Science Jargon Band Name of the Day: “Parasitic Castration”

I recently made a classic move in experimental marine ecology, scraping barnacles off of rocks. My main motivation was to set up a small experiment testing habitat use by snails, but I had another mission. I wanted to dissect a few barnacles to see if I could find any predators or parasites hanging out inside the barnacle shell (“test”). I’d been reading about a fly that only lays its eggs on barnacles, and when the larvae hatch they crawl inside barnacle tests to feed on the unprotected tissues and hide from waves (more on that in a later post, hopefully).

On this day, I found no fly larvae, but I did come across a cool parasite. At first glance, this grubby creature looked as though it could have been an insect larva. On closer inspection, the head, legs, and arrangement of segments made me think of a crustacean more than an insect.


This animal is most likely a female Hemioniscus balania, an isopod that lives as an parasite on barnacles. Isopods are familiar to many of us from their terrestrial incarnations such as woodlice (aka roly polies, pill bugs, or potato bugs), but they are an incredibly widespread and diverse group of crustaceans, occurring both on land and in nearly every environment in the ocean.


What makes this particular isopod so cool is its morphology, ecology, and life history. Its genus name, Hemioniscus, means “half woodlouse,” which I think derives from the fact that only the anterior (“forward”) portion of the animal resembles an isopod. When most isopods molt, or shed their old exoskeleton to reveal a new, slightly bigger exoskeleton underneath, they molt the posterior (“back”) half first and then their anterior half second.1 Somehow, this animal has incomplete molting of some kind that allows it to retain the typical isopod segmentation in front while turning into a giant blob in the back,2 a “mullet bug” of sorts (new common name, anyone?).


Young isopods are free-living males and look like typical isopods. They gain entry to barnacles and start to act as parasites. Eventually, they will turn into a bloated female like the one pictured above.3 Here’s where it gets crazy. They feed entirely off of the ovarian fluids of the barnacle, preventing the barnacle from making eggs and shunting a lot of the barnacle’s precious energy directly to the parasite. This is where the term “parasitic castration” comes from. Since barnacles are simultaneous hermaphrodites, they can still function as a male, but you can imagine this form of parasitism could have major impacts on barnacle populations.4

Reproduced from Blower and Roughgarden 1987

Reproduced from Blower and Roughgarden 1987


1- see Johnson W.S., E. Stevens, and L. Watling. 2001. Reproduction and development in marine peracaridans. Advances in Marine Biology 39:107–261.

2- see Williams, J.D. and C.B. Boyko. 2012. The global diversity of parasitic isopods associated with crustacean hosts (Isopoda: Bopyroidea and Cryptonicoidea). PLoS ONE 7:e35350.

3- see Crisp, D.J. 1968. Distribution of the parasitic isopod Hemioniscus balani with special reference to the east coast of North America. Journal of the Fisheries Research Board of Canada 25:1161-1167.

4- see Blower, S. and J. Roughgarden. 1987. Population dynamics and parasitic castration: a mathematical model. The American Naturalist 129:730-754.

Worshiping the Plankton in Caprellid City

While we often think of docks and piers covered in attached organisms like mussels and algae, there are also plenty of freely moving organisms like crustaceans and fish that benefit from the habitat provided by attached critters. Last month, I noticed that the submerged portions of the docks in Bodega Harbor were covered in a waving mess of tiny animals. These creatures were none other than caprellid amphipods of the species Caprella mutica, which is non-native in California but commonly found in harbors and estuaries. However, I had never seen such a dense collection of the animals in my life. Check out this video to see what I mean.

Most of the caprellids are engaged in body-waving motion, which is an active method for capturing food from the water. Their long antennae are covered in fine hair-like projections resembling a comb that can trap plankton and detritus. Many of the caprellids are hanging on to an arborescent (tree-like or branching) bryozoan called Bugula neritina (also non-native). That is the bushy purple stuff, which is actually a colony of many interconnected animals. Caprellids like to hang on to something, so it’s easy to see how the non-native bryozoan with all of its branches might benefit the caprellids by providing many “perches.” I wonder if the caprellid offers any benefit to the bryozoan, like preventing other animals from overgrowing it, or if they disrupt feeding of the colony’s tiny animals (“zooids”).

Here are a couple of other things to watch for in the video:

at 1:15, you can see that two caprellids at the bottom of the screen appear to be engaging in crustacean fisticuffs.

at 1:25, you will see a group of small caprellids filter feeding around the inhalant siphon of a native sea squirt (Ascidia ceratodes).

Key West at a Crossroads


credit: Arnaud Girard @

Next week voters in Key West, Florida will decide whether or not the Key West City Commission can conduct a Feasibility Study designed to determine the environmental and economic impact of widening the city’s main ship channel. Widening the channel has been deemed necessary by some locals (aka “conchs,” a nickname that refers to the overfished snail) in order to allow bigger cruise ships to make Key West a port of call. As a former resident of Key West – I lived there from first through third grade – and a concerned scientist, I have been following this story over the past few months.  Here’s my take on the issue.

Key West is a city that depends on tourism, so it seems natural that conchs would want to facilitate the transit of cash carrying visitors. Yet, much of this tourism relies on the fact that Key West is one of the most tropical places one can find in the US and its warm, shallow waters teem with life. The island city is located in the middle of the Florida Keys National Marine Sanctuary, which encloses the third largest barrier reef in the world and the only one in the United States. So, it’s also understandable that many conchs would oppose any action that would threaten an ecosystem that already bears its share of insults (overfishing, climate change, coastal development).

I guess the decision about whether to widen the channel or not has a lot to do with what locals want from their Key West. Do they want to their commercial district to consist of wall-to-wall trinket stores offering t-shirts that read “I’m with stupid,” or do they want to foster local artists and fisherman who offer a glimpse into what the Keys really are, a biodiversity hotspot­ and our closest connection to the Caribbean. Ok, to be fair the city already has enough trinket stores that walking down Duval Street is not so much fun, except possibly during Fantasy Fest.

So what exactly would the environmental impact of widening the Key West channel be? Aside from directly removing organisms that live on the seafloor, dredging – essentially shoveling out a deep passageway – would bring an incredible amount of sediment from the bottom of the sea into the water. Sure, a lot of sediment would be hauled away to be used for some other purpose (maybe to fill in a marsh or create a new island), but a lot of it would end up suspended in the water. This would decrease the amount of light reaching the bottom, reducing the ability of corals and seagrasses to photosynthesize. The sediments would eventually settle, but much of it would “land” in areas where corals reside and potentially bury them. The combined effects of blocked sunlight and a blanket of sediment could only harm the corals that form the foundation of an entire ecosystem. Moving forward, the bigger cruise ships will bring more people to Key West, which will undoubtedly put more pressure on coastal habitats through land, water, and energy usage.

To get a glimpse of what suspended sediments look like in Key West and how many local fishermen feel about the referendum and the ecosystem, check out these videos.

It’s amazing how much sediment is kicked up when big-ass cruise ships move through the channel, but imagine how much sediment would be lifted off the bottom if the channel was dredged. And, would even bigger big-ass cruise ships continue to kick up sediments as they chug into Key West Harbor after dredging?

I initially figured the referendum to be a sneaky way for the City Commission to get the channel dredged, perhaps by spinning the Feasibility Study results. But after reading a recent piece in a local newspaper, it seems like the referendum may be even more insidious (although I hope it ends up as a boneheaded move). It turns out (SURPRISE) that dredging in the Florida Keys National Marine Sanctuary is prohibited and it may not be possible to conduct a study even if the referendum passes. This either leaves the City Commission looking like they missed a major memo or like they are planning ahead. At this point, it really seems like the referendum is just a way to start the processes of lifting the ban on dredging by forcing a view of public support and economic incentive.

The Florida Keys and the surrounding waters are a national treasure and deserve protection from overdevelopment. Living there as a boy inspired me to study marine ecology and I go back as often as I can to explore and fish with old friends. But, the area is drastically different than it was even twenty years ago and thinking about what it will look like in the future is worrying at best. I totally understand that local businesspeople want to keep their businesses strong and continue to make Key West an incredible tourism hub, but there has to be a balance that takes into account both the flow of tourist dollars and the natural capital that makes the Keys what they really are. I hope the citizens of Key West realize this when they go to the polls next Tuesday.