Kelp Forests of False Bay: The Ocean’s Natural Engineers

Throughout the past two weeks I have spent with Cape RADD, I have been captivated by the natural beauty of False Bay time and time again. From diving alongside the inquisitive Cape fur seals of Partridge’s Point to being greeted by graceful humpback whales breaching along the horizon— the breathtaking wildlife in this bay never ceases to amaze me. Yet, despite the impressive range of charismatic wildlife, I have been lucky enough to encounter, one unique characteristic of this bay has left me in awe: the kelp forests. 

The kelp forests of False Bay, together known as The Great African Sea Forest, play a crucial role in maintaining balance within the biodiverse ecosystems of Southern Africa. Classified as “ecosystem engineers,” the kelp forests foster highly productive habitats for the vast array of organisms that inhabit these waters. While kelp forests can be found across the globe, the forests prevalent in False Bay are distinct in that they are expanding in size at a consistent rate– attributable to the bay’s ideal water temperatures and nutrient content. Due to the significant influence, they have on the stability of marine ecosystems, it is imperative that these kelp forest ecosystems can continue to thrive without the threat of preventable, yet increasing, disruptions to environmental stability.

Although they can appear relatively simple at a glance, the anatomy of an individual Giant Brown Kelp (Ecklonia maxima) is capable of serving as both a habitat and food source for marine life. A kelp plant is composed of three main parts: the holdfast, the stipe, and the fronds. The holdfast anchors the plant to the ocean floor, providing resistance against strong currents and providing shelter to small invertebrates. Extending vertically up from the holdfast is the flexible stipe, reaching towards the water’s surface and allowing the plant to rhythmically sway back and forth with the surge. Extending outwards from the top of the stipe are the fronds, which allow for photosynthesis and filter rays of the sun as they cast beams of light upon the ocean floor. Each of these 3 features has distinct functionalities; together, they contribute to the development of a dynamic ecosystem.

In addition to being an ecosystem engineer, kelp plants also display a dual nature, acting as both keystone species and keystone hosts. As keystone species, they possess the ability to shape environments and influence the survival of interacting species, defining the structure and functionality of marine ecosystems. As hosts, the giant kelp occupying False Bay provides shelter to a diverse variety of other keystone species. A number of invertebrates and vertebrates seek shelter amidst the dense kelp blades or under the cover of the compact holdfast– up to a thousand different species can be found on a single kelp plant!

“It’s almost like the forest mind— you can really feel it, that big creature. It was a thousand times more awake and intelligent than I am. It is like a giant underwater brain operating over millions of years, and it just keeps everything in balance.”

Craig Foster, My Octopus Teacher

However, despite kelp’s remarkable ability to uphold ecological balance, intricate ecosystems can also be susceptible to unforeseen disturbances, especially in relation to the effects of anthropogenic interference. Each and every species inhabiting an ecosystem plays an integral role in overall productivity, thus, a diversion beyond ordinary abundance or behaviour of a single species can lead to a subsequent cascading effect. This effect has been exhibited in the past, one instance being the invasion of the South African rock lobster in the early 2010s, in kelp forests east of Cape Hangklip.

A sudden and significant increase in the population of rock lobsters, natural predators of the cape urchin, resulted in a disruptive effect extending beyond the populations of these two species and into the stability of the greater community. The sudden influx of lobsters led to a decrease in urchins, which in turn resulted in an overabundance of macroalgae and the elimination of encrusting coralline populations. Being a keystone species, kelp plays a major role within this interconnected web. Each of these species interacts with kelp in various ways– grazing, cohabitation, reliance for shelter– and disruptions to these symbiotic relationships can skew ecological balance via top-down cascades. Regardless of the kelp forest’s powerful ability to regain balance, escalating impact from human activity can substantially inhibit this natural mechanism.

Despite the increasing abundance of kelp in False Bay, many interacting species are facing growing threats resulting from the effects of climate change and the exploitation of marine resources. With these threats on the rise, it is crucial that we continue to explore the constructive role humans can play within this cycle and how we can aid in maintaining this natural balance through comprehensive conservation efforts and outreach. Cape RADD embraces this approach to conservation through hands-on research and citizen science, aiming to permeate the barrier between the scientific world and everyday people interested in making valuable contributions to marine research. After all, the kelp forests are not only essential ecosystem engineers, but they create the enchanting underwater landscapes for which False Bay is renowned. Participating in Cape RADD’s snorkel/scuba for science programs will give you the opportunity to experience these ethereal forests for yourself while assisting with the progression of marine conservation here in South Africa.