 m. Nearly all larvae swam directionally
in open water and near reefs. In open water, the average swimming direction of all larvae was towards the island, and 80%
(4 of 5) swam directionally (p < 0.05, Rayleigh's test). Larvae swam directionally over the reef while looking for settlement sites. The frequency of behaviours
by larvae differed between two reefs of different exposure and morphology. Depending on site, 26 to 32% of larvae released
adjacent to reefs swam to open water: of these, some initially swam towards or over the reef before swimming offshore. In
some cases, offshore-swimming seemed to be due to the presence of predators, but usually no obvious cause was observed. Depending
on the reef, 49 to 64% of the larvae settled. Non-predatory reef residents aggressively approached 19% of settlers. Between
5 and 17% of the larvae were eaten while approaching the reef or attempting to settle, primarily by lizardfishes but also
by wrasses, groupers and snappers. A higher percentage of larvae settled in the second week of our study than in the first.
Average time to settlement was short (138 s ± 33 SE), but some larvae took up to 15 min to settle. Average settlement depth
was 7.5 to 9.9 m, and differed between locations. No settlement took place on reef flats or at depths <4.2 m. Larvae did not
appear to be selective about settlement substrate, but settled most frequently on live and dead hard coral. Late-stage larvae
of coral trout are capable swimmers with considerable control over speed, depth and direction. Habitat selection, avoidance
of predators and settlement seem to rely on vision.
Received: 7 July 1998 / Accepted: 26 January 1999 相似文献
10.
The pattern of settlement over time of three broadcast spawning coral species (Cyphastrea serailia, Acanthastrea lordhowensis, and Goniastrea australensis) from the Solitary Islands (30°00′S; 153°20′E) was studied in 1995 and 1996 in order to determine the maximum length of time
these larvae could remain in the water column and still retain the ability to settle and metamorphose. Larvae were maintained
in aquaria and the number which had settled on biologically-conditioned tile pairs was monitored every 5 to 10 d. While the
majority of larvae settled quickly after becoming competent, some larvae survived and settled for extended periods after spawning.
Competency periods ranged from 26 d for C. serailia to 56 d for G. australensis and 78 d for A. lordhowensis. These data greatly extend the known competency periods for larvae of broadcast-spawning corals and indicate the potential
for transport of broadcast-spawned coral larvae over large distances. Medium to long-distance larval dispersal of the species
studied provides a mechanism for their widespread distribution in subtropical regions, on reefs which are often widely spaced
and relatively isolated.
Received: 27 May 1997 / Accepted: 27 November 1997 相似文献
11.
E. Mutlu 《Marine Biology》2001,138(2):329-339
The distribution of moon jellyfish (Aurelia aurita Linnaeus, 1758) in the Black Sea was determined from plankton samples collected above the anoxic zone (maximum depth 200 m)
in the summer, winter and spring during 1991–1995. Distribution was patchy. Average biomass ranged from 98 to 380 g m−2, and abundance varied from 2 to 14 individuals m−2. Biomass and abundance peaked in late spring and summer. The distribution was correlated with hydrographic features in the
Black Sea, with higher concentrations occurring at the peripheries of anticyclonic eddies. Centers of the two main cyclonic
gyres generally had a low biomass of A. aurita. From July 1992 to March 1995, the populations were largely concentrated in offshore regions. A. aurita were confined to the upper part of the mixed layer. Smaller A. aurita (≤1 cm) were present in early spring (March), and individuals reached maximum size in the summer. Release of the epyhrae
occurred in spring on the northwestern shelf of the sea when the seawater temperature was 11–12 °C. Microscopic analysis of
stomach contents showed that copepods and mollusks form their main diet.
Received: 3 September 2000 / Accepted: 29 September 2000 相似文献
12.
Contribution of salps to carbon flux of marginal ice zone of the Lazarev Sea, southern ocean 总被引:3,自引:0,他引:3
In order to estimate the in situ grazing rates of Salpa thompsoni and their implications for the development of phytoplankton blooms and for the sequestration of biogenic carbon in the high
Antarctic, a repeat-grid survey and drogue study were carried out in the Lazarev Sea during austral summer of 1994/1995 (December/January).
Exceptionally high grazing rates were measured for S. thompsoni at the onset of a phytoplankton bloom (0.2 to 0.8 μg chlorophyll a l−1) in December 1994, with up to ≃160 μg of plant pigments consumed by an individual salp of 7 to 10 cm length per day. Dense
salp swarms extended throughout the marginal ice zone, consuming up to 108% of daily phytoplankton production and 21% of the
total chlorophyll a stock. Due to the much faster sinking rates and higher carbon content of salp faecal pellets, the efficiency of downward
carbon flux through salps is much higher than through the other major grazers, krill and copepods. S. thompsoni can thus export large amounts of biogenic carbon from the euphotic zone to the deep ocean. With the observed ingestion rates
during December 1994, this flux could have attained levels of up to 88 mg C m−2 d−1, accounting for the bulk of the vertical transport of carbon in the Lazarev Sea. However, in January 1995, when phytoplankton
concentrations exceeded a threshold level of 1.0 to 1.5 μg chlorophyll a l−1, salps experienced a drastic reduction in their feeding efficiency, possibly as a result of clogging of their filtering apparatus.
This triggered a dramatic reversal in the relationship, during which a dense phytoplankton bloom developed in conjunction
with the collapse of the salp population. Increases in the biomass and geographic range of the tunicate S. thompsoni have occurred in several areas of the southern ocean, often in parallel with a rise in sea-surface temperature during sub-decadal
periods of warming anomalies.
Received: 10 August 1997 / Accepted: 21 October 1997 相似文献
13.
E. M. Harper 《Marine Biology》1997,127(3):449-453
It has been suggested that mature oysters attach to their natural substrata by means of a combination of a modification of
the prismatic outer-shell layer formed within the periostracum and a “pressing” action of the mantle (Yamaguchi 1994). However, marine surfaces are seldom smooth enough
to allow adhesion without the addition of a fluid adhesive to allow electromagnetic interactions to hold the two bodies together.
An electron microscope study of the attachment of the oyster Saccostrea cucullata to its natural substrata has confirmed the presence of a crystalline calcareous cement. The cement shows a range of spherulitic
and irregular blocky textures that are reminiscent of diagenetic cement fabrics. Their form suggests that the cement crystallises
from a calcium-carbonate-saturated liquor trapped between the underside of the shell and the substratum, with crystallites
nucleating on all bounding surfaces of the void.
Received: 30 May 1996 / Accepted: 9 August 1996 相似文献
14.
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
15.
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
16.
The benthic dinoflagellate Gambierdiscus spp. is the primary causative agent of ciguatera fish poisoning in French Polynesia. However, the initiation of ciguatera
outbreaks and the factors that control ciguatoxin production in this dinoflagellate are still poorly understood. In this paper,
we present some original data concerning the seasonal abundance and toxicity of natural populations of Gambierdiscus spp. based on a long-term survey in a ciguateric site of the island of Tahiti. From February 1993 to December 1997, Gambierdiscus spp. population densities were monitored weekly in the Atimaono barrier reef of Papara in relation to temperature and salinity.
Densities peaked at 4992 cells g−1 in October 1994 and constituted ≥1000 cells g−1 on several occasions. A total of 58 blooms were recorded in the area, of which 65% occurred in 1995 and 1996 alone. Our data
confirmed the high endemicity of Gambierdiscus spp. in the Papara area. Refined analysis of our raw data by a principal-component analysis of processes (PCAP) revealed
a seasonality in cell densities from February 1993 to May 1995. During this period, Gambierdiscus spp. populations tended to reach maximum abundance at the beginning and end of the hot season. In contrast, salinity did
not appear to be a determining factor in the seasonal abundance of this dinoflagellate. The noticeable increase in both peak
densities and frequency of blooms further noticed in 1995 and 1996 was preceded by unusually high water temperatures in January
to April 1994, concomitant with a severe coral-bleaching episode. During the course of the study, a total of 303 × 106 cells obtained from 48 successive blooms was harvested. Toxicity screening revealed that toxin production was maximum from
October 1994 through December 1996. No correlation was found between toxicity of these blooms and their biomass nor the seasonal
pattern of temperatures. It is suggested that the toxicity of naturally-occurring blooms of Gambierdiscus spp. and, consequently, the severity of ciguatera incidents in a given area, is mainly dependent on the clonal nature of
cells which coexist within local populations of this dinoflagellate.
Received: 12 October 1998 / Accepted: 15 June 1999 相似文献
17.
The Belizean reef coral Agaricia tenuifolia Dana forms aggregations in which rows of thin, upright blades line up behind each other. On average, the spacing between
blades increases with depth and hence with decreasing ambient irradiance. We designed and built a small, inexpensive light
meter and used it to quantify the effect of branch spacing on light levels within colonies at varying distances from branch
tips. Concurrently, we measured photosynthetic pigment concentrations and population densities of symbiotic dinoflagellates
(zooxanthellae) extracted from coral branches of colonies with tight (≤3 cm) vs wide (≥6 cm) branch spacing, collected at
15 to 17 m and from colonies with tight branch spacing collected at 1 to 2 m. Light levels decreased significantly with tighter
branch spacing and with distance from the branch tips. Total cellular pigment concentrations (chlorophylls a, c
2
and peridinin) as well as chlorophyll a:c
2
and chlorophyll a: peridinin ratios all increased significantly with distance from the branch tip, indicating very localized differences in
photoacclimation within individual branches. Zooxanthellae from colonies with widely-spaced branches displayed significantly
lower chlorophyll a:c
2
and chlorophyll a:peridinin ratios, and were present at significantly higher population densities than those from colonies with tightly-spaced
branches collected at the same depth (15 m). Tightly-spaced colonies collected from shallow environments (1 to 2 m) displayed
pigment ratios similar to those from widely-spaced colonies from deeper water (15 m), but maintained zooxanthellae populations
at levels similar to those in tightly-branched colonies from deeper water. Thus, variation in colony morphology (branch spacing
and distance from branch tip) can affect symbiont physiology in a manner comparable to an increase of over 15 m of water depth.
These results show that a host's morphology can strongly determine the microhabitat of its symbionts over very small spatial
scales, and that zooxanthellae can in turn display steep gradients in concordance with these altered physical conditions.
Received: 12 June 1997 / Accepted: 24 June 1997 相似文献
18.
Direct-developing intertidal Lasaea spp. occur in the North Atlantic as both continental margin and oceanic island populations. We conducted a molecular phylogenetic
analysis of representative populations in order to test colonization hypotheses for North Atlantic oceanic islands. Thirty
individuals each were collected in 1995 and 1996 from two continental putative source populations (Florida, Iberia) and two
oceanic island populations (Bermuda, Azores). They were sequenced for a 462 nucleotide portion of the mitochondrial large
ribosomal subunit (16S) gene. No amphi-Atlantic genotypes were detected: Bermudan lineages co-clustered exclusively with Floridian
congeners, and Azorean samples formed an exclusive clade with Iberian haplotypes. Our data indicate that geographical proximity
to continental source populations is a better predictor of phylogenetic relationships in North Atlantic Lasaea spp. than present-day oceanic surface circulation patterns. The phylogenetic trees generated are not consistent with colonization
of oceanic islands by indirect-developing ancestral lineages or by truly trans-oceanic rafting events. However, they are consistent
with predicted topologies resulting from limited (≤ 2000 km), long-distance colonization by rafting (against present-day circulation
patterns in the case of the Azores) and from anthropogenic introductions.
