Chemosensitivity in the Sea Urchin Paracentrotus lividus (Echinodermata: Echinoidea) to Food-Related Compounds: An Innovative Behavioral Bioassay

Abstract

Like other animals, echinoderms rely on chemical senses to detect and localize food resources. Here, we evaluate the chemical sensitivity of the sea urchin Paracentrotus lividus to a number of stimuli possibly related to food, such as a few sugars, compared to the blue-green algae Spirulina (Arthrospira platensis). To do this we developed a simple, innovative method based on the recording of “urchinograms” estimating the movements of spines, pedicellariae, tube feet, and eventually of the whole sea urchin, in response to chemicals, while keeping both the whole animal and the stimulus in their natural environment, underwater. Our results show that Spirulina is a highly stimulating compound for the sea urchin, by acting in a dose-dependent manner. The animals resulted also sensitive, even if to a lesser extent, to some sugars, such as the monosaccharide glucose, but not to its isomer fructose, while among disaccharides, they sensed cellobiose, but not sucrose or trehalose. From an applied point of view, any insight into the chemical sensitivity of sea urchins toward potential food-related compounds may lead to the discovery of key chemicals that would help improve the efficiency and reduce the costs of dietary substrates for optimization of intensive rearing strategies. Although this method has been developed for P. lividus, it will be suitable to evaluate the chemical sensitivity of other echinoderms and other marine invertebrates characterized by low mobility.

Blue-Green Algae as Stimulating and Attractive Feeding Substrates for a Mediterranean Commercial Sea Urchin Species, Paracentrotus lividus

“…The sea urchins were singularly exposed to the stimuli in a plastic tank (12.5 cm long × 7 cm wide × 7 cm high) containing ca. 350 mL of seawater (SW), according to the procedure used by Solari et al [45]. Two plastic tubes (40 cm in length, 0.4 cm in diameter) connected the two opposite short ends of the tank to a peristaltic pump (Gilson, Minipuls Evolution ® ) using two different channels, which acted as the inflow and outflow terminals for delivery and removal of the stimuli (flow rate of 10 mL/min; Figure S1).…”

“…All amino acids were first dissolved in SW at 10 −1 mol/L and stored frozen as stock solutions. On the day of the experiments, they were thawed and diluted in SW to be used at the three different increasing concentrations 10 −5 , 10 −3 , and 10 −1 mol/L [45,51]. The finely hashed powder of Klamath microalgae was suspended in SW at 5 mg/mL and then diluted at 2, 1, 0.1, and 0.01 mg/mL.…”

“…Spirulina (Arthrospira platensis) has proved to be an effective integrator in the formulation of fish feeds [42,43], and some benefits, such as roe enhancement and gamete production, have also been reported for the sea urchin species P. lividus [44]. Coherently, this sea urchin was recently found to display marked chemosensitivity to spirulina [45], and this evidence suggests the need to carry out further research on the bioavailability of proper nutrients for the preparation of biologically and economically optimized feeds for aquaculture purposes.…”

“…We also tested the stimulating efficacy of a few amino acids selected among the most abundant (weight ratio) ones from the biochemical composition of the Klamath blue-green algae to ascertain if the stimulating effects of the latter may be attributable, at least in part, to its single components of the aminoacidic fraction. To perform this, we used a method that assessed the movements of spines, tube feet, pedicellariae, and finally, the entire individual as a response to chemicals, which has previously been employed on the same sea urchin species [45].…”

“…Moreover, since chemical sensitivity does not necessarily imply attractive or repulsive chemotaxis, as a second aim of this study, we evaluated the attractivity level of Klamath, as compared to that of Arthrospira platensis, another blue-green alga for which stimulating effectiveness on this sea urchin was previously detected [45].…”