North Pacific Seastar population decline?
July 25, 2010 by BayKeeper
Filed under Featured, Wild Things
The beautiful, but destructive North Pacific Seastar (Asterias amurensis) first arrived in Port Phillip Bay in the 1990s in ship ballast water. As they eat practically anything live or dead that they can climb onto, they thrived in the local conditions where they have few natural predators. In less than 10 years they became the most common animal in the Bay. The fact that that the females are estimated to produce over 20 million eggs could have something to do with it! Naturally, there are concerns that they could out-compete native seastar species.
North Pacific Seastar - it's own worst enemy?
NPS’s tend to spend the summer months in the deeper, central Bay waters, and move nearer to shore in winter. Over the past 5 winters Earthcare volunteers have taken advantage of this seasonal migration to remove thousands of these pests from St Kilda harbour. The most recent cull, conducted today, found hundreds compared to the usual thousands; and young native seastars were noted.
Along with this promising result, several divers have reported not seeing NPS’s in the south of the Bay over the past year. Have they disappeared altogether, or simply eaten themselves out and moved to another area? Baykeeper is keen to hear any reports of NPS’s from around the Bay. Have you seen more or less this winter?
Hi Baykeeper
Re: the Northern Pacific Seastar. I’ve seen plenty of these ghastly pests on McCrae and Rosebud beaches this winter. Maybe as many as in previous years.
I’m sorry but I have to take issue with you saying they are beautiful. I hate the sight of them. Perhaps, as with other pest plant and animal species, once I know the destruction they can cause, their “beauty” completely disappears – for me anyway. I just picture them munching up the native scallop populations, which they apparently do with ease, as the scallop does not recognise the NPS as a predator and just stays in dangers way until too late. And, I hear they first arrived in the Derwent River from Japan in ships arriving to fill up with our Tasmanian native forest woodchips. From there they quickly arrived in PPBay in the 1990s in ballast water. That they have become the most common creature in the Bay in that short time doesn’t help my opinion of them (or the shipping industry) either.
That’s good news those pesty North pacific Seastars are diminishing.
As mentioned, there are promising signs, but there’s still a question mark as to whether they actually are declining. There is a real need for an ongoing systematic survey around the whole Bay.
At McCrae, right in front of the Life Saving Club in approx 3 meters of water is a thriving colony of these pests.They are decimating the local shellfish and their numbers are increasing at an alarming rate.They have totally destroyed a large amount of juvenile Oysters and are now into the Pippis.
A do nothing attitude promoted by the Govt Dept leaves me wondering.
Thanks for your report Barry. There’s no doubt that North Pacific Seastars are up there with rabbits and cane toads in their impact on local ecosystems. I’d suggest the government attitude would be different if it was ‘personal property’ that the pests were decimating. The do nothing option is aided by the ‘out-of-sight-out-of-mind’ factor. As far as I’m aware, the state government hasn’t even resourced a systematic monitoring program. Of course there have been incidental, anecdotal reports from various scientists from time to time. But it’s been left to community groups to defend their local patch. Earthcare St Kilda has been culling NPS’s from St Kilda Harbour for the past 6 years; and collecting data in the process. It would be great if similar approaches were adopted by local groups around the Bay.
I swim most days at Dendy St. Beach, Brighton (summer & winter). The NP Seastars moved in with a vengeance this winter, eating every shellfish including Periwinkles.
Our resident population of Stingrays have disappeared and also all fish except Toadies and Whitebait.
I have been gathering the NP Seastars (while swimming) for the last couple of months and binning them, averaging about 400 – 500 per week. The population has now decreased considerably along the reefs where I swim.
It is good to see the Native Seastars still in considerable numbers. But we also have a problem with the Japanese Kelp taking over all the rock areas
Thanks a million for letting us know of your observations and your ongoing action to clear the NPSs from your patch Sam. I hope you’ll keep it up for many years to come! It would be great if you kept a written record too. The decline you’ve noted in Stingrays and Seastars may just be a seasonal thing, or something else again. I’ve noticed Japanese Kelp in St Kilda harbour for many years now and would be interested to hear of any other locations in the Bay. Keep on swimming!
Checked an area in front of the McCrae lighthouse that was infested with these pests and noted that they have almost gone. I started to remove them some months ago but gave up due to water temperature and it seemed I was losing the battle.I did notice a large number were washed ashore over the winter months when strong Northerly winds persist.The 10 that I found were binned.
Heaps of Stingrays,Banjo Sharks and 3 nice Eagle Rays
Thanks for your report Barry. keep us posted! By all reports NPS’s move to shallower waters colder (winter?) months and return to deeper waters as temperatures increase. They’re more likely to be picked up by wave action when they’re in shallower water too. That seems to fit with your observations.
I have now managed to clear (of NPSS) an area of 400 m x 100 m at Dendy Beach and very few have returned. I am now clearing the southernmost 100 m. ( I gathered 200+ in 30 mins the other day ). A couple were much larger than my handspan and these had very fat centre sections.
There are now a lot of one, two and three armed NPSS, so something is eating them, probably other NPSS, although I have only ever picked one up that was eating another’s arm.
There are still plenty of Native Seastars
There are signs of the stingrays returning (craters), although I haven’t sighted any, yet.
A 6′+ Eagle Ray was sighted yesterday about 200 m offshore (way past where I venture)
A lot of very young Smooth Toadfish, must be the breeding season; plus a Dusky Morwong
Thanks a million Sam! If every beach had a custodian like you the local habitats would be much safer for native species. Your news that something is eating them is especially interesting. It would be brilliant if you keep a journal tracking seasonal changes in the NPS population in your patch. Would love to hear more in the future!
Only the occasional NPSS in “my cleared area” now. I thought that maybe they had retreated to deeper water because the water temp was up to 20c on the weekend (back to 17c this am).
However I swam to the far southern section of Dendy Beach today (where I hadn’t been before) and picked up 30 NPSS in one small area of seagrass, so it appears that I haven’t been wasting my time.
I’m pleased to note that the idea of community action to remove North Pacific Seastars seems to be building momentum. As you’ve demonstrated Sam, it is possible to at least remove them from localised areas. That has to be beneficial to native species in those areas.