A refugium teeming with pods is certainly worth a try for anyone who is overwhelmed with broods of fry but nevertheless wants to give the newborns a chance, however slender that may be. The natural food of seahorse fry in the ocean is zooplankton, and research suggests that the bulk of this consists of larval copepods for many seahorse species.
The sort of simplified refugium-based rearing system you’re contemplating is similar to a "natural nursery," as described below, Lelia:
The Natural Nursery.
This is a very small-scale, low-maintenance rearing system sometimes employed by harried home hobbyists who are too busy for the brutal feeding regimen and maintenance schedule most other nurseries require. Natural nurseries rely on lots of live rock for biofiltration and are usually set up more or less as a refugium would be. That means lots of macroalgae to provide natural filtration and no predators of any sort, which allows thriving populations of copepods, amphipods and other microfauna to build up over time. The idea is that the overworked aquarist can simply cull through his seahorse’s latest brood, release the hardiest of the newborns in the natural nursery, and allow them to fend for themselves. Sometimes a netful of newly hatched brine shrimp is added now and then to supplement the natural microfauna on which the fry survive, but this is done sporadically at best to stave off the appearance of hydroids and Aiptasia anemones that might otherwise rapidly take over the nursery. The natural filtration provided by the live rock and beds of macroalgae reduces the need for water changes to a minimum and feeding is drastically curtailed compared to other types of nurseries.
As you might expect, most of the fry are lost during the first week or two with this method, but some may manage to find enough natural fodder to survive and it’s not uncommon for a few of them to thrive on their own. That’s all the hobbyist is hoping for with this system and such meager survivorship is considered a victory, since the only alternative in many cases is to sacrifice the entire brood without attempting any rearing whatsoever.
This method of rearing is most successful when the natural nursery/refugium is large and the number of fry it is asked to support is small. For instance, Liisa Coit has used a 5-foot seagrass refugium this way quite successfully when rearing dwarf seahorses (Coit, pers. com.). It is best suited for raising benthic seahorse fry but is also worth a try for raising pelagic fry when there is no other alternative. <Close quote>
So attempting to rearing seahorse fry as you describe will result in very high mortalities, but it is far from hopeless, and it is not uncommon for one or two of the fry to hang in there against all odds and find enough natural fodder to grow and prosper. For example, Heather Hall maintained a rearing program for Hippocampus capensis at the London Zoo that was proving to be too successful, prompting a change in their rearing protocol. In order to keep from being overrun with captive-bred capensis, the Zoo was forced to resort to unusual methods to reduce the reproductive rate of their colony. She describes her experience raising these bountiful breeders as follows: "H. capensis is a relatively prolific species. Brood sizes average about 50 babies… Since survival rate is high with good husbandry and diet, it is easy to become overpopulated with animals. In order to avoid overpopulation we have tried different ways of managing the population in our collection. Separating the sexes was employed in several tanks. Sexes were kept isolated in groups of 20. We found that this led to many problems. The animals exhibited a number of stress signs: disease outbreaks increased and aggression was high between males. Females became swollen with eggs and suspected egg binding occurred. Respiration rates and twitching also increased. Therefore, we decided to separate the sexes of our seahorses no longer. Animals in the display tank are allowed to reproduce as normal, and young are only removed when required. Some young survive in the display tank, feeding on naturally available foods and make it to adulthood. To keep the generations turning over, we can remove up to 20 individuals and raise them in the holding tanks. They can be given special attention there and their growth monitored. This method has worked well for us" (Bull and Mitchell, 2002, p30).
In the end, H. capensis fry at the London Zoo were simply left to their own resources in the display tank with their parents, yet some of them routinely survived to adulthood on their own with no special care whatsoever. Those are benthic babies and the situation is a little different with Hippocampus erectus fry, but certainly worth a try, Lelia.
I don’t have any designs for the type of refugium you are planning, Lelia, but it seems quite feasible and should make an interesting project for a do-it-yourselfer. As an example, Charles Delbeek likes to use glass shrimp and cleaner shrimp that are too large to be eaten in the refugium for his seahorse tank, where the regular reproduction of these hermaphroditic crustaceans will provide a continuous supply of nutritious nauplii for his ponies: "There is a method that can be used to offer an occasional supply of live food for your sea horses. By setting up a separate system housing several species of shrimp such as the common cleaner shrimp (Lysmata amboinensis) or peppermint shrimp (lyse model wurdemanni), or Rhynchocinetes uritai or R. durbanensis, you can get a fairly regular supply of live shrimp larvae. These species are best to use since they can live in large groups and spawn on a regular basis. Such a system is commonly called a refugium. A refugium is a small (10-20 gallon) aquarium that contains live sand, live rock and/or macroalgae such as Caulerpa. It is plumbed such that water from your main system is pumped to the refugium and then returns via an overflow to the main tank. For this type of arrangement to work, the refugium must be slightly higher than the main tank. Shrimp are added to the refugium and within a few months they should start spawning and hatching eggs every few weeks. The larvae are then carried back to the main tank by the overflow, where they become a food source for your sea horses. Of course other life will also thrive in the refugium and it is not unusual for copepods, mysis and crab larvae to also be produced on a regular basis. The key to the refugium is to keep predators out of the system so that the smaller micro-crustacean population can thrive. You would need a fairly large and productive refugium to produce enough food to maintain even a pair of sea horses, so at best, a typical refugium can provide a nice source of supplemental live food; the basic daily diet still needs to be provided by you in the form of the frozen foods mentioned above." (Delbeek, November 2001, "Horse Forum," FAMA magazine)
Aside from the one Delbeek favors, refugia are available in a number of different designs. For example, there are easy-to-install external hang-on refugia and in-tank refugia as well as sump-style refugia that are mounted beneath the main. In the case of the latter, Barb, the refugium is installed exactly like any other sump. Here are a couple of online sites where you can look up more information on refugia, including articles explaining how to set up and install a refugium of your own:
Click here: Refugium Setups Information – From About Saltwater Aquariums
Click here: Refugiums
Best of luck setting up a refugium-based nursery tank that will allow you to rear some of your seahorse fry with a little less effort on your behalf, Lelia!