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Apoptosis or programmed cell death is a fundamental process essential for an organism's development and homeostasis in the immune system of both vertebrates and invertebrates. However, little is known about apoptotic processes in marine bivalves which require further investigation to elucidate mechanisms and identify molecular effectors of cell death pathways. In this study, we characterized cellular and molecular mechanisms of apoptosis induced by lipopolysaccharide (LPS) in New Zealand Greenshell™ mussel (Perna canaliculus) haemocytes. Mussel haemocyte samples were exposed to different LPS concentrations (0, 50 and 100 μg ml−1) and incubated at 19 °C for 3 h prior to assessment of various cell health parameters via flow cytometry assays and GC/MS-based metabolomic analyses. Flow cytometry results showed slightly higher, but non-significant differences in production of reactive oxygen species between LPS-exposed and control (no LPS) samples. However, percentages of apoptotic cells determined via depolarization of the mitochondrial membrane potential and caspase-3/7 activity in LPS-exposed samples were significantly higher than in control samples, providing mechanistic information regarding initiation and progression of the apoptotic cascade. The metabolite profile of LPS-exposed haemocytes showed elevated levels of 11 metabolites compared to that of the control. These metabolites may be involved in protein and lipid degradation as a consequence of apoptosis and other immune or physiological responses. This study demonstrates that LPS could trigger apoptosis in mussel haemocytes and provides insights into apoptotic processes in mussel haemocytes. Such knowledge could be useful for understanding the immune responses of farmed bivalves to waterborne pathogens and identification of molecular biomarkers for disease management in aquaculture.

While tissue-specific immune responses are well-understood in mammals, such studies are lacking for marine bivalves. In this study, we investigated immune responses in gill, hepatopancreas and haemolymph of mussels (Perna canaliculus Gmelin, 1791) following experimental infection with Vibrio sp. DO1 (V. coralliilyticus/neptunius-like isolate). Significant differences in metabolite profiles and metabolic responses between tissues were observed. Overall, haemolymph and gills shared common metabolic responses characterized by increases in itaconic acid and decreases in other amino acids (e.g., BCAAs, lysine, tryptophan) and fatty acids (e.g., DHA, EPA, palmitoleic acid). Increases in itaconic acid, decreases in fatty acids, and increases in amino acids were found in hepatopancreas tissues. The alterations of these metabolites suggest osmotic stress, oxidative stress, changes in amino acid metabolism and protein synthesis in the immune system of P. canaliculus caused by Vibrio sp. infection. Interestingly, the accumulation of itaconic acid in all three tissues of infected mussels suggests that this metabolite has an important role in the mediation of bivalve antimicrobial activities and immune responses. These results indicate that careful consideration should be given to tissue sampling choices for immunological and metabolomics studies. In addition, further investigations are needed to elucidate mechanistic responses across different tissues associated with pathophysiological processes in bivalves.

Temperature fluctuations during the live storage and transport of bivalves are known to be one of the most important stressors for these markets. However, the biological mechanisms that induce these stresses and the immunological responses to stressors are not currently understood. In this study, a gas chromatography–mass spectrometry (GC–MS based) metabolomics approach was used along with flow cytometry to characterize the responses of clams during aerial exposure in two different storage conditions (ice and no ice) and storage periods (1 h and 6 h). The results showed a significant increase in haemocyte mortality and ROS production in clams exposed to room temperature (no ice) and after 6 h compared to low temperature (with ice) and 1 h, respectively. The metabolite profiles of clam haemolymph in all groups revealed changes of many metabolites between the different temperatures and sampling times. Among them, lactic acid, succinic acid, malic acid, fumaric acid and glutamic acid were identified as significantly affected by both storage condition and period. These results indicate that clam storage stresses produced biological disturbances related to energy metabolism, which was switched from aerobic to anaerobic metabolism. These findings provide insights regarding the specific metabolic consequences of bivalve live storage and transport, which may lead to improved product handling along the supply chain. In addition, this study demonstrates the effective use of metabolomics and flow cytometric approaches on bivalve haemolymph as a non-destructive shelf life assessment method.

