HERON ISLAND

The Great Barrier Reef has earned its place as one of the great wonders of the world. Visible from space, it is 2,300 km long and comprises of 2900 reefs and 900 islands to explore.

The Great Barrier Reef started to develop approximately 600,000 years ago and a combination of physical and biological factors made conditions suitable for the growth of many types of coral species (450 known hard coral and 150 soft coral species) over geological time.

Heron Island forms part of the Capricorn Bunker group of reefs located at the southern end of the Great Barrier Reef. The vegetated cay island was named after the bird species, the reef heron, recently renamed the eastern reef egret (Egretta sacra). It has taken 11,000 years to develop.

The reef around Heron Island is a type of shelf reef. Its location and exposure to the elements: waves, wind, ocean currents, climate and extreme weather events, have contributed to the type of coral, plant and animal species that inhabit the reef. Induced pressure from animal activity, for example, grazing and colonisation, play a part in its continual growth.

Heron Island attracts a population of 900 of the 1625 species of fish inhabiting the Great Barrier Reef, for example, parrotfish, butterfly fish, trevally, wrasse, triggerfish and sea perch.

Parrotfish are interesting to observe. Some researchers have made mistakes in the past, identifying species due to an anomaly not apparent in other fish species. For instance, the ability of parrotfish to change gender (sequential hermaphrodite) and colour (polychromatism) throughout their lives. Most species start as plain coloured, small females (initial phase) and at certain points in their lives, transform into bright coloured, large males (terminal phase).

The parrotfish diet consists of algae, scraped off coral by using specialised teeth. The coral remains are excreted from the fish as sand. Research studies estimates these fish produce 30% of the sand around reefs and are one of the marine animals that play an important role in maintaining coral reef health.

At night some parrotfish species have been observed to envelope themselves in a cocoon of mucous. Apparently, the cocoon masks their scent from reef predators, like the moray eel (Family Muraenidae).

Nests made by wedge-tailed shearwaters (Ardenna pacifica), bridled tern (Onychoprion anaethetus) and the black noddy (Anous minutus) bird species can be spotted all over the island. The nesting burrows of shearwaters, shelter chicks waiting for their parents to return with food. Other species that live and breed on the island all year round include the buff banded rail (Gallirallus philippensis), the eastern reef egret (Egretta sacra), bar shouldered dove (Geopelia humeralis), black-faced cuckoo-shrike (Coracina novaehollandiae), capricorn silver eye, sacred kingfisher (Todiramphus sanctus), white-bellied sea eagle (Haliaeetus leucogaster), the silver gull (Chroicocephalus novaehollandiae), and migratory and visiting bird species. Black noddies are the pretty black and white birds that nest in the pisonia trees (Pisonia grandis).

These forests produce a sticky sap, which can unfortunately, trap black noddies, supplementing the cycle of nutrients from guano and plant material. You can also find screw palms, casuarina, she oak and other plant and grass species as you wander around the island.

If you’re visiting Heron from November to January, loggerhead turtles (Caretta caretta) and green turtles (Chelonia mydas) make their way slowly onto beaches at night to lay their eggs. The turtle’s sensitivity to any artificial light (torches etc.) can distract or disorientate them. Moving too close to a nesting turtle might also cause them to panic, so it is recommended to maintain a safe distance of approximately 10 metres away. Just listening to them breathing in the darkness while they lay their eggs is an amazing experience.

Heron Island is but a small microcosm of the Great Barrier Reef, which forms the biggest tropical Marine Reserve and the largest protected World Heritage Area. It may have taken its time to develop into the extraordinary beauty it is today, but wasn’t it well worth the wait.

Please take a look at the University of Queensland’s Centre for Marine Studies link for a bird’s eye view of Heron Island.

http://www.science.uq.edu.au/content/facilities/hirs-virtual-tour/

Written by Gabrielle Ahern

Salty Wave Blue – Into all things ecology.

http://www.saltywave.blue

Follow @SaltyWaveBlue on @Instagram and @Twitter

If you would like to see images of marine life in coral reef environments, please take a look at my Pinterest site: https://www.pinterest.com/saltywave

Book

Photographic Field Guide: Birds of Australia. An Australian Museum / Reed New Holland Publication. Text by Jim Flegg. 2006. Second Edition.

These links provide some great views, photographs, videos and information about Heron Island and the Great Barrier Reef.

