Jonathan P. A. Gardner

Population genetic subdivision in the New Zealand greenshell mussel (Perna canaliculus) inferred from single-strand conformation polymorphism analysis of mitochondrial DNA

Single‐strand conformation polymorphism (SSCP) analysis of the NADH IV region of the mitochondrial DNA (mtDNA) molecule in greenshell mussels (Perna canaliculus) indicated strong population genetic structuring in this endemic New Zealand species. A northern and a southern group were differentiated by frequency shifts in common haplotypes and by the occurrence of a unique southern haplotype at ≈ 20% frequency. This split occurred south of Cook Strait (the body of water between the North and the South Island) at ≈ 42° S latitude. Northern populations were less genetically diverse than southern populations and mussels from the west coast of the South Island were most distinct from northern mussels. We hypothesize that the unique haplotype VIII originated in the lower South Island, and that its spread northwards was obstructed by the opening of Cook Strait ≈ 15 000–16 000 years ago and the subsequent establishment of present‐day surface water circulation patterns in Greater Cook Strait. We suggest that present‐day strong tidal flows and turbulent mixing of water masses in Cook Strait, and intense up‐welling on the east and west coasts in this region, represent a barrier to gene flow between mussels located in the North Island and northern South Island vs. mussels in most of the South Island and Stewart Island.

Shoreline Changes and Sediment Redistribution at Palmyra Atoll (Equatorial Pacific Ocean): 1874–Present

Abstract Reef islands of Palmyra Atoll in the northern Line Islands, equatorial Pacific Ocean, underwent mainly minor natural changes in shape and size between 1874 and 1940. Many major changes occurred between 1940 and 1945 when military construction created a dredged channel into the lagoon, enlarged several islands, joined most islands around the lagoon system into a continuous roadway, constructed a causeway separating two lagoons, and created several new islands. Overall, land area approximately doubled and land volume approximately trebled during this period, and the construction affected water circulation between reef flats and lagoons. Since 1945, the atoll has been largely uninhabited, construction and most maintenance of the newly-created shoreline has ceased, and coastlines of larger islands have simplified by infilling of bays and erosion of promontories, at net rates of up to 1.8 m/y. Narrower land masses have been broken into multiple smaller arcuate islands with intervening shallow channels. Sediment moves mainly westward along ocean coasts, into lagoons on lagoon coasts, and via tidal currents where causeways have been breached. In the east, Barren Island appeared and began growing from natural causes well before military construction. After purchase by The Nature Conservancy, the atoll was designated a U.S. National Wildlife Refuge in 2001. This protection offers the opportunity to observe coastal processes operating in the absence of the efforts to protect infrastructure typically associated with inhabited atolls.

The Mytilus edulis species complex in southwest England: effects of hybridization and introgression upon interlocus associations and morphometric variation

Loglinear analysis of electrophoretic data from two hybrid Mytilus edulis x galloprovincialis populations in southwest England revealed non-significant associations between genotypes at four allozyme loci, each of which is partially diagnostic for differences between the two taxa. Significant non-random genotypic associations within the context of the non-significant model involved all four assayed loci equally, consistent with their occurrence in a relatively tight linkage group. Multivariate analyses were used to examine electrophoretic variation from the two hybrid populations, and morphometric variation in the hybrid populations and in four allopatric (two M. edulis and two M. galloprovincialis) populations from western Europe While the number of hybrid mussels is high at both sites (22% at Croyde, 53% at Whitsand) the two taxa have largely maintained the genetic differences which exist between them in allopatry. However, morphological differences between the taxa have been eroded for mussels within the hybrid zone, whereas these differences are quite pronounced for mussels from allopatric populations. It is proposed that each taxon within the genus maintains its genetic identity, despite high dispersal potential, widespread hybridization, and high levels of introgression, as a result of adaptation to different environments. The worlwide occurrence of all four Mytilus hybrid zones at ecotones between recognized biogeographical provinces which are characterized by differences in temperature and salinity is consistent with such an interpretation.

Effects of seston variability on the clearance rate and absorption efficiency of the mussels Aulacomya maoriana, Mytilus galloprovincialis and Perna canaliculus from New Zealand

The clearance rates (CR in l g−1 h−1) and net absorption efficiencies (AE) of three co-occurring mytilid species were estimated to determine the effects of variation in ambient seston quantity (total particulate matter, TPM, mg l−1) and quality (particulate organic matter, POM, mg l−1; percent organic matter, PCOM=POM/TPM) on these physiological functions. CRS estimates were significantly different among the species (Mytilus galloprovincialis>Perna canaliculus=Aulacomya maoriana), but were not correlated with differences in species-dependent mean body size (P. canaliculus>M. galloprovincialis>A. maoriana). AE estimates were independent of mean body weight, and did not differ among the species. For all three species, CR responded in a simple linear manner to seston organic content, either in terms of POM (for A. maoriana and M. galloprovincialis), or PCOM (for P. canaliculus). The AE response, although also of a simple linear type, was species-dependent and involved interactions of two or three seston components: TPM, POM and PCOM for A. maoriana; POM and PCOM for M. galloprovincialis; and TPM and PCOM for P. canaliculus. For all three species, seston variation explained 15–20% of the variation in CR and 52–59% of the variation in AE. Comparisons among the species indicated that two very different responses to variation in seston quantity and quality exist. First, significant differences in CR result from species-dependent differences in the magnitude of the response to seston variation. Second, species-dependent responses to variation in seston variation resulted in the similarity of the AE responses. Thus, the three species appear to have evolved different strategies for dealing with seston variation, but with the end result that their AE responses do not differ. Finally, no evidence was found of a negative association between CR and AE for any of the three species, suggesting that under the seston conditions experienced in this work, these species do not have the physiological compensatory capacity to reduce CR in order to increase AE. The importance of a comparative (i.e., multi-species) approach utilising ambient seston is emphasised by the findings of this research if we are to understand better the feeding and digestive physiologies of suspension-feeding organisms such as mussels.

Local endemicity and high diversity characterise high-latitude coral-Symbiodinium partnerships

Obligate symbiotic dinoflagellates (Symbiodinium) residing within the tissues of most reef invertebrates are important in determining the tolerance range of their host. Coral communities living at high latitudes experience wide fluctuations in environmental conditions and thus provide an ideal system to gain insights into the range within which the symbiotic relationship can be sustained. Further, understanding whether and how symbiont communities associated with high-latitude coral reefs are different from their tropical counterparts will provide clues to the potential of corals to cope with marginal or changing conditions. However, little is known of the host and symbiont partnerships at high latitudes. Symbiodinium diversity and specificity of high-latitude coral communities were explored using denaturing gradient gel electrophoresis (PCR-DGGE) analysis of the internal transcribed spacer regions (ITS1 and ITS2) of the ribosomal DNA at Lord Howe Island (31°S; Australia), and the Kermadec Islands (29°S; New Zealand). All but one host associated with clade C Symbiodinium, the exception being a soft coral (Capnella sp.) that contained Symbiodinium B1. Besides ‘host-generalist’ Symbiodinium types C1 and C3, approximately 72% of the Symbiodinium identified were novel C types, and zonation of symbionts in relation to environmental parameters such as depth and turbidity was evident in certain host species. The high-latitude Symbiodinium communities showed little overlap and relatively high diversity compared with communities sampled on the tropical Great Barrier Reef. Although host specificity was maintained in certain species, others shared symbionts and this potential reduction of fidelity at high-latitude locations may be the result of locally challenging and highly variable environmental conditions.

Effect of vessel voyage speed on survival of biofouling organisms: implications for translocation of non-indigenous marine species

This study experimentally determined the effect of different vessel voyage speeds (5, 10 and 18 knots = 2.6, 5.1 and 9.3 ms−1, respectively) and morphological characteristics including growth form (solitary or colonial), profile (erect or encrusting) and structure (soft, hard or flexible) on the survival of a range of common biofouling organisms. A custom built hydrodynamic keel attached to the bottom of a 6 m aluminium powerboat was used to subject pre-fouled settlement plates for this purpose. Vessel speeds of 5 and 10 knots had little effect on the species richness of biofouling assemblages tested, however richness decreased by 50% following 18 knots treatments. Species percentage cover decreased with increasing speed across all speed treatments and this decrease was most pronounced at 10 and 18 knots, with cover reduced by 24 and 85% respectively. Survival was greatest for organisms with colonial, encrusting, hard and/or flexible morphological characteristics, and this effect increased with increasing speed. This study suggests that there is predictive power in forecasting future introductions if we can understand the extent to which such traits explain the world-wide distributions of non-indigenous species. Future introductions are a certainty and can only provide an increasing source of new information on which to test the validity of these predications.

The effect of vessel speed on the survivorship of biofouling organisms at different hull locations.

This study used a specially designed MAGPLATE system to quantify the en route survivorship and post-voyage recovery of biofouling assemblages subjected to short voyages (<12 h) across a range of vessel speeds (slow, medium, fast; in the range 4.0–21.5 knots). The effect of hull location (bow, amidships and stern) was also examined. While no significant differences were evident in en route survivorship of biofouling organisms amongst hull locations, biofouling cover and richness were markedly reduced on faster vessels relative to slower craft. Therefore, the potential inoculum size of non-indigenous marine species and richness is likely to be reduced for vessels that travel at faster speeds (>14 knots), which is likely to also reduce the chances of successful introductions. Despite this, the magnitude of introductions from biofouling on fast vessels can be considered minor, especially for species richness where 90% of source-port species were recorded at destinations.