The steady increase in abalone aquaculture production throughout the world has attracted growing interest in the application of new technologies, such as omics approaches for abalone research. Many omics techniques, such as genomics, transcriptomics, proteomics, and metabolomics are becoming established in abalone research and are beginning to reveal key molecules and pathways underlying many biological processes, and to identify associated candidate biomarkers of biological or environmental processes. In this contribution, we synthesize the published omics studies on abalone to highlight the current state of knowledge, open questions, and future directions. In addition, we outline the challenges and limitations of each omics field, some of which could be overcome by integrating multiple omics approaches – a future strategy with great potential for contributing to improve abalone production.

The New Zealand geoduck clam Panopea zelandica (Quoy and Gaimard, 1835) is among the largest burrowing clams throughout the world. However, the effects of size scaling on physiology have not been studied for any geoduck species. In this study, we determined the allometric coefficients of respiration rate (RR) and clearance rate (CR) for P. zelandica. The allometric coefficients (β) of RR and CR in P. zelandica were 0.73 ± 0.03 and 0.62 ± 0.07, respectively. Since the clearance rate and oxygen consumption of bivalves are known to scale with dry weight, these coefficients may be used as mass exponent correction in physiological studies for P. zelandica.

Information regarding the variability of mussel metabolite levels and haemocyte quality over time is required to estimate the reproducibility of methods commonly used to investigate shellfish health. Apart from establishing confidence in transport time and transport medium of experimental animals, metabolism-quenching is a crucial step to ensure reflection of adequate metabolome composition at the time of sample collection. Considering the status of Perna canaliculus as a lucrative aquaculture product and as a research model, the effects of different transportation conditions and quenching methods on the haemolymph metabolome was investigated using gas chromatography–mass spectrometry analyses. Haemocyte viability was also measured as a consequence of transportation stress via flow cytometry. Mussels submersed in water during transport showed smaller changes in haemocyte numbers compared to mussels transported in aerated boxes, which showed a significant decrease in haemocyte viability over 24-h of transport. Significant changes in energy metabolism were inferred following transport in both holding systems over time highlighting a shift towards anaerobic energy production. Several metabolites declined over time, being highest at the onset of sampling and lowest after 24-h. Yet a number of metabolites linked to one‑carbon metabolism peaked after 6-h of transport. The quenching of metabolism in haemolymph samples devoted to metabolomics analysis were assessed following freezing in liquid nitrogen, dry-ice-ethanol-slurry, dry ice and standard ice. The sampling of animals on-site followed by metabolite quenching with liquid nitrogen should be considered as the optimal quenching method. However, the use of dry-ice-ethanol-slurry or dry ice alone still ensures reliable samples for metabolomics analysis and provides an alternative method particularly when sampling in the field where liquid nitrogen may be inaccessible and/or dangerous. The use of standard ice resulted in the most variation and should not be used; especially if fatty acids are the targeted metabolite group. Following this work, it is suggested to minimise transport time of mussels as much as possible, while using water as a transport medium where possible, and quenching samples based on metabolites of interest.

Understanding the parameters required for a reliable hatchery seed production of the endemic geoduck clam Panopea zelandica (Quoy and Gaimard, 1835) is crucial if New Zealand is to develop a geoduck aquaculture industry. To provide the foundation for routine geoduck larval rearing practices, this study reports on physiological, morphological, and behavioral characteristics throughout the larval developmental process. P. zelandica larvae were reared at 17 °C and 35 ppt, and fed continuously with Tisochrysis lutea and Chaetoceros calcitrans in a flow-through system. The initial veliger stocking densities ranged from 50 to 200 larvae mL − 1 , while residual algal levels were maintained at 20,000 to 80,000 cells mL − 1 in three rearing batches. Larval behavior and morphology were described through observation using video recordings, photomicrographs and scanning electron microscopy. The larval development took 16–19 days from first D-veliger and metamorphosis occurred across a wide size range (300–375 μm shell length). The increase in shell length was linear over time and correlated with the deposition of striae in the prodissoconch II. The ingestion rate followed a power function with time and was closely correlated with the development of the alimentary system, including mouth, esophagus, stomach, style sac, intestine, and digestive gland. Rearing with an initial stocking density of 100 larvae mL − 1 and residual algal background of 20,000 cells mL − 1 resulted in about 76% survival and 15 μm d − 1 growth rate. The results of the preliminary production trials inform rearing practices and provide biological descriptions that appear to be effective as a baseline protocol for the successful commercial production of P. zelandica larvae. Statement of relevance This is the first detailed study of larval development within hatchery conditions for the New Zealand endemic geoduck clam ( Panopea zelandica ). We identified timing of larval developmental stages, including metamorphosis and growth and feeding parameters that are relevant for successful rearing practices of this species for commercial production.

Recent efforts to cultivate subtidal New Zealand geoducks ( Panopea zelandica Quoy and Gaimard, 1835) in intertidal areas have been challenged due to daily hypoxia. Hence, further understanding of physiological responses of geoducks of different sizes under different oxygen partial pressures (PO 2 ) is required to optimize their husbandry. Without this knowledge, the risk of increasing cultivation costs due to growth depression and mortality may increase in both magnitude and frequency. Hence, this study investigated the respiration, aerobic scope, critical oxygen partial pressure (P c O 2 ), and oxygen regulation capacity from normoxia to hypoxia in two size classes of fed and starved P. zelandica . The P c O 2 was determined to be ~ 4 kPa for all geoduck groups. The respiration rates of fed small geoducks decreased significantly from normoxia (16.7–~21 kPa) to mild hypoxia (P c O 2 –16.7 kPa). Conversely, the respiration rates of starved geoducks from both size classes, and large fed geoducks were maintained at a constant level when exposed to the same change in oxygen concentration. However, all geoducks experienced decreased respiration rates during severe hypoxia (0 kPa–P c O 2 ). In addition, overall oxyregulatory capacity, assessed using a regulation index, was affected by size rather than by nutritional stress. Large geoducks maintain oxygen consumption across an oxygen gradient more effectively than small geoducks. Also, the aerobic scope of small geoducks decreased significantly with declining PO 2 , while large geoducks maintained their aerobic scope under hypoxia. Hence, to avoid stress and maximize growth potential of cultivated geoducks, smaller individuals should be grown in areas that remain normoxic, whereas larger individuals may be transferred to on-growing sites that experience periodic hypoxia, potentially including tidal emersion. Statement of relevance The New Zealand geoduck clam ( Panopea zelandica ) has been identified as an emerging aquaculture species. However, efforts to cultivate geoducks intertidally have been challenged due to daily hypoxia. Hence, this study reports on physiological responses (respiration, aerobic scope, critical oxygen partial pressure, and oxygen regulation capacity) of geoducks of different sizes under different oxygen partial pressures to optimize their husbandry.

Vibrio parahaemolyticus is a causative agent of the acute hepatopancreatic necrosis disease (AHPND) that leads to massive mortalities in penaeid shrimp aquaculture worldwide. Mitigation of the significant economic losses caused by AHPND are hampered by knowledge gaps in the pathogenic mechanism of V. parahaemolyticus infection in shrimp. To provide insights into this infection mechanisms, molecular responses of shrimp exposed to V. parahaemolyticus were measured via a metabolomics approach. A gas chromatography–mass spectrometry (GC–MS) platform was employed to generate metabolite profiles of haemolymph from Penaeus vannamei shrimp challenged with V. parahaemolyticus and control shrimp (not exposed to the pathogen). The results revealed increases of several intermediates in the citric acid (TCA) cycle (cis-aconitic acid, citric acid, fumaric acid, isocitric acid and succinic acid) and phosphoenolpyruvic acid (PEP), as well as decreases of six amino acids (threonine, asparagine, 4-aminobutyric acid, histidine, ornithine, glutamine) in challenged shrimp compared to controls. A pathway analysis identified 11 significantly changed pathways due to V. parahaemolyticus infection, which were mostly amino acid metabolisms, TCA cycle and gluconeogenesis. The results suggest an increase in metabolic rate and elevated TCA cycle and gluconeogenesis activities in Vibrio-challenged shrimp due to the high energy demand of the associated immune response. The study provides important new findings about the pathogenic mechanisms of V. parahaemolyticus invasion in shrimp at the metabolic level. Further metabolomics investigations may lead for identification of metabolite biomarkers of V. parahaemolyticus infection for early detection of AHPND.

