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[BPT02-04] Computed tomography scanning reveals morphological development of a burrow produced by the tiger pistol shrimp Alpheus bellulus
Trace fossils made by ancient animals provide information on the activities of their producers. However, improving our understanding of trace fossils requires the analysis of their modern analogs. In this study, we investigate morphology of a burrow produced by a modern benthic crustacean with computed tomography (CT) scanning to reveal its four-dimensional morphology. Because crustaceans are known to show a wide habitat range from shallow to deep sea and have lived since the Paleozoic era, they are suitable for burrow forming experiment as a modern analog of trace fossils.
The tiger pistol shrimp Alpheus bellulus used in this study was placed in each of the five tanks, and a light-shielding plate was set on the bottom to enable the shrimp to produce burrow easily. The CT images were taken at intervals of 10 to 30 minutes immediately after the start of burrowing by the shrimp. Then, morphological changes of the burrow were imaged with CT data processing, and we calculated surface area, volume, depth, diameter, and length of the burrow. Additionally, we calculated the growth rate of burrow surface area, volume, depth and length.
The surface area and volume of all burrows increased immediately after the start of the experiment, but the growth rates of them gradually decreased. The variation in the value of each diameter gradually got smaller. The depth sharply increased immediately after the start of the experiment and then moderately increased. The length of almost burrows significantly increased immediately after the start of, but then the growth rate gradually decreased. In addition, weak positive correlations were recognized between the carapace length and growth rates of the volume, depth, length, and surface area increase rate though there was almost no correlation between the carapace length and growth rates of the length.
The increase of the growth rate of surface area and volume immediately after the start of the experiment and no reactions by shrimp to food during burrowing indicate that a burrowing is high priority for shrimp. The increase of burrow depth growth rate immediately after the start of the experiment suggests that a hiding against predators is prioritized in the early stage of burrowing. Furthermore, the weak positive correlation between carapace length and volume indicates that larger shrimp produces larger burrow. Additionally, the growth rate of burrow to the shrimp size could be also positively correlated.
This study four-dimensionally observed burrow morphology of the tiger pistol shrimp Alpheus bellulus. The method used in this study can be applied to various burrowing organisms, and can contribute to further understandings of benthic ecology and paleoecology.
The tiger pistol shrimp Alpheus bellulus used in this study was placed in each of the five tanks, and a light-shielding plate was set on the bottom to enable the shrimp to produce burrow easily. The CT images were taken at intervals of 10 to 30 minutes immediately after the start of burrowing by the shrimp. Then, morphological changes of the burrow were imaged with CT data processing, and we calculated surface area, volume, depth, diameter, and length of the burrow. Additionally, we calculated the growth rate of burrow surface area, volume, depth and length.
The surface area and volume of all burrows increased immediately after the start of the experiment, but the growth rates of them gradually decreased. The variation in the value of each diameter gradually got smaller. The depth sharply increased immediately after the start of the experiment and then moderately increased. The length of almost burrows significantly increased immediately after the start of, but then the growth rate gradually decreased. In addition, weak positive correlations were recognized between the carapace length and growth rates of the volume, depth, length, and surface area increase rate though there was almost no correlation between the carapace length and growth rates of the length.
The increase of the growth rate of surface area and volume immediately after the start of the experiment and no reactions by shrimp to food during burrowing indicate that a burrowing is high priority for shrimp. The increase of burrow depth growth rate immediately after the start of the experiment suggests that a hiding against predators is prioritized in the early stage of burrowing. Furthermore, the weak positive correlation between carapace length and volume indicates that larger shrimp produces larger burrow. Additionally, the growth rate of burrow to the shrimp size could be also positively correlated.
This study four-dimensionally observed burrow morphology of the tiger pistol shrimp Alpheus bellulus. The method used in this study can be applied to various burrowing organisms, and can contribute to further understandings of benthic ecology and paleoecology.