For thousands of years marine animals either tried to resist change, which is the reason they have become extinct, or they had to adapt to the ever changing environmental factors encountered day in and day out. Husbandry techniques have improved so much over the last ten years or so, enabling livestock to grow and thrive in captivity, which is immensely pertinent and exciting to the marine aquarium hobby. Protein skimmers, chillers, testing kits, lighting and the prodigious knowledge we have been fortunate to be inundated with, all have contributed to, atleast, part of the success stories we have heard about or witnessed first hand in the marine hobby. Marine fish and invertebrate reproduction, on the other hand, has not been portrayed as prominently as the husbandry aspects of the hobby have. Coral reproduction paints an even more sullen picture as a major stumbling block within the marine hobby. Hopefully, within due time, we will, not only, gain a better understanding of coral reproduction hurdles facing us in a captive environment but can also become successful at cultivating various species of corals.
As far as natural reefs and those replicated in our aquariums, mariculture and aquaculture processes will need to take on greater importance if both are to be successful and thrive. Captive breeding tactics as a potent way of preserving our delicate and diverse reefs will be of utmost significance in coming years, since only about 1% of exported corals have been raised by mariculture or aquaculture. Combining this dilemma with other challenges facing our reefs, like pollution, over fishing, habitat destruction, global warming and ocean acidification and not only do we have a serious problem on our hands but the living animals that inhabit these reefs, could succumb to the same devastating repercussions.
Fortunately, upscaled aquaculture funding programs and practices have been implemented recently, as a means of reducing the stress placed on our reefs to try to and meet the demand for aquatic animals in the marine hobby. The University of Maine and Oceans, Reefs and Aquariums represent, just two, such institutions dedicated to ensuring the future of the marine aquarium hobby remains promising and prosperous while aiding in the conservation and preservation of our natural reef environment.
Tridacna clams, sea horses, green and spotted mandarin, cleaner gobies, pseudochromis’, damselfish, banggai cardinalfish, clownfish and peppermint shrimp represent some of these animals that are being born and raised in captivity. Ongoing pursuance is expected to produce other significant accomplishments through aquacultural practices and research like the rearing of various species of tangs and angelfish.
When it comes to coral, their are two distinct forms of reproduction. The first being asexual or vegetative and the second is called sexual reproduction. Many of you are familiar with asexual reproduction since many of you perform this type of feat without even knowing it. Basically, when you cut or prune a coral to make frags, you are, in essence, causing a coral to reproduce, asexually. And all the while, this is being performed without the use of a females egg or males sperm to produce a daughter colony. This is also evident in the wild as a direct result of storms or predation. Autotomy is another form of asexual reproduction where the mother colony will release a part of itself to hopefully adhere elsewhere where more favorable conditions are apparent. This process is more commonly encountered in aquaria as a direct result of stress.
Tim Wijgerde in his article entitled “Coral Reproduction- Part 1: Biology” states that their are other forms of asexual reproduction as well. Included in his list are intratentacular budding, extratentacular budding, dripping, polyp bailout, polyp expulsion and anthocauli which is only displayed by members of the Fungiidae family.
Based on Tim’s information in his article combined with my experience gained throughout my many years in the hobby and research findings, I will now provide a brief synopsis of each in easy to grasp terms. Intratentacular and extratentacular budding are very similar. More commonly known as fission, intratentacular budding occurs when a single corallite, which consists of a skeletal cup made of calcium carbonate, within a mother colony splits into two daughter corallites within that same corallite such as in species of favia brain coral. Extratentacular budding takes place in corals such as Montastrea where the parent coral produces a daughter corallite on the exterior of the corallite wall. The new daughter corallite is smaller than the other corallites and gives the appearance of being squeezed in between the other corallites as well.
Dripping occurs and can best be described as a slow detachment or separation of tissue from the mother coral to an area below it. This process provides the mother coral to produce clones of itself as a reproductive means. The new daughter coral may, or may not, contain a skeleton as a result of the dripping form of asexual reproduction.
Polyp bailout is nothing more than a last ditch effort for corals of the Pocilliporidae family to survive. Basically, the mother coral releases just the tissue from a corallite to leave the mother and find another location in which to adhere with two small filaments attached to the base of the polyp.
Polyp expulsion occurs when a mother coral releases a polyp and its skeleton of corallite to drift and settle in another area that may be better suited for it and as a form of reproduction.
The last form, called anthocauli, is encountered in plate corals or Fungiids. This is illustrated best as the mother fungii decalcifying part of itself to produce a daughter clone of itself. many times with this type of asexual reproduction, the daughter fungiids remain attached to the mother and aquarists break them apart to establish baby plate corals elsewhere.
Asexual reproduction can either be a defense mechanism illustrating that something is not right with the coral and it is using this tactic as a last ditch effort at attempts towards its survival. The other scenario that many corals use asexual reproduction is that it enables the mother colony to carry on the species, so to speak, and without the effort often times associated with sexual reproduction.
This concludes the first of two parts dealing with asexual reproduction in corals, its implications and different types of asexual reproduction techniques that helps to ensure the survival of the particular coral species that employs this type of reproduction. Hopefully, this article will also educate you as to possible scenarios illustrated by the corals that you possess in your tanks and be better able to understand what is going on with these corals if any of these scenarios carries out.
In part two of this series, I will discuss sexual reproduction and corals and the various ways corals participate in this fascinating behavior and possibility of you experiencing this in your aquariums.