Trip Report – 4 March 2017 :   South Coast seaweeds

One of the most prominent seaweeds on Wellington’s south coast is Lessonia variegata.   It has a robust holdfast, much-branched stipes, and linear unbranched blades.

Wellington turned on a calm, warm day as we ventured to Te Raekaihau, the point between Houghton Bay and Lyall Bay.   Learning some of the common seaweeds was the goal for the trip.   The turnout was great, being boosted by several visitors, including a contingent from the Levin Native Flora Group.   We were fortunate to be joined by seaweed experts Maren Preuss and Joe Buchanan, who are current and former students at Victoria University, respectively.

Although the nominal trip leader, I’m only a beginner with seaweeds.   In the last year or so, I’ve picked up a few basics using Wendy Nelson’s book, New Zealand seaweeds.   An illustrated guide, and NIWA’s free online Beautiful Browns.   A guide to the large brown seaweeds of New Zealand.   It is these big brown seaweeds that I’ve found the easiest to learn, and I suggest they are a good group for anyone to begin with.   I’ve also found an excellent way to learn seaweeds is by uploading photos to the citizen-science web site www.naturewatch.org.nz and receiving crowd-sourced identifications.

Another common Wellington seaweed is Ecklonia radiata.   It has a flattened blade with lobes branching from a wide central axis.   The stipes are cylindrical and unbranched.

New Zealand is home to some 800 species of seaweeds, which are also known as marine macro-algae.   Alongside the brown seaweeds are the greens and reds.   These major groups differ in the coloured pigments that they use to photosynthesise.   Some of the green species are relatively easy to identify.   It is the third and biggest group of seaweeds in NZ, the reds, which I find the hardest; there are many species, and many seem bewilderingly similar, at least to me.

The brown seaweeds that we saw included: Durvillaea antarctica (bull kelp), distinctive for its immense size; Hormosira banksii (Neptune’s necklace) with its linked brown spheres; Landsburgia quercifolia with its oak-shaped blades, the introduced and weedy Undaria pinnatifidia with its frilly base; Macrocystis pyrifera (giant kelp) which has floats between its blades and main axis; Lessonia variegata with linear blades from much-branched ‘stalks’; Ecklonia radiata with many lobes from a flattened central axis that arises from a robust cylindrical stalk; Carpophyllum maschalocarpum (common flapjack) with flattened blades and axes; species of Cystophora with branched, tubular “leaves”; and two species of Marginariella with their distinctive cylindrical fertile structures.   Greens included the self-evidently named sea lettuce (Ulva), sea rimu (Caulerpa brownii), and sea grapes (Caulerpa geminata).

Both of the Marginariella species around Wellington are characterised by clusters of cylindrical reproductive structures in among their ribbon-like blades.   They also have floats.   In the pictured species, M. urvilliana, the floats are spherical.   (BotSoc memory-aid: the floats are the shape of the globe, which was what Jules Dumont d’Urville, whom the species is named after, circumnavigated.) The other species, M. boryana, has elliptic, rugby ballshaped floats, and seems to be more common on Wellington beaches.

With their great diversity of colours and structures, seaweeds are an enchanting group of plants.   If you give them a bit of attention next time you’re at a beach, you’re likely to be rewarded, not only by their aesthetics, but also by seeing repeated patterns; that’s the first step in beginning to know them.

Participants : Dave Allen, Liz Allen, Joe Buchanan, Eleanor Burton, Rita Chin, Leita Chrystall, Gavin Dench, Lynette Fischer, Frances Forsyth, Jill Goodwin, Bryan Halliday, Susan Hansard, John Hobbs, Chris Horne, Sheena Hudson, Stuart Hudson, Vanessa James, Brenda Johnston, Alison Lane, John Leggott, Rodney Lewington, Leon Perrie (leader), Maren Preuss, Lea Robertson, Darea Sherratt, Sunita Singh, Julia Stace, Ian Townsend, Brian Tyler, Judith Tyler, Julia White, David Willyams.