North Pacific Seastar population decline?

BayKeeper — Sun, 25 Jul 2010 10:04:20 +0000

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?

Seastar survival strategy

BayKeeper — Sun, 28 Mar 2010 10:42:11 +0000

Curiously, the Magnificent Biscuit Seastar Tosia magnifica is reported as relatively common in waters up to 5m in Victoria and Tassie, but is only found in deep water (to 200m) in South Australia. Just one more of those marine mysteries! But it may well be that this ability to use a range of depths will be the key to the species survival in the face of competition for food from the introduced pest North Pacific Seastar Asterias amurensis.

Magnificent Biscuit Seastar - pic by Susie Inglis

As Susie Inglis’ pic from Hobsons Bay shows, the Magnificent Biscuit Seastar is a dainty little critter. At around 45mm wide they’d be no match in an arm wrestle with the much larger and more abundant North Pacific Seastar. Lets hope their choice of depth is SA may give them safe haven from these unwelcome pests.

NP Seastars came to Port Phillip Bay in ship ballast water in the mid 1990′s and rapidly became the most abundant creature in the Bay. The fact that they’ll eat practically anything (living or dead) that they find on the seabed is a big part of their success. Whereas Magnificant Biscuit Seastars, believed to graze on living plants, aren’t so easily pleased.

Port Phillip Baykeeper » North Pacific Seastar

North Pacific Seastar population decline?

Seastar survival strategy