Who introduced the theory of red tide?
Who introduced the theory of red tide? What are the instruments he used in investigating or studying red tide?
Here are two papers written by Nerlie Abram, and one by Nerlie and a group of scientists, all cover the threat to coral reefs posed by red tide and the theories on how wildfires contribute to the growth of red tide.
PhD student (final year) Research School of Earth Sciences,
: THE NEW THREAT TO CORAL REEFS
Smoke from fires raging through tropical forests near coastal reefs can cause an algal bloom capable of killing virtually all coral and fish for hundreds of kilometres, according to new research by Australian National University scientists.
This discovery explains the mysterious death of nearly all coral and fish in a 400 kilometre stretch of the Mentawai Islands reef, southwest of Sumatra in Indonesia, in 1997.
In a paper published in the latest issue of Science, a team of ANU researchers reveal that nutrients in smoke from the 1997 Indonesian wildfires produced a large algae bloom, known as a red tide, that suffocated the reef ecosystem – over a distance equivalent to around a quarter of Australia’s Great Barrier Reef.
By examining the skeletal growth and geochemistry of Porites corals, researchers led by Ms Nerilie Abram, were able to track the environmental factors which led to the red tide. In examining fossilised corals, they found the red tide had been the worst in 7000 years.
“This was an extreme event and almost six years on, the reefs still haven’t recovered,” says Nerilie. “We fear that future fires could further damage the reefs before they can recover.”
The researchers found that thick smoke from the 1997 Sumatra fires released almost 11,000 tonnes of iron into the atmosphere. The iron acted as a fertiliser, increasing water nutrient levels and providing the extraordinary conditions which led to the red tide algal bloom. The bloom led to reef death by asphyxiation.
Cores from rare corals that survived the 1997 red tide showed a clear hiatus in growth at the time of the fires.
“When fires burn they release nutrients and this study has shown that these nutrients can create serious problems for coral reefs.”
“Indonesia’s reefs are the most diverse in the world and are an important source of new corals that help to rejuvenate Australia’s coral reefs. They are estimated to generate approximately US$4 billion a year in tourism, fishing and employment for Indonesia.”
“Unfortunately they are also among the most threatened reefs in the world and conservation projects are of high-priority.”
"It is expected that this new threat to coral reefs and other coastal ecosystems will increase in the future as global warming and forest clearing lead to more wildfires."
Nerilie is presenting her research to the public for the first time thanks to Fresh Science, a national program to bring public attention to the remarkable unsung achievements of young Australian scientists. Nerilie will be speaking to the public and school students about her work on Tuesday 19 and Wednesday 20 August at the Melbourne Museum.
PhD student (final year) Research School of Earth Sciences,
Fire: the new threat to coral reefs
Coral reef death during the 1997 Indian Ocean Dipole linked to Indonesian wildfires
Fires represent a new and unexpected threat to coral reefs. It has been found that the nutrients released by wildfires can produce large algae blooms in the ocean that suffocate fish and coral. Global warming has seen a recent increase in wildfires and this trend is expected to continue, raising the future risk to coral reefs.
Coral reefs, the so-called “rainforests of the sea”, are being threatened by fire. That is the finding of scientists working at the Australian National University.
Over recent years, global warming has combined with forest clearing to produce some of the worst wildfires in history. In 1997 the wildfires in Indonesia burnt out of control for over five months, blanketing southeast Asia and northern Australia in thick smoke and leading to major environmental and health problems.
Now, new research from the ANU’s Research School of Earth Sciences has found a link between wildfires and reef death in Indonesia. “When fires burn they release nutrients and this study has shown that these nutrients can create serious problems for coral reefs”, says Nerilie Abram, the leader of this research.
Indonesia’s reefs are the most diverse in the world and are an important source of new corals that help to rejuvenate Australia’s coral reefs. They are estimated to generate around US$4 billion a year in tourism, fishing and employment for Indonesia. Unfortunately they are also among the most threatened reefs in the world and conservation projects are of high-priority.
Ms Abram has been studying a reef in western Indonesia where nearly all of the coral and fish mysteriously died in 1997. Reef death extended over 400km, equivalent to around ¼ the length of Australia’s Great Barrier Reef. Now it has been shown that nutrients in smoke from the 1997 fires produced a large algae bloom, known as a red tide, that suffocated the reef ecosystem.
Using fossil corals this research has also shown that over the last 7000 years the reefs had not previously experienced a red tide like 1997. “This was an extreme event and five-and-a-half years on the reefs still haven’t recovered”, says Ms Abram. It i
The incidence and extent of wildfires is predicted to increase with future global warming. Understanding this new link between forest wildfires and coral reef death will be important in efforts to preserve these environments for future generations.
Qualifications: The Australian National University, BSc Advanced (Hons); The University of Sydney, 2000, First class honours and university medal
Nominated by: Michael Gagan Fellow Research School of Earth Sciences, The Australian National University
Ph (2) 9645-5956 or (2) 6125-5177
Commonwealth of Australia - Department of Education, Science & Training
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and our other sponsors for their generous support
Coral Reef Death During the
1997 Indian Ocean Dipole Linked
to Indonesian Wild .res
Nerilie J.Abram, *Michael K.Gagan, Malcolm T.McCulloch,
John Chappell, Wahyoe S.Hantoro 2
Geochemical anomalies and growth discontinuities in Porites corals from western Sumatra, Indonesia, record unanticipated reef mortality during anomalous Indian Ocean Dipole upwelling and a giant red tide in 1997. Sea surface temperature reconstructions show that although some past upwelling events have been stronger,there were no more analogous episodes of coral mortality during the past 7000 years,indicating that the 1997 red tide was highly unusual.We show that iron fertilization by the 1997 Indonesian wild fires was suffcient to produce the extraordinary red tide, leading to reef death by asphyxiation.These findings highlight tropical wild fires as an escalating threat to coastal marine ecosystems.
Coral reefs, the most diverse of all marine ecosystems, are increasingly threatened by human activities, climate change, and disease (1–3). The exact nature and potential impact of these threats are still unclear in many
cases, making effective conservation diffi-cult. The vulnerability of reefs to climate change became fully evident in 1997–1998 when elevated sea surface temperaures (SSTs) linked to global warming and a strongEl Nin˜ o caused widespread coral bleaching and mortality throughout the tropical oceans(3–5). Bleaching was particularly severe in
the central and western Indian Ocean, where approximately 59% of reefs were damaged, creating large socioeconomic problems (3). Although SSTs in the central-western tropical Indian Ocean were anomalously warm during
1997, the eastern sector was unusually cool. These cool SSTs were the result of recently discovered coupled ocean-atmosphere dy-namics (6, 7), termed the Indian Ocean Di-pole(IOD). The anomalously cool SSTs in the eastern
Indian Ocean during 1997, together, with the economic and political crisis inIndonesia at this time,
led to the status of coral reefs in western Indonesia being largelyoverlooked during systematic surveys of the
1997–1998 coral bleaching event. Here, we report on the unanticipated and catastrophic death in late 1997 of the Men-tawai Islands reef ecosystem, located off-shore of suothwest sumatra, Indonesia, in the equatorial eastern Indian Ocean (Fig.1). Before 1997, more than 101 species of hard corals (8), including centuries-old col-onies
of Porites (9, 10), provided a diversereef ecosystem around the Mentawai Is-lands. During the 1997 IOD, enhanced southeasterly trade winds drove strong up-welling along the southwest coast of Sumatra, causing SSTs in the Mentawai
reefs to drop by around 4°C (Fig. 1) (6, 7). At the same time, convective rainfall over Indonesia was dramatically reduced, and wildfires produced thick smoke coverage over southeast Asia (6, 7). In late 1997, near the peak of the IOD, close to 100% of the coral and fish in the Mentawai reef ecosystem were killed. Local reports (11) suggest that reef death was associated with a large phytoplankton bloom (red tide) and, together with our reef surveys in 1999 and
2001, show that the ecosystem collapse stretched _400 km from North Pagai Is-land to Nias (Fig. 1). Although no detailed scientific surveys of the reefs were made during or shortly after the demise of the Mentawai reefs, the skeletal
growth and geochemistry of Porites sp. Corals provide a powerful tool for reconstructing the events that led to the reef mortality. We used the skeletal growth of modern and fossil Porites from the Mentawai reefs to evaluate the phys-ical
record of reef death. The magnitudes of recent and prehistoric IOD events were recon-structed using high-resolution (fortnightly to weekly) measurements of skeletal strontium/ calcium ratios (Sr/Ca) as a proxy for SST, in conjunction with oxygen isotope ratios (_ 18 O), which reflect SST and salinity (12, 13). Stable carbon isotope ratios (_ 13 C) and manganese (Mn) and rare earth element (REE) concentra-tions were also used as proxies for biological activity (14) around the time of the 1997 reef mortality. These coral records allow us to eval-uate the timing and likely cause of the cata-strophic 1997 reef death, as well as the history of any similar events over the past 7000 years. Cores from two rare colonies that recovered from the 1997 mortality event both display a clear hiatus in skeletal growth during 1997. The
growth hiatuses are marked by algal inclusions and a distinct skeletal unconformity across the entire colony surface that is clearly visible in hand specimens and x-ray images. The high-resolution_ 18 O signal of one of these corals, when matched to the instrumental SST record, shows that the unconformity spans a period of approximately 6 months, beginning in December 1997, shortly after the peak of IOD upwelling (Fig. 2A). The timing of this unconformity is
consistent with local reports (11) of reef death in late December and into January. No live corals without unconformities could be found in the area of reef death; however, a continuous record of 1997–1998 was produced
from a coral core collected from South Pagai Island, immediately to the south (Fig. 1). The high-resolution _ 18 O and laser ablation– inductively coupled plasma–mass spectrometry (LA-ICP-MS) Sr/Ca signals from this coral clearly record the IOD upwelling anomaly dur-ing 1997 (Fig. 2B). Approximately 2 weeks after the peak of the 1997 IOD, a sharp increase in coral _ 13 C is matched by abrupt increases in Mn and REEs [lanthanum (La) and yttrium ( Y) are
shown as representative signals in Fig. 2B]. These geochemical enrichments all peak in late December/early January and are synchronous with the timing of reef death (Fig. 2). We inter-pret the increases in coral _ 13 C, Mn, and REEs
as the signature of a large phytoplankton bloom (supporting online text), reflecting the preferen-tial uptake of 12 C by phytoplankton (15) and reducing conditions produced by high levels of decomposing organic matter (14, 16–18). This
coral evidence is consistent with eyewitness ac-counts (11) that the Mentawai reef mortality was associated with a massive red tide that extended several hundred kilometers along the island chain during December 1997–January 1998.
Red tides can kill marine organisms through poisoning from toxins produced by phytoplankton (19). Oxidation of abundant dead biomass in the water column can also kill corals and other marine organisms by asphyxiation (20, 21). The strong enrich-ments in coral Mn and REEs in late 1997 provide evidence for low oxygen levels in the water column at the time of the Mentawai reef mortality and suggest that asphyxiationwas the likely cause of death for thecoral andfish. Phytoplankton production during redtides is driven by high concentrations of nu-trients
in the surface ocean (19, 21), as hap-penswhen ocean upwelling brings cool nitro-gen(N)– and phosphorus (P)–enriched waterto the surface (22–24). Ocean productivity in the Indonesian region is generally proportion-al
to the strength of upwelling (22), and the severity of the 1997 Mentawai reef death raises the question of whether the magnitudes of the IOD upwelling and red tide during1997 were unprecedented. Coral Sr/Ca and _ 18 O records of the 1994 IOD accurately track the magnitude and duration of the cool SST anomaly observed in the instru-mental
record of this event (Fig. 3). These geo-chemical records, together with the coral x-ray images, show that coral growth was continuous during the 1994 IOD, even though its magnitude was similar to that of the 1997 event. There is
also no coral _ 13 C or trace element evidence for a large algal bloom associated with the 1994 IOD upwelling (Fig. 2 and fig. S1). Counting of annual coral density bands places two more up-wellings identified by coral Sr/Ca and _ 18 O ther-mometry at 1961 and 1877 A.D. (Fig. 3), both of which are known from historical and other proxy records to be years of extreme climatic condi-tions (7, 25, 26) indicative of IOD events. This correlation confirms that before 1997, there were no significant growth hiatuses in this massive Porites colony for at least 120 years. Even though there is no evidence for coral death or a red tide (fig. S1) during 1877, Sr/Ca thermo-metry shows the magnitude of upwelling to be equivalent to that of the strong 1997 IOD (Fig. 3). IOD upwellings even stronger than the 1997 event are evident in the Sr/Ca and _ 18 O records of fossil Porites from the Mentawai reefs (Fig. 3). The largest of these events is marked by a cool SST anomaly of 5.8°C, which is 1.9°C stronger than the cooling during the 1997 IOD. In total, seven paleoupwelling events ranging from 2.8° to 5.8°C in magnitude have been examined using fossil coral geochemistry, and in all cases there is no x-ray evidence for discon-tinuous coral growth during upwelling. The du-ration of the prehistoric upwellings indicated by coral thermometry is similar to that of modern IOD events, further confirming the x-ray evi-dence that there was no significant break in coral growth during even the largest event (Fig. 3).Moreover, there is no _ 13 C evidence for a red tide associated with any of the paleoupwellings(fig. S1), and the absence of growth unconform-itiesin a suite of 48 Porites cores dating back to7000 years before the present (supporting online text, table S1, and fig. S2) further supports the conclusion that 1997-type coral death did not accompany past upwelling events.
