What Are These Mystery Animals From Charleston Waters?
Case File No. 1
Case Opened: April 21, 2016
On April 21, students from Sumter High School arrived at DNR’s research center in Charleston, ready to cruise the Harbor and learn about estuaries aboard the E/V Discovery. Our marine educators set out the trawl net in the waters of Charleston Harbor, which they use to give students a glimpse of the plants and animals living in South Carolina coastal waters. Part of the fun is that every trawl is a surprise – the educators never know what they’ll haul in – and April 21 was no exception.
Educator Emily Foy noticed a dozen tiny, jellylike masses in the net. She quickly identified them as nudibranchs (nood-uh-brenk), a type of sea slug, and brought them back to a DNR classroom after the program concluded. We photographed the little mollusks as they wriggled around a plastic container. Post-glamor shoot, we had to know – what kind of nudibranchs were these?
Staff from the benthic taxonomy lab were consulted. A former DNR taxonomist was consulted. Strangers on the internet were consulted. No one could reliably confirm the identity of our mystery species.
Case File No. 2
Case Opened: July 28, 2016
Specimens were collected on a COASTSPAN survey near Cape Romain Wildlife Refuge. The goal of these surveys, conducted by members of SCDNR's inshore fisheries section, is to capture and study young sharks in South Carolina estuaries. The team catches more than just sharks, though – on July 28, they hooked an abandoned crab pot (not uncommon, unfortunately!) in which several animals had become trapped, including a female stone crab with an apron full of eggs. Biologist Bryan Frazier shook out the lucky crab over the side of the boat – and several gelatinous blobs fell out and landed on the boat as well.
Again, the signs pointed to nudibranchs. Interestingly, this time the individuals collected from the crab pot showed variations in their coloring. Though each had an orange-pink body dappled with white spots, the appendages on their backs (called cerata) ranged from dark brown to flame-tinged purple.
Again, though, the specific species was unclear. With over 2,000 nudibranch species worldwide, narrowing down the possibilities is a daunting task – even when you work with highly knowledgable taxonomists.
In a way, it actually was strangers on the internet who helped us solve both mysteries.
All thanks go to an obscure scientific paper published a decade ago in a small journal: “A KEY TO THE BENTHIC SHELL-LESS OPISTHOBRANCH GASTROPODS OF NORTH CAROLINA,” by researchers Tony Fernando and Philip Skip Kemp. A biological key is a little like a choose-your-own adventure book for nature lovers: at each set of questions, you choose the answer that most closely resembles the leaf, pollen grain, or nudibranch you're trying to identify. Does the nudibranch have an orange stripe down the center of its head or two white stripes? Most questions are a lot harder for a nonspecialist to answer: Are its rhinophores lamellate or slightly tubercle? (Thank goodness for Google.) Question by question, the possible species are whittled down to the likeliest match.
With the help of the key and a few other papers, the mystery sea slugs appear to be as follows:
Case File No. 2: Spurilla braziliana (formerly Spurilla neapolitana), which lives along the western Atlantic and munches on anemones. You can see, in the tiny white tips at the end of each appendage on its back, the stinging cells that this nudibranch recycles from its prey and uses to protect itself -- one of the neatest tricks of the nudibranch.
Got a mystery marine species you need help identifying? Send pictures to CoastalResourcesBlog@dnr.sc.gov!