Abstract
This study aims to evaluate the effect of light-emitting diodes (LEDs) of different wavelengths on the embryonic development, covering behavior, righting behavior, and phototaxis of collector urchins (Tripneustes gratilla). The collector urchins were divided into three groups according to the type of LED illumination they received: full-spectrum (400–750 nm wavelength), red light (630 nm), or blue light (450 nm). The results of the embryonic development experiment indicated that the blue LED group had the highest proportion of embryos reaching the prism stage at the 24th hour and the highest proportion of embryos entering the 4-arm pluteus stage, but it also had the highest death rate at the 48th hour. The full-spectrum and red LED groups exhibited similar speeds of embryonic development. In the experiment on covering behavior performed on adult urchins, our findings indicated that the blue LED group gripped the most acrylic sheets for cover, exhibiting the most covering behavior, followed by the full-spectrum group and then the red LED group. Moreover, behavior varied with coloration, as collector urchins with a lower level of melanin exhibited more covering behavior than those with a higher melanin level. In addition, the righting behavior experiments demonstrated that the blue LED group spent the longest time righting themselves. It is possible that the relatively strong stimulation from the blue LED illumination led to a higher level of stress in the collector urchins and hence slowed their righting. The phototaxis experiment revealed the most significant negative phototactic response in collector urchins when they were under the blue LED light, followed by the full-spectrum light; the red LED light did not induce any positive or negative phototactic response in the collector urchins. This experimental result verified collector urchins’ high sensitivity to and dislike of the blue LED light. The study results confirmed that the blue LED light environment accelerated the embryonic development of collector urchins; however, the relatively strong stimulation from that light also caused them to engage in covering behavior or move away from the light. These results indicate that short-wavelength irradiation significantly affects the embryonic development and behavior pattern of this species.
Highlights
Sea urchins are invertebrates with a crucial role in the marine benthic ecosystem as well as high value as an aquaculture product in the international market
The demand for high-quality sea urchins over the last three decades has led to the intensive harvest and exploitation of natural sea urchins; in light of this overharvesting and the decreasing numbers of sea urchins in various countries, sea urchin farming has become an industry with high potential
Among those illuminated by a blue light-emitting diodes (LEDs) light for 24 h, 13.59% reached the blastula stage (Figure 1A), and 18.12% reached the gastrula stage (Figure 1B), 67.96% reached the prism stage (Figure 1C); the death rate was 0.33%
Summary
Sea urchins are invertebrates with a crucial role in the marine benthic ecosystem as well as high value as an aquaculture product in the international market. Sea urchins have a complicated life cycle. They undergo in vitro fertilization where male and female sea urchins fertilize and ovulate into the water, respectively, to complete insemination. Previous studies have pointed out that UVB radiation can cause sea urchin embryo malformations, changes in specific gene expression and the expression of pressure proteins (Bonaventura et al, 2005), and even embryonic cell apoptosis (Lesser et al, 2003). It has been confirmed that light wavelength affects the embryonic development of sea urchins. At present, proposed explanations for this sea urchin behavior can be summarized into six hypotheses: defense against natural enemies, reflex behavior, prevention of dehydration, ancillary feeding behavior, protection against damage from waves and suspended solids in the water, and to avoid over-exposure to light (Barros et al, 2020)
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