From the Caribbean to Antarctica

Dr Anjani Ganase provides a review of recent scientific studies on Manta rays, tropical forests, Antarctic sea ice and coral reefs.

Manta Ray nursery off Florida 

Monitoring of the giant oceanic manta ray (Mobula birostris) populations along the southeast coast of Florida has led scientists to believe that there is a manta ray nursery. Most of the mantas observed in the area were immature. This nursery would be one of three identified globally. The tracking of manta species over the years within this specific area reveal a high return to the area; some individuals were recorded multiple times over the four-year window.

 

Manta ray with diver, Socorro. Credit: Hannes Klostermann / Ocean Image Bank

Manta rays are relatively understudied yet the giant oceanic manta ray is endangered according to the IUCN (International Union for Conservation of Nature) red list. Genetic research also indicates the Western Atlantic rays may be a distinct species, referred to as the Caribbean Manta Ray (Mobula cf. birostris). Research conducted in the area reveal a population of a lesser-known species of manta, the sickle fin devil ray (Mobula tarapacana), an olive-green variant occurring in the waters off the east coast of the US and Gulf of Mexico. This elusive species can be found in tropical water around the world, and yet little is known about their ecology. Mantas are long-lived species (45 years at least) with a slow reproductive cycle, rearing one pup every two to three years. The identification of their nursery grounds and protection of these habitats are critical to the conservation of the majestic creatures. Industrial and fishing activities overlap with the nursery and range of the mantas. Surveys carried out among the fisherfolk highlight that while that many fishers do support the protection of mantas, many struggled to identify manta species, and do not know techniques to safely remove fishing line and hooks from the manta. Engagement with the fishing community would boost the conservation effort.

 

Human exploitation and consumption study

A study done by the University of Victoria, Canada reveals that 31 % of all vertebrate species are exploited by humans. Exploitation broadly refers to any animal harvested from the wild for food, clothing, poisons, pharmaceuticals, pet trade, chemical manufacturing, fuels, fibres, jewellery, display, sport hunting and research. The research group used data collected on 47,000 species from the IUCN and revealed that up to 15,000 species were being exploited by humans. A comparison with other non-human predators shows that humans exploit as much as 300 times above the average number of species exploited by other animals for any given geographic area. The predator closest in numbers to humans with respect to the diversity of prey is the Eurasian-Eagle Owl (552). While 55 % of the vertebrates were exploited for food consumption, exploitation for the pet trade and for medicine were just as high. Fish (marine and freshwater species – 78 %) make up the largest proportion of consumed species, while birds, amphibians and reptiles were mostly exploited for the pet trade. A significant proportion of mammals were also exploited for clothing and medicine. The highest level of exploitation occurs along the tropical and oceanic areas, where highest biodiversity occurs. About 40 % of the species are threatened by the exploitation with 4 % or over 580 species facing extinction, and a whopping 36 % are mammals.

 

Tropical forests and climate change

 A recent study showed that plants no longer photosynthesise at temperatures above 46.7 C. The findings support a study done in 1864 which estimated the failure point to be around 50 C. Photosynthesis refers to the chemical reaction that uses sunlight to convert water and carbon dioxide to energy in the form of sugar and oxygen. The process of photosynthesis supports all life on earth and is the basis of the global food web. The temperature failure point was found using the leaves of 147 species of plants. While the real-world application is less certain, scientists estimate that currently many tropical forests rarely exceed the critical temperatures (midday temperatures). However, under drought conditions, sections of the Amazon may experience temperatures above the critical value and sun-exposed trees were observed to be dying off at disproportionately higher rates. Unfortunately, a 4-degree rise in global average temperature under the worst-case scenario for global warming is likely to result in widespread die-off by 2100. Understanding such tipping points is critical for setting climate targets below potentially disastrous ecological failures.

 

Climate change devastation

In 2022, the lowest ever sea ice extent in Antarctica was recorded since the 45 years of satellite tracking. Sea ice refers to the frozen seawater that floats on the surface and extends outward from the mainland. The sea ice extent expands during the winter months of Antarctica (March to October) and then contracts during the summer months. Many marine organisms, such as the Emperor Penguins, live permanently on sea ice, and the loss of the sea ice can result in plummeting populations. Emperor Penguins located west of the Antarctic Peninsula have recently lost their entire fledgling populations. Satellite imagery from January 2023 showed 100 % sea ice loss that resulted in Emperor Penguins abandoning the site. This caused the total loss of the chick populations, still in fledgling phase and unable to swim. The satellite imagery reveals the loss of sea ice from directly under their feet. At some locations, the images show remnants of the populations trapped on an iceberg; eventually these populations disappear as penguins require stable ice to raise their young.

 

Coral bleaching alert for Trinidad and Tobago. Credit: NOAA Coral Reef Watch

 

Meanwhile, the Caribbean region is currently experiencing some of the warmest air and sea temperatures in recent history. The unusual warm temperatures are largely driven by El Niño conditions riding the wave of a warming climate. This week, NOAA’s Coral Reef Watch placed Trinidad and Tobago under Bleaching Alert Level 2 and it is expected to remain at this level for the next three months. Under Level Two conditions, widespread coral bleaching and mortality are expected. After the heat wave, corals become prone to disease outbreaks. There’s not much that can be done during the bleaching event, however long-term protection and management can build coral resilience and improve recovery. Such practices are urgently needed as many actions take over ten years to see the benefits.

 

The Caribbean coral reef and the Antarctic sea ice are indicators of the far-reaching impacts of global climate change.

 

 

References

Darimont, C.T., Cooke, R., Bourbonnais, M.L. et al. Humanity’s diverse predatory niche and its ecological consequences. Commun Biol 6, 609 (2023). https://doi.org/10.1038/s42003-023-04940-w 

Doughty, C.E., Keany, J.M., Wiebe, B.C. et al. Tropical forests are approaching critical temperature thresholds. Nature (2023). https://doi.org/10.1038/s41586-023-06391-z

J.H. Pate et al. Multiple datasets confirm range extension of the Sicklefin Devil Ray Mobula tarapacana in the western North Atlantic Ocean off the eastern USA. Journal of the Marine Biological Association of the United Kingdom. Published April 24, 2023. doi: 10.1017/S002531542300022X.

J.H. Pate, C. Macdonald and J. Wester. Surveys of recreational anglers reveal knowledge gaps and positive attitudes towards manta ray conservation in Florida. Aquatic Conservation Marine and Freshwater Ecosystems. Vol. 21, June 2021, p. 1410. doi: 10.1002/aqc.3508.

J.H. Pate and A.D. Marshall.Urban manta rays: potential manta ray nursery habitat along a highly developed Florida coastline. Endangered Species Research. Published online September 3, 2020. doi: 10.3354/esr01054.

 Fretwell, P.T., Boutet, A. & Ratcliffe, N. Record low 2022 Antarctic sea ice led to catastrophic breeding failure of emperor penguins. Commun Earth Environ 4, 273 (2023). https://doi.org/10.1038/s43247-023-00927-x