Monterey Bay Aquarium Research Institute

Marine Botany

Antithamnion defectum

Growth Experiment

Because Antithamnion dendroidem was growing in the some of the plastic aquarium tubs in the outdoor lab of Hopkins Marine Station, I decided to do a small experiment to test the rate of settlement and growth of Antithamnion spores. I knew that adult Antithamnion tetrasporophytes were present in the tanks within 4-6 weeks, and must have grown from spores transported in from the running sea water pumped from the bay. To try to get a more accurate estimate for how long it takes for spore settlement, I placed five clear microscope-slide cover slips on the bottom of a tub in which Antithamnion was already growing, and five cover slips into a new tub in which nothing was growing. I checked the cover slips twice a week for spore settlement and germling growth. The table below shows the results so far.

Cover slips in Tank With Antithamnion

Day # 5 7 12

# germlings

Cover slip 1 0 0 8

Cover slip 2 0 0 2

Cover slip 3 0 0 17

Cover slip 4 0 0 7

Cover slip 5 0 0 9

Cover slips in Clean Tank

Day # 5 7 12

# spores

Cover slip 1 0 0 2

Cover slip 2 0 0 0

Cover slip 3 0 0 1

Cover slip 4 0 0 1

Cover slip 5 0 0 2

On day 12, the germlings on the cover slips from the tank with Antithamnion ranged from single cells to nine cells, although the average cell number was 1. All of the germlings from the cover slips in the clean tank were single-celled, and a few had not germinated yet and were still spores. The pictures below show germlings of various cell numbers.

On day 14, I checked the slides to look for new settlement as well as growth of the germlings that were present on day 12. I had marked the position of some distinct germlings on the coverslip so that I could find them again two days later. There were many more new settlements, and from what I could tell, the germlings had grown at most 1 cell in two days. The major eveidence for this was on the second slide from the empty tub which had no germlings or spores on day 12, and one germling with one cell on day 14. Some of the sporelings which I had found on day 12 were dead when I found them on day 14, suggesting a high degree of mortality with the early stages of life, something common of most organisms.

Timing of the Antithamnion Life-Cycle

A study in 1955 grew Antithamnion in culture and found that once tetraspores are released, germling gametophytes grew within one month. Within three months, spermatangia and procarps were present. Within four months, carposporophytes were present on some female gametophytes. Carposporophytes developed within 18 days of fertilization. [11] The rapid life-cycle of Antithamnion is consistent with its competitive, opportunistic life-style.

Apical Growth

In the Ceramiaceae family, growth occurs in bands located apically or basally in each cell. Axial cells in Antithamnion defectum have two bands; however, most of the cell elongation occurs from the basal band of each axial cell. [12]

Antithamnion and Light Levels

Research has found that Antithamnion plumula has a maximum growth rate at a light flux of 17 ergs/sec per square millimeter in the range of 380-720 nm. When 2-4% of the incident light is screened out using dilute solutions of eosin-yellow dye (0.1-0.2 mg/l), the growth rate increases by 150%. Further increasing the dye concentration and blocking more light causes a decrease in growth rate. Normal growth can occur even up to 42% of incident light removal. Green light in the spectrum of 500-540 nm has been shown to inhibit growth, and phycoerythrin, an accessory photosynthetic pigment of most red algae, protects the algae by absorbing green light. The yellow dye is believed to have enhanced the phycoerythrin effect of protection. [13]

This preference of Antithamnion plumula (and perhaps other species?) for lower light levels could further explain why it is not found in the intertidal, why it is common subtidal, and why it would prefer to grow on the underside of Nereocystis stipes at the surface as seen in the Markham study in 1969.

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References and Acknowledgements

Last updated: Feb. 05, 2009