Environemntal chage in coral reefs

Reef response to sea-level and environmental changes during the last deglaciation: Integrated Ocean Drilling Program Expedition 310, Tahiti Sea Level

by Elizabeth Abbey

Camoin G, Seard C, Deschamps P, Webster J, Abbey E, Braga JC, Iryu Y, Durand N, Bard E, Hamelin B, Yokoyama Y, Thomas A, Hendersone G, Dussouillez P. Geology. DOI: 10.1130/G32057

Spatial Analyses of Benthic Habitats to Define Coral Reef Ecosystem Regions and Potential Biogeographic Boundaries along a Latitudinal Gradient

by Brian Walker

Marine organism diversity typically attenuates latitudinally from tropical to colder climate regimes. Since the... more Marine organism diversity typically attenuates latitudinally from tropical to colder climate regimes. Since the distribution of many marine species relates to certain habitats and depth regimes, mapping data provide valuable information in the absence of detailed ecological data that can be used to identify and spatially quantify smaller scale (10 s km) coral reef ecosystem regions and potential physical biogeographic barriers. This study focused on the southeast Florida coast due to a recognized, but understudied, tropical to subtropical biogeographic gradient. GIS spatial analyses were conducted on recent, accurate, shallow-water (0–30 m) benthic habitat maps to identify and quantify specific regions along the coast that were statistically distinct in the number and amount of major benthic habitat types. Habitat type and width were measured for 209 evenly-spaced cross-shelf transects. Evaluation of groupings from a cluster analysis at 75% similarity yielded five distinct regions. The number of benthic habitats and their area, width, distance from shore, distance from each other, and LIDAR depths were calculated in GIS and examined to determine regional statistical differences. The number of benthic habitats decreased with increasing latitude from 9 in the south to 4 in the north and many of the habitat metrics statistically differed between regions. Three potential biogeographic barriers were found at the Boca, Hillsboro, and Biscayne boundaries, where specific shallow-water habitats were absent further north; Middle Reef, Inner Reef, and oceanic seagrass beds respectively. The Bahamas Fault Zone boundary was also noted where changes in coastal morphologies occurred that could relate to subtle ecological changes. The analyses defined regions on a smaller scale more appropriate to regional management decisions, hence strengthening marine conservation planning with an objective, scientific foundation for decision making. They provide a framework for similar regional analyses elsewhere.

Twenty-five years of change in scleractinian coral communities of Daya Bay (northern South China Sea) and its response to the 2008 AD extreme cold climate event

by Gilbert Price

Chen, T., Yu, K., Shi, Q., Li, S., Price, G., Wang, R., Zhao, M., Chen, T., Zhao, J., 2009. Twenty-five years of change in scleractinian coral communities of Daya Bay (northern South China Sea) and its response to the 2008 AD extreme cold climate event. Chinese Science Bulletin 54, 2107-2117.

