Thursday, September 21, 2017

The effects of hurricanes on coral reefs


Anjani Ganase, marine biologist, looks at how hurricanes affect coral reef ecosystems

Coral reef ecosystems are shaped by their surroundings. The amount of light they receive, the temperature of the water column, even the movement of the water (currents) all govern whether a coral species can survive and reproduce. As corals are only mobile during their larval phase, the spot where they choose to settle and grow becomes a very important choice; not too hot or cold, just enough light and shelter. As a result, we find shifts in coral reef types as environments change. However, despite a coral’s ability to adapt to long-term environmental conditions, similar to us on land, coral reefs can also be devastated by large disturbances that bring destruction or death. One example is hurricanes.

Hurricane force winds uproot trees and damage infrastructure on land. These same winds drive intense wave surges along coastlines, causing violent and irregular water movement that can be felt at great depths. Water movement is a part of a coral’s life, especially those living in the shallows, where the shape and size of the coral might be determined by the rhythmic movement of the water. However, the powerful waves generated by the hurricane can break and overturn even the hardest coral structure. Damage at greater depths is two-fold, directly breaking corals because of surging water; and secondly, from debris falling from the shallows.

Apart from the physical stress that the surging waters exert on the reef benthos, the turmoil of water movement from hurricanes also tends to mix the upper portions of the ocean’s water column, homogenising water conditions to the depths. Usually, seawater becomes naturally colder and saltier with depth; and organisms pick and choose the depth that best satisfies their needs. Drastic changes in temperature, salinities, oxygen concentrations and other conditions can result in death of small fish and invertebrates, such as lobsters that are unable to tolerate the extremely low salinities as a result of the excess rainfall. Larger mobile creatures, including bigger fish, sharks and marine mammals can escape the hurricane by moving to other areas. One study on black tip sharks observed that they moved away from the reef when hurricanes approached and returned following the storm, and suggested that the sharks were able to detect changes in the surrounding pressures driven by the storm (Heupel et al. 2003).


BEFORE: A healthy coral reef on the Great Barrier Reef before being hit by a category 5 cyclone (Cyclone Ita). Photo by XL Catlin Seaview Survey
AFTER: The same coral reef after being hit by a category 5 cyclone (Cyclone Ita). Photo by XL Catlin Seaview Survey

The effects of hurricanes may still be felt days after the storm has moved on. Waters can continue to surge days after a hurricane. In addition, the runoff from the land can carry sediment down to the coastal ecosystems, burying corals and muddying the water column blocking out the sunlight. The large amount of fresh water run off from the rivers also continues to reduce salinity. The recovery of the corals and associated marine life, greatly depends on subsequent disturbances, whether it is another hurricane or man-made, as well as whether the long-term environmental conditions continue to promote coral recruitment and growth.

On longer time scales, the frequency of hurricanes experienced in an area also governs the resultant community composition of coral reefs. Some locations in the Caribbean are hit more frequently by hurricanes, such as the Bahamas, which is impacted by hurricanes almost annually. In contrast, Trinidad and Tobago, the southernmost islands in the Caribbean, have a history of very low hurricane disturbance. The time between hurricane impacts on coral reefs in the Bahamas is much shorter compared to that in Trinidad and Tobago. This means that coral reefs in the Bahamas are likely to be very different to Tobago’s. Bahamian reefs are therefore likely to be composed of species that have faster growth rate, and therefore able to recover quickly between storms.

Studies have shown that full recovery of coral reefs (regrowth of corals) following a hurricane can be as quick as five years if no other storm hits. However, it has also been shown that overall Caribbean reefs have become impaired in their ability to recover from hurricanes; they recover at a slower rate (> 8 years) if at all, to their pre-disturbed states (Gardner 2005). Sometimes the recovery is too slow to allow sufficient regrowth of coral skeleton before another hurricane passes. This recovery impairment of corals can be related to additional stressors that are experienced by the corals. Interestingly, the impacts of hurricanes on coral reefs were more intense during the 1980s, but this does not mean that hurricanes have become less damaging to coral reefs (in fact, we know that hurricanes have become more intense over the last forty years); rather coral reefs are being more damaged by other disturbances at a greater rate. These other disturbances are typically man-made, which alter the long-term living conditions of the reef environment making it less suitable for corals. 

On top of the standard management of coral reefs that is important to sustain long-term coral health, there is need for a recovery management plan for reefs following significant disturbance events. If a coral reef has been badly damaged following a hurricane, areas of severe coral loss should be temporarily closed to fisheries and recreational use in the following years. This will reduce the number and frequency of stressors acting on the reef and help the reef to recover. Furthermore, any nearby land-based activity that may affect the reef should also be limited and monitored closely until the reef has recovered to a state where it can once again act as a buffer to other disturbances.

References:
Gardner, T. A., Cote, I. M., Gill, J. A., Grant, A., & Watkinson, A. R. (2005). Hurricanes and Caribbean coral reefs: impacts, recovery patterns, and role in long‐term decline. Ecology, 86(1), 174-184.

Heupel, M. R., Simpfendorfer, C. A., & Hueter, R. E. (2003). Running before the storm: blacktip sharks respond to falling barometric pressure associated with Tropical Storm Gabrielle. Journal of fish biology, 63(5), 1357-1363.

Thursday, September 14, 2017

Climate change, like hurricanes, calls for non-partisan policy and responses


Anjani Ganase, marine biologist, discusses the response of small island states to extreme events like hurricane Irma. This feature was first published in the Tobago Newsday, September 14, 2017

In the wake of hurricane Irma, the strongest hurricane ever recorded in the Atlantic basin closely followed by hurricane Jose, the question of whether climate change is affecting the frequency and intensity of hurricanes in the Caribbean has once again come into question. Unfortunately, at the moment there is no certainty of whether the intense and frequent hurricanes of a single year are a result of human induced trends. Only future observations over multiple years and a better historical cyclone record will allow us to determine whether these trends are part of a long-term natural cycle or the result of a warming planet. What we do know, based on the climate assessment reports provided by the intergovernmental panel on climate change, (IPCC) is that cyclone activity in the Atlantic basin has been increasing since the 1970s. It is also predicted (although unlikely to be detected at the moment) that the frequency of more intense hurricanes is likely to grow as a result of warmer sea surface temperatures (IPCC Report 2013). Warmer water results in more water vapour, which fuels the hurricane system.
 
The NOAA satellite captures a geocolor image of Hurricane Irma as it passes the eastern end of Cuba. Photo credit: NOAA/CIRA
The IPCC predicts the effects of warmer atmospheric temperatures on small-island nations, some of which will certainly occur over the next 100 years. One major problem is sea-level rise, and the myriad issues that come with it, including coastal erosion, especially during periods of storm surge and high wave activity. Seawater will undermine infrastructure; contaminate ground water and sewerage systems, as well as freshwater ecosystems. Current observations show that the Caribbean has a mean sea-level rise rate of 1.8mm/ year, which is similar to the global average, while sea-level rise around the Pacific islands is increasing at a much faster rate. In regard to other weather patterns, under both future scenarios (business as usual carbon emissions and reduced carbon emissions), it is expected that warmer atmospheric temperatures will result in extended dry seasons and droughts in the southern Caribbean, while there will be more rainfall during the wet season in the northern Caribbean. All these changes will have direct impacts on the ecosystems – watersheds, agricultural lands, wetlands, mangroves and coral reefs - that we rely on for our livelihoods.

It is virtually certain that global mean sea level rise rates are accelerating.  Projected increases to the year 2100 (RCP4.5: 0.35 m to 0.70 m) superimposed on extreme sea level events (e.g. swell waves, storm surges, El Niño-Southern Oscillation) present severe sea flood and erosion risks for low-lying coastal areas and atoll islands (high confidence).- IPCC

Other ecological impacts from warmer conditions include the potential increase in the transmission of diseases, including vector borne diseases such as Zika, Chikungunya and Dengue that infect our population, as well as other diseases that can infect flora and fauna. Furthermore, cases of respiratory illnesses, such as asthma and allergies related to the dust clouds originating from a more arid Sahara basin and travel across the Atlantic to the eastern Caribbean is also expected to increase  (IPCC Report 2014).

WHAT DO WE NEED TO DO?
Adaptation to climate change generates larger benefit to small islands when delivered in conjunction with other development activities, such as disaster risk reduction and community-based approaches to development (medium confidence). Addressing the critical social, economic, and environmental issues of the day, raising awareness, and communicating future risks to local communities will likely increase human and environmental resilience to the longer-term impacts of climate change.” – Recommendation by the IPCC

Whether it is stronger hurricanes, sea level rise, drought or biological invasion, it is crucial that governments heed these warnings and work out transparent plans to reduce the risk of impact. Trinidad and Tobago has been fortunate to have a stable economy from the oil and gas industry but there is need for major investments into mitigating impacts. This should be done with transparency and with community engagement, so that climate awareness and action enter our homes and lives. While maintaining infrastructure and instilling stricter policies on housing and business development (especially development near important ecosystems and along coastlines and river ways) will help reduce economic damage, much of the future relies on the protection of our natural ecosystems and community awareness.

