Damien Burrows

Large-scale dieback of mangroves in Australia’s Gulf of Carpentaria: a severe ecosystem response, coincidental with an unusually extreme weather event

This study records and documents the most severe and notable instance ever reported of sudden and widespread dieback of mangrove vegetation. Between late 2015 and early 2016, extensive areas of mangrove tidal wetland vegetation died back along 1000km of the shoreline of Australia’s remote Gulf of Carpentaria. The cause is not fully explained, but the timing was coincident with an extreme weather event; notably one of high temperatures and low precipitation lacking storm winds. The dieback was severe and widespread, affecting more than 7400ha or 6% of mangrove vegetation in the affected area from Roper River estuary in the Northern Territory, east to Karumba in Queensland. At the time, there was an unusually lengthy period of severe drought conditions, unprecedented high temperatures and a temporary drop in sea level. Although consequential moisture stress appears to have contributed to the cause, this occurrence was further coincidental with heat-stressed coral bleaching. This article describes the effect and diagnostic features of this severe dieback event in the Gulf, and considers potential causal factors.

Biology, distribution and host-range of the sawfly, Lophyrotoma zonalis (Hym., Pergidae), a potential biological control agent for the paperbark tree, Melaleuca quinquenervia

Since its introduction into southern Florida at the beginning of this century, the Australian paperbark tree,Melaleuca quinquenervia (Cav.) S. T. Blake, has become a major economic and environmental pest. A project to develop biological control agents for this tree in Australia began in 1986. Among a number of potential agents, a defoliating sawfly,Lophyrotoma zonalis (Rohwer) (Hymenoptera: Pergidae), was selected for further study. The larvae of this sawfly are conspicuous defoliators ofMelaleuca trees in northern Queensland. We collected these sawflies from Cairns to Mackay in northern Queensland, and they are also known from the Northern Territory and New Guinea. The life-cycle from egg to adult takes about 12 weeks. The egg, larval and pupal stages are parasitized by dipteran and hymenopteran parasites. We conducted 2234 larval no-choice feeding tests on 46 plant species from 20 families. Although feeding occurred on 35 of these plant species,M. quinquenervia and its close relative,M. leucadendra (L.) L., were preferred. In oviposition tests, larvae only emerged from egg cases laid onM. quinquenervia andM. leucadendra. Our extensive field surveys of nearly 70 tree species foundL. zonalis eggs and larvae only on several closely relatedMelaleuca species. The potential effectiveness of this sawfly as a biocontrol agent is discussed and estimated using the Goeden-Harris scoring system. Quarantine studies of this insect began in Florida in early 1994.RésuméDepuis son introduction dans le sud de la Floride au début du siècle,Melaleuca quinquenervia (Cav.) S. T. Blake (Myrtacées) est devenu un grave fléau tant sur le plan économique qu’écologique. Un projet fut lancé en 1986 en Australie pour développer un programme de lutte biologique contre cet arbre. Parmi les nombreux agents potentiels, une tenthrèdeLophyrotoma zonalis (Rohwer) (Hym. : Pergidae), a été choisie pour faire l’objet d’une étude approfondie. Les larves de cette espèce sont en effet connues pour être des défoliatrices deMelaleuca dans le nord du Queensland. Des tenthrèdes ont donc été récoltées de Cairns à Mackay dans le nord du Queensland et leur presence a aussi été relevée dans les Territoires du Nord et en Nouvelle-Guinée. Le cycle de développement de l’œuf à l’adulte dure environ 12 semaines. Les stades oeuf, larve et pupe sont parasités par des diptères et par d’autres hyménoptères. Nous avons fait 2 234 essais sur 46 espèces de plantes appartenant à 20 familles en présentant des larves à un seule espèce de plante. Bien que 35 de ces plantes aient pu être choisies comme nourriture,M. quinquenervia et une espèce procheM. leucadendra (L.) ont été préférées. Dans les tests d’oviposition, les larves n’ont émergé que des oeufs déposés surM. quinquenervia etM. leucadendra. Une recherche de terrain plus étendue sur presque 70 espèces d’arbres a permis de trouver des œufs et des larves deL. zonalis seulement sur plusieurs espèces très voisines deMelaleuca sur le plan taxonomique. L’efficacité potentielle de cette tenthrède comme auxiliaire est discutée et estimée selon la méthode de notation de Goeden-Harris. Des études de cet insecte ont commencé en quarantaine en Floride au début de 1994.

