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1.
During two years of sampling, 747 larval and 1,379 juvenile spotted seatrout,Cynoscion nebulosus, were collected in Tampa Bay, Florida; 93% were less than 75 mm SL. Length-frequency distributions and otolith analysis showed that spawning took place from early April until late October. Two seasonal spawning peaks (spring and summer) were made up of many smaller peaks, apparently timed with moon phases. Plankton samples contained larvae that measured up to about 7 mm SL (17 d old). Larvae collected from an upper bay station were less numerous and larger than those collected at other stations. The presence of small larvae from middle and lower bay stations indicated that spawning probably took place from the middle bay to nearshore Gulf waters. Juveniles used seagrass beds as their major habitat, but they were also found in unvegetated backwaters. Spotted seatrout grew to about 35 mm SL in 2 months, 84 mm SL in 4 months, and 140 mm SL in 6 months. Eighty-five percent of the alimentary tracts in larvae were empty; those with food contained primarily copepods. Eleven percent of the stomachs of juveniles were empty. Fish and shrimp were the most important food groups in the diets of fish >15 mm SL. Intraspecific comparisons of diets showed high dietary overlap between larval fish and those measuring 8–15 mm SL and among size classes >15 mm SL.  相似文献   

2.
During the summer of 2004, four hurricanes (Charley, Frances, Ivan, and Jeanne) affected Florida between August 13 and September 27. Two storms (Frances: category 2 and Jeanne: category 3) made landfall in the southern portion of the Indian River Lagoon (IRL) on the east-central coast of Florida. The presence of Florida Fish and Wildlife Conservation Commission's long-term fisheries monitoring program in the IRL provided a unique opportunity to examine the effects of large tropical events on estuarine fish communities. Increased sampling efforts to monitor the effects of tropical disturbances on the fish community within the IRL and one of its major tributaries (St. Sebastian River) were initiated within days after the passing of the last hurricane (Jeanne). The objectives of the study were to characterize changes to the composition of the fish community within the lagoon and river immediately after the passage of two hurricanes, and to examine the recovery of the fish communities. Analyses indicated that immediately after the last hurricane passed, community diversity within the estuary decreased following these storms due to the absence of many marine species, whereas the fish community within the St. Sebastian River shifted to one containing a greater percentage of freshwater species. Recovery of the community structure to pre-hurricane conditions was evident within several weeks following the last hurricane, and by mid December 2004 (ca. 3 mo after the last storm), there was little difference between the pre-hurricane and post-hurricane fish communities.  相似文献   

3.
Benthic resource utilization by, red drum (Sciaenops ocellatus) and spotted seatrout (Cynoscion nebulosus) was studied in a restored, mangrove-rimmed impoundment (Cabbagehead Bayou) of Upper Tampa Bay, Florida, and in a nearby, natural site of unaltered tidal regime (Double Branch Bay). Diets of fish captured from August 1990 to May 1992 were determined from stomach content analysis. Simultaneously, food availability was evaluated by sampling benthic macroinvertebrates, mobile decapods, and small fish. Red drum and spotted seatrout utilized the restored habitat 1 yr after it was opened to tidal influence. Both species also were collected in the natural mangrove. Although there were noted differences in benthic assemblages between the two sites, red drum and spotted seatrout exhibited flexibility in diet, feeding on abundant and accessible prey. The high abundance of microcrustacea, such as amphipods, on detritus accumulated in the restored habitat constituted a main food resource for both fish species. Major food items in the diet of small (<200 mm) red drum were amphipods, mysids, and nereid and arenicolid polychaetes. Large (200–590 mm) red drum fed on polychaetes, xanthid crabs, palaemonid shrimp, and small fishes. Spotted seatrout preyed primarily upon mysids, shrimp, and small fishes, and to a lesser extent, upon a nereid polychaete. Our findings on fish feeding in a restored mangrove impoundment indicated that the detrital-associated benthic community is utilized by reinvading fish within a short time period, suggesting that not only habitat but food resources were augmented by the reopening of this wetland.  相似文献   

