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1.
2.
We studied the effects of grazing by two species of sea urchins on two species of kelp (Macrocystis pyrifera and Pterygophora californica) in the San Onofre kelp bed in southern California from 1978 through 1981. Both red sea urchins, Strongylocentrotus franciscanus, and white sea urchins, Lytechinus anamesus, were abundant and lived in aggregations. The purple sea urchin (S. purpuratus) was rare at the study site and was not studied. The aggregations of red urchins were either relatively small and stationary (for over 3 yr) or relatively large and motile (advancing at about 2 m mo–1). Both stationary and moving aggregations were observed at the same time, and within 100 m of one another. Stationary aggregations of red urchins probably subsisted mainly on drift kelp and had no effect on kelp recruitment or on adult kelp abundance. In contrast, red sea urchins in large, motile aggregations or fronts ate almost all the macroalgae in their path. The condition of their gonalds indicated that red urchins in fronts were starved relative to red urchins in the small, stationary aggregations. Large, motile aggregations developed after 2 yr of declining kelp abundance (probably due largely to storms). We propose that a scarcity of drift algae for food results in a change in the behavior pattern of the red urchins and thus leads to the formation of large, motile aggregations. The aggregations of white urchins, which occurred along the offshore margin of the kelp bed, were large, but relatively stationary. The white urchins rarely ate adult kelps, but grazed extensively on early developmental stages of kelps and evidently prevented seaward expansion of the bed. The spatial distribution of both types of red urchin aggregations appeared to be unrelated to predation pressure from fishes or lobsters.Please address all requests for reprints to the senior author at his present address. 相似文献
3.
Selective consumption and facilitation by mesograzers in adult and colonizing macroalgal assemblages
Grazing pressure on macroalgae in littoral communities may vary with algal species, the age of an algal individual and grazer
identity. Previous studies on alga–grazer interactions have shown that grazer preference for an algal species may release
another one from interspecific competition. We measured the impacts of four common grazer taxa and the natural grazer guild
on macroalgal communities at both their colonization and adult stages, and compared the impacts to grazer exclosures. The
grazer effects were stronger on colonizing than on adult macroalgae; grazers did not reduce the total density of adult algae.
Grazers both feed on propagules and indirectly facilitate other algae, depending on the grazer or algal species. Hydrobia species increased the settlement of spores of the red alga Ceramium tenuicorne. Similarly, the gastropod Theodoxus fluviatilis tended to facilitate one crustose algal species, but decreased the propagule density of annual filamentous algae, suggesting
a preference for one species to the advantage of another. Effects of crustacean mesograzers on the studied macroalgae were
weak. These results indicate that northern Baltic macroalgae are limited to grazing mainly during their colonization stage. 相似文献
4.
Point sources of pollution (e.g. industrial and municipal outfalls) may produce ecological impacts at distant locations if pollutants affect dispersive propagules. We used laboratory experiments to determine how water-column exposure to produced water (=the aqueous fraction of oil and gas production that is typically discharged into coastal waters) influences the colonization potential of giant kelp (Macrocystis pyrifera) zoospores on the bottom. Zoospores were maintained in suspension at relatively low densities in 18-liter containers and exposed to one of five concentrations of produced water for varying amounts of time. Zoospore swimming generally decreased with increasing produced-water concentration and exposure duration; however, the specific pattern of decrease differed between experimental trials done on different dates. The effect of exposure duration on the ability of swimming zoospores to attach to plastic dishes placed on the bottom varied with produced-water concentration. Zoospores placed in produced-water concentrations of 1 and 10% showed a steady decline in their ability to attach with increased exposure; lower concentrations of produced water had no such effects. The percentage of zoospores that germinated after attachment varied tremendously with exposure duration and date of experimental trial. Zoospores that settled during the first 12 h after release had very poor rates of germination, indicative of a short precompetent period. Surprisingly, exposure of suspended zoospores to high concentrations of produced water during the first 12 h reduced this precompetent period and greatly improved germination success on the bottom. The magnitude of this enhancement, however, varied among dates. The results suggest that adverse effects of discharging produced water on planktonic zoospores of giant kelp would most likely be limited to the immediate vicinity of the outfall. 相似文献
5.
