Many authors have tested a large number of tagging methodologies on sea urchins, either with the aim to study the growth of urchins, their movement patterns, the dynamics of their populations, or their ecology and development in the natural environment. Different types of markings, both external and internal, have been used for the individual identification of sea urchins since the year 1935. Since the year 1969, marking techniques based on different chemical substances were also implemented, either by immersion in fluorochrome baths or by injecting these substances directly into the sea urchin. There is a clear need to collect all the existing information to date related to the marking methodologies for sea urchins, to establish the most appropriate marking methodology for each species of sea urchin, depending on the objective and duration of the study to be performed.
This report presents for the first time a complete review of tagging methodologies used until the date in different species of sea urchins, from physical methods, such as the use of Passive Integrated Transponder (PIT) Tags, Anchor tags, and so on, to chemical ones, in which different fluorochromes are used that adhere to the calcified structures of the sea urchin and are subsequently detected using a fluorescence microscope.
We also analyzed the effectiveness of the methods used in each case, comparing the survival rate, the tag retention rate, or the recapture rate of tagged urchins obtained with each tagging methodology.
The evolution of the physical tags for sea urchins should be oriented toward the development of more durable markings over time, which allow marking urchins of smaller diameter and which in turn present a higher retention rate in the long term, both in captivity conditions and in the natural environment. The chemical tags should be aimed at reducing costs through the development of methods, where the mark can be visualized without the need of fluorescence microscopes, the development of methods in which the dyes can be reused, and finally to the development of techniques that allow to visualize the fluorochrome marks externally, without the need to sacrifice the urchin for the mark detection.