4.
We compared (1) ichthyoplankton composition and (2) basin and channel habitat ichthyofauna and seagrass densities between 1984–1985 and 1994–1996 in Florida Bay. Stations and sampling techniques employed in 1984–1985 were duplicated in the 1994–1996 study.Thalassia testudinum, Halodule wrightii, andSyringodium filiforme densities within most of the basin and channel strata sampled in 1994–1996 had decreased by as much as 100%. We did not observe changes in the total density of juvenile and small adult fishes coincident with the reductions in seagrass densities except in the deep-water channel habitats. There was an increase in the proportion of the total ichthyofauna represented by pelagic atherinids, engraulids, and clupeids, particularly the engraulidAnchoa mitchilli, and a concomitant decrease in the proportion represented by canopy-dwelling and morebenthic-dwelling seagrass inhabitants. This suggested a shift toward a planktonic-feeding community. We observed an increase in the density and frequency of engraulid larvae, particularly in the western and Gulf of Mexico portions of Florida Bay, but no significant changes in densities of the commonly collected ichthyoplankton that are demersal as adults (i.e., Gobiidae, Callionymidae, and Blennioidei).Lucania parva, Eucinostomus spp.,Lagodon rhomboides, Floridichthys carpio, Haemulon plumieri, andSyngnathus floridae represented nearly 86% of the juvenile and small adult fish collected in 1984–1985 but represented only 29% of the ichthyofauna a decade later. The distribution of juvenile spotted seatrout had expanded into the central and northeastern basins of our sampling area, perhaps in response to reduced salinities or to the availability of food resources.  相似文献   

5.
The first advisory to limit consumption of Florida Bay fish due to mercury was issued in 1995. Studies done by others in the late 1990s found elevated water column concentrations of both total Hg (THg) and methylmercury (MeHg) in creeks discharging from the Everglades, which had its own recognized mercury problem. To investigate the significance of allochthonous MeHg discharging from the upstream freshwater Everglades, we collected surface water and sediment along two transects from 2000 to 2002. Concentrations of THg and MeHg, ranging from 0.36 ng THg/L to 5.98 ng THg/L and from <0.02 ng MeHg/L to 1.79 ng MeHg/L, were elevated in the mangrove transition zone when compared both to upstream canals and the open waters of Florida Bay. Sediment concentrations ranged from 5.8 ng THg/g to 145.6 ng THg/g and from 0.05 ng MeHg/g to 5.4 ng MeHg/g, with MeHg as a percentage of THg occasionally elevated in the open bay. Methylation assays indicated that sediments from Florida Bay have the potential to methylate Hg. Assessment of mass loading suggests that canals delivering stormwater from the northern Everglades are not as large a source as direct atmospheric deposition and in situ methylation, especially within the mangrove transition zone.  相似文献   

6.
A study was carried out in fall 1987 to determine if red drum (Sciaenops ocellatus) spawned in the southern portion of Mosquito Lagoon, Florida, 30 km from the nearest tidal pass. Weekly plankton tows were taken from mid-September to mid-November. Floating sciaenid eggs were removed from the samples and incubated 16–36 h: 329 red drun eggs were hatched. Viable red drum eggs were collected from October 27 to November 18 at salinities of 29‰ to 32‰ and water temperatures of 21°C to 23°C. The largest number of eggs was collected on November 4, during a full moon. This is the first documentation of red drum spawning in an estuary. The physiography and high salinity (which are more characteristic of marine than estuarine waters) of Mosquito Lagoon were probable factors in producing this phenomenon.  相似文献   