For small tube-building amphipods that live on the algae they consume, food and habitat are tightly linked. This study compared
two closely related amphipods to determine whether the species’ algal preferences are based on the food value of the algae
or on some other aspect of their algal habitat. Ampithoe lacertosa and Peramphithoe humeralis are both abundant on Shannon Point beach (Anacortes, Washington, USA; 48°30.542′ N, 122°41.070′ W) but specialize on different
algae. In observations and laboratory experiments conducted July–September 1997, 2007, and 2008, the two species exhibited
markedly different choices of food and habitat when offered six common macroalgae. Ampithoe
lacertosa ate all algae offered, but preferentially built tubes on the green alga Ulva
lactuca. Survival was relatively low among juveniles maintained on single species diets, except when they were fed Mazzaella splendens. Conversely, P.
humeralis consumed primarily the brown kelp Saccharina latissima, Alaria
marginata, and Desmarestia
ligulata and preferred those species for tube building. Juvenile P.
humeralis could not survive on a diet of U.
lactuca or M. splendens. While A.
lacertosa builds simple, temporary tubes and relocates frequently, P.
humeralis is a highly thigmotactic species that builds long-term, complex tubes on the alga it prefers to eat. Feeding and habitat
preferences of the two species were not clearly linked to nitrogen content of the algae, C:N ratio, or toughness of the algal
tissue. Instead, preferences of the species may be related to their mobility and the permanence of the tubes they build. Ampithoe
lacertosa and P.
humeralis also use different feeding strategies; the former appears to mix algae to produce a high-quality diet, while the latter is
more selective and has a capacity for compensatory feeding. The species are abundant on the same protected rocky shores, but
specialize on different algae for habitat and food. Results suggest that the nutritional requirements of these sympatric mesograzers
differ considerably and even closely related species can exhibit divergent behavioral strategies. 相似文献
6.
The effects of exposure to ultraviolet radiation (UVR), 280–400 nm, in different life histories and development stages of the kelps, Lessonia nigrescens and L. trabeculata, collected in the south-east Pacific coast (30°S) were evaluated in the laboratory. Germination and viability (motile zoospores, settled spores), diameter of the primary cell of the gametophytes, percentage of female gametophytes, fertility and sporophytes production were measured after exposure to three radiation treatments (PAR; PAR + UVA; PAR + UVA + UVB). The effects of UVR in young sporophytes (diploid stage) were evaluated as changes in maximal quantum yield of chlorophyll fluorescence of photosystem II (PSII) (F
v/F
m). A significant decrease in all variables was observed for the treatment that included UVB (PAR + UVA + UVB) after 2 and 4 h of exposure, in relation to the control. The motile spores were more sensitive to UVR exposure compared to settled spores and gametophytes, suggesting that along with an increase in ontogenetic development; there is an increase in the tolerance to UVR. In addition, it was observed that early stages of the intertidal L. nigrescens were more tolerant to UVR compared to the subtidal L. trabeculata. These results allow initially to infer that UVR may be regarded as an important environmental factor influencing the upper limit of distribution of these species, mainly through its detrimental effects on the early stages of the life cycle. 相似文献
7.