Received: 17 December 1998 / Accepted: 7 June 1999 相似文献
19.
Moerisia lyonsi Boulenger (Hydrozoa) medusae and benthic polyps were found at 0 to 5‰ salinity in the Choptank River subestuary of Chesapeake
Bay, USA. This species was introduced to the bay at least 30 years before 1996. Medusae and polyps of M. lyonsi are very small and inconspicuous, and may occur widely, but unnoticed, in oligohaline waters of the Chesapeake Bay system
and in other estuaries. Medusae consumed copepod nauplii and adults, but not barnacle nauplii, polychaete and ctenophore larvae
or tintinnids, in laboratory experiments. Predation rates on copepods by medusae increased with increasing medusa diameter
and prey densities. Feeding rates on copepod nauplii were higher than on adults and showed no saturation over the range of
prey densities tested (1 to 64 prey l−1). By contrast, predation on copepod adults was maximum (1 copepod medusa−1 h−1) at 32 and 64 copepods l−1. Unexpectedly, M. lyonsi colonized mesocosms at the Horn Point Laboratory during the spring and summer in 4 years (1994 to 1997), and reached extremely
high densities (up to 13.6 medusae l−1). Densities of copepod adults and nauplii were low when medusa densities were high, and estimated predation effects suggested
that M. lyonsi predation limited copepod populations in the mesocosms. Polyps of M. lyonsi asexually produced both polyp buds and medusae. Rates of asexual reproduction increased with increasing prey availability,
from an average total during a 38 d experiment of 9.5 buds polyp−1 when each polyp was fed 1 copepod d−1, to an average total of 146.7 buds polyp−1 when fed 8 copepods d−1. The maximum daily production measured was 8 polyp buds and 22 medusae polyp−1. The colonizing potential of this hydrozoan is great, given the high rates of asexual reproduction, fairly wide salinity
tolerance, and existence of a cyst stage.
Received: 29 October 1998 / Accepted: 3 March 1999 相似文献
20.
Sessile marine invertebrate larvae can recognize suitable settlement substrata by using various environmental cues, including
organic/microbial biofilms. In laboratory choice assays, the effect of biofilms of varying ages on the settlement behaviour
of two fouling organisms was assessed. The species included the arborescent cheilostome bryozoan Bugula flabellata (Thompson) and the solitary ascidian Ciona intestinalis (L.), both of which are characteristic of temperate sublittoral hard substratum assemblages in northwest Europe. Experiments
were carried out using polystyrene petri dish substrata preconditioned with multispecies biofilms from natural laboratory-aquarium
seawater for 1, 3, 6 or 12 d. Unfilmed (new, initially sterile) dishes were used as control substrata. Whereas the coronate
larvae of B. flabellata generally were inhibited by biofilming, irrespective of film age, the settlement of tadpole larvae of C. intestinalis was facilitated on biofilmed substrata, and numbers of settled larvae generally increased with biofilm age: the highest mean
numbers were counted on 12 d-old biofilms. In C. intestinalis, settlement and metamorphosis are processes which can be temporally separate and are possibly induced by different environmental
cues. This study therefore distinguished between C. intestinalis larvae which were attached to the biofilm surface by the anterior, and those larvae entrapped by the biofilm but not settled
in the conventional meaning of the term. As reported in previous studies, we did observe that such entrapped larvae could
subsequently attach and develop successfully into sessile juveniles. Both the numbers of “attached” and “trapped” tadpoles
increased with biofilm age. Assuming that “settlement” is essentially a process involving the active behavioural response
of larvae to environmental cues, it seems that the facilitated attachment of C. intestinalis onto biofilmed substrata is due to the combined effect of active habitat selection and passive deposition/“entrapment” of
larvae onto the “sticky” substratum.
Received: 21 August 1996 / Accepted: 21 November 1996 相似文献