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Author: Parker H. House Publisher: ISBN: Category : Languages : en Pages : 95
Book Description
In many marine ecosystems worldwide, overfishing is a prominent cause in removing large predatory fishes from ecological communities. Fluctuation in the abundance of higher trophic level species can transform an ecosystem's structure and function by altering trophic interactions through density-mediated top-down control. Accordingly, understanding the extent to which humans indirectly influence a community through altering predator abundance is of critical importance. Thus, during the summer of 2013 and 2014 the impacts of fishing on the trophic structure and community assemblage of kelp forest fishes were examined within the Southern California Bight. In 2013, I tested whether decreased abundance through fishing for higher trophic level predators relieves predation pressure on lower trophic level prey. Using a combination of underwater survey techniques, density (no. fish/100 m2) and biomass (g/100 m2) of conspicuous fish species were sampled inside and outside of three long-standing Marine Protected Areas (MPAs) off La Jolla, Santa Catalina Island, and Anacapa Island, California. I found that secondary carnivore and herbivore/omnivore trophic levels significantly decreased outside of MPAs. Inversely, the primary carnivore trophic level biomass increased outside of MPAs. Species-level results revealed a lower abundance outside MPAs of large kelp bass (> 25 cm) and higher densities of its prey, kelp perch. My results show overall fish trophic level changes due to fishing pressure, and provide support for a weakening of top-down control on the kelp perch population through the removal of predatory fishes outside MPAs. To investigate the possible return of the historically overfished apex predator of the kelp forest fish community, I censused the giant sea bass (Stereolepis gigas) population at eight sites off Santa Catalina Island from mid-June through mid-August, 2014. Three possible spawning aggregations were identified at the sites Twin/Goat, The V's, and Little Harbor. The giant sea bass population at these sites primarily consisted of individuals 1.2 - 1.3 m long (total length, TL) with small and probably newly mature fish (estimated to be 10 - 11 years old) observed in aggregations. However, larger individuals 1.8 - 1.9 m TL accounted for the majority of the population biomass. Overall, mean spawning stock biomass of giant sea bass was 36.3 kg/1000 m2. Providing a general comparison of mean biomass among the trophic levels of kelp forest fishes off Santa Catalina Island revealed a nearly top-heavy biomass pyramid. The relatively high abundance of giant sea bass provides evidence that this species is recovering at kelp forests off Santa Catalina Island, and possibly throughout the Southern California Bight. The removal or recovery of predators can greatly influence an ecosystem. As more recent studies suggest that indirect community effects of fishing and protection can take up to decades to detect, it is necessary to document the continued changes on the structure, function, and dynamics of the kelp forests and rocky reefs off southern California.
Author: Parker H. House Publisher: ISBN: Category : Languages : en Pages : 95
Book Description
In many marine ecosystems worldwide, overfishing is a prominent cause in removing large predatory fishes from ecological communities. Fluctuation in the abundance of higher trophic level species can transform an ecosystem's structure and function by altering trophic interactions through density-mediated top-down control. Accordingly, understanding the extent to which humans indirectly influence a community through altering predator abundance is of critical importance. Thus, during the summer of 2013 and 2014 the impacts of fishing on the trophic structure and community assemblage of kelp forest fishes were examined within the Southern California Bight. In 2013, I tested whether decreased abundance through fishing for higher trophic level predators relieves predation pressure on lower trophic level prey. Using a combination of underwater survey techniques, density (no. fish/100 m2) and biomass (g/100 m2) of conspicuous fish species were sampled inside and outside of three long-standing Marine Protected Areas (MPAs) off La Jolla, Santa Catalina Island, and Anacapa Island, California. I found that secondary carnivore and herbivore/omnivore trophic levels significantly decreased outside of MPAs. Inversely, the primary carnivore trophic level biomass increased outside of MPAs. Species-level results revealed a lower abundance outside MPAs of large kelp bass (> 25 cm) and higher densities of its prey, kelp perch. My results show overall fish trophic level changes due to fishing pressure, and provide support for a weakening of top-down control on the kelp perch population through the removal of predatory fishes outside MPAs. To investigate the possible return of the historically overfished apex predator of the kelp forest fish community, I censused the giant sea bass (Stereolepis gigas) population at eight sites off Santa Catalina Island from mid-June through mid-August, 2014. Three possible spawning aggregations were identified at the sites Twin/Goat, The V's, and Little Harbor. The giant sea bass population at these sites primarily consisted of individuals 1.2 - 1.3 m long (total length, TL) with small and probably newly mature fish (estimated to be 10 - 11 years old) observed in aggregations. However, larger individuals 1.8 - 1.9 m TL accounted for the majority of the population biomass. Overall, mean spawning stock biomass of giant sea bass was 36.3 kg/1000 m2. Providing a general comparison of mean biomass among the trophic levels of kelp forest fishes off Santa Catalina Island revealed a nearly top-heavy biomass pyramid. The relatively high abundance of giant sea bass provides evidence that this species is recovering at kelp forests off Santa Catalina Island, and possibly throughout the Southern California Bight. The removal or recovery of predators can greatly influence an ecosystem. As more recent studies suggest that indirect community effects of fishing and protection can take up to decades to detect, it is necessary to document the continued changes on the structure, function, and dynamics of the kelp forests and rocky reefs off southern California.
