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Sydney Rock Oysters – a life under threat

The Sydney Rock Oyster (Saccostrea glomerata) is endemic to Australia and New Zealand and is a quintessential member of Australia’s aquaculture industry. But the life of Sydney Rock Oysters is under threat; increasing anthropogenic pressures on coastal ecosystems have caused wide spread losses of these commercially valuable species2,3,4. In a recent seminar by Doctor Emma Thompson at the Sydney Institute of Marine Science, in conjunction with Macquarie University, she explained her research on the threats and impacts of disease on the Sydney Rock Oyster [Figure 1].

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Figure 1: Sydney Rock Oyster, Saccostrea glomerata

A Rich History of Oysters

The Sydney Rock Oyster has been a commercially important species in Australia and in particular NSW since colonial times. Dr Thompson explains that the lime from mortar used in old Government House was in fact from the shells of ground Sydney Rock Oysters. The first oyster farm was originally set up in the Georges River back in 1872; where even today, Oyster farms still persistent on the Georges River1. Currently Sydney Rock Oysters are the largest contributor in aquaculture and account for half of Australia’s edible oyster production1. This outcome has been as a result of an exponential increase in aquaculture as well as the plateauing of marine capture rates since the 1990’s1.

Factors of Disease

For Disease to take hold of a population, a number of factors must be in place [Figure 2]. Aquaculture is especially prone to outbreaks in disease for a number of reasons; the densities of which animals are grown in aquaculture allows for an ease of transmission between viable hosts1,2. The marine environment also provides an optimal environment for disease transmission, aided by flow regimes and a stable medium2.

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Figure 2: Factors of disease

QX disease and its Implications

The QX disease; originally ‘Queensland Unknown’ (after its origin), is now described as Marteilia sydneyi is one of the potent threats facing Sydney Rock Oyster populations with mortality rates of up to 98% in some instances2. M. sydneyi is commonly found in the gut of oysters, where it is of little concern to the oyster and can be readily killed off by enzymes in the oyster’s blood cells2. It is the enzyme phenoloxidise (PO) that produces melanin, which in turn seeks out and destroys the M. sydneyi parasite2.  The fact that M. sydneyi is quite widespread in Sydney Rock Oyster populations, but QX outbreaks only occur in a number of areas provided an interesting conundrum to biologists. It was determined that a reduction of salinity was inducing an environmental stress great enough to reduce the effectiveness of PO and allow the proliferation of M. sydneyi2. The parasite prevents the oyster from feeding and also attacks the immune system. QX has had massive implications on Sydney Rock Oyster populations, the aquaculture industry and has led to the rapid propagation of the non-native Pacific Oyster Crassostrea gigas2. Pacific Oysters are fast growers and are often able to outcompete their native counterparts; the Sydney Rock Oyster. The competition by the Pacific Oyster has led to the decline of the dominance of the Sydney Rock Oyster and eventuated in a gradual ecosystem shift.

These threats coupled with economic losses led to intervention by the Department of Primary Industries (DPI); who in 1990 introduced a selective breeding program to enhance the survivorship of the Sydney Rock Oyster2. The breeding program has generated a number of highly selected for traits; producing a QX resistant oyster, a winter resistant oyster and a fast growing oyster. Today researchers such as Dr Thompson are constantly monitoring the health of Sydney Rock Oyster populations from a molecular level right through to an ecosystem level changes. Studies have observed effects of metal contamination, ocean acidification, disease and environmental stressors by comparing selectively bred oysters with wild populations2,3,4.

What the future holds

Dr Thompson explains whilst there is still a number of threats facing, the Sydney Rock Oyster’s future is secure; a recent grant with Macquarie University will lead the way for a new molecular study for the Sydney Rock Oyster, including the approval of an entirely new breeding program. This new breeding program will mean the cessation of the current breeding program that had been running for the last 20 years. The new program will create a more scientifically based selective breeding line and prevent potential inbreeding. A study is then planned to determine if this new program will impact wild Sydney Rock Oyster Populations through broadcast spawning. This research will further support the management of the Sydney Rock Oyster and continue its profitability as a key member of Australia’s aquaculture industry.

References

  1. Nell, J.A. 1993. Farming the Sydney rock oyster (Saccostrea commercialis) in Australia. Reviews in Fisheries Science, 1(2): 97-120.
  2. Raftos, D.A. & Peters, R. 2003. The role of phenoloxidase suppression in QX disease outbreaks among Sydney rock oysters (Saccostrea glomerata). Aquaculture, 223(1-4): 29-39.
  3. Parker, L., Ross, P. & O’Connor, W.A. 2009. The effect of ocean acidification and temperature on the fertilization and embryonic development of the Sydney rock oyster Saccostrea glomerata. Global Change Biology, 15(9): 2123-2136.
  4. Thompson, E.L., Taylor, D.A., Nair, S.V., Birch, G., Haynes, P.A. & Raftos, D.A. 2011. A proteomic analysis of the effects of metal contamination on Sydney Rock Oyster (Saccostrea glomerata) haemolymph. Aquatic Toxicology, 103(3-4): 241-249.

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  1. Olivia Garnett.http://www.abc.net.au/reslib/201112/r873198_8536029.jpg

6. Cody Beckley http://glenriddlemaintenance.blogspot.com.au/2010_09_01_archive.html

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Biologging: Keeping Tabs on the Ecology and Behavior of Aquatic Animals

The study of the ecology and behaviour of marine animals can be a difficult task, especially the study of pelagic species. In order to successfully study these creatures an alternate method of analysis must be employed; this method is known as biologging. Biologging is the use of a miniaturized animal attachment tag for logging or relaying data from a free ranging animal1. Whilst the marine environment causes a number of difficulties, biologging still has had a rich history of use in the study of marine species1,2. In a presentation by phD student Stephanie Brodie of UNSW at the Sydney Institute of Marine Science, she outlines a number of uses of biologging; including examples from her own research.

Biologging

The first recorded use of a biologger in the marine realm was in 1964 when Kooyman, attached a biologger to a Weddell Seal in the Antarctic to measure dive capacity1. Since then a biologgers have greatly increased in complexity and decreased in size1,2. Biologgers can be used to detect a number of measurements including depth, temperature, salinity, acceleration and heart rate2.

Brodie explains that today there are four main types of tagging options; Archival: these biologgers store vast amounts of data on board, but require retrieval from the animal1. Another option is satellite tracking; this is used for long term deployments, relaying movements in real time, but require the animal to break the water’s surface in the presence of an overhead satellite1. The last is a Pop-up Satellite Archival Tag (PSAT) and combines both the archival and satellite tags in one; making it both effective, but expensive1. Acoustic telemetry is yet another method of leading the movements of aquatic animals; these biologgers are cheap, long lastly and are often surgically inserted into the animal1,2,4. This method requires an acoustic receiver to record and time stamp the data4.

Cuttlefish Breeding and Acoustic Telemetry

The Giant Australian Cuttlefish, Sepia apama has been of interest for a number of years with population numbers declining rapidly. Acoustic telemetry and accelerometers were used in a study by Payne et al (2010) to determine breeding duration of sexes and to estimate energy expenditure3. Using acoustic telemetry, they found that males were present at breeding grounds for a significantly longer duration than females, in order to mitigate the effects of sexual competition3. Whilst using accelerometers and known biological requirements, metabolic rate can be deduced for the Giant Cuttlefish during breeding season3.

Lifestyles of Yellow-tail Kingfish

Yellow-tail Kingfish are a pelagic fish of considerable recreational and commercial importance in Australia. Stephanie Brodie’s own research project centers on the Kingfish; Kingfish captured, are tagged with accelerometers and swum through a swim tunnel at controlled speeds (Figure 1). Kingfish acceleration and oxygen consumption is then measured, and from this data Brodie has found that increases in swim speed are correlated to increased metabolic rate4. Brodie has then released these animals back into the water; tracking diurnal movements, migrations and metabolic rate. Thus far her results have indicated that a Kingfish need to consume 3% of its body weight in teleost prey per day to cover their complete energy expenditure (movement, growth and reproduction)4.

steph brodie surgery by al moglashan

Figure 1 Stephanie Brodie preforms surgery on a Kingfish, inserting a Biologger: taken by Al McGlashan6.

Marine Mammals as Oceanographers

One of the more unique applications of Biologgers has come from a study in Antarctica, where recent data has shown a new source of Antarctic bottom water. Antarctic bottom water is the cold dense water found at great ocean depths; it is also a vital component in global ocean circulation5. Previously three regions around Antarctica have been described as sources for Antarctic Bottom Water; but using biologgers attached to elephant seals (Mirounga leonine),a fourth location of Antarctic Bottom Water formation has been discovered5. Elephant seals frequently dive to great depths; up to 1800m in some foraging events. Using conductivity-temperature-depth (CTD) sensors, seals were able to map the extent of the Antarctic Bottom Water formation at Cape Darnley5.

Undoubtedly, Biologgers are a fantastic tool for biologists and have applications on the land, sea and in the air. They have enabled us to determine population dynamics, behavioral ecology, assisted in conservation efforts, as well as recent oceanographic applications. Below are a number of references and readings on the history and uses of biologgers in biology.

 

References

  1. Roper-Coudert, Y., Beaulieu, M., Hanuise, N. & Kato, A. 2009. Diving into the world of biologging. Endangered Species Research, 10: 21-27.
  2. Rutz, C. & Hays, G.C. 2009. New Frontiers in biologging science. Biology letters, 5(3): 289-292.
  3. Payne, NL; Semmens, JM and Gillanders, BM. Examination of Giant Australian Cuttlefish ‘Sepia Apama’ Breeding Behaviour through Acoustic Telemetry [online]. South Australian Naturalist, The, Vol. 84: 1, 2010: 38-41.
  4. Brodie, S. 2014. Unpublished data.
  5. Ohshima, K. I., Fukamachi, Y., Williams, G. D., Nihashi, S., Roquet, F., Kitade, Y., Tamura, T., Hirano, D., Herraaiz-Borreguero, L., Field, I., Hindell, M., Aoki, S. & Wakatsuchi, M. (2013). Antarctic Bottom Water production by intense sea-ice formation in the Cape Darnley polynya. Nature Geoscience, 6(3): 235-240.

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  1. Mcglashan, A. http://www.abc.net.au/radionational/programs/scienceshow/img4451jpg/5306964

 

Silencing HIV: a new approach in viral reservoir stabilization

HIV is without a doubt one of the greatest viral threats faced by humanity in the 21st century. With a life cycle  that can be as short as 1-2 days from viral cell infection, the virus is able to replicate and in turn release additional virus cells amongst the host. In combination with reverse transcription, the virus is able to mutate quite rapidly and most threateningly; at high genetic diversity1. In a recent discussion by Doctor Tony Kelleher from the Kirby Institute, UNSW Medicine; in conjunction with Macquarie University Hospital’s medical seminars, Doctor Kelleher explains his cutting edge research into potential HIV treatments.

CART – Combined Anti-Retroviral Therapy

As potential vaccinations for HIV/AIDS are currently some years away, HIV must be treated rather than cured. Today the most predominant treatment for HIV is combined Antiretroviral Therapy or cART2. Doctor Kelleher explains whilst cART is somewhat of an effective treatment it has a number of pitfalls; cART does not impact on the viral reservoir. A viral reservoir refers a cell type or location within the host in which a virus’ replication primarily  takes place; it is more stable than the remaining actively replicating virus1. It is this persistence of a viral reservoir in HIV that makes the virus difficult to both treat and cure. If cART is interrupted chances of morbidity and mortality are greatly increased, meaning that cART is a treatment for life; which in many cases can be problematic towards the individual in treatment2. Furthermore prolonged treatment with cART can lead to potential health issues of its own with an acute toxicity build up with the patient2.

Berlin Patient

The Berlin Patient refers to two individuals that have been known to be functional cleared of HIV. The most known patient is Timothy Ray Brown, found cured in 2008 as a result of an allogeneic hematopoietic stem cell transplant3. The donor was found to be homozygous for CCR5 delta32 deletion and henceforth meant the HIV was unable to enter the host’s cells without a functional CCR5 gene; theoretically curing the patient3. The success of this treatment has led to the inspiration for a number of unique and novel studies such as siRNA and post transcriptional gene silencing.

siRNA and Post Transcriptional Gene Silencing

The discovery of small interfering RNA or silencing RNA (siRNA) is only recent and was first described in plants as a ‘post-transcriptional gene silencing’4. siRNA have be proven to play a crucial role in gene expression and therefore have generated a substantial interest as potential treatments for viruses such as HIV-1. The targeting of HIV-1 promoters in vitro siRNA has already been shown to silence HIV-1 gene replication4(Figure 1). Dr Kelleher outlines that siRNA and post transcriptional gene silencing has a number of advantages over the traditional cART; once the HIV-1 gene expression is switched off there is no viral turnover and less risk of resistance and viral escape within the patient. This method also allows for the stabilization of the viral reservoir and the patient to cease cART.