Nitrogen- versus phosphorus-limited growth and sources of nutrients for coral reef macroalgae 总被引:10,自引:0,他引:10
S. T. Larned 《Marine Biology》1998,132(3):409-421
Recent investigations of nutrient-limited productivity in coral reef macroalgae have led to the conclusion that phosphorus,
rather than nitrogen, is the primary limiting nutrient. In this study, comparison of the dissolved inorganic nitrogen:phosphorus
ratio in the water column of Kaneohe Bay, Hawaii, with tissue nitrogen:phosphorus ratios in macroalgae from Kaneohe Bay suggested
that nitrogen, rather than phosphorus, generally limits productivity in this system. Results of nutrient-enrichment experiments
in a flow-through culture system indicated that inorganic nitrogen limited the growth rates of 8 out of 9 macroalgae species
tested. In 6 of the species tested, specific growth rates of thalli cultured in unenriched seawater from the Kaneohe Bay water
column were zero or negative after 12 d. These results suggest that, in order to persist in low-nutrient coral reef systems,
some macroalgae require high rates of nutrient advection or access to benthic nutrient sources in addition to nutrients in
the overlying water column. Nutrient concentrations in water samples collected from the microenvironments inhabited or created
by macroalgae were compared to nutrient concentrations in the overlying water column. On protected reef flats, inorganic nitrogen
concentrations within dense mats of Gracilaria salicornia and Kappaphycus alvarezii, and inorganic nitrogen and phosphate concentrations in sediment porewater near the rhizophytic algae Caulerpa racemosa and C. sertularioides were significantly higher than in the water column. The sediments associated with these mat-forming and rhizophytic species
appear to function as localized nutrient sources, making sustained growth possible despite the oligotrophic water column.
In wave-exposed habitats such as the Kaneohe Bay Barrier Reef flat, water motion is higher than at protected sites, sediment
nutrient concentrations are low, and zones of high nutrient concentrations do not develop near or beneath macroalgae, including
dense Sargassum echinocarpum canopies. Under these conditions, macroalgae evidently depend on rapid advection of low-nutrient water from the water column,
rather than benthic nutrient sources, to sustain growth.
Received: 1 December 1997 / Accepted: 9 July 1998 相似文献
8.
W. K. Fitt 《Marine Biology》1984,81(1):9-17
Symbiotic dinoflagellates, Symbiodinium microadriaticum (=zooxanthellae), may gain access to aposymbiotic hosts (i.e., those lacking zooxanthellae) by chemosensory attraction of the motile algae by the potential host or via an intermediate host. Laboratory experiments showed that motile zooxanthellae were attracted to intact aposymbiotic host animals, but not to starved symbiotic hosts. Fed symbiotic hosts and brine shrimp (Artemia sp.) nauplii also attracted motile zooxanthellae. The attraction of these zooxanthellae was directly correlated with nitrogen levels in the seawater surrounding the hosts; thus ammonia and possibly nitrate could be atractants. Brine shrimp nauplii, acting as intermediate hosts actively ingested both motile and non-motile zooxanthellae. the ingested zooxanthellae tended to remain morphologically unaltered during and after passage through the gut of the brine shrimp. Capture and ingestion of brine shrimp containing zooxanthellae by aposymbiotic scyphistomae of the jellyfish Cassiopeia xamachana led to infection of the scyphistomae with zooxanthellae. Zooxanthellae isolated from 17 different species of coelenterates and molluscs could be transferred via brine shrimp to the endodermal cells of the scyphistomae. However only 10 of these isolates persisted to establish a permanent association with C. xamachana. Scyphistomae in suspensions of motile zooxanthellae responded by a classical coelenterate feeding response, which may facilitate ingestion of the potential symbionts and establishment of a symbiosis. 相似文献
9.
We studied the lipid dynamics (lipid contents, classes and fatty acids) during oogenesis and early embryogenesis of 7 viviparous
and 3 oviparous deepwater chondrichthyans. Mature pre-ovulated ovarian follicles of all species were high in lipid content,
indicative of large energetic expenditure and high maternal investment. Larger lipid reserves were found in viviparous dogshark
(28–36% wet weight, ww) compared to oviparous chimaeras (19–24% ww) and catshark, F. boardmani (18% ww). Neutral lipids and monounsaturated fatty acids were the main source of lipidic energy during vitellogenesis and
gestation. For most species, there was a peak in total lipid content, levels of storage lipids and essential fatty acids at
time of ovulation. Interspecific variation of total lipid yolk reserves and lipid class profiles was largely explained by
differences in parity mode, reproductive (continuous vs. non-continuous oocytes development) strategy and depth-related physiological adaptations. Fatty acid profiles were less variable
among species with the most important fatty acids including: 16:0, 18:1ω9, 20:1ω9, 20:4ω6 and 22:6ω3. These findings provide
a greater biochemical understanding of different maternal-embryonic relationships among chondrichthyans, which can be used
as a baseline for subsequent comparative studies. 相似文献
10.