Harvest and transport of farmed mussels are known to impose stress on the crop species. However, not much is known about molecular pathways underlying these physiological stresses. The present study investigated the effects of harvesting on the metabolome of the haemolymph and hepatopancreas of green-lipped mussels (Perna canaliculus), complemented by assessments of behaviour and survival under simulated dry and re-immersion live shipment scenarios. The gas chromatography–mass spectrometry (GC–MS)-based metabolomics approach was used to compare the metabolite profiles of control mussels (sampled directly from growing lines) with mechanically harvested mussels and post-transport mussels (after 3 h transport in water). The results showed differences in a large number of metabolites in both haemolymph and hepatopancreas of post-harvest and post-transport mussels when compared to the control state. These metabolites are generally involved in energy metabolism, amino acid metabolism, protein degradation and fatty acid metabolism. Mechanical harvesting induced metabolite changes typically associated with increased energy demand and a rapid transition to anaerobic glycolysis. Some metabolites began to return to baseline levels following a subsequent 3 h immersion during transportation. Re-immersion was also effective in prolonging life in mussels emersed in 9 °C air for three days. However, after six days emersion the mussels were moribund, dying after a total of 7.8 ± 1.0 days in air or in the re-immersion tank. The findings highlight the importance of acute metabolic trauma in determining post-harvest outcomes and the potential role for transient recovery systems.

Recent advances in high-throughput technologies for omics analyses and bioinformatics for data interpretation have led to the application of omics approaches across all fields of life sciences. There has also been an expansion of omics research in immune studies of marine invertebrates, such as bivalves to gain insights into pathogenic infections and disease progression. Many of these omics studies have been conducted on haemocytes and haemolymph, which are the most important components of the bivalve immune system. Characterization of transcriptomes, proteomes and metabolomes of bivalve haemocytes in response to pathogenic infections and other environmental stressors have revealed valuable information regarding the mechanisms that drive the innate immune system in response to stress challenges, as well as insights regarding complex host-pathogen-environment interactions across bivalve species. For instance, detailed analysis of haemocyte transcriptomes has resulted in the discovery of a number of coding and non-coding transcripts involved in immune and stress responses. In addition, comprehensive examination of the proteome and metabolome of bivalve haemocytes following stress exposure has helped identify changes in the physiological status of the organism, including specific molecular pathways involved in these processes. Furthermore, the differently expressed molecules that have been identified through these omics studies can be used as candidate biomarkers with applications in breeding selection programs, disease diagnosis and environmental monitoring. However, despite these significant biotechnological advances, the application of omics tools for bivalve haemocyte research is currently hindered by several challenges and bottlenecks. In this contribution, we aim to review the major advances, current perspectives and future directions of three main omics (transcriptomics, proteomics and metabolomics) with regards to their application in bivalve haemocyte and aquaculture research.

