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1.
We examined the spatial and temporal variability in drift macroalgal abundance in two seagrass dominated estuarine systems
on the Texas coast: Redfish Bay (in the Copano-Aransas Estuary) and Lower Laguna Madre. Measurements of benthic macroalgal
variability were made in conjunction with a suite of biotic (seagrass biomass, percent cover, blade width and length, shoot
density, epiphyte biomass, seagrass blade C:N ratios, and drift macroalgal abundance and composition) and abiotic (inorganic
nitrogen and phosphorus concentrations, chlorophylla, total suspended solids, light attenuation, salinity, temperature, total organic carbon and porewater NH4
+) indicators. All parameters were measured at 30 sites within each estuary semiannually from July 2002 to February 2004. Principal
components analysis (PCA) was used to examine relationships between drift macroalgal abundance and biotic and abiotic parameters.
In both Redfish Bay and Lower Laguna Madre, drift macroalgal distribution was widespread, and during three of four sampling
periods, abundance was equal to abovegro und biomass ofThalassia testudinum, the dominant seagrass. Drift macro algal abundance was highly variable within sites, between sites, and between seasons
in both estuaries. No significant differences in drift macroalgal abundance were found between Redfish Bay and Lower Laguna
Madre. In Redfish Bay, drift macroalgae (90.1±10.2 gm−2) tended to accumulate in bare patches within seagrass beds. In Lower Laguna Madre, drift macroalgae (72.7±10.7 gm−2) tended to accumulate in areas of dense seagrass cover rather than in bare areas. We found no relationship between drift
macroalgal abundance and low (<2μM) water column nutrient concentrations, and although several of our measured parameters
were related to drift macroalgal abundance, none alone sufficiently explained the variability in abundance noted between the
two estuarine systems. The contrasting patterns of macroalgal accumulation between Redrish Bay and Lower Laguna Madre likely
reflect differences in water circulation characteristics between the two regions as dictated by local physiography, in cluding
the shape and orientation of the lagoons, with seasonal variations in macroalgal abundance related to changes in freshwater
inflow and nutrient loading. 相似文献
2.
This paper examines how perennial Aster tripolium and annual Salicornia procumbens salt marshes alter the biomass, density, taxon diversity, and community structure of benthic macrofauna, and also examines
the role of elevation, sediment grain size, plant cover, and marsh age. Core samples were collected on a fixed grid on an
intertidal flat in the Westerschelde estuary (51.4° N, 4.1° E) over 5 years (2004–2008) of salt marsh development. In unvegetated
areas, macrobenthic biomass, density, and taxon diversity were highest when elevation was highest, benthic diatoms were most
abundant, and sediment median grain size was smallest. In contrast, in salt marsh areas, macrobenthic biomass and taxon diversity
increased with median grain size, while the effects of elevation and diatom abundance on macrobenthic biomass, density, and
diversity were not significant. In fine sediments, macrofaunal community structure in the salt marsh was particularly affected;
common polychaetes such as Nereis diversicolor, Heteromastus filiformis, and Pygospio elegans had low abundance and oligochaetes had high abundance. Marsh age had a negative influence on the density of macrofauna, and
A. tripolium stands had lower macrofaunal densities than the younger S. procumbens stands. There were no significant effects of marsh age, plant cover, and vegetation type on macrobenthic biomass, taxon diversity,
and community structure. The results highlight that ecosystem engineering effects of salt marsh plants on macrofauna are conditional.
Organic enrichment of the sediment and mechanical hindering of macrofaunal activity by plant roots are proposed as plausible
mechanisms for the influence of the salt marsh plants on macrofauna. 相似文献
3.
