If someone had told me 10 years ago that my profession as an adult would involve playing around with beakers of eggs and sperm and helping males and females get sexy in the lab I wouldn’t have believed them.
No, I am not a sex therapist or an IVF doctor, but a marine biologist who studies seaweed sex.
Yes, that’s right, my research for the past five or so years has focused (among other things) on the reproductive ecology of large seaweeds such as kelp; how this influences where and when we find them in the ocean; how they are all related; and how they will be affected by human-induced events such as climate change and coastal development.
Seaweeds are a lot smarter than we think. Aside from being extremely important as a habitat and/or food source for many marine plants and animals (including abalone and crays), they have evolved sophisticated mechanisms to help them reproduce at exactly the right time, to ensure fertilisation success and thus survival of the species.
Different seaweeds reproduce in different ways, ranging from very simple systems not unlike our own, to complex “tri-phasic” cycles that involve numerous different reproductive products and growth stages which look very different.
Some are hermaphrodites and produce eggs and sperm in the same structure. For these seaweeds, fertilisation success is perhaps easier since eggs and sperm are naturally close by, but “selfing” is common whereby eggs from one individual are fertilised by sperm from the same individual.
Other “dioecious” species (such as the common Crayweed and Neptune’s Necklace) have separate male and female plants that release eggs and sperm (gametes) into the ocean for reproduction.
Both hermaphroditic and dioecious species have evolved sensitive mechanisms to help synchronise gamete release to concentrate eggs and sperm and ensure successful fertilisation.
One of the most common mechanisms of seaweed sex involves reproduction that is cued to tidal cycles.
For example, some common intertidal brown seaweeds only release eggs and sperm on slack or high tides when the ocean is calm.
These seaweeds can ‘sense’ the height of the tide via mechanisms that detect the amount of blue light that reaches them in the water column.
They can also tell whether the ocean is calm or rough by the amount of dissolved inorganic carbon in the thin boundary layer of water around them.
Other seaweeds, including many intertidal species, reproduce when they are exposed at low tide. Eggs and sperm are extruded from the seaweeds due to hydrostatic pressure as the seaweed dries.
These gametes are encased in wet mucous that prevents them from drying out. It also helps the gametes drip down under the canopy of seaweed onto the rock where it is cooler.
Many eggs will be fertilised rapidly and the resulting baby seaweeds (zygotes that are about a tenth of a millimetre in size) will produce adhesives to attach to the rock.
Others will remain unattached and, upon the next incoming tide, be washed away to travel around in the ocean currents.
As you can probably tell, seaweeds have fascinated and excited me for years. I hope that by shedding some light on their interesting lives, you too will be able to appreciate them as a truly amazing component of marine biodiversity that is central to the health of our oceans, and thus deserving of protection as much as any other organism.
The Nature Coast Marine Group has an extensive program of activities where members can have fun learning about our marine environment.
To find out more about the Group phone Bill Barker on 4473 5304 or Andrew Green 4474 2886.
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