Plankton survey of Asterias amurensis larvae in coastal waters of Victoria (August ‐ September 2012) Final Report Alastair Hirst1, Nathan Bott2, and Randall Lee3 1 Fisheries Victoria, Department of Primary Industries 2 SARDI Aquatic Sciences, South Australia 3 Environment Protect Authority April 2013 Fisheries Victoria Department of Primary Industries If you would like to receive this Contact Details: Dr Alastair Hirst Fisheries Management & Science, Fisheries information/publication in an Victoria accessible format (such as large PO Box 114, Queenscliff Victoria 3225 print or audio) please call the Authorised by the Victorian Government, Customer Service Centre on: 2a Bellarine Hwy, Queenscliff, Victoria 3225 136 186, National Relay Service/ Printed by DPI Queenscliff, Victoria TTY: 133 677, Published by the Department of Primary or email Industries. [email protected] Copyright The State of Victoria, Department of General disclaimer Primary Industries, 2013 This publication may be of assistance to you but the State of Victoria and its employees do not This publication is copyright. No part may be guarantee that the publication is without flaw of reproduced by any process except in accordance any kind or is wholly appropriate for your with the provisions of the Copyright Act 1968. particular purposes and therefore disclaims all liability for any error, loss or other consequence Preferred way to cite: which may arise from you relying on any Hirst, A., Bott, N., and R. Lee (2013) – Plankton information in this publication. survey of Asterias amurensis larvae in Victorian coastal waters ‐ Final Report. Fisheries Victoria Technical Report No. 178, Department of Primary Industries, Queenscliff, Victoria, Australia. ISSN 1835‐4785 ISBN 978‐1‐74326‐421‐8 (Print) Survey of Asterias larvae ii Executive Summary This report was commissioned to investigate the Wilsons Promontory flowing across Bass Strait incidence of northern Pacific seastar (Asterias to the north coast of Tasmania and returning to amurensis) larvae in Victorian coastal waters, the Victorian coast off Point Hicks as part of a following the discovery of adult seastars at San gyre that dominates central Bass Strait. Remo (Western Port) in September 2011 and in Asterias larvae were also detected in Western the Tidal River estuary (Wilsons Promontory Port, Andersons Inlet and Tidal River during National Park) in May 2012. this survey. The most likely source of larvae in This study used a combination of plankton these bays and inlets is the intrusion of larvae surveys and hydrodynamic modelling to from the open coast. Whilst there is good examine the distribution of Asterias larvae in evidence that adult populations of seastars have coastal waters between Port Phillip Bay (PPB) been eradicated from Andersons Inlet and Tidal and Port Welshpool in eastern Victoria. River estuary, the presence of adult seastars in Western Port can neither be confirmed nor Zooplankton assemblages were sampled dismissed based on the results of this survey. during August ‐ September 2012 using a 90 This is because the Asterias larvae detected in μm mesh plankton net. The quantity of Western Port may have either arrived from PPB Asterias DNA (larvae) in plankton samples or originated from a source population within was measured using a genetic probe Western Port. Asterias larvae may also be The behaviour of Asterias larvae in coastal present in Shallow Inlet, but this location was waters between PPB and Cape Liptrap was not surveyed during this study. modelled using hydrodynamic and Overall the pattern of Asterias incursions at dispersion models. Andersons Inlet, Western Port and Tidal River Asterias larvae were detected in coastal waters appears consistent with natural range expansion between PPB and Wilsons Promontory during via larval dispersal; with PPB as the main source August ‐ September 2012. This finding is of larvae in the region. supported by hydrodynamic modelling of Managers will need to be vigilant to prevent the buoyant particles simulating the behaviour of spread of Asterias along the coastline between Asterias larvae exported from PPB. The PPB and Wilsons Promontory. The presence of hydrodynamic and dispersion model estimated larvae in coastal waters between PPB and larvae could reach the coast off Tidal River in Wilsons Promontory indicates further incursions approximately 44 days, well within the larval are likely in Western Port, Andersons Inlet, duration of 79–112 days for Asterias. around Wilsons Promontory, but also possibly Asterias larvae were not detected in coastal in systems where Asterias has not previously waters east of Wilsons Prom (i.e. Corner Inlet been recorded (e.g. Shallow Inlet). Protected and Port Welshpool) during August ‐ September embayments such as Waratah Bay may also be 2012. As no major currents connect the west and susceptible, given the presence of larvae at east coasts of Wilsons Promontory, the absence relatively high levels in this region. of larvae along this coastline is consistent with We recommend further sampling along the west the influence of the prevailing currents in Bass coast of Victoria between PPB and Cape Otway, Strait and their role in transporting Asterias and further east along the East Gippsland coast larvae. to confirm the outputs of the modelling and the Currents in Bass Strait are primarily influenced pattern of larval dispersal described in this by the prevailing wind direction (SW) and tides. report. Sampling should also be undertaken in Prevailing currents in Bass Strait flow Shallow Inlet, to confirm the presence/absence of principally eastwards, diverging south at larvae in this system. Survey of Asterias larvae iii Table of Contents Executive Summary ............................................................................................. iii Introduction ............................................................................................................ 1 Aim of this study ....................................................................................................................................................... 1 This report ................................................................................................................................................................... 2 Methods ................................................................................................................... 3 Plankton sampling ..................................................................................................................................................... 3 Hydrodynamic modelling ........................................................................................................................................ 3 Results ...................................................................................................................... 7 Plankton sampling ..................................................................................................................................................... 7 Hydrodynamic modelling ........................................................................................................................................ 7 Discussion ............................................................................................................. 11 Distribution of Asterias larvae .............................................................................................................................. 11 Role of larval dispersal in causing new outbreaks of Asterias? ..................................................................... 12 Could the geographical pattern of Asterias outbreaks in Victoria be explained by other vectors? ......... 13 Conclusions ............................................................................................................................................................... 13 Acknowledgements ............................................................................................. 15 References ............................................................................................................. 16 Survey of Asterias larvae iv List of Tables Table 1. Locations sampled in this survey including map codes used in figure 1, date and geographical position……………………………………………………………………………………………………. 5 Table 2. Genetic assay results showing the presence and quantity of Asterias DNA (pg/5 min tow) in each plankton sample.......................................................................................................................................... 8 List of Figures Figure 1. Map of sample locations (for location codes see Table 1). ................................................................... 6 Figure 2. Bubble plot showing the quantity of Asterias DNA (pg/ 5 minute plankton tow) recorded at each location between PPB and Port Welshpool. ................................................................................................... 9 Figure 3. 200 day simulation of continuous larval release (total of 96000 particles) from Port Phillip Bay between July and November shown as cumulative counts of visits per cell. The dispersion model provides an indication of the likelihood of Asterias larvae presence and key pathways. ...................... 10 Figure 4. Directionally average currents for Bass Strait displaying residual velocity vectors (m/s). Source: SEA (south‐east Australia) hydrodynamic model (Greer et al. 2008) ......................................................