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Mapping and analyzing the Florida Reef Tract in Palm Beach County in relation to major storm events in a GIS databaseUnknown Date (has links)
The Florida Reef Tract in Southeast Florida is made up of hard-bottom formations. The shape and size of the tract is constantly changing. One major factor contributing to these changes is the movement of sand. This is influenced by location-based, human-induced, and natural factors. These shifting sands cover or uncover reef structure. Images of the Florida Reef Tract in Palm Beach County were analyzed by the Department of Geosciences at Florida Atlantic University, using a partially automated method of mapping. There are notable changes in reef structure throughout the years 2004-2006, in which many major storm events occurred in the region. A time series analysis was conducted throughout these years. Losses and gains of reef structure were quantified and compared throughout the county as a whole, in beach renourishment project areas, and inlet intervals. Trends suggest that the major storms of 2004-2006 may have had effects on the reef tract. / by Joseph G. Pitti. / Thesis (M.A.)--Florida Atlantic University, 2011. / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2011. Mode of access: World Wide Web.
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Characterization of symbiotic algae, genus Symbiodinium, in corals at St. Lucie reef, FloridaUnknown Date (has links)
The unique coral reef at St. Lucie Reef (Stuart, FL) persists despite environmental variability from extensive freshwater discharges, summer upwelling, and thermal
instability. By examining the symbiotic zooxanthellae, or Symbiodinium, that reside
in corals, we can gain insight to coral physiology impacted by local stressors. Two
scleractinian corals, Montastraea cavernosa and Pseudodiploria clivosa were sampled
over 1.5 years, including both wet and dry seasons. Zooxanthellae were isolated and
quantitatively characterized using standard measurements and molecular techniques.
Both coral species varied in zooxanthellae biomass, where Pseudodiploria clivosa had
Higher cell densities and chlorophyll concentrations than Montastraea cavernosa. Over
time, these parameters varied, but were not significantly altered by fresh water discharge events. Symbiodinium diversity and abundance were identified by ITS2 region amplification and next-generation sequencing .Novel associations between Symbiodinium and each coral explained the observed physiological differences. The symbioses remained stable throughout and could indicate local adaptation for St. Lucie Reef corals. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2014. / FAU Electronic Theses and Dissertations Collection
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Climate change effects on dimethylated sulphur dynamics in tropical coral reef systemsGreen, Tamara Kirsty January 2019 (has links)
Dimethylsulphoniopropionate (DMSP) and dimethylsulphoxide (DMSO) (collectively DMSP/O) are produced by marine algae, including symbiotic algae within corals. These sulphur compounds are important not only in sulphur cycle dynamics but also in potentially mediating atmospheric conditions, alleviating the effects of climate change and contributing to reef health. Most research has focused on the production of DMSP and its major degradation product, the climatically active gas, dimethylsulphide (DMS) by Acropora corals in the Great Barrier Reef. However, mechanisms for the production and release of DMSP/O by different reef taxa is poorly understood. Recently the importance of mesophotic reefs as refugia for shallow water corals has been postulated, however their role in the marine sulphur cycle is unknown. This research aimed to improve our understanding of the contemporary and climate change induced seawater and tissue production of DMSP/O in a range of reef environments and taxa. This was achieved through a combination of laboratory and field - based studies, using modern and established techniques. An effect of both elevated temperature and OA on increased tissue and seawater concentrations of DMSP/O production is reported in field and laboratory studies. Contrasting effects of benthic cover on tissue DMSP/O distributions and seawater DMSP are also noted. The importance of the physical and hydrodynamic environment on biogeochemical connectivity both within a reef and between neighbouring reefs is also focussed on. Crucially, however, the novel tissue and seawater data from mesophotic sites suggests that deeper reefs could affect the biogeochemistry of their shallow water counterparts. The key finding from this work is that climate change will result in increased seawater DMSP concentrations via two mechanisms; through the increase of cellular production of DMSP/O in all reef taxa, and by increasing the biomass of prolific DMSP producers as reefs transition to a fleshy/macroalgal assemblage. Whilst this could potentially mediate the effects of climate change, it will probably also worsen overall reef health, lead to a restructuring of reef communities from the microbial level upwards and will have possibly permanent and deleterious effects on overall ecosystem function.