The shallow kelp forest at Santa Catalina Island, California (33.45 N, −118.49 W) is distinguished by several canopy guilds
ranging from a floating canopy (Macrocystis pyrifera), to a stipitate, erect understory canopy (Eisenia arborea), to a short prostrate canopy just above the substratum (Dictyopteris, Gelidium, Laminaria, Plocamium spp.), followed by algal turfs and encrusting coralline algae. The prostrate macroalgae found beneath E. arborea canopies are primarily branching red algae, while those in open habitats are foliose brown algae. Densities of Corynactis californica, are significantly greater under E. arborea canopies than outside (approximately 1,200 versus 300 polyps m−2 respectively). Morphological differences in macroalgae between these habitats may affect the rate of C. californica particle capture and serve as a mechanism for determining polyp distribution and abundance. Laboratory experiments in a unidirectional
flume under low (9.5 cm s−1) and high (21 cm s−1) flow speeds examined the effect of two morphologically distinct macroalgae on the capture rate of Artemia sp. cysts by C. californica polyps. These experiments (January–March 2006) tested the hypothesis that a foliose macroalga, D. undulata, would inhibit particle capture more than a branching alga, G. robustum. G. robustum, found predominantly under the E. arborea canopy did not affect particle capture. However, D. undulata, found predominantly outside of the canopy, inhibited particle capture rates by 40% by redirecting particles around C. californica polyps and causing contraction of the feeding tentacles. These results suggest that the morphology of flexible marine organisms
may affect the distribution and abundance of adjacent passive suspension feeders. 相似文献
11.
UV-radiation can affect depth-zonation of Antarctic macroalgae 总被引:17,自引:0,他引:17
Due to depletion of stratospheric ozone over polar regions of the Northern and Southern Hemispheres UV-B-radiation has increased
at the surface of the earth. Measurements of variable chlorophyll fluorescence were conducted to document UV-induced photoinhibition
of photosystem II in cultivated macroalgae with different depth distributions in Antarctica. The reactions during artificial
UV-exposure were observed on a short time scale (hours) and in light–dark cycles over several days. The nine species of investigated
macroalgae show great differences in UV-tolerance of the photosynthetic process. Photosynthesis of the studied green algae
was inhibited to a minor degree, while the brown algae showed an intermediate inhibition of photosynthesis. The response of
the studied red algae varied with species. The differences in the degree of inhibition and recovery of photosynthetic efficiency
and capacity indicate that UV-radiation is one important factor affecting the vertical distribution of macroalgae in nature.
Received: 11 December 1997 / Accepted: 27 March 1998 相似文献
12.
L. Axelsson 《Marine Biology》1988,97(2):287-294
An automatically operated method for high precision measurements of steady-state photosynthesis by macroalgae was developed. Changes in pH and oxygen content of seawater passing the algae in a flowthrough system, could be measured with extremely high accuracy over very long periods of time. The method is especially suitable for measurements on flowthrough systems with high rates of water exchanges (i.e. short retention time), and can be used to study exchange processes for marine plants, animals and small ecosystems. Since the same measuring unit is used for several flowthrough chambers, the method is very suitable for comparisons between different species, or between differently pretreated specimens of the same species (e.g. in toxicological studies). The method was used to study the ratio: [oxygen production] to [CO2+H+ uptake] at different light intensities for several macroalgae belonging to different systematic groups and from different habitats. At lower photosynthetic rates this ratio was similar for all of the algae studied (1.17±0.02). For brown algae of the fucacean family, the ratio increased by 0.08 units at higher photosynthetic rates. This increase was thought to be related to the crassulacean acid metabolism (CAM)-like strategies connected to these algae. For all other algae studied, the ratio remained constant or decreased slightly (at most by 0.04 units) at higher photosynthetic rates. The relations between the abovementioned ratio and the photosynthetic quotient are discussed on a theoretical basis. 相似文献
13.