Richard E. Matheson David K. Camp Susan M. Sogard Kimberly A. Bjorgo 《Estuaries and Coasts》1999,22(2):534-551
The fauna of seagrass-covered mud banks in Florida Bay, documented in the mid 1980s prior to recent seagrass die-off, phytoplankton blooms, and other ecosystem changes, was reexamined in the mid 1990s for faunal changes that might be associated with environmental perturbations. During both decades, decapod crustaceans and fishes were collected with 1-m2 throw traps from seagrass beds at six sites that differ in the amount of freshwater and/or marine influence and in seagrass community metrics. The most common faunal changes were declines in seagrass-canopydwelling forms and increases in benthic forms. At three sites with relatively lush seagrass meadows, above-ground seagrass standing crop declined and abundance of the benthic predatory fishOpsanus beta increased. The degree of faunal change among these sites appeared to be related either to salinity variability or to the degree of exposure to the ecosystem changes that have taken place in Florida Bay. At two sites with poorly developed seagrass meadows, seagrass standing crop and canopy height did not change significantly between decades, but there was an increase in shoot density and total leaf area. The animal communities at these sites were characterized by significant increases in the abundance of benthic crustaceans. At the site on the edge of Rankin Lake, the basin where seagrass die-off was first observed in Florida Bay during 1987, seagrass standing crop, canopy height, shoot density, and leaf area declined significantly between decades, but species richness of both crustaceans and fishes increased. The abundance of canopy-dwelling crustaceans and fishes declined markedly at this site, whereas the abundance of benthic forms less dependent on seagrass cover generally increased. In retrospect, we believe the fauma at this site during the 1980s, characterized by high productivity but few species, was already showing signs of the stresses that led to the seagrass die-off that began in 1987. 相似文献
4.
Hilary A. Neckles Blaine S. Kopp Bradley J. Peterson Penelope S. Pooler 《Estuaries and Coasts》2012,35(1):23-46
We evaluated a hierarchical framework for seagrass monitoring in two estuaries in the northeastern USA: Little Pleasant Bay,
Massachusetts, and Great South Bay/Moriches Bay, New York. This approach includes three tiers of monitoring that are integrated
across spatial scales and sampling intensities. We identified monitoring attributes for determining attainment of conservation
objectives to protect seagrass ecosystems from estuarine nutrient enrichment. Existing mapping programs provided large-scale
information on seagrass distribution and bed sizes (tier 1 monitoring). We supplemented this with bay-wide, quadrat-based
assessments of seagrass percent cover and canopy height at permanent sampling stations following a spatially distributed random
design (tier 2 monitoring). Resampling simulations showed that four observations per station were sufficient to minimize bias
in estimating mean percent cover on a bay-wide scale, and sample sizes of 55 stations in a 624-ha system and 198 stations
in a 9,220-ha system were sufficient to detect absolute temporal increases in seagrass abundance from 25% to 49% cover and
from 4% to 12% cover, respectively. We made high-resolution measurements of seagrass condition (percent cover, canopy height,
total and reproductive shoot density, biomass, and seagrass depth limit) at a representative index site in each system (tier
3 monitoring). Tier 3 data helped explain system-wide changes. Our results suggest tiered monitoring as an efficient and feasible
way to detect and predict changes in seagrass systems relative to multi-scale conservation objectives. 相似文献
5.
S. J. Turner J. E. Hewitt M. R. Wilkinson D. J. Morrisey S. F. Thrush V. J. Cummings G. Funnell 《Estuaries and Coasts》1999,22(4):1016-1032
The spatial arrangement of seagrass beds varies from scales of centimeters to meters (rhizomes, shoot groups), meters to tens of meters (patches), to tens of meters to kilometers (seagrass landscapes). In this study we examine the role of patch scale (patch size, seagrass % cover, seagrass biomass), landscape scale (fractal geometry, patch isolation) and wave exposure (mean wind velocity and exceedance) variables in influencing benthic community composition in seagrass beds at three intertidal sites in northern New Zealand (two sites in Manukau Harbour and one site in Whangapoua Harbour). Analysis of univariate community measures (numbers of individuals and species, species richness, diversity and evenness) and multivariate analyses indicated that there were significant differences in community composition inside and outside of seagrass patches at each of the three sites. Partialling out the spatial and temporal components of the ecological variation indicated that seagrass patch variables explained only 3–4% of the patch scale variation in benthic community composition at each of the sites. The temporal component was more important, explaining 12–14% of the variation. The unexplained variation was high (about 75%) at all three sites, indicating that other factors were influencing variation in community composition at the scale of the patches, or that there was a large amount of stochastic variation. Landscape and wave exposure variables explained 62.5% of the variation in the species abundance data, and the unexplained variation at the landscape level was correspondingly low (12%). Canonical correspondence analysis produced an ordination that suggests that, while mean wind velocity and exceedance were important in explaining the differences between the communities in the two harbours, spatial patterning of the habitat, primarily fractal dimension, and secondarily patch isolation (or some factors that were similarly correlated), were important in contributing to variability in community composition at the two sites in Manukau Harbour. This study suggests that spatial patterning of seagrass habitat at landscape scales, independent of the patch scale characteristics of the seagrass beds, can affect benthic community composition. Community composition inside and outside seagrass habitats involves responses to seagrass bed structure at a series of hierarchical levels, and we need to consider more than one spatial scale if we are to understand community dynamics in seagrass habitats. 相似文献
6.