A comparison of genetic diversity between cultured and wild populations, and a test for genetic introgression in the New Zealand greenshell mussel Perna canaliculus (Gmelin 1791)

We evaluated whether genetic material from offspring of greenshell mussels, Perna canaliculus (Gmelin 1791), obtained from Kaitaia, northern New Zealand, and transferred to mussel farms around the country, had introgressed into wild (naturally occurring) mussel stocks. The potential extent of genetic introgression of this northern mussel DNA was assessed by analysis of allozyme, mitochondrial SSCP and RFLP, and nuclear RAPD markers. Cultured and wild populations throughout New Zealand showed an absence of biochemical genetic differentiation at seven protein-encoding loci, meaning that allozyme analysis was not a suitable tool to address the question of genetic introgression. For the DNA marker techniques, a haplotype specific to mussels originating from Kaitaia was identified only using mitochondrial composite markers. However, this composite marker occurred at low frequency in the Kaitaia population and not in any other populations and, therefore, could not be used to measure introgression of Kaitaia genes into wild populations. MtDNA and RAPD analyses revealed that North Island and Greater Cook Strait mussels were genetically different from lower South Island, particularly South Island west coast mussels, and the wild Stewart Island population. Furthermore, the two marker types showed that cultured mussels were significantly differentiated from wild mussels. These two findings clearly indicate that at the molecular level, population subdivision exists in P canaliculus. The SSCP and RFLP markers did not show any evidence of genetic introgression of spat moved from the north into southern mussel populations. The RAPD markers, however, showed that the wild Stewart Island population (HSB) fell outside the northern and the southern clades of populations. The HSB population is located near an aquaculture site that has been seeded with mussels from Kaitaia for over a decade. Our RAPD data are consistent with the possibility of genetic introgression of genes from northern populations into this southern population. We recommend that genetic analysis of wild mussel populations in the vicinity of stocked areas be carried out regularly

Absence of population genetic differentiation in the New Zealand greenshell mussel Perna canaliculus (Gmelin 1791) as assessed by allozyme variation

Genetic variation in the endemic New Zealand greenshell mussel, Perna canaliculus (Gmelin 1791), was examined using starch-gel electrophoresis at seven protein-coding loci (Idh; Acon-1; Acon-2; Gpd; Pgi; Pgm; Pgd) in 35 populations (N=1038 mussels). For all loci and all populations, Fishers exact tests indicated highly significant departures from Hardy-Weinberg equilibrium (HWE), but this overall result was caused by significant heterozygote deficiencies at only two loci (Pgm and Pgd), and in only three northern populations (Kuaotunu, Te Haumi and Days Bay). Allelic and genotypic differentiation between population pairs at individual loci and across all loci were nonsignificant, and genotypic disequilibrium at each locus pair was also nonsignificant for all populations. Genetic variation in all populations was high (mean heterozygosity, 0.210+/-0.113), while Neis D among populations was very low (0.002+/-0.002). Low population subdivision (θ=-0.001+/-0.002) and high levels of gene flow (Nm(p)=10.18; Nm(θ)=infinity) also indicated that the single panmictic unit model best explains population genetic homogeneity in P. canaliculus over a north-south distance >2000 km. Lack of genetic subdivision in this species is discussed in light of two previous allozyme studies, with differing results: one suggested that a north-south division exists between greenshell mussel stocks, and the other suggested that population structure in this species can be explained through isolation by distance model modified by local hydrology.

Seafloor massive sulfide deposits support unique megafaunal assemblages: Implications for seabed mining and conservation.

Mining of seafloor massive sulfides (SMS) is imminent, but the ecology of assemblages at SMS deposits is poorly known. Proposed conservation strategies include protected areas to preserve biodiversity at risk from mining impacts. Determining site suitability requires biological characterisation of the mine site and protected area(s). Video survey of a proposed mine site and protected area off New Zealand revealed unique megafaunal assemblages at the mine site. Significant relationships were identified between assemblage structure and environmental conditions, including hydrothermal features. Unique assemblages occurred at both active and inactive chimneys and are particularly at risk from mining-related impacts. The occurrence of unique assemblages at the mine site suggests that the proposed protected area is insufficient alone and should instead form part of a network. These results provide support for including hydrothermally active and inactive features within networks of protected areas and emphasise the need for quantitative survey data of proposed sites.