Life in the shallows becomes a trap for baby sharks

July 21, 2020

Scientists can now explain how baby reef sharks tolerate living in the sometimes-extreme environments of their nurseries--but, they also say these habitats face an uncertain future which may leave newborn sharks 'trapped'.

The lead author of the study is Ian Bouyoucos, a PhD student at the ARC Centre of Excellence for Coral Reef Studies at James Cook University (Coral CoE at JCU).

"Nearshore, shallow water nurseries provide food and abundant shelter where baby blacktip reef sharks can avoid bigger predators, such as other sharks," Mr Bouyoucos said.

Though the word 'nursery' conjures images of soft, nurturing environments, these shallows are anything but. The habitats can be 'extreme', with dramatic changes in temperature and oxygen levels.

"It's not a nice place really, in terms of environmental conditions," said co-author Associate Professor Jodie Rummer, also from Coral CoE at JCU. The extremes of the shallows can mean high temperatures and low oxygen levels, which can be a strain at best.

"But we found the growth rate and metabolism of baby sharks is resilient to the temperature changes they currently face in these shallow habitats," Mr Bouyoucos said.

"We also found the sharks with a greater tolerance for higher temperatures had a greater tolerance for low oxygen levels, which is really promising."

Dr Rummer said mother blacktip reef sharks usually give birth close to shore. There may be, at most, only four pups born at a time with perhaps only one surviving.

"Essentially from the day they are born, these sharks have to be pretty tough in how their bodies work in order to tolerate these harsh environmental conditions," Dr Rummer said.

The research was conducted within the largest shark sanctuary in the world--the French Polynesian shark sanctuary. The top threat to sharks worldwide is overfishing, but sharks are protected within the 4.8 million square kilometre sanctuary.

Though the young sharks appear resistant to extreme changes the authors warn, as waters get warmer with climate change, future populations are threatened. While the sanctuaries might successfully remove the number one threat to these sharks, they don't protect against their second biggest threat: climate change.

"We know that healthy ocean ecosystems need healthy predators, and that healthy predators need healthy ecosystems--you can't have one without the other," Dr Rummer said.

She says newborn sharks have a narrow window of time in nursery habitats, where they have to grow, learn to hunt, and not get eaten.

"So, if these ecosystems disintegrate under climate change, the baby sharks fall into a 'trap'," Dr Rummer said.

"If they choose less harsh habitats, they lose their food and protection. If they remain within the safe, shallow nurseries, they suffer the effects of warming waters and decreasing oxygen levels. A trap, indeed."

Mr Bouyoucos says while these sharks can cope with these challenging conditions now, they are approaching their limits.

"There are already extreme fluctuations and extreme highs going on in the shallows--and the conditions are only getting worse," he said.

"We have to ask, will reef sharks continue to adapt and evolve over generations at a pace that's fast enough to keep up with climate change?"
-end-
PAPER

Bouyoucos I, Morrison P, Weideli O, Jacquesson E, Planes S, Simpfendorfer C, Brauner C, Rummer J. (2020). 'Thermal tolerance and hypoxia tolerance are associated in blacktip reef shark (Carcharhinus melanopterus) neonates'. Journal of Experimental Biology. DOI: 10.1242/jeb.221937

CONTACTS

Ian Bouyoucos (currently in USA)
E: ian.bouyoucos@my.jcu.edu.au

Jodie Rummer (Townsville, Australia)
P: +61 (0) 439 166 171
E: jodie.rummer@jcu.edu.au

ARC Centre of Excellence for Coral Reef Studies

Related Climate Change Articles from Brightsurf:

Are climate scientists being too cautious when linking extreme weather to climate change?
Climate science has focused on avoiding false alarms when linking extreme events to climate change.

Mysterious climate change
New research findings underline the crucial role that sea ice throughout the Southern Ocean played for atmospheric CO2 in times of rapid climate change in the past.

Mapping the path of climate change
Predicting a major transition, such as climate change, is extremely difficult, but the probabilistic framework developed by the authors is the first step in identifying the path between a shift in two environmental states.

Small change for climate change: Time to increase research funding to save the world
A new study shows that there is a huge disproportion in the level of funding for social science research into the greatest challenge in combating global warming -- how to get individuals and societies to overcome ingrained human habits to make the changes necessary to mitigate climate change.

Sub-national 'climate clubs' could offer key to combating climate change
'Climate clubs' offering membership for sub-national states, in addition to just countries, could speed up progress towards a globally harmonized climate change policy, which in turn offers a way to achieve stronger climate policies in all countries.

Review of Chinese atmospheric science research over the past 70 years: Climate and climate change
Over the past 70 years since the foundation of the People's Republic of China, Chinese scientists have made great contributions to various fields in the research of atmospheric sciences, which attracted worldwide attention.

A CERN for climate change
In a Perspective article appearing in this week's Proceedings of the National Academy of Sciences, Tim Palmer (Oxford University), and Bjorn Stevens (Max Planck Society), critically reflect on the present state of Earth system modelling.

Fairy-wrens change breeding habits to cope with climate change
Warmer temperatures linked to climate change are having a big impact on the breeding habits of one of Australia's most recognisable bird species, according to researchers at The Australian National University (ANU).

Believing in climate change doesn't mean you are preparing for climate change, study finds
Notre Dame researchers found that although coastal homeowners may perceive a worsening of climate change-related hazards, these attitudes are largely unrelated to a homeowner's expectations of actual home damage.

Older forests resist change -- climate change, that is
Older forests in eastern North America are less vulnerable to climate change than younger forests, particularly for carbon storage, timber production, and biodiversity, new research finds.

Read More: Climate Change News and Climate Change Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.