Most of our major towns in Trinidad and Tobago – Scarborough, Port of Spain and San Fernando - lie on the coasts. The Caroni and Nariva swamps collect much of the water from rainfall and will buffer the inundation events of the sea during storms. Keeping these waterways clear will help flood-prone areas. Preserving mangrove areas will reduce the damaging effects of storm surge. Coral reefs also act as natural wave breaks against storm surge, and the protection of the reefs from over-exploitation and pollution will give them the best chance to adapt to changing climate conditions and therefore to continue to serve their important economic roles. Preserving the rainforest, stricter laws on deforestation and squatting on watershed areas, will increase the storage capacity of water reserves and reduce wasted water, especially important during times of drought.

Another major problem noted by the IPCC is: the inaction inherent in the mismatch of the short-term time scale on which government decisions are generally taken compared with the long-term time scale required for decisions related to climate change. Governments need to implement policies that mandate climate change infrastructure; on the understanding that such policies must be non-partisan by nature, so that policies cannot be overturned from one government administration to the next.
 
Low lying islands, such as Malé the capital of the Maldives in the Indian Ocean, are under threat of rising sea levels. Photo credit: Shahee Ilyas (https://creativecommons.org/licenses/by-sa/3.0/)
Link to the latest IPCC Reports:




Friday, September 8, 2017

The Tropicalisation of Temperate Ecosystems

Anjani Ganase, marine biologist, looks at how climate change and warming ocean temperatures are impacting temperate marine ecosystems adjacent to tropical marine life.

The average land and sea surface temperature of the planet has increased by about 0.8 °C over the last one hundred years. Although this does not appear to be a significant number, a change of less than one degree can affect the timing of seasonal changes in plants and animals: breeding season, migration routes, flowering and fruiting of plants. Springtime activities in both animals and plants have been recorded to be occurring progressively earlier since the 1960s, including the arrival of butterflies and birds, delayed autumnal departures of migrating birds, as well as earlier breeding patterns in amphibians (Walther et al 2002). Apart from shifts in the timing of events, there have also been recordings of shifts or expansion in the range of plants and animals, in particular sedentary organisms, towards the poles and high altitudes as temperatures warm and providing other living conditions remain suitable.

We have also experienced the detrimental effects of tropical diseases, spread as a result of El Niño occurring on top of current warming temperatures; allowing the spread to temperate regions in the southeastern United States, China and Europe (Carminade et al 2017). What is seen on land can also be observed in the oceans.

Surveys carried out on marine ecosystems have observed changes in neighbouring temperate marine ecosystems as sea surface temperatures rise. There are places around the world that are heating up much faster, where currents originating in the tropics carry warmer waters to cooler temperate areas. The most famous in our region is the Gulf Stream, which flushes into the north Atlantic and bathes the northeast coastline of the US and Bermuda with warm water.

Other regions with similar current patterns have seen significant changes in the marine ecosystems where the current carrying warmth also brings passengers, such as coral reef fish and larvae of tropical organisms. These are able to survive for longer periods under current temperate conditions.

Tropical coastal ecosystems are primarily composed of coral reefs, which create the calcium carbonate framework used as foundational infrastructure utilised by a diverse array of other marine organisms. On the other hand, temperate ecosystems are made up of canopies formed by kelp forests and Sargassum beds, which play the infrastructural role by creating algal forests, also rich in marine life. While tropical herbivorous fish control the growth of macroalgae on corals; in temperate zones, the invasion of tropical fish to temperate kelp and Sargassum habitats will result in uncontrolled predation of the foundation species and the degradation of the ecosystem.

Underwater photographs from Tosa Bay (Southern Japan) showing: (a) well-developed Kelp bed in the early 1990s; (b) overgrazed kelp bed (‘isoyake’) in October 1997; (c) rocky barren area in January 2000; (d) coral communities present in January 2013. Image sourced from Verges et al (2014). Photograph credits: (a–c) Zenji Imoto and (d) Yohei Nakamura.
THE ISOYAKE PHENOMENON

Thousands of hectares of kelp forests have been lost over the last thirty years in southern Japan. This deforestation or the conversion of marine algal forests to barren sea bottoms is referred to as ‘Isoyake’ (literally burnt rock) by the local Japanese fisherman. Apart from warm waters being less favourable to the health of kelp forests, the algae are being fed upon by intruding tropical herbivores that graze on the palatable kelp, which prevents regrowth. Over time, the barren seascapes become occupied by large table-forming coral communities in place of the macroalgae (Verges et al. 2014). Coral may be good for tropical ecosystems but they cannot provide the same functions as kelp forest required by dependent temperate communities. The loss of these habitats also has severe repercussions in the fisheries industry that rely on the marine products that come from the kelp forest. The abalone fisheries crashed in Japan because the abalone disappeared when kelp forests were lost.

Similar trends are being observed along the Australia’s east coast where the southward currents of the EAC (Eastern Australia Currents) have increased the connectivity between the Great Barrier Reef and temperate marine ecosystems off southeast Australia, including Sydney (Figueira and Booth 2010). The EAC introduces tropical fish and larvae to temperate waters, but cold temperatures often limit the survival of these fish over winter. However, one study showed that the chances of tropical juvenile fish surviving winter will increase as winter temperatures warm, providing that other living conditions remain favourable (Figueira and Booth 2010). Hypothetically, while Nemo may currently be able to visit 42 Wallaby Way, Sydney to reminisce about his childhood adventures during the warmer months of the year; in the future, he may be able to permanently reside in some of Sydney’s prime real estate and not have to retreat to the Great Barrier Reef.

What does this mean about the future of our tropical marine ecosystems? If coral reefs are shifting pole wards, what will be replacing them in the waters that become too warm for their comfort? Unfortunately, oceans are continuing to warm and coral bleaching events are expected to increase in frequency. On the heels of the longest ever global coral bleaching event ever recorded (2015 – 2017) the future of coral reefs is bleak. The Caribbean also experienced a mass burning of coral reefs. For our coral reefs to survive, we all need to push for better climate change policies to reduce carbon emissions quickly.

Do we know what are the current targets for reduction of carbon emissions in Trinidad and Tobago and for the rest of the Caribbean? Are they enough?
Coral bleaching in the Maldives captured by The Ocean Agency, XL Catlin Seaview Survey, Richard Vevers in May 2016 during the latest major global coral bleaching event.

References:
Carminade, C., Turner, J., Metelmann, S., Hesson, J. C., Blagrove, M. S. C., Solomon, T., Morse, A. P., Baylis, M. (2017) Global risk model for vector-borne transmission of Zika virus reveals the role of El Niño 2015. Proceedings of the National Academy of Sciences of the United States of America, 114: 119 – 124.

Figuiera, W. F. and Booth, D. J. (2010), Increasing ocean temperatures allow tropical fishes to survive overwinter in temperate waters. Global Change Biology, 16: 506–516. doi:10.1111/j.1365-2486.2009.01934.x

Vergés A. et al. 2014, The tropicalization of temperate marineecosystems: climate-mediated changes in herbivory and community phase shifts. Proc. R. Soc. B 281: 20140846. http://dx.doi.org/10.1098/rspb.2014.0846

Walther, G. R., Post, E., Convey, P., Menzel, A., Parmesan, C., Beebee, T. J., Bairlein, F. (2002). Ecological responses to recent climate change. Nature, 416 (6879), 389-395.




Thursday, September 7, 2017

The need to include healthy marine ecosystems in Tobago's business model

Anjani Ganase, marine scientist, calls upon business to claim its share of ocean wealth by conserving and managing our islands’ resource. First published in the TT Chamber of Industry and Commerce' Contact magazine, vol 17 no 2, Focus on Tobago

We think of the ocean and its resources as vast and endless. Goods and services provided by the ocean for humans have been estimated to be about 24 trillion USD in assets (World Wildlife Fund, 2015) more than the economy of most nations. These goods include fishing, harvesting of materials and procurement of medicine, as well as services through shoreline protection, wave energy extraction, shipping and tourism. This asset value is grossly underestimated, as it doesn’t consider the crucial roles of the ocean in regulating climate, the air we breathe and stabilising temperature, nor does it consider the intrinsic cultural value that we place on the ocean (WWF 2015). But the resources of the ocean have been depleted more in our lifetime than ever before. 

Today, statistics show that humankind’s grasp has outreached the resource capacity of the ocean. Over 90 % of all the big fish stocks are gone, and by 2050 there will be more plastic in the ocean than fish if trends continue. Over the last 40 years, the biodiversity of marine life has dropped by 39 %, while marine habitats are declining at alarming rates. Mangrove ecosystems are being removed faster than the forests, and many coral reefs in the Caribbean have been reduced to about 20 % of its original cover (WWF 2015). In the Pacific, the Solomon Islands have lost five islands potentially due to climate related rising sea levels; the government of Kiribati has already bought land in Fiji to relocate their citizens, refugees of climate change. The Caribbean is already being negatively impacted by severe weather patterns, more intense hurricanes, and warming ocean waters.