Author: Samuel Charles Ginther Publisher: ISBN: Category : Languages : en Pages : 85
Book Description
The susceptibility of ecosystems to the introduction of non-native species has increased drastically with the development of advanced transportation technologies. It is now quite common for organisms to be easily transported by humans across physiological, ecological, or behavioral barriers that once served as natural population constraints. Despite this increased rate of introductions to locations that were previously unreachable, most organisms that are introduced perish because they are not able to withstand the new environmental pressures of the introduced location, or there are simply not enough conspecifics to perpetuate the population. However, when introduced organisms are able to thrive and reproduce, they may have devastating economic or ecological consequences. A new opportunity to document and understand the effects of an invasive alga on native community members has presented itself in southern Californian waters. Native to northeastern Asia, Sargassum horneri is a macroalga that was presumably transported in ballast water and discovered in Long Beach Harbor in 2003. By 2006 it had spread to the western side of Santa Catalina Island, California, and within a year spread along the entire leeward coast, forming dense stands in numerous areas. Although not all exotic species are ecologically harmful, S. horneri has attributes (fast growing and occurs in high densities) that may allow it to readily establish and out compete marine flora critical to the community structure of fishes. The purpose of this study aimed to document the effects of S. horneri on kelp forest fishes at Santa Catalina Island, California. I first employed observational, correlative methods to explore the role of S. horneri in shaping biotic and abiotic habitat characteristics of reefs and fish assemblages. I also explored habitat characteristics that predict fish assemblage structure, as well as species-specific responses of fish to habitat predictor variables during 4 distinct time periods. Fish assemblages changed over the course of my 4 sampling periods, and a number of habitat variables (including S. horneri) explained variation in fish assemblage during those times. However, there is more evidence that favors M. pyrifera as a driver of fish assemblage change, as indicated by species-level responses. Additionally, a field experiment testing whether the removal of S. horneri from reef areas affected the fish assemblage was used to evaluate whether patterns documented in the observational portion of my study that could be attributed to S. horneri do in fact appear to be caused by the invasive alga. Removing S. horneri from established areas of reef did not affect multivariate or univariate metrics of fish assemblage over the course of 7 sampling periods. Removal and control (unaltered) areas of reef contained strikingly similar fish assemblages, fish richness, and fish densities over time. Despite a drastic change in reef landscape, it appears that M. pyrifera, rather than S. horneri, was a more significant driver of differences in kelp forest fish assemblages observed in my study. Second, I compared the role of relatively low-lying S. horneri and vertically extensive M. pyrifera in shaping recruitment patterns of a popular sport fish (Paralabrax clathratus) by using an observational and experimental study. I first examined kelp bass recruit abundance on naturally standing S. horneri and M. pyrfera to better understand how fish recruitment rates differ between the introduced and native species. Additionally, I experimentally isolated 3 treatments (M. pyrifera only, S. horneri only, and M. pyrifera and S. horneri together) over a sandy bottom to understand whether the presence of S. horneri, and increased benthic complexity for young fish, enhances kelp bass recruitment. An overwhelming majority of kelp bass recruited to M. pyrifera, and larger recruits were located in the bottom two-thirds of the thalli. Kelp bass recruitment was were observed with S. horneri, regardless of whether the alga was alone or paired with M. pyrifera. Similar to my observational results, larger kelp bass recruits were observed in the bottom third of M. pyrifera treatments. Additionally, I found that the presence of larger, predatory conspecifics explained a spatial pattern of declining recruitment rates across treatment plots. My study presents the first evidence that S. horneri negatively impacts the recruitment of an important southern California reef fish. Results from both of my studies offer contrasting outlooks on S. horneri's role in southern California kelp forests. When focusing on the entire fish assemblage, little evidence is in favor of S. horneri as a driver of kelp forest fish structure. However when focusing on a particular early life history characteristic of a common kelp forest fish, the effects of S. horneri are dramatically negative. The contrasting results of my studies are important reminders for the need of additional studies to generate a more comprehensive understanding of this invasive alga's impact on kelp forest organisms.