A technique was developed to separate and test bacterial cell surface-bound compounds and their exudates (biofilm matrix) for marine invertebrate larval settlement experiments. A broth culture (preventing biofilm formation) was used to obtain planktonic cell suspensions without exudates (PCo). Biofilm cell suspensions with their exudates (BCx) were obtained by growing the cells on marine agar (allowing biofilm formation) before suspending in seawater. A biofilm cell suspension without exudates (BCo) was obtained by washing BCx cells thoroughly before suspending in seawater. Three separate marine bacteria ( Macrococcus sp. AMGM1, Bacillus sp. AMGB1 and Pseudoalteromonas sp. AMGP1) were used to test PCo, BCx, and BCo suspensions for their ability to induce settlement of mussel larvae ( Perna canaliculus ). BCx suspensions of Macrococcus sp. AMGM1 and Bacillus sp. AMGB1 significantly induced settlement (over 70%) compared with their corresponding PCo and BCo suspensions and the sterile control plates. Conversely, BCx suspensions of Pseudoalteromonas sp. AMGP1 did not induce mussel larval settlement, and were highly toxic to the larvae. In addition, PCo and BCo treatments of Pseudoalteromonas sp. AMGP1 had no effect on larval settlement or mortality, compared with control plates. Results show that the tested bacterial cells alone (devoid of their biofilm exudates) do not induce settlement or mortality in this mussel species, and that their exudates contain the chemical cues that affect larval development and survivability. Thus, this work highlights the importance of appropriately separating exudates from bacterial cells to test surface-bound compounds in settlement cue experiments.

Larval settlement responses of the ribbed mussel, Aulacomya maoriana Iredale 1915, were investigated after exposure to various chemicals and mono-species bacteria. Identification of settlement inductive compounds assists in the elucidation of intermediary biochemical mechanisms involved in the neuronal control of settlement behaviour downstream from primary cue reception. Neuroactive compounds and amino acids (potassium ions, GABA, acetylcholine, l -Phenylalanine, l -Tyrosine, dopamine, epinephrine, l -Tryptophan, and 5-HTP) and planktonic bacteria, biofilms and biofilm exudates of Macrococcus sp. AMGM1, Bacillus sp. AMGB1, and Pseudoalteromonas sp. AMGP1 were tested for their abilities to induce larval settlement. Toxicity effects of each treatment also were simultaneously identified by recording larval mortalities. Results indicate that all chemicals used induced larvae to settle, with acetylcholine being the most effective (~ 24% at 10 −6 M compared to l -Tryptophan (~ 32%) and GABA (~ 59%). Our data suggest that catecholamines (and their precursors) play an important role in the biochemical mechanisms of settlement for A . maoriana . While serotonin precursors did induce low levels of larval settlement at some concentrations, high toxicity responses to 5-HTP at 10 −5 M, combined with complete settlement inhibition indicate that the mechanism of action may be more complex than can be elucidated in this study. Larval settlement responses to bacterial treatments were low for planktonic and biofilm phases across all three strains, and settlement inhibition was observed when larvae were exposed to biofilm exudates of all bacterial strains. Comparisons of A . maoriana responses to other endemic and worldwide distributed mussel species are provided as a means to highlight potential evolutionary differences in chemoreception mechanisms.

article i nfo Herein, we present the first laboratory study on the effects of pharmacologically active compounds on larval settlement of the green-lipped mussel, Perna canaliculus. Competent hatchery-reared larvae were exposed to seawater containing excess K + in the form of KCl and K2SO4 and the neurotransmitters γ-aminobutyric acid (GABA) and acetylcholine. Both KCl and K2SO4 were identified as active inducers of larval settlement with maximum inductions occurring after exposures to 10 and 7.5 mM, respectively. Peak settlement response to KCl was higher (N64%) than that achieved with K2SO4 (N41%). GABA did not induce larval settlement and displayed toxic and settlement inhibitive effects at 10 �4 and 10 �3 M. Acetylcholine induced larval settlement (N49%) at 10 �4 M with minimal acute toxic effects (LCb10%). To gain insight into the class of acetylcholine receptors involved, atropine was used to block the muscarinic-type receptors. Atropine treatment alone did not inhibit settlement compared to control assays, indicating that muscarinic-type receptors are not involved in settlement behavior. Furthermore, results showed that atropine did not significantly decrease acetylcholine induced settlement responses, which suggests an active role of the nicotinic-type receptors in the biochemical pathways of mussel settlement. Results of this study provide new insights on the mechanism of settlement behavior in