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Small, no-take marine protected areas and wave exposure affect temperate, subtidal reef communities at Marmion Marine Park, Western AustraliaRyan, Kylie A. January 2008 (has links)
[Truncated abstract] The ecological effects of marine protected areas (MPAs) in temperate ecosystems are poorly understood relative to their tropical counterparts. The limited number of rigorous empirical studies supporting existing theoretical models, increasing public awareness of the importance of marine conservation strategies and legislative requirements to review management effectiveness provide further impetus to study temperate MPAs. Investigations should consider confounding effects of natural variability if MPA effects are to be clearly demonstrated. This research helps to address these needs by investigating the short term effects of sanctuary zones (no-take MPAs where fishing is prohibited) and wave exposure at Marmion Marine Park, Western Australia. The three sanctuary zones at Marmion Marine Park are extremely small (0.061 0.279 km2) compared to most reported in the literature. The sanctuary zones are nested within a larger, fished zone (94.95 km2). The sanctuary zones have been protected from fishing since the year 2000. A post-hoc, asymmetrical sampling design was used in this study and involved surveys of fishes, mobile invertebrates and macroalgae at one sanctuary zone and two fished sites (controls) at each of three successive, subtidal reef lines. The three reef lines are exposed to a gradient in wave energy. The size structure and abundance of the heavily exploited Panulirus cygnus (Western Rock Lobster) were positively affected by protection from fishing in sanctuary zones, despite the highly mobile nature of this migratory species. The mean abundance of legal size lobsters was higher in sanctuary zones compared to fished sites during an interannual study (2003, 2005 and 2006). The total abundance of lobsters and the mean abundance of legal size lobsters were higher at inshore and offshore sanctuary zones compared to fished control sites during a 2005/2006 fishing season study. These zoning effects did not vary with the time of survey. ... Furthermore, the abundance of large lobsters in sanctuary zones decreased with the duration of the 2005/2006 fishing season. Similarly, it is likely that sanctuary zones are too small relative to the movement of fishes to adequately protect stocks of some targeted species. The small sanctuary zones at Marmion are unlikely to offer protection to highly mobile species over the long term. And finally, ecological assemblages within each level of wave exposure are distinct. Consequently for each assemblage type, the current reserve design does not include replication of sanctuary zones and does not offer any 'insurance' in the event of isolated impacts affecting a particular zone. This study has identified the benefits and deficiencies of the design and function of small no-take temperate MPAs in Western Australia. An increase in the size and number of sanctuary zones within each wave exposure level will help to address the v shortfalls of the zoning scheme and enhance the conservation benefits of management at Marmion Marine Park. More generally, this study demonstrates that the mobility of the species to be protected from fishing should be considered when designing MPAs. Lessons learned from this work will be beneficial for the future management and conservation of resources in the region and elsewhere.
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The development and application of benthic classifications for coral reef ecosystems below 30 m depth using multibeam bathymetry : Tutuila, American SamoaLundblad, Emily Ruth 07 June 2004 (has links)
Coral reef ecosystems are the most diverse on earth, and their subsistence is being
threatened by natural and adverse anthropogenic patterns and processes. In an effort to
understand and protect these marine environments, several programs have outlined
strategies and initiatives. For example, the United States Coral Reef Task Force���s
Mapping and Information Working Group has outlined a specific goal to map all coral
reefs below 30 m depth by 2009. This study contributes to achieving that goal for three
sites around the island of Tutuila, American Samoa, lying in the heart of the South
Pacific. American Samoa, a U.S. territory, is home to the Fagatele Bay National Marine
Sanctuary, the smallest and most remote in the United States, and to the National Park of
American Samoa. Extensive modern scientific surveys were implemented around the
territory in 2001 and have since continued and increased. The presence of protected
areas and the existence of scientific data collected with state of the art technology have
made the site a priority for the Coral Reef Task Force. In this study, methods for
classifying surficial seafloor characteristics as bathymetric position index (BPI) zones
and structures were developed and applied to the study sites. BPI zones and structures
were classified by using algorithms that combine high-resolution (1 m) multibeam
bathymetry and its derivatives: bathymetric position index at multiple scales and slope.
The development of algorithms and the classification scheme involved the use of
historical and current classification studies and three-dimensional visualization. In
addition, the BPI zones and structures were compared to limited biological, geological,
and physical attributes recorded during accuracy assessment surveys (photos) and towed
diver surveys (video). A rugosity (surface ratio) analysis was added to the study to give a
picture of the seafloor roughness. The BPI zone and structure classifications overlap and
extend existing classifications from Ikonos satellite imagery for water depths shallower
than 30 m. Methods, data and classifications developed and applied in this study will be
available to the public as a benthic habitat mapping tool (ArcGIS extension), in an online
GIS data archive, and on a compact disc attached to this thesis. They contribute to a
broader understanding of the marine and coastal environment and will serve as a baseline
of information for benthic habitat mapping and future biological, ecological, and
geological surveys. The baseline gives a good indication of characteristics that may
indicate areas of high biodiversity. The final maps presented here are especially useful to
managers, researchers and scientists that seek to establish and monitor a wider and more
effective network of marine and coastal protection. / Graduation date: 2005
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Chemically mediated competition, herbivory, and the structure of coral reefsRasher, Douglas B. 03 July 2012 (has links)
Corals, the foundation species of tropical reefs, are in rapid global decline as a result of anthropogenic disturbance. On many reefs, losses of coral have coincided with the over-harvesting of reef herbivores, resulting in ecosystem phase-shifts from coral to macroalgal dominance. It is hypothesized that abundant macroalgae inhibit coral recovery and recruitment, thereby generating ecological feedback processes that reinforce phase-shifts to macroalgae and further diminish reef function. Notwithstanding, the extent to which macroalgae directly outcompete coral, the mechanisms involved, and the species-specificity of algal-coral competition remains debated. Moreover the capacity for herbivores to prevent vs. reverse ecosystem phase-shifts to macroalgae and the roles of herbivore diversity in such phenomena remain poorly understood. Here I demonstrate with a series of field experiments in the tropical Pacific and Caribbean Sea that multiple macroalgae common to degraded reefs directly outcompete coral using chemical warfare, that these interactions are mediated by hydrophobic secondary metabolites transferred from algal to coral surfaces by direct contact, and that the outcomes of these allelopathic interactions are highly species-specific. Using field observations and experiments in the tropical Pacific, I also demonstrate that the process of herbivory attenuates the competitive effects of allelopathic algae on corals by controlling succession of algal communities, and that the herbivore species responsible for macroalgal removal possess complementary tolerances to the diversity of chemical defenses deployed among algae, creating an essential role for herbivore diversity in reversing ecosystem phase-shifts to macroalgae. Lastly, I demonstrate with field experiments in the tropical Pacific that algal-coral competition simultaneously induces allelochemicals and suppresses anti-herbivore deterrents in some algae, likely due to trade-offs in the productions of defense metabolites with differing ecological functions. Together, these studies provide strong evidence that chemically mediated competitive and consumer-prey interactions play principal roles in coral reef degradation and recovery, and should provide resource managers with vital information needed for effective management of these ecologically and economically important but threatened ecosystems.
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Sedimentology, coral reef zonation, and late Pleistocene coastline models of the Sodwana Bay continental shelf, Northern ZululandRamsay, Peter John. January 1991 (has links)
This geostrophic current-controlled Zululand/Natal shelf displays a unique assemblage of interesting
physical, sedimentological and biological phenomena. The shelf in this area is extremely narrow
compared to the global average of 75km, and is characterised by submarine canyons, coral reefs, and
steep gradients on the continental slope. A shelf break occurs 2.1km to 4.1km offshore and the shelf
can be divided into a northern region and a southern region based on the presence or absence of a
defined shelf break. The southern shelf has a poorly-defined shelf break whilst the northern shelf has
a well-defined break at -65m. The poor definition of the shelf break on the southern shelf can possibly
be attributed to the presence of giant, climbing sand dunes offshore of Jesser Point at depths of -37m
to -60m. The northern shelf has a series of coast-parallel oriented patch coral reefs which have
colonised carbonate-cemented, coastal-facies sequences.
The northern shelf can be divided into three distinct zones: inner-, mid-, and outer-shelf zones. The
inner-shelf is defined as the area landward of the general coral reef trend, with depths varying from
0m to -I5m and having an average gradient of 1.1. The mid-shelf is defined by the general coral reef
trend, varying from -9m over the shallow central axis of the reefs to -35m along the deep reef-front
environments. The outer-shelf is seaward of the coral reefs and occurs at a depth range of -35m to -
65m. Gradients vary from 1° in the south to 2.5° in the northern part of the study area, and are steep
compared to world average shelf gradient of 0.116°.
Four submarine canyons occur in the study area and are classified as mature- or youthful-phase
canyons depending on the degree to which they breach the shelf. The origin of these canyons is not
related to the position of modern river mouths but can probably be linked to palaeo-outlets of the
Pongola and Mkuze River systems. It is suggested that the canyons are mass-wasting features which
were exploited by palaeo-drainage during regressions. The youthful-phase canyons appear to be mass-wasting features associated with an unstable, rapidly-deposited, progradational late Pliocene sequence
and a steep upper continental slope. The mature-phase canyons were probably initiated by mass-wasting
but have advanced shoreward, breaching the shelf, due to their link with the palaeo-outlets
of the Pongola and Mkuze Rivers during late Pleistocene regressions.
Evidence of modem canyon growth has been noted on numerous SCUBA diving surveys carried out
on the canyon heads. These take the form of minor wall slumps and small-scale debris flows. The
canyons are also supplied with large quantities of sand in the form of large-scale shelf subaqueous
dunes generated and transported by the Agulhas Current. As these bedforms meet the canyons the
sediment cascades down the canyon thalweg and causes erosion and downcutting of the canyon walls
and floor thereby increasing the canyon dimensions.
Late Pleistocene beachrock and aeolianite outcrops with or without an Indo-Pacific coral reef veneer
are the dominant consolidated lithology on the shelf. These submerged, coast-parallel, carbonate cemented,
coastal facies extend semi-continuously from -5m to -95m, and delineate late Pleistocene
palaeocoastline events. The rock fabric of these high primary porosity lithologies shows grains floating
in a carbonate cement with occasional point-contacts. Grains are mostly quartz (80-90%), minor K-feldspar
and plagioclase (5-10%), and various lithic fragments. The rocks contain conspicuous organic
grains including foraminifera, bivalve, echinoid, bryozoan, red algal, and occasional sponge spicule
fragments; these commonly display replacement fabrics or iron-stained rims. The dominant
sedimentary structures found in these sandstone outcrops include high-angle planar cross-bedding and
primary depositional dip bedding. Palaeocurrent directions sngest a palaeoenvironment dominated
by a combination of longitudinal and transverse dunes with wind directions similar to those observed
forming the modem dune systems. Erosional features evident on the submerged beachrocks and
aeolianites include gullies trending in two different directions and sea-level planation surfaces with or
without the presence of potholes.
The unconsolidated sediment on the shelf is either shelf sand, composed mainly of terrigenous quartz
grains; or bioclastic sediment which is partially derived from biogenic sources.
The quartzose sand from the inner-shelf is generally fine-grained, moderately- to well-sorted, and
coarsely- to near symmetrically-skewed. Carbonate content is low, and varies between 4-13%.
Quartzose sand from the outer-shelf is fine-grained, moderately- to well-sorted, and coarsely- to very
coarsely-skewed. The inner-shelf quartzose sand is better sorted than the outer-shelf sand due to
increased reworking of this sediment by the high-energy swell regime. Sediment from the shallower
areas of the outer-shelf (< -50m) is better sorted than sediment from depths of greater than -50m.
Generally wave-reworking of quartzose shelf sand from the Sodwana Bay shelf results in greater
sediment maturity than that observed from geostrophic current effects or a combination of geostrophic
and wave-reworking. This sediment was derived by reworking of aeolian and beach sediments,
deposited on the shelf during the period leading up to the Last Glacial Maximum (15 000 - 18 000
years B.P.) when sea-level was -130m, during the Holocene (Flandrian) transgression.
Bioclastic sediment on the Sodwana Bay shelf is defined as having a CaC03 content of greater than
20% and is a mixture of biogeoically-derived debris and quartzose sand. The distribution of bioclastic
sediment in the study area is widespread, with reef-derived and outer-shelf-derived populations being
evident. This sediment consists of skeletal detritus originating from the mechanical and biological
destruction of carbonate-secreting organisms such as molluscs, foraminifera, alcyonaria, scleractinia,
cirripedia, echinodermata, bryozoa, porifera. The reef-derived bioclastic population is confined to
depths less than -40m in close proximity to reef areas, whereas the shelf-derived bioclastic population
occurs at depths greater than -40m and is derived from carbonate-producing organisms on deep water
reefs and soft-substrate environments on the shelf.