Fortunately, some countries have found long-term sustainable solutions to save valuable ocean resources through the use of marine protected areas. The designation of marine sanctuaries, such as coral reefs, mangroves and offshore seamounts, has been shown to increase the abundance of marine life both inside and outside the protected areas. This has boosted the stock in the fishing areas, despite the concern of the local fishers. The tourism industry also benefits from marine sanctuaries, as snorkelling and diving sightseers are attracted to larger fish and marine life within the sanctuaries. Protected mangrove ecosystems buffer coastlines from storms, and act as nurseries for juvenile marine life. With proper enforcement, the recovery of marine areas along with profitable returns has occurred in as little as five years after the establishment of the marine sanctuaries. Communities on island nations worldwide, including Fiji, The Philippines, Bahamas, St Lucia and the Netherlands Antilles, have reported improved fisheries and tourism with long-term sustainability through the use of marine sanctuaries.

An overview of pristine paradise, Englishman’s Bay, Tobago. By preserving ecosystems both above and below the water, we can maintain its natural beauty for all to enjoy.

TOBAGO'S MARINE BIODIVERSITY
Tobago is a hub of marine biodiversity. Tobago’s waters support the development of coral reefs along most of its sheltered coastline, while the nutrients in the water column also provide food for an array of marine life. Located between the Caribbean Sea and the Atlantic Ocean, Tobago is on migration routes for many marine mega fauna, including sharks, whales and dolphins. The exclusive economic zone (EEZ) for Trinidad and Tobago is 16 times greater than the combined landmass of the two islands, most of it around Tobago. The waters and coastal habitats of Tobago can be used to enhance and diversify Tobago’s economy with adventure and educational tourism. However, it is crucial to conserve the product, the natural habitats and the marine life.

Tobago has a real chance of benefitting from conservation; and there are small businesses with environmental goals already showing the way. Businesses that explore the coral reefs, such as dive centres – Environmental Research Institute Charlotteville (ERIC) and Frontier Divers at Store Bay - seek to provide educational experiences, where visitors acquire diving skills and learn about coral reef ecology. Visitors become involved in local conservation activities, such as coral health monitoring surveys, garbage removal dives or guided hunts of the invasive lionfish. Tobago has shown entrepreneurship in eco-tourism through the development of low impact accommodation with limited land clearing, sustainable water usage and alternative energy supplies: examples can be found in Man O’ War Bay Cottages in Charlotteville, Footprints at Culloden and especially in Castara where the entire village participates in the Castara Tourism Development Association. These examples ensure sustainability, incorporating the services of local operators in community-run enterprises.

Investments in conservation business should include services, such as field research facilities and technical support staff for managing Tobago’s numerous ecosystems. By providing lab and field technical support to visiting groups, we continue to learn about our own ecosystems, adding to the repertoire of Tobago’s natural wonders. However, there must be a mandate for protection and enforcement of marine and terrestrial sanctuaries at all levels – community, business and government. The government’s role includes creating policy that is pro-environment, actively enforcing management of protected area, as well as establishing green infrastructure – proper waste (sewerage) management facilities, recycling centres and renewable energy supplies. Jobs in the public sector can be created through the training of Tobagonians for eco-tourism. The Main Ridge Forest Reserve is a living example. We can do the same for protected areas of the marine EEZ. These jobs regulate tourist traffic, provide information (visitor centres and shops), oversee the use of the areas and continually update regulation as we learn more about our ecosystems. Above all, there is a need for the government to invest in appropriate infrastructure, technology and education. Businesses can be built on skill development in ecosystem research and management. Together, we can all support Tobago’s brand: clean, green, safe and serene.


References:
Albert, S., Leon, J., Grinham, A.R., Church, J. A., Gibbes, B. R., Woodroffe, C. D. (2016) Interactions between sea-level rise and wave exposure on reef island dynamics in the Solomon Islands. Environmental Research Letters, 11, 054011.

World Economic Forum (2016),The New Plastics Economy; Rethinking the future of plastics
Hoegh-Guldberg, O. et al. (2015) Reviving the Ocean Economy: the case for action – 2015. WWF International, Gland, Switerland, Geneva, 60 pp.