The genetic structure of New Zealand's coastal benthos: using the estuarine clam Austrovenus stutchburyi, to determine rates of gene flow and population connectivity

For many benthic marine taxa, dispersal over large distances is dependent on a pelagic larval phase. It is through the dispersal process that benthic taxa can found new populations, colonise disturbed or degraded habitats and achieve genetic exchange between geographically separated subpopulations. While it is widely accepted that the dispersal process is important in determining the dynamics of many marine communities, difficulties associated with the direct measurement of larval dispersal mean that detailed knowledge of the mechanisms controlling larval transport has been elusive. Consequently, indirect methods, such as population genetics, have been used to estimate dispersal pathways. This thesis examines the population genetic structure of New Zealand’s coastal benthos with the aim of enhancing our understanding of population connectivity, as well as identifying physical and biological processes that might influence population genetic structure. The population genetic structure of New Zealand’s coastal benthos was examined in a quantitative literature review. Divergence between northern and southern populations was identified as the most frequently reported population genetic structure, with the divergence most often located in central New Zealand. Additional population structure although rare, was reported for a number of taxa, particularly those restricted to estuaries and with life history traits indicative of limited dispersal potential. A significant negative correlation between pelagic larval duration (PLD) and genetic divergence suggests that PLD may be a useful proxy for a species’ dispersal ability. However, variation in estimates of divergence for taxa with limited PLDs suggests that other factors may also influence dispersal potential. To determine whether populations of an estuarine organism with life history traits indicative of widespread dispersal are genetically subdivided, I examined the population genetic structure of the clam Austrovenus stutchburyi using the mitochondrial gene cytochrome oxidase c subunit I (COI). Analyses indicated that dispersal was limited and that gene flow was mostly occurring among estuaries in close proximity. Genetic boundaries were detected in central New Zealand, about the East and North Capes and in the south of the South Island. Similar boundaries have been reported for estuarine taxa lacking a dispersive larval phase suggesting that distribution and habitat requirements may influence patterns of gene flow. To further investigate gene flow among estuaries, I conducted a multi-scale genetic analysis of A. stutchburyi populations on New Zealand’s west coast Analyses of COI and microsatellite loci showed populations to be well connected within estuaries and at the regional sampling scale (≤ 156 km) although not at a national scale (≤ 1226 km). Distance among populations explained much of the observed genetic variation as did distance between estuaries. Long stretches of open coast appear to act as barriers to dispersal among A. stutchburyi populations. However, as long stretches of open coast also coincide with putative hydrodynamic dispersal barriers there is some uncertainty about the roles of barriers versus inter-estuary distance in generating the observed divergences. Within-estuary genetic differences were evident from COI analyses, but may result from local adaptation to within-estuary environmental gradients. I conclude that genetic connectivity among populations of New Zealand’s estuarine taxa is generally low relative to coastal species. The data presented here also suggest that migration among patchily distributed habitats, such as estuaries, will be dependent on the spatial arrangement of habitats. Consequently, patchily distributed taxa may experience low rates of ecologically meaningful connectivity, requiring relatively cautious management at small spatial scales to ensure the persistence of intact biological communities in the face of persistent anthropogenic and natural disturbances

Short Note: Report of mummified leopard seal carcass in the southern Dry Valleys, McMurdo Sound, Antarctica.

The wide spread occurrence of mummified seal and penguin carcasses tens of kilometres from the open ocean is an interesting phenomenon occurring in the Antarctic Dry Valleys. Mummified seal carcasses were first reported by Scott’s expedition in 1903 (Scott 1969), and live seals and seal carcasses have since been reported many kilometres from the nearest ice-free ocean. Seal carcasses found in the McMurdo Dry Valleys are predominantly crabeater seals (Lobodon carcinophaga (Hombron & Jacquinot)) with a smaller number of Weddell seals, (Leptonychotes weddellii (Lesson)), also reported. Here we present only the second published report of a leopard seal carcass from the McMurdo Dry Valleys

