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Publications by Richard Stafford-Bell

The establishment of clonal marine plant populations, including the seagrass Zostera muelleri (Zo... more The establishment of clonal marine plant populations, including the seagrass Zostera muelleri (Zosteraceae), may be more dependent on the availability of viable vegetative fragments rather than seed. New populations may establish through long-distance dispersal of viable vegetative fragments, potentially increasing genetic diversity and resilience to anthropogenic or naturally occurring disturbance. A number of activities can dislodge vegetative fragments of Z. muelleri (leaves, rhizomes and roots) from the sediment. These fragments can remain positively buoyant, floating on the surface of the water. As the time since dislodgement increases, buoyancy may become reduced, causing fragments to move lower into the water column. However, what is not known is how long these fragments remain buoyant and potentially viable for recolonization. To address this knowledge gap, we collected wrack samples (n = 125) of Z. muelleri from four Victorian estuaries. Fragments were floated in outside aquaria for up to ten weeks, with subsamples tested for metabolic activity using tetrazolium violet. Porosity of seagrass rhizomes was also investigated to understand the influence of lacunae (large air filled spaces within plant tissues) on the flotation of vegetative fragments. The average proportion of potentially viable fragments collected in wrack ranged from 3.6% (SD = 2.23) to 11.2% (SD = 5.9). While there was a steady decline in the buoyancy of fragments across the ten-week period, initial buoyancy was relatively high, with approximately 50% of the fragments remaining positively buoyant for the initial five weeks. The viability of fragments following flotation was high. One hundred percent of fragments (n = 25 per assay) remained viable after floating for three weeks, with only a marginal decline (=96% viability) occurring after five weeks. When considered in conjunction with the highly porous nature of seagrass rhizomes (lacunae accounted for 45.2% of total volume), our findings indicate that the species may be capable of prolonged periods of transport dispersal within the marine environment.

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Episodic freshwater events within coastal environments may influence germination and early-stage ... more Episodic freshwater events within coastal environments may influence germination and early-stage seedling development within the seagrass Zostera muelleri. Hypocotyl hairs have the potential to provide anchorage to sediments, initiate geotropism and facilitate water uptake. To this point, production of these structures in seagrasses has received little attention in the literature though they may significantly influence their ability to maintain populations within estuarine environments. Early-stage development of Z. muelleri was examined under various salinity, temperature and light conditions using a fully fac-torial design. We found that germination rates declined significantly with increasing salinity, with the greatest germination occurring in treatments subjected to 24-h darkness at either 15 or 20 • C. Hypocotyl hair initiation was influenced by both temperature and salinity. Seeds which germinated at 20 • C in 24-h darkness had significantly more germinants developing hypocotyl hairs than the other treatments. Although the initiation of hypocotyl hairs was generally greater under higher salinity concentrations, germinants subjected to lower salinity conditions had a greater likelihood of developing fully extended hypocotyl hairs. Based on our results, freshwater pulses that occur shortly after seed maturation could initiate year round germination in temperate regions. Furthermore, germinants stored at salinities of less than 16ppt showed greater elongation of hypocotyl hairs, indicating such pulses would also aid in the development of these structures. The timing of freshwater pulses may exert control over the recruitment and long-term survival of the species.

