Reefs Through the Looking Glass

2011 ◽  
Vol 17 ◽  
pp. 95-110 ◽  
Author(s):  
Dennis K. Hubbard
Keyword(s):  
Community Structure ◽  
Coral Reefs ◽  
Sea Level ◽  
Anthropogenic Impacts ◽  
Time Averaging ◽  
Acropora Palmata ◽  
Spatial And Temporal Scales ◽  
The Past ◽  
The Future ◽  
Geologic Record

Coral reefs have experienced a profound shift in community structure in recent decades, a pattern that contrasts with the apparent constancy of Caribbean reef zonation over the past 2 million years. The abrupt decline in branching Acropora palmata and massive frame-builders like Montastrea annularis in the Caribbean is troubling, and similar patterns have been reported from virtually every ocean. As we ponder the future of coral reefs, we must be mindful that our best monitoring records span perhaps half a century – and those are exceedingly rare. “Pristine” reefs may not have existed since Columbus sailed for the new world, and anthropogenic impacts probably extend even farther back in time.Despite the vagaries of evolutionary change, taphonomy and time averaging, the geologic record still represents a unique source of important information about the processes that have controlled community structure and reef building in the absence of human influences. The creation of rigid and elevated structures requires calcification rates that are capable of filling the accommodation space created by rising sea level. This has been complicated over the past three to four decades as accelerated sea-level rise has been joined by a suite of stresses that probably slow accretion. Explaining the recent reef decline and posing realistic models of future change will require an understanding of carbonate cycling in the past, the processes that have been involved and a quantitative assessment of how anthropogenic stresses are affecting both.At the least a look back in time may help to constrain the thresholds at which change might be expected to occur in the future. At best, the context gained from examining the “recent” geological past may provide insights into which possible solutions are most consistent with observed patterns at larger spatial and temporal scales.

scholarly journals Coral mortality induced by the 2015–2016 El-Niño in Indonesia: the effect of rapid sea level fall

2017 ◽  
Vol 14 (4) ◽  
pp. 817-826 ◽  
Author(s):  
Eghbert Elvan Ampou ◽  
Ofri Johan ◽  
Christophe E. Menkes ◽  
Fernando Niño ◽  
Florence Birol ◽  
...  
Keyword(s):  
Coral Reefs ◽  
Sea Level ◽  
El Niño ◽  
Reef Flat ◽  
El Nino ◽  
Differential Mortality ◽  
Altimetry Data ◽  
Bathymetric Range ◽  
The Past ◽  
Coral Genus

Abstract. The 2015–2016 El-Niño and related ocean warming has generated significant coral bleaching and mortality worldwide. In Indonesia, the first signs of bleaching were reported in April 2016. However, this El Niño has impacted Indonesian coral reefs since 2015 through a different process than temperature-induced bleaching. In September 2015, altimetry data show that sea level was at its lowest in the past 12 years, affecting corals living in the bathymetric range exposed to unusual emersion. In March 2016, Bunaken Island (North Sulawesi) displayed up to 85 % mortality on reef flats dominated by Porites, Heliopora and Goniastrea corals with differential mortality rates by coral genus. Almost all reef flats showed evidence of mortality, representing 30 % of Bunaken reefs. For reef flat communities which were living at a depth close to the pre-El Niño mean low sea level, the fall induced substantial mortality likely by higher daily aerial exposure, at least during low tide periods. Altimetry data were used to map sea level fall throughout Indonesia, suggesting that similar mortality could be widespread for shallow reef flat communities, which accounts for a vast percent of the total extent of coral reefs in Indonesia. The altimetry historical records also suggest that such an event was not unique in the past two decades, therefore rapid sea level fall could be more important in the dynamics and resilience of Indonesian reef flat communities than previously thought. The clear link between mortality and sea level fall also calls for a refinement of the hierarchy of El Niño impacts and their consequences on coral reefs.

Origin and Geomorphology

2006 ◽  
Author(s):  
Thomas S. Bianchi
Keyword(s):  
Sea Level ◽  
Rate Of Change ◽  
Interglacial Period ◽  
Continental Margins ◽  
Before Present ◽  
Sea Level Changes ◽  
The Past ◽  
Constant Rate ◽  
Geologic Record ◽  
The U.S

