Sea lettuce and Tauranga's abundance of it went under the microscope at yesterday's Tauranga Harbour Symposium.

Hosted by the Bay of Plenty Regional Council, the University of Waikato and Priority One the symposium presents the latest research on the harbour, most of which is still underway.

Sea lettuce washes up in Tauranga Harbour.

Intercoast PhD student Alex Port is studying sea lettuce and developing mathematical models to indicate how and where it grows.

He estimates there is 2400 kg of wet weight sea lettuce near the Waikareao Estuary channel per tide.

He is not yet able to say if the sea lettuce is originating from the estuary or out in the harbour.

The estimates are a result of transects Alex has mapped where sea lettuce is counted at different depths, photographed and videoed.

He has also set up a sea lettuce cage near the Waikareao Estuary mouth with vertical nets to help capture sea lettuce in the water for weighing.

The aim of his research is to build a model that takes into account the biology and nutrients of the sea lettuce and describes what is going on when there is a bloom.

'I only care about the why, the process, not the outcome,” says Alex.

Another scientist studying the impact of sea lettuce on the harbour is Clarisse Niemand, who is covering square metres of intertidal sand at Tuapiro with sea lettuce to determine the impact the weed mat has on the shellfish, snails and other marine life, which feed the birdlife and fish.

Sea lettuce in Tauranga Harbour can have a world-wide effect, says Clarisse. The migratory birds, the Godwits nest in Alaska, but their main feeding grounds are in New Zealand.

'What we do here can impact on a very much larger scale,” says Clarisse.

By recording and measuring the impacts of the decaying sea lettuce she will study how the much sea lettuce is too much, and how long the beach communities take to recover.

A question from the audience about whether the scientists are considering the fertiliser works outfall as the nutrient source for sea lettuce was answered by University of Waikato chair of marine sciences professor Chris Battershill, who says the large sea lettuce blooms are also being seen outside the harbour.