Phytoplankton species were grown in batch cultures in the presence of the water-soluble fraction (WSF; 50 and 100%) of a Mexican crude oil (Isthmus Cactus). The algae exhibited various responses ranging from retarded growth to stimulation of growth. The cellular content of chlorophylla and the lipid composition of the algae were examined. Four algae, the bacillariophytesNitzschia closterium andAsterionella glacialis, the cryptophytesRhodomonas lens, and the chlorophyteDunaliella tertiolecta, exhibited retarded growth. In most of these algae, cellular chlorophylla, lipid pigments, glycolipids and triglycerides decreased whereas sterols and hydrocarbons accumulated. Phospholipids did not exhibit any specific pattern of change during the experiments. The cyanophyteAgmenellum quadruplicatum and the bacillariophyteSkeletonema costatum were less sensitive to the WSF. The cell yield of the dinophyteProrocentrum minimum was stimulated by the WSF. In these three latter species, lipid pigments were enhanced or remained at control levels. We concluded that the toxic effect of the WSF disrupts the biosynthesis mechanisms required for a functional photosynthetic apparatus (biosynthesis of chlorophylla, glycolipids and lipid pigments) in sensitive algae, a phenomenon coupled to sterol accumulation in these algae. 相似文献
14.
Eliecer Díaz Christine Güldenzoph Markus Molis Christopher McQuaid Martin Wahl 《Marine Biology》2006,149(6):1301-1311
Variabilities in the responses of several South African red and green macroalgae to direct grazing and the responses of one green alga to cues from grazers were tested. We used two feeding experiments: (1) testing the induced responses of three red and one green algae to direct grazing by mesograzers and (2) a multi-treatment experiment, in which the direct and indirect effects of one macrograzer species on the green alga Codium platylobium were assessed. Consumption rates were assessed in feeding assays with intact algal pieces and with agar pellets containing non-polar extracts of the test algae. Defensive responses were induced for intact pieces of Galaxaura diessingiana, but were not induced in pellets, suggesting either morphological defence or chemical defence using polar compounds other than polyphenols. In contrast, exposure to grazing stimulated consumption of Gracilaria capensis and Hypnea spicifera by another grazing species. In the multi-treatment experiment, waterborne cues from both grazing and non-grazing snails induced defensive algal traits in C. platylobium. We suggest that inducible defences among macroalgae are not restricted to brown algae, but that both the responses of algae to grazers and of grazers to the defences of macroalgae are intrinsically variable and complex. 相似文献
15.
Patrik Kraufvelin Ann Lindholm Morten Foldager Pedersen Lars Andreas Kirkerud Erik Bonsdorff 《Marine Biology》2010,157(1):29-47
The littoral zone of temperate rocky shores is normally dominated by perennial macroalgae (e.g. Fucus, Ascophyllum, Laminaria), but nutrient enrichment and/or permanently decreased wave action may lead to structural community changes from dominance
of perennials to increased amounts of annual opportunistic species (mainly green algae). Macroalgal biomass, diversity and
production as well as relationships between the two latter were studied using Solbergstrand’s rocky shore mesocosms in SE
Norway in connection with a long-term experimental manipulation of nutrient addition and wave action (high and low levels
of both factors applied in a crossed way to eight outdoor basins). After more than 2 years of experimental treatment, the
total standing stock of macroalgae was larger in low nutrient than in high nutrient treatments as well as in high wave compared
to low wave treatments (in autumn only). For macroalgal functional groups, bushy and filamentous brown and filamentous red
algae were generally favoured by low nutrient concentrations, while annual filamentous and sheet-like green algae were stimulated
by the nutrient enrichment. There was only one significant interaction between nutrient enrichment and wave action (for brown
filamentous algae in autumn) and also only one significant main effect of the wave treatment (for bushy brown algae in autumn).