7.
An unusually persistent red tide event caused by the ichthyotoxic dinoflagellate Karenia brevis occurred along the southwest Florida coast in 2005. Extensive fish kills led to concerns regarding the effect of red tide on fish populations and their subsequent recruitment. Community structure differences were analyzed for all small- and large-bodied nekton species collected by fisheries-independent monitoring from 1996 through 2006. Indices of abundance of five economically important fish species were also calculated from this time period. A significant change in small- and large-bodied nekton community structure was apparent from summer 2005 through spring 2006. Declines in the annual recruitment of juvenile spotted seatrout (Cynoscion nebulosus), sand seatrout (Cynoscion arenarius), and red drum (Sciaenops ocellatus) were evident in 2005 and 2006. Species-specific subadult and adult abundances, however, were consistent with those of previous years. These community shifts and species-specific declines appear to be associated with the red tide event.  相似文献   

8.
Three gear types were used to collect finfish species from several tributaries of the South Creek estuary near Aurora, North Carolina, to ascertain whether a man-initiated marsh and creek system resembled adjacent natural areas in finfish species composition and abundance. Project Area II was the man-initiated area constructed in 1983 as up-front mitigation by North Carolina Phosphate Corporation prior to its anticipated mining in the headwaters of nearby natural wetlands. Two creeks served as controls throughout the study: Drinkwater Creek and Jacks Creek. Otter trawls were used monthly from July 1984 through December 1988. Wegener rings were used in April, July, and October from 1984 through 1987. An experimental gill net was used monthly from June 1984 through 1985. A total of 48 finfish species was captured during the study; only 14 species (29.2%) were common among gear types. The species collected were mud sunfish, blueback herring, alewife American shad, striped anchovy, bay anchovy, inland silverside, American eel, silver perch, Atlantic menhaden, crevalle jack, common carp, spotted seatrout, weakfish, sheepshead minnow, gizzard shad, ladyfish, chain pickerel, banded killifish, mummichog, striped killifish, rainwater killifish, mosquitofish, naked goby, green goby, white catfish, brown bull-head, pinfish, longnose gar, green sunfish, pumpkinseed, bluegill, redear sunfish, spot, Atlantic croaker, largemouth bass, white perch, striped bass, striped mullet, white mullet, golden shiner, summer flounder, southern flounder, yellow perch, bluefish, Atlantic needlefish, hogchoker, andTilapia species. Abundance of finfish species was a function of gear type. Bay anchovy and spot represented about 85% of all fish in trawl samples. The remainder was comprised of 27 other species. In Wegener rings, five species—bay anchovy, menhaden, rainwater killifish, spot, and inland silverside—each represented over 10% of all fish collected. Croaker and striped mullet each comprised more than 5% of all fish collected in Wegener rings, but were present in substantial numbers only in 1985. Based on trawl samples, the total number of finfish collected from Project Area II during the period 1984–1988 was statistically similar to those collected from the control creeks; Wegener ring data analysis indicated significantly greater catches in Project Area II compared to the control creeks. Bay anchovy catches were not significantly different among the three creeks by either trawl or Wegener ring. The same result was true for Atlantic menhaden and southern flounder. The abundance of spot in trawl samples from Project Area II was significantly greater than for the control creeks; abundance in ring samples from Project Area II was statistically similar to Jacks Creek, but significantly higher than Drinkwater Creek. The number of Atlantic croaker in Project Area II trawl samples was significantly lower than for the cotnrol creeks. Wegener rings did not sample croaker effectively.  相似文献   

9.
Predicting population- and ecosystem-level benefits of habitat restoration minimally requires an understanding of the link between the trophic ecology of a species and their use of a habitat. This study combined novel, non-lethal natural tracers of trophic ecology with acoustic tagging techniques to examine spatial and temporal patterns of habitat use of spotted seatrout Cynoscion nebulosus on Half Moon Reef (HMR), a recently restored oyster reef in Matagorda Bay, Texas. Forty-one spotted seatrout (408?±?25 mm total length) were captured at HMR, surgically implanted with acoustic transmitters, and monitored by an array of underwater listening stations from December 2015 to August 2016. Patterns of presence-absence on HMR were strongly influenced by water temperature, and to a lesser extent, salinity and tidal height. Overall, spotted seatrout residency to HMR was low, with fish being present on the reef 24% of days. When present, individual fish exhibited strong site-attachment to small portions of the reef. Residency to HMR increased significantly with size, while scale stable isotope analysis revealed fish exhibiting high residency to HMR occupied significantly smaller isotopic niches. If indeed smaller fish with decreased residency rely upon a wider range of prey items across multiple habitats than larger, more resident individuals, restored oyster reef habitat may be expected to primarily benefit larger spotted seatrout.  相似文献   

