Symbiosis and More

by E.R. Cross

Recreational divers develop their own underwater interests. For some, satisfaction will come from simply being there as a passive observer. Marveling at the myriad life forms that let you share their environment is exciting to some.

Eventually, divers are attracted to one or more of the kinds of life and begin to become aware of their special meaning. The particular interests of divers will depend on knowledge gained about the various animals and the environment. One of the notions developed by some divers is that big (or most) must be best. Such is not always the case. There is no treasure more valuable than knowledge, particularly that obtained about the world in which you venture as a diver.

Granted, sharks, Manta Rays, moray eels and such creatures command a divers attention;for the sake of safety if for no other reason. However, for pure enthrallment during a dive it is hard to beat studying interactions between the smaller organisms or between those organisms and the environment. One of the most fascinating is symbiosis. The co-existence may be as parasitism, mutualism or commensalism.

Generally, a parasite is an organism living in or on another living organism from which it obtains all or part of its organic nutrients. The host does not usually receive any benefits from this.

The photo in this Technifacts is of one of the mollusks parasitic to the seastar Linckia multifora. Starfish are abundant along most seashores of the world. Because of their colorful markings and abundance they are some of the first forms of sealife noted by both beachcombers and divers and are usually easy to study. For the student of sealife, starfish are of the Phylum Echinodermata, which includes sand dollars, brittlestars, sea urchins and sea cucumbers.

Animals in this phylum make interesting specimens for study by divers. Their habitat is benthic, from the shoreline to the deepest oceans. They are usually harmless and can be handled (with care in the case of spiny specimens). They are greedy feeders. Most, I think, are carnivorous and feed on barnacles and mollusks. The Spiny Starfish, Acanthaster planci feeds (mostly) on coral polyps. Occasionally I have noted some seastars wrapped around a crab. I have also observed some eating dead fish. A complete study of the habits of starfish by divers would reveal much presently unknown information. A good project: take your slate, camera or video camera with you on dives and record what you observe about starfish. Particularly, Technifacts would like to know more about which stars are hosts to parasites of any kind; mollusks or other parasitic life.

The starfish known as Linckia multifora is prey to the parasitic shell Stilifer linckia as well as the very unusual shell Thyca crystallina. More on it in a later Technifacts. S. linckia may reach a length of 6 to 8mm.

If your dive is conducive to observation, please report any observed information about parasitism in shells or other marine life. Send to E.R. Cross, c/o Technifacts, Skin Diver Magazine, 6420 Wilshire Boulevard, Los Angeles, CA 90048-5515. You are much more likely to find something new in your life by studying the small things in the sea than feeding sharks or riding mantas. It is safer, too. The information you provide may appear in a future Technifacts when I periodically review this subject.

Out of the Past

At the reunion of two pre WW II Navy vessels, two SDM readers inquired about the divers on board the vessels in the mid to late 1930s. Can anyone help with the names of members of the dive crews aboard the U.S.S. Dobbin from 1934 to 1937 or the U.S.S. Blackhawk from 1937 to 1941? Both vessels were destroyer tenders (ADs). In the era of concern, the Dobbin was based in San Diego; the Blackhawk in the China station until after WW II started. Both vessels carried a complement of divers. The Blackhawk dive crew consisted of a chief petty officer (probably a divemaster) and four enlisted men. Possibly one of those was a first class diver and the rest second class; probably trained on board. The Dobbin had a similar crew. If you have any information on the dive crews of these vessels please send it to E.R. Cross at the address provided above.


Limited sport diving can be enjoyed by a good swimmer without diving equipment of any kind. But new dimensions in pleasure, comfort, mobility and safety are added with the use of a mask, flippers and snorkel. These are the basic aids to skin diving or snorkeling.

There is nothing that can compare with snorkeling. A mask, flippers and a snorkel make a complete outfit. (A swim suit is required in most areas). It is a healthy, body building sport that is kind to the human body and to the environment. But beware! There are potential hazards in swimming and diving with only a mask, flippers and snorkel. The simplicity and very basic equipment requirements do not remove the threat of the alien environment.

The elements in the triangle of safety are the same for all diving. To be able to establish the triangle a diver must have adequate knowledge of the environment, the proper equipment and the physical ability to handle the equipment and to cope with environmental conditions. Also, the animal and plant life in the sea are not always friendly.

From the very first issue of Skin Diver, in December 1951, to the present issue, my first choice for diving information continues to be the advertisements in this magazine. Granted, diving now stresses scuba, computers and other high tech equipment. However, the basic kinds of equipment of the purist skin diver;mask, flippers and snorkel;are still the principal survival equipment you will need for that great adventure in snorkel diving.