Paul C. Southgate

Early Larval Development of the Sydney Rock Oyster Saccostrea glomerata Under Near-Future Predictions of CO2-Driven Ocean Acidification

ABSTRACT Anthropogenic emissions of carbon dioxide (CO2) from fossil fuel combustion and deforestation are rapidly increasing the atmospheric concentration of CO2 and reducing the pH of the oceans. This study shows that predicted near-future levels of ocean acidification have significant negative effects on early larval development of the Sydney rock oyster Saccostrea glomerata (Gould, 1850). CO2 was added to seawater to produce pH levels set at 8.1 (control), 7.8, and 7.6 (actual pH values were 8.11, 7.81, and 7.64, respectively). These treatments represent present-day surface ocean pH, as well as upper (&Dgr; pH ≈ -0.3) and lower (&Dgr; pH ≈ -0.5) pH predictions for the surface oceans in 2100. With decreasing pH, survival of S. glomerata larvae decreased, and growth and development were retarded. Larval survival decreased by 43% at pH 7.8 and by 72% at pH 7.6. Antero-posterior measurement (APM) was reduced by 6.3% at pH 7.8 and 8.7% at pH 7.6, and dorso-ventral measurement (DVM) was reduced by 5.1% atpH 7.8 and 7.5% at pH 7.6. The percentage of empty shells remaining from dead larvae decreased by 16% atpH 7.8 and by 90% at pH 7.6 indicating that the majority of empty shells dissolved within 7 days at pH 7.6. Scanning electron microscope images of 8-day-old larvae show abnormalities on the shell surface at low pH suggesting (1) problems with shell deposition, (2) retarded periostracum formation, and/or (3) increased shell dissolution. Larval life-history stages are considered particularly susceptible to climate change, and this study shows that S. glomerata larvae are sensitive to a high-CO2 world and are, specifically, negatively affected by exposure to pH conditions predicted for the worlds oceans for the year 2100.

Fouling animals and their effect on the growth of silver-lip pearl oysters, Pinctada maxima (Jameson) in suspended culture

A comparison was made of the growth of 1-year-old silver-lip (or gold-lip) pearl oysters, Pinctada maxima, cleaned every 2, 4 or 8 weeks or after 16 weeks. The diversity of fouling animals was recorded and their dry weight (DW) estimated. Survival was 100% in all treatments, with the exception of a single death in one replicate cleaned every 4 weeks. The DW of fouling animals increased steadily over the first 10 weeks of the experiment before declining during weeks 10 to 16. Significant (P < 0.05) differences in the DW of fouling animals between treatments was observed and pearl oyster growth was affected by fouling. The wet weight, shell height and shell length of pearl oysters cleaned every 2 or 4 weeks was significantly greater (P < 0.05) than that of pearl oysters cleaned every 8 weeks or after 16 weeks. The most common fouling animals were barnacles, Pinctada spp., Pteria spp., Crassostrea spp. and polychaete worms. Some pearl oysters that were left uncleaned for 8 or 16 weeks had shell deformities caused by Pteria spp. invading the shell margin. Based on this study, fouling animals should be removed on a monthly basis to maximise growth and reduce the risk of growth deformities. More regular cleaning, whilst having no deleterious effects on pearl oyster growth or survival, appears to be unnecessary and may add to operational costs.

Marine invertebrate skeleton size varies with latitude, temperature and carbonate saturation: implications for global change and ocean acidification

There is great concern over the future effects of ocean acidification on marine organisms, especially for skeletal calcification, yet little is known of natural variation in skeleton size and composition across the globe, and this is a prerequisite for identifying factors currently controlling skeleton mass and thickness. Here, taxonomically controlled latitudinal variations in shell morphology and composition were investigated in bivalve and gastropod molluscs, brachiopods, and echinoids. Total inorganic content, a proxy for skeletal CaCO3 , decreased with latitude, decreasing seawater temperature, and decreasing seawater carbonate saturation state (for CaCO3 as calcite (Ωcal )) in all taxa. Shell mass decreased with latitude in molluscs and shell inorganic content decreased with latitude in buccinid gastropods. Shell thickness decreased with latitude in buccinid gastropods (excepting the Australian temperate buccinid) and echinoids, but not brachiopods and laternulid clams. In the latter, the polar species had the thickest shell. There was no latitudinal trend in shell thickness within brachiopods. The variation in trends in shell thickness by taxon suggests that in some circumstances ecological factors may override latitudinal trends. Latitudinal gradients may produce effects similar to those of future CO2 -driven ocean acidification on CaCO3 saturation state. Responses to latitudinal trends in temperature and saturation state may therefore be useful in informing predictions of organism responses to ocean acidification over long-term adaptive timescales.

The effect of chemical cues on settlement behaviour of blacklip pearl oyster (Pinctada margaritifera) larvae

Inducing more rapid or greater degree of settlement of blacklip pearl oyster (Pinctada margaritifera) larvae using chemical cues can significantly improve the commercial hatchery production of this valuable species. For this purpose, epinephrine, norepinephrine and γ-aminobutyric acid (GABA) were assessed at four concentrations (10−2, 10−3, 10−4 and 10−5 M), and in conjunction with plastic filaments for their ability to induce settlement of P. margaritifera larvae. In all concentrations tested, neither epinephrine nor norepinephrine had a significant effect on settlement and crawling behaviours of P. margaritifera larvae. Settlement of larvae occurred after 24 h in the presence of GABA at concentrations of 10−3 and 10−4 M; however, mortality was high (32%) at a concentration of 10−3 M. Settlement and crawling behaviours were significantly greater (P<0.05) and mortality significantly lower (P<0.05) in the presence of plastic filaments alone than those exposed to GABA at a concentration of 10−4 M. However, larvae in the presence of plastic filaments and exposed to GABA showed significantly reduced (P<0.05) swimming behaviour and significantly greater (P<0.05) crawling and settlement behaviours than larvae in the presence of GABA alone or plastic filaments alone. The presence of GABA increased settlement of P. margaritifera larvae onto plastic filaments from 14% in treatments with plastic filaments only, to 25% in the treatment with plastic filaments and GABA. The result of this study showed that GABA has a potential to increase the settlement rate of P. margaritifera larvae in hatcheries.

Improving the n − 3 HUFA composition of Artemia using microcapsules containing marine oils

Preparation of gelatin-acacia microcapsules containing cod liver oil or squid oil, and their use for highly unsaturated fatty acid (HUFA) enrichment of Artemia nauplii is described. These microcapsules were readily ingested by Artemia nauplii and were visible in the gut a few minutes after the start of enrichment. Ingestion of microcapsules containing cod liver oil or squid oil resulted in a significant increase in the HUFA content of nauplii after only 1 h. The level of HUFA enrichment was influenced by the density of nauplii during the enrichment procedure; a reduction in the density of nauplii resulted in a large increase in their HUFA content. The levels of HUFA enrichment achieