My wife Barbara and I recently spent two three-month periods in Bonaire, diving almost every day. One of our favorite photographic subjects was the Caribbean Reef Squid, a creature with amazing brainpower, keen vision, and a unique ability to communicate.
Sepioteuthis sepiodea have cigar-shaped bodies and are 10-20cm long, including the ten tentacles that are fixed in a circle around the mouth. Two of the arms are stronger/longer than the others. Along the mantle (body) are undulating fins and under the head is a funnel that can be turned in various directions and used for ‘jet’ propulsion. Internally, the Reef Squid has three hearts and blue blood (since it uses a blue, copper-containing protein called hemocyanin for binding oxygen).
Found throughout the Caribbean Sea, Bahamas and south Florida, adult Caribbean reef squid during the day often gather in schools – called ‘shoals’ – of four to 30 individuals; at night they disperse to hunt individually.
Voracious eaters, they consume 30-60% of their body weight daily, eating small fish, crabs and shrimp. They catch prey using their two larger tentacles and then use the other eight to move the food to the mouth, where a strong and sharp beak is used to cut the prey into pieces that can be further processed by a raspy tongue called a radula.
For camouflage and for surprisingly complex communication Reef Squid can rapidly change skin color and pattern by sending nerve pulses to receptors called chromatophores. In addition to a basic brown they display a zebra, a striped and a saddle pattern. In complex situations, such as the need to signal one thing to a female on the left and another to a rival male on the right, they can even use one pattern on one side and another pattern on the other.
Courtship occurs within a shoal several times during the day and year-round.
Like other cephalopods, Reef Squid are semelparous, meaning that the adult dies shortly after reproducing. After competing with two to five other males, during which they usually display a zebra pattern, the victor – typically the largest – approaches the female and calms her by alternately gently stoking her with his tentacles and then briefly moving away. Courtship may continue for up to an hour, during which the male may display a stripe pattern and the female a saddle pattern. The actual mating happens quickly. He attaches a sticky packet of sperm to the female’s body, displaying a pulsating pattern as he does so. The female places the packet in her seminal receptacle and, accompanied by the male, finds a suitable place – such as under a rock – to lay her eggs in small clusters. Some claim that the female dies immediately after laying eggs, but naturalists and writers Ned and Anna Deloach observed a shoal of 13 squid over the course of a week and observed egg-laying on the third day without a reduction in the shoal count. However, there is agreement that after reproducing both the male and female will be dead within a month.
On average, squid have seven confrontations an hour with predators and employ a number of different strategies to protect themselves.
Perhaps the most important is that of shoaling, during which the school has the advantage of many eyes. Typically, the shoal arranges itself in a column with the larger individuals positioned as sentinels at each end. When a sentinel signals alarm, the squid have a number of options.
If the threat is mild, the response may be intimidation by extending the body fully and orienting perpendicular to the threat so as to emphasize size or by displaying special patterns, including flashing two or four ‘eye’ spots. Threats a bit more serious may result in attempting to blend into the background by using camouflage patterns.
If flight is desirable, the direction of retreat may be hidden by the ejection of black ink. Rapid retreat is accomplished by jetting away. First, the squid expands its mantle, which fills the pallial cavity with water. Body muscles are then contracted to expel the water through the special funnel.
If it has propelled itself above the surface, it can employ its fins as wings to ‘fly’ an ability that has only recently been certified by scientists, even though it will come as no surprise to cruisers who have found ink spots on the side of a hull or a cadaver on the deck.