Bloom Season is on its Way

What You Need to Know

by Grant Pitcher

Image credit:  Grant Pitcher

By Marie Smith, CSIR

The days are getting longer, the temperatures are rising, and the odd GP numberplate has been spotted on the steets of Cape Town – summer is clearly on its way! As the familiar southeaster starts to blow in late September, it not only causes water temperatures at Clifton to drop from “refreshing” to “frostbite”, but also brings new nutrients to the surface ocean along the west coast. These conditions create the perfect combination of sunshine and sustenance for the proliferation of microscopic plant-like organisms known as phytoplankton.

Although these little critters are a vital part of the marine food chain – like the grass of the ocean – there are unfortunately some bad apples that can be harmful to both people and marine life. While some produce toxins that can be taken up to by shellfish, making them poisonous to humans, others can damage or clog the gills of various ocean creatures. There are also those types that take the party a little bit too far, quickly growing into massive groups that can even change the colour of the water to brown or red – these are known as red tides. Although they are not necessarily dangerous they can start causing lots of problems for the locals if they hang around in one spot for too long, particularly if they all die and decompose!

Phytoplankton have a noticeable effect on the colour of the ocean, turning surface waters from azure all the way through to pea-soup green and even butter-chicken red. These effects can be seen and measured from space by sensitive satellite sensors, allowing us here at the marine Earth Observation group of the CSIR to keep an eye the on the concentrations and sizes of these blooms, and how they change over the summer season. This also allows us to notify the relevant authorities or aquaculture farms if we spot a bloom to watch out for. So while the rest of the country are getting their bathing suits and umbrellas ready for a nice hot summer, we will be gearing up to face the phytoplankton fiesta that is heading to our shores.