The substantial Greenshell mussel aquaculture industry in New Zealand is heavily reliant on one major source of wild spat at Ninety Mile Beach, at the northern end of the country. The spat of Perna canaliculus arrives intermittently at the beach attached to seaweed and other debris whereupon it is harvested for seeding mussel farms around the country. Periods of low or non-existent spat arrival at the beach have caused major disruption to the aquaculture production of this species. In an attempt to better understand the daily, monthly, and inter-annual patterns in the arrival of spat at Ninety Mile Beach, the harvesting records of spat harvesters for 1990 to 1999 were analyzed in relation to historical records of wind speed and direction, tidal range, water temperature, and modeled swell height and direction. For the long-term data set, spatfall events and the amount of spatfall increased markedly with strong offshore winds. On days with high tidal range, there tended to be an increase in the amount of spatfall, but this trend was not significant statistically. Daily and seasonal water temperature records did not show a significant effect on the timing or the scale of spatfall events. However, low swell height in the onshore direction was associated with a significant increase in spatfall events and amounts. Within the 9 year data set, storm events (wind speeds > 20 m s − 1 ) were most frequent during May to October. An average lag time of 4 months was found between peak storm events and the subsequent peak in spatfall events and amounts of spatfall occurring in September to October. Years with a greater number of storm events were also associated with significantly higher number of spatfall events and amounts of spatfall. Storminess and water temperature are associated with El Nino/La Nina episodes, which greatly influence the wind climate of New Zealand. During El Nino periods mussel farm managers could greatly reduce their risk of a shortfall in natural spat supply interrupting mussel production by securing sufficient spat to stock their farms from the large but less frequent spatfall events. Overall, the results provide valuable insight into possible ecological and oceanographic processes involved in spat arrival and will help with better utilization of the spat resource for this major mussel aquaculture industry.

The effects of water flow and air bubbles on byssal attachment were investigated for re-settled juvenile mussels, Perna canaliculus. Three water flow regimes (∼1, 5, and 10 cm/s), and with/without air bubble treatments were used to test the number of juveniles (3–5 mm in length) settled on filamentous plastic plants within flow-through tanks. As expected, mussel attachment was higher for mussels within high flow and lowest for mussels within low water flows, but air bubbles did not significantly affect initial mussel attachment. A subsequent increase in water flow to 13 cm/s for 5 min to all treatment combinations was used to test the strength of byssal attachment (measured by the number of detached mussels). These experiments indicate that both high water flow and air bubbles caused fewer mussel detachments than lower flows and no addition of air bubbles. Furthermore, the number of byssal threads was greater for mussels previously exposed to high water flows and air bubbles, indicating that these mechanical stimuli result in greater production of byssal threads as a means to attain a stronger hold on their substrates. The implications of these results are discussed for mussel settlement and retention under natural and farm conditions.