Large-scale subaqueous dunes form in the unconsolidated sediment on the outer-shelf due to the
Agulhas flow acting as a sediment conveyor. These dunes are a common feature on the Sodwana Bay
shelf occurring as two distinct fields at depths of -35m to -70m, the major sediment transport direction
being towards the south. The two dune fields, the inner- and outer subaqueous dune fields, are
physically divided by Late Pleistocene beachrock and aeolianites ledges. A bedform hierarchy has been
recognised. The larger, outer dune field appears to have originated as a system of climbing bedforms
with three generations of bedforms being superimposed to form a giant bedform, while the inner dune
field has a less complex construction. The largest bedforms are those of the outer dune field off Jesser
Point, being up to 12 m high, 4 km long and 1.2 km wide. A major slip face, with a slope of 8° is
present.
Bedload parting zones exist where the bedform migration direction changes from south to north.
Three bedload parting zones occur in the study area at depths of -60m, -47m and -45m; two in the
inner dune field and one in the outer dune field. These zones are invariably located at the southern
limits of large clockwise eddy systems. Such eddies appear to be the result of topographically induced
vorticity changes in the geostrophic flow and/or the response to atmospheric forcing caused by coastal
low-pressure system moving up the coastline.
It has been demonstrated that the inner subaqueous dune sediment conveyor is not active all the time
but only during periods . of increased current strength when the Agulhas Current meanders inshore.
The smaller bedforms in the outer dune field undergo continuous transport due to the current velocity
on the shelf edge outer dune field being higher than the velocity experienced on the inner dune field.
The very large 2·D dune which forms the outer dune field is probably not active at present: this is
inferred due to the shallow angle of the mega-crest lee slope (8°).
The very large Sodwana Bay subaqueous dune fields may be compared with the very large,
reconstructed, subaqueous dunes which occur in Lower Permian sediments of the Vryheid Formation,
northern Natal. These Permian dunes are represented, in section, as a fine- to medium-grained distal
facies sandstone with giant crossbeds. These large-scale bedforms are unidirectional, but rare
directionally-reversed, climbing bedforms do occur, this directional reversal may be related to bedload
parting zones. On the evidence presented in this thesis, it is proposed that these Permian subaqueous
dunes may be ancient analogues of the modem subaqueous dune field on the Sodwana Bay shelf.
Positive-relief hummocks and negative-relief swale structures are fairly common in the fine-grained,
quartzose shelf sand at depths of -30m to -60m. These appear to be transitional bedforms related to
the reworking by storms of medium 2-D subaqueous dunes. These hummocky structures may be the
modem equivalent of hummocky cross-stratification noted in the geological record, and if so, they are
probably the first to have ever been observed underwater.
The occurrences of ladderback ripples on the Sodwana Bay shelf at depths of -4m to -17m, suggest that
subtidal ladderback ripples may be more common than previously thought. Ladderback ripples are
common features of tidal flats and beaches where they form by late-stage emergence run-off during
the ebb tide. They are generally considered diagnostic of clastic intertidal environments. The mode
of formation on the Sodwana Bay shelf is different from the classic late-stage emergence run-off model
of intertidal occurrences, being a subtidal setting. Subaqueous observations indicate that ladderback
ripples are not environment-specific, and that additional evidence of emergence is therefore necessary
to support an intertidal setting in the rock record: ladderback ripples alone are insufficient to prove
an intertidal environment.
The coral patch reefs of the northern Natal coast are unique, being the most southerly reefs in Africa,
and totally unspoilt. The Zululand reefs are formed by a thin veneer of Indo-Pacific type corals which
have colonised submerged, late Pleistocene beachrocks and aeolianites. Two-Mile Reef at Sodwana Bay
has been used to develop a physiograpbic and biological zoning model for Zululand coral reefs, which
has been applied to other reefs in the region. Eight distinct zones can be recognised and differentiated
on the basis of physiographic and biological characteristics. The reef fauna is dominated by an
abundance of alcyonarian (soft) corals, which constitute 60-70% of the total coral fauna. The Two-Mile
Reef zoning model has been successfully applied to larger reefs such as Red Sands Reef, and smaller
patch reefs (Four-Mile and Seven-Mile Reefs) in the same general area.