Surprisingly, the high nutrient treatments supported a higher diversity of macroalgae, whereas the low nutrient treatments
generally showed higher production rates. Moreover, significantly negative correlations were found between macroalgal diversity
and primary productivity in both summer and autumn. This study shows that it is the biological components of the communities
subjected to external forcing (nutrient addition or decreased wave action) that regulate production and this contradicts the
common misperception that resource production in natural systems simply can be fast-forwarded by fertilization. The negative
relationships between diversity and productivity, although a consequence of unexpected results for diversity and production,
are also novel and hint towards species identities having more important functional consequences than general species dominance
patterns and the amount of species per se. These results also emphasise the context dependency of findings within the field
of biodiversity and ecosystem functioning. 相似文献
16.
The short-spined toxopneustid sea urchin Tripneustes gratilla feeds on a wide variety of algal species and on sea grasses. However, the urchin does show preferences when offered a selection
of macroalgal species, which it encounters in nature. Preferences among macroalgae were evident in field-collected urchins
exposed to pair-wise tests where the variable was either the consumption rate of the algae or observation of which algal species
the urchins chose to touch with their lantern teeth. Exposure of lab-housed urchins to one of five species of macroalgae for
5 months did not seem to alter preferences of urchins in three of the exposure groups, but those exposed to Padina sanctae-crucis seemed to show an enhanced preference for this species when offered a choice of the five species of macroalgae at the end
of the exposure period, and those exposed to Gracilaria salicornia seemed to avoid the species when offered the choice of the five species. Perhaps more ecologically important than their preferences
were two other observations on these urchins: first, when offered only a single species of algae, the urchins on four of five
diets ate the same quantity per day. Second, when simultaneously offered the choice among the five macroalgal species, the
urchins consumed more macroalgae per day than when offered only one species. These urchins move about a meter a day. They
probably encounter food resources in a relatively coarse-grained fashion and have evolved to eat what is available. Because
of their limited movements, their habitat overlap with grazing fishes, their acceptance of a wide variety of macroalgae and
their preference for macroalgae, these native urchins are thought to have the potential to serve as biological control agents
of alien and invasive macroalgae, which have come to dominate some reef zones normally occupied by corals in Hawaii. 相似文献
17.
We observed kelp gametophytes endophytic in the cell walls of 17 species of red algae from the San Juan Islands, Washington,
USA. Host algae were collected primarily from three sites dominated by different kelp assemblages, including (1) a subtidal
site dominated by Agarum fimbriatum Harvey, (2) a second subtidal site dominated by Nereocystis luetkeana (Mertens) Postels et Ruprecht, and (3) a floating dock on which the dominant kelp species were Alaria marginata Postels et Ruprecht, Laminaria groenlandica Rosenvinge, and Costaria costata (C. Agardh) Saunders. Most hosts were filamentous [e.g. Pleonosporium vancouverianum (J. Agardh) J. Agardh, Callithamnion acutum Kylin], or polysiphonous [e.g. Polysiphonia paniculata Montagne, Pterosiphonia dendroidea (Montagne) Falkenberg]; however, similar endophytes were also observed in membranous or bladed red algae [e.g. Membranoptera platyphylla (Setchell et Gardner) Kylin, Polyneura latissima (Harvey) Kylin]. Dozens to hundreds of separate kelp gametophytes were associated with single host thalli. In many cases,
the gametophytes developed conspicuous oogonia raised above the thallus surface on characteristic stalks. Presumed zygotes
developed through typical embryonic stages into juvenile sporophytes. We argue that the endophytic habit plays an important
role in the biology of kelp gametophytes.
Received: 5 May 1998 / Accepted: 6 May 1999 相似文献
18.
