Although sea spiders are certainly creepy and may have eight legs like land-dwelling spiders, sea spiders are only distantly related. The sea spiders identified here are more interested in eating coral than eating pods in a reef tank, which makes them all the more scary!
Acanthastrea-Eating Sea Spiders: Not Reef Safe
Here’s another one for your nightmares! For years I had heard rumors of a stealthy Acanthastrea predator, but I had yet to find one (to my relief.) A while back, I attended a coral fragging demonstration, and along with my frag freebie, I also received these lil buggers.
Phylum: Arthropoda (joint-legged invertebrates)
Subphylum: Chelicerata
Class: Pycnogonida (sea spiders)
Order: Pantopoda
Rumor has it that these spiders tend to prefer Acanthastrea (typically called “acans”) corals, but they have also been found on other large polyp stony corals (LPS). Thankfully I eradicated these spiders before I had a chance to find out if they would infect my other LPS corals as well.
This Acan-eating spider shown below (hereafter referred to as AES) has (or had, I should say) eight legs. This is likely a female as the males have a specially modified leg (called an oviger) for carrying eggs (unless I knocked that leg off accidentally too) (Cowles, 2009). As you can see, there is practically no body – it is mostly legs. On the left side of the AES in the photo are the chelicerae (mouth parts) and the proboscis (tubular mouth part for ingestion). As mentioned – these are not true spiders! (Although they still give me the heebie jeebies!)
How to Identify AES:
AES are nearly colorless, so they blend in quite well with the coral. Even after a thorough visual inspection of the coral prior to dipping, I only found these after they fell off in the dip. The ones I found were about 1 cm in diameter (nearly half an inch). So, I recommend a good coral dip prior to introducing the coral into your tank. As they can rapidly eat Acanthastrea corals, proper identification of sea spiders is critical.
How to Treat AES:
Various dips may be effective against AES; however, multiple dips may be required to eliminate any recently-hatched eggs (most dips are not effective on marine pest eggs).
Hydrogen peroxide dip: This is my preferred method for AES. This dip creates bubbles that will actually lift the AES off the coral – they usually can’t hold on! Use this dip with caution as overdoing it can cause serious coral damage. Also, only dip LPS in it. Soft corals and small polyp stony (SPS) corals do not typically respond well.
CoralRx, Lugols, and other commercially-available dips: Although I haven’t used these dips on AES, they should work…possibly with varying levels of effectiveness. Several brands tout effectiveness against pycnogonida (sea spiders).
Natural predators: Certain wrasses and other typical pod-eating-vertebrates may eat AES, but I’m not aware of any definite natural controls.
Manual removal: If your eyes are good enough (or are helped with a magnifying glass), you may be able to manually remove AES with tweezers or a pick. However, you may miss some and end up with a worse problem down the road.
Other: I am not aware of any in-tank treatments (other than possible natural predators). Additionally, Bayer insecticide is a common hobbyist treatment for marine pests; however, it was not designed for reef usage. Please read the label.
AES Conclusion:
Although Acanthastrea-Eating Spiders are quite creepy-looking, they are not a horrible pest to eradicate. They are highly susceptible to coral dips and can even be manually removed. If you know you have AES, please be a responsible reefkeeper and do not pass your coral on without at least notifying the new owner.
Zoanthid-Eating Sea Spiders: Not Reef Safe
Note how different the AES above is from the Zoanthid-Eating Spider (ZES) shown below. The AES is much larger and has a much smaller (proportionally) body. Both have eight legs.
The photo below is of a zoanthid-eating spider that came off a zoanthid colony during a dip in CoralRx. It is in a water droplet on the top of a water test card for size reference.
How to Identify ZES:
ZES are extremely tiny, so they hide quite well in the coral. And, they are able to attach themselves very well inside the zoathid polyp. Even after a thorough visual inspection of the coral prior to dipping, I only found these after they fell off in the dip. The ones I found were about 3-5mm in diameter. So, I recommend a good coral dip prior to introducing the coral into your tank. Since they can devour Zoanthid corals, proper identification of sea spiders is critical.
How to Treat ZES:
Various dips may be effective against ZES; however, multiple dips may be required to eliminate any recently-hatched eggs (most dips are not effective on marine pest eggs).
Hydrogen peroxide dip: This is not an ideal treatment for ZES, as soft corals (zoanthids) do not typically respond well.
CoralRx, Lugols, and other commercially-available dips: These ZES photos were taken after removal with CoralRx, so these preparations may have varying degrees of effectiveness based on brand/solution.
Natural predators: Certain wrasses and other typical pod-eating-vertebrates may eat ZES, but I’m not aware of any definite natural controls.
Manual removal: If your eyes are good enough (or are helped with a magnifying glass), you may be able to manually remove ZES with tweezers or a pick. However, you may miss some and end up with a worse problem down the road.
Other: I am not aware of any in-tank treatments (other than possible natural predators). Additionally, Bayer insecticide is a common hobbyist treatment for marine pests; however, it was not designed for reef usage. Please read and follow the label.
Zoanthid-Eating Sea Spiders Conclusion:
Although Zoathid-Eating sea spiders are quite creepy-looking, they are not a horrible pest to eradicate. They are highly susceptible to coral dips and can even be manually removed. If you know you have AES, please be a responsible reefkeeper and do not pass your coral on without at least notifying the new owner.
References:
Cowles, Dave, “Phoxichilidium femoratum (Rathke, 1799),” https://inverts.wallawalla.edu/Arthropoda/Chelicerata/Pycnogonida/Phoxichilidium_femoratum.html, accessed 18 January 2021.
Not just those, I’ve dealt with one species of sea spider that eats platygyras, leptastreas, galaxeas and hydroids
Oh mercy, how awful! Thanks for sharing! There’s so much to be learned about the oceans…