首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 140 毫秒
1.
Current information on feeding habits of the numerous small invertebrates concentrated among seagrass blades has been inadequate to predict basic food requirements, natural influences of these crowded animals on their shared foods, or the animals’ resulting influences on each other. Apparently detrital food webs in seagrass meadows are reported frequently, but recent data from various seagrass meadows and other environments indicate that such detritus is often refractory to digestion by microorganisms and small invertebrates. A summary of literature on natural feeding habits among common seagrass meadow invertebrates, and detailed analyses of foraging by the commonest invertebrates in NW Gulf of Mexico seagrass meadows, show various degrees of feeding selectivity for epiphytic algae. Different species of epiphytes progressing along a seagrass blade can provide a gradient of food types and abundance for detailed studies on selective feeding. For minimal disturbance to feeding behavior, remote photographic sampling coupled with microacoustic monitoring and immediate, high-resolution gut analyses enable one to compare foraging frequencies on different foods to the available areas of those foods. Such comparisons can be interpreted for evidence of selectivity when an animal forages on a food more frequently than is expected by chance movement over the available areas of food. Feeding appears to be most frequent while the various invertebrates are among epiphytic algae at night, not while they are on bottom detritus. Based on available evidence from various detrital and other food webs, an hypothesis for future research is derived in which particular ephemeral algae are generally selected over other foods, but detritus may be important insteads when particular epiphytic foods are scarce. Even when total detrital foods are common, highly selected foods may be limited among such densely populated animals as in seagrass meadows.  相似文献   

2.
Studies of fish assemblages between natural and newly recolonized (<4 yr) seagrass meadows have shown no significant differences in community composition between meadow types. However, comparison of natural and well-established (31 yr) recolonized seagrass meadows in the Indian River Lagoon, Florida, showed that, although patterns in fish assemblages are complex and not always consistent, differences were evident. Species richness was higher in natural meadows during spring and autumn while density and species richness were higher in recolonized meadows during summer. Juveniles of all but the five most abundant species were more common in one or the other meadow type. Additionally, species composition was distinctly different between recolonized and natural seagrass meadows, as indicated by UPGMA cluster analysis based on the Morisita-Horn similarity index, Spearman'sr s (r s>0.05 in all but one case), and a maximum of only 58.5% species in common. There were also significant differences in the length-frequency distribution for six of seven abundant species. Our results suggest that a well-established recolonized seagrass meadow has the potential to maintain species complements distinct from nearby natural meadows. Reasons for our differing results may include differences in seagrass morphology and collecting techniques between our study and the former studies. Additionally, species may have a longer time to establish specific habitat-use patterns in well-established compared to newly-formed recolonized meadows. Recolonized seagrass meadows appear to be as suitable a habitat as natural meadows for juvenile and small adult fishes.  相似文献   

3.
Spatial and temporal patterns of distribution and abundance were examined for postsettlement sciaenids collected from seagrass meadows in the Aransas Estuary, Texas. Overall, 5443 sciaenid larvae and early juveniles were identified from biweekly epibenthic sled collections taken from August 1994 to August 1995. Eight species were present in seagrass meadows, with five accounting for over 99.9% of sciaenids collected: silver perch (Bairdiella chrysoura), spotted seatrout (Cynoscion nebulosus), spot (Leiostomus xanthurus), Atlantic croaker (Micropogonias undulatus), and red drum (Sciaenops ocellatus). Settlement to seagrass meadows was partitioned temporally with little overlap among the five species. Postsettlers from inshore spawners (B. chrysoura, C. nebulosus, S. ocellatus) inhabited seagrass meadows during the spring and summer, while individuals from offshore spawners (L. xanthurus, M. undulatus) were present in the late fall and winter. Densities ofB. chrysoura, C. nebulosus, S. ocellatus were highest for small individuals (4–8 mm SL) and these taxa remained in seagrass sites through the early juvenile stage. Conversely,L. xanthurus andM. undulatus maintained longer pelagic periods and generally entered seagrass meadows at larger sizes (10–14 mm SL). Moreover, these taxa were only temporary residents of selected seagrass meadows, apparently migrating to alternative habitats shortly after arrival. During peak settlement, mean and maximum densities among species ranged from 0.1 m?2 to 0.8 m?2 and 0.7 m?2 to 23.8 m?2, respectively. Density and mean size of possettlement sciaenids differed significantly between seagrass species (Halodule wrightii, Thalassia testudinum) and among sites within the estuary.  相似文献   

