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11.
Joel S. Steward Robert W. Virnstein Lori J. Morris Edgar F. Lowe 《Estuaries and Coasts》2005,28(6):923-935
Seagrass protection and restoration in Florida’s Indian River Lagoon system (IRLS) is a mutual goal of state and federal programs.
These programs require, the establishment of management targets indicative of seagrass recovery and health. We used three
metrics related to seagrass distribution: areal coverage, depth limit, and light requirement. In order to account for the
IRLS’s spatial heterogeneity and temporal variability, we developed coverage and depth limit targets for each of its 19 segments.
Our method consisted of two steps: mapping the union of seagrass coverages from all availabe mapping years (1943, 1986, 1989,
1992, 1994, 1996, and 1999) to delineate wherever seagrass had been mapped and determining the distribution of depth limits
based on 5,615 depth measurements collected on or very near the deep-edge boundary of the union coverage. The frequency distribution
of depth limits derived from the union coverage, along with the median (50th percentile) and maximum (95th percentile) depth
limits, serve as the seagrass depth targets for each segment. The median and maximum depth targets for the IRLS vary among
segments from 0.8 to 1.8 and 1.2 to 2.8 m, respectively.Halodule wrightii is typically the dominant seagrass species at the deep-edge of IRLS grass beds. We set light requirement targets by using
a 10-yr record of light data (1990–1999) and the union coverage depth limit distributions from the most temporally stable
seagrass segments. The average annual light requirement, based on the medians of the depth limit distributions, is 33 ± 17%
of the subsurface light. The minimum annual light requirement, based on of the 95th percentile of the depth distributions,
is 20 ± 14%; the minimum growing season light requirement (March to mid September) is essentially the same (20 ± 13%). Variation
in depth limits and light requirements, is probably due to factors other than light that influence the depth limit of seagrasses
(e.g., competition, physical disturbance). The methods used in this study are robust when applied to large or long-term data
sets and can be applied to other estuaries where grass beds are routinely monitored and mapped. 相似文献
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Alisha L. Steward Jonathan C. Marshall Fran Sheldon Bronwyn Harch Satish Choy Stuart E. Bunn Klement Tockner 《Aquatic Sciences - Research Across Boundaries》2011,73(4):551-566
Dry river beds are common worldwide and are rapidly increasing in extent due to the effects of water management and prolonged
drought periods due to climate change. While attention has been given to the responses of aquatic invertebrates to drying
rivers, few studies exist on the terrestrial invertebrates colonizing dry river beds. Dry river beds are physically harsh
and they often differ substantially in substrate, topography, microclimate and inundation frequency from adjacent riparian
zones. Given these differences, we predicted that dry river beds provide a unique habitat for terrestrial invertebrates, and
that their assemblage composition differs from that in adjacent riparian zones. Dry river beds and riparian zones in Australia
and Italy were sampled for terrestrial invertebrates with pitfall traps. Sites differed in substrate type, climate and flow
regime. Dry river beds contained diverse invertebrate assemblages and their composition was consistently different from adjacent
riparian zones, irrespective of substrate, climate or hydrology. Although some taxa were shared between dry river beds and
riparian zones, 66 of 320 taxa occurred only in dry river beds. Differences were due to species turnover, rather than shifts
in abundance, indicating that dry river bed assemblages are not simply subsets of riparian assemblages. Some spatial patterns
in invertebrate assemblages were associated with environmental variables (irrespective of habitat type), but these associations
were statistically weak. We suggest that dry river beds are unique habitats in their own right. We discuss potential human
stressors and management issues regarding dry river beds and provide recommendations for future research. 相似文献
15.
