by simon
Why are the oceans important? The importance of wildlife.

The importance of the oceans, their wildlife and ecosystems

The land and oceans are part of one system: Earth. So when we ask, why are the oceans important? We’re asking about our own future. Life began in the ocean billions of years before the first plants or animals colonised land. Oceans regulate the state of our atmosphere because they are 99 per cent of the volume of living space for animals and wildlife is the mechanism that drives stability.

Climate change has always been the symptom of biodiversity loss … that’s to say, the breakdown of the complex connectivity between lifeforms that allows Earth to flex in response to changing conditions. Ocean wildlife has, for the large part, acted as a buffer against the most catastrophic effects and since about fifty million years ago, has kept our climate quite stable.

Industrial fishing only happened recently in our planet’s history and this reduction in the abundance of wildlife represents our greatest challenge for survival.

Below you will find a range of articles designed to inspire an understanding of the magnitude of animal impact on our oceans.

What’s more important, the ocean or the land?

The importance we bestow on the land is anthropocentric because we live there. It’s naturally important to us that we protect it. Nonetheless, if life in the ocean dies, we suffer irreversible changes to land-based ecosystems and climate.

In this article, we take a look at many of the ways that land and oceans are linked together.

The answer to the question, ‘why are the oceans important’, is that we live on the land but the oceans regulate Earth’s temperature. The oceans are equally vital to the land we live on.

Latest posts about why the oceans are important

Where are Melbourne’s coral reefs?

Did you know that a marine sanctuary in northern Port Phillip Bay is home to some of the best examples of our region’s coral reefs? Melbourne’s coral reefs are at Ricketts Point Marine Sanctuary but despite their importance, this biotope hasn’t yet been recognised as significant. In actual fact, the existence of these reefs is barely recognised.

Our reefs are already threatened by rise in sea temperatures and nutrient input into the bay. But they also face a new and unexpected threat. Scientists are proposing to establish kelp beds in the marine sanctuary. The first stage of this work is a huge sea urchin cull. But sea urchins are a naturally-occurring and conspicuous component of this coral reef biotope.

When pressed, Parks Victoria scientists have admitted that they forgot to include the reefs in their assessment. They do not even know where the coral reefs are located, and that introducing kelp would threaten these important and rare habitats. Furthermore, kelp has never occurred in abundance at this site.

If we really want to protect our marine ecosystems we first need to understand and value what we have. So, before we take drastic action, here is a little introduction about the temperate coral reefs in our marine parks.

Here is a video of the coral reefs at Ricketts Point. The areas of ‘barren’ dominated by urchins are green coral reef. Urchin barrens form part of the description of this important biotope.

What do Melbourne’s coral reefs look like?

Temperate coral reef in northern Port Phillip Bay looks barren. It’s slow growing compared to many of its tropical counterparts [1]. The reef is not a lush coral reef like we’re used to seeing in the tropics. Instead, it is boulder-like with lots of bare rock and, importantly, sea urchins.

Here are two examples of sea urchins living in association with temperate coral reef in different parts of south-east Australia:

Melbourne's coral reefs. Example from Montague Island, NSW

Montague Island, NSW. Green coral and the sea urchin Centrostephanus rodgersii

Melbourne's coral reefs. The best are under threat?

Port Phillip Bay, VIC. Green coral and the sea urchin Heliocidaris erythrogramma

The dominant corals we see in Melbourne’s coral reefs are green coral (Plesiastrea versipora) and octocoral (Erythropodium hicksoni).

Our sea urchin is the purple urchin, a native species. Please note, it is NOT INTRODUCED, as some people might think. Green coral varies in colour from white to cream and bright green. Octocoral is grey but can appear orange when the polyps are extended.

Photo Gallery: Coral Reef off Beaumaris

Here are some photos of coral reef taken in about 50cm of water all along the shore in Beaumaris.

Green coral biotope description for the Melbourne region

Parks Victoria has a long-term Subtidal Reef Monitoring Program in Victoria [4]. The primary objective is to provide information on the status of Victorian reef flora and fauna. It has this to say about Ricketts Point:

Ricketts Point (Site 5) and Halfmoon Bay (Site 6) were predominantly Sargassum-Caulerpa assemblages. At both sites, the dominant species have been the green mat forming species The habitats at both sites include sea urchin barrens, in which encrusting coralline algae and the stony coral Plesiastrea versipora are common. The sites differ in the presence of Caulerpa brownii, Caulerpa longifolia and Cladophora prolifera at Halfmoon Bay and higher abundances of P. versipora at Ricketts Point.

Biotope description

Grazed barren with crustose coralline algae and PlesiastreaGrazed barrens with crustose coralline algae, stony coral Plesiastrea and small thallose algal patches. Soft coral Erythropodium hicksoni may be present. Grazed by sea urchins.
The description of a reef biotope including Green Coral from Northern Port Phillip Bay. From the Victorian Reef Monitoring Database and Indicators Victorian Reef Monitoring Database and Indicators Document Control Sheet [2]. Note, specific coral biotopes are being classified and will be added later.

The relationship between green coral reef and sea urchins

Sea urchin abundance in northern Port Phillip Bay is not strongly associated with so-called ‘barrens’. The diagram below is adapted from the Port Phillip Bay Sea Urchin Survey 2019/2020. These show three locations from northern Port Phillip Bay. The left hand grids represent urchin abundance and the ‘high’ densities are highlighted in red. The corresponding ‘vegetated’ or ‘non-vegetated’ cover is represented in the right-hand grids. In ten out of 12 instances of ‘high’ sea urchin abundance, the reef was still vegetated.

Melbourne's coral reefs. The best are under threat?

Bare-looking ground with urchins does not mean barren

Calling areas with lots of sea urchins ‘unvegetated’ might not mean they are barren at all. They can be temperate coral reef. In Williamstown ‘The [golden] kelp Ecklonia radiata is only sparse and not a dominant habitat forming algae in [Jawbone Marine Sanctuary, Williamstown]. The green algae Enteromorpha and the encrusting coral Plesiastrea can be important habitat forming biota on the reef.’ [2].

Also in Williamstown, scientists found that octocoral presented a barrier to grazing sea urchins ‘which allowed localised growth of seaweeds on barren ground despite sea urchin (Heliocidaris erythrogramma) densities locally exceeding 40 individuals per m2.’ It’s unlikely to have been a barrier, so much as a functional component of the ecosystem. Two animals (or plants) occurring side-by-side have a relationship that balances out.

Similarly, in Ricketts Point Marine Sanctuary, Caulerpa can be dominant (the green fluffy weed in the foreground of Image B). This is poisonous to sea urchins so when it dominates the urchins go into a kind of torpor and bury themselves under the reef. The system is so dynamic that ‘barrens’ can form in a matter of months as the urchins return to action, then disappear again later (Image A was only 8 months later).

Melbourne's coral reefs. The best are under threat?

Image A: A sponge at Ricketts Point, (Imogen Mannins, 4 September, 2022, from Facebook)

Melbourne's coral reefs. The best are under threat?

Image B: The same sponge (from behind) from 22 January 2022 (Simon Mustoe).

A new threat to green coral reefs in northern Port Phillip Bay

Marine ecosystems in Port Phillip Bay are threatened by the legacy nutrient input (from the Yarra River catchment and Western Treatment Plant) and an almost total loss of resident reef fish. Coral reefs are under the same pressures but they also rely on sea urchins. Sea urchins and coral reefs go hand-in-glove, regulating each others’ abundance.

Scientists at Montague Island in New South Wales have observed that “Preliminary observations suggest that stable populations of herbivorous sea urchins at 5–15 m depth contribute to the success of this coral in sheltered temperate sites”[3].

Are sea urchins really ‘overabundant’, like the scientists are telling us?

The evidence suggests not – at least not in marine parks like Ricketts Point [5]. Even if they are in places, Parks Victoria scientists have admitted that they do not know where the coral reefs are. They also admit, that overlooking our precious coral reefs from their work, is a serious scientific omission. Sea urchins are a principle driver of ecosystem dynamics that keep these ecosystems in balance.

If sea urchins can be over-abundant, so too can kelp or coral. For example, Black (1971) did the first ever surveys of Port Phillip Bay [6]. At that time, she reported that ‘reefs [of] the star coral Plesiastrea occurs in some cases almost to the exclusion of other species.’

Based on a definition of over-abundance used today, this would make green coral a pest.

But the reality is more nuanced. Like urchins, coral is as animal. It forms a relationship with plants and animals around it, to become part of the ecosystem. Scientific papers routinely cite how one animal excludes another, or eats another, but that’s a gross over-simplification of an ecosystem. In reality, corals, urchins, kelp and countless other life forms, create a dynamic structure. There is just as much cooperation as resistance to each other. We have to be very careful pointing the blame for imbalance at one species that we regard as being a pest, before acknowledging the role of all animals together.