Fine-tuning for the tropics: application of eDNA technology for invasive fish detection in tropical freshwater ecosystems

Invasive species pose a major threat to aquatic ecosystems. Their impact can be particularly severe in tropical regions, like those in northern Australia, where >20 invasive fish species are recorded. In temperate regions, environmental DNA (eDNA) technology is gaining momentum as a tool to detect aquatic pests, but the technologys effectiveness has not been fully explored in tropical systems with their unique climatic challenges (i.e. high turbidity, temperatures and ultraviolet light). In this study, we modified conventional eDNA protocols for use in tropical environments using the invasive fish, Mozambique tilapia (Oreochromis mossambicus) as a detection model. We evaluated the effects of high water temperatures and fish density on the detection of tilapia eDNA, using filters with larger pores to facilitate filtration. Large‐pore filters (20 μm) were effective in filtering turbid waters and retaining sufficient eDNA, whilst achieving filtration times of 2–3 min per 2‐L sample. High water temperatures, often experienced in the tropics (23, 29, 35 °C), did not affect eDNA degradation rates, although high temperatures (35 °C) did significantly increase fish eDNA shedding rates. We established a minimum detection limit for tilapia (1 fish/0.4 megalitres/after 4 days) and found that low water flow (3.17 L/s) into ponds with high fish density (>16 fish/0.4 megalitres) did not affect eDNA detection. These results demonstrate that eDNA technology can be effectively used in tropical ecosystems to detect invasive fish species.

Translocation and Spread of Piscivorous Fishes in the Burdekin River, North-eastern Australia

The distribution of the biogeographically distinctive fish fauna of the Burdekin River, north-eastern Australia, is largely determined by the presence of a large waterfall located at the lower quarter of the river’s length. Downstream of the falls, assemblages are characterised by the presence of piscivorous fishes whereas such species are largely absent from upstream reaches. Sleepy cod (Oxyeleotris lineolatus), a large piscivorous gudgeon, was first introduced into the upper reaches of the Burdekin River in 1980 and other releases, both official and unofficial, have occurred subsequently. The population remained small and restricted to the site of introduction for a decade, but expanded in size and distribution after the occurrence of a large flood and entry into a prolonged period of drought. This gudgeon is now present in every tributary system of the Burdekin Basin. Despite the occurrence of substantial temporal variation in fish abundance due to a highly variable flow regime, negative impacts on one species, a small gudgeon (Mogurnda adspersa), are evident. Both deliberate and accidental releases of other species into the upper Burdekin River have also occurred, often to satisfy recreational fishing demand. Such species are typified by large size and piscivorous habit, characteristics alien and inimical to the native fish fauna. It is hypothesised that these piscivorous species may have even greater impact than O. lineolatus in some tributary systems of the upper Burdekin River.

The temperature regimes of dry-season waterholes in tropical northern Australia: potential effects on fish refugia

The ephemeral rivers in northern Australia break up into a series of waterholes during the long, dry summer season. These in-stream waterholes provide vital habitat for the survival of aquatic biota during this period. We describe how high-time-resolution (20 min) waterhole temperature measurements made in the Flinders and Gilbert Rivers in tropical northern Australia were used to derive thermal frequency curves that show how often waterhole temperature exceeded any given temperature threshold. During the summer period, temperatures near the surfaces of waterholes were often above that suitable for the optimum growth of some tropical fish (31°C). At the bottom of waterholes, this exceedance occurred less often, and in turbid waterholes that were stratified, temperatures rarely exceeded this threshold. Temperatures that could be lethal to some fish (34°C) also were exceeded at the surface of waterholes, but rarely, if ever, at the bottom of waterholes. An energy-balance model was used to estimate daily mean waterhole temperature with good accuracy (±1 K) at all but the sites where wind speed may have been >2 m/s (assumed in the model). The model also was used to predict the effects of climate change on waterhole temperature and the change in exceedance of thermal thresholds. A 2 K climate warming raised waterhole temperature by ∼1 K. However small this increase might seem, it led to a doubling of the length of time water temperatures were in excess of thresholds around 31°C.

