Papers by John van den Hoff
Marine Ornithology
Offspring growth measurements provide an integrated measure of parental investment (foraging effo... more Offspring growth measurements provide an integrated measure of parental investment (foraging effort and success) and an indicator of offspring future survivorship. We present an average growth (mass) trajectory for Wandering Albatross Diomedea exulans chicks (n = 26) weighed at sub-Antarctic Macquarie Island during four breeding seasons between 1956 and 1962. Specified growth parameters were estimated using a nonlinear mixed model for an extension of the Gompertz model and, as an alternative, cubic smoothing splines within a linear mixed model. Both modelling approaches revealed that the chicks from Macquarie Island gained mass more slowly and reached a lower maximum mass than chicks weighed at Bird Island (South Georgia), the only other temporally aligned study for this species. After reaching maximum mass, chicks from Bird Island lost mass faster than Macquarie Island chicks, resulting in very similar fledging masses for chicks at both islands. One explanation for the different gr...
Polar Research, 2009
Species of the genus Pyramimonas (Prasinophyceae) are a common, widespread, but minor component o... more Species of the genus Pyramimonas (Prasinophyceae) are a common, widespread, but minor component of the Antarctic marine phytoplankton. They are often associated with the seasonal sea-ice environment. Pyramimonas gelidicola was isolated from the water column of a saline Antarctic lake, and observations on the organism's life history as it grew in unialgal cultures were made. The alga proved to be pleomorphic: capable of producing several morphologically distinct life stages. We recorded motile single-celled quadriflagellates that formed two statistically distinct size classes, a rare uniflagellate cell-type, and aggregations of quadriflagellate cells, multilobed forms and an encystment stage. Multilobed forms and cell aggregations, never before observed in an Antarctic Pyramimonas species, are presumed to be growth medium-induced morphotypes. Multilobed forms contained an equal number of nuclei and lobes, suggesting that they are the product of asexual reproduction. Some of the morphotypes we report here may never be observed under natural field conditions, but the potential for this alga to alternate between morphotypes is clearly demonstrated.
Environmental Pollution, 2010
Biota foraging south of the ACC are not bioaccumulating detectable PFC burdens as the current inh... more Biota foraging south of the ACC are not bioaccumulating detectable PFC burdens as the current inhibits north-south exchange of surface waters.
Marine Biology, 2015
A novel classification system was applied to the sea level anomaly (SLA) environment around Mario... more A novel classification system was applied to the sea level anomaly (SLA) environment around Marion Island. We classified the SLA seascape into habitat types and calculated percentage of habitat use of ten juvenile southern elephant seals (SES). Movements were compared to SLA and SLA slope values indicative of ocean eddy features. This classification provides a measure of habitat change due to seasonal fluctuations in SLA. Some of the seals made two migrations in different seasons, each of similar duration and proportions of potential foraging behaviour. The seals in this study did not use any intense eddy features, but their behaviours varied with SLA class. Potential foraging behaviour was positively influenced by negative SLA values (i.e. areas of below average sea surface height). Searching behaviour during the winter was more likely at eddy edges where high SLA slope values correlated with low SLA values. Though the seals did not forage within newly spawned eddies, they did forage near the sub-Antarctic front. Plankton and other biological resources transported by eddies formed at the subtropical convergence zone are evidently concentrated in this region and enhance the food chain there, forming a foraging ground for juvenile SES from Marion Island.
Aquatic Biology, 2012
Marine mammals forage in dynamic environments characterized by variables that are continuously ch... more Marine mammals forage in dynamic environments characterized by variables that are continuously changing in relation to large-scale oceanographic processes. In the present study, behavioural states of satellite-tagged juvenile southern elephant seals (n = 16) from Marion Island were assessed for each reliable location, using variation in turning angle and speed in a state-space modelling framework. A mixed modelling approach was used to analyse the behavioural response of juvenile southern elephant seals to sea-surface temperature and proximity to frontal and bathymetric features. The findings emphasised the importance of frontal features as potentially rewarding areas for foraging juvenile southern elephant seals and provided further evidence of the importance of the area west of Marion Island for higher trophic-level predators. The importance of bathymetric features during the transit phase of juvenile southern elephant seal migrations indicates the use of these features as possible navigational cues.
Ecology, May 1, 2011
Knowledge of the trophic functioning of Southern Ocean ecosystems is critical to their understand... more Knowledge of the trophic functioning of Southern Ocean ecosystems is critical to their understanding and management. Marine ecosystem models, often used to explore the potential impacts of human disturbance and climate change, and for fisheries stock assessments, generally rely on suitable data to underpin the parameterization of taxon attributes and diets. Diet-related data from published and unpublished data sets and studies were collated into a single consistent data set, circum-Antarctic in scope, with two principal tables. The first table relates to direct sampling methods of dietary assessment, including gut, scat, and bolus content analyses, stomach flushing, and observed feeding. It currently comprises ;25 000 records from 300 studies and includes information on .1000 taxa. The second table is a compilation of stable isotope values (currently 1500 records from 20 studies, covering 200 taxa). Each record in these two tables includes details such as the location and date of sampling, predator size and mass, prey size and mass, and estimates of dietary importance.
BMC evolutionary biology, 2016
Models that predict changes in the abundance and distribution of fauna under future climate chang... more Models that predict changes in the abundance and distribution of fauna under future climate change scenarios often assume that ecological niche and habitat availability are the major determinants of species' responses to climate change. However, individual species may have very different capacities to adapt to environmental change, as determined by intrinsic factors such as their dispersal ability, genetic diversity, generation time and rate of evolution. These intrinsic factors are usually excluded from forecasts of species' abundance and distribution changes. We aimed to determine the importance of these factors by comparing the impact of the most recent climate regime change, the late Pleistocene glacial-interglacial transition, on two sympatric, ice-dependent meso-predators, the emperor penguin (Aptenodytes forsteri) and Weddell seal (Leptonychotes weddellii). We reconstructed the population trend of emperor penguins and Weddell seals in East Antarctica over the past 75,...
Polar Biology, 2003
Male southern elephant seals (Mirounga leonina
Polar Biology, 2007
Total numbers of adult female southern elephant seals (cows) breeding at Macquarie Island were de... more Total numbers of adult female southern elephant seals (cows) breeding at Macquarie Island were determined for 19 of the 52 year period between 1952 . Totals for 1952 (exc. 1959 were estimated from the relationship between censuses of the isthmus study area and concurrent censuses for the whole island. Totals for 1987-2004 were obtained by direct census of the entire island in mid-October. Cow numbers decreased from a maximum of about 40,000 in the 1950s to a minimum of 18,300 in 2000, but then increased slightly to 19,200 in 2004. Nonlinear and post-hoc linear analysis of the count data identified 1999 as the year when the exponential rate of change (r) slowed from -1.4% per annum to near zero. The rate of change was not uniform for each census sub-area counted (1987)(1988)(1989)(1990)(1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004), suggesting that certain terrestrially based density-dependent mechanisms were influencing the annual distribution of cows.
The ice-free Vestfold Hills is deeply dissected by fjords and has a number of lakes and lagoons w... more The ice-free Vestfold Hills is deeply dissected by fjords and has a number of lakes and lagoons with seasonal connection to the sea. These diverse aquatic habitats vary greatly in salinity, ice cover, temperature, water depth and water column mixing. As part of ongoing studies on these water bodies, we have sampled the plankton from a basin at the head of Ellis Fjord, some 10 km from the open sea, where the temperature was 2. 6OC and the salinity was between 37.6 and 38.4%o. In enriched cultures from a 25 I sample taken from this basin we have found the loricate choanoflagellates, Acanthoeca brevipoda, Acanthocorbis unguiculata, Diaphanoeca grandis, Stephanoeca complexa, S. norrisii and S . diplocostata. From this site we describe the new species Acanthocorbis tintinnabulum. The 25 I sample was integrated over 0.8 m which encompassed the boundary layer between oxic and anoxic waters. The sample was stored at ca. 4OC for 3 weeks and was anaerobic for that period. The species enriched from the sample were therefore able to withstand prolonged anoxia.