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Figure 1: Twostep process of siRNA gene silencing5

The implications of Doctor Kelleher’s research is huge, the effective treatment of HIV-1 will not only prolong the lives of patients, but vastly improve their quality of living. The advancement of treatments such as this lends to our understanding of this deadly virus and how it operates, bringing us one step closer towards a cure.

References

  1. Blankson, J.N., Persaud, D. & Siliciano, R.F. 2002. The challenge of viral reservoirs in HIV-1 infection. Annual Reviews of Medicine, 53: 557-593.
  1. Schouten, J., Cinque, P., Gisslen, M., Reiss, P. & Portegies, P. 2011. HIV-1 infection and cognitive impairment in the cART era: a review. AIDS, 25: 561-575.
  1. Yukl, S.A., Boritz, E., Busch, M., Bentsen, C., Chun T-W., Douek, D., Eisele, E., Haase, A., Ho, Y-C., Hutter, G., Justement, J.S., Keating, S., Lee, T-H., Li, P., Murray, D., Palmer, S., Pilcher, C., Pillai, S., Price, R.W., Rothenberger, M., Schacker, T., Siliciano, J., Siliciano, R., Sinclair, E., Strain, M., Wong, J., Richman, D. & Deeks, S.G.2013. Challenges in Detecting HIV Persistence during Potentially Curative Interventions: A Study of the Berlin Patient. PLoS Pathogens, 9(5): e1003347.
  1. Suzuki, K., Marks, K., Symonds, G., Cooper, D.A., Kelleher, A.D., Hattori, S., Okada, S., Ahlenstiel, C., Maeda, Y., Ishida, T., Millington, M. & Boyd, M. 2013. Promoter targeting shRNA suppresses HIV-1 infection in vivo through transcriptional gene silencing. Molecular Therapy – Nucleic Acids, 2: e137.

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  1. McManus, M. and Sharp, P. 2002. Gene silencing in mammals by small interfering RNAs, Nature reviews genetics, 3(10): 737-747.

 

The Mystery of Bat Antiviral Immunity

Bats are most commonly known as creatures of the night; but few know their full potential as a reservoir of deadly viruses. In a recent seminar at Macquarie University; Doctor Michelle Baker of the Australian Animal Health Lab, Geelong, Victoria;explains how the unique Bat immune system responds to a host of deadly viruses they appear to happily coexist with. The Australian Animal Health Lab is a CSIRO funded, state of the art facility aimed at protecting Australia’s livestock, aquaculture and the public’s health from range of infectious diseases. Research on Bats tends to focus on immunology, genomics, pathogen discovery, the movements and transfer of virulence and potential vaccination remedies1. Doctor Baker’s work centres on the species of Megachiroptera (Megabats); Pteropus alecto or the Black Flying Fox [below – Figure 1].

Black_Flying_Fox_(Pteropus_alecto)

Figure 1: Pteropus alecto taken from  http://en.wikipedia.org/wiki/Black_flying_fox

Bat Facts

Bats are the second most abundant and species rich of the mammalian group, yet they remain one of the least studied groups1. Bats are interesting creatures due to a number of reasons; they are the only mammal with powered flight, are long lived in relation to body size (up to 40 years), show low incidences of tumours and have long history associated with some of the globes most deadly viruses1. Studies have shown that over 100 viruses are associated with Bats. The top 5 most deadly viruses carried by Bats include: Rabies, Ebola, SARS, Hendra and the Marburg viruses2. Remarkably Bats show no symptoms of illness even whilst being associated with multiple viruses at one time; it is only the rabies virus that on occasion negatively impacts the Bats health2.

Bat Immunology

The study of Bats as virus reservoirs and their unique immunity to the diseases they carry is quite a young area of study, only truly taking flight in 2008. One of the key studies within this field was the Bat Genome Project which sequenced the genomes of two bat species: Pteropus alecto (The Black Flying Fox) and Myotis davidii (David’s Myotis) and thereby set the foundation for all future studies on Bat immunology3. One of the most significant discoveries to come from this project was the identification of changes in innate immunes genes involved in interferon production; or simply how the Bat’s immune system works.

Interferons (IFN) are proteins created and released by a hosts (in this case, a Bat) cells in response to the threat of pathogen such as a virus. IFN’s are a potent first line of defence against viral infection, keeping a virus in an ‘antiviral state’ as well as stopping the virus from spreading2,4. Studies have focused on two key interferons: alpha (α) and beta (β) in which Bats have the fewest IFNα loci in comparison to a number other mammals. Bat immunology presents us with another interesting fact; IFNα is invariably expressed within the Bat’s immune system and isn’t induced following stimulation (e.g. experimental infection)4. What makes this situation more extraordinary is the fact that IFNα is in fact toxic at high levels4. It is this rapid control of viral replication that potentially holds the key for a Bats ability to coexist with these deadly viruses4. This would mean that Bats are constantly primed for viral defence, a defence that would presumably be at a high cost towards the host; surprising given the long lifespan of these unique mammals.

The study of Bat immunology is still in its infancy; the continuation of studies such as these has huge implications to our understanding of viral responses and the mechanics of viral spill overs, which not only have huge economic implications but the safety of human life.

Bat References

  1. Baker ML, Schountz T, Wang L–F. 2013. Antiviral Immune Responses of Bats:  A Review. Zoonoses and Public Health, 60:1, 104-116.
  2. Bean, A.G.D., Baker, M.L., Stewart, C.R., Cowled, C. Deffrasnes, C., Wang, L-F. & Lowenthal, J.W. 2013. Studying immunity to zoonotic diseases in the natural host – keeping it real. Nature Reviews Immunology, 13(12): 851-861.
  3. Zhang, G., Cowled, C., Shi, Z., Huang, Z., Bishop-Lilly, K.A., Fang, X., Wynne, J.W., Xiong, Z., Baker, M.L., Zhao, W., Tachedjian, M., Zhu, Y., Zhou, P., Jiang, X., Ng, J., Yang, L., Wu, L., Xiao, J., Feng, Y., Chen, Y., Sun, X., Zhang, Y., Marsh, G.A., Crameri, G., Broder, C.C., Frey, K.G., Wang, L.F. & Wang, J. 2013. Comparative Analysis of Bat Genomes Provides Insight into the Evolution of Flight and Immunity. Science, 339(6118): 456-460.
  4. Zhou, P., Cowled, C., Wynne, J., Ng, J., Wang, L. & Baker, M.L. 2013. Type I interferon in bats: Is it special? Cytokine, 63(3): 313-314.

 

 

 

Geographic Information Systems: What is it? And how does it help biologists?

Geographic Information Systems or GIS as it is commonly referred to as, belongs to the discipline of Spatial Information Science (SIS). GIS allows the visualization, analysis, interpretation and study of relationships and trends of various levels of data1. In a recent seminar by Dr Michael Chang and Dr Alana Grech from Macquarie University’s Department of Environment and Geography, they explain how GIS is far more than a Google maps program and plays a vital role in the study of biological sciences.

GIS has a range of applications allowing it to be used in a number of fields and agencies including; Government, business, utilities, communications, social science, marine and climate science as well as wildlife management1. Speakers both outlined a number of examples where GIS analysis has assisted in the investigation of biological processes and regions. A large portion of Dr Grech’s work being focused on marine systems; especially the Great Barrier Reef.

Dugong Habitat Protection

The Great Barrier Reef World Heritage Area (GBRWHA) covers a vast area along the Queensland coast and is home to a diverse array of marine life including the Dugong. The Dugong is a vulnerable species listed under a number of conservation protocols including the Australian Government’s Biodiversity and Conservation Act 19992. Dugongs are specialist feeders on seagrass and therefore are highly correlated to the availability of their food resource. Increasing anthropogenic (human) pressures on these seagrass meadows have threatened Queensland’s population of dugongs suggesting a need for greater management of conservation efforts; this is where GIS comes into play.

The study by Grech & Marsh (2007) used aerial surveys as a method of collecting data on dugong abundance and distribution along the Queensland coast. Using various GIS programs this data was overlaid with areas where seagrass is present to generate zones of conservation value [Figure 1].

map1

Figure 1: Areas of Dugong density and areas of conservation value off the coast of QLD, generated by GIS software1.

The capabilities of GIS are furthermore on show in the study by Grech et al (2011) where again the seagrass habitats of Dugongs along the Queensland coast is assessed. This study is comprises of a broad scale overview of the threats facing these seagrass habitats by generating a cumulative threat score, signifying areas at the highest risk along the coast. Threats include agricultural run-off, boat damage, dredging, netting, shipping accidents, trawling and the impact of urban infrastructure3. Studies such as this allows threat ‘hot spots’, where multiple threats occur at the same locality; to be deciphered by conservation planners and in turn allow for a greater protection plan of these zones.

Cumulative Threat Mapping

One of GIS’ greatest strengths for conservation planning is its ability to rank and overlay threating processes, whether they are manmade or natural; to generate cumulative threat maps. Dr Grech explains cumulative threat maps as those that incorporate all types of habitats including sea grasses, reef assemblages and barrens allowing for a greater ecosystem perspective on the vulnerability of each habitat type. These also measure the irreplaceability of a particular site; meaning the GIS program analyses the site in regards to sites importance in regards to sustaining viable populations that may or may not be solely dependent on that site.

Studies from the Mediterranean and Black Sea provide a firsthand example of how GIS and cumulative threat mapping can assist in the learning and conservation planning of threat ‘hot spots’. Over the years Mediterranean and Black Sea has suffered from intensive anthropogenic practices such as commercial fishing, pollution and shipping damages4. The Micheli et al (2013) study highlights the role of GIS in cumulative threat mapping, portraying areas undergoing low to high levels of threatening processes [Figure 2].

map 2

Figure 2: Culumative threat map of the Mediterranean and Black Sea, zoning areas under a threat category seen in the legend4.

In a perfect world, all ecosystems under threat receive adequate funding and protection means in order to maintain and protect biodiversity, but unfortunately this is rarely the case. GIS arms conservational biologists with a greater set of tools to tackle the difficult task of protecting and managing biodiversity into the future in the most effective and cost efficient manner. GIS gives biologists so much now, but what will it bring us in the future?
References and additional readings:

  1. NOAA. Geographic Information Systems. www.nmfs.noaa.gov/gis/ Assessed 26/4/14.

2. Grech, A. & Marsh, H. 2007. Prioritising areas for dugong conservation in a marine protected ares using spatially explicit population model. Applied GIS, 3(2): 1-14.

3. Grech, A., Coles, R. & Marsh. 2011. A broad-scale assessment of the risk to coastal seagrass from cumulative threats. Marine Policy, 35: 560-567.

4. Micheli, F., Halpern, B.S., Walbridge, S., Ciriaco, S., Ferretti, F., Fraschetti, S., Lewison, R., Nykjaer, L. Rosenberg, A.A. 2013. Cumulative Human Impacts on Mediterranean and Black Sea marine ecosystems: assessing current pressures and opportunities. PLOS ONE 8(12): e79889.

Grech, A., Marsh, H. & Coles, R. 2008.  A spatial assessment of the risk to a mobile marine mammal from bycatch. Aquatic Conservation: Marine and Freshwater Ecosystems, 18(7): 1127-1139.

Fear and Feeding: Predator-Prey Behaviour in light of overfishing

It goes without saying that humanity has long taken the marine world for granted. The overfishing of the oceans top predators has often led to great shifts in the distribution and abundances of a wide variety of species, but little work has emphasised on the indirect impacts of this threat; altered behaviour. Doctor Robert Warner of the University of California, Santa Barbara recently discussed his research in this field at a recent seminar at Macquarie University.

Image

Figure 1: ‘Fishing down the marine foodweb’. Top predators occupy the highest trophic levels. taken from Pauly & Maclean 20031.

Over the years the trend of restoring degraded and overfished marine habitats has been on the rise and has generally been met with a great deal of success, with the implementation of a number of marine reserves. Recovery and declining ocean ecosystems allow a snap shot of predator/prey relationships, in heavily fished and pristine waters. Areas that have or are currently suffering from heavy fishing often see a reduction in top predator densities. Examples of these top predators can include sharks, tuna and various marine mammals. Doctor Warner’s research has looked at the vast array of impacts that overfishing has had on reef ecosystems and in particular predator/prey relationships

In the presence of high predator abundances, prey species are often introverted, taking minimal risks in fear of becoming the snack. Behavioural responses include ‘encounter avoidance’; avoiding a predator that has recently entered the vicinity. This response can occur instantly across the entire assemblage of fishes with the introduction of a predator. Predator presence can also initiate enhanced vigilance; where the prey species are on the lookout for potential predators. High predator abundances have also been known to reduce foraging excursions of prey species leading to declines of fish health (discerned by fish weight) compared to those found in low predator abundances 2.A study by Fox & Bellwood also shows that prey behaviour is also impacted on diurnal scale with predator avoidance being attributed to nocturnal foraging in reef fishes3. Areas of high risk to prey species are often denoted by the greater abundance of macro-algae (source of food for herbivorous fish) located on reefs, indicating a strong presence of predators reducing foraging behaviour in herbivorous fishes3.

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Figure 2: Excursion distance of reef fishes in the presence of predators. Diagram a) Limited fishing/High predator presence, low excursion distance from reef. Diagram b) Heavily fished/low predator presence, high excursion distance from reef. Image created by David Connolly.

The Impact of fishing on top predators not only impacts predator abundance and diversity, but has a range of deeper ecological consequences. Dr Warner explains that widespread fishing has reduced the overall body size decline of top predators. Shifts to smaller predators leads to; slower predators, allows only the smaller consumption of prey (as a result of mouth size) and a shift in preferred prey. In the case of marine predators, size matters. In a study conducted on the predatory hog fish between fished and unfished environments finding no evidence of any reproductive events taking place outside of the marine reserve as opposed to 55 reproductive events occurring within the marine sanctuary4.

The Impact of fishing has also been shown to influence reproductive events and the facilitation of young prey fishes. In a study conducted on the bumphead parrotfish (Bolbometopon muricatum) a series of curious instances of aggressive head butting between males was observed prior to reproductive events was observed5. This unique behaviour took place within the confines of the Wake Atoll, a near pristine environment that has yet to feel the negative impacts of fishing. Ritualized head butting had not been previously documented and is hypothesised that overfishing reduces population densities to a level, that a competition for reproductive sources (females, mating grounds) is disguised5. The removal of larger predators in sex changing fishes as a result of overfishing further poses a threat to ecosystem function. The study of the female to male sex changing California sheephead (Semicossphus pulcher) has shown that the removal of large males, has led to a shift towards a smaller body size and the faster maturation of females into the male sex6. The improper management of sequential hermaphrodites such as the California sheephead runs the risk of sex ratio skewing, sperm limitation and reproductive failure; all of which could cause population collapse6.

Dr Warner believes that if conservation efforts are to be truly successful the indirect impacts of overfishing and the strain of top down fishing, such as behaviour should be accounted for. This field of research has the opportunity to alter the mindset of current and future management plans of marine reserves and the permittance of fishing within these zones. Additional information on this topic can be gleamed from the sources below.

References

1 Pauly, D & Maclean, J. 2003. In a perfect ocean: fisheries and ecosystems in the North Atlantic Ocean. Island Press, Washington D.C. p 175.

2 Walsh, S.M., Hamilton, S.L., Ruttenberg, B.I., Donovan, M.K. & Sandin, S.A. 2012.Fishing top predators indirectly affects condition and reproduction in a reef-fish community. Journal of Fish Biology, 80: 519-537.

3 Fox, R.J. & Bellwood, D.R. 2011. Unconstrained by the clock? Plasticity of diel activity rhythm in a tropical reef fish, Siganus lineatus. Functional Ecology, 25(50 1096-1105

4 Munoz, R.C., Burton, M.L., Brennan, K. & Parker, R.O. 2010. Reproduction, habitat utilization, and movements of hogfish (Lachnolaimus maximus) in the Florida Keys, U.S.A.: comparisons from fished versus unfished habitats. Bulletin of Marine Science, 86(1): 93-116.

5 Munoz, R.C., Zgliczynski, B.J., Laughlin, J.L. & Teer, B.Z. 2012. Extraordinary aggressive behaviour from the giant coral reef fish, Bolbometopon muricatum, in a remote marine reserve. PLOS one, e38120.

6 Hamilton, S.L., Caselle, J.E., Standish, J.D., Schroeder, D.M., Milton, S.L., Rosales-Casian, J.A. & Sosa-Nishizaki, O. 2007. Size-selected harvesting alters life histories of a temperate sex-changing fish. Ecological Applications, 17: 2268-2280.

Social Spiders: Sharing is Caring

When we think of Huntsman spiders, we think of eight legs of pure Arachnid stalking the Australian bush land in solitude in search of their next meal. Dr. Linda Rayor of Cornell University is out to change this misconception: with a recent seminar at Macquarie University on the sociality of the Australian Huntsman Delena Cancerides.D. cancerides is one of only 85 of the 44,500 known spider species said to take part in a social lifestyle and like all Huntsman (Sparassidae: Deleninae) species, do not build webs for prey capture and in fact forage nocturnally1.

alan henderson

Delena Cancerides. A photo by Alan Henderson5

How do we define sociality in spiders? Firstly, we must remove ourselves from the preconceived notions of other known social insects such as bees and ants. Social spiders live in foraging societies as opposed to reproductive groups, common in other forms of social living2. These colonies are led by a single dominant female, not unlike many households today, and are responsible for the protection of not only the colony’s members but the retreat itself (the spiders home).Colonies generally consist of 1-4 cohorts of offspring, with a large variation of offspring instars (age) within each colony.

instar

Figure 2: Instars of Delena Cancerides1

D. cancerides exhibits social behavior through the act of prey sharing, where a percentage of prey caught by larger, more mature spiders is brought back to the retreat to be shared with the younger, immature spiders. The concept of sibling rivalry is almost entirely void in D. cancerides as this act is not only highly beneficial towards the younger spiders of the colony (increased weight); but incurs a completely negligent impact on the mature ‘sharing’ huntsmen1. The complexity of prey sharing in D. cancerides becomes even more unique when incidence of cannibalism in other species of spiders is taken into account3. Solitary spiders will often cannibalize other siblings or spiders they encounter in preference to prey sharing, tough love4? Dr. Rayor suggests a level of tolerance between siblings of the colony in D. cancerides, giving homage to the age old saying ‘sharing is caring’.

Making this colonial behavior a possibility is the spiders’ ability to recognize nest mates, generally thought to occur through chemical signaling, allowing the matriarchal spider to defend the colony from foreign colonial invaders whilst adequately protecting members of her own colony until they mature3. D. cancerides offspring will often remain in the retreat for 45 weeks before dispersing (at sexual maturation) from the colony in search of food and mates. This behavior not only mimics the life of the common teenager, but is also congruent with delayed mobility and feeding from birth in comparison to solitary huntsman4.

The spiders’ strict habitat also procures a strong area of interest in these social creatures; after all, home is where the food is. Rayor explains that retreats are often only a few centimeters deep and commonly found in the decaying remains of Acacia species6. D. cancerides often suffer from enormous pressures as a result habitat saturation, meaning the retreats available are at full occupancy. Rayor’s observations have shown that as available retreats become rarer, occupancy is increased leading to the potential ‘take-over’ of the retreat by a rival female. Retreats can often be ‘a ticking time bomb’ as decaying trees often have a limited window of occupancy before decomposition leads to its inhabitable. Once a retreat has completely degraded the inhabiting colony is lost as result6.

Dr Rayor’s work on D. cancerides has further shed light on the evolutionary advantage of a social lifestyle, where the benefits of sharing outweigh the costs. Studies such as this continue to advance out knowledge in the complexities of social interaction in arachnid species. D. Cancerides is not the only social huntsman studied by Rayor with D. lapidocola and D. melanochelis, also declared subsocial species. To learn more about sociality in Spiders and in particular the work by Linda Rayor on D. cancerides see the works below:

1Yip,E. & Rayor, L. 2013. The influence of siblings on body condition in a social spider: is prey sharing cooperation or competition? Animal Behaviour 85(6): 1161-1168.

2Whitehouse, M. E. A. & Lubin, Y. 2005. The functions of societies and the evolution of group living: spider societies as a test case. Biological Review 80, 347-361.

3 Yip, E. C., Clarke, S. & Rayor, L. S. 2009. Aliens among us: Nestmate recognition in the social huntsman spider, Delena cancerides. Insectes Sociaux 56, 223-231.

4 Yip, E.C. & Rayor, L. 2013. Maternal care and subsocial behavior in spiders, Biological Reviews, doi: 10.1111/brv.12060

5 Image: Henderson, A. Taken from: http://www.biodiversitysnapshots.net.au/bdrs-core/public/speciesInfo.htm?spid=282&mode=fieldguide

6Rowell, D. M. & Avilés, L. 1995. Sociality in a bark-dwelling huntsman spider from Australia, Delena cancerides Walckenaer (Araneae: Sparassidae). Insectes Sociaux, 42, 287-302.