Geologically speaking, estuaries are ephemeral features of the coasts. Upon formation, most begin to fill in with sediments and, in the absence of sea level changes, would have life spans of only a few thousand to tens of thousands of years (Emery and Uchupi, 1972; Schubel, 1972; Schubel and Hirschberg, 1978). Estuaries have been part of the geologic record for at least the past 200 million years (My) BP (before present; Williams, 1960; Clauzon, 1973). However, modern estuaries are recent features that only formed over the past 5000 to 6000 years during the stable interglacial period of the middle to late Holocene epoch (0–10,000 y BP), which followed an extensive rise in sea level at the end of the Pleistocene epoch (1.8 My to 10,000 y BP; Nichols and Biggs, 1985). There is general agreement that four major glaciation to interglacial periods occurred during the Pleistocene. It has been suggested that sea level was reduced from a maximum of about 80 m above sea level during the Aftoninan interglacial to 100 m below sea level during the Wisconsin, some 15,000 to 18,000 y BP (figure 2.1; Fairbridge, 1961). This lowest sea level phase is referred to as low stand and is usually determined by uncovering the oldest drowned shorelines along continental margins (Davis, 1985, 1996); conversely, the highest sea level phase is referred to as high stand. It is generally accepted that low-stand depth is between 130 and 150 m below present sea level and that sea level rose at a fairly constant rate until about 6000 to 7000 y BP (Belknap and Kraft, 1977). A sea level rise of approximately 10 mm y−1 during this period resulted in many coastal plains being inundated with water and a displacement of the shoreline. The phenomenon of rising (transgression) and falling (regression) sea level over time is referred to as eustacy (Suess, 1906). When examining a simplified sea level curve, we find that the rate of change during the Holocene is fairly representative of the Gulf of Mexico and much of the U.S. Atlantic coastline (Curray, 1965).

scholarly journals Divergence of seafloor elevation and sea level rise in coral reef ecosystems

2017 ◽  
Vol 14 (6) ◽  
pp. 1739-1772 ◽  
Author(s):  
Kimberly K. Yates ◽  
David G. Zawada ◽  
Nathan A. Smiley ◽  
Ginger Tiling-Range
Keyword(s):  
Coral Reef ◽  
Coral Reefs ◽  
Sea Level Rise ◽  
Sea Level ◽  
Anthropogenic Impacts ◽  
Regional Scale ◽  
Coastal Hazards ◽  
Carbonate Production ◽  
Coral Reef Ecosystems ◽  
Study Sites

Abstract. Coral reefs serve as natural barriers that protect adjacent shorelines from coastal hazards such as storms, waves, and erosion. Projections indicate global degradation of coral reefs due to anthropogenic impacts and climate change will cause a transition to net erosion by mid-century. Here, we provide a comprehensive assessment of the combined effect of all of the processes affecting seafloor accretion and erosion by measuring changes in seafloor elevation and volume for five coral reef ecosystems in the Atlantic, Pacific, and Caribbean over the last several decades. Regional-scale mean elevation and volume losses were observed at all five study sites and in 77 % of the 60 individual habitats that we examined across all study sites. Mean seafloor elevation losses for whole coral reef ecosystems in our study ranged from −0.09 to −0.8 m, corresponding to net volume losses ranging from 3.4  ×  106 to 80.5  ×  106 m3 for all study sites. Erosion of both coral-dominated substrate and non-coral substrate suggests that the current rate of carbonate production is no longer sufficient to support net accretion of coral reefs or adjacent habitats. We show that regional-scale loss of seafloor elevation and volume has accelerated the rate of relative sea level rise in these regions. Current water depths have increased to levels not predicted until near the year 2100, placing these ecosystems and nearby communities at elevated and accelerating risk to coastal hazards. Our results set a new baseline for projecting future impacts to coastal communities resulting from degradation of coral reef systems and associated losses of natural and socioeconomic resources.

scholarly journals Glacier dynamics over the last quarter of a century at Jakobshavn Isbræ

2015 ◽  
Vol 9 (5) ◽  
pp. 4865-4892
Author(s):  
I. S. Muresan ◽  
S. A. Khan ◽  
A. Aschwanden ◽  
C. Khroulev ◽  
T. Van Dam ◽  
...  
Keyword(s):  
Mass Loss ◽  
Sea Level Rise ◽  
Sea Level ◽  
21St Century ◽  
Greenland Ice Sheet ◽  
Outlet Glacier ◽  
The Past ◽  
Glacier Dynamics ◽  
The Future ◽  
Oceanic Forcing