Author: Publisher: ISBN: Category : Electronic books Languages : en Pages : 45
Book Description
Habitat use of a species is a vital component in explaining the dynamics of natural populations. For mobile marine species such as fishes, describing habitat heterogeneity at a seascape scale is essential because it quantifies the spatial extent to which fishes are interacting with their environment. Here, we explored the relationships between habitat metrics and the density and size of coastal rocky reef fishes across a seascape that is naturally fragmented. Multibeam sonar and GIS analysis were employed to create a seascape map that explicitly depicted bathymetry and spatial configuration of rocky reefs in southern California. Georeferenced subtidal transect surveys were conducted across this seascape to describe habitat attributes, including the density of macroalgae, and record the number and size of fishes. To compare the relative influence of habitat metrics, individual variables were grouped into macroalgae, bathymetry, and spatial configuration components, allowing for comparisons of within-patch to surrounding habitat metrics in describing the numerical density, biomass density, average size, and maximum size of five abundant rocky reef fishes. We found that responses to different habitat components were dependent on particular species, the choice of spatial scale, and the inherent characteristics of the seascape itself. Notably, the relative influence of seascape components were dependent on the configuration of the seascape; where fishes in a more isolated and less-connected seascape were more influenced by spatial configuration than a seascape with greater habitat connectedness. This study demonstrates that explicit habitat maps allow for a more comprehensive understanding of population structure when describing fishes across large spatial scales.
Author: Glenn R. VanBlaricom Publisher: Springer Science & Business Media ISBN: 3642728456 Category : Science Languages : en Pages : 261
Book Description
The impetus for this volume comes from two sources. The first is scientific: by virtue of a preference for certain large benthic invertebrates as food, sea otters have interesting and significant effects on the structure and dynamics of nearshore communities in the North Pacific. The second is political: be cause of the precarious status of the sea otter population in coastal California, the U.S. Fish and Wildlife Service (USFWS) announced, in June 1984, a proposal to establish a new population of sea otters at San Nicolas Island, off southern California. The proposal is based on the premise that risks of catastrophic losses of sea otters, due to large oil spills, are greatly reduced by distributing the population among two geographically separate locations. The federal laws of the U.S. require that USFWS publish an Environmental Impact Statement (ElS) regarding the proposed translocation of sea otters to San Nicolas Island. The EIS is intended to be an assessment of likely bio logical, social, and economic effects of the proposal. In final form, the EIS has an important role in the decision of federal management authority (in this case, the Secretary of the Interior of the U.S.) to accept or reject the proposal.
Author: Harold Mooney Publisher: Univ of California Press ISBN: 0520278801 Category : Nature Languages : en Pages : 1008
Book Description
This long-anticipated reference and sourcebook for CaliforniaÕs remarkable ecological abundance provides an integrated assessment of each major ecosystem typeÑits distribution, structure, function, and management. A comprehensive synthesis of our knowledge about this biologically diverse state, Ecosystems of California covers the state from oceans to mountaintops using multiple lenses: past and present, flora and fauna, aquatic and terrestrial, natural and managed. Each chapter evaluates natural processes for a specific ecosystem, describes drivers of change, and discusses how that ecosystem may be altered in the future. This book also explores the drivers of CaliforniaÕs ecological patterns and the history of the stateÕs various ecosystems, outlining how the challenges of climate change and invasive species and opportunities for regulation and stewardship could potentially affect the stateÕs ecosystems. The text explicitly incorporates both human impacts and conservation and restoration efforts and shows how ecosystems support human well-being. Edited by two esteemed ecosystem ecologists and with overviews by leading experts on each ecosystem, this definitive work will be indispensable for natural resource management and conservation professionals as well as for undergraduate or graduate students of CaliforniaÕs environment and curious naturalists.
Author: Brian Zgliczynski Publisher: ISBN: 9781321622058 Category : Languages : en Pages : 181
Book Description
The removal of apex predators is widely recognized to have broad ecological consequences for terrestrial and aquatic communities. In marine systems, the direct effects of fisheries exploitation include altering the community standing stock (biomass), species composition, and size-structure of the fish assemblage. Although the direct effects of fisheries exploitation are well documented, there is increasing evidence that the non-lethal effects of predation can also strongly influence the structure and function of ecological communities. In this dissertation I set out to increase our understanding of the effects of predators on coral reef fish assemblages by conducting a series of large-scale natural experiments across groups of Pacific islands spanning gradients of human population density and oceanographic productivity within four distinct geopolitical regions. My dissertation research reveals striking evidence for the effects of fisheries exploitation and oceanographic productivity on coral reef fish assemblages in three key areas. First, I found strong evidence that the effects of fisheries exploitation are not restricted to large-bodied species from higher-trophic levels but are realized throughout the entire fish assemblage and across multiple trophic groups. Importantly, I show that multiple forms of fisheries exploitation may be present on coral reefs, indicating the complex nature of coral reef fisheries. Second, I show strong evidence of biophysical coupling with gradients of oceanographic productivity and alterations in predatory fish abundance on the body condition, growth rates, maximum size, and longevity of coral reef fishes. I also observe a breakdown of natural coupling at inhabited islands, suggesting that local human impacts are capable of homogenizing life history traits of fishes even when strong environmental gradients are present. Third, I show that the trophic structure of coral reef fish assemblages are more tightly linked to changes in oceanographic productivity than to predatory fish abundance. I observed trophic channeling, a process by which different basal sources of energy entering the system can remain isolated on coral reefs forming distinct pathways up through the food web to top-level carnivores. In summary, my dissertation provides important insight into the mechanisms that structure marine communities and the direct and indirect effects of removing predators from marine ecosystems.
