Sources and sinks of larval settlement in Jasus edwardsii around New Zealand: Where do larvae come from and where do they go?

Abstract

Isolated adult populations tend to be interconnected via the larval stage. New Zealand red rock lobster Jasus edwardsii larvae metamorphose 12 to 24 mo after hatching. Because of this long larval life, J. edwardsii provides a useful species for studying population connectivity using satellite-derived ocean currents. In this study, tracks of J. edwardsii larvae originating from different populations are simulated to build a statistical picture of larval dispersal. By adding an algorithm for larval metamorphosis, and tuning the algorithm parameters to fit observed post-metamorphosis settlement patterns, we estimate where settlement in each population originated (i.e. larval sources), and also where larvae from each population settle (i.e. larval sinks). There are likely to be 4 major geographical areas for larval dispersal around New Zealand. In the far north, both sources and sinks are non-local. Along the east coast of the North Island, because of entrainment by the Wairarapa Eddy, sources are both local and distant, whereas most sinks are local. In contrast, to the south of the South Island, most sources are local, whereas sinks are both local and distant. The Chatham Islands form a separate geographical area, with primarily non-local sources and local sinks. The results are robust to differences in the physical model, but sensitive to metamorphosis algorithm parameters. This indicates that understanding larval behaviour is the most critical aspect in determining larval connectivity.KEY WORDS: Jasus edwardsii · Lobster · Larval dispersal · Numerical modelling · New Zealand · Phyllosoma · Settlement 354: 201-217, 2008 and perhaps of any benthic organism (Bradbury & Snelgrove 2001). Rock lobster larvae are known as phyllosomas (from the Greek phullon, meaning 'leaf,' and soma, meaning 'body') due to their transparent leaf-like morphology. Phyllosomas metamorphose into post-larval pueruli, which then swim shoreward to settle in the coastal zone. Pueruli have poorly developed mouth parts (Nishida et al. 1990) and apparently rely almost entirely on stored energy for their migration shoreward, implying a limit to the distance they can migrate. Resale or republication not permitted without written consent of the publisherMar Ecol Prog SerBecause of the long larval life and limited swimming range of the pueruli, there must be some mechanism that keeps phyllosomas close enough to the coast (or brings them back) to allow them to metamorphose and then recruit successfully. Off the east coast of the North Island, phyllosomas get entrained in the Wairarapa Eddy, a semi-permanent anticyclonic eddy (Roemmich & Sutton 1998); this leads to the high levels of puerulus settlement observed south of East Cape (Booth 1994, 2002, Chiswell & Roemmich 1998. In contrast, there has been no definitive explanation of any entrainment mechanism that leads to the high settlement seen in the southwest of the South Island (part of CRA 8). It has been suggested that phyllosomas can be carried across the Tasman Sea within their lifet...

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

“…By comparing our results with an earlier study by Chiswell and Booth (2008), we are able to determine whether the prevailing current regimes in the region are likely to be the predominant forces driving the population structure and also explore the significance to the levels of genetic differentiation we reported. Rock lobster connectivity patterns L Thomas and JJ Bell…”

“…The results from the model showed significant exchange among most regions, and the authors identified four major geographic areas associated with rock lobster larval dispersal around New Zealand: (1) the far north, (2) the east coast of the North Island, (3) the South Island and (4) the Chatham Islands. 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).…”

“…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.…”

“…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. The aim of their study was to identify source-sink relationships between the different rock lobster management areas (CRA zones of which there are currently nine).…”

“…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. One possible exception to this might be found at the bottom of the South Island, for which there is evidence for high levels of self-recruitment.…”