Phylogeography of New Zealand’s coastal benthos

During the past 30 years, 42 molecular studies have been undertaken in New Zealand to examine the phylogeography of coastal benthic invertebrates and plants. Here, we identify generalities and/or patterns that have emerged from this research and consider the processes implicated in generating genetic structure within populations. Studies have used various molecular markers and examined taxonomic groups with a range of life histories and dispersal strategies. Genetic disjunctions have been identified at multiple locations, with the most frequently observed division occurring between northern and southern populations at the top of the South Island. Although upwelling has been implicated as a cause of this disjunction, oceanographic evidence is lacking and alternative hypotheses exist. A significant negative correlation between larval duration and genetic differentiation (r2 = 0.39, P < 0.001, n = 29) across all studies suggests that larval duration might be used as a proxy for dispersal potential. However, among taxa with short larval durations (<10 days) there was greater variability in genetic differentiation than among taxa with longer pelagic periods. This variability implies that when larval duration is short, other factors may determine dispersal and connectivity among populations. Although there has been little congruence between the phylogeographic data and recognised biogeographic regions, recent research has resolved population subdivision at finer spatial scales corresponding more closely with existing biogeographic classifications. The use of fast-evolving and ecologically significant molecular markers in hypothesis-driven research could further improve our ability to detect population subdivision and identify the processes structuring marine ecosystems

Word Ways Challenges (Part 3)

For an introduction to this series of articles classifying and summarizing unsolved logological problems in Word Ways, see the February 1979 Word Ways

Word Ways Challenges (Part 2)

For an introduction to this series of articles classifying and summarizing unsolved logological problems in Word Ways, see the February 1979 issue

Word Ways Challenges (Part 1)

Word Ways has presented a great many challenges, explicit and implicit, since 1968; many were never taken up, and many are not available to newer readers. In this series of articles, we have attempted to gather them in one place

Monitoring of subtidal reef biota off Motuotau Island in relation to dredge spoil dumping by the Port of Tauranga Ltd 2014-2018

Background • Dredge spoils generated from the development and maintenance of the Port of Tauranga is disposed of on the inner shelf off Mt Maunganui. • Major channel deepening and widening programmes were undertaken in 1992 and 2015/16. Maintenance dredging is undertaken more regularly. • Since 1990, monitoring has been conducted to determine if the dumping of dredge spoils was affecting subtidal reef communities around Motuotau Island, as island off Mt Maunganui beach and inshore of the dredge spoils disposal area. • Three sites at Motuotau have been monitored since 1990. A site to the east of Motuotau has been monitored as a control site and two sites to the north-east and north-west of Motuotau have been monitored as impact sites. • Monitoring has consisted of photographic monitoring of permanent transects close to the reef-sand boundary to record (a) changes in the elevation of the seabed relative to the rocky reef, and (b) changes in the biological community over time. • Monitoring has taken place in 1990, 1991, 1993, 1995, 1998, 2001, 2006, 2009 and 2012. • One of the difficulties of the monitoring programs was that the marker pins, which are cemented onto the reef, would often be dislodged between surveys and would need to be reinstated prior to each new survey taking place. This made it difficult to be sure that the same section of reef was monitored on each occasion and that the measurement of changes in seabed height was accurate. • In 2013, a decision was made to reinstate marker pins for the permanent transects. In January 2014, holes were drilled into the reef and stainless steel rods were secured in these holes using epoxy cement. It is unlikely that these marker pins will ever be dislodged from the reef. • At the same time, the monitoring methodology was reviewed and a number of changes recommended. Most significantly, it was decided that the reef being monitored as a control site did not really constitute a control against the effects of dredge spoil dumping and subsequently all three sites would be considered as impact sites. • Monitoring took place in January and May 2014, November 2015 and April 2018 and is reported on here. Findings • Marker pins were reinstated in January 2014 and four and a half years later remain solidly in place. • In general terms, the reefs around Motuotau appear to be healthy and in a state that is comparable to other reefs of similar depth, aspect and exposure along the Bay of Plenty coastline. • The 2014, 2015 and 2018 surveys did not record any major changes in the biological communities of the reefs around Motuotau. • Measurements of the distance between the bottom marker pin at each site and the reefsand boundary indicate that the reefs are not being inundated by dredge spoils. Seabed heights have fluctuated by as much as 30 cm since 2014 and this is not thought to be outside the scale of fluctuations that would naturally occur given the aspect and energy environment of the surveyed reefs. • Photographic surveys continue to prove useful in capturing information about the diversity of subtidal reef communities. Although there is some evidence of minor changes in these communities over time this is to be expected. There is also evidence of stability in these communities with a number of sponges on these transects having been present for several decades

Inland extent of the Weddell Sea Rift imaged by new aerogeophysical data

Peer reviewedPostprin