This study was designed to investigate seasonal changes on food available for benthic consumers in relation to tidal levels
and sediment depth in an estuarine beach. The relationships between the biochemical characteristics of sedimentary organic
matter and benthic macrofauna were analyzed quarterly over 2 years (from January 1997 to January 1999), in an estuarine soft
intertidal zone from the NW coast of Spain (42°64′04″N, 8°88′36″W). Sediment samples were collected to provide a two-dimensional
view of macroinfauna distribution in the intertidal zone and its relationship with the quantity and quality of the organic
matter. The nutritional value of organic matter (i.e., lipid, protein, and carbohydrate) and the content of chlorophyll a of the sediment were measured. Macrofaunal assemblages and food availability in the sediment were studied at three tidal
levels on the shore: two intertidal and one supratidal. Macroinfauna and biochemical compounds showed a clear vertical stratification
with the highest macrofaunal abundance at the superficial layer of the sediment, where redox potential discontinuity was also
observed. Crustaceans were found mainly inhabiting the supratidal level of the estuarine beach, while polychaetes and mollusks
occupied the intertidal level. Food availability, measured as biopolymeric carbon, and also chlorophyll a from the sediment were better related to macroinfauna abundance, biomass, and abundance of main taxonomic groups. Macrofauna
assemblages showed particular distribution in both vertical and horizontal ranges suggesting specific preferences to several
abiotic factors. No clear seasonal pattern was found in macrofauna and sedimentary organic characteristics suggesting that
macrofaunal assemblages are controlled by complex and unpredictable factors, including small-scale changes in substrate and
hydrological characteristics. 相似文献
7.
Coastal lagoons are ubiquitous along coastlines worldwide. Here, we compare the abundance of epifauna, seagrass-associated macroinvertebrates, and small fish across a gradient of seagrass cover in shallow coastal lagoons of the northern Gulf of Mexico. Two of the lagoons had little or no seagrass cover (0–18.8 %), and four had high cover (83.8–97.5 %). All of the lagoons were partially covered with fringing marsh. We hypothesized that, due to habitat redundancy between seagrass beds and fringing marshes, seagrass-associated fish and macroinvertebrates would not be largely reduced despite the large differences in seagrass cover among the lagoons. Our results support this hypothesis. For most sampling dates, we did not find significant differences in fish and macroinvertebrate abundance among the lagoons and, when we did, several highly vegetated lagoons did not have larger abundances than sparsely vegetated lagoons. The extreme shallowness of the lagoons studied (<1 m) may also provide further protection from large predatory fishes in the absence of seagrasses. Our results also suggest that marsh detritus, by providing habitat for epifauna and helping maintain prey availability, may further temper reductions in seagrass-associated fishes and macroinvertebrates following seagrass decline. The results highlight the importance of marsh-bordered, shallow lagoons as habitat for small fish and macroinvertebrates regardless of seagrass cover. This study contributes to the characterization of habitat redundancy in coastal ecosystems and pinpoints the importance of considering all habitats in concert for the proper understanding and management of coastal ecosystems. 相似文献
8.
A broad-scale survey of seagrass species composition and distribution along Florida's central Gulf Coast (known as the Big
Bend region) was conducted in the summer of 2000 to address growing concerns over the potential effects of increased nutrient
loading from adjacent coastal rivers. Iverson and Bittaker (1986) originally surveyed seagrass distribution in this region
between 1974–1980. We revisited 188 stations from the original survey, recording the presence or absence of all seagrass species.
Although factors such as accuracy of station relocation, differences in sampling effort among studies, and length of time
between surveys preclude statistical comparisons, several interesting patterns emerged. While the total number of stations
occupied by the three most common seagrass species,Thalassia testudinum, Syringodium filiforme, andHalodule wrightii, was similar between the two time periods, we observed a change in the number of records of each species as well as changes
in distribution with depth.T. testudinum andHalophila engelmanni occurrence declined in the deepest areas of the region, while the number of stations occupied byS. filiforme andH. wrightii increased in nearby areas. We observed several localized areas of seagrass loss, frequently associated with the mouths of
coastal rivers. These results suggest that increased nutrient loading to coastal rivers that discharge into the Big Bend area
may be affecting seagrasses by increasing phytoplankton abundance in the water column, thus changing water clarity characteristics
of the region. 相似文献
9.