Total nitrogen (TN), total phosphorus (TP), and total suspended solids (TSS) loadings [log (kg ha−1 yr−1)] were regressed against seagrass depth limits (percent of depth-limit targets) to back-predict the load limits or allocations
(kg ha−1 yr−1 or kg yr−1) necessary to meet targeted seagrass depth limits in the Indian River and Banana River (IRBR) lagoons, Florida. Because the
load allocations can be applied as total maximum daily loads (TMDL) for the IRBR (U.S. Environmental Protection Agency mandate),
the method and results are developed and presented toward that end. The regression analyses indicate that the range of surface-discharge
load limits (nonpoint + point source), per watershed area, required to achieve the desired depth limits for seagrass in the
IRBR are approximately 2.4–3.2 kg ha−1 yr−1 TN, 0.41–0.64 kg ha−1 yr−1 TP, and 48–64 kg ha−1 yr−1 TSS. This simple regression method may have application to other shallow estuarine lagoons or bays where seagrass growth
is limited by light and water transparency, water transparency is strongly affected by watershed pollutant loadings, water
residence times are sufficiently long to allow seagrass coverage to respond to and covary with total load inputs, and multiyear
monitoring has yielded sufficient variability in both pollutant loadings and seagrass coverages to develop a statistically
meaningful relationship. 相似文献
16.
David L. Kirchman Benedikt Meon Hugh W. Ducklow Craig A. Carlson Dennis A. Hansell Grieg F. Steward 《Deep Sea Research Part II: Topical Studies in Oceanography》2001,48(19-20)
We hypothesized that dissolved carbohydrates would be large components of the labile dissolved organic carbon (DOC) pool and would support much bacterial growth in Antarctic waters, especially the Ross Sea, since previous work had observed extensive phytoplankton blooms with potentially high production rates of carbohydrates in Antarctic seas. These hypotheses were tested on cruises in the Ross Sea and Antarctic Polar Front Zone as part of the US JGOFS program. Concentrations and fluxes of free glucose (the only free sugar detected) were very low, but dissolved polysaccharides appeared to be important components of the DOC pool. Concentrations of dissolved combined neutral sugars increased >3-fold during the phytoplankton bloom in the Ross Sea and were a large fraction (ca. 50%) of the semi-labile fraction of DOC. The relatively high concentrations of dissolved combined neutral sugars, which are thought to be quite labile, appear to explain why DOC accumulated during the phytoplankton bloom was degraded so quickly once the bloom ended. Some of the polysaccharides appeared to be more refractory, however, since dissolved combined neutral sugars were observed in deep waters (>550 m) and in early spring (October) in the Ross Sea, apparently having survived degradation for >8 months. The molecular composition of these refractory polysaccharides differed from that of polysaccharides sampled during the phytoplankton bloom. Fluxes of DOC were low in the Ross Sea compared to standing stocks and fluxes of particulate material, but the DOC that did accumulate during the phytoplankton bloom appeared to be sugar-rich and relatively labile. 相似文献
17.
Cryptic Blooms: Are Thin Layers the Missing Connection? 总被引：1，自引：0，他引：1
Margaret A. McManus Raphael M. Kudela Mary W. Silver Grieg F. Steward Percy L. Donaghay James M. Sullivan 《Estuaries and Coasts》2008,31(2):396-401
Harmful algal blooms (HABs) are common in Monterey Bay, CA, and have resulted in repeated closures of shellfish fisheries
and the poisoning and death of marine mammals. In the majority of instances, HAB events in this region are first detected
by the presence of sick or dying animals. The phrase “cryptic blooms” was adopted to denote the appearance of poisoning at
higher trophic levels with no prior evidence of a large phytoplankton bloom. We hypothesize that the onset of many HAB events
goes undetected because the bloom is initially concentrated in discrete thin subsurface layers in the water column that are
easily missed by conventional sampling and monitoring methods. In this paper, we report on the detection and monitoring of
a subsurface layer of phytoplankton in northern Monterey Bay, CA, using a high-resolution, autonomous profiler. This ‘thin
layer,’ which measured from 10 cm to 3 m in thickness (85% < 2 m; 54% < 1 m), persisted over a 7-day period near the base
of the pycnocline. The phytoplankton assemblage in the layer was primarily composed of a multi-species assemblage of Pseudo-nitzschia including the toxin-producing species Pseudo-nitzschia australis. Concentrations of toxic phytoplankton (P. australis), cyanobacteria, and bacteria in the layer were significantly higher than outside the layer (P < 0.05). Counts of total Pseudo-nitzschia spp. showed similar levels of enrichment in the layer compared to outside the layer. Our findings indicate that, when monitoring
for HABs, it is critical to sample at scales appropriate to resolve thin layers. Thin layers have been identified as a common
recurrent feature in a variety of coastal systems, suggesting that the use of autonomous high-resolution vertical profilers
coupled with targeted sampling, could allow more timely detection of HABs in many coastal environments. 相似文献
18.
