Superannuation funds are reviewing their existing mandates with BlackRock and Barclays Global Investors (BGI) following the merger between the two firms.

Tasmania-based superannuation fund Tasplan has already terminated BGI from its Australian equities portfolio. Westscheme and legalsuper are currently assessing their mandates with their respective asset consultants.

Tasplan had appointed BlackRock and BGI quant-style mandates worth $100 million each.

Tasplan's review of the managers was prompted by the resultant exposure of a single manager, according to Tasplan general manager Neil Cassidy.

"After the merger, BlackRock effectively managed 50 per cent of Tasplan's Australian share portfolio and the manager risk ... was considered to be too great," Cassidy said.

The board of Tasplan has withdrawn the BGI component of the BlackRock mandate and appointed SG Hiscock to manage a concentrated portfolio of shares, and appointed $20 million to Eley Griffiths Group as part of a small caps mandate.

"The remaining portion will be spread across our existing managers, which includes the BlackRock 150/50 strategy," Cassidy said.

Westscheme has about $780 million in enhanced Australian equities mandates with both BlackRock and BGI.

"A number of consequences have resulted from the merger [between BlackRock and BGI] including staff departures. As a result, we will be reviewing our mandates with the two firms in conjunction with our asset consultant," Westscheme chief executive Howard Rosario said.

In particular, Westscheme's portfolio does not have the necessary diversification now the two firms have merged, according to Rosario.

Legalsuper, which has a fixed income mandate with BlackRock, is also reviewing its mandate.

"When mergers take place, there will always be changes. We have not taken any action as yet. It is more a case of simply reviewing the relationship at the moment," legalsuper chief executive Andrew Proebstl said.