Melbourne's coral reefs. The best are under threat?
A patch of green coral reef near the shore at the Teahouse Reef, Ricketts Point Marine Sanctuary. This shows the diversity of colour forms. There are nearly 30 colonies in this one image.

Why are we introducing golden kelp?

Black (1971) found Golden Kelp in only one out of seven monitoring locations at Ricketts Point. Subsequent surveys in 2009 and also found significant cover of coral reef but scarcity of golden kelp [3]. This accords with the findings in Williamstown, that suggest octocoral suppresses urchin abundance. Though again, it’s unlikely to suppress, as much as form a balance with urchins.

So, why are we introducing Golden Kelp to Ricketts Point? Kelp are coral opposites. Kelp shades coral from receiving the sunlight it needs to survive. At what stage does regeneration of Golden Kelp become a new problem? When is it ‘over abundant’ and has be culled to restore coral reefs? Golden Kelp was never dominant at Ricketts Point.

The reasoning behind work being done in our marine parks is questionable.

Another problem is Undaria or Japanese Kelp. Recognised as being among the 100 worst invasive species in the world, it is a nationally significant marine pest, on the Australian Priority Marine Pest List (APMPL). Yet the scientists’ own evidence tells us that Undaria becomes established once urchins are culled [7].

After Undaria first got established last century, Port Phillip Bay’s seaweed forests began to decline. This was well before urchin abundance was considered a problem. Peaks in urchin abundance only started to occur since about 2012, following a break in the millennial drought. The last two years of La Niña won’t have helped but it’s part of long-term cycles. Urchins could not have been the cause of decline in the past, as the two events happened decades apart.

Melbourne's coral reefs
A Port Jackson (which eats sea urchins) swims between an overhang of Golden Kelp and an area of bare ground festooned with green coral and sea urchins. Is this too many sea urchins? It’s a question that has yet to be answered.

Let’s recognise Melbourne’s precious green coral reefs

Before we start majorly tampering with animal culls we need to recognise our coral reefs. Why not make it your mission to learn more about our temperate coral reefs this year? They are easy to see just offshore.

Meanwhile, is it wise to call ‘a ‘pause’ on the ill-founded introduction of kelp? Our precious green coral reefs might face this new threat, one of our own making. Our efforts to restore habitat by over-stating the threat of urchins too, may further imbalance the ecosystem we are trying to protect.

A leading Parks Victoria scientist has even said they would rather see Undaria beds than barrens. The logic seems to be that Undaria at least provides habitat. But that’s the point. Some habitats, including coral reefs, look barren when they are in actual fact thriving. Equally, habitats that look pretty and are thriving can be poor.

Most of all, how can we proceed to manipulate our marine park ecosystems with honesty or integrity, after admitting we have no knowledge of where the most precious of Melbourne’s coral reefs are even situated?

References

  1. Burgess SN, McCulloch MT, Mortimer GE, Ward TM (2009) Structure and growth rates of the high-latitude coral: Plesiastrea versipora. Coral Reefs 28:1005–1015
  2. Edmunds, Matt & Flynn, Adrian. (2016). Victorian Reef Monitoring Database and Indicators Victorian Reef Monitoring Database and Indicators Document Control Sheet. 10.13140/RG.2.2.30760.49926.
  3. Barton, Jan, Pope, Adam and Howe, Steffan 2012, Marine protected areas of the Victorian embayments bioregion part 1: Port Phillip Bay Parks Victoria, Melbourne, Vic.
  4. Edmunds M, Stewart K and Pritchard K (2009) Victorian subtidal reef monitoring program: the reef biota in the Port Phillip Bay Marine Sanctuaries. Parks Victoria Technical Series No. 67. Parks Victoria, Melbourne.
  5. Graham, T., Carnell, P. & Warren-Myers, F. (2020) Port Phillip Bay Sea Urchin Survey 2019/2020. The University of Melbourne and Deakin University.
  6. Black, H.J. (1971) Port Phillip Bay Survey 2. Memoirs of the National Museum of Victoria. 32. pp 129-170.
  7. Carnell, Paul & Keough, Mick. (2014). Spatially variable synergistic effects of disturbance and additional nutrients on kelp recruitment and recovery. Oecologia. 175. 10.1007/s00442-014-2907-9.
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