There’s a wild world thriving in the meandering waterways and coastal strip of our largest city.
Beneath the familiar waters of our largest city, a wild world is thriving.
IHAVE A SUNRISE DATE WITH A SEAHORSE. It’s at Manly Cove, so I’m up early, driving across Sydney Harbour Bridge, racing the rising sun. The traffic is already a headache; Google Maps shows a further delay in my predicted arrival time; and I still need to f ind a car park, get my dive gear together, check my camera and locate my muse – potentially tricky considering its tiny size and cryptic appearance and behaviour. As an underwater photographer, I work mostly away from major urban centres. But here I am, turning onto the notoriously hectic Military Road and driving with barely enough elbow room towards Sydney’s populous Northern Beaches. I arrive as the pastel pink and blue hues of f irst light colour the sky and quickly enter the water. Finning along the sandy bottom towards the net of Manly Cove’s swimming enclosure, the water is surprisingly clear as blue swimmer crabs and harvest cuttlef ish hustle for my attention.
Minutes later I f ind my quarry – a charismatic creature, just 15cm long, covered in hard body armour and grasping the net with its prehensile tail. The stress of the morning rush hour melts away with the rising sun as I capture a portrait within the last shafts of dawn light.
Sydney’s sun-spangled waters are central to the city’s national and international reputation. But I’ve often wondered how much life lies submerged, hidden away from the above-water pressures of Australia’s biggest city and its ever-sprawling human population. So now I’ve seen proof of the city’s growing reputation as a seahorse haven. But what else is veiled from view beneath the opaque surface of the waters near some of our most iconic landmarks, beaches and headlands?
GEOLOGICALLY, SYDNEY HARBOUR is a river valley that was drowned as the sea level rose about 11,000 years ago at the onset of the present interglacial period. But from a marine ecology perspective it’s one of the world’s most modif ied estuarine systems. Along with Port Hacking, Botany Bay, Pittwater and the Hawkesbury River, the harbour is one of a series of deep waterways in the Sydney Basin that drain along a shallow coastal strip between Palm Beach and Cronulla.
These waters support habitats strongly inf luenced by wave energy, water depth, bottom type and salinity. Exploring them is like swimming through storybook pages filled with a fascinating cast of colourful characters.
A series of rocky reefs along Sydney’s coast lies separated by vast swathes of mobile sediment that withstand large and powerful waves. In the shallows, these are covered in seaweed forests (see AG 139) sheltering common seadragons feeding on swarms of tiny mysid shrimp.
Also here are giant cuttlef ish, with pigment organs – chromatophores – in their skin that change instantly, both in colour and texture, to transform these behaviourally complex creatures from f lamboyant billboards to masters of disguise. Down in deeper waters, these reefs are covered in a living veneer of colour created by gardens of sponges, ascidians and tunicates in all shapes and sizes.
Blue gropers are a recurring and much-loved part of coastal Sydney, famed for their tame behaviour, large size (up to 40kg), blubbery lips and peg-like teeth. One or two dominant males are usually in an area, along with several females. When a male dies or leaves, the largest female changes sex to become a replacement male. Many of Sydney’s resident gropers have been affectionately named by adoring locals – such as Bluey off Clovelly Beach.
Seven aquatic reserves protect Sydney’s most accessible and biologically diverse coastal areas. Cabbage Tree Bay Aquatic Reserve at Manly is one of the most popular, where snorkellers can spot southern eagle rays, dusky whaler sharks and crimson banded wrasse, all occasionally swimming around discarded junk like old motorbikes.
Within Sydney Harbour’s estuarine environments, waters are generally shallower, more sheltered and prone to the inf luences of tide and salinity. Here, softer sediments are perfect habitat for bizarre molluscs, polychaete worms, echinoderms and crustaceans. Three aquatic reserves also afford protection for some of Sydney’s estuarine habitat at Towra Point in Botany Bay and Shiprock in Port Hacking.
Stands of marine vegetation – including mangroves, seagrass and saltmarsh – provide oases for wading birds such as stilts and pelicans, and habitat for juvenile f ish and marine invertebrates. Several species of seagrass are found in Sydney Harbour, with most at shallow depths in the outer harbour. Mangroves are a declining habitat worldwide, so it’s reassuring to learn Sydney Harbour’s mangrove cover has increased since European settlement. In contrast, saltmarsh has fallen dramatically due to foreshore development. Only an estimated 37ha remain.
These days consideration of the marine environment is now required through the planning and approval process for the installation of marine infrastructure. Developments, for example, over marine vegetation are heavily regulated, with significant penalties for unauthorised harm to aquatic plant species.
IT’S A DARK, SHADOWY world in Sydney’s swimming enclosures and beneath jetties. Differences in shade, orientation and water f low are strong drivers of marine plant and animal life around these artificial habitats. Such places have proved beneficial for species such as seahorses, which thrive on swimming enclosure nets because they increase food and provide refuge from predation.
Deep in Sydney Harbour, the calm waters around Chowder Bay are home to striate anglerf ish. Perfectly adapted to the soft sediment and low-lying sponge habitat here, this species has exquisite camouf lage and uses its f ins like feet to walk along the sea f loor. It also has a built-in lure for attracting prey and a large mouth to eat them. Common Sydney octopuses are here too, their distinctive white pupils and rust-coloured arms emerging from lairs under rock ledges.
Sydney’s marine environment is exposed to most threats faced globally by coastal cities, including habitat loss, foreshore development, pollution, stormwater run-off and introduced pests. But many plant and animal inhabitants appear not only to be coping with the shortcomings, but finding their own strongholds.
Since coastal ecolog ist Professor Peter Steinberg was appointed Director and Chief Executive Officer of the Sydney Institute of Marine Science (SIMS) in 2009, he’s become acutely aware of the critical role played by an organisation such as his in ensuring the health of Sydney’s estuarine and coastal ecosystems by providing local research that supports their management.
“I get reminded of the importance of our work every time I look out my office window,” he says. “There are people sailing, people f ishing, transport vessels, cruise ships, not to forget all of the houses and foreshore infrastructure that line the coast – it’s the perfect visual for the work we do.”
Human-based threats to and impacts on Sydney’s waterways are relentless and increasing as more people are drawn to the city’s waterways. “It is ironic that we can potentially love our waterways to their detriment,” Peter says, “so at SIMS we are trying to understand what people think, what they value about the waterways and what that means about how you manage it.”
To address some urban threats, SIMS researchers are now taking steps towards practical ecological interventions to improve existing infrastructure. “The reason is that if we don’t get in there and start doing things now, then it might be too late very soon,” Peter explains. “I think there has been a big shift in environmental science globally to interventions, and that takes on a whole bunch of forms – from restoration ecology, to rehabilitation ecology, to green or eco-engineering.”
Sydney Harbour, for example, is extensively modif ied, with more than half the shoreline replaced by artificial structures such as seawalls, jetties and piers. “We initially built structures that didn’t look like natural habitats, but we can now construct things that facilitate natural marine communities,” Peter says. “We are starting to deploy prototypes and designs in Sydney Harbour to better connect the manmade environment with the natural environment.”
An example is designing seawalls with niches and crevices to increase colonisation by marine species such as seaweed, oysters, f ish and crabs. Design of these ecologically friendly seawalls makes them more like natural rocky intertidal areas, with increased habitat complexity and a gradually sloping face to dissipate wave ref lection.
“One challenge is trying to f ind cost-effective ways of retrof itting existing, smooth-surfaced vertical seawalls that don’t integrate well with the natural environment,” Peter says. “We’re having some success using tiles created by our collaborators with a 3D printer, which can be attached to pre-existing seawalls and allow us to introduce complexity and structure to the surface.”
Having seen positive results of SIMS’ work in the Sydney area, Peter realised the model could be applied to similar urban harbours elsewhere. The World Harbour Project (WHP) resulted from SIMS-led work and was launched in 2014 at the IUCN World Parks Congress, held in Sydney. It began with 14 partners and has grown to include 31, a global initiative based on the idea that
Design of these ecologically friendly seawalls makes them more like natural rocky intertidal areas.
A pair of young explorers chase a school of baitfish trapped in a rock pool by a receding tide near Bondi Beach, along one of Australia’s busiest coastlines.
As crayweed forests are restored along Sydney’s coast, species such as this pink sea urchin and other invertebrates seek shelter in the habitat created by the fronds.
Coastal ecologist Professor Peter Steinberg, Sydney Institute of Marine Science Director and CEO, heads research to improve management of Sydney’s marine environment.