The video was shot on a shoal offshore in a stretch of the Mar Ligure coast, where the groupers had long since practically disappeared and where already in several dives we have seen small specimens of Epinephelus marginatus, the endemic Brown Grouper of the Mediterranean Sea.
The bottom is rocky and varies from a depth between 36 and 43 meters, where there are many caves and crevasses that characterize some rock and coralligenous walls, the ideal habitat of the Grouper, during some dives we saw several individuals of more or less 45 cm in length, probably the females, who shy and wary, fled as soon as the diver was present. I managed to film one that after a quick glance immediately hid, probably annoyed by the bubbles and the lights from the camera. The presence of many females in a territory also makes one think of the presence of the largest specimens, the males, even if we have not met them at the moment. We are in fact in the summer in the reproduction season of this species.
The brown grouper is a protogynous hermaphrodite (i.e. the gonad first develops the female part and then the male part) with a slow life cycle: individuals mature as females only around five years of age, i.e. more or less 45 cm in length, and around 9-12 years old, when they reach 60-90 cm, they undergo a sexual inversion, becoming males ready for reproduction. The maximum size that can be reached by the brown grouper is about 120 cm, which corresponds to an age of at least forty years. Reproduction for these animals is a complex event, during which colonies formed by a dominant male and several females are formed, and particular colors and behaviors are used.
The transformation from female to male also depends on socio-behavioral stimuli: if there are many large individuals, it is not said that all change sex becoming male, because they would not be necessary. On the contrary, if the population is made up of only young individuals, then some will change sex and become males before reaching 60-90 cm in size.
The colors of the brown grouper, called “liveries”, have been observed and described by more than one researcher; the most spectacular are related to the period of reproduction, but even in normal conditions the colors may change slightly in response to different stimuli.
Anyone who has encountered a small grouper underwater has been able to observe that it is able to “change color”, that is, to accentuate the contrast between the light spots and the dark base color, within a second: this reaction serves to confuse them better with algae and sponges that encrust the bottom. On other occasions, the light spots can disappear almost completely for a short time, but the reason is still not clear: it seems that this is a color linked to aggression.