Well, for starters, I see no problems with the cleanup crew for your aquarium. The nassarius and Cerith snails are perfectly appropriate and desirable, the blue leg hermit crab is one of the micro-hermits that can be used with seahorses, and the starfish are okay providing you can keep them alive (sand sifting starfish can be challenging in that regard and do best in large, well-established tanks with a relatively deep sand bed).
The mushroom corals and gorgonians are excellent choices for a seahorse tank, and there is no need to change anything as far as they are concerned.
Nor do I have any problem with the fish in your current lineup with respect to seahorses, Kyme. I have found that chromis often do very well with ponies as long as the aquarium is large enough, and the other species are completely unobjectionable. (Percula clown fish and false Percula clownfish are the only Amphiprion species I recommend keeping with seahorses.)
I am a bit concerned about your Mandarin goby, however, Kyme. Don’t get me wrong — I absolutely love the psychedelic coloration and peaceful nature of Mandarin dragonets! There’s no disputing that they are gorgeous little fishes and make ideal tankmates for seahorses in the right type of setup. They are docile, slow-moving, passive fish that are beautifully marked and very deliberate feeders. And they are quite hardy fish providing they can be fed properly. They have a heavy slime coat that seems to make them quite resistant to protozoan parasites such as Cryptocaryon irritans.
But, as you know, in order to do well, mandarins need a large, well-established aquarium loaded with live rock or live rock rubble that’s teeming with copepods and amphipods. Mandrins must have continuous opportunities to graze on suitable live foods or they generally slowly waste away and starve to death. In the right system, they can thrive, and will often learn to take small pieces of frozen Mysis, but they do best in well-established reef systems or aquariums with at least 1 pound of live rock or LR rubble per gallon, a mature sand bed, and a refugium that can continually replenish the pod population in the tank. Those are typically the conditions that are necessary to assure they have adequate suitable live prey.
Mandarins are bottom feeders that normally do not take food from the water column, so they do best in a well-established aquarium of 100 gallons or above with a large foot print that can accommodate plenty of live sand, small pieces of live rock, live rock rubble, and macroalgae. I am worried that your manderin goby may have difficulty scrounging up enough live copepods and amphipods in an aquarium of only 40 gallons. Try target feeding and on tempting the Mandarin to eat small, bite-size pieces of frozen Mysis (Hikari frozen Mysis and Mini Mysis by H2O Life are the smallest brands of Mysis). And please consider adding a refugium to your 40-gallon seahorse tank, Kyme, as discussed below:
For best results, set up Gammarus amphipods, copepods, feeder shrimp, and other live foods species in a refugium that’s connected to the main tank. That way the Gammarus and copepods and other small crustaceans can build up a very large population well they are safely protected from any predators within the refuge, and some of them will be steadily released into the main tank to replenish the supply of live foods for your Mandrins and/or seahorses.
A refugium is simply a self-contained protected area, isolated from the main tank but sharing the same water supply, which provides many of the same benefits as a sump. A refugium can help newly added fish or invertebrates easily acclimate to a new tank. It can provide a safe haven for injured fish or corals to regenerate damaged tissue without the need for a separate quarantine tank. But perhaps its main benefit for the seahorse keeper is provide a protected area where macroalgae can be grown and small live prey items (copepods, amphipods, Caprellids, etc.) that will eventually become a food source for the inhabitants of the main portion of the tank can be cultured safely, allowing their population to build up undisturbed.
For instance, Charles Delbeek likes to use colonial shrimp species 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), peppermint shrimp (Lysmata amboinensis), and especially Camel Shrimp (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 or Gracilaria. 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. Some of the pods and larval crustaceans will then be carried from the refugium into the sea horse tank in the water that overflows from the refuge. 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).
In addition to help keeping your Mandarin goby well fed, installing such a refugium would also provide the seahorses with live food treats on a regular basis.
As far as stocking your 40-gallon aquarium system goes, Kyme, I would not recommend adding a pair of Mustangs or Sunbursts (Hippocampus erectus) to an aquarium that already houses a pair of H. kelloggi seahorses. The issue is not so much a problem with over stocking the aquarium, but rather the fact that the H. kelloggi are such a fragile, delicate seahorse species and have proven to be very prone to disease problems in the aquarium. I hate to be the bearer of bad news, but I don’t believe the H. kelloggi seahorses are going to survive for any length of time in a reef tank at tropical water temperatures, and when they fall ill, they are liable to develop highly contagious bacterial infections that could threaten any other seahorses in the same tank.
To put it in a nutshell, Kyme, the Hippocampus kelloggi that are available nowadays have proven to be very problematic. For the past couple of years, I have been getting numerous e-mails from H. kelloggi owners urgently requesting help with treating various health problems, so it doesn’t appear to be a particularly hardy strain of seahorses at this stage in its development. I believe part of the problem is simply that H. kelloggi have not been cultured or selectively bred for aquarium life as other species that have been around much longer, and as a result, the kelloggi are just not as well adapted to aquarium conditions as of yet.