Australian Veterinary Journal
Polar Biology, 2015
For growth, the mixotrophic ciliate Mesodinium rubrum sequesters organelles from ingested prey. F... more For growth, the mixotrophic ciliate Mesodinium rubrum sequesters organelles from ingested prey. Feeding in the field is poorly known; however, isolates of an Antarctic M. rubrum strain are maintained in culture on a diet of Teleaulex/Plagioselmis/Geminigera-like cryptophytes, suggesting that cryptophyte presence may be an important factor controlling M. rubrum distribution and abundance in nature. We augmented field surveys with published findings to establish the distribution of both M. rubrum and a Geminigera-like cryptophyte in a range of East Antarctic aquatic environments. We also studied their overwinter abundances in Ace Lake to determine whether a predator-prey relationship existed between the two species in this natural enclosed ecosystem. The ciliate and the cryptophyte co-occurred in the majority of sites sampled which ranged widely in salinity (2.2-150 %) and temperature (-3.0-16°C). We observed a cyclic relationship in species abundances in Ace Lake, implying population growth for M. rubrum responded to changed cryptophyte abundance. Mesodinium rubrum likely exerts top-down pressure on cryptophyte abundances in natural enclosed ecosystems especially under low-light winter conditions. The ciliate can be considered an apex predator in highly truncated food webs.
Polar Biology, 2014
Alien species pose an increasing threat to the biodiversity of the Antarctic region. Several alie... more Alien species pose an increasing threat to the biodiversity of the Antarctic region. Several alien species have established in Antarctic terrestrial communities, some representing novel functional groups such as pollinators and predators, with unknown impacts on ecosystem processes. We quantified the unintentional introduction of alien invertebrates to the Antarctic region over a 14-year period (2000-2013). To do this, probable pathways (Australian Antarctic cargo operations) and endpoints (research stations) for invertebrate introductions were searched. In addition, we undertook a stratified trapping programme targeting invertebrates on supply vessels in transit to the Antarctic region and also at cargo facilities in Australia during the 2012-2013 austral summer field season. Our results show that a diverse suite of invertebrate taxa were being introduced to the Antarctic region, with 1,376 individuals from at least 98 families observed or trapped during the sampling period. Many individuals were found alive. Diptera, Coleoptera and Lepidoptera were the most common taxa, comprising 74 % of the collection. At the family level, Phoridae (small flies) and Noctuidae (moths) were most commonly observed. Individuals from 38 different families were repeatedly introduced over the study period, sometimes in high numbers. Food and large cargo containers harboured the most individuals. These findings can assist in improving biosecurity protocols for logistic activities to Antarctica, thereby reducing the risk of invasions to the Antarctic region.
A total of 1423 stomach samples were taken from Patagonian toothfish, Dissostichus eleginoides, c... more A total of 1423 stomach samples were taken from Patagonian toothfish, Dissostichus eleginoides, caught by bottom trawls at two fishing grounds near Macquarie I., over three fishing seasons. Fish were caught at depths ranging from 500 to 1290 m, and ranged in size from 310 to 1490 mm total length. The 462 stomach samples (32%) that contained prey items indicated that toothfish preyed on a broad range of species including fish, cephalopods and crustaceans (58%, 32% and 10% biomass, respectively), suggesting that they are opportunistic predators. The bathypelagic fish Bathylagus sp. was the most important fish prey (14% dietary biomass); however, nototheniid, macrourid, morid and myctophid fish were also taken. The squid Gonatus antarcticus was also an important prey species (16% biomass), and many other cephalopod species were taken in low frequency. Prawnlike crustaceans (Nematocarcinidae, Mysididae, Sergestidae and Euphausiidae) were the most important crustaceans taken (9% of prey biomass). Significant inter-seasonal and inter-fishing-ground differences in diet were found, but dietary composition was not related to fishing depth, fish size (with the exception of one fishing ground in one season) or the time of day of capture. Comparison with other studies reveals biogeographical differences in the diet of toothfish. D i e t o f P a t a g o n i a n t o o t h f i s h S . D . Go l d s w o r t h y e t a l . M F 0 0 0 7 5
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Papers by John van den Hoff