10.
Metal contamination of estuarine sediments is an increasing problem in Florida and elsewhere as urbanization extends into previously undeveloped areas. Effective estuarine management practices require scientifically valid tools to assess the extent of estuarine contamination. Interpretation of anthropogenic metal contributions has been hampered by the fact that natural metal concentrations in sediments vary by orders of magnitude in different sediments. Normalization of metal concentrations to a reference element, aluminum, appears to be a promising method for comparing estuarine sediment metal concentrations on a regional basis. In this paper we describe an interpretive method based on the relationship between sediment metals and aluminum derived from statewide data on natural estuarine sediments in Florida. We show how the method can be used to interpret metal concentrations with an example using data from the Miami River and Biscayne Bay.  相似文献   

11.
Historical profiles of metal accumulation have been generated for the lower St. Johns River and Hillsborough Bay, Florida, in cores representing approximately 50 yr of sediment and metal accumulation. These profiles demonstrate that Cd, Pb, and Zn are enriched in these Florida estuarine sediments. Pb enrichment has decreased since the mid 1970s because of reduced use of leaded gasoline. In the St. Johns River, most metals exhibit a trend of increasing enrichment with time. Cd enrichment significantly decreased between 1970 and 1975 as a result of reduced discharges into the river and control of aquatic vegetation. In Hillsborough Bay, enrichment factors for most metals are relatively high and show little change downcore. Cr, Cu, and Ni border on enrichment and Pb, Cd, and Zn are enriched. The results of this study are consistent with other studies of surficial-sediment metal concentration in other Florida estuaries.  相似文献   

12.
Field data of tidal current speeds collected January 9–31, 1990, in Sebastian Inlet, which connects the Atlantic Ocean and the Indian River Lagoon on the east coast of central Florida, show that the average Eulerian and Stokes residual currents are both lagoonward. This pattern can be used to explain the long-term trend of accumulations of marine sediments on the flood tidal delta adjacent to the lagoon end of the inlet. Numerical model results indicate that the long-term Stokes residual current is mainly determined by the tidal characteristics of the lagoon and ocean, and subsequently, are less variable. The long-term lagoonward Eulerian current, on the other hand, is interrupted by episodic weather events such as frontal storms. Storms can cause the abrupt superelevation of instantaneous water-levels on the lagoon side of the inlet. The short-lived pulses of freshwater inflow into the lagoon associated with storms could be discharged through the inlet instantaneously. Both the instantaneous superelevation of lagoon water levels and freshwater outflow can cause temporary reversal of Eulerian residual current in the inlet. Therefore, the general residual flow pattern in Sebastian Inlet is not only determined by the tidal characteristics of the Atlantic Ocean and Indian River Lagoon but also by the wind and precipitation associated with episodic storms, and by the long-term mean sea-level difference between the lagoon and the ocean.  相似文献   