Author: Kristina Yoshida Publisher: ISBN: Category : Languages : en Pages : 108
Book Description
Freshwaters ecosystems support extraordinary biodiversity relative to their extent and provide important societal benefits. As such, freshwater environments and biota are often heavily impacted by anthropogenic activities. Freshwater fishes in Mediterranean-climate regions are especially impacted because of large human populations in these regions and extensive agricultural production, extensive river modification for flood control and to meet societal demands, and because these systems are heavily invaded by non-native organisms. The distribution and ecology of freshwater fishes in Mediterranean-climate regions are also influenced by the distinct wet and dry periods and the high inter-annual variability in precipitation. Thus, efforts to manage and conserve native fishes in Mediterranean-climate regions require understanding both the effects of human disturbance and the strong seasonality that characterizes these regions. In this dissertation, I examine the relationship between land use and Mediterranean seasonality on freshwater fishes in streams within the greater San Francisco Bay region in California, USA. In my second chapter, I use a multivariate approach to explore variability among fish communities in 25 Bay Area watersheds. I found that a combination of local (water conductivity) and watershed-scale factors (percent forested watershed, watershed area, elevation) were important predictors of fish communities across sites. Furthermore, watershed-scale factors had indirect effects on fish communities through their influence on a local-scale factor, water conductivity. The results of this chapter highlight the importance of considering both the direct and indirect effects of watershed-scale factors on freshwater fish communities. In my third chapter, I continued my analysis of land use and fish communities with a focus on contemporary land change. For this chapter, I performed a resurvey study, surveying the habitat and fish communities in 32 sites in the Alameda Creek Watershed that had been surveyed by Dr. Robert Leidy in the mid-1990s, including sites in the rapidly urbanizing Livermore Valley region. Again using a multivariate approach, I found that the increase in urbanization across an approximately 16-year period was related to change in fish community composition, a decline in native species richness, and a decline in a common native cyprinid - changes that were not observed in another part of the watershed that has experienced little land use change in the last 16 years. The relationship between land use change and fish community change was strongest when considering land use change at a local scale. These results suggest that ongoing land change alters fish communities and that contemporary resurveys are an important tool for examining how freshwater taxa respond to recent and ongoing environmental change. In my final chapter, I assessed how seasonal drought, a characteristic feature of Mediterranean-climate systems, influenced food webs in a small intermittent stream in Marin County, CA that provides rearing habitat for threatened steelhead trout (Oncorhynchus mykiss). I used stable isotopes of carbon and nitrogen to characterize food web structure and the trophic position of a suite of predators in this system, including O. mykiss and several macroinvertebrate predators. I compared food web snapshots across time, as well as between permanent and temporary pools. I found that the intermittent stream food web remained relatively stable across time and did not differ between pool types. However, I also found significant changes in the trophic position, niche width, and mean [delta]13C values for aquatic predators. This study provides an important first look at the trophic ecology of an imperiled fish species in intermittent streams during the summer drought season, and emphasizes that food chain length increases across the drought season, possibly because invertebrate prey are concentrated with declining water levels. In conclusion, my research shows that anthropogenic factors at the watershed scale influence instream conditions and freshwater fish communities, and emphasizes that contemporary changes in land use can have subtle changes on fish community structure, which may be indicative of future declines of extirpations of native fishes. Finally, my research shows that changing conditions across the summer drought season lead to shifts in the trophic ecology of some, but not all, aquatic predators, including threatened steelhead trout. Overall my research contributes to a growing body of research that demonstrates how multi-scale natural and anthropogenic factors influence freshwater fishes in Mediterranean-climate region.
Author: Parker H. House
Author: Parker H. House
Author: Samuel Charles Ginther
Author: Michael S. Foster
Author: 
Author: Glenn R. VanBlaricom
Author: Harold Mooney
Author: Brian Zgliczynski
Author: Kristina Yoshida
Author: Susan D. Kocher
Author: