LEMON SHARKS

The barrier reef around Heron Island attracts many marine vertebrates, among them various members of the Class Condrichthyes, who hold the mantle of keystone predator.

At birth the lemon shark, Negaprion acutidens (Carcharhinidae), measures 60 – 65 cm in length and can grow to 380 cm TL (male). The average size of a litter is 6 – 12 pups. The lemon shark is an active predator, whose behaviour is affected by the different conditions of its environment, for example, water temperature, currents, prey in the area and time of year, to name but a few. Its habitat includes tropical, shallow inshore and offshore waters in coral reef, lagoon and mangrove estuary environments.

Species within the Carcharhinid family have a complex social and reproductive behavior as compared to other families of shark. Studies have revealed the reef shark is geared to learn about its reef habitat due to a more developed telencephalon in the brain.

With growing maturity the lemon shark’s diet has been observed to change. As juveniles they feed on teleosts, crustaceans and molluscs around shallow waters, but as adults, they switch to teleost and cartilaginous fish in pelagic waters. This may reflect the change in visual pigments, which occurs, rapidly enhancing its ability to hunt prey at night, along with its developing olfactory senses and important electro receptive ability. After hunting for prey all night, sharks seek shelter in the reef during the day.

Adult sharks hunt in pelagic or open ocean environments, while juvenile sharks hunt opportunistically during the day and twilight close to shore in the reef lagoon. Sharks have been observed to work as a group when hunting for food. They herd schools of reef fish toward the shoreline and with nowhere else to go the fish are vulnerable to attack. The sharks complete their hunt by ram feeding on the cornered fish.

Lemon sharks do not feed on a regular basis. They eat on average 2.68 % of their own body weight in short bursts and invest more time in digestion. Their stomachs are usually voided within 25 – 41 hours. The voiding mechanism is executed by the scroll valve, which everts to flush out any parasites.

Studies suggest a combination of factors: the sharks coral reef habitat, competition between different parasite species and the number of parasites living on a shark, contribute to the demise of a shark’s health, leading in some cases to its early death. Despite the sharks efforts to reduce the chance of infection, opportunities for parasites to infect a shark are increased by the shark’s own behavior, for example, its hunting location and the type of fish it consumes.

Lemon sharks remain connected to a specific coral reef habitat throughout their lives. The IUCN Redlist has listed the species as Vulnerable. By nature they are quite a shy animal but dangerous if provoked. Current threats to lemon shark populations include: shark fisheries, dynamite fishing, pollution and mangrove deforestation due to its limited home range.

Lemon sharks are really fascinating animals, and if you would like to know more about their biology and ecology, please refer to the following sources of information, local library or 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 images of sharks in their marine environment, please take a look at my Pinterest site: https://www.pinterest.com/saltywave

Web Links

IUCN Redlist

http://www.iucnredlist.org/details/41836/0

Wildscreen Arkive

http://www.arkive.org/sharptooth-lemon-shark/negaprion-acutidens/

FishBase

http://www.fishbase.org/summary/896

Atlas of Living Australia

http://bie.ala.org.au/species/urn:lsid:biodiversity.org.au:afd.taxon:6f8bfc6c-b9ef-4bc5-8808-ae02105cb3f2#

FANTASTIC PLASTIC

Going for a walk along the beach is something everyone loves to do. I like to go for a swim, do some fishing or just take photos.

Footprints along a beach. Photo ©  Stefan Villiger

Unfortunately, some beaches are littered with rubbish washed in with the tide or from illegal dumping. Research by the CSIRO has found three quarters of the rubbish floating in waters off the Australian coast is plastic and its density ranges from a few thousand pieces to more than 40, 000 pieces of plastic per square kilometre.

The type of plastic items people find on beaches. Photo © Chris Richardson

This is an incredible amount of plastic but high demand for plastic goods has increased the occurrence of this kind of debris in our oceans and the resulting negative impacts to marine life and their habitat. Leather back and green sea turtles often mistake floating plastic bags for a jellyfish. Due to the animal’s unique anatomy, the bags lodge in their throat or stomache, with the animal eventually dying from starvation.

Image of a plastic bag. Photo © Auke Jongbloed

Sadly, this is also the case for other marine wildlife like sharks and birds. CSIRO have reported 67% of short-tailed shearwaters inhabiting waters along Australia, New Zealand and the Southern Ocean consume plastic items, such as, rubber, foam, string and glow sticks, as the birds mistake it for their natural prey, while foraging out at sea. Negative effects on marine animals are not just isolated to stress from swallowing plastic and starvation; they include the chemicals the animals can absorb into their bodies.

Beautiful Australian beach. Photo © Gabrielle Ahern

The Australian government and local councils provide opportunities for recycling. For instance, at refuse stations, apart from your rubbish, you can drop off metal, plastic, electrical goods or green waste. Shops in some states in Australia have stopped providing plastic bags as an incentive for consumers to bring their own. This is working but people still rely on plastic bags because they are a fast and easy solution.

The fantastic plastic mix over land and sea can make way for its more natural counterpart if:

•    community awareness programs increased,

•    new environmental and maritime laws were introduced, and

•    alternative products to plastic were made more accessible and affordable.

Marine debris. Photo © Elvis Santana

But in the meantime, everyone can contribute to conservation in simple ways.

•    Use an alternative to plastic bags, cups, straws, etc. Lots of people do this already, which is great.

•    Take part in a conservation project during a holiday, gap year or any time you want to, locally or overseas. For example, look after animals in Africa; survey turtles at Mon Repos in Queensland; assist research about Ningaloo Reef in West Australia; or contribute to studies about the Amazon rainforest, just as a suggestion.

•    Throw discarded nets or fishing lines into the rubbish.

•    Change the way you do things at home, at work or in general.

Australian beach. Photo © Gabrielle Ahern

Plastic debris floats like a small island of destruction. It is ironic that people risk their own lives daily to save marine wildlife and their habitats, and a lot of people do the right thing by the practices they follow, but long term, so many more animals suffer in silence, thanks to these discarded souvenirs of modern convenience.

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 reptiles like turtles in their marine environment, please take a look at my Pinterest site: https://www.pinterest.com/saltywave

Links to some great community based organisations involved with marine conservation & clearing the oceans of plastic debris.

Take 3: http://www.take3.org.au/main/page_home.html

Take 3 is a not-for-profit organisation formed in Australia in 2009 that aims to raise awareness of plastic pollution (marine debris) by encouraging each visitor to the beach, waterway or…anywhere to simply take 3 pieces of rubbish with them when they leave and dispose of it thoughtfully. We also encourage everyone to reduce unnecessary plastic consumption – and make our lives a little less plastic!”

Project Aware: http://www.projectaware.org

Project AWARE Foundation is a growing movement of scuba divers protecting the ocean planet – one dive at a time. We’re focusing in on two major ocean issues –Sharks in Peril and Marine Debris, or trash in our ocean.”

Surf Rider Foundation: http://www.surfrider.org.au

Surfrider Foundation Australia is a registered not for profit sea-roots organisation dedicated to the protection of Australia’s waves and beaches through Conservation, Activism, Research and Education C.A.R.E.”

SALTY FORESTS

Mangrove trees gnarled and bent appearances reflect the dynamic conditions they live in. Not many plant species can survive such a harsh marine environment. These salty forests are constantly exposed to the elements during low tide events and inundated by salty water during high tide. But these extremes play to their favour, and for many animals, mangroves are nurseries, shelter and food.

Mangrove forest at Nudgee Beach. Photo © Gabrielle Ahern

The exposed roots and tree trunks of mangroves provide habitat for juveline fish species like the mudskipper (Periophthalmus spp.,) mangrove jack (Lutjanus argentimaculatus), barramundi (Lates calcarifer), snapper (Pagrus auratus), blue threadfin (Eleutheronema tetradactylum), sea mullet (Mugil cephalus) and bream (Acanthopagrus australis).

Australia is home to a great diversity of mangrove species with 22 genera from 19 plant families containing 41 species. Some of the more common varieties that thrive along the foreshores of estuarine, riparian and wetland areas include Avicennia integra (endemic to Australia only), River Mangrove (Aegiceras corniculatum), Grey Mangrove (Avicennia marina), Orange Mangrove (Bruguiera gymnorhiza), Yellow Mangrove (Ceriops australis) and the Spotted Mangrove (Rhizophora stylosa).

Mangrove trees growing at Nudgee Beach. Photo © Gabrielle Ahern

Mangroves are similar to coral reefs, in that they are nutrient poor. So what is the secret to their success?

The secret is a combination of factors. One of these factors involves anaerobic bacteria in the sediment, which helps breakdown leaf litter produced by the mangrove trees, providing food to other animals. For example, mangrove or mud crab (Scylla serrate), mud lobster (Thalassina anomala), banana prawns (Penaeus merguiensis), king prawns (Penaeus plebejus), mudwhelks (Pyrazus ebininus), mangrove oysters (Saccostrea commercialis) and barnacles (attached to tree trunks and roots), plankton, pistol shrimps and polychaete worms.

High tide inundates the mangrove forest creating protected nurseries for fish, crustaceans and sharks.
Photo © Gabrielle Ahern

Larger animal species that inhabit mangrove communities include estuarine crocodiles (Crocodylus porosus listed as vulnerable under the NC Act), white-bellied mangrove snake (Fordonia leucobalia), little file snake (Acrochordus granulatus), and lizards: mangrove monitor (Varanus indicus) and rusty monitor (Varanus semiremex).

Mangroves are linked to other marine and terrestrial communities (salt marshes, estuaries, freshwater wetlands and coral reefs). The moving tides transport food from mangrove sites to communities deficient in carbon.

Mangrove trees are opportunists and take advantage of space along the coastline to establish forests.
Photo © Gabrielle Ahern

Over thousands of years, deposits of iron sulphides have formed in the sediments around mangrove communities, as a result of an interaction with sulphides in seawater, which is rich in iron oxide and organic matter. The very conditions mangroves need to grow in. The fact this system successfully traps toxic acid sulfate soils and is trophically linked to other animals and plant systems, emphasises the importance of mangroves.

Unfortunately, mangrove communities have been managed badly. There are examples of mangroves being used as dumpsites for rubbish or removed to advance the development of urban, marine, mining, industrial and agricultural development.

If mangrove trees are removed, the sediments are exposed to the air, with sulphuric acid forming when oxygen reacts with iron sulphide. The reaction is catastrophic to the fine balance of marine ecosystems. Toxic chemicals leach into the water, causing widespread fish kills and long-term negative impacts to invertebrate communities. Their removal destroys breeding grounds, shelter, sources of food, disrupts the normal behaviour of animals that inhabit them and the environmental processes that protect the landscape.

Nudgee Beach boardwalk meanders through the mangrove forest. There are places along the way to enjoy the views, listen to the sounds and spot a few crabs in the mud. Photo ©  Gabrielle Ahern

There are some beautiful walks that meander through these salty forests. Some of the inhabitants you might spot depending on the time of day / night or where you are located include the black flying-fox (Pteropus alecto), little red flying-fox (Pteropus scapulatus), and the grey-headed flying-fox (Pteropus poliocephalus listed as vulnerable by the EPBC Act); and the false water rat (Xeromys myoides).

Migratory birds use these areas as breeding grounds, and for some species, they are a permanent home. Some of the birds inhabiting mangroves are: egrets (Ardea species), Australian white ibises (Threskiornis molucca); royal spoonbills (Platalea regia); cormorants (Phalacrocorax species); mangrove robin (Eopsaltria pulverulenta); mangrove golden whistler (Pachycephala melanura); white-breasted whistler (P. lanioides); broad-billed flycatcher (Myiagra ruficollis); shining flycatcher (M. alecto); mangrove gerygone (Gerygone levigaster); red-headed honeyeater (Myzomela erythrocephala); varied honeyeater (Lichenostomus versicolour); black butcherbird (Cracticus quoyi); lorikeets (subfamily Loriinae) and Australian pied imperial pidgeons (Ducula bicolor).

Shorebirds are a familiar presence. The mangroves provide valuable shelter and food.
Photo © Gabrielle Ahern

Mangroves are remarkable for their strange bent over shapes and the plethora of animals and plants that thrive in their forests despite the extreme conditions they are exposed to. For more information about mangroves and their interesting biodiversity, please check out the following links or references.