D. Lirman T. Thyberg R. Santos S. Schopmeyer C. Drury L. Collado-Vides S. Bellmund J. Serafy 《Estuaries and Coasts》2014,37(5):1243-1255
Nearshore benthic habitats of Biscayne Bay fit the prediction of communities at risk due to their location adjacent to a large metropolitan center (Miami) and being influenced by changes in hydrology through the activities of the Comprehensive Everglades Restoration Plan (CERP). We examine whether the proposed programmatic expansion of mesohaline salinities through the introduction of additional fresh water would result in: (1) increases in seagrass cover; (2) expansion in the distribution and cover of Halodule; and (3) a reduction in the dominance of Thalassia, as hypothesized by CERP. Seagrasses were present at 98 % of sites where they covered 23 % of the bottom. Salinity was the only physical variable with a significant relationship to the occurrence of all SAV taxa. Occurrence of Thalassia, Halimeda, and Penicillus increased significantly with increasing salinity, but Halodule, Syringodium, Laurencia, Udotea, Batophora, Caulerpa, and Acetabularia showed a significant negative relationship with salinity. Mesohaline habitats had higher cover of seagrass and Halodule, and reduced dominance by Thalassia. Thus, we expect increases in the extent of mesohaline habitats to achieve the established CERP goals. We also examined the nutrient content of seagrass blades to evaluate whether: (1) nutrient availability is higher in areas close to canal discharges; and (2) tissue nutrient levels are related to seagrass abundance. The low abundance of Thalassia along the shoreline is not only due to its exclusion from low-salinity environments but also by higher nutrient availability that favors Halodule. Percent N and P, and N:P ratios in seagrass tissue suggest that Biscayne Bay receives high N inputs and is P-limited. Thus, increased P availability may facilitate an expansion of Halodule. The data presented suggest that increased mesohaline salinities will increase seagrass abundance and support co-dominance by Halodule and Thalassia as hypothesized, but raise concerns that current high N availability and increases in P may prompt a shift away from seagrass-dominated to algal-dominated communities under scenarios of enhanced fresh water inputs. 相似文献
10.
Anna R. Armitage Thomas A. Frankovich Kenneth L. Heck James W. Fourqurean 《Estuaries and Coasts》2005,28(3):422-434
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
11.
Margaret O. Hall Michael J. Durako James W. Fourqurean Joseph C. Zieman 《Estuaries and Coasts》1999,22(2):445-459
The Florida Bay ecosystem has changed substantially in the past decade, and alterations in the seagrass communities have been particularly conspicuous. In 1987 large areas ofThalassia testudinum (turtlegrass) began dying rapidly in western Florida Bay. Although the rate has slowed considerably, die-off continues in many parts of the bay. Since 1991, seagrasses in Florida Bay have been subjected to decreased light availability due to widespread, persistent microalgal blooms and resuspended sediments. In light of these recent impacts, we determined the current status of Florida Bay seagrass communities. During the summer of 1994, seagrass species composition, shoot density, shoot morphometrics, and standing crop were measured at 107 stations. Seagrasses had been quantified at these same stations 10 yr earlier by Zieman et al. (1989).T. testudinum was the most widespread and abundant seagrass species in Florida Bay in both 1984 and 1994, and turtlegrass distribution changed little over the decade. On a baywide basis,T. testudinum density and biomass declined significantly between surveys; mean short-shoot density ofT. testudinum dropped by 22% and standing crop by 28% over the decade.T. testudinum decline was not homogeneous throughout Florida Bay; largest reductions in shoot density and biomass were located principally in the central and western bay. Percent loss ofT. testudinum standing crop in western Florida Bay in 1994 was considerably greater at the stations with the highest levels of standing crop in 1984 (126–215 g dry wt m−2) than at the stations with lower levels of biomass. While turtlegrass distribution remained consistent over time, both the distribution and abundance of two other seagrasses,Halodule wrightii andSyringodium filiforme, declined substantially between 1984 and 1994. Baywide,H. wrightii shoot density and standing crop declined by 92%, andS. filiforme density and standing crop declined by 93% and 88%, respectively, between surveys. Patterns of seagrass loss in Florida Bay between 1984 and 1994 suggest die-off and chronic light reductions were the most likely causes for decline. If die-off and persistent water-column turbidity continue in Florida Bay, the long-term future of seagrasses in the bay is uncertain. 相似文献
12.
