Another Worry From Global Warming: Parasites that EAT Starfish SPERM!!!

(Figure 1b from Stickle et al. 2005, Invertebrate Biol. 120: 88-95)

This week, we have what sounds like a horrific title: Starfish Sperm Eating Parasites!

Parasites are weird and freaky...and how many people out there knew that Sea Stars even HAD parasites???

yes! they do. So, let's get to it!

1. The Parasite- and....it does WHAT???
So, in the early 2000s, Bill Stickle, a marine biologist at Louisiana State University authored several studies looking at the parasitic relationship between a ciliated protozoan Orchitophrya stellarum (described way back in 1907) and several different sea stars from the North Pacific.

(Figure 1A from Stickle et al. 2005, Invertebrate Biol. 120: 88-95)

in a series of papers published by his lab, including this one (2005), this one (2007) and this one (2001) (this wasn't all of them) , they describe the close relationship this parasite has with its host(s).

2. Orchitophrya LIVES AMONG and EATS starfish Sperm! Yes that's right! These little single-celled animals probably enter through the gonopores (although there's lots of big spaces for a tiny critter to enter on a starfish) and invade the gonads/testes of male sea stars (location indicated below with red arrows) and get right to work eating up all of their little starfish baby-makers!

Interestingly, the parasites do NOT attack the ovaries (female reproductive structures).

(modified from Wikipedia commons)

Apparently, these parasites were FILLED with phagosomes (digestive bodies) which included numerous sperm in various stages of digestion.

Here is a pic of one of these guys right in the middle of a spermalicious FEAST!

(Figure 1b from Stickle et al. 2005, Invertebrate Biol. 120: 88-95)

This has some MAJOR impact on the amount of sperm produced by the host species, which are particularly ripe in brooding winter males and spring-summer broadcasting males (i.e., when they are ejecting sperm into the water and females are ejecting eggs into the water at the same time).

But WHAT species? Well, apparently, these parasites like asteriids..which are very familiar beasts such as (this is an incomplete list)

Pisaster ochraceus
Leptasterias spp.
and...the North Pacific Asterias amurensis (now invasive in Australia). Early studies on the interaction between the parasite and their hosts were actually performed on this species...
The Atlantic Asterias forbesi, was actually one of the first species discovered to host the parasite-from populations in Europe and the east coast of North America, which may be where it originated. But its unclear how/where this happened..

3. Orchitophrya is a KICK-ASS Starfish sperm-eating Parasite! (but can live life on its own)

(Figure 1A from Stickle et al. 2005, Invertebrate Biol. 120: 88-95)

Stickle's lab discovered that the parasites CAN actually live outside and away from sea stars, but they become smaller, they become less developed and their mouth actually moves away from the front of their body!!

Now, when you FEED them asteriid starfish sperm? ALL of these changes REVERSE themselves!! So, Orchitophrya is considered a "facultative" parasite...that is it can live free of the host when it needs to do so.

The range of the parasite seems to have gotten as far south as Washington but based on several of the surveys taken there were only a few regions that had unusually low sperm outputs from parasitized male adults.

3. When it gets (global warming) HOT, the parasites get BUSY.
There has been much concern over what will happen to various marine invertebrates as global warming intensifies. And there has been some concern about how, even our local faunas, such as the Ochre Stars will be affected.

A new paper by Amanda Bates, Bill Stickle and Christopher Harley in the Journal of Experimental Marine Biology and Ecology uses some lab results to postulate what might happen to Orchitophrya under higher temperature conditions...

The authors isolated the parasite and cultured it. Then exposed it to Pisaster ochraceus
and Patiria miniata
at variable temperatures-the control versus 10 and 15 degrees C.

Interestingly, the parasite much prefers Pisaster to Patiria, which further details how specific the relationship is...Orchitophyra likes asteriids (e.g., Pisaster, Evasterias, and Asterias)

Higher temperatures led not only to increased DENSITY of parasites but also infection INTENSITY.. That is, greater amounts of the male testes were infected.

(Fig. 3 from Bates et al. 2010)

The end result? After 21 days, so much of the sperm in the testes has been consumed that effectively, the hosts have partly to completely lost their "reproductive potential". That's effectively castration (emasculation?). Yikes!

So, what does that mean?

As all good scientists do, the authors warn that lab results don't always translate directly into what you see out in the "wild". There's a lot of variation in temperature of local areas and of course, the various populations and so on.. and more work needs to be done..

HOWEVER, they do note an interesting case of temperature increase of 1.5 degrees C per decade from 1976 to 1997 in Tokyo Bay. The temperature increase corresponded to the first detection of the parasite in Tokyo Bay in 1996! So, maybe some cause for concern is here?
This is a great example of how global warming's effect could conceivably extend beyond simply the direct effects on marine faunas. Who knows what weird combination of dominos could be altered?

In this case, the changes in water chemistry may benefit some asteroids (as indicated here), but on the other hand, SO will their parasites!

Speaking of unintended impacts, I can only wonder how many extra hits I will get from disappointed people who were looking for out of context key words in this blog's title... :-)