The Effect of Swimming Modes And Mophological Attributes On The Energetics Of Coral Reef Fishes Swimming In A Wave-Surge Flow
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Soerensen, Mathias Schakmann
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Marine Science
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Water flow conditions in shallow-water marine ecosystems are commonly dominated by a wave-surge flow and specifically on coral reefs we observe an immense diversification in morphology and swimming modes of fishes that are linked to their swimming performance. Recently, a few experimental studies have found that in wave-surge conditions the energetic requirements for fishes to station-hold are greatly increased and field studies suggest that fishes ability to occupy these unsteady, dynamic flow regimes is dependent on their swimming mode and morphological attributes. However, previous experimental studies have not examined a combination of diverse morphologies with an adequate range of wave-surge intensities that have been observed in the field. In this study, we used a modified swimming respirometer to create simulated wave-surge flows with variations in frequency and average velocity. The range of simulated wave-surge flows tested was within the range of flow conditions observed on sheltered and exposed reefs in both calm and stormy conditions. This study examined two different aspects of the energetics of swimming in wave-surge flows. In the first part, we quantified the swimming costs associated with station-holding in six levels of both unidirectional and bidirectional wave-surge flows to separate the costs of acceleration and turning using the goldring surgeonfish, Ctenochaetus strigosus, a pectoral-fin swimmer. We determined that turning during station-holding increased the cost by up to 2-fold while the added acceleration costs were minimal. In the second study, we quantified the cost of station-holding in steady water flows and simulated bidirectional wave-surge flows for four coral reef fish species, one BCF swimmer and three pectoral fin swimmers, with a variation of body and fin morphologies. We found that, while the BCF swimmer had low costs associated with steady swimming, it had a higher effect of wave frequency on the swimming costs compared to the MPF swimmers. However, the pectoral fin swimmer with a high aspect ratio fins had both low swimming costs in the steady and wave-surge flows. Lastly, the body fineness ratio of the fishes was the largest predictor of NCOS with ratios close to 4.5 resulting in the lowest NCOS in the wave-surge flow.
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Hawaii Pacific University