Marine Parks help resist invasive pests

Southeast Australia is an ocean warming “hotspot” – a region where temperature at the ocean’s surface is increasing more rapidly than elsewhere. That means this part of Australia is like an outdoor laboratory for understanding nature’s response to climate change. In research published this week in Nature Climate Change, we found that marine reserves in this regional “hotspot” are important in reducing the effects of climate change on different species. As oceans warm, subtropical species migrate into temperate regions. This creates new communities where groups of species may meet for the first time.

One species that has already extended its range is the spiny sea urchin. This urchin has grazed down the seaweed beds attached to rocky reefs as it has moved southward, leaving a swath of barren patches in its path. Habitat reserves protected from fishing within marine reserves appear to deter the urchin. Here, predatory lobsters grow to a size where they can feed on incoming urchins. Marine reserves can also allow a diverse set of predatory fish to develop. These fish may feed on other warmwater migrants, making it harder to colonise the area.

Over 20 years, information has been collected on the fishes from the Maria Island Marine National Park in Tasmania and nearby sites open to fishing. This allows us to look into the past to understand what has changed. With warming water, fishes that eat seaweed have increased in both the protected and fished communities. These herbivorous species are typically limited to more tropical latitudes where warmer temperatures speed their digestion of seaweed. But now they are being seen in areas previously too cool for them. The proliferation of herbivores has led to greater numbers of species in the region as a whole and, because many of these species have new characteristics, also greater diversity in the functional roles species play in these communities.

Communities in the marine reserve also turned out to be quite resilient. The number and diversity of species in the reserve remained more stable from year to year, as well as across decades, when compared to areas that have been open to fishing. Reserves also limited colonisation by warm-water species moving into the area. This might be because the reserves supported the return of large-bodied temperate species, such as the blue-throated wrasse, which may feed on new migrants.

Marine reserves have the potential to buffer climate-related biological variability, as well as to limit the spread of range-extending species. While marine reserves are valuable for creating thriving biological communities, they also help us understand ecological change in the absence of fishing. The new knowledge gained from Maria Island was possible because the long-term data on fish species could be usefully compared against nearby fished areas. If our findings play out in other marine reserves, we can be assured that protected habitat networks will enhance the health of our oceans in an era of human influence and climate change.

Fish stock increasing around Whitsundays MPA

The good news is, despite increasing pressures from fishing and greater stresses on the reef, fish numbers in the Whitsundays have doubled since the 1980s

Source: Catalyst Dr David Williamson

In 1999, about five percent of the Whitsundays marine park area was within no-take zones. In 2004, the reef was rezoned, and now about a third of the marine park, is now protected. The rezoning was highly controversial at the time. There were concerns green reserves would cause remaining areas to be overfished and degraded, but those populations have remained stable. The Whitsundays are high-use tourism places, they’re also very highuse recreational fishing areas. The main target species are coral trout and snapper. Despite heavy fishing pressure, recent research has shown a large increase in coral trout populations, it’s at least doubled within the reserves in the first three to five years. This isn’t that unusual and often happens when you declare a reserve. The surprise was that it also increased fish stocks outside the reserve and appeared to provide a protected breeding population. Scientists are able to sample tissues from adult fish within reserves, compare DNA and find linkages between where the fish end up and where it came from. About 28% of the reef area within the reserves, is contributing about 50% of all the baby fish that are arriving in the sampled island group. It’s a benefit to the genetic and biodiversity of coral reefs, and it restocks areas that are currently fished. One of the other unexpected things that was found with green zones on these inshore reefs is a lower incidents of coral diseases within the areas that are closed to fishing. It is thought that the physical act of fishing and dropping lines on the reef and causing little minute scars on corals, breaking off branches of corals, is causing a site where infections can get in and start to take over the coral. There is up to a sevenfold higher incidents of disease in places that are open to fishing, relative to places that are closed to fishing. The reserve fish are repopulating surrounding areas partly because the big fish in reserves produce more eggs. However, 99% of those are eaten, and rest are swept out to sea where they shouldn’t be making any difference to local stocks. However, it appears that they find their way back ‘home’. Juvenile fish, just a few millimetres long, make a conscious decision on which direction to travel. Some little fish can swim for 120km even without food. Close to the reef they can then smell and hear the reef from about 4km away. There is a whole range of chemistry that comes off reefs. Like, for example, mucus from corals – fish can differentiate between different species of corals, and even their own species. By no means can green (no take) reserves solve all the complex problems ahead for the Great Barrier Reef, but they may give at least some tropical reef species a fighting chance.