P. Sheridan 《Estuaries and Coasts》2004,27(5):781-792
Structural equivalence between seagrass restoration sites and adjacent natural seagrass beds on the mid Texas coast was assessed
six times between April 1995 and May 1997. Throw traps and corers were used for quantitative sampling. Restoration sites were
2.7 to 6.6 yr old when first sampled and 3.7 to 8.2 yr old when last sampled. There were few significant differences in water
column, seagrass, or sediment characteristics, in fish and decapod (nekton) densities, or in nekton and benthos community
compositions between restored and natural seagrass habitats at any time during the study period. Differences in densities
of dominant benthic invertebrates were regularly observed, with greater densities of more taxa observed in natural seagrasses
than in restored beds. Densities of Class Oligochaeta and the polychaetePrionospio heterobranchiata are proposed as potential indicators of structural equivalence in restored seagrasses. This study indicates that seagrass
restorations in the vicinity of Corpus Christi, Texas, exhibit minimal quantitative differences in community structure (except
for benthos) relative to adjacent natural seagrass beds after 3 to 5 yr. 相似文献
13.
Variation with Depth in Temperate Seagrass-Associated Fish Assemblages in Southern Victoria,Australia 总被引：1，自引：0，他引：1
Neil Hutchinson Gregory P Jenkins Andrew Brown Timothy M Smith 《Estuaries and Coasts》2014,37(4):801-814
Variability in the abundance and distribution of seagrass-associated fish assemblages was examined at different depths in a temperate bay in southern Australia. Depth differences in seagrass-associated fish assemblages are poorly known but this information is critical given that seagrass loss can occur at specific depths depending on the cause. Overall, 69 species of fish from 26 families were recorded, with higher species richness in shallow than deep beds, with 12 species found only in deep beds and 22 species found only in shallow beds. While the total fish abundance (i.e. abundance of all species recorded) varied between years and seasons, and to some extent between sites, it was significantly higher in shallow than deep seagrass beds in the majority of cases. Although there was some variation between sites, seagrass tended to be longer and have a higher biomass in shallow than deep beds during both spring and autumn throughout the study. A positive relationship between seagrass biomass/length and total fish abundance/species richness was apparent. Assemblage structure tended to be distinct at each depth, with the largest species recorded in shallow seagrass. Large numbers of small schooling fish, such as atherinids, dominated in shallow seagrass but were not found in deep seagrass. Loss of seagrass could therefore have varying implications for distinct assemblages found at different depths. 相似文献
14.
15.
A eutrophication gradient was assembled from four spring-fed estuaries and four surface-fed estuaries to determine whether changes in zooplankton and hyperbenthos abundance along the gradient were gradual or abrupt. For 1 year in each estuary, monthly faunal surveys were conducted during nighttime flood tides using oblique plankton-net tows, producing abundance data for 316 taxa. Indicator taxa for the spring-fed and surface-fed groups were identified from a combination of abundance and encounter frequencies. Seventeen of the 20 strong indicator taxa for the spring-fed group (85 %) were benthic, whereas 10 of the 13 strong indicators for the surface-fed group (77 %) were plankton-oriented. The eight communities were ordinated by canonical analysis of principal coordinates (CAP); the estuarine faunas were found to be uniquely distributed along the principal CAP axis. Success of blind reclassification of plankton samples to their respective estuaries of origin ranged from 75 to 100 % (mean, 91 %). Given the assembled gradient was composed of distinctive communities that were distributed across a broad range of trophic states, the transition between benthic and plankton-oriented indicators was investigated and found to be abrupt, with strong shifts occurring nearer the oligotrophic end of the gradient. The CAP ordination agreed with trends in light attenuation, but not dissolved oxygen. We conclude that the abrupt faunal shifts were likely related to differences in basal resource (primary producer) availability brought about by differences in light environment. Abrupt loss of benthic basal resources will affect benthic consumers and those plankton-oriented consumers that intermittently depend on benthic biomass pathways whenever plankton-based pathways are unproductive. 相似文献
16.
Following extensive seagrass die-offs of the late 1980s and early 1990s, Florida Bay reportedly had significant declines in water clarity due to turbidity and algal blooms. Scant information exists on the extent of the decline, as this bay was not investigated for water quality concerns before the die-offs and limited areas were sampled after the primary die-off. We use imagery from the Advanced Very High Resolution Radiometer (AVHRR) to examine water clarity in Florida Bay for the period 1985 to 1997. The AVHRR provides data on nominal water reflectance and estimated light attenuation, which are used here to describe turbidity conditions in the bay on a seasonal basis. In situ observations on changes in seagrass abundance within the bay, combined with the satellite data, provide additional insights into losses of seagrass. The imagery shows an extensive region to the west of Florida Bay having increased reflectance and light attenuation in both winter and summer begining in winter of 1988. These increases are consistent with a change from dense seagrass to sparse or negligible cover. Approximately 200 km2 of these offshore seagrasses may have been lost during the primary die-off (1988 through 1991), significantly more than in the bay. The imagery shows the distribution and timing of increased turbidity that followed the die-offs in the northwestern regions of the bay, exemplified in Rankin Lake and Johnson Key Basin, and indicates that about 200 km2 of dense seagrass may have been lost or severely degraded within the bay from the start of the die-off. The decline in water clarity has continued in the northwestern bay since 1991. The area west of the Everglades National Park boundaries has shown decreases in both winter turbidity and summer reflectances, suggestive of partial seagrass recovery. Areas of low reflectance associated with a majorSyringodium filiforme seagrass meadow north of Marathon (Vaca Key, in the Florida Keys) appear to have expanded westward toward Big Pine Key, indicating changes in the bottom cover from before the die-off. The southern and eastern sections of the Bay have not shown significant changes in water clarity or bottom albedo throughout the entire time period. 相似文献
17.
Eutrophication has caused strong shifts from perennial seagrass to opportunistic macroalgae and phytoplankton in many coastal ecosystems worldwide, yet responses of the primary-producer assemblage can vary with regional environmental and nutrient-loading conditions. The wider consequences of this variable primary-producer response on the associated animal community are little known. We used large-scale field surveys across 12 study sites with low or high eutrophication levels in two geographic provinces in Atlantic Canada to examine region-specific responses of macrofauna associated with eelgrass beds. In both regions, abundances of all groups increased with eutrophication, but species richness of mobile fishes and invertebrates decreased. Generally, filter feeders, epibenthic detritivores and some herbivores increased, while more hypoxia sensitive species declined. Small fishes and invertebrate predators increased with eutrophication mirrored by decreases in their prey. Despite similar general trends, our results show distinct shifts in species composition in each geographic region associated with differences in food availability and predation refuge offered by phytoplankton and opportunistic epiphytic or benthic macroalgae as well as tolerance to an increasingly hostile physico-chemical environment. So far, the continued persistence of eelgrass beds at our “highly” eutrophied sites indicates intermediate eutrophication levels with short-term benefits for some species. However, the loss of sensitive species and decrease in species richness highlight that eutrophication has already changed seagrass ecosystems in Atlantic Canada. Our work suggests that mitigating these changes will require regional-scale management. 相似文献
18.
A large data set, collected under the national Danish monitoring program, was used to evaluate the importance of photon flux density (PFD), relative wave exposure (REI), littoral slope, and salinity in regulating eelgrass cover at different depth intervals in Danish coastal waters. Average eelgrass cover exhibited a bell-shaped pattern with depth, reflecting that different factors regulate eelgrass cover at shallow- and deep-water sites. The multiple logistic regression analysis was used to identify regulating factors and determine their role in relation to eelgrass cover at different depth intervals. PFD, REI, and salinity were main factors affecting eelgrass cover while littoral slope had no significant effect. Eelgrass cover increased with increasing PFD at water depths of more than 2 m, while cover was in versely related to REI in shallow water. This pattern favored eelgrass cover at intermediate depths where levels of PFD and REI were moderate. Salinity had a minor, but significant, effect on eelgrass cover that is most likely related to the varying costs of osmoregulation with changing salinity. The analysis provided a useful conceptual framework for understanding the factors that regulate eelgrass abundance with depth. Although the regression model was statistically significant and included the factors generally considered most important in regulating eelgrass cover, its explanatory power was low, especially in shallow water. The largest discrepancies between predicted and observed values of cover appeared in cases where no eelgrass occurred despite sufficient light and moderate levels of exposure (almost 50% of all observations). These discrepancies suggest that population losses due to stochastic phenomena, such as extreme wind events, played an important regulating role that is not adequately described by average exposure levels. A more thorough knowledge of the importance of such loss processes and the time scales involved in recovery of seagrass populations after a severe disturbance are necessary if we are to understand the regulation of seagrass distribution in shallow coastal areas more fully. 相似文献
19.