Geographic variation in polyphenolic levels of Northeastern Pacific kelps and rockweeds 总被引:1,自引:0,他引:1
K. L. Van Alstyne J. J. McCarthy III C. L. Hustead D. O. Duggins 《Marine Biology》1999,133(2):371-379
Brown algal polyphenolic compounds are secondary metabolites whose functions may include protecting plants from pathogens
or damage by UV radiation, and deterring feeding by herbivores. We present here the first analysis of spatial variation (at
scales from tens of meters to hundreds of kilometers) in concentration of these compounds in two orders of brown algae from
the northeastern Pacific Ocean. In kelps (order Laminariales), variation among sites was significant in only 25% of species
examined and was consistent within families (high in the Alariaceae and low in the Laminariaceae and Lessoniaceae). In rockweeds
(order Fucales, family Fucaceae), site variation was high in three of four species examined. Both the proportion of high polyphenolic
kelp species and the magnitude of spatial variation within species from both kelps and rockweeds were much higher than would
have been predicted from previous studies in other regions. In one kelp (Laminaria groenlandica), significant differences between sites occurred at scales of only tens of meters. No latitudinal clines were observed. Differences
in phenolic concentrations of kelps spanned nearly an order of magnitude in one species, Hedophyllum sessile. Phenolic levels were significantly higher in members of the Fucales than the Laminariales, but showed no significant differences
between intertidal and subtidal species.
Received: 22 July 1996 / Accepted: 26 October 1998 相似文献
19.
V. A. Gerard 《Marine Biology》1982,66(1):27-35
An adult giant kelp plant (Macrocystis pyrifera), moved from an inshore kelp forest to an offshore, low-nitrogen environment near Santa Catalina Island, California (USA), maintained growth for 2 wk on internal nitrogen reserves. Frond elongation rates decreased significantly during the third week, and plant growth rate (wet wt) dropped from an initial inshore rate of 3.6 to 0.9% d-1. During this 3 wk period, nitrogen contents and free amino acid concentrations decreased, while mannitol and dry contents increased in frond tissues. After depletion of internal nitrogen reserves, the nitrogen content of lamina and stipe tissues averaged 1.1 and 0.7% dry wt, respectively. The experimental plant was exposed to higher ambient nitrogen concentrations during the last 2 wk. Rates of frond elongation and plant growth increased, but nitrogen content and amino acids in frond tissues remained low. Of the total nitrogen contained in frond tissue of the plant before transplantation, 58% was used to support growth in the absence of significant external nitrogen supply. Amino acids constituted a small proportion of these internal nitrogen reserves. Net movement of nitrogen occurred within large fronds, but not between different frond size classes. The nitrogen content of holdfast tissue remained relatively constant at 2.4% dry wt and accounted for 18 to 29% of the total nitrogen. Holdfast nitrogen was not used to support growth of nitrogen-depleted fronds. In comparison to Laminaria longicruris, which is adapted to long seasonal periods of low nitrogen availability, M. pyrifera has small nitrogen-storage capacity. However, internal reserves of M. pyrifera appear adequate to make nitrogen starvation uncommon in southern California kelp forests. 相似文献
20.
Aquaculture studies have revealed that polyunsaturated fatty acids are critical for maintaining substantial growth, survival
and reproductive rates, and high food conversion efficiencies for a wide variety of marine and freshwater organisms. The aim
of this study was to investigate the gross biochemical and fatty acid composition of both neutral and polar lipid compartments
of the razor clam Solen marginatus throughout embryonic and larval development. High levels of stored reserves in S. marginatus eggs allow a short larval development, lasting only 8 days. The energy required for embryogenesis was obtained from stored
proteins. During larval development from D-shaped veliger until settlement, protein, lipid, and carbohydrate reserves were
indistinctly stored for metamorphosis. Although total lipids increased, fatty acids in both neutral and polar lipids decreased
during embryonic development. The depots allow a short larval development in which settlement is reached with lower amounts
of stored neutral and polar lipids than the contents found in the oocytes. Non-methylene-interrupted dienoic fatty acid levels
were similar to those of some polyunsaturated fatty acids, with increasing percentages at the onset of metamorphosis. This
study indicates that S. marginatus exhibits a different pattern in the use of gross biochemical and fatty acid reserves during larval development compared to
other razor clam and bivalve species, mainly due to the large size of its eggs and the short larval development stage reported
in this species. 相似文献