Sun J et al. (2021), Interaction among sea urchins in response to fo...

ECB-ART-49183

Sci Rep 2021 May 11;111:9985. doi: 10.1038/s41598-021-89471-2.

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Interaction among sea urchins in response to food cues.

Sun J , Zhao Z , Zhao C , Yu Y , Ding P , Ding J , Yang M , Chi X , Hu F , Chang Y .

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Interaction among sea urchins remains largely uninvestigated, although the aggregation of sea urchins is common. In the present study, 1, 15 and 30 sea urchins Strongylocentrotus intermedius (11.06 ± 0.99 mm in test diameter) were placed in a 1 m2 circular tank, respectively. Movement behaviors were recorded for 12 min to investigate potential interactions among sea urchins. After the 12-min control period, we added food cues into the tank and recorded the changes in sea urchins' behaviors. For the first time, we here quantified the interactions among sea urchins in laboratory and found that the interactions varied with food cues and with different densities. The sea urchins dispersed in random directions after being released. There was no significant difference in the movement speed and the displacement of sea urchins among the three density groups (1, 15 and 30 ind/m2). The interaction occurred when sea urchins randomly contacted with the conspecifics and slowed down the movement speed. The speed of sea urchins after physical contacts decreased by an average of 40% in the density of 15 ind/m2 and 17% in the density of 30 ind/m2. This interaction resulted in significantly higher randomness in the movement direction and lower movement linearity in 15 and 30 ind/m2 than in 1 ind/m2. After the introduction of food cues, the movement speed, displacement and dispersal distance of sea urchin groups decreased significantly in all the three densities. The dispersal distance and expansion speed of sea urchins were significantly lower in 30 ind/m2 than those in 15 ind/m2. The present study indicates that the interaction among sea urchins limits the movement of individual sea urchin and provides valuable information into how large groups of sea urchins are stable in places where food is plentiful.

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	Figure 1. Behavioral changes (mean ± SEM) of sea urchins when they randomly contacted conspecifics in different density groups without the food cues. Movement speed, displacement and centrifugal distance of sea urchins in the 1, 15 and 30 ind/m2 groups without the food cues (A–C). Speed of sea urchins before, during and after the contacts in 15 ind/m2 (D, left) and the speed per 5 s (D, right). Speed of sea urchins before, during and after contact in 30 ind/m2 (E, left) and the speed per five seconds (E, right). Movement linearity and mean result length R of sea urchins in 1, 15 and 30 ind/m2 without the food cues (F,G).
	Figure 2. Behavioral changes (mean ± SEM) of individuals in response to the food cues. Movement speed of sea urchins without and with the food cues in the three density groups (A–C). Movement displacement of sea urchins with and without the food cues in the three density groups (D–F). Dispersal distance of sea urchins with and without the food cues in the three density groups (G–I).
	Figure 3. Behavioral changes (mean ± SEM) of sea urchins exposed to the food cues when they randomly contacted conspecifics in different density groups. Movement linearity, mean result length R and dispersal distance of sea urchins exposed to the food cues in 1, 15 and 30 ind/m2 (A–C). Speed of sea urchins before, during and after the contact in 15 ind/m2 when exposed to the food cues (D, left) and speed per 5 s (D, right). Speed of sea urchins before, during and after the contact in 30 ind/m2 when exposed to the food cues (E, left) and speed per 5 s (E, right). Expansion speed of sea urchins exposed to the food cues in 15 and 30 ind/m2 (F–H).
	Figure 4. Diagram of the experiment. The period without the food cues was from 0 to 12 min, the period with the food cues was from 14 to 26 min.

References [+] :

Filbee-Dexter, The present is the key to the past: linking regime shifts in kelp beds to the distribution of deep-living sea urchins. 2017, Pubmed, Echinobase