Physicochemical Properties, Functionalities, and Antioxidant Activity of Protein Extracts from New Zealand Wild Sea Cucumbers (Australostichopus mollis).

This study investigated the physicochemical properties, functionalities, and antioxidant capacities of protein extracts from wild sea cucumber Australostichopus mollis collected from four distinct locations in New Zealand. Protein was extracted from sea cucumber body walls using trypsin enzymatic extraction, followed by cold acetone precipitation. The amino acid analysis revealed high glycine (189.08 mg/g), glutamic acid (119.45 mg/g), and aspartic acid (91.91 mg/g) concentrations in all samples. The essential amino acid indexes of the protein extracts (62.96, average) were higher than the WHO/FAO standard references, indicating the excellent protein quality of A. mollis. Furthermore, protein extracts from A. mollis demonstrated superior emulsifying activity (202.3-349.5 m2/g average) compared to commercial soy and whey protein isolates under all tested pH conditions, and enhanced foaming capacity (109.9-126.4%) and stability (52.7-72%) in neutral and acidic conditions. The extracts also exhibited good solubility, exceeding 70% across pH 3-11. Antioxidant capacities (ABTS and DPPH free radical scavenging activity and ferric reducing antioxidant power) were identified in A. mollis protein extracts for the first time, with clear variations observed among different locations. These findings elucidate the advantageous functional properties of protein extracts from wild New Zealand A. mollis and highlight their potential application as high-quality antioxidant food ingredients.

Genetics and ontogeny are key factors influencing thermal resilience in a culturally and economically important bivalve.

Increasing seawater temperatures coupled with more intense and frequent heatwaves pose an increasing threat to marine species. In this study, the New Zealand green-lipped mussel, Perna canaliculus, was used to investigate the effect of genetics and ontogeny on thermal resilience. The culturally and economically significant mussel P. canaliculus (Gmelin, 1971) has been selectively-bred in New Zealand for two decades, making it a unique biological resource to investigate genetic interactions in a temperate bivalve species. Six selectively-bred full sibling families and four different ages, from early juveniles (6, 8, 10 weeks post-fertilisation) to sub-adults (52 weeks post-fertilisation), were used for experimentation. At each age, each family was exposed to a three-hour heat challenge, followed by recovery, and survival assessments. The shell lengths of live and dead juvenile mussels were also measured. Gill tissue samples from sub-adults were collected after the thermal challenge to quantify the 70 kDa heat shock protein gene (hsp70). Results showed that genetics, ontogeny and size influence thermal resilience in P. canaliculus, with LT50 values ranging between 31.3 and 34.4 °C for all studied families and ages. Juveniles showed greater thermotolerance compared to sub-adults, while the largest individuals within each family/age class tended to be more heat sensitive than their siblings. Sub-adults differentially upregulated hsp70 in a pattern that correlated with net family survival following heat challenge, reinforcing the perceived role of inducible HSP70 protein in molluscs. This study provides insights into the complex interactions of age and genotype in determining heat tolerance of a key mussel species. As marine temperatures increase, equally complex selection pressure responses may therefore occur. Future research should focus on transcriptomic and genomic approaches for key species such as P. canaliculus to further understand and predict the effect of genetic variation and ontogeny on their survival in the context of climate change.

Oxidative Damage and Antioxidants as Markers for the Selection of Emersion Hardening Treatments in GreenshellTM Mussel Juveniles (Perna canaliculus).

Transport out of the water is one of the most challenging events for juvenile Perna canaliculus and can be a highly inefficient process, with many juveniles subsequently being lost following extended periods of emersion. Hardening techniques offer a possible method for reducing transport-related stress. In this study, different hardening treatments (short, long and intermittent sub-lethal emersion) were used to prepare ~1.2 mm P.canaliculus for transport (20 h) and subsequent reoxygenation stress during re-immersion (i.e., recovery). The oxidative stress responses, resettlement behaviour, respiration rates and survival of the mussels after transport and during recovery were all assessed. Short emersion (1 h) as a hardening treatment prior to transport did not cause major stress to the mussels, which maintained respiration at control levels, showed significantly stimulated antioxidant defences during recovery, showed greater resettlement behaviour and remained viable after 24 h of recovery. In comparison, the long and intermittent emersion treatments negatively impacted oxidative stress responses and affected the viability of the mussels after 24 h of recovery. This study showed that exposing juvenile P.canaliculus to a mild stress prior to transport may stimulate protective mechanisms, therefore eliciting a hardening response, but care must be taken to avoid overstressing the mussels. Improving the management of stress during the transport of juvenile mussels may be key to minimising mussel losses and increasing harvest production, and biomarkers associated with oxidative stress/antioxidant metabolism could be valuable tools to ensure emersion hardening does not overstress the mussels and reduce survival.

Physiological responses of juvenile New Zealand geoduck (Panopea zelandica) following emersion and recovery.

The New Zealand geoduck clam is a unique seafood delicacy, with animals selling for up to $US 220-330/kg. Stress accumulated during transport of juveniles to grow-out sites represent a bottleneck in the aquaculture process. In this study, the physiological responses of juvenile geoducks following emersion (3- and 8-h), and recovery (1- and 5-days) were investigated. An integrated approach of flow cytometry, osmolality and metabolomics, along with behavioural assessments was used. Both cellular and chemical haemolymph parameters and metabolite profiles were recorded for P. zelandica juveniles and are reported herein for the first time. An increase in haemolymph osmolality was experienced with an increase in emersion period, with significant differences seen between the 3- and 8-h emersion groups after 5 days of recovery. Viability measures of haemocytes varied insignificantly between experimental groups, creating baseline ranges. The proportion of haemocytes undergoing respiratory burst activity did not appear to be affected by emersion and re-immersion. Haemocyte mitochondrial membrane potential was highest following 1-day of recovery, likely linked to metabolic readjustment, and increased glycolysis, taking place following emersion. Metabolomics analyses suggest that protein, lipid and carbohydrate metabolite classes assist with energy production in geoducks. Activation of anaerobic metabolic pathways, with a high dependence on succinate, were prominent in the 8-h exposure group, with metabolic recovery still taking place following 5-days of immersion, mainly due to proteins restoring energy reserves. Elucidating the physiological responses of juvenile geoduck subjected to transport stress can aid cultivation methods already underway to develop a novel, high value aquaculture industry.

A new method to localise and quantify oxidative stress in live juvenile mussels.

Stress and survival of the juvenile New Zealand green-lipped mussel, Perna canaliculus, is a poorly understood bottleneck in the ecological and economic performance of a significant aquaculture crop. This species was therefore selected as a model organism for the development of a new method to quantify oxidative stress in whole individuals. An in vivo ROS-activated stain (CellROX™) was administered to anaesthetised, translucent juveniles that were subsequently formaldehyde fixed and then visualised using confocal microscopy. Subsequent application of image analysis to quantifying ROS-positive tissue areas was successfully used to detect stress differences in juvenile mussels exposed to varying levels of emersion. This integrated method can be used to localise and quantify ROS production in individual translucent bivalve life stages (larval and juvenile), while relative stability following fixation greatly expands potential practical field applications. This article has an associated First Person interview with the first and third authors of the paper.