Early settlement patterns of the mussel Perna canaliculus were investigated within water tanks exposed to different water flow regimes and oxygen concentrations. Hatchery-reared larvae and wild juvenile mussels (0.5–3.0 mm in maximum length) collected from the surf zone and subtidal habitats at Ninety Mile Beach, northern New Zealand, were used for the laboratory settlement experiments. Combinations of three water flow regimes (∼1, 5, and 10 cm/s) and three oxygen concentrations (∼6, 9, and 12 mg/L) were established within replicated tanks, each containing standardized, artificial filamentous substrata. The mortality and settlement of larvae and re-settlement of juveniles were recorded for each tank during a 24-h period. Mortality was highest at low water flows, and decreased consistently with increasing water flows for larvae (∼55–5%) and juvenile mussels (∼70–50% for subtidal, and 23–4% for surf zone mussels), but increasing oxygen concentration caused a decrease only in the mortality of the larvae, not the juveniles. For larvae, settlement increased with increasing water flow, both on the filaments and on the tank rims at the water surface, and higher oxygen concentrations appeared to enhance larval settlement. Hourly larval settlement counts within filaments suggest that exploratory behavior (i.e., settlement and re-settlement) takes place within low and medium water flows, but not under high water flows. However, settlement always was higher within filaments compared to the tank rims for larvae, and for juveniles collected from the surf zone and subtidal habitats. While oxygen concentration did not significantly affect settlement of juveniles, mussels collected from the surf zone had slightly higher settlement rates than those collected from subtidal habitats. This study further illustrates the complexity of larval and juvenile settlement and re-settlement processes for P. canaliculus . In particular, pre-harvesting history/environment, as well as the physical conditions present after harvesting, may determine survival and re-settlement of mussels within natural and farm conditions.

The spatial and temporal variability in density and distribution of mussel larvae and spat associated with bottom-drifting algae was investigated at Ninety Mile Beach, northern New Zealand, between October 1998 and April 2000. Analyses of plankton tows conducted at in-shore and off-shore sites around the southern end of Ninety Mile Beach revealed highest mussel larval densities during spawning peaks in July 1999. Higher densities generally were found in-shore versus off-shore, and in southern versus northern sites. Dredging of the sandy bottom at the same sites indicated that drift algae occur in greater quantities in-shore at the southern end of the beach, compared to off-shore and northern sites. The clumps of mostly filamentous red algae almost exclusively contain spat of Perna canaliculus. Dredged algal samples also showed that smaller mussels ( 1 mm) are more common at the end of the spawning period in January. In addition, spatial and temporal patterns of algal and spat composition and arrival to the beach were investigated from beach-cast algal samples. Mussel densities in beach-cast algal samples were highest between July and September and lowest between January and May, in agreement with local spawning and larval availability patterns. A distinct, consecutive shift of mussel size-class dominance throughout the year was observed in the beach-cast material, with the density of smallest mussels peaking in August and largest mussels peaking in January. Analyses of six large algal rafts that were dispersed northward by the predominant along-shore current revealed a marked and consistent pattern of both increasing mussel size and algal branching in the northern direction, along the trajectory of the rafts. The dynamic patterns of mussel larval/juvenile dispersal and transport observed in this study provide a framework to develop future sustainable management and conservation strategies for natural mussel and algal populations, upon which the commercial mussel industry in New Zealand currently depends.

Unique physical and biological conditions at Ninety Mile Beach, northern New Zealand, are responsible for an accumulation of unusually high amounts of mussel spat, Perna canaliculus , found nowhere else in the country. These massive quantities of mussel spat are collected from the beach (>140,000 tonnes/year) and transported to the aquaculture farms, where they supply 80% of the industry's mussel seed requirements. Direct settlement of mussels, P. canaliculus , from the plankton to suspended ropes in the water column was investigated at Ninety Mile Beach, northern New Zealand. Mussel spat-collecting ropes were placed at two sites (inside and outside Ahipara Bay) and at three different depths. The abundances of mussels within three size classes were recorded monthly during two spawning seasons in 1999 and 2000. Small mussels ( 1.0 mm) were relatively more abundant at greater depths (18 m water depth) in September–December. Larger mussels are thought to have transferred from tumbling algae covered with mussels, which are readily transported by hydrodynamic processes near the seafloor. Although higher mussel abundances generally were found at the site inside the bay, these differences were not strongly supported by statistical analyses. The present research provides the first evidence that artificial ropes deployed at Ahipara Bay may be of commercial value to spat collectors on the beach and the mussel farm industry. These ropes could be used as predictors of spatfall arrivals, which are collected at the beach and used to seed the mussel farms. Furthermore, ropes could possibly be used as a new and more reliable means of harvesting the massive quantities of mussel spat available at Ninety Mile Beach, northern New Zealand.