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 mangrove forests, please take a look at my Pinterest site: https://www.pinterest.com/saltywave

Online Resources

Mangrove Watch Australia

http://www.mangrovewatch.org.au/index.php?option=com_content&view=category&layout=blog&id=52&Itemid=300137

Accessed: 18 February 2016

The Encyclopedia of Earth – Wetlands Mangrove Ecology

http://www.eoearth.org/view/article/159955/

Accessed: 18 February 2016

Mangroves of Australia by the Marine Education Society http://www.mesa.edu.au/mangroves/mangroves04.asp

Accessed: 18 February 2016

SAND DUNES

North Stradbroke Island may be a sand dune island but it harbours an interesting, if not unique array of plant ecosystems. North Stradbroke Island is located 40 kilometres east of Brisbane, approximately 270 36’ 31. 32” S 1530 26’ 40. 12” E and enjoys a subtropical coastal climate.

The dune islands slowly formed over thousands of years, as layers of sand were gradually deposited by both changes in sea level and strong winds from the South East. Some of the corals that are found underneathe the fresh water lakes on North Stradbroke Island can be dated between 119 to 132 thousand years ago. It is second to Fraser Island as the largest sand island in the world, 38km long and 11 km wide. It is also the largest sand dune island in a chain that forms a protective barrier around Moreton Bay.

In the geological past, North Stradbroke Island was connected to the mainland via land bridges. These bridges enabled the spread of many plant species. Over time, sea level rise gradually isolated the island. The plants spread out and diversified, forced to adapt to the islands unique geomorphology and climate. Today, the island harbours approximately 450 plant species.

North Stradbroke Island represents a range of ecosystems. For example, there are about 6 sand systems, some dating back as far as 120 thousand years ago. Sand dunes form when wind blown sand is trapped by vegetation to form ridges. These ridges protect the small gullies below. Beach Spinifex (Spinifex sericeus), Pig Face (Carpobrotus glaucescens) and Beach Primrose (Oenothera drummondii) are species common to the outer edge of a dune community and play an important role in stabilising the sand.

Beach spinifex are perfectly suited to the dynamic environment of a dune, their structure and function have been shaped by its harsh conditions. But you might wonder how any plant could survive in such a nutrient poor environment like a sand dune. The reason? Its symbiotic relationship with a fungi species. These fungi grow all over the root system of the Spinifex. They fix the nutrients (except nitrogen) covering small grains of sand and pass these nutrients onto the Spinifex. This relationship is similar to coral species’ partnership with zooxanthellae (a microscopic algae that shares the products of photosynthesis, sugar, with its coral host).

Coastal Wattle (Acacia sophorae) and Coastal Sheoak (Casuarina equisetifolia) grow in dense communities and are protected by the sand ridges that form along the dunes. Coastal Wattle is an Australian native spreading shrub, considered to be a pioneer species that populates coastal sand dunes. Its success is based on its association with a nitrogen fixing soil bacteria called Rhizobium. The bacteria are present in root nodules, a formation on the roots initiated by the bacteria. The Rhizobium fix the atmospheric nitrogen present in sediment and make the nitrogen available to the shrub in a form the plant can absorb. In exchange, the Rhizobium receives the products of photosynthesis, sugar, from the plant. Coastal Wattle usually grows to a height of 3 metres and can spread out to between 10 to 15 metres.

Coastal Sheoak also fix nitrogen in the sediment through its symbiotic association with a species of fungi called Mycorrhizal. Sheoak grow quite densely in dune communities and probably owe their success to their ability to use leaf litter to their advantage quickly.

Sand dune ecosystems like the ones located on North Stradbroke Island are an amazing example of how the plants exposure to the elements has affected their adaptations to survive. The dune communities highlight their fragility and emphasise how important plants are to the health of marine and terrestrial ecosystems.

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 sand dunes and tropical islands, please take a look at my Pinterest site: https://www.pinterest.com/saltywave

References

Stradbroke Island – Official Website

http://stradbrokeisland.com

Australian Plants – A Simple Botany of Wattles                  

http://anpsa.org.au/APOL8/dec97-1.html

Australian National Herbarium – Australian Fungi 

http://www.cpbr.gov.au/fungi/mycorrhiza.html

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