Coral reefs worldwide are becoming increasingly and detrimentally impacted upon by a variety of factors including... more Coral reefs worldwide are becoming increasingly and detrimentally impacted upon by a variety of factors including significant climate changes, such as global warming and increased El Nino-Southern Oscillation activity. Generally, the persistence of coral reefs, especially at low-latitudes, is governed, in part, by sea surface temperatures not exceeding the critical limit (∼30°C) at which mass mortality can occur. Thus, it is thought that corals living at high-latitudes (i.e., currently cooler sea surface temperatures) will likely respond more favourably to hypothesized future temperature increases than corals living at low-latitudes (i.e., currently warmer sea surface temperatures). Consequently, high-latitude coral communities may have the potential to act as regions of refugia for many coral species in the face of potential future global warming. The Daya Bay (22°31′–22°50′N), northern South China Sea, contains several high-latitude non-reefal coral communities and represents one of the most northerly distributions of scleractinian corals within the region. Significantly, Daya Bay has experienced dramatic warming in both air and sea surface temperatures throughout the past 50 years. In this paper, we analyze 25 years of change in the Daya Bay coral communities, based both on historic surveys and our latest 2006–2008 regional ecological surveys. Our results suggest that, contrary to predictions, there have been significant declines in coral cover within the Daya Bay during the past 25 years (i.e., 76.6% coral cover in 1983/1984 to only 15.3% coral cover by 2008). Such changes also reflect a significant shift in the most abundant coral species, from Acropora pruinosa to Favites abdita. Most of the modern coral communities became established between 15 and 30 years ago, corresponding to a period of increased winter sea surface temperature. However, very few colonies have become established within the last 15 years, despite a more intense period of warming. By taking into account additional factors, we hypothesize that direct anthropogenic impacts, rather than climatic events, have both restricted the development, and drove the decline, of Daya Bay coral communities in the last 15 years. The Daya Bay has also been subjected to occasional extreme cold events during the past 50 years, with the most recent occurring in early 2008 (13 January–13 February). During the 2008 cold event, the lowest air temperature reaches only 6.6°C, and the mean sea surface temperature for February fall to < 14°C, including six continuous days at 12.3°C. Significantly, the sea surface temperatures fall below the hypothesized critical lower temperature threshold (∼13°C) that commonly leads to mass mortality in scleractinian coral communities. Surprisingly, our coral community surveys, conducted both before (August 2007) and after (late February 2008) the extreme 2008 cold event, demonstrate that the Daya Bay coral ecosystems are barely impacted upon during the cold period. Those observations suggest that the Daya Bay scleractinian coral communities have developed adaptations to low sea surface temperatures. Overall, our data support the hypothesis that high-latitude coral communities, such as Daya Bay, have the potential to act as areas of refugia for scleractinian corals in the advent of potential future global warming.

Protein expression and genetic structure of the coral Porites lobata in an environmentally extreme Samoan back reef: does host genotype limit phenotypic plasticity?

by Rob Toonen

The degree to which coral reef ecosystems will be impacted by global climate change depends on regional and local... more The degree to which coral reef ecosystems will be impacted by global climate change depends on regional and local differences in corals’ susceptibility and resilience to environmental stressors. Here, we present data from a reciprocal transplant experiment (RTE) using the common reef building coral Porites lobata between a highly fluctuating back reef environment that reaches daily environmental extremes typically considered stressful, and a more stable, neighboring forereef. Protein biomarker analyses assessing physiological contributions to stress resistance showed evidence for both genotypic and environmental influence on biomarker response. Genotypic influence was strongest for ubiquitin-conjugated proteins with consistently higher levels found in back reef source colonies both pre and post transplant when compared to their forereef conspecifics. Additionally, genetic comparisons of back reef and forereef populations revealed significant population structure in both the nuclear ribosomal and mitochondrial genomes of the coral host (FST=0.146 p<0.0001, FST=0.335 p<0.0001 for rDNA and mtDNA respectively), while algal endosymbiont populations were identical between the two sites. We propose that the genotype of the coral host may drive limitations to the physiological responses of these corals when faced with new environmental conditions. This result is important in understanding genotypic and environmental interactions in the coral algal symbiosis and how coral may respond to future environmental changes.

Geomorphology of submerged reefs on the shelf edge of the Great Barrier Reef: The influence of oscillating Pleistocene sea-levels

by Elizabeth Abbey

Abbey, E., Webster, J.M., Beaman, R.J., 2011 Geomorphology of submerged reefs on the shelf edge of the Great Barrier Reef: The influence of oscillating Pleistocene sea-levels. Marine Geology. 288: 61-78.

The submerged reefs on continental margins and surrounding oceanic islands are important archives of past climates,... more The submerged reefs on continental margins and surrounding oceanic islands are important archives of past climates, eustatic sea-level oscillations and oceanographic processes. Australia's north eastern submerged shelf edge reefs have previously been explored, but all studies have been limited by either low-resolution single beam profiles or by their limited spatial extent. The aim of this study is to improve the understanding of the origin and development of submerged shelf edge reefs, terraces and related features on the Great Barrier Reef (GBR), and the influence of Pleistocene sea-level oscillations on their distribution and geomorphology. We investigated the first large-scale (1400 km2) 3D bathymetry and acoustic backscatter dataset of four widely-spaced sites located across ca. 650 km along the shelf edge at Ribbon Reefs 1–5, Noggin Pass, Viper Reef and Hydrographers Passage. We provide a comprehensive description and systematic classification of the shelf edge features, and constrain their spatial distribution and geomorphologic variability using a wide range of quantitative morphometrics. Fifteen features are defined, four of which are the focus of this study, including terraces, pinnacles, ridges and channels. Using modern reefs within the GBR for comparison, we interpret these as fringing reefs, patch and barrier reefs and tidal channels respectively. The influence of gross shelf geomorphology and oceanographic factors driving the observed variability within and between sites is discussed in conjunction with Mid-Late Pleistocene sea-level oscillations. We observed two distinct types of reef growth characterised by the degree of development, which we interpret as analogous to juvenile and mature modern reefs of the GBR. Juvenile reefs are very common and occur within each site at depths of less than 50 m to greater than 100 m. They are defined as discontinuous peaked barrier reefs, peaked patch reefs and fringing reefs. Mature reefs are less common and develop exclusively at a depth range of ca. 50–70 m. These reefs are defined as flat-topped continuous barrier and double barrier reefs. Through a comparison with published Mid-Late Pleistocene sea-level oscillations, we note that the depth range of mature reefs is consistent with the depth of repeated low-amplitude (< 20 m) eustatic sea-level oscillations, and independent of the relative time spent at sea-level. We conclude that repeated low-amplitude sea-level rises provide the much-needed accommodation space for vertical accretion that is not provided during stillstands, without inducing reef drowning, which can be caused by high-amplitude sea-level rise. Low-amplitude sea-level falls are also less detrimental than high-amplitude falls, in terms of habitat compression. Together, the effects of enhanced reef accretion and limited habitat compression at depths of 50–70 m have lead to a concentrated net gain in vertical relief that is not observed elsewhere on the shelf edge.

The stratigraphy of Barbuda, West Indies

by Martin Brasier

Ecology of recent sediment-dwelling and phytal foraminifera from the lagoons of Barbuda, West Indies

by Martin Brasier

Smith TB, Nemeth RS, Blondeau J, Calnan JM, Kadison E, Herzlieb S (2008) Assessing coral reef health across onshore to offshore stress gradients in the US Virgin Islands. Marine Pollution Bulletin 56:1983-1991

by Tyler Smith

Managing the effects of anthropogenic disturbance on coral reefs is highly dependant on effective strategies to assess... more Managing the effects of anthropogenic disturbance on coral reefs is highly dependant on effective strategies to assess degradation and recovery. We used five years of field data in the US Virgin Islands to investigate coral reef response to a potential gradient of stress. We found that the prevalence of old partial mortality, bleaching, and all forms of coral health impairment (a novel category) increased with nearshore anthropogenic processes, such as a five-fold higher rate of clay and silt sedimentation. Other patterns of coral health, such as recent partial mortality, other diseases, and benthic cover, did not respond to this potential gradient of stress or their response could not be resolved at the frequency or scale of monitoring. We suggest that persistent signs of disturbance are more useful to short-term, non-intensive (annual) coral reef assessments, but more intensive (semi-annual) assessments are necessary to resolve patterns of transient signs of coral health impairment.

Videre: Drawing and Evolutionary Architectures

by Paul Cureton

Draft Only

Analyzing the works of the seascape architect Wolf Hilbertz (1938 -2007), coral scientist Dr Thomas Goreau, architect... more Analyzing the works of the seascape architect Wolf Hilbertz (1938 -2007), coral scientist Dr Thomas Goreau, architect Newton Fallis and collective, the paper considers the development of ‘self organizing’ natural building materials developing a mode of working - Cybertecture (Cybernetics & architecture) (Hilbertz 1970). This investigation focuses particularly on that of Biorock® the mineral accretion technology. This process creates artificial coral reefs which are stronger and more resilient to degrading factors found on natural reefs. The technology exemplifies an evolutionary environmental system, a coral which is more reliant, tradable, multiplies in growth three to five times faster than normal, protects coastline, and grows fish populations through its constantly evolving habitat (Hilbertz, Goreau 1970, 1992, 2008). Importantly the technology has wide implications for restoring, designing and managing fragile and threatened coral ecosystems thus creating an emerging field of Seascape Architecture (Goreau, Hilbertz 2005).