Investigational piscivory of some juvenile Australian freshwater fishes by the introduced Mozambique tilapia Oreochromis mossambicus

Experimental tanks were used to observe predatory effects in three different size classes of Mozambique tilapia Oreochromis mossambicus (one of the worlds most widespread exotic species and generally regarded to be a herbivore or both herbivore and detritivore) when tested against 10 juvenile Australian freshwater fish species, and significant levels of predation against all were recorded. There was a general trend for larger O. mossambicus to kill more prey and this was also reflected in a separate series of experiments using juvenile barramundi Lates calcarifer over a range of size classes. Predatory effects by O. mossambicus broadly reflected the accepted models of predator-prey interactions, being that mortality (and survival) was closely related to relative body size and mouth gape limitation. Experimental evidence for piscivory in O. mossambicus was supported by field sampling that detected prey fish remains in 16% of all fish surveyed (n = 176). The recognition of active piscivory by O. mossambicus in laboratory and field situations is the first such evidence, and suggests a need to re-evaluate the nature of their effects in introduced environments.

A New Species of Freshwater Eel-tailed Catfish of the Genus Tandanus (Teleostei: Plotosidae) from the Wet Tropics Region of Eastern Australia

Tandanus tropicanus, new species, is described based on specimens from streams in the wet tropics region of northeast Queensland. Previously, two species were recognized in the genus Tandanus: T. tandanus of eastern Australia and T. bostocki of Western Australia. A combination of meristic and morphometric characters distinguishes the new species from all congeners. Further, taxonomic distinctness based on morphologic differences between the new species and all congeners is corroborated by genetic analyses.

How might an exotic fish disrupt spawning success in a sympatric native species

Little is known of the underlying behavioural mechanisms that allow invasive species to gain an ecological foothold in novel environments. We tested how the exotic Mozambique tilapia (Oreochromis mossambicus) might affect spawning success in groups of the native Australian eastern rainbowfish (Melanotaenia splendida splendida) under experimental tank conditions using the presence of either an isolated O. mossambicus male or a small breeding group of O. mossambicus males and females. Both egg production and the proportion of eggs fertilised in M. s. splendida were significantly reduced by over 70% and 30%, respectively, in the presence of O. mossambicus breeding groups, but were not significantly affected by the presence of only a single O. mossambicus male. These results suggest that the reproductive activities of O. mossambicus may severely disrupt the spawning success of this native rainbowfish and indicates that the ecological impacts of O. mossambicus might be far more serious than is currently thought.

A comparison of temperature regimes in dry-season waterholes in the Flinders and Gilbert catchments in northern Australia

Dry-season waterholes in ephemeral rivers provide vital habitat for aquatic biota, whose survival is dependent on the waterholes lasting throughout the dry season with temperatures that are not lethal. To examine this in the Flinders and Gilbert Rivers, 20-min temperature measurements were taken during the 2012–2013 dry season in 10 waterholes in each catchment. These data were used to derive thermal-frequency curves that quantify how often waterhole temperature exceeds thresholds for (1) the optimum growth of tropical fish and (2) their lethal temperature. Waterholes that remained deeper than ~0.5m throughout the dry season provided thermally suitable fish refugia, especially if they were turbid, because this decreased the risk of exposure to undesirable temperatures at the bottom of the waterhole. However, surface temperatures in these waterholes often exceeded optimal and even potentially lethal temperatures, so fish may have had to move to cooler water at the bottom of these waterholes. The risk to aquatic species in waterhole refugia is, therefore, primarily determined by depth, with shallow waterholes presenting the greatest risk because they become thermally unsuitable well before (1–2 months) they fully dry out.

Presence and absence of non‐native fish species in the Wet Tropics region, Australia

Distributional records of non-native fish species were identified in the Wet Tropics region, Far North Queensland, Australia, through a compilation of published records and expert knowledge. A total of 1106 records were identified comprising 346 presence and four uncertain records for at least 13 species, and 756 absence records. All current presence records consist of six species from the families Cichlidae and Poeciliidae with established self-sustaining populations in the region, probably affecting the highly diverse native fish fauna.