In the weeks following the 2011 Rena oil spill, a series of surveys was initiated on eight rocky intertidal reefs to describe the distribution of oil and to assess the impacts of oil on ecological communities. Consistent but relatively low cover of oil occurred at two sites (Mt Maunganui and Moturiki). The area covered by oil had decreased by c. 90% after 5 months due to natural weathering processes. There were immediate effects of oil fouling on the mussel Limnoperna pulex and its associated fauna, with reductions in the number of mussels and infaunal taxonomic richness. However, no ecological effects on any of the communities were detectable after 1 month. Overall, the ecological effects of the Rena oil spill on rocky shore intertidal communities were small and not long-lasting, but we stress that this does not consider potential sublethal effects and their consequences on organisms. 相似文献
19.
Freshly excreted droppings from Canada geese (n=80), black swans (n=80), ducks (n=80) and gulls (n=80) were collected from sites around New Zealand. The droppings were enumerated for Escherichia coli, enterococci and Salmonella spp., and for the presence/absence of Cryptosporidium spp. Overall prevalence of E. coli and enterococci in samples was 95% and 94%, respectively. Cryptosporidium spp. was detected in 2% of the samples, whereas no Salmonella spp. were detected in the survey. Preliminary estimates of daily microbial outputs suggest that ducks will produce the highest loadings of E. coli and enterococci per bird, whereas Canada geese will produce the highest loadings of Campylobacter spp. per bird. This study provides the first set of indicator and pathogen counts for one of the largest sources of diffuse faecal contamination of natural waters in New Zealand. 相似文献
20.
DR Schiel 《新西兰海洋与淡水研究杂志》2013,47(3):374-391
Abstract This paper reviews interactions involving stands of macroalgae on rocky reefs, and presents new data on changing sea surface temperatures (SSTs), as a contribution to the celebration of the fiftieth anniversary of the Leigh Marine Laboratory (LML) of the University of Auckland. The focus is on trophic interactions involving predators, sea urchins and large brown algae, particularly trophic cascades. Of the 369 publications arising from work at LML, 40 have been on key aspects of these trophic interactions. Quantitative investigations of the structure of kelp bed communities and mechanistic studies involving manipulative field-based experiments, essentially a bottom-up perspective based on habitats and key species, dominated the research through the 1980s. From the mid-1990s onwards, the focus was more on marine reserves and a hierarchical, top-down perspective of community structure, with a particular focus on the role of predatory fish, and marine reserves as a tool of management. I discuss these models of community structure of kelp beds within the wider context of the New Zealand nearshore zone, the varying biogeographic regimes around the coastline, diffuse stressors and the changing nearshore climate. I show there appears to have been a significant warming trend in SST in northeast and northwest New Zealand over the past 30 years. I conclude that a trophic effects model is unlikely to apply to much of the coastline of New Zealand, and that a model involving multiple effects, including bottom-up forces, environmental and climatic influences, species' demographics, and catchment-derived sedimentation is more appropriate for kelp communities over most of the country. New management models are needed to safeguard marine resources and the services they provide. 相似文献