Trans-Tasman Sea larval transport: Is Australia a source for New Zealand rock lobsters?

Abstract

Two species of rock lobster (Palinuridae) are commonly found in coastal waters around both New Zealand and Australia. Both species have a relatively long larval phase, which raises the question of how populations can be maintained in regions where the mean flow advects larvae away from the coast. Previous work shows that Jasus edwardsii is genetically indistinguishable between Australia and New Zealand, whereas Sagmariasus verreauxi may be genetically different between the 2 countries. Satellite altimeter data are used here to test the hypothesis that Australia acts as a source of larvae for some New Zealand populations, and to investigate if there is a physical mechanism for the apparent lack of gene flow for S. verreauxi. A Lagrangian approach is used in which the western Tasman Sea is seeded with numerical drifters to build up a statistical summary of the likely distribution of larval trajectories. Ignoring biological factors, about 9% of J. edwardsii and about 2% of S. verreauxi larvae might be expected to arrive in New Zealand waters within their respective larval lifetimes. An order-of-magnitude estimate shows that even with extremely high mortality, these rates are high enough for trans-Tasman larval flow to contribute to and possibly maintain some New Zealand populations. Larval flow across the Tasman Sea should be sufficient to maintain transTasman genetic homogeneity in both species. We suggest that 1 reason that S. verreauxi may not be genetically homogenous is that in order to arrive in New Zealand within 1 larval lifetime, they have to cross the Tasman Sea north of the productive Subtropical Front where there is not enough prey to sustain them. KEY WORDS: Lobster larvae · Tasman Sea · Modelling Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 247: [173][174][175][176][177][178][179][180][181][182] 2003 (approximately 200 km diameter) permanent eddies, such as the Wairarapa Eddy shown in Fig. 1 (Booth & Stewart 1992, Chiswell & Booth 1999. These eddies appear to retain phyllosomas long enough for them to develop into the post-larval puerulus stage, and then swim back to the coast.There is a substantial fishery for Jasus edwardsii on the southwest coast of South Island, and the presence of these South Island populations, away from the influence of the east coast eddies, raises the question of how they are maintained. Mean dynamic height field ( Fig. 1) shows no evidence of permanent eddies off the west coast of New Zealand that could entrain phyllosomas, so it appears that these populations are maintained by a mechanism other than entrainment of phyllosomas offshore.It has been suggested that Australia acts as a source of Jasus edwardsii larvae, and that phyllosomas drift across the Tasman Sea before metamorphosing near the west coast of New Zealand (Booth et al. 1990, Booth & Ovenden 2000. Large breeding stocks of J. edwardsii are found in Australia along the southern New South Wales, Victorian, Tasmanian, and South Australian coasts (Phill...

Lost at sea: genetic, oceanographic and meteorological evidence for storm-forced dispersal

“…The general importance of this is that it shows how stochastic weather effects may lead to drifting organisms arriving in areas that would not be predicted by dispersion on ocean currents alone. Increasingly, studies of various organisms, ranging from rock lobsters [48] to kelp [49], are showing that many factors aside from prevailing oceanographic conditions may influence dispersal trajectories.…”

Testing the consistency of connectivity patterns for a widely dispersing marine species

“…The SouthWest coast of New Zealand supports a productive J. edwardsii fishery with high levels of annual recruitment (Booth and Breen, 1992); however, there are no apparent oceanographic retention mechanisms in the region to trap larvae and facilitate self-recruitment (Heath, 1980;Chiswell et al, 2003). This implies that the larvae recruiting to this coast are coming from another source.…”

“…In addition to these four geographic regions, Chiswell and Booth (2008) identified high levels of local settlement at the bottom of the South Island and suggested that populations in this region are likely to be maintained by self-recruitment. Using a similar modeling approach, Chiswell et al (2003) investigated trans-Tasman dispersal rates and estimated that 9-14% of J. edwardsii larvae originating from the south east coast of Australia would be able to reach the west coast of New Zealand, which was used to explain the genetic homogeneity for J. edwardsii on the basis of mitochondrial DNA data (Ovenden et al, 1992).…”

“…Specifically, we used our genetic data to provide estimates of contemporary rates of gene flow and estimates of demographic connectivity to test the findings of the earlier oceanographic models that predicted dispersal patterns of J. edwardsii across the Tasman Sea (Chiswell et al, 2003) and throughout New Zealand (Chiswell and Booth, 2008). Given that the results from the New Zealand scale model (Chiswell and Booth, 2008) revealed high levels of larval exchange between management areas throughout New Zealand, we hypothesized that the genetic structure of J. edwardsii would reflect those findings and reveal a relatively homogenous population.…”

“…However, although the existing genetic data suggest homogeneity, extensive oceanographic modeling studies for J. edwardsii suggest that some source-sink dynamics exist. These models have estimated New Zealand-scale patterns of connectivity (Chiswell and Booth, 2008) and also the supply of recruits from Australia to New Zealand (Chiswell et al, 2003). Chiswell and Booth (2008) used a Lagrangian modeling approach, applying time varying ocean currents (1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003) derived from a satellite altimeter to track the paths of individual J. edwardsii larvae released from different locations around New Zealand.…”