Botany Photo of the Day

This entry is the second in a BPotD series for UBC Research Week, organized by Connor Fitzpatrick.

Dr. Rob DeWreede, Professor Emeritus in the Department of Botany, maintains a algae research lab at UBC. He provided today's photographs and write-up (note: the first photograph is courtesy of Dr. Colin Bates).

These photographs are of the kelp, Laminaria setchellii, a species of brown algae (Phaeophyceae). Both photographs were taken in Barkley Sound, which is located on the west coast of Vancouver Island, British Columbia, Canada. It is a region of much marine research, as it is adjacent to the site of the Bamfield Marine Sciences Centre, a research and teaching centre owned by three universities in British Columbia and two in Alberta.

Laminaria setchellii is a perennial seaweed, frequently found in the low intertidal and shallow subtidal zone, attached to rocks and, as here, intermingled with the seagrass Phyllospadix coulteri. As with all kelps, this macroscopic stage (the sporophyte) releases spores which germinate into separate microscopic male and female gametophytes, which in turn produce sperm and eggs, respectively. The egg, held on the female gametophyte, releases pheromones (chemicals which attract the motile sperm cells). The fertilized egg develops on the female gametophyte, overgrows the female gametophyte, and develops into a new diploid sporophyte phase.

Laminaria setchellii has been of interest to a number of students in the laboratory of Dr. DeWreede in the Department of Botany of the University of British Columbia. Ecological studies have included research on age structure and biomechanics of this kelp. Reports from the early 1900s suggested that some kelps had growth rings, and suggested also that these may be annual rings. We developed techniques that indicated that these rings are indeed formed annually, by much the same process responsible for the growth rings in trees. This knowledge opened a doorway of ecological investigation previously closed, e.g. research on age-related processes of these algae. We carried out research on the age distribution of populations of Laminaria setchellii under different ecological conditions, age-related reproductive effort, and age-related mortality. We discovered, for example, that individuals of Laminaria setchellii commonly live as long as 12 years, sometimes 20 – 24 years. Our studies on age-related reproductive effort enable us to test some hypotheses concerning reproductive effort in annual vs. perennial species of organisms, using seaweeds (research done by Terrie Klinger).

In addition, students in our laboratory have studied biomechanical properties of Laminaria setchellii, attempting to understand how these algae are able to tolerate the immense forces imposed on them by crashing waves generated by winter storms. For example, allowing for the greater density of water compared to air, crashing storm waves can impose forces equivalent to those generated by winds of 1000 km/hr! We investigated whether exposure to greater wave impact results in thicker stipes, larger holdfasts, or greater tissue strength, and the impact (on survival of Laminaria setchellii) of invertebrates such as crabs burrowing into the holdfast tissue (research done by Sophie Boizard). One conclusion from the data is that holdfasts of L. setchellii are “over-engineered”, as holdfasts of smaller diameter are attached with similar tenacity as larger holdfasts. However, if a holdfast segment is removed from the seaward-facing portion of the holdfast this results in significantly higher mortality than an identical segment removed from the lateral side of the holdfast. This result makes sense as a seaward-facing holdfast component experiences greater tensile stress than a lateral segment of the holdfast in breaking waves. Similarly, Laminaria setchellii holdfasts are asymmetrical, with more tissue allocated to seaward and shoreward parts of the holdfast.

Insights such as these are providing botanists and marine ecologists with a greater appreciation of the ways these fascinating organisms cope with some astounding physical forces, and how these apparently simple organisms can be used to test theories applicable to photosynthetic organisms more generally.