4.
  相似文献   

5.
Seagrasses are marine angiosperms that form extensive submarine meadows in the photic zone where carbonate producing biota dwell as epiphytes on the leaves or as infaunal forms, and act as prolific carbonate sediment factories. Because seagrasses have a low preservation potential and records of exceptionally well‐preserved and plant material from marine settings are rare, these palaeoenvironments are difficult to identify in the rock record. Consequently, sedimentological and palaeontological proxies are the main indicators of the presence of seagrass‐dominated ecosystems. This work investigates the skeletal assemblage of Modern (Maldivian and western Mediterranean) and fossil (Eocene; Apula and Oman carbonate platforms and Oligocene; Malta platform) seagrass examples to characterize the skeletal assemblage of modern and fossil seagrasses. Two main types of grains, calcareous algae and foraminifera, constitute around 50% of the bioclastic sediment in both tropical Maldivian and temperate Mediterranean scenarios. However, in the tropical setting they are represented by green algae (Halimeda), while in the Mediterranean they are represented by corallinacean red algae. In contrast, in the Eocene examples, the foraminifera are the most conspicuous group and the green algae are also abundant. The opposite occurs in the Maltese Chattian, which is dominated by coralline algae (mean 42%), although the foraminifera are still abundant. It is suggested to use the term foralgal to identify the seagrass skeletal assemblage. To discriminate between red algae and green algae dominance, the introduction of the prefixes ‘GA’ (green algae) and ‘RA’ (red algae) is proposed. The investigated examples provide evidence that the green algae–foralgal assemblage is typical of tropical, not excessively dense seagrass meadows, characterized by a well‐illuminated substrate to support the development and calcification of the Halimeda thallus. Contrarily, the red algae‐foralgal assemblage is typical of high density tropical to subtropical seagrass meadows which create very dense oligophotic conditions on the sea floor or in temperate settings where Halimeda cannot calcify.  相似文献   

6.
The nutritional ecology of macroherbivores in seagrass meadows and the roles of grazing by urchins, fishes and green turtles in tropical systems and waterfowl in temperate systems are discussed in this review. Only a few species of animals graze on living seagrasses, and apparently only a small portion of the energy and nutrients in seagrasses is usually channeled through these herbivores. The general paucity of direct seagrass grazers may be a function of several factors in the composition of seagrasses, including availability of nitrogen compounds, presence of relatively high amounts of structural cell walls, and presence of toxic or inhibitory substances. The macroherbivores, however, can have a profound effect on the seagrass plants, on other grazers and fauna associated with the meadow, and on chemical and decompositional processes occurring within the meadow. Grazing can alter the nutrient content and digestibility of the plant, as well as its productivity. Removal of leaf material can influence interrelations among permanent and transient faunal residents. Grazing also interrupts the detritus cycle. Possible consequences of this disruption, either through acceleration or through decreased source input, and the enhancement of intersystem coupling by increased export and offsite fecal production, are discussed. The extent and magnitude of these effects and their ecological significance in the overall functioning of seagrass meadows only can be speculated, and probably are not uniform or of similar importance in both tropical and temperate seagrass systems. However, areas grazed by large herbivores provide natural experiments in which to test hypotheses on many functional relations in seagrass meadows.  相似文献   

7.
We investigated the effects of differing spatial scales of seagrass habitat architecture on the composition and abundance of settling bivalves in a sub-tropical seagrass community. The density of newly settled bivalves was generally greater atThalassia testudinum grass bed edge (<1 m) compared to interior portions of the bed (>10 m). Deviation from this generalized pattern occurred when high densities of newly settled tulip mussels (Modiolus americanus) were recorded from the interior of the meadow, associated with aggregations of adult mussels. Bivalve settling densities appear to reflect settlement shadows of passively delivered larvae, bedload transport of newly settled individuals from unvegetated regions, as well as gregarious settlement among adult conspecifics. We also investigated the impact of seagrass patch shape and size on settlement by using artificial seagrass units (ASU) in separate short-term and long-term experiments. We found a positive relationship between ASU perimeter and bivalve abundance, suggesting that larval encounter rates with seagrass habitat may determine initial settlement patterns. Using ASUs we also investigated the relative role seagrass epiphytes play in determining the density of settling bivalves. Results showed greater settling densities where epiphytic secondary structure was elevated compared to controls, and bivalve density was significantly greater when ASUs were fouled with a natural community of epiphytes, suggesting that both microstructure and biofilms positively influenced bivalve settlement. We conclude that structural components of seagrass habitats increase bivalve settlement at multiple spatial scales, including epiphytic micro-structure, small-scale patch shape and size, and large-scale within habitat differences.  相似文献   

