Starfish (split from Wildlife Sightings)

[David B]

Split from Wildlife Sightings (http://www.secularcafe.org/showthread.php?t=251)

The starfish population is exploding round here at the moment.

I've noticed a cycle, based on mussel populations.

The starfish will eat the mussels, then the population of starfish will crash, new mussels will stick to the rocks and grow, and in a few years the starfish population will explode again.

That's what I figure from my own observations, anyway.

http://i419.photobucket.com/albums/pp275/dble_photo/160309002.jpg

[BWE]

David B,

I did my research on a particular issue surrounding starfish population fluctuation. While it's possible that you are seeing a cycle, it's more likely you are witnessing normal feeding behavior. Starfish have some sense that alerts them when another starfish has found food. It's like a very slow feeding frenzy. :D

If you are seeing a high fluctuation in population, you would likely be noticing other odd things about the local tidepools.

Their predators include mostly sand dwelling fish, sharks, sometimes flounder, skates and etc. so overfishing can lead to a boom and bust cycle in cold water areas. In warm water areas, they go crazy on the coral so they just keep expanding, eventually, I guess they run out of reef and crash.

But agricultural runoff might have more to do with it. In water thick with organic nutrients, the dissolved oxygen tends to drop and starfish get to eat without fear of the fish who don't like low oxygen levels. Of course, sometimes that spells disaster too. Oxygen levels can drop below the levels needed to sustain life in places called hypoxic or anoxic zones. The starfish move in and die in those cases though.

[David B]

David B,

I did my research on a particular issue surrounding starfish population fluctuation. While it's possible that you are seeing a cycle, it's more likely you are witnessing normal feeding behavior. Starfish have some sense that alerts them when another starfish has found food. It's like a very slow feeding frenzy. :D

I guess that they just gorge while they can and then move on, then.

I've seen lots of gluts over the course of my life here, at intervals of a few years, and in this case it does seem to be influenced by the state of the mussels. After such a glut the bigger ones go, and next year, or even later this year, I expect to see the low water rocks covered with very small mussels.

They are getting highly predated by herring gulls above low water mark, but sometimes in the past at such times I've snorkel dived at low tide, and seen a much higher starfish density below LWM than in the pools, and stranded on rocks or on the beach.

If you are seeing a high fluctuation in population, you would likely be noticing other odd things about the local tidepools.

Don't think so, either now or in the past.

Their predators include mostly sand dwelling fish, sharks, sometimes flounder, skates and etc. so overfishing can lead to a boom and bust cycle in cold water areas. In warm water areas, they go crazy on the coral so they just keep expanding, eventually, I guess they run out of reef and crash.

I was assuming - always dangerous - that they run out of mussels, and crash.

But agricultural runoff might have more to do with it. In water thick with organic nutrients, the dissolved oxygen tends to drop and starfish get to eat without fear of the fish who don't like low oxygen levels. Of course, sometimes that spells disaster too. Oxygen levels can drop below the levels needed to sustain life in places called hypoxic or anoxic zones. The starfish move in and die in those cases though.

I live in an area where water quality is good - it's monitored by the EC for bathing safety, and we do well - and where there are very big tides, and hence a massive movement of water, so I'd be tempted to rule them out.

I live on the South coast of Pembrokeshire, Wales.

David

[BWE]

I was assuming - always dangerous - that they run out of mussels, and crash.



The topology of the bottom (I love saying that) matters a lot on that case. You're only seeing the intertidal zone for the most part. The critters roam. If you had a 100km of mussels lining the rocks just below low-tide and suddenly one year, they were overtaken by Asteroidea and eventually all the mussels were eaten and the ecosystem changed dramatically afterward, and the starfish disappeared, you'd be likely to be seeing a boom/bust. But at a rocky shoreline in a northern clime, you're describing normality for stars.

[David B]

I've been watching the local boom and bust of the starfish in the tidal zone and just below the tidal zone for decades, and find it really interesting.

I hope to pick your brains about it over the next few days.

I'll try and formulate some questions over the next couple of days, if you don't mind.

David

[BWE]

No problem. It just occurred to me, how many different species do you notice regularly? And, are anemones in the area proliferating at the same time as the starfish?

The oceans aren't as stable as they were when I did my research. A drastic fishery decline off the coast is actually quite likely.

[David B]

No problem.



Splendid

It just occurred to me, how many different species do you notice regularly?

Just the ones in the pic, and brittlestars is the best I can do there.

And, are anemones in the area proliferating at the same time as the starfish?

Never thought about it, but I have a good idea about how many anemones I would expect to see. I have quite a busy work schedule over the next few days, but I'll go and look.

The oceans aren't as stable as they were when I did my research. A drastic fishery decline off the coast is actually quite likely.

It's possible, but I haven't heard of any major complaints from local anglers, either from the shore or from boats. Mackerel have declined in my lifetime, though, though there is still the occasional glut. The seal population is healthy, AFAIK. I don't see dolphins or porpoises (at the distance I used to see them, I couldn't tell the difference) like I did 40 years ago, though.

And the pattern of boom and bust in the local starfish population seems pretty regular, since I first noticed it, perhaps 40 years ago.

David

[BWE]

Yeah. Chances are you are noticing them when they move through. It's a big ocean.

[David B]

So how fast can they move, then? When I've watched them it seems to be pretty damn slow. They can get picked up by waves in the shallows, of course. I don't suppose that there would be a way for them to use tidal currents as means of getting about? As a far fetched speculation, if they detect signs of starfish feeding activity at one state of tide, then raising some arms to allow themselves to be picked up by the tide, and carried towards the feeding frenzy, like tumbleweeds in the wind, when the tide turns?

Hmm. Very far fetched!

I've been thinking about what such a high density could eat when they are not on the rocks, and recalling that we occasionally, on some of the local beaches, get a glut of cockles. These tend to be short lived - above the LWMS people tend to grab them, but I guess that if there is a cockle glut above LWMS, then there would be one below it, too.

So I'm speculating that starfish might have something to do with that?

David

[BWE]

Is it seasonal by any chance? Quite a few species spawn seasonally and cluster during spawning. Of the kinds that do, you'd probably notice some of them lifting up on their rays like a hand with all the fingertips touching the ground. If you do discover that, pick up one of the ones in that position and you'll see, depending on the species, little globs of goo in between her rays. That's the female. They stick around long enough to get the babies started so they don't get 'et by the mussels. :) Of course, eating the mussels is a bonus too.

Fascinating creatures. Sometimes heavy concentrations are related to heavier than normal rainfall since the larvae are a little less buoyant in lower salinity.

[Brianna]

Hmmm. Tasty little creatures.

[David B]

The invasion is over - just a very few starfish left.

This rock usually has loads of eating sized mussels on it

http://i419.photobucket.com/albums/pp275/dble_photo/April132009020.jpg

Lots of opened mussels in this photo

http://i419.photobucket.com/albums/pp275/dble_photo/April132009021.jpg

There are still places where there are lots of small mussels, and a few places where there are still edible sized ones, but the mussel population has pretty much crashed following the starfish visitation.

What with weather and work, I never did get to examine the starfish closely - next time.

David

[Matty]

where are the pics taken Dave? Gower way?

Strange, we rarely saw starfish down our way in Cornwall, i've seen some when out snorkelling and maybe the odd one in the rock pools but never as many as that first pic. I have however picked a few thousand mussels in my time so maybe i and the other locals out ate them :)

Not tempted to feed one through a sieve?