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Comparative heat stress study of acorn barnacles Tetraclita japonica and Tetraclita squamosa of Cape D’aguilar, Hong Kong

Westwood, Nicholas (2012) BIOM21 20121
Degree Projects in Biology
Abstract
Abstract:

The physiological responses of two Hong Kong acorn barnacles, Tetraclita japonica and T. squamosa differed under identical heat stress conditions. Both species experienced increased body temperature and mantle water osmolality with higher temperatures and prolonged emersion time. Species comparisons however, showed that T. japonica had warmer body temperatures and more concentrated osmolality than T. squamosa. The difference in response to heat stress suggests a strategic mechanism in accordance with their microhabitat and vertical distribution on Hong Kong shores. Mid-intertidal T. japonica response may be indicative of a water retention strategy to combat longer emersion periods with higher desiccation risk whereas... (More)
Abstract:

The physiological responses of two Hong Kong acorn barnacles, Tetraclita japonica and T. squamosa differed under identical heat stress conditions. Both species experienced increased body temperature and mantle water osmolality with higher temperatures and prolonged emersion time. Species comparisons however, showed that T. japonica had warmer body temperatures and more concentrated osmolality than T. squamosa. The difference in response to heat stress suggests a strategic mechanism in accordance with their microhabitat and vertical distribution on Hong Kong shores. Mid-intertidal T. japonica response may be indicative of a water retention strategy to combat longer emersion periods with higher desiccation risk whereas low-intertidal T. squamosa respond more effectively at reducing body temperature to alleviate potentially acute heat damage. Understanding these differences may help in predicting differential effects of climate change on the future abundance and distribution of these species.

Popular science summary:

Can everyone handle the heat?

As humans, most of us enjoy time in the sun and often take vacations to seek warmer climates. However, with more pleasant climates comes much heeded caution. Over exposure to high temperatures and sun can be permanently damaging to our physiology and health. With lengthy periods in the sun we can become dehydrated and our skin can burn under damaging UV rays. Fortunately, we have the behavioural sophistication to cope with these damaging factors and protect ourselves from sudden changes in climate, usually through rehydration of simply avoidance.

My study looks at organisms lacking the mobility to evade such harmful climatic conditions during periods of prolonged heat stress. The study organisms examined are barnacles, crustaceans found fixed to hard substrate in intertidal rocky shores around the world. On tropical shores we find different species of barnacle between shore heights. My study aimed to investigate the tolerance of two different barnacle species to heat stress based on their vertical distributions on rocky shores.

Several hundred barnacles were removed using hammers and chisels from intertidal rocky shores in Hong Kong. Barnacle species Tetraclita squamosa were removed from low shores whilst Tetraclita japonica were removed from a slightly higher position. A series of experiments were designed to explore the physiological responses of these species under different environmental simulations, mimicking the conditions found on typical tropical rocky shores. By exposing these animals to a wide range of heat stress scenarios, a data set of physiological responses was recorded to indicate how each species responds differently.

The results showed that barnacle species from the lower shore, T. squamosa maintained lower body temperatures over time at different temperatures but greater water loss. In contrast higher shore T. japonica showed warmer body temperatures but greater water retention. Given their distributions on rocky shores, the lower barnacle species experience a more frequent interaction with water and less exposure to direct sun. Taking this into account, along with the physiological data collected we could speculate a difference in adaptive mechanisms of barnacles to heat stress at different shore heights.

Ultimately we concluded that barnacles that inhabit a moister environment lower on the shore would opt to relieve body temperature through evaporative water loss mechanisms rather than hold water. Unsurprisingly, when these barnacles experienced longer periods outside water there physiology could not tolerate the excessive water loss. On the other hand, the higher shore T. japonica retain water at the cost of higher body temperatures, enabling them to tolerate the heat stress for longer.

Using these findings we can try to predict the future ecology of these species and others like them in terms of future climate change. We have seen that based on shore distribution certain organisms are able to tolerate present day climate. However, with potential temperature increase many species may not be able to handle their new environment thus resulting in widespread distribution and abundance shifts in intertidal zones around world.

