Going green

Sea lettuce is a naturally-occurring green algae that grows in coastal regions around the world. It grows in sheets that sometime resemble the leaves of butter lettuce. At least one rather stringy species is native to New Zealand where seasonal blooms can clog harbours and deposit thick, rotting mounds along pristine beaches.

Last weekend, while visiting my mother in Mount Maunganui, I found the main beach carpeted by fresh deposits of sea lettuce. I’d never seen such an extensive bloom before. At least a hundred metres of beach front had been inundated by a sea of green. Mum says these blooms have become more frequent in recent years. I vaguely recall small deposits along the shore as a child, but nothing as extensive as the sight the greeted me in the weekend.

Critics claim nutrient rich run-off from surrounding farmland is to blame. However, research reveals a surprisingly strong correlation between blooms and El Nino weather patterns. During an El Nino winds blow predominantly from the west. Persistent winds push warm coastal water along New Zealand’s east coast away from the land. Cooler, nutrient rich, deep ocean water rises in its place and blooms swiftly follow. These verdant reproductive bursts go unnoticed until stormy weather washes tones of green deposits along the shore and into sheltered bays.

Debate currently focuses on the impact of global warming on the frequency and strength of El Nino weather patterns. The phenomenon is a result of extensive warming of the Pacific Ocean’s surface along the South American coast. This heat sink draws the planet’s atmosphere away from Australia and New Zealand, creating warmers temperatures and drought conditions in these nations.

It’s shame to see the beauty of Mount Maunganui’s beaches desecrated by these blooms. Even more so as the Summer cruise ship season gets underway. Tourism is a regional growth industry and the city’s stunning beaches constantly surprise and delight visitors.