Jason C. Wyda Linda A. Deegan Jeffrey E. Hughes Melissa J. Weaver 《Estuaries and Coasts》2002,25(1):86-100
Estuarine seagrass ecosystems provide important habitat for fish and invertebrates and changes in these systems may alter their ability to support fish. The response of fish assemblages to alteration of eelgrass (Zostera marina) ecosystems in two ecoregions of the Mid-Atlantic Bight (Buzzards Bay and Chesapeake Bay) was evaluated by sampling historical eelgrass sites that currently span a broad range of stress and habitat quality. In two widely separated ecoregions with very different fish faunas, degradation and loss of submerged aquatic vegetation (SAV) habitat has lead to declines in fish standing stock and species richness. The abundance, biomass, and species richness of the fish assemblage were significantly higher at sites that have high levels of eelgrass habitat complexity (biomass >100 wet g m?2; density <100 shotts m?2) compared to sites that have reduced eelgrass (biomass <100 wet g m?2; density <100 shoots m?2) or that have completely lost eelgrass. Abundance, biomass, and species richness at reduced eelgrass complexity sites also were more variable than at high eelgrass complexity habitats. Low SAV complexity sites had higher proportions of pelagic species that are not dependent on benthic habitat structure for feeding or refuge. Most species had greater abundance and were found more frequently at sites that have eelgrass. The replacement of SAV habitats by benthic macroalgae, which occurred in Buzzards Bay but not Chesapeake Bay, did not provide an equivalent habitat to seagrass. Nutrient enrichment-related degradation of eelgrass habitat has diminished the overall capacity of estuaries to support fish populations. 相似文献
20.
Kelly M. Darnell Tim J. B. Carruthers Patrick Biber Ioannis Y. Georgiou Thomas C. Michot Ronald G. Boustany 《Estuaries and Coasts》2017,40(5):1288-1300
Seagrasses are submerged marine plants that are anchored to the substrate and are therefore limited to assimilating nutrients from the surrounding water column or sediment, or by translocating nutrients from adjacent shoots through the belowground rhizome. As a result, seagrasses have been used as reliable ecosystem indicators of surrounding nutrient conditions. The Chandeleur Islands are a chain of barrier islands in the northern Gulf of Mexico that support the only marine seagrass beds in Louisiana, USA, and are the sole location of the seagrass Thalassia testudinum across nearly 1000 km of the coastline from west Florida to central Texas. Over the past 150 years, the land area of the Chandeleur Islands has decreased by over half, resulting in a decline of seagrass cover. The goals of this study were to characterize the status of a climax seagrass species at the Chandeleur Islands, T. testudinum, in terms of leaf nutrient (nitrogen [N] and phosphorus [P]) changes over time, from 1998 to 2015, and to assess potential drivers of leaf nutrient content. Thalassia testudinum leaf nutrients displayed considerable interannual variability in N and P content and molar ratios, which broadly mimicked patterns in annual average dissolved nutrient concentrations in the lower Mississippi River. Hydrological modeling demonstrated the potential for multiple scenarios that would deliver Mississippi River water, and thus nutrients, to T. testudinum at the Chandeleur Islands. Although coastal eutrophication is generally accepted as the proximate cause for seagrass loss globally, there is little evidence that nutrient input from the Mississippi River has driven the dramatic declines observed in seagrasses at the Chandeleur Islands. Rather, seagrass cover along the Chandeleur Islands appears to be strongly influenced by island geomorphological processes. Although variable over time, the often elevated nutrient levels of the climax seagrass species, T. testudinum, which are potentially driven by river-derived nutrient inputs, raises an important consideration of the potential loss of the ecosystem functions and services associated with these declining seagrass meadows. 相似文献