Mediocre Fringing Reefs

Mediocre Fringing Reefs (MFR) or the Inshore Reefs of the GBR

A fringing reef near Bowen

The GBR is famous throughout the world but there are other corals along the Queensland coast that are not nearly as spectacular. These will be referred to as the Mediocre Fringing Reefs (MFR) to distinguish them clearly from the offshore Great Barrier Reef. The MFR are the very small reefs that occur in isolated patches along the mainland coast; they are also to be found on some of the islands. They are called “fringing” because they are on fringes of the land. Most biologists call these reefs the “Inshore Great Barrier Reef” because they are all close to the land.

This is in contrast to the “Offshore” reefs that are what most people would call the GBR. The GBR is a long way from the coast. But the name, “Inshore”, which is perfectly reasonable to describe the fringing reefs, has been responsible for a great deal of misinterpretation when statements are made about possible damage to these reefs.

If there is any damage to corals caused by sediment and pesticides washing off farms, it could only occur on these inshore reefs. They are the frontline when it comes to the effects of pollution. The “Offshore” reefs are too far away. The problem is that the name, “Inshore” Great Barrier Reef, implies that these reefs are a major part of the GBR. The inshore reefs are, however, tiny and mediocre in appearance in contrast to the rest of the GBR. The term, Mediocre Fringing Reef (MFR), underlines the point that the inshore reefs are not Great in area or quality, and are not a Barrier either. Even the MFR are barely affected by human influence (See chapters 4, 5 and 6).

The Mediocre Fringing Reefs such as Paluma Shoals shown in Figure 2.7 are usually very small, often not much bigger than a few tennis courts. Tiny compared to the huge reefs of the GBR, they are much too small to see in Figure 2.3. The water is shallow and the coral rarely goes deeper than 10 metres compared to more than 50 metres for the GBR which can be 100 km further offshore. The total coral on the MFR is very small – perhaps no more than one or two percent of the coral on the GBR although, surprisingly, there has never been a published detailed measurement of their total area.

The corals of the MFR are also often visually mediocre in comparison to the GBR,[1] and often hard to see because the water is rarely sparkling clear as it is on the GBR, which is bathed in the deep clear waters of the Pacific. Instead, waves stir up the sea bed of the shallow MFR reefs making visibility often less than a couple of metres – not a good place to take tourists snorkeling. The coral species are often very different from the GBR as they have to be tolerant to lots of mud. They also have to deal with hotter water in summer and colder water in winter because the shallowness of the water allows much greater swings of temperature swings to occur.[2] If nothing else, the MFR demonstrate that corals are not like a “canary in a coalmine.” They form robust ecosystems that can live under very adverse conditions, in many cases with very high coral cover.[3]

Figure 2.7 Paluma Shoals. A very Mediocre Fringing Reef north of Townsville. Waves stir the naturally muddy seabed. It is not a place to take tourists but it is a heathy reef and some parts have very high coral cover. Biologists often claim that reefs and shoals like this have been damaged by mud from farms and dredging, but geological evidence indicates they were always dirty reefs (see sediments section). (Photo: Piers Larcombe)

Tourist boats zoom past the isolated coral of the MFR on the way to the GBR. The MFR is very close to the coast, so these corals are occasionally covered by plumes of water coming from flooding rivers, and from mud stirred up by dredges. It is claimed that erosion of mud and pesticides from farms flows into the rivers and is ultimately affecting the MFR. The following chapters will show this is unlikely, but an important point is that the MFR are a very small area. Even if the influence of farm pollution and dredging on the MFR is significant, it only occurs rarely and only on a few of the reefs of the MFR which are, in total, only about one percent of the coral on the GBR.

So, in summary, pollution may be affecting, for short periods, a small fraction of one percent of the coral. This worst-case scenario is hardly the complete catastrophe of the effects of farm pollution and dredging which the world has been told about.

Some scientists have claimed[4] that the growth rate of corals for the Inner reefs of the GBR has declined by five per cent between 1930 and 2008. These scientists split the GBR into three categories; inner, middle and outer. For inner reefs, they measured a five percent reduction, which sounds like it applies to one–third of the Reef. But this inner GBR, the Mediocre Fringing Reefs, is only about one per cent of the coral on the GBR. Thus, in this instance, there is a reduction in growth rate of five percent on a tiny fraction of the reef. This is not nearly so serious as the reported claims suggest.

It should be added that the same scientists measured a growth rate increase of 10 percent for the other 99 percent of the GBR, the “middle and outer” GBR. This is unequivocally a good news story.

It is essential to emphasise that the argument is not that the MFR are not important just because they are not beautiful. Any coral is important no matter where it lives. Most of my work on the GBR has been on the MFR. They might be not nearly as beautiful as the outer GBR reefs but they are still remarkable. But, when thinking of the MFR, a mental picture of the sparkling clear water, brilliant coral, and immense size of the GBR is a serious misconception.

When looking at the various threats to the GBR, it will often be necessary to stress this point. This is because many claims of great damage to the GBR, such as pollution from farm pesticides, apply only to the Mediocre Fringing Reefs, not to the Great Barrier Reef.  The public have been given a completely wrong impression of the scale of the problem.

[1] Perry, C.T. and Larcombe, P. (2003). Marginal and non-reef-building coral environments. Coral Reefs, 22(4), pp.427–432.

[2] Mao, Y. and Ridd, P.V. (2015). Sea surface temperature as a tracer to estimate cross‐shelf turbulent diffusivity and flushing time in the Great Barrier Reef lagoon. Journal of Geophysical Research: Oceans, 120(6), pp.4487–4502.

[3] Morgan, K.M., Perry, C.T., Johnson, J.A. and Smithers, S.G. (2017). Nearshore Turbid-Zone Corals Exhibit High Bleaching Tolerance on the Great Barrier Reef Following the 2016 Ocean Warming Event. Frontiers in Marine Science, 4:224.

[4] D’Olivo, J.P., McCulloch, M.T. and Judd, K. (2013). Long-term records of coral calcification across the central Great Barrier Reef: assessing the impacts of river runoff and climate change. Coral Reefs, 32(4), pp.999–1012.

%d bloggers like this: