Madeleine van Oppen
I was originally trained in marine ecology, developed as an ecological geneticist post-BSc and began to study corals in 1997 and coral-associated microorganism in 2000. My microbial studies were initially limited to the dinoflagellate endosymbionts of corals, but more recently I have ventured into the study of other microbial groups that inhabit corals, including prokaryotes, viruses, and fungi.
My group’s current research focuses on the field of coral reef restoration, in particular the development of coral stock better able to cope with disturbed environments and predicted future ocean conditions (assisted evolution). This includes the manipulation of microbial communities associated with corals, laboratory evolution of algal endosymbionts, selective breeding of corals, and the conditioning of corals to predicted future ocean conditions.
I completed my PhD on the molecular biogeography of seaweeds at the University of Groningen (Netherlands) in 1995, and subsequently conducted postdoctoral positions at the University of East Anglia, UK (speciation in cichlid fishes), and James Cook University, Australia (Molecular relationships in the coral genus Acropora, and Genetic diversity and specificity of acroporid coral-dinoflagellate symbioses). In 2001, I took up a position at the Australian Institute of Marine Science (AIMS), Townsville. I commenced my position as a professor in the School of BioSciences, University of Melbourne, in 2015, while still maintaining a part-time position as Senior Principal Research Scientist at AIMS. I currently hold an Australian Research Council Laureate Fellowship (2019-2023).
Linda is an environmental microbial ecologist, who has studied many different complex microbial communities ranging from host associated through to free living in numerous environments. Her research has covered mammalian microbiomes of marsupials, humans, ruminants and horses; and the microbiota of non-mammals including corals and sponges. Environmental microbiomes explored in Linda’s research span wastewater treatment (aerobic and anaerobic), solid waste digestion (landfill and composting), bioelectric systems and microbiologically influenced corrosion. The numerous methods she develops and employs in her research allow elucidation of microbial complexity and function in these diverse biomes.
- Postdoctoral researchers
Pranali's current research centres around the understanding of symbiotic interactions between algal dinoflagellate and bacterial species that are crucial for coral health. She uses a range of advanced visualisation and biophysical techniques to study coral dinoflagellate and bacterial associations. Her previous research experiences broadly involved the study of microalgal photosynthesis, phytoplankton-zooplankton interactions and microalgal transgenics.
Pranali holds a joint PhD degree in Applied Biology from the Indian Institute of Technology Bombay, India and Monash University, Australia. Apart from being a scientist, Pranali is an intermediate-level yogi and a decent cyclist.
I completed my PhD in late 2020 on the feasibility of bacterial probiotics in mitigating climate change in cnidarians at The University of Melbourne. In early 2021 I transitioned to a research fellow position in the same group. My research interests are in applied microbiology strategies to enhance resilience to climate change. Specifically, my current research looks to understand the functions of individual bacterial species in their symbiosis with coral and to manipulate those functions to promote coral survival during periods of thermal stress.
Outside of research, I am an advocate for equity in science opportunities for women, members of the LGTBIA+ community, people of color, indigenous community members, minorities, people with disabilities, and anyone else who has ever felt that they do not belong. I serve as co-Chair of the BioSciences Early Career Academics Committee (UoM), am a member of the People and Culture Committee (UoM), and was recently elected a member of the International Society for Microbial Ecology (ISME) Early Career Scientist Committee.
Patrick is a molecular ecologist at Macquarie University currently based at the University of Melbourne, with a research focus on coral resilience to climate change. Using omics technologies and comparative genomics, he investigates genomic adaptations and their impact on the thermal tolerance of corals and their algal symbionts. Current projects include genome and transcriptome sequencing of heat evolved algal symbionts to identify molecular mechanisms that support an increased thermal tolerance. Previously, Patrick worked as a postdoctoral fellow with CSIRO's Synthetic Biology Future Science Platform and the University of Melbourne, and completed his PhD in Marine Science at the Australian Institute of Marine Science in Townsville, Australia.
If Patrick is not in the laboratory, he is passionate about innovative technologies that improve environmental conservation and science communication.
My research focuses on coral reef conservation and restoration. I commenced my postdoc at the University of Melbourne in 2019 and my project examines the feasibility of enhancing coral climate resilience via the introduction of resilient microalgal endosymbionts. I completed my PhD at the Australian Institute of Marine Science and the University of Melbourne, exploring the potential of hybridization as a tool for coral reef conservation.
My Honours Degree at the Australian National University investigated the calcification responses of corals to diurnal variation in seawater carbonate chemistry. Other than coral reefs, I have also been involved in research on marine micro-plastics, radioactive dating, and isotope analysis. Outside the office, I am passionate about science outreach and aviation, and serve as a helicopter flight instructor.
I am originally from Lyon, France, where I completed all my studies. I did both my master’s and my PhD under the supervision of Dr’s Abdelaziz Heddi and Anna Zaidman-Rémy, and worked on the obligate symbiosis between the cereal weevil Sitophilus and its bacterial endosymbiont Sodalis pierantonius. S. pierantonius provides its insect host with vitamins and amino acids, allowing Sitophilus to thrive exclusively on cereals. As such, Sitophilus is considered as a major crop pest around the world. In a first project, I investigated the mechanisms preventing a chronic host immune activation because of the constant association with immunogenic bacteria. Then, I studied how this association is modulated across the insect's lifecycle, particularly during metamorphosis.
In 2019, I joined Prof. Madeleine van Oppen’s lab in Melbourne for my first postdoc. My project is part of the important effort to enhance coral’s climate resilience through assisted evolution. My projects involve the identification and characterization of closely-associated bacterial symbionts of Symbiodiniaceae and cnidarians, and in fine the genetic engineering of those symbionts to improve stress resistance in the coral holobiont.
- Postgraduate researchers
Cecile Ravn Gøtze
Originally from Denmark, I have always been surrounded by a long coastline which early on sparked a life-long penchant for the sea. Following a career in design and tailoring, I decided to pursue a more engaging and satisfying career path and so I completed my Master’s degree in Microbial Ecology at the University of Copenhagen. Inspired by findings on the importance of the gut microbiome in mammalian health, I have since become fascinated with studying microbial activity and coral-associated microbes through microsensor and genetic approaches.
It has long been known that corals are comprised of a wide array of microorganisms, although a lot remains unknown about the interplay between microbial partners and coral host. Under the supervision of Prof Madeleine van Oppen, Prof Linda Blackall and Dr. Lone Høj the majority of my graduate research will be carried out at the Australian Institute of Marine Science, AIMS. Here, I will try to decipher coral microbiome interactions and function by studying the minimal microbiome, which constitutes the smallest subset of coral-associated symbiont on which the host depends for its survival.
I received my Bachelor of Science in Biology from the Free University in Berlin, Germany, but I conducted the research for my undergraduate thesis at GEOMAR Helmholtz Centre for Ocean Research Kiel, Germany. There, I worked in the research unit of Marine Evolutionary Ecology and analysed the transgenerational phenotypic plasticity of marine sticklebacks to simulated climate change. Afterwards, I completed my Master of Science in Biological Oceanography at Christian-Albrecht University of Kiel. During my master thesis in the unit Marine Symbioses at GEOMAR and Phuket Marine Biological Center, Thailand, I tested whether a coral microbiome transplantation procedure using a fresh tissue homogenate of heat tolerant donor colonies of Pocillopora verrucosa can increase coral bleaching resilience of heat sensitive conspecifics. After my studies, I continued to work as a research assistant at GEOMAR and performed a similar study with Porites lutea colonies.
I started my PhD at the end of 2019 under the supervision of Prof.’s Madeleine van Oppen, Linda Blackall and David Francis. My research aims at developing successful bacterial probiotics and probiotic techniques that enhance coral bleaching resilience. I am working with the sea anemone Exaiptasia diaphana and one coral species, Galaxea fascicularis.
(Information to come)
I am interested in using genetic and molecular approaches to better understand and inform the conservation of wildlife. I completed my Bachelor of Biomedical Science and Bachelor of Science (Hons) majoring in Genetics and Ecology and Conservation at Monash University. During my Honours year, I investigated whether the mitochondrial genomes of Australian birds have evolved under climate-driven selection.
I began my PhD in 2018, supervised by Madeleine van Oppen, Peter Harrison, Ary Hoffmann and Craig Humphrey. My research investigates interspecific hybridisation as a novel option for reef management, particularly in the context of producing more resilient coral stock (compared to the native stock) for coral reef restoration initiatives.
Originally from Paris, France, I pursued my tertiary studies in the UK where I completed a BSc in Biology at the University of Bristol, followed by a MSc in Biotechnology at the University of Edinburgh. After my studies, I worked at the Interdisciplinary Centre of Marine and Environmental Research in Porto, Portugal, on the discovery of marine natural products in cyanobacteria. During this time I started to investigate the capacity of free-living Symbiodiniaceae to form symbiolites (i.e., microbialites containing Symbiodiniaceae cells).
I joined the Marine Microbial Symbioses group in early 2020 as a PhD candidate under the supervision of Professor Madeleine van Oppen. I am currently based at the Australian Institute of Marine Science, where my research is focused on establishing new symbioses between aposymbiotic corals and heat stress tolerant Symbiodiniaceae that were previously developed through experimental evolution. These bioengineered corals will be tested for improved bleaching resilience at elevated temperatures, in the hope of developing a new approach for coral reef conservation and adaptation.
I completed my BSc in Physics and Genetics, and an Honours in Genetics, at the University of Western Australia. My honours project involved developing a computational pipeline to differentiate members of the Bemisia tabaci cryptic species complex using nanopore sequencing data. This sparked an interest in the field of bioinformatics, and so I decided to study it further.
Currently, I am in the MSc (Bioinformatics) program at the University of Melbourne. My project, under the supervision of Dr. Patrick Buerger and Dr. Rahul Rane, is to compare and analyse the transcriptomes of heat-evolved Symbiodiniaceae strains.
From the US by way of Brisbane and New Zealand I hold a Bachelors in Science (Biology and Statistics) and Masters in Bioscience Enterprise from The University of Auckland. Metabolomics was the discipline in which I was “baptised by acetone” at the Villas-Boas lab, University of Auckland. Subsequently I forayed into the business of Nanotechnology and Consumer Healthcare. I am now studying the Masters in Bioinformatics at the University of Melbourne under the supervision of Professor Madeleine van Oppen and Dr. Patrick Buerger, my research involves genomic analysis of Symbiodiniaceae samples bred under different heat stress regimens.
I completed a Bachelor of Science at the University of Melbourne, with a major in genetics. I've always had an interest in both cell biology and conservation biology so I decided to continue my studies through a Master of Science (Biosciences) under the supervision of Madeleine van Oppen and Wing Chan. My research project is investigating whether it is possible to induce sexual reproduction in the algal symbiont Symbiodininaceae as a way to accelerate experimental evolution.
I am originally from China and completed a major in marine biology at the University of Melbourne in 2020. After some volunteering experiences in laboratory, I explored my interest in understanding the physiological processes underlying the ecological phenomenon. I am currently studying a Master of Bioscience, supervised by Madeleine van Oppen, Linda Backall and Ashley Dungan. My research project focuses on the metabolic interactions between sea anemone (Exaiptasia diaphana, a model organism for corals) and its symbiotic bacteria, and aims to understand the functions of bacterial symbionts in the coral host and their effects on coral physiology.
I studied a Bachelor of Science with a major in Genetics at The University of Melbourne. During my undergraduate studies, I completed a summer research internship at CSIRO, where I observed how genetic technologies are being implemented to preserve ecosystems, strengthening my interest in environmental conservation. I am currently studying a Master of Science (Biosciences) supervised by Madeleine van Oppen and Justin Maire. My research project focuses on the symbiosis between coral algae and their associated bacteria, and aims to characterise the function of bacterial strains believed to play a role in algal climate resistance.
Originally from Japan, I completed a Bachelor of Science with a major in Environmental Science at the University of Melbourne in 2019. During my undergraduate studies, I gained an interest in the conservation of species sustainability and diversity under climate change scenarios. I started studying a Master of Science (BioSciences) under the supervision of Prof. Madeleine van Oppen and Dr. Wing Chan in 2020. My research project involves the examination of bleached corals which have lost their associated Symbiodiniaceae species, and aims to understand the establishment of the different Symbiodiniaceae genera within adult corals.
- Other staff
Sanjida Halim Topa – Research Assistant
I am originally from Bangladesh. I came to Melbourne to pursue my doctoral degree in late 2013 after finishing bachelor’s in pharmacy. I completed my PhD in early 2018 from Swinburne University of Technology under supervision of Professor Linda Blackall. My PhD thesis was entitled “Quorum quenching processes through surface treatments”. My research focused on a crucial problem of biomedical science; biofilm formation (one of the phenotypes of bacterial quorum sensing) which is one of the major reasons for development of antibiotic resistance and implant device failure in biomedical science. I have been involved in different industry funded research projects in Swinburne focusing on antimicrobial resistance since then.
Currently I am working as a research assistant in Professor Madeleine van Oppen’s lab in the field of coral and this mostly includes the microbial communities associated with corals.
Katarina Damjanovic – Research Assistant
After completing a Master's degree in Life Sciences at the Swiss Federal Institute of Technology in Lausanne, I moved to Australia in 2015 for my doctoral studies. I completed my PhD under the supervision of Prof. van Oppen and Prof. Blackall at the University of Melbourne, with the practical part of my project undertaken at the Australian Institute of Marine Science (AIMS), in Townsville. My PhD project consisted in investigating the transmission mode of coral-associated bacteria and in exploring the potential to manipulate bacterial communities associated with coral early life stages.
I now hold a part time position as an experimental scientist at AIMS and continue working as a casual research assistant for the Marine Microbial Symbioses Lab. In this role, I am contributing to a project which aims at deciphering the coral minimal microbiome. When not in the laboratory, I spend nearly all my free time rock climbing.
Luka Meyers – Research Assistant
I completed a Bachelor of Environmental Science/Bachelor of Marine Science and Management at Southern Cross University, in Northern NSW. With a keen interest in marine invertebrates, I took a semester off my studies to research the ecology and behaviour of two exploited Holothuroid species (Stichopus vastus and Thelenota anax) at Lizard Island Research Station. I began working with corals when I joined Prof. Peter Harrison’s team as a research assistant. The work involved collecting and rearing coral spawn in the field and at the Australian Institute of Marine Science (AIMS), releasing the cultured larvae back onto degraded reefs and monitoring recruitment. In 2020, I was selected by Dr. Wing Chan to determine the effect of ocean acidification on the skeletal structure of hybrid and purebred coral recruits using 3D X-ray microscopy and scanning electron microscopy at the Centre of Microscopy, Characterisation and Analysis (CMCA) in Perth. Earlier this year, I joined the Marine Microbial Symbiosis group as a research assistant, where I maintain coral stocks and assist on a variety of experiments.
Sarah Jane Tsang Min Ching – Lab manager & Research assistant
Originally from the tropical island Mauritius, I completed my Bachelor of Science at Northeastern University in Boston, USA with a double major in Marine Biology and Environmental Science with a concentration in Wildlife Studies. I joined the Marine Microbial Symbiosis group in early 2019 as a Master of Science (BioSciences) candidate under the supervision of Professor Madeleine van Oppen and Drs Wing Chan and Patrick Buerger. During that time, I investigated the physiological performance of cnidarian animals that associate with different types of lab-evolved Symbiodiniaceae and determined the potential trade-offs that could result from establishing symbiosis with those algal symbionts.
After the completion of my MSc at the end of 2020, I stayed on with the Marine Microbial Symbiosis group as the Lab Manager and I was also appointed as the Research Assistant for the Bacterial-Algal Symbiosis project funded by the Gordon and Betty Moore Foundation. As the Lab Manager, I oversee many tasks and responsibilities including, but not limited to, the proper functioning and maintenance of equipment and infrastructure, ensuring compliance and that all biosafety documentation are up to date, the coordination of purchases, and the training of new lab members. As the Research Assistant, I am responsible for the culturing and maintenance of our study organisms which include several bacterial species as well as the Symbiodiniaceae Breviolum minutum. I also work closely with the appointed Research Associate, Dr. Pranali Deore, assisting her with any tasks in our investigation of the symbiotic formation and maintenance between bacteria and dinoflagellate endosymbionts (Symbiodiniaceae) of corals.
Kelly – Lab Dog
Kelly is a three-year-old golden retriever. While in the office she specialises in mental health and emotional support, her full time job is as a breeding dog for Seeing Eye Dogs Vision Australia. Elite Seeing Eye Dogs are sourced from SEDs own “in-house” breeding program. Kelly lives and goes to work with her Breeder Carer, Ashley, where she enjoys all the comforts of dog life. See SEDs breeder caring web page for more information.
Ocean – Lab Dog
Ocean is a puppy-in-training for Seeing Eye Dogs Vision Australia. When she grows up, Ocean hopes that one day she will be an invaluable part of someone’s life who is blind or has low vision. For now, she’ll focus on learning basic obedience, getting comfortable in working environments, and being exposed to the noises of everyday life. Ocean lives and goes to work with her puppy raiser, Ashley, and Auntie Kelly. See SEDs puppy caring web page for more information.
Camila Pintos – Former MSc student
I completed a Bachelor of Biotechnology in 2017 in my home country, Paraguay. Here, I was involved in research projects in the field of environmental and industrial biotechnology, studying the bioprospecting capabilities of isolated bacteria. After that I completed the Master of Biotechnology at The University of Melbourne under the supervision of Prof. Linda Blackall. My project used metabarcoding analysis to screen microbial species present in river samples from the Murray-Darling Basin togain understanding about the ecosystem. My research interests are in the field of applied microbial diversity and bioprospection.
Giada Tortorelli – Former PhD student
I received my BSc in Marine Biology and my MSc in Biodiversity and Evolution from the Alma Mater Studiorium University of Bologna, Italy. As a master and then postgraduate student, I investigated the impacts of global warming on the reproduction of a scleractinian temperate coral along a natural temperature and solar radiation gradient; it is here that I developed a deep interest and passion in coral biology. As a PhD candidate in the Marine Microbial Symbioses Group at the University of Melbourne, I work under the supervision of Prof McFadden, Prof van Oppen and Prof Davy. My focus is the symbiosis between Cnidarian and Symbiodiniaceae dinoflagellates that power coral reefs, using the anemone Exaiptasia diaphana as model organism to study corals. I am interested in the initial steps during the establishment of this mutualistic association: based on the hypothesis that Symbiodiniaceae endosymbionts and Apicomplexa parasites arose from a common ancestor that invented a powerful recognition system and mechanisms for invading and surviving in the host, my main aim is to investigate the inter-partner signalling and molecular events that allow recognition between host and photosymbionts in the setup of symbiosis.
Ashley Dungan – Former PhD student and Research Assistant
Originally from NY, USA, I completed my Bachelors of Science degree in Biology in 2011, conducting a senior research project in the field of environmental microbiology. I completed my Master’s degree at Nova Southeastern University in Florida under Dr. Nicole Fogarty, where I studied the impact of ocean acidification on the calcification of Caribbean adult and juvenile corals. After graduating in 2015, I worked for Mote Marine Laboratory in the Florida Keys as a Staff Chemist in the Ocean Acidification program; there I continued my work with corals and began working with Diadema antillarum, the long-spined sea urchin. Beginning early 2017, I joined Prof.’s Madeleine van Oppen and Linda Blackall at the University of Melbourne as a Ph.D student. My current research focuses on developing a bacterial probiotic to mitigate coral bleaching and assessing the efficacy of that probiotic using the model organism for corals, Exaiptasia diaphana. My research interests are in the field of climate change, coral reef ecosystems, and assisted evolution.
Giulia Holland – Former Research Assistant
I completed my Bachelor of Science at The University of Melbourne, majoring in marine biology with a broad interest in ecology and climate change. Having completed a research project at the Marine Microbial Symbiont Facility during my undergraduate degree where I characterised the bacterial communities in Exaiptasia diaphana, I now work as a research assistant at the MMSF. Here, I am helping to characterise the prokaryotic microbiome of the corals Plesiastrea verispora and Galaxea spp., through the collection of pure cultures and metabarcoding. In 2019, I began a Master of Environment at The University of Melbourne.
Ruby Vanstone – Former MSc student and Research Assistant
Leon Hartman – Former PhD Student
Microbial communities hosted by cnidarians show evidence of both dynamism and stability, with change suggestive of adaptation by the holobiont to environmental stress. My research investigates whether Exaiptasia diaphana's thermal tolerance can be enhanced through manipulation of its prokaryotic communities. Comparison of metabolite production by thermally stressed anemones inoculated with native and manipulated communities will be used to measure the effect of this approach.
Katarina Damjanovic – Former PhD Student
After completing both Bachelor and Masters degrees in Life Sciences at the Swiss Federal Institute of Technology in Lausanne (Switzerland), I started my PhD in October 2015 at the University of Melbourne. The major part of my research is conducted at the Australian Institute of Marine Science in Townsville, where I investigate the feasibility of manipulating coral-associated bacteria (with the aim to enhance coral stress tolerance). Focusing on the corals Acropora tenuis and Platygyra daedalea (both broadcast spawners), as well as Pocillopora acuta (also a brooder), my experiments consist in inoculating early life stages of these corals with microbiomes and assessing the efficiency and persistence of the inoculations. Larvae and recruits exposed to various microbes are reared under controlled conditions and their microbiomes are regularly characterised through 16S rRNA gene metabarcoding. I also use fluorescence in situ hybridisation microscopy to gain insights into the transmission modes of bacteria in A. tenuis and P. acuta.
Keren Maor-Landaw – Former Postdoctoral Researcher
My post-doctoral studies focus on membrane transporters that are crucial to the cnidarian-Symbiodiniaceae symbiotic relationship. The symbiotic algae provide energy by transferring their photosynthetic production to the host and in return derive benefits from the host in the form of nutrients and shelter. Successful exchange of compounds through membranes is a fundamental key feature enabling the effective partnership and must be facilitated by proteins in the cellular membranes of each of the partners as well as in the symbiosome interface.
As a PhD student in Bar Ilan University, Israel, supervised by Prof. Oren Levy, I explored how corals respond to climate change and which cellular processes are involved during environmental stress. I compared the gene expression response of corals possessing different morphologies and corals from different ecosystems – sub tropical to temperate corals.
My MSc at Haifa University, Israel, under the supervision of Prof. Dan Tchernov and Prof. Sarit Larisch, was focused on the apoptotic enzyme Caspase 3 in a Mediterranean coral following an ocean acidification scenario, and its correlation to a unique ecophenotye.
Hannah Epstein – Former PhD Student
I am a PhD candidate at the ARC Centre of Excellence for Coral Reef Studies at JCU and the Australian Institute of Marine Science under the supervision of Prof. Madeleine van Oppen, Prof. Philip Munday and Dr. Gergely Torda. My research explores the main drivers of community composition in the coral microbiome to inform the development of microbiome engineering techniques that may enhance climate resilience in corals. My project is part of a larger collaborative study led by Madeleine van Oppen and Ruth Gates (Hawai’i Institute of Marine Science) researching assisted evolution approaches for corals in the face of climate change.
Hannah completed her PhD in October 2018 and is now a postdoctoral research fellow at the University of Victoria, Canada.
Leela Chakravarti – Former PhD Student
Sam Girvan – Former Masters Student
With a keen interest in marine biology and genetics I completed my Bachelor of Science at the University of Melbourne with a double major in zoology and marine biology. I finished my Masters of Bioscience degree in 2019 under the supervision of Dr.'s Patrick Buerger and Madeleine van Oppen at the University of Melbourne. My research project aimed to discover whether the algae-associated bacterial communities have evolved alongside the algae, potentially allowing the observed increase in algal thermal tolerance determined from previous studies.
Roy Belderock – Former Masters Student
I completed my masters at University of Amsterdam. My main interests are conservation genetics, adaptation and symbiotic interactions in reef ecosystems. Especially the interest in symbiotic interactions is what brought me to this lab.
In the past I gained experience studying reproductive isolation in Caribbean giant barrel sponges by applying histological techniques in combination with DNA barcoding. At the Marine Microbial Symbiont Facility, I expanded on that skill set with Symbiodiniaceae reinfection experiments on Exaiptasia diaphana. In addition, I also worked on inducing sexual reproduction of E. diaphana. The larvae could help the team to study the Symbiodiniaceae recognition pathway in early life stages.
Gabriela Lozano Rodriguez – Former Research Assistant
I am passionate about working to preserve the environment and have worked on a number of projects in this field. Before moving to Australia to study a Master of Biotechnology at the University of Melbourne, I spent five years working in environmental, chemical and pharmaceutical industries in Mexico. My earlier research projects have related to the purification, structural elucidation and mechanism of action of toxins produced by fire coral (Millepora alcicornis) to understand its potential medicinal applications. I am currently working as a Research Assistant at the Marine Microbial Symbioses Group at the University of Melbourne where I am working to develop a spawning protocol for multiple genotypes of coral. I love the outdoors and spend as much time as I can hiking and playing flag football.