8.
Recolonization dynamics from disturbance on a Philippine mixed seagrass meadow, containing species spanning more than 10-fold in rhizome elongation rates and reproductive effort, was examined by following the recovery of a 1,200 m2 gap over 2.5 yr. The objective was to assess the contribution of contrasting species to the recovery process and to evaluate the importance of sexual versus vegetative colonization. Large, slow-growing species,Thalassia hemprichii andEnhalus acoroides, that produce large, broadly-dispersed seeds dominated sexual colonization with a total of 2,643 and 210 seedlings, respectively, recruiting to the area. Despite very rapid turnover of sexual recruits, the high frequency of seedling establishment ensured successful development of new patches in areas devoid of vegetation, leading to a scattered and evenly distributed presence of vegetation inside the gap. The small seagrass speciesCymodocea rotundata andHalodule uninervis, characterized by fast rhizome elongation rates but low reproductive output and limited seed dispersal, were the major contributors to the overall 450 m2 increase in vegetation cover through fast lateral extension (144±6 cm yr−1) from meadow edge and surviving patches, forming a compact vegetation cover in one edge of the denuded area. We conclude that contrasting recruitment strategies in the mixed-species seagrass community examined have implications for colonization potential at different spatial scales. Fast clonal growth is only an efficient mechanism for colonization of disturbances within established meadows (small gaps), whereas the large species, which combined high reproductive output with high seed dispersal capacity, may act to accelerate the colonization process in large gaps or distant from established meadows.  相似文献   

9.
In the late 1970s and early 1980s an inventory of seagrass distribution in southeast Australia was made from multiscale aerial photographs using a simple analog mapping method, referred to here as theCamera lucida technique. Four priority estuaries were remapped in 2003, also using multi-scale aerial photographs, but using a geographic information system (GIS)-based analog mapping technique. We quantified the degree of error that arose when estimates of seagrass distribution were compared for the two techniques be ressessing. with GIS, the same aerial photographs used earlier for four estuaries: Port Hacking, Bermagui River, Merimbula Lake, and St Georges Basin.Camera lucida produced a larger estimate of total seagrass area than GIS in all four locations: 8% of total seagrass area or 12.9 ha in Port Hacking, 15% or 5 ha in Bermagui River, 20% or 38.0 ha in Merimbula Lake, and 243% or 502.2 ha in St Georges Basin. The consistent and moderate discrepancy in Port Hacking, Bermagui River, and Merimbula Lake was attributed mainly to differences betweenCamera lucida and GIS, such as the tendency ofCamera lucida to overestimate seagrass area by amalgamating disjunct seagrass patches into continuous meadows. The large discrepancy at St Georges Basin was attributed to interoperator error; i.e., the operators who mapped photographs taken in 1979 had widely differing interpretations of the aerial photographs. A 20-yr trend was calculated for each estuary using either theCamera lucida or revised GIS value as the start point. Perceived management status of the seagrass depended greatly on the initial data used. In St Georges Basin, a catastrophic decline (65%, 553.9 ha) occurred based on theCamera lucida-GIS comparison but only a small decline (14.7%, 51.8 ha) when all photos were GIS assessed, In view of the technical developments in habitat mapping, evaluation of change in seagrass abundance using remote sensing needs an assessment of intra-operator error, inter-operator error, and systemic error before maps produced by superseded technology are considered useful baselines.  相似文献   

10.
Seagrass meadows are often cited as important nursery areas for newly settled red drum even though many estuaries, such as Galveston Bay, Texas, support large numbers of red drum and have limited seagrass cover, suggesting the use of alternate nursery areas. We examined patterns of habitat use for newly settled red drum at six sampling areas in Galveston Bay; two areas had seagrass beds and four areas had no seagrass. We measured densities in different habitat types using epibenthic sleds and enclosure samplers. Peak recruitment of young red drum to the estuary occurred during September through December. Highest densities of new settlers were found in seagrass meadows (primarilyHalodule wrightii), but when seagrass was absent, the highest densities of red drum occurred along theSpartina alterniflora marsh edge interface. Densities were relatively low on nonvegetated bottom away from the marsh edge. We also examined density patterns in other habitat types at selected sampling areas and found no red drum within marsh vegetation away from the marsh edge interface (5 and 10 m into the marsh interior). Oyster reefCrassostrea virginica was sampled using lift nets, and we found no red drum using this habitat, although adjacent seagrass and marsh interface habitats were used. Even though red drum densities in marsh edge were low relative to seagrass, the large areal extent of marshes in the bay complex probably makes marsh edge the most important nursery habitat for red drum in Galveston Bay.  相似文献   

11.
Grazing by small epifauna on live seagrass leaves was formerly viewed as unimportant in controlling plant biomass and growth, instead researchers focused on the indirect benefits of small invertebrates that crop algal competitors. Recent evidence shows that the emerald nerite Smaragdia viridis preferentially ingests seagrass leaf tissue. In contrast, the button snail Modulus modulus feeds on epiphytes and periphyton coating the leaves. We conducted laboratory microcosm and field experiments to investigate how the different feeding preferences of these seagrass-associated snails affect turtlegrass Thalassia testudinum primary production. Data revealed that after 24 h S. viridis reduced foliar biomass (25%) and chlorophyll (30%) and injured the equivalent of 50% of daily seagrass growth per shoot. Conversely, M. modulus did not affect these variables. Our results emphasize that in subtropical seagrass communities not all small epifauna browse off leaf surfaces and some can have important direct negative impacts on their seagrass host.  相似文献   

12.
Direct census of shoots tagged in permanent plots was used to assess the present (2000–2002)Posidonia oceanica population dynamics in 25 meadows along the Spanish Mediterranean Coast. Shoot density ranged from 154±8 to 1,551±454 shoots m−2, absolute shoot mortality from 5±0 to 249±53 shoots m−2 yr−1, and absolute shoot recruitment from <5 ±1 to 62±42 shoots m−2yr−1. Specific shoot mortality and recruitment rates, which are mathematically and statistically (p>0.05) independent of shoot density, varied from 0.015±0.006 to 0.282±0.138 yr−1 and 0.018±0.005 to 0.302±0.093 yr−1, respectively. Absolute shoot mortality rate was scaled to shoot density (Pearson correlation, r=0.78, p<0.0001), and variability in specific shoot recruitment rate was partially due to differences in the percentage of growing apexes, which produce most of the recruits within the population (Pearson correlation, r=0.50, p<0.001), demonstrating the existence of structural constraints on shoot demography. Shoot half-life was estimated to range from 2.5 to 60.4 yr and meadow turnover times between 6.7 yr and more than a century, provided current estimates of shoot mortality, recruitment rates, and density remain uniform. There were differences in shoot mortality and recruitment at the regional scale, with the meadows developing along the coast of the Spanish mainland experiencing the highest shoot mortality (Tukey test, p<0.05) and tending to exhibit the highest shoot recruitment. The low shoot recruitment did not balance shoot mortality in most (60%) of the meadows, showing a prevalence of declining populations among the 25 meadows studied (Wilcoxon ranked sign test, p<0.0005). This study demonstrates the power of direct census of seagrass shoots in permanent plots to evaluate the present status of seagrass meadows, to detect on-going population decline, and to provide some insight onto the possible factors involved. The incorporation of direct census of seagrass meadows to monitoring programs will help provide the early-warning signals necessary to support management decisions to conserve seagrass meadows.  相似文献   