Many people suspect that the H. kelloggi are merely pen raised, and have therefore not benefited from the sort of intensive aquaculture and selective breeding that produces superior captive-bred livestock here in the US. Net pens are a low-tech, low-maintenance method of farming seahorses that basically involves raising them in large enclosures in coastal waters. It is a common practice in Indonesia, many Asian countries, and the Philippines. In some cases, entire lagoons may be fenced off for that purpose. In the simplest form of pen rearing, broodstock are released into these enclosures, and then they and their progeny are pretty much allowed to fend for themselves thereafter. Any offspring that survive to marketable size are periodically harvested from the holding pens or lagoons.
The benefit of this technique is that it allows seahorses to be raised cheaply, and therefore produces specimens for the aquarium trade that are relatively inexpensive. (It is the low-cost of the H. kelloggi that attracts most hobbyists.) The downside is that pen raising does not strengthen and improve the seahorses generation after generation, making them ever better adapted for aquarium conditions, as does Western-style aquaculture. So the pen raised ponies are not generally as hardy and adaptable as captive-bred-and-raised seahorses.
Such operations (net pens) are controversial with environmentalists for a number of reasons. Since the enclosures are open to the ocean, there is a real risk that adults or their fry may escape from the pens and establish colonies in the wild that may pose a threat to endemic seahorse populations. The pens are no barrier to disease organisms or parasites, so pathogens and parasites imported on foreign broodstock may spread to fishes in the wild (or vice versa). Wastes from the high density of penned animals are carried directly to ocean on prevailing tides and currents and may have a negative environmental impact on the surrounding area. There is no way to monitor the penned animals, hence no way to determine whether the seahorses they contain are actually born and raised in the enclosures or are merely wild-caught seahorses maintained in holding pens prior to being shipped off to unsuspecting consumers.
Pen-grown ponies can thus be risky for the hobbyist because of the circumstances under which they were raised. In essence, a mesh barrier is all that separates them from wild seahorses. There is no guarantee they will be disease free. Although many of them learn to accept frozen Mysis, there is no guarantee they will eat frozen foods since they are often accustomed to foraging for live prey. There is no guarantee they will be able to adjust to aquarium conditions since they are essentially raised in the sea. There is no guarantee that they are even captive bred, since the pens are not secure and livestock is introduced and removed from the pens and lagoons on a continuous basis. There is no guarantee they will be friendly and sociable rather than shying away from their keepers, since they are unaccustomed to the human presence. Pen-raised ponies are particularly misleading because they are almost never advertised as such — they are typically called captive raised or even captive bred seahorses, which can lead the unwary consumer to assume that they have been painstakingly raised using intensive mariculture techniques and rearing protocols. Nothing could be further from the truth.
In light of the health problems so many home hobbyists have been having with their H. kelloggi for some time now, I have been discussing the needs and requirements of this species with advanced aquarists and experts that have worked with H. kelloggi in the past. The consensus seems to be that the current crop of H. kelloggi are being shipped out to hobbyists while they are still too young (the two-inch long juveniles are no more than 3-4 months old) and that they are not well adapted to aquarium conditions because they are likely being pen raised. The tiny H. kelloggi juveniles would fare better if they allowed them to grow up for a few more months and shipped them at the age of around six months.
However, the primary problem folks have been having with their H. kelloggi may be due to their temperature requirements. The people I conferred with maintained that H. kelloggi is a deepwater seahorse and is therefore adapted for lower light levels than most seahorses and also requires cool water temperatures (Lisa Coit et al., pers. com.). They feel that this species should be maintained in temperate tanks rather than tropical aquaria, and that H. kelloggi will only thrive if they are maintained at a water temperature of 68°F or less (Lisa Coit et al., pers. com.). They report that if the H. kelloggi are maintained at standard aquarium temperatures for a tropical marine aquarium (i.e., 75°F-78°F) they will be plagued by various bacterial infections and suffer as a result.
So there are several problems with the H. kelloggi, Kyme. They are likely being pen raised in Asia, they are being shipped to the consumer while they are way too young and small to thrive, and they are being kept in tropical aquariums rather than the cool water or temperate tanks that they need. This combination of unfavorable circumstances is quite deadly and is dooming most all of the H. kelloggi that come into this country to an early demise. Heat stress is making the H. kelloggi susceptible to a variety of health problems, but especially bacterial infections, most often Vibrio in one form or another.
In short, the odds are stacked against your new H. kelloggi doing well in a tropical aquarium with live corals and reef fish for any length of time. If you do not have a temperate aquarium unavailable that you could relocate the H. kelloggi to, Kyme, then it would probably be best if you return the small H. kelloggi as soon as possible, before they develop any sort of health problems.
If all is going well with your aquarium for the next few weeks after you return or relocate the H. kelloggi, then you could possibly consider adding a pair of Mustangs or Sunbursts to your 40-gallon aquarium system. For best results, I would recommend that you complete the Ocean Rider seahorse training program while you are waiting to see if all of the specimens in the aquarium do well once they H. kelloggi have been removed, Kyme. That would be a productive use of your time while you are waiting and it would assure that you have an excellent understanding of the aquarium care and requirements of Mustangs and Sunbursts before you acquire a pair. Completing the seahorse training course also earns certification as a "preferred customer" with Ocean Rider and authorizes you to purchase their seahorses.
If you would like to give the seahorse training program a try, Kyme, just send a brief e-mail to me off list ([email protected]) with your first and last name, which I need for our records, and I will get you started out with the first lesson right away.
Best wishes with all your fishes (and invertebrates), Kyme!