Energetics and behavior of coral reef fishes during oscillatory swimming in a simulated wave surge

Abstract

Oxygen consumption rates were measured for coral reef fishes during swimming in a bidirectional, oscillatory pattern to simulate station-holding in wave-induced, shallow-water flows. For all species examined, increases in wave intensity, as simulated by increases in frequency and amplitude of oscillation, yielded increased metabolic rates and net costs of swimming (NCOS; swimming metabolic rate minus standard metabolic rate). Comparing species with different swimming modes, the caudal fin swimming Kuhlia spp. (Kuhliidae) and simultaneous pectoral-caudal fin swimming Amphiprion ocellaris (Pomacentridae) turned around to face the direction of swimming most of the time, whereas the median-paired fin (MPF) swimmers, the pectoral fin swimming Ctenochaetus strigosus (Acanthuridae) and dorsal-anal fin swimming Sufflamen bursa (Balistidae), more frequently swam in reverse for one half of the oscillation to avoid turning. Contrary to expectations, the body-caudal fin (BCF) swimming Kuhlia spp. had the lowest overall NCOS in the oscillatory swimming regime compared with the MPF swimmers. However, when examining the effect of increasing frequency of oscillation at similar average velocities, Kuhlia spp. showed a 24% increase in NCOS with a 50% increase in direction changes and accelerations. The two strict MPF swimmers had lower increases on average, suggestive of reduced added costs with increasing frequency of direction changes with this swimming mode. Further studies are needed on the costs of unsteady swimming to determine whether these differences can explain the observed prevalence of fishes using the MPF pectoral fin swimming mode in reef habitats exposed to high, wave-surge-induced water flows.

Swimming in unsteady water flows: is turning in a changing flow an energetically expensive endeavor for fish?

“…The goldring surgeonfish used in this study are common in wave-exposed areas of coral and rocky reefs (Hobson, 1974) and, therefore, may be more efficient at acceleration. It is also possible that the added costs of accelerating with each wave cycle are offset with energy savings during a passive deceleration phase (Marcoux and Korsmeyer, 2019).…”

“…In shallow, wave-swept habitats, station-holding fishes have to continuously accelerate and decelerate to match the changing water speeds, which can increase the amount of energy used relative to steady-state swimming (Liao, 2007;Roche et al, 2014). Furthermore, the adjustment of swimming speeds is coupled with changes in water flow direction, requiring backward swimming or a whole-body rotation to face the flow (Marcoux and Korsmeyer, 2019). Alternatively, the fishes can seek refuge to ease or escape the challenge of dealing with the water flows.…”

“…More recently, however, studies of swimming in unsteady water flows have incorporated changes in swimming direction and oscillatory speeds more typical of wave-swept habitats (i.e. unidirectional or bidirectional oscillatory water flow) (Roche et al, 2014;Marcoux and Korsmeyer, 2019).…”

“…A study on a temperate, estuarine labriform swimmer, the surfperch Cymatogaster aggregata, found that a unidirectional, unsteady flow simulating a wave surge without the turning component increased the energetic cost of swimming by 25% compared with swimming in a steady flow, in part owing to added energetic costs of acceleration and deceleration (Roche et al, 2014). A recent study by Marcoux and Korsmeyer (2019) examined station-holding swimming performance and behavior of several coral reef fish species in a simulated wave surge. They found that median and paired fin (MPF) swimmers, such as labriform swimmers, were more cost-efficient as wave frequency increased than body caudal fin (BCF) swimmers, and MPF swimmers more frequently swam backwards instead of turning despite an increase in pectoral fin beat frequency associated with backward swimming.…”

“…These results suggest that turning is an expensive behavior. However, owing to flow limitations in the experimental setup, the study was only able to simulate wave surge at the lower end of the conditions found naturally in terms of wave amplitudes and water flow velocities, and could not make direct comparisons with steady swimming costs Marcoux and Korsmeyer, 2019). Thus, the extent of the added costs for stationholding, and what proportion is due to the potential costs of acceleration or turning, is unclear.…”