Advisor: Per Carlsson and Gray A. Williams
Master´s Degree Project 30 credits in Marine Ecology. 2012
Department of Biology, Lund University and SWIRE Institute of Marine Science, University of Hong Kong (Less)
Please use this url to cite or link to this publication:
author
Westwood, Nicholas
supervisor
organization
course
BIOM21 20121
year
type
H2 - Master's Degree (Two Years)
subject
language
English
id
3633190
date added to LUP
2013-04-12 13:48:34
date last changed
2013-04-12 13:48:34
@misc{3633190,
  abstract     = {Abstract: 

The physiological responses of two Hong Kong acorn barnacles, Tetraclita japonica and T. squamosa differed under identical heat stress conditions. Both species experienced increased body temperature and mantle water osmolality with higher temperatures and prolonged emersion time. Species comparisons however, showed that T. japonica had warmer body temperatures and more concentrated osmolality than T. squamosa. The difference in response to heat stress suggests a strategic mechanism in accordance with their microhabitat and vertical distribution on Hong Kong shores. Mid-intertidal T. japonica response may be indicative of a water retention strategy to combat longer emersion periods with higher desiccation risk whereas low-intertidal T. squamosa respond more effectively at reducing body temperature to alleviate potentially acute heat damage. Understanding these differences may help in predicting differential effects of climate change on the future abundance and distribution of these species.

Popular science summary:

Can everyone handle the heat?

As humans, most of us enjoy time in the sun and often take vacations to seek warmer climates. However, with more pleasant climates comes much heeded caution. Over exposure to high temperatures and sun can be permanently damaging to our physiology and health. With lengthy periods in the sun we can become dehydrated and our skin can burn under damaging UV rays. Fortunately, we have the behavioural sophistication to cope with these damaging factors and protect ourselves from sudden changes in climate, usually through rehydration of simply avoidance. 

My study looks at organisms lacking the mobility to evade such harmful climatic conditions during periods of prolonged heat stress. The study organisms examined are barnacles, crustaceans found fixed to hard substrate in intertidal rocky shores around the world. On tropical shores we find different species of barnacle between shore heights. My study aimed to investigate the tolerance of two different barnacle species to heat stress based on their vertical distributions on rocky shores. 

Several hundred barnacles were removed using hammers and chisels from intertidal rocky shores in Hong Kong. Barnacle species Tetraclita squamosa were removed from low shores whilst Tetraclita japonica were removed from a slightly higher position. A series of experiments were designed to explore the physiological responses of these species under different environmental simulations, mimicking the conditions found on typical tropical rocky shores. By exposing these animals to a wide range of heat stress scenarios, a data set of physiological responses was recorded to indicate how each species responds differently.

The results showed that barnacle species from the lower shore, T. squamosa maintained lower body temperatures over time at different temperatures but greater water loss. In contrast higher shore T. japonica showed warmer body temperatures but greater water retention. Given their distributions on rocky shores, the lower barnacle species experience a more frequent interaction with water and less exposure to direct sun. Taking this into account, along with the physiological data collected we could speculate a difference in adaptive mechanisms of barnacles to heat stress at different shore heights. 

Ultimately we concluded that barnacles that inhabit a moister environment lower on the shore would opt to relieve body temperature through evaporative water loss mechanisms rather than hold water. Unsurprisingly, when these barnacles experienced longer periods outside water there physiology could not tolerate the excessive water loss. On the other hand, the higher shore T. japonica retain water at the cost of higher body temperatures, enabling them to tolerate the heat stress for longer.

Using these findings we can try to predict the future ecology of these species and others like them in terms of future climate change. We have seen that based on shore distribution certain organisms are able to tolerate present day climate. However, with potential temperature increase many species may not be able to handle their new environment thus resulting in widespread distribution and abundance shifts in intertidal zones around world.

Advisor: Per Carlsson and Gray A. Williams
Master´s Degree Project 30 credits in Marine Ecology. 2012
Department of Biology, Lund University and SWIRE Institute of Marine Science, University of Hong Kong},
  author       = {Westwood, Nicholas},
  language     = {eng},
  note         = {Student Paper},
  title        = {Comparative heat stress study of acorn barnacles Tetraclita japonica and Tetraclita squamosa of Cape D’aguilar, Hong Kong},
  year         = {2012},
}