Abstract. Observations over the past two decades show substantial ice loss associated with the speedup of marine terminating glaciers in Greenland. Here we use a regional 3-D outlet glacier model to simulate the behaviour of Jakobshavn Isbræ (JI) located in west Greenland. Using atmospheric and oceanic forcing we tune our model to reproduce the observed frontal changes of JI during 1990–2014. We identify two major accelerations. The first occurs in 1998, and is triggered by moderate thinning prior to 1998. The second acceleration, which starts in 2003 and peaks in summer 2004, is triggered by the final breakup of the floating tongue, which generates a reduction in buttressing at the JI terminus. This results in further thinning, and as the slope steepens inland, sustained high velocities have been observed at JI over the last decade. As opposed to other regions on the Greenland Ice Sheet (GrIS), where dynamically induced mass loss has slowed down over recent years, both modelled and observed results for JI suggest a continuation of the acceleration in mass loss. Further, we find that our model is not able to capture the 2012 peak in the observed velocities. Our analysis suggests that the 2012 acceleration of JI is likely the result of an exceptionally long melt season dominated by extreme melt events. Considering that such extreme surface melt events are expected to intensify in the future, our findings suggest that the 21st century projections of the GrIS mass loss and the future sea level rise may be larger than predicted by existing modelling results.

scholarly journals Integrating Oceanographic Data and Benthic Community Structure Temporal Series to Assess the Dynamics of a Marginal Reef

2021 ◽  
Vol 8 ◽  
Author(s):  
Julia Biscaia Zamoner ◽  
Anaide Wrublevski Aued ◽  
Luis Carlos Pinto Macedo-Soares ◽  
Vitor André Passos Picolotto ◽  
Carlos Alberto Eiras Garcia ◽  
...  
Keyword(s):  
Community Structure ◽  
Coral Reefs ◽  
Wave Energy ◽  
Structural Changes ◽  
Anthropogenic Impacts ◽  
Benthic Communities ◽  
Structural Complexity ◽  
Marine Species ◽  
Oceanic Islands ◽  
Brazilian Province

Reefs are the richest marine ecosystems. Their benthic communities generate structural complexity and participate in nutrient cycles, providing habitat and food for many marine species. These ecosystems have been threatened by local and global anthropogenic impacts and changes in community structure have led to loss of biodiversity, ecosystem function and services worldwide. Most studies about these structural changes have been conducted in Caribbean and Indo-Pacific coral reefs. In the Southwestern Atlantic, where reefs are naturally algae-dominated, these efforts are incipient, especially at oceanic islands where local anthropic impacts tend to be lower, and natural and climate-induced fluctuations might be easily detected. We conducted the first temporal assessment of benthic communities and the influence of oceanographic parameters between 2013 and 2019 in Fernando de Noronha (FNA), the largest Brazilian oceanic archipelago. We annually sampled benthic communities in FNA’s shallow reefs (2–21 m) using photoquadrats, quantified and gathered organisms in major groups according to their functional roles. We also characterized and tested “sea surface temperature,” “marine heatwaves,” “diffuse attenuation coefficient,” and “wave energy” influence for the same period. The most abundant groups were epilithic algal matrix (EAM; mean annual coverage: 23–60%), macroalgae (15–35%) and calcifiers (15–29%), followed by cyanobacteria (1–37%), suspension/filter-feeders (<2%), zoanthids (<1%) and other invertebrates (<0.1%). EAM was negatively correlated with “marine heatwaves” and positively correlated with “wave energy,” while macroalgae and calcifiers showed opposite responses to “marine heatwaves” and “wave energy,” respectively. Cyanobacteria was positively correlated with “marine heatwaves.” The dominance of EAM and macroalgae was already described for reefs along the Brazilian Province and we demonstrated the persistence of this structure over the years in FNA, with the exception of 2019 when there was a substantial increase of cyanobacteria after a strong marine heatwave. Our results suggest a flickering dynamic between EAM and macroalgae, which vary according to the oceanographic conditions, reinforcing its distinct dynamics from most tropical coral reefs. However, the increase of cyanobacteria added to projections of more frequent and stronger marine heatwaves worldwide indicate possible structural changes in this community. Continued monitoring of community and oceanographic drivers is key for better understanding and predicting changes in important marginal reefs.

How past sea-level changes can inform future planning: A case study from the Macleay River estuary, New South Wales, Australia

The Holocene ◽  
2014 ◽  
Vol 24 (11) ◽  
pp. 1591-1601 ◽  
Author(s):  
Sarah A McGowan ◽  
Robert GV Baker
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
New South ◽  
New South Wales ◽  
River Estuary ◽  
The Past ◽  
Case Study Area ◽  
South Wales ◽  
The Future

Climate change poses many challenges for the future management and development of the coastal zone. Uncertainties in the rate of future sea-level rise reduce our ability to project potential future impacts. This study seeks to further develop the past–present–future methodology proposed in Baker and McGowan and apply it to an additional case study, the Macleay River estuary, New South Wales (NSW), Australia. The past–present–future methodology uses evidence from the past, the Holocene and Pleistocene, to formulate a response function that can be used to project future sea-level heights. Three scenarios for 2100 were developed to emphasise the uncertainties surrounding future sea levels and the need to consider multiple sea-level rise scenarios when planning for the future: a best case (90 cm rise), mid-case (2.6 m rise) and worst case (5 m rise). Light detection and ranging (LiDAR) data were used to project each of the three scenarios onto the case study area of South West Rocks. The methodology was tested by using shell samples extracted from cores which were AMS dated to determine whether or not Holocene estuarine conditions correlated with the proposed future sea-level rise inundation scenarios. We also conducted an audit of potentially affected infrastructure and land uses, and proposed possible future adaptation strategies for the case study area.