In this thesis extensive use has been made of Hutton's uniformitarian principles. Hutton's doctrine
is particularly relevant to the study of depositional processes and relict shorelines. Coastal processes
and weather patterns during the late Pleistocene were broadly similar to modem conditions enabling
direct comparisons to be made. A computer-aided facies analysis model has been developed based on
textural statistics and compositional features of carbonate-cemented coastal sandstones. Many
attempts have been made to distinguish different ancient sedimentary depositional environments, most
workers in this field having little success. The new method of facies reconstruction is based on:
(1) underwater observations of sedimentary structures and general reef morphology;
(2) a petrographic study of the reef-base enabling flve facies: aeolianite, backbeach,
forebeach, swash, and welded bar facies to be recognised, which control the
geomorphology of Two-Mile Reef;
(3) cluster and discriminant analysis comparing graphic settling statistics of acid-leached
reef-base samples with those of modem unconsolidated dune/beach environments.
The results of this analysis demonstrated that the beachrocks and aeolianites on the shelf formed
during a regression and that late Pleistocene coastal facies are similar to modem northern Zululand
coastal environments, which have been differentiated into aeolian, backbeach, forebeach, swash, &
welded bar.
A late Pleistocene and Holocene history of the shelf shows that during the late Pleistocene, post
Eemian regressions resulted in deposition and cementation of coast-parallel beachrocks and
aeolianites, which define a series of four distinct palaeocoastline episodes with possible ages between
117 000 and 22 000 years B.P. The beachrock/aeolianites formed on the shelf during stillstands and
slow regressions, and the gaps between these strandline episodes represent periods of accelerated sealevel
regression or a minor transgressive phase which hindered deposition and cementation. The
formation of these lithologies generated a considerable sediment sink in the nearshore zone. This
reduced sediment supply and grain transport in the littoral zone during the Holocene, and probably
enhanced landward movement of the shoreline during the Flandrian transgression.
Prior to the Last Glacial Maximum, the beachrock/aeolianite sedimentary sequence was emergent and
blanketed by shifting aeolian sands. The Pongola River, which flowed into Lake Sibaya, reworked the
unconsolidated sediments on the shelf, and exploited the route of least resistance: along White Sands
and Wright Canyon axes. The erosion resulting from fluvial denudation in Wright Canyon has caused
this canyon to erode some of the beachrock/aeolianite outcrops which form palaeocoastline episode 2
and entrench the canyon to a deeper level; this eroded the shelf to a distance of 2km offshore.
During the Flandrian transgression the unconsolidated sediment cover was eroded, exposing and
submerging the beachrock/aeolianite sequence. Flandrian stillstands caused erosional features such
as wave-planed terraces, potholes, and gullies to be incised into beachrock and aeolianite outcrops;
these are seen at present depths of -47m, -32m, .26m, -22m, -17m to -15m, and -12m. High energy
sediment transfers, in an onshore direction, resulted in the deposition of sand bars across the outlet
of Lake Slbaya's estuary and the development of a 130m + coastal dune barrier on a pre-existlng,
remnant Plelstocene dune stub. Sea-level stabilised at its present level 7 000-6 000 years B.P. and coral
reef growth on the beachrock/aeolianite outcrops probably started at 5 000 years B.P. A minimum age
for the formation of the northern Zululand coral reefs has been established at 3780 ± 60 years B.P.
A mid Holocene transgression relating to the Climatic Optimum deposited a + 2m raised beach rock
sequence. This transgression eroded the coastal dune barrier and caused a landward shoreline
translation of approximately 40m. A minor transgression such as this can be used as a model for
coastal erosion which will result from the predicted 1.5m rise in sea-level over the next century. This
rise in sea-level could result in a 30m landward coastline translation of the present coastline, ignoring
the influence that storms and cyclones will have on the coastline configuration. / Thesis (Ph.D.)-University of Natal, Durban, 1991.
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Fishing for resilience : herbivore and algal dynamics on coral reefs in Kenya.Humphries, Austin Turner January 2014 (has links)
Herbivory is a key process that mediates the abundance of primary producers and community composition in both terrestrial and aquatic ecosystems. On tropical coral reefs, changes in herbivory are often related to phase shifts between coral-dominance and dominance by seaweeds, or foliose macroalgae. Resilience or capacity to resist and reverse such phase shifts is, therefore, viewed as a critical function on coral reefs. This thesis used grazer exclusion and assay experiments at six sites within three different fisheries management regimes in Kenya to identify the impacts of herbivores (sea urchins and fishes) on algal dynamics in the context of coral reef resilience. First, I examined the grazing rates necessary to prevent phase shifts by quantifying consumption and algal production. Here, I found that, over a 390-day experiment, at least 50 percent of algal production must be consumed to avoid accumulation of algal biomass. Using video observations, I also showed that scraping parrotfishes remove more algae (per unit of fish biomass) than previously assumed, and that sea urchins, if released from predation, have similar impacts to fishes. Then I focused on algal succession, and found that sea urchins and fishes have different effects that are mediated by their abundances and species composition. Where sea urchins were less abundant and parrotfishes absent (e.g. young fisheries closures), progression of algae from turfs to early and then late successional macroalgae occurred rapidly and within 100 days. I then turned my focus to the removal of already established macroalgae (grown for > 1 yr in the absence of herbivores) and showed that sea urchins and browsing fishes were able to remove significant amounts of macroalgae where either herbivore was abundant. However, using multiple-choice selectivity assays and in situ video recordings, I found that browsing fishes fed very selectively with low overlap in diet among species, leading to low functional redundancy within a high diversity system. Finally, using long-term survey data (from 28 sites) to build a 43-year chronosequence, I showed that it is possible that the effects of herbivory will not be constant across transitions from open fishing to fishery closures through non-linear grazing intensity. Therefore, increases in herbivory within fisheries closures may not be immediate and may allow a window of opportunity for algae to go from turf to unpalatable macroalgae until scraping and browsing fishes fully recover from fishing (~ 20 years). The findings in this thesis are novel and raise concern over the potential implications of the slow recovery of parrotfishes or, given lower than expected functional redundancy in grazing effects, the absence of even one browsing fish species in fisheries closures. Overall, this thesis highlights the importance of herbivore community dynamics in mediating interactions among algae, and provides new insights for conservation and management actions that attempt to bolster the resilience of coral reefs.
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Social-Ecological Dynamics of Coral Reef Resource Use and ManagementFreed, Sarah J. 25 July 2013 (has links)
This dissertation investigates social and ecological factors that facilitate effective management of coral reefs as social-ecological systems. Meta-analytical and field-based methods were employed to examine current management challenges and identify strategies that improve management effectiveness and coral reef health. A meta-analysis was used to evaluate biological indicators of reef health in relation to the types of fishing regulations in place (no-take areas, gear restriction areas, and periodic closures) and the actor groups (community-based, co-management, state, private) involved in management efforts for coral reef fisheries throughout the world. Other than enhancement of fish biomass within no-take areas that was significantly greater than in gear restriction areas, most biological indicators benefitted similarly from management techniques of no-take areas and gear restriction areas. Community-based and co-management were the best performing management arrangements for some biological outcomes but require further case studies to verify findings. Investigation of management effects by region indicated that previously degraded reefs received fewer benefits from management implementation than did relatively healthier reefs. For field investigations, the Comoros islands in the Western Indian Ocean served as a model for tropical coral reefs with challenging socioeconomic contexts, high biodiversity, and high vulnerability to coral reef degradation. Empirical study at 21 sites was used to identify the relative effects of natural and anthropogenic threats to coral reefs of the Comoros. Most previous studies of reef health focus on primarily natural factors or a single anthropogenic threat. This study examined suites of natural factors and human activities to identify the relative importance of each on reef health. Human activities including fishing, sand extraction, and beachfront housing and development were the best predictors of reef health status.
Most notably, human population and fishing predicted fish richness, abundance, and biomass with seasonal variation in the effects, while site orientation strongly predicted benthic cover. Field studies in the Comoros were also used to investigate the roles of community and state actors in co-management and compare effectiveness of comanagement across sites with varying levels of actor participation. Effective management was found to occur with community or `meta-community' (in this case, a Marine Protected Area in which the efforts of several communities were organized) participation in governance and support of state or external agents, while resilient management that overcame considerable challenges was found to occur only with strong community participation and leadership in governance. External agents were found to contribute to development of meta-community governance structure and initiation of community participation through education and capacity building. The findings from these studies reveal that coral reef management can be improved through context appropriate regulations that address detrimental human activities and through wide acceptance and participation in governance with cooperation among states, communities, and external agents.
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Multiple stressor effects on coral physiology and biogeochemistryDobson, Kerri January 2021 (has links)
No description available.
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