The fronts of the Prince Edward Islands

The fronts of the Prince Edward Islands

Every summer, approximately 300,000 macaroni and 80,000 rockhopper penguins return to the Prince Edward Islands to breed. During this period, their need to return regularly to the island to provision offspring constrains the distance they can travel to find resources. This makes them dependent on allochthonous prey i.e. originating from somewhere else.

Macro- and mesoscale processes in the vicinity of the Prince Edward Islands are largely driven by fluctuations in the positions of the sub-Antarctic Front (SAF) and Antarctic Polar Front (APF). During years when the fronts are close to the islands, currents are stronger. During years when the fronts are farther away, currents are weaker. The proximity of the SAF and APF to the islands determines the composition of the zooplankton species. For example, when the SAF is closer to the islands, increased intrusions of warmer waters carry sub-tropical and sub-Antarctic species. Conversely, when the SAF is farther north, Antarctic species are more common. These processes influence the type of resources available to penguins during the breeding season.

The animation below represents daily maps of sea surface temperature anomalies. In 2011/12 and 2013/14, conditions were much warmer than in 2012/13. Note the positions of the fronts.

Interestingly, the dive depths of penguins were consistently to 40 to 60 m in 2011/12 and 2013/14, but during 2012/13, when cooler conditions persisted, dive depths were considerably deeper and penguins ate more fish. This highlights the role that the frontal systems play in delivering food to the Prince Edward Islands.

Eddies and filaments

Eddies and filaments

Imagine you are standing on a rock at the edge of the sea, gazing out at the seemingly infinite expanse of ocean that stretches to the horizon. You are hungry, really really hungry. In fact, you haven't eaten for three weeks! Now, jump into that ocean and try find some food. Where would you go? How would you know where you are when you can no longer see land? It's a pretty mindblowing thought to think that there are millions of animals out there that do that all the time. Part of my PhD thesis involves trying to understand how macaroni and rockhopper penguins manage to find food during the resource-limited winter months. During this time they spend six consecutive months at sea, never returning to land.

Thanks to satellites and the work of organisations like Aviso, anybody can find out what the ocean was doing anywhere in the world at any given time. For instance, I wanted to find out whether macaroni and rockhopper penguins were using mesoscale eddies and/or submesoscale filaments. These oceanographic processes are known to aggregate and sustain elevated concentrations of zooplankton and fish, and thus act as important foraging areas for many marine predators. Nobody, however, has investigated whether crested penguins utilise these structures during the winter period. The graphic below shows the movements of a macaroni penguin in relation to sea level anomaly (SLA - eddies) and finite-size Lyapunov exponent (FSLE - submesoscale filaments). Notice how the penguin encounters the eddy on May 26th and only leaves on July 21st. That's nearly two months at the same eddy. Also take notice of how the penguin moves in relation to the filaments.

Phytoplankton and Penguins

Phytoplankton and Penguins

Phytoplankton are perhaps the most important group of organisms on our planet. They are microscopic, single-celled galaxies that come in many different shapes and sizes...

The Jumping Spider and the Ant

The Jumping Spider and the Ant

A few weeks ago I was admiring the veggie patch behind our house when I noticed the red pepper plant had a leaf with another stray leaf resting on it...

Oil spill in Goukamma Nature Reserve

Oil spill in Goukamma Nature Reserve

On the 9th of August a German owned vessel, the Kiani Satu, was on its way from Cape Town to Gabon when it ran aground in Goukamma Nature Reserve and Marine Protected Area. The 168 m long vessel was carrying 15 000 tons of rice and 330 tons of fuel oil.

Following the event someone remarked: "While there is no current threat to the environment, we hope the ship is towed off soon before this turns into another Seli 1."

Since then oil has been leaking out of the vessel which has washed up on beaches and even entered the Goukamma estuary. The damages to local sandy beach and rocky shore ecological systems are likely to be massive, and already there have been incidences of birds completely covered in oil.

The oil also threatens our valuable estuaries, which are integral to providing refugia for juvenile fish and are also home to the world's only populations of the Knysna seahorse. Unfortunately, oil has already breached the Goukamma estuary and with the swell expected over the next few days, it is possible that the ship will break up further, spilling more oil into the sea. Let's hope that the organisations working around the clock to sort out this problem will be able to reduce the extent of the spill and that the insurance company will cough up to pay all the bills necessary for the clean up operation.

Dungeons!

Dungeons!

In a twist of oceanographical fate, a five metre swell with an 18 second period surged over one of the world's most beautiful big wave reefs. Twiggy Baker, John John Florence, Albee Layer, Frank Solomon, Mike Schlebach, Andy Marr, Simon Lowe and others were there to harvest the stoke.

Huge thanks to Steve Benjamin from Animal Ocean for taking me out there! Check out the video I filmed and edited featured on ZigZag.

Cape Town Fog

Cape Town Fog

It was Friday the 24th of May and the fog on the Atlantic seaboard was heavy. Steve predicted it would roll into the city and into Camp's Bay, so we headed up the mountain to search for a fresh perspective of our beautiful city. True enough, as the sun set and the land cooled, the fog rolled in boisterously under the full moon and the city disappeared.

Rock Kestrel

Rock Kestrel

Once upon a time there was a pair of rock kestrels that bred at Dias Beach in the reserve. That time is now and this season they laid four eggs (Anthony Van Zyl; pers. comm.). Last week I was lucky enough to glimpse one of the youngsters (photo below) all grown up and munching on a black girdled lizard (which are often seen sunbathing on the rocks).

Note: adults have grey head feathers whereas this is absent in the juveniles.

Bain's Kloof Pass

Bain's Kloof Pass

My Thursdays don't usually involve ravines, but I'm so glad this one did. Bain's Kloof is a beaut, with a delicious stretch of rapids, waterfalls and natural pools, it's a biophilic's haven for adventure. When hopping from rock to rock the pools appear as pale cups of rooibos inviting one in for a sip, and as you venture below bearing a mask and snorkel, an emerald green universe beams hello. Little redfins swim about with curiousity, 'What's this strange creature doing in our pool?'.

I was really impressed with the health of this stretch of the Witte River and the communities it supports. Submerged pebbles and boulders were teeming with sensitive invertebrates, such as stonefly larvae and leptophlebids. We watched with fascination as stoneflies rested momentarily on the water's surface, only to be gobbled up by the alert redfins below. Frogs croaked upstream whilst those nearer to us splashed into the water to hide away. Dragonflies whizzed past us warily, although Ffi managed to get intimate with one after it crash landed in the pool in front of us. We even caught a glimpse of a tiny snake swimming through one of the pools.