Behavioural and physiological effects of shoaling in a coral reef fish

Nadler, Lauren Elizabeth (2016) Behavioural and physiological effects of shoaling in a coral reef fish. PhD thesis, James Cook University.

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Animals must rapidly perceive, process and react to sensory information from their ambient environment in order to survive. For this reason, many animal species partake in cooperative group behaviours to enhance their survival, as having "many-eyes" increases an individual's chances of being informed of important stimuli. Fish shoals (social groups offishes) are a classic example of a prolific, cooperative group behaviour found in nature. Approximately 50% of all fish species in the world's oceans shoal at some point during their lives. Therefore, effective execution of this behaviour is essential for the survival and success of many ecologically and economically important fish species. Shoaling provides benefits to a range of processes, including foraging, reproduction, social learning, predator avoidance and energetic demand. These benefits may vary depending on shoal composition and environmental conditions, but these effects remain poorly understood.

To better understand the costs and benefits of shoal membership, this thesis examined how factors external to and within the shoal affect the energy use by group members. These studies used the shoaling tropical damselfish Chromis viridis as a model species, as it thrives in the laboratory and is abundant near my study site at the Lizard Island Research Station (URS) in the northern Great Barrier Reef, Australia, making experimental laboratory manipulations possible.

Predator avoidance is one of the most important and well-studied benefits of grouping behaviour. In coordinated schools, predators have trouble focusing on specific prey to attack, creating a "confusion effect" that allows the group to benefit from higher survival. However, studies suggest that school cohesion and coordination may exhibit plasticity in response to environmental factors. In Chapter 2, I investigated the effect of water flow regime at a school's home reef on escape performance. Schools were collected from shallow reefs surrounding URS. The relative flow regimes for each collection site were measured over a three-week period. The school's escape response to an aerial mechanical stimulus was recorded in high-speed (240 fps) in a laminar flow swim tunnel. While school coordination and cohesion were unaffected by water flow regime, individual fast-start performance improved significantly in schools collected from high-flow regime reefs when compared to those from lower flow habitats.

The level of familiarity among the individuals of a group is also likely to impact school coordination and cohesion. Familiarity is a trait that develops following a prolonged period of social interaction among individuals and aids in fitness-enhancing processes such as foraging and social learning. Therefore, in Chapter 3, using the approach outlined for Chapter 2, I examined if familiarity of school members influenced the timing, maneuverability and propulsive performance of escape responses in fish schools. Members of familiar schools exhibited superior escape performance, with shorter latency times (higher reactivity), greater average turning rates (increased maneuverability) and longer distances covered (greater propulsive performance) than individuals from unfamiliar schools.

Group living may also induce a "calming effect" on individuals, reducing overall metabolic demand. This effect could occur by minimising the need for individual vigilance and reducing stress when allowed to associate with conspecifics. However, this effect has proved challenging to quantify due to the difficulty in isolating individuals for testing. In Chapter 4, I examined the effect of shoaling on metabolism and body condition. Using a novel respirometry methodology for social species, we found that the presence of visual and olfactory cues from shoal-mates led to a reduction in the estimated minimum metabolic rate of individuals. Fish held in isolation for one week also exhibited a reduction in body condition when compared to those held in shoals.

To better understand the results of my previous three chapters in the context of projected future global change, I examined the effect of elevated carbon dioxide on familiarity and metabolism in shoaling fish in Chapter 5. Shoals were acclimated to one of three CO₂ treatments: control (450 μatm), mid-CO₂ (750 μatm) or high-CO₂ (1000 μatm), with the latter representing projected CO₂ conditions for the year 2100. Familiarity was examined using a choice test. Under control conditions, individuals preferentially associated with familiar shoal-mates. However, this association was lost under both elevated CO₂ treatments. Yet, this loss of familiarity did not impact the calming effect of shoaling on metabolism (as measured using the methodology outlined in Chapter 3). Under all CO₂ treatments, individuals exhibited a significantly lower metabolic rate when measured in a shoal versus alone, highlighting the complexity of shoal dynamics and the processes that influence shoaling's benefits.

Understanding how organisms behave as a group is essential for assessing responses at the population and community level, particularly in socially and environmentally dynamic ecosystems such as coral reefs. My results suggest that individual behaviour and physiology is greatly influenced by both group living and habitat characteristics. Yet, these dynamics may be modulated by differences in shoal composition, through traits like familiarity, and projected future global change conditions. However, some benefits of group living, like the calming effect, may persist under climate change, potentially through sensory redundancy. These studies highlight the complexity of social behaviours on coral reefs and suggest that degree of sociality should be considered in studies on behaviour and physiology of coral reef fishes.

Item ID: 46428
Item Type: Thesis (PhD)
Keywords: behaviour; behavioural ecology; body condition; Chromis viradis; Chromis, claming effect; coral reef fishes; damselfishes; effect of predation; energetics; Great Barrier Reef; Lizard Island; metabolism; olfactory cues; physiology; predator response; respirometry; sense organs; senses; shoaling; shoals social groups; visual cues
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Publications arising from this thesis are available from the Related URLs field. The publications are:

Chapter 4: Nadler, Lauren E., Killen, Shaun S., McClure, Eva C., Munday, Philip L., and McCormick, Mark I. (2016) Shoaling reduces metabolic rate in a gregarious coral reef fish species. Journal of Experimental Biology, 219 (18). pp. 2802-2805.

Date Deposited: 22 Nov 2016 02:22
FoR Codes: 06 BIOLOGICAL SCIENCES > 0602 Ecology > 060203 Ecological Physiology @ 30%
06 BIOLOGICAL SCIENCES > 0602 Ecology > 060205 Marine and Estuarine Ecology (incl Marine Ichthyology) @ 30%
06 BIOLOGICAL SCIENCES > 0608 Zoology > 060801 Animal Behaviour @ 40%
SEO Codes: 97 EXPANDING KNOWLEDGE > 970106 Expanding Knowledge in the Biological Sciences @ 50%
96 ENVIRONMENT > 9608 Flora, Fauna and Biodiversity > 960808 Marine Flora, Fauna and Biodiversity @ 50%
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