Reef Biosearch

http://www.greatbarrierreefs.com.au/parrotfish/

National Geographic

http://animals.nationalgeographic.com.au/animals/fish/parrot-fish/

Onboard – The Tourism Operators Handbook for the Great Barrier Reef

http://onboard.gbrmpa.gov.au/home/marine_park/what_makes_the_reef_special

Heron Island – Great Barrier Reef

http://www.heronisland.com/Turtles-and-Birds.aspx

Caitlin Seaview Survey – An underwater view of the coral reefs around Heron Island

http://catlinseaviewsurvey.com/panorama/?url=http%3A%2F%2Fembed.panedia.com%2Fvst%2Fuwe%2Fvstplayeruwe%3Fmulti%3Dpypmmntf%26map%3Dtqvqslkj%26start%3D600463&call_type=internal&start_url=surveys/great-barrier-reef-and-coral-sea/heron-island

GHOST NETS

Commercial fishing boats have negatively impacted wild fisheries with nets that don’t discriminate between size class and the reproductive maturity of fish species. Most boats are equipped with technology that target a school of fish, with one catch potentially wiping out the next generation, leaving some populations depleted or completely destroyed. Recovery takes a while, and the disappearance of key stone species over time affects the collective ecology and abundance of marine animals and plants. Each year approximately 640,000 tonnes of fishing gear and nets are discarded by the fishing industry. Is it game, set and match in the world’s oceans?

Conservation of the Reef along the east coast of Australia with the Great Barrier Reef Marine Park has made a huge difference to the abundance of tropical reef fish and other marine life. ‘No take’ and ‘take’ zones guide recreational and commercial fishers to places where fish and crabs etc., can be legally caught.

The ‘no take’ zones allow animals to breed without fishing pressures, which in turn increases the numbers of wild fish available in ‘take zones’. Marine Parks around Australia’s coastline and worldwide, continue to positively affect marine life abundance and diversity, supported by community awareness campaigns.

More people are investing their expertise and knowledge into aquaculture as a sustainable alternative to the wild caught fisheries. There are a range of methods used to breed fish, crustaceans, shellfish and algae for restaurants and the markets, in fresh water or saltwater aquaria/ponds. Similar to any competition, aquaculture has encountered its fair share of criticism; but improved technologies have made it more commercially viable.

Nets abandoned by fishing crews, continue to make a big haul at sea though, fatally trapping whales, dugongs, fish, crocodiles, sea birds, sharks, seals and dolphins, as they drift along the oceans currents. Recently, a spate of shark attacks along beaches prompted the introduction of drum lines in New South Wales to curb the risk to surfers and swimmers. Drones equipped with cameras are currently being trialled to alert authorities if shark activity is observed along beaches. This method combined with drum lines is considerably less threatening to marine species, compared to the use of nets.

Turtles and seabirds recurrently swallow or are entangled by fishing line, tackle, plastic debris and nets, despite efforts led by community groups like Clean Up Australia to remove marine debris and rubbish in general. One of the hotspots for discarded fishing nets is the Gulf of Carpentaria in Australia’s north. Seven species of marine turtle are listed as threatened, including the Hawksbill, Green, Olive Ridley, and Flatback turtles. Ghost nets are the common cause of death.

Ghost nets are a serious environmental hazard, not just to animals, but also to anyone going out on a boat. A net can jam an engine. If you spot an injured animal, please contact a wildlife rescue association or a veterinary clinic for assistance; and safely throw discarded nets or tackle into a bin. It’s just one thing to do, but if we all do it, this deadly game out at sea might be over for good.

Written by Gabrielle Ahern

Salty Wave Blue – Into all things ecology.

http://www.saltywave.blue

Follow @SaltyWaveBlue on @Instagram and @Twitter

If you would like to see images of animals like turtles, rays, whales and seals in their marine environment, please take a look at my Pinterest site: https://www.pinterest.com/saltywave

COLOUR OF CLAMS

Clams and their beautiful coloured mantles are just one of the many amazing marine animals that attract millions of visitors each year to the Great Barrier Reef. I studied clam populations on reefs around Heron Island as an undergraduate Marine Studies student at the University of Queensland. It was a great opportunity to observe the variation in mantle colour across reef locations.

Clams belong to Class Bivalvia, Family Tridacnae, and range in size from 15 cm long in Tridacna crocea to more than one metre long in Tridacna gigas. Similar to corals, zooxanthellae (Symbiodinium microadriactum) live inside a clam’s tissues. These symbionts can also be found in gorgonians, sea anenomes and jellyfish. These zooxanthellae are the reason why clam behaviour is often compared to plants.

Just like plants, clams need sunlight. In the mantle, clams possess what are known as, eyespots or iridophores. These pigment cells can sense light conditions and trigger a response in the clam. For instance, if light is poor, the clam improves conditions for the zooxanthellae to photosynthesise by extending its mantle out or using its shell to reflect sunlight back onto the mantle, by holding its valves wide apart. If sunlight is too intense, the iridophores also protect the clam’s zooxanthellae from harmful ultraviolet radiation by reflecting light away.