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Aquatic Mammals, 2012

AbstractA largely unregulated seal-swim industry exists in Port Phillip Bay, Victoria, Australia.... more AbstractA largely unregulated seal-swim industry exists in Port Phillip Bay, Victoria, Australia. This study has documented four fur seal behaviours in response to vessel traffic and presence of swim-mers in order to determine the impact of tourism activities on Australian fur seals (Arctocephalus pusillus doriferus). Behavioural responses of fur seals to the presence of a total of 135 vessels (tour = 61 and recreational = 74) were collected on 42 research trips over the peak austral summer tour-ist period (November 2007 to February 2008). After considering all studied variables, vessel dis-tance, the number of swimmers undertaking seal-swim activities, and the number of recreational vessels were found to influence seal behaviour. Aggressive behaviour displays by fur seals were influenced by the presence of recreational vessels within close proximity to the study site (< 200 m); haul-out events initially increased as a result of the presence of swimmers undertaking seal-swim activities; and occurrences of fur seals entering the water increased in response to the distance of approaching tourism vessels to the study site. Statistical analyses found no clear indicator influ-encing the number of threat postures displayed by fur seals. While a weak linear relationship was identified between the indicators (i.e., presence of recreational vessels, presence of swimmers, and the distance of tour vessels) and the three behav-iours displayed by fur seals, post hoc tests failed to achieve significantly different means for each of the indicators. This preliminary research into the impact of swim-with tourism upon A. pusillus doriferus will provide valuable baseline data for the future. The long-term research into the effects of this particular tourism industry on fur seal behaviour may ensure wildlife managers develop appropriate regulations for seal tourism interac-tions that promote a sustainable marine tourism industry within Port Phillip Bay.

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Conference Presentations by Richard Stafford-Bell

The establishment of clonal marine plant populations including the seagrass Zostera muelleri may ... more The establishment of clonal marine plant populations including the seagrass Zostera muelleri may be more dependent on the availability of viable vegetative fragments rather than seed. Vegetative fragments of Z. muelleri consisting of leaves, rhizomes and roots can dislodge from the sediment due to natural or anthropogenic activities. Generally, these fragments are buoyant and persist in the water column until they sink and decompose or are carried ashore to form wrack. What is not known however, is how long dislodged fragments can remain viable and if they have the ability to form new populations. Wrack samples (n=125) were collected from four Victorian estuaries to determine the proportion of potentially viable seagrass and the potential for regrowth. Hand collected fragments were floated in a mesocosm for up to five weeks and then tested for metabolic activity using tetrazolium violet. Porosity of seagrass rhizomes was also investigated to understand the influence of lacunae on floatation of vegetative fragments. Viability of seagrass fragments was high. The average proportion of potentially viable fragments collected in wrack ranged from 3.64% (SD=2.23) to 11.2% (SD=5.90), while 96% of fragments (n=24) tested with tetrazolium violet remained viable after a floatation period of five weeks. These factors, when considered in conjunction with the highly porous nature of seagrass rhizomes (lacunae accounted for 45.2% of total volume) indicate the species is potentially capable of prolonged periods of movement within the marine environment. By extrapolation, new populations could potentially establish that are physically well removed from source populations.

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Hypocotyl hairs, single celled structures that develop soon after seed germination, provide ancho... more Hypocotyl hairs, single celled structures that develop soon after seed germination, provide anchorage to sediments, initiate geotropism and may facilitate water uptake. The ability of germinating seedlings of marine angiosperms to produce these structures may significantly influence their ability to maintain
populations within estuarine environments. Such physiological adaptations that allow for greater attachment to the substrate by germinating seedlings would provide a competitive advantage. The development of hypocotyl hairs on germinants
of the intertidal seagrass Zostera muelleri Irmisch ex Asch. was examined under differing temperature, salinity and light regimes. Hypocotyl hairs developed across the majority of the convex surface of the hypocotyls and was significantly influenced by both temperature (F2, 33 = 12. 06, p = 0. 002)
and salinity (F5, 30 = 28. 21, p = <0. 001). Seeds which germinated at 20°C in 24-h darkness had significantly more germinants developing hypocotyl hairs than all other treatments. Although the development of hypocotyl hairs
was generally greater under higher salinity concentrations, germinants stored under lower salinity conditions had a greater likelihood of developing fully extended hypocotyl hairs, with greater extent than those stored at higher salinity concentrations. Considering that the requirements for ideal germination and hypocotyl hair development in Z. muelleri are somewhat constrained, the control of freshwater inputs may have a direct influence on the ability of Z. muelleri germinants to develop these structures which may ultimately influence their capacity to disperse. As such, the relationships between the physico-chemistry of the water column and hypocotyl hair development should be considered in the management of this ecologically important species.

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Aquatic Mammals, 2012

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