Sea-level modelling: The past and the future

1987 ◽  
Vol 18 (1-4) ◽  
pp. 41-59 ◽  
Author(s):  
Bruce Denness
Keyword(s):  
Sea Level ◽  
The Past ◽  
The Future

Artificial time-averaging of marsh foraminiferal assemblages: linking the temporal scales of ecology and paleoecology

Paleobiology ◽  
2002 ◽  
Vol 28 (2) ◽  
pp. 263-277 ◽  
Author(s):  
Ronald E. Martin ◽  
Scott P. Hippensteel ◽  
Daria Nikitina ◽  
James E. Pizzuto
Keyword(s):  
Sea Level ◽  
Regression Models ◽  
Abundant Species ◽  
Time Averaging ◽  
National Wildlife Refuge ◽  
Temporal Scales ◽  
Near Surface ◽  
The Past ◽  
Multiple Regression Models ◽  
Species Abundances

Multiple regression models were developed for seasonal test inputs to, and preservation of, marsh foraminiferal assemblages for a two-year period at Bombay Hook National Wildlife Refuge (BHNWR; Smyrna, Delaware). Seasonal assemblages were quite variable and yielded poor regression models. However, signal/noise ratios were amplified using artificially time-averaged (ATA) assemblages, in which separate dead and live abundances of the most abundant species were summed for all seasons. Regression models that used ATA species abundances to retrodict original sample depths accounted for up to ~99% (p < 0.0001) and ~91% (p < 0.023) of the variation of dead and live ATA assemblages, respectively, and usually retrodicted sample depths within 2–3 cm of actual depths.Artificially time-averaged assemblages were also used to extract multidecadal- to centennial-scale sea-level signals from near-surface assemblages at BHNWR formed during the past few centuries. The BHNWR sea-level curve closely resembles one previously published for marshes in Clinton, Connecticut (also based on foraminifera). The technique of artificial time-averaging therefore links the temporal scales of ecology and paleobiology by extracting high-resolution paleoenvironmental signals preserved in the fossil record.

scholarly journals Coral mortality induced by the 2015–2016 El-Niño in Indonesia: the effect of rapid sea level fall

2016 ◽  
Author(s):  
Eghbert Elvan Ampou ◽  
Ofri Johan ◽  
Christophe E. Menkes ◽  
Fernando Nino ◽  
Florence Birol ◽  
...  
Keyword(s):  
Coral Reefs ◽  
Sea Level ◽  
El Niño ◽  
Reef Flat ◽  
El Nino ◽  
Differential Mortality ◽  
Altimetry Data ◽  
Bathymetric Range ◽  
The Past ◽  
Coral Genus

Abstract. The 2015–2016 El-Niño and related ocean warming has generated significant coral bleaching and mortality worldwide. In Indonesia, first signs of bleaching were reported in April 2016. However, this El Niño has impacted Indonesian coral reefs since 2015 through a different process than temperature-induced bleaching. In September 2015, altimetry data shows that sea level was at its lowest in the past 12 years, affecting corals living in the bathymetric range exposed to unusual emersion. In March 2016, Bunaken Island (North Sulawesi) displayed up to 85 % mortality on reef flats dominated by Porites, Heliopora and Goniastrea corals with differential mortality rates by coral genus. Almost all reef flats showed evidence of mortality, representing 30 % of Bunaken reefs. For reef flat communities which were living at a depth close to the pre-El Niño mean low sea level, the fall induced substantial mortality likely by higher daily aerial exposure a least during low tide periods. Altimetry data was used to map sea level fall throughout Indonesia, suggesting that similar mortality could be widespread for shallow reef flat communities, which accounts for a vast percent of the total extent of coral reefs in Indonesia. The altimetry historical records also suggest that such event was not unique in the past two decades, therefore rapid sea level fall could be more important in the dynamics and resilience of Indonesian reef flat communities than previously thought. The clear link between mortality and sea level fall also calls for a refinement of the hierarchy of El Niño impacts and their consequences on coral reefs.

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