13.
Porewater (i.e., groundwater) samples were collected from multi-level piezometers across the freshwater-saltwater seepage face within the Indian River Lagoon subterranean estuary along Florida’s (USA) Atlantic coast for analysis of the rare earth elements (REE). Surface water samples for REE analysis were also collected from the water column of the Indian River Lagoon as well as two local rivers (Eau Gallie River, Crane Creek) that flow into the lagoon within the study area. Concentrations of REEs in porewaters from the subterranean estuary are 10-100 times higher than typical seawater values (e.g., Nd ranges from 217 to 2409 pmol kg−1), with submarine groundwater discharge (SGD) at the freshwater-saltwater seepage face exhibiting the highest REE concentrations. The elevated REE concentrations for SGD at the seepage face are too high to be the result of simple, binary mixing between a seawater end-member and local terrestrial SGD. Instead, the high REE concentrations indicate that geochemical reactions occurring within the subterranean estuary contribute substantially to the REE cycle. A simple mass balance model is used to investigate the cycling of REEs in the Indian River Lagoon and its underlying subterranean estuary. Mass balance modeling reveals that the Indian River Lagoon is approximately at steady-state with respect to the REE fluxes into and out of the lagoon. However, the subterranean estuary is not at steady-state with respect to the REE fluxes. Specifically, the model suggests that the SGD Nd flux, for example, exported from the subterranean estuary to the overlying lagoon waters exceeds the combined input to the subterranean estuary from terrestrial SGD and recirculating marine SGD by, on average, ∼100 mmol day−1. The mass balance model also reveals that the subterranean estuary is a net source of light REEs (LREE) and middle REEs (MREE) to the overlying lagoon waters, but acts as a sink for the heavy REEs (HREE). Geochemical modeling and statistical analysis further suggests that this fractionation occurs, in part, due to the coupling between REE cycling and iron redox cycling within the Indian River Lagoon subterranean estuary. The net SGD flux of Nd to the Indian River Lagoon is ∼7-fold larger than the local effective river flux to these coastal waters. This previously unrecognized source of Nd to the coastal ocean could conceivably be important to the global oceanic Nd budget, and help to resolve the oceanic “Nd paradox” by accounting for a substantial fraction of the hypothesized missing Nd flux to the ocean.  相似文献   

14.
There is a net discharge of water and nutrients through Long Key Channel from Florida Bay to the Florida Keys National Marine Sanctuary (FKNMS). There has been speculation that this water and its constituents may be contributing to the loss of coral cover on the Florida Keys Reef tract over the past few decades, as well as speculation that changes in freshwater flow in the upstream Everglades ecosystem associated with the Comprehensive Everglades Restoration Plan may exacerbate this phenomenon. The results of this study indicate that although there is a net export of approximately 3,850 (±404) ton N year?1 and 63 (±7) ton P year?1, the concentrations of these nutrients flowing out of Florida Bay are the same as those flowing in. This implies that no significant nutrient enrichment is occurring in the waters of the FKNMS in the vicinity of Long Key Channel. Because of the effect of restricted southwestward water flow through Florida Bay by shallow banks and small islands, the volume of relatively high-nutrient water from central and eastern portions of the bay exiting through the channel is small compared to the average tidal exchange. Nutrient loading of relatively enriched bay waters is mediated by tidal exchange and mixing with more ambient concentrations of the western Florida Bay and Hawk Channel. System-wide budgets indicate that the contribution of Florida Bay waters to the inorganic nitrogen pool of the Keys coral reef is small relative to offshore inputs.  相似文献   

15.
Local species populations that are more numerically abundant and occupy a greater proportion of the landscape relative to other species often recover more quickly (i.e., are more resilient) following local-scale environmental perturbations. In a companion study, we found that seatrout juvenile populations were distributed more broadly across Tampa Bay, Florida, and numerical abundance was generally much higher than those of similar-sized red drum, suggesting that spotted seatrout may also be generally more resilient to population declines than red drum. Following major population declines over a 12-year period (1996–2008), we found that larger juveniles of seatrout (51–100 mm standard length) simultaneously gained numerical abundance and broadened their spatial distribution generally within the next year. Population recovery in the same size of juvenile red drum generally took multiple years, and distribution and abundance increases were not always concurrent during the recovery period. Despite their overall higher abundance and broader spatial distribution, the smaller-sized juveniles of spotted seatrout (15–50 mm standard length (SL)) did not always recover more quickly from population declines compared with similar-sized red drum. Populations of the smaller-sized juveniles of both species often took multiple years to recover and showed non-concurrent increases in distribution and abundance during recovery. Despite their relatively narrow spatial distribution, juveniles of red drum may increase their overall resilience to local environmental perturbations by occupying multiple isolated patches across the Tampa Bay landscape. Monitoring dynamics of numerical abundance and spatial distribution may be helpful in gauging relative population resilience to facilitate overall management of these fishery populations.  相似文献   

16.
Reef fishes, such as gray snapper, support important recreational and commercial fisheries and use a variety of habitats throughout ontogeny. Gray snapper juveniles may be found in estuarine nursery areas, such as seagrass beds, or mangrove shorelines, while adults are most often found in deep channels and farther offshore, associated with hard-bottom habitats. Juvenile and subadult gray snapper were collected from 1996 through 2009 during long-term fishery-independent monitoring of several estuarine systems along the Gulf and Atlantic coasts of Florida. Indices of abundance and habitat suitability were constructed for gray snapper to determine size-specific relationships between abundance, habitat, and environmental conditions. Juvenile and subadult gray snapper were collected year-round only in the southernmost estuaries but were most common from July through December in all estuaries sampled. In addition to timing of estuarine occupancy, abundance varied with latitude; gray snapper were more frequently collected in warmer, southern estuaries. In general, gray snapper were most abundant in euhaline areas with a high percentage of submerged aquatic vegetation (SAV) and, in most cases, where overhanging shoreline vegetation was also present. Annual abundance varied over the sampling period, with some juvenile peaks in abundance translating to subadult peaks in subsequent years. Although strong correspondence between juvenile and subadult populations was not observed in all systems, long-term, broad-scale habitat selection patterns as described in this study are critical to more effectively assess populations of estuarine-dependent species.  相似文献   

17.
Historic changes in water-use management in the Florida Everglades have caused the quantity of freshwater inflow to Florida Bay to decline by approximately 60% while altering its timing and spatial distribution. Two consequences have been (1) increased salinity throughout the bay, including occurrences of hypersalinity, coupled with a decrease in salinity variability, and (2) change in benthic habitat structure. Restoration goals have been proposed to return the salinity climates (salinity and its variability) of Florida Bay to more estuarine conditions through changes in upstream water management, thereby returning seagrass species cover to a more historic state. To assess the potential for meeting those goals, we used two modeling approaches and long-term monitoring data. First, we applied the hydrological mass balance model FATHOM to predict salinity climate changes in sub-basins throughout the bay in response to a broad range of freshwater inflow from the Everglades. Second, because seagrass species exhibit different sensitivities to salinity climates, we used the FATHOM-modeled salinity climates as input to a statistical discriminant function model that associates eight seagrass community types with water quality variables including salinity, salinity variability, total organic carbon, total phosphorus, nitrate, and ammonium, as well as sediment depth and light reaching the benthos. Salinity climates in the western sub-basins bordering the Gulf of Mexico were insensitive to even the largest (5-fold) modeled increases in freshwater inflow. However, the north, northeastern, and eastern sub-basins were highly sensitive to freshwater inflow and responded to comparatively small increases with decreased salinity and increased salinity variability. The discriminant function model predicted increased occurrences of Halodule wrightii communities and decreased occurrences of Thalassia testudinum communities in response to the more estuarine salinity climates. The shift in community composition represents a return to the historically observed state and suggests that restoration goals for Florida Bay can be achieved through restoration of freshwater inflow from the Everglades.  相似文献   

18.
This paper describes the results of 10 years of water quality monitoring in the Indian River Lagoon Florida, with special emphasis on the relationships between trends in climatic conditions and the distribution, composition, and abundance of the phytoplankton community. The Indian River Lagoon, which spans 220 km of Florida’s east coast, is a region of particular concern because of the rapid rate of human development throughout the region and the hydrologically restricted character of the lagoon, which heightens the potential for algal bloom. Water sampling was carried out on a monthly to twice-monthly basis at six sites located in the northern and central lagoon. The 10-year study included both extended periods of below and above average rainfall. A number of ecologically distinct regions exist within the lagoon, which differ considerably in water exchange properties and watershed inputs. The northern lagoon is characterized by longer water residence times, lower phosphorus concentrations, higher nitrogen concentrations, and more stable salinity conditions than the central lagoon. Mean phytoplankton biovolumes were substantially higher at the sites in the northern lagoon than at the sites in the central lagoon, and algal blooms were more common and intense in the former region. Inter-annual patterns of phytoplankton biovolume were also different in the northern and central lagoon. In the northern lagoon, phytoplankton biovolumes were lowest during the drought period, from the autumn of 1998 to the spring of 2001. By contrast, algal bloom events in the central lagoon were not only less frequent but were not tied to periods of high rainfall. The most widespread and common bloom formers were the potentially toxic dinoflagellate Pyrodinium bahamense var. bahamense and two centric diatoms, Dactyliosolen fragilissimus and Cerataulina pelagica. Many of the biovolume peaks observed over the study period were attributable to these three species. The results of time series modeling of phytoplankton dynamics further highlighted the disparities between the two regions of the lagoon in terms of the suite of parameters that best predict the observed trends in the biomass of phytoplankton. Overall, the outcome of this initial modeling effort in the Indian River Lagoon suggests that time series approaches can help define the factors that influence phytoplankton dynamics.  相似文献   

19.
Stable isotopic ratios of carbon and oxygen (δ13C and δ18O) from mollusk shells reflect the water quality characteristics of Florida Bay and can be used to characterize the great temporal variability of the bay. Values of δ18O are directly influenced by temperature and evaporation and may be related to salinity, δ13C values of δ13C are sensitive to organic and inorganic sources of carbon and are influenced by productivity. Analyses of eight mollusk species from five short-core localities across Florida Bay show large ranges in the values of δ13C and δ18O, and reflect the variation of the bay over decades. Samples from southwester Florida Bay have distinct δ13C values relative to samples collected in northeastern Florida Bay, and intermediate localities have intermediate values.13C values of δ13C grade from marine in the southwest bay to more estuarine in the northeast. Long cores (>1m), with excellent chronologies were analyzed from central and eastern Florida Bay. Preliminary analyses ofBrachiodontes exustus andTransenella spp. from the cores showed that both δ13C and δ18O changed during the first part of the twentieth century. After a century of relative stability during the 1800s, δ13C decreased between about 1910 and 1940, then stabilized at these new values for the next five decades. The magnitude of the reduction in δ13C values increased toward the northeast. Using a carbon budget model, reduced δ13C values are interpreted as resulting from decreased circulation in the bay, probably associated with decreased freshwater flow into the Bay. Mollusk shell δ18O values display several negative excursions during the 1800s, suggesting that the bay was less evaporitic than during the twentieth century. The isotope records indicate a fundamental change took place in Florida Bay circulation early in the twentieth century. The timing of the change links it to railroad building and early drainage efforts in South Florida rather than to flood control and water management measures initiated after World War II.  相似文献   

20.
Fifteen species of elasmobranchs, eight sharks and seven rays, have been recorded with reasonable certainty from the Indian River lagoon system on the central east coast of Florida. We collected four shark and six ray species during a three and one-half year study of the northern portion of the lagoon system. Five of these appear to be year-round residents, and the remainder utilize the area only at restricted times of the year or as a nursery ground. The most abundant resident species areDasyatis sayi, D. sabina, andCarcharhinus leucas. Pristis pectinata, once a common resident species, has been extirpated from the lagoons. The distribution of ocean inlets and salinity appear to be major factors affecting diversity and numbers of elasmobranchs in the Indian River system.  相似文献   

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