Mantle colour of clam species is a poorly researched topic. The notion that mantle pigmentation in clams differs in clams across a coral reef has not been researched widely. Interestingly, studies have shown clams are sensitive to the blue (450nm), blue-green (490nm) and ultraviolet (360nm) colours in the spectrum. Light quality on the reef may affect mantle colour, with clams expressing different pigments, or perhaps a clam’s genetic adaptation to a particular reef habitat influences the type of zooxanthellae inhabiting its mantle tissues. I noted a trend in colour for different reef zones during my fieldwork and related this data to previous reports, which have suggested clams might share symbionts with other invertebrate species in a particular zone.

Further investigation into the mantle colour of clams by applying molecular biology might reveal why particular colour patterns occur. Research could also concentrate on how clams can adapt to changing light or temperature conditions by genetic variability.

Clams are quite a stable organism and can adapt to changes in their habitat over time. However, fishing pressure has dramatically reduced populations of clams in the pacific region, leading to the extinction of several species. Conservation methods that use aquaculture assist the remediation of wild clam populations on the reef and supply aquariums with different species.

Clams are interesting to observe in their natural environment. During my research, I noted variations in colour mantle between clam populations across the reef zones and between the two sites on Heron Island. While your exploring the reef, it is definitely a feature worth looking out for.

For more information, check out the world-wide-web.

Written by Gabrielle Ahern

Salty Wave Blue – Into all things ecology.

http://www.saltywave.blue

Follow @SaltyWaveBlue on @Instagram and @Twitter

If you would like to see beautiful images of clams in their coral reef habitat, please take a look at my Pinterest site: https://www.pinterest.com/saltywave

COCONUT CRAB

A visit to the tropics would not be the same without seeing palm trees and coconuts along the beach. Palm trees are home to a lot of different animals but one in particular stands out. The coconut crab (Birgus latro) is the largest land living arthropod in the world and is related to the hermit crab. It is also known as the robber crab or palm thief.

These crabs are known for climbing up a palm tree holding a coconut. Using their strong legs, they drop the coconut to the ground to open the husk and access the coconut flesh. Getting down is no problem because the crab simply drops off the palm tree, surviving falls of at least 4.5 m unharmed.

Its only similarity to the hermit crab involves inhabiting snail shells to protect their soft bodies as juveniles. But as an adult, the coconut crab discards the shell to develop a tough exoskeleton. This is the reason why coconut crabs grow so large, with leg spans of 1 m and body lengths of 40 cm.

Coconut crabs populate the islands around the Indian Ocean and central Pacific Ocean, especially where coconut palm trees grow. Not much information is known about these populations, with the IUCN listing the species as being ‘Data Deficient’. Conservation plans are underway to protect the coconut crab to develop a better understanding about their ecology.

Coconut crabs live in burrows and rock crevices, lining them with coconut husks. Their large pincer claw blocks the entrance to maintain a moist environment. Their burrow protects them while moulting their exoskeletons for 3 to 16 weeks or to reduce water loss from heat during the day.

Coconut crabs have no natural predators, aside from humans and other coconut crabs. Some studies have suggested their activity is affected by the presence of humans. Instances of crabs being attacked by rats on some islands has been reported, but coconut crabs also kill and eat rats. Apart from coconuts and rats, the crab’s diet includes, fruit, nuts and carrion. They use their strong sense of smell to locate food.

Coconut crabs live on the land all their lives. During mating season the female returns to the beach during high tide to release her fertilised eggs. Once hatched, the larvae experience several stages of development while in the plankton, and are prey for many animals.

After several weeks, the juveniles drop to the sea floor and return to the shore, where they find an empty snail shell or broken pieces of coconut shell as shelter. They gradually lose the ability to live in water and reach maturity after 5 years. The coconut crab can live for quite a long time, nearly 60 years.

Written by Gabrielle Ahern

Salty Wave Blue – Into all things ecology.

http://www.saltywave.blue

Follow @SaltyWaveBlue on @Instagram and @Twitter

If you would like to see images of animals in their marine environment, especially coconut crabs and hermit crabs, please take a look at my Pinterest site: https://www.pinterest.com/saltywave

References

http://www.bbc.com/earth/story/20141208-huge-crabs-that-munch-on-coconuts

http://www.christmasislandwildlife.com/crabs.htm

https://en.wikipedia.org/wiki/Coconut_crab

http://phys.org/news/2012-11-gain-insights-behaviour-coconut-crab.html