13.
Cyclonic storms are large-scale disturbances which cause extensive damage in coastal ecosystems. On 25 November 2013, Cyclone Lehar made a significant impact on the coastal areas of Andaman and Nicobar Islands. We observed the pre- and post-Lehar cyclonic effects on the seagrass meadows at Ross and Smith Island, North Andaman. The study indicates that the seagrass meadows are composed of Halodule uninervis, Halophila ovalis, Halodule pinnifolia and Thalassia hemperichii species. Seagrass beds of approximately 1.96 ha (approx. 63 %) were destroyed in the cyclone.  相似文献   

14.
We examined the spatial extent of nitrogen (N) and phosphorus (P) limitation of each of the major benthic primary producer groups in Florida Bay (seagrass, epiphytes, macroalgae, and benthic microalgae) and characterized the shifts in primary producer community composition following nutrient enrichment. We established 24 permanent 0.25-m2 study plots at each of six sites across. Florida Bay and added N and P to the sediments in a factorial design for 18 mo. Tissue nutrient content of the turtlegrassThalassia testudinum revealed a spatial pattern in P limitation, from severe limitation in the eastern bay (N:P>96:1), moderate limitation in two intermediate sites (approximately 63:1), and balanced with N availability in the western bay (approximately 31:1). P addition increasedT. testudinum cover by 50–75% and short-shoot productivity by up to 100%, but only at the severely P-limited sites. At sites with an ambient N:P ratio suggesting moderate P limitation, few seagrass responses to nutrients occurred. Where ambientT. testudinum tissue N:P ratios indicated N and P availability was balanced, seagrass was not affected by nutrient addition but was strongly influenced by disturbance (currents, erosion). Macroalgal and epiphytic and benthic microalgal biomass were variable between sites and treatments. In general, there was no algal overgrowth of the seagrass in enriched conditions, possibly due to the strength of seasonal influences on algal biomass or regulation by grazers., N addition had little effect on any benthic primary producers throughout the bay. The Florida Bay benthic primary producer community was P limited, but P-induced alterations of community structure were not uniform among primary producers or across Florida Bay and did not always agree with expected patterns of nutrient limitation based on stoichiometric predictions from field assays ofT. testudinum tissue, N:P ratios.  相似文献   

15.
In many areas of the North American mid-Atlantic coast, seagrass beds are either in decline or have disappeared due, in part, to high turbidity that reduces the light reaching the plant surface. Because of this reduction in the areal extent of seagrass beds there has been a concomitant diminishment in dampening of water movement (waves and currents) and sediment stabilization. Due to ongoing declines in stocks of suspension-feeding eastern oysters (Crassostrea virginica) in the same region, their feeding activity, which normally serves to improve water clarity, has been sharply reduced. We developed and parameterized a simple model to calculate how changes in the balance between sediment sources (wave-induced resuspension) and sinks (bivalve filtration, sedimentation within seagrass beds) regulate turbidity. Changes in turbidity were used to predict the light available for seagrass photosynthesis and the amount of carbon available for shoot growth. We parameterized this model using published observations and data collected specifically for this purpose. The model predicted that when sediments were resuspended, the presence of even quite modest levels of eastern oysters (25 g dry tissue weight m?2) distributed uniformly throughout the modeled domain, reduced suspended sediment concentrations by nearly an order of magnitude. This increased water clarity, the depth to which seagrasses were predicted to grow. Because hard clams (Mercenaria mercenaria) had a much lower weight-specific filtration rate than eastern oysters; their influence on reducing turbidity was much less than oysters. Seagrasses, once established with sufficiently high densities (>1,000 shoots m?2), damped waves, thereby reducing sediment resuspension and improving light conditions. This stabilizing effect was minor compared to the influence of uniformly distributed eastern oysters on water clarity. Our model predicted that restoration of eastern oysters has the potential to reduce turbidity in shallow estuaries, such as Chesapeake Bay, and facilitate ongoing efforts to restore seagrasses. This model included several simplifiying assumptions, including that oysters were uniformly distributed rather than aggregated into offshore reefs and that oyster feces were not resuspended.  相似文献   

16.
When compared with nearby unvergetated areas, seagrass meadows contain a dense and strikingly rich assemblage of vertebrates and invertebrates. Most recent literature has focused on evaluating the role of predation in structuring seagrass faunal communities; however, habitat complexity, abundance of food and sediment stability may also be important. This paper summarizes studies relating predator-prey relationships to different features of the seagrass system. This review suggests that the abundance of many species, both epifauna and infauna, is positively correlated with two distinct aspects of plant morphology: 1) the root-rhizome mat, and 2) the plant canopy. A scheme was developed that defines the conditions under which any particular species will be abundant or rare in a seagrass assemblage. This scheme is based on prey and predator characteristics (e.g., epifaunal vs. infaunal, tube-dweller vs. nontube dweller, burrowers vs. nonburrowers, and large vs. small as adult) and on characteristics of the seagrasses (e.g., leaf morphology, shoot density, shoot biomass, structural complexity of the meadow, and root-rhizome density and standing crop).  相似文献   

17.
Organic carbon from sediments collected in Texas seagrass meadows was enriched in 13C by an average of 6.6% relative to organic carbon from offshore sediments. Within the South Texas hay system examined. δ13C values became increasingly more typical of offshore sediments with increasing distance from seagrass meadows. This permits the use of carbon isotope data as a measure of the relative contributions of seagrasses and plankton to sedimentary organic matter.  相似文献   

18.
The clonal growth of 9 seagrass species was modeled using a simulation model based on observed clonal growth rules (i.e., spacer length, rhizome elongation rates, branching rates, branching angle) and shoot mortality rates for seagrass species. The results of the model confirmed the occurrence of complex, nonlinear growth of seagrass clones derived from internal dynamics of space occupation. The modeled clones progressed from a diffuse-limited aggregation (DLA), dendritic growth, identified with a guerrilla strategy of space occupation, to a compact (Eden) growth, comparable to the phalanx strategy of space occupation, once internal recolonization of gaps, left by dead shoots within the clone, begins. The time at which seagrass clones shifted from diffuse limited to compact growth was predictable from the branching angle and frequency of the species and varied from 1 yr to several decades among species. As a consequence the growth behavior and the apparent growth strategy of the species changes with the development of the clones. The results of the model demonstrate that the emergent complexity of seagrass clonal growth is contained within the simple set of growth rules that can be used to represent clonal growth.  相似文献   

19.
The combined effects of nutrient enrichment and grazing by isopods and amphipods on abundances of seagrass epiphytes were tested inZostera marina L. (eelgrass) microcosms. Using epifluorescence microscopy, densities of epiphytic diatoms, cyanobacteria, heterotrophic flagellates, and heterotrophic bacteria were enumerated after 1 mo and 2 mo of treatment. In general, numbers of diatoms decreased, in the presence of grazers and showed little response to nutrient enrichment, whereas numbers of cyanobacteria increased with nutrient enrichment and showed little response to grazing. Thus, macrofaunal grazing maintained a photoautotrophic community domainated by cyanobacteria, particularly under nutrient enriched conditions. Following 2 mo of treatment, dense macroalgal growth under nutrient-enriched conditins with grazers absent appeared to limit populations of both epiphytic autotrophs. Patterns of abundance of heterotrophic bacteria suggested that the original bacteria population was nutrient limited. Bacteria populations may have been limited by organic carbon supplies at the end of the experiment. Abundances of heterotrophic flagellates and bacteria were strongly correlated on both sampling dates. Results suggest that heterotrophic flagellates might serve as a link between heterotrophic bacterial production and higher trophic levels in seagrass epiphyte food webs.  相似文献   

20.
Fish and decapod entry into small (1.5 m2) artificial seagrass habitats positioned on an open sand area in a New Jersey estuary was examined to determine if immigration varied between day and night. To encounter the structured habitats, colonizers had to cross an expanse of bare sand, with its presumably higher predation risk. Contrasts in abundance in the artificial seagrass plots between dawn and dusk indicated higher nighttime immigration for four species, including the fishesFundulus heteroclitus andMyoxocephalus aenaeus, and the caridean shrimpsPalaemonetes vulgaris andHippolyte pleuracanthus. Size-frequency distributions of colonizers varied between day and night for two fish species,Menidia menidia andSyngnathus fuscus, with a greater proportion of smaller individuals immigrating to the artificial seagrass at night.Callinectes sapidus also displayed a diel contrast in size distribution but, for this species, proportionately more small individuals colonized the plots during the day. We suggest that diel variability in predation risk and/or diel patterns in motor activity may be responsible for these patterns in immigration.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号