It is clear from the coral growth and paleo-temperature records that the catastrophic re-sponse of the Mentawai reefs to the 1997 IOD upwelling was highly unusual. However, the magnitude of the 1997 IOD event was not un-usual,
and evidently the intensity of the red tide was greater than would be expected on the basis of the strength of IOD upwelling alone. This implies that additional sources of nutrients must have supported the massive red tide that led to
the death of the Mentawai reef ecosystem. Primary productivity in coastal upwelling systems is generally iron (Fe)–limited, with ex-ternal inputs of Fe required to balance the up-welled sources of macronutrients (N and P) (27,
28). Atmospheric deposition of dust and volcan-ic ash is a potential mechanism for increasing Fein the surface ocean, thereby enhancing algal blooms and red tides (19, 29, 30). Using an empirical relation established from a wide range
of ocean provinces (31), the mean Sea-viewing Wide Field-of-view Sensor (SeaWiFS) chloro-phyll a concentration of 5 mg m _3 for the Men-tawai red tide in December 1997 (24) equates to primary productivity rates of approximately
1.6 g of C m _2 day _1 (13) and is similar to the productivity of the destructive red tides that oc-cur in the Gulf of Mexico after Fe deposition from Saharan dust (19). The calculated flux of Fe required to sustain the Mentawai red tide
would have been 30 to 150 _g m _2 day _1( Table 1) (13, 32). However, the average depo-sition rate of bioavailable aeolian Fe in this area amounts to only 3 _g m _2 day _1 (33), indicat-ing that an additional source of Fe was required
to support the Mentawai red tide. We propose that the additional Fe required tosupport the Mentawai red tide was provided by atmospheric fallout from the 1997 Indonesian wildfires. Widespread land clearing and in-creased
forest disturbance in recent years have greatly increased the intensity and extent of In-donesian wildfires, which occur during El Nin˜o and/or IOD droughts. In 1997, this culminated in the worst wildfires in the recorded history of
southeast Asia (6, 25, 34). On Sumatra alone, at least 15,000 km 2 of land burned during the 1997 wildfires (35), releasing large quantities of nutri-ents and entrained terrestrial particles to the at-mosphere (35, 36). Anomalous equatorial east-erlies (6) resulted in persistent transport ofsmoke over the Mentawai Islands from Septem-ber
to December 1997.Fossil coral ages and _...2 _ age ranges are in calibrated years before the present (yBP).
On average, 46% of the Sumatran smoke plume was located over the region of IOD upwelling, with the highest density of smoke consistently located over the Mentawai area (38). Deposition of these fire particulates (19) would have been assisted by the 500 mm of rainfall received by the Men-tawai region during the 1997 wildfires and by atmospheric subsidence over the cold SST anomaly (6). Weakening and reversal of the monsoon and equatorial winds (7) in December 1997 also would have acted to further concen-trate nutrients and plankton into the Mentawai region from the upwelling plume offshore. Approximately 1.1 _ 10 4 metric tons of Fe were released from the Sumatran wild-fires
during 1997 (35, 39), and exposure to sunlight and acid conditions during atmos-pheric transport in the smoke plume (36) would have allowed up to 90% of the Fe toexist as bioavailable Fe(II) (40). Only 0.2 to 0.8% of the Fe released from the Sumat-ran wildfires was required as bioavailable Fe(II) in the Mentawai region to meet the total Fe requirements of the 1997 red tide ( Table 1) (13, 41). Although these calcula-tions are estimates, it is clear that the 1997
Sumatran wildfires were a large potential source of Fe that could have promoted the extraordinary productivity in the upwelled water around the Mentawai Islands. The proposed link between the death of the Mentawai Islands reef ecosystem and the 1997 Indonesian wildfires has implications for the fu-ture health of coral reefs. Widespread tropical
wildfire is a recent phenomenon (25, 34), the magnitude and frequency of which are increas-ing as population rises and terrestrial biomass continues to be disrupted (34). Where back-ground nutrient supplies in reef waters are ele-vated
or human activities have reduced upper trophic levels (42), reefs are likely to become increasingly susceptible to large algal blooms triggered by episodic nutrient enrichment from wildfires. Therefore, in addition to their impact on forest ecology and human health, tropical wildfires may pose a new threat to coastal marine eco-systems that could escalate into the 21st century.