Project Pentaceraster

I wrote before that my research project here involves figuring out the basic feeding relationships of starfish in the Galapagos subtidal system. This fits into a larger framework of understanding the connections between different species in this system, including economically important species such as carnivorous fish and Leslie's Hexaplex snails, and ecologically important species such as grazing sea urchins and herbivorous fish.

A sampling of starfish species, clockwise from top left: Nidorellia armata (chocolate chip star); Phataria unfascialis (blue sea star); Pharia pyramidata (yellow spotted star); and the ever-awesome Pentaceraster cumingi (Panamic cushion star)

I am focusing my efforts on Pentaceraster for now because we have preliminary evidence that it eats sea urchins, making it a potentially important link in the food web. It is also quite abundant, so it makes up a substantial amount of standing biomass. On our dives, I have been overturning Pentaceraster along the transect to (1) take measurements of their size using my amazing starfish-measurers - I've further modified them a little by taking off a weight and adding a clip to the end; and (2) recording what they are munching on, if anything. Pentaceraster eats by everting its stomach onto its lunch, so it's easy to tell if it is feeding when I overturn it. It is not as easy to ID its lunch as it pulls its stomach back in.

Measuring the radial length (=length of one arm) of a Pentaceraster star. The transect tape is just visible in the top right.

Overturned Pentaceraster retracting its stomach. I go digging through all the bits and find out exactly what's in its mouth.

We also ran a cage trial with a recycled cage from an old experiment. Eventually I am planning to use larger cages to test the effects of including vs. excluding Pentaceraster from an area, but I need to know how well these cages will hold a starfish. We'll be back at this site next week, so I'll be able to see if Mr Pentaceraster has escaped from my setup.

Setting up the cage with Jon.

Final cage setup. One Pentaceraster and five Eucidaris sea urchins (two are clearly visible).