Through the application of such technology, an accreted city of coral is envisioned - Autopia Ampere. The early stage of the project involved large scale hand drawings of possible outcomes and issues in construction and production (Fallis 2010). The drawings of Autopia can be considered as heuristic and also visionary in the testing of ideas - (Videre, Latin. to see). The author’s composite drawings present this vision as a method to understanding the project as a form of ‘dialogic drawing’ (Dee 2004). From this basis there is a consideration of the role of hand drawing, its decline and its relation to other visualization techniques-arguing the case for the maintenance of this particular ‘visionary’ species (a morphological type) of drawing in architectural practice (Evans 1996, 2000). This is a type of drawing which arguably can ‘influence’ and ‘work out’ to provide or image heuristically charged solutions, spaces and structures to our changing climate.

Coral reef encruster communities and carbonate production in cryptic and exposed coral reef habitats along a gradient of terrestrial disturbance.

by Jennie Mallela

Mallela J (2007) Coral reef encruster communities and carbonate production in cryptic and exposed coral reef habitats along a gradient of terrestrial disturbance. Coral Reefs 26:775-785

Variation in deglacial coralgal assemblages and their paleoenvironmental significance: IODP Expedition 310, "Tahiti Sea Level"

by Elizabeth Abbey

Abbey, E., Webster, J.M., Braga, J.C., Sugihara, K., Wallace, C.C., Iryu, Y., Potts, D., Done, T., Camoin, G., Seard, C., In press. Variation in deglacial coralgal assemblages and their paleoenvironmental significance: IODP Expedition 310, "Tahiti Sea Level". Global and Planetary Change.

Keywords: Submerged reefs, terraces, backstepping, sea level rise, deglacial, coralgal assemblages, reef drowning

Fossil reefs are valuable recorders of paleoenvironmental changes during the last deglaciation, and detailed... more Fossil reefs are valuable recorders of paleoenvironmental changes during the last deglaciation, and detailed characterizations of coralgal assemblages can improve understanding of the behavior and impacts of sea-level rise. Drilling in 2005 by the Integrated Ocean Drilling Program (IODP) Expedition 310 explored submerged offshore reefs from three locations around Tahiti, French Polynesia and provides the first look at island-wide variability of coralgal assemblages during deglacial sea-level rise. We present the first detailed examination of coral and coralline algal taxonomy and morphology from two sites on Tahiti (offshore Tiarei and offshore Maraa). Sixteen cores ranging in depth from 122 m to 45 m below sea-level represent reef growth from 16 ka to ca. 8 ka (Camoin, G.F., Iryu, Y., McInroy, D.B. and the IODP Expedition 310 Scientists, 2007. IODP Expedition 310 reconstructs sea level, climatic, and environmental changes in the South Pacific during the last deglaciation. Scientific Drilling, 5: 4-12). Twenty-six coral species, twelve coral genera and twenty-eight coralline algal species were identified from 565 m of core and over 400 thin sections. Based on these data, and in comparison with modern and fossil analogs, seven coral and four algal assemblages have been identified in the deglacial sequences in Tahiti, representing a range of environments from less than 10 m to greater than 20-30 m water depth. Deglacial reef initiation varied at sites based on the available substrate, and early colonizers suggest water conditions at all sites were unfavorable to sensitive corals, such as Acropora, prior to ca. 12.5 ka. Mainly shallow-water (< 10-15 m) corals and coralline algal assemblages developed continuously throughout both sites from 16 ka to ca. 8 ka, suggesting coralgal assemblage variation is more influenced by factors such as turbidity and water chemistry than sea-level rise alone.