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Effects of eliminating interactions in multi-layer culture on survival, food utilization and growth of small sea urchins Strongylocentrotus intermedius at high temperatures.

ABSTRACT: Poor growth and disease transmission of small sea urchins Strongylocentrotus intermedius in summer greatly hamper the production efficiency of the longline culture. Reducing the adverse effects of high stocking density while maintaining high biomass is essential to address these problems. Here, we conducted a laboratory experiment to simulate the multi-layer culture for sea urchins at ambient high temperatures (from 22.2 to 24.5 °C) in summer for ~ 7 weeks. Survival, body size, lantern growth, gut weight, food consumption, Aristotle's lantern reflex, 5-hydroxytryptamine concentration, pepsin activity and gut morphology were subsequently evaluated. The present study found that multi-layer culture led to significantly larger body size than those without multi-layer culture (the control group). This was probably because of the greater feeding capacity (indicated by lantern growth and Aristotle's lantern reflex) and food digestion (indicated by morphology and pepsin activity of gut) in the multi-layer cultured sea urchins. These results indicate that multi-layer is an effective approach to improving the growth efficiency of sea urchins at high temperatures. We assessed whether eliminating interaction further improve these commercially important traits of sea urchins in multi-layer culture. This study found that eliminating interactions displayed greater body size and Aristotle's lantern reflex than those not separated in the multi-layer culture. This approach also significantly reduced the morbidity compared with the control group. These novel findings indicate that eliminating interactions in multi-layer culture greatly contributes to the growth and disease prevention of sea urchins at high temperatures. The present study establishes a new technique for the longline culture of sea urchins in summer and provides valuable information into the longline culture management of other commercially important species (e.g. scallops, abalones and oysters).

SUBMITTER: Hu F

PROVIDER: S-EPMC8302603 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:BackgroundThe spatial distribution of spawners and temporal parameters of spawning in motile invertebrates with external fertilization might influence reproductive success. However, to date, data on the prespawning and spawning behaviors of broadcast spawners in the field have been scarce and mostly qualitative. The present study was intended to clarify the behavioral adaptations of two sea urchin species, Strongylocentrotus intermedius and Mesocentrotus nudus, using quantitative analysis of their behavior during mass spawning events under natural conditions.MethodsWe analyzed in situ video recordings of sea urchin behavior obtained during six spawning seasons (2014-2019). The total number of specimens of each sea urchin species and the numbers of spawning males and females were counted. Quantitative parameters of sea urchin spawning (numbers of gamete batches, release duration of one gamete batch, time intervals between gamete batches and total duration of spawning) and movement (step length of spawners and nonspawners before and during spawning and changes in distances between males/nonspawners and females) were determined.ResultsFor each species, 12 mass spawning events were recorded in which 10 or more individuals participated. The temporal dynamics of the numbers of males and females participating in mass spawning were well synchronized in both species; however, males began to spawn earlier and ended their spawning later than females. In both species, the most significant intersex difference was the longer spawning duration in males due to the longer pause between gamete batches. The total duration of gamete release did not differ significantly between sexes. The average duration of sperm release during mass spawning events was longer than solitary male spawning. Males and females showed significant increases in the locomotion rate 35 min before the start of spawning and continued to actively move during spawning. An increase in movement rate before spawning in males and females was induced by environmental factor(s). Nonspawners of both species showed increased locomotion activity but in the presence of spawning neighbors and less prominently than spawners. On a vertical surface, both echinoids moved strictly upward. On flat surfaces, males, females and nonspawners of both echinoids became closer during spawning.DiscussionWe showed that two sea urchin species with planktotrophic larvae display similar behavioral adaptations aimed at enhancing reproductive success. The high sensitivity of sea urchins, primarily males, to some environmental factors, most likely phytoplankton, may be considered a large-scale adaptation promoting the development of mass spawning events. The longer spawning duration in males and increased movement activity before and during spawning in both sexes may be considered small-scale adaptations promoting approach of males and females and enhancing the chances of egg fertilization.

Project description:Small sea urchins Strongylocentrotus intermedius (1-2 cm of test diameter) are exposed to different environments of light intensities after being reseeded to the sea bottom. With little information available about the behavioral responses of S. intermedius to different light intensities in the environment, we carried out an investigation on how S. intermedius is affected by three light intensity environments in terms of phototaxis, foraging and righting behaviors. They were no light (zero lx), low light intensity (24-209 lx) and high light intensity (252-2,280 lx). Light intensity had obvious different effects on phototaxis. In low light intensity, sea urchins moved more and spent significantly more time at the higher intensity (69-209 lx) (P = 0.046). S. intermedius in high light intensity, in contrast, spent significantly more time at lower intensity (252-690 lx) (P = 0.005). Unexpectedly, no significant difference of movement (average velocity and total distance covered) was found among the three light intensities (P > 0.05). Foraging behavior of S. intermedius was significantly different among the light intensities. In the no light environment, only three of ten S. intermedius found food within 7 min. In low light intensity, nine of 10 sea urchins showed successful foraging behavior to the food placed at 209 lx, which was significantly higher than the ratio of the number (two of 10) when food was placed at 24 lx (P = 0.005). In the high light intensity, in contrast, significantly less sea urchins (three of 10) found food placed at the higher light intensity (2,280 lx) compared with the lower light intensity (252 lx) (10/10, P = 0.003). Furthermore, S. intermedius showed significantly longer righting response time in the high light intensity compared with both no light (P = 0.001) and low light intensity (P = 0.031). No significant difference was found in righting behavior between no light and low light intensity (P = 0.892). The present study indicates that light intensity significantly affects phototaxis, foraging and righting behaviors of S. intermedius and that ~200 lx might be the appropriate light intensity for reseeding small S. intermedius.

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Effects of eliminating interactions in multi-layer culture on survival, food utilization and growth of small sea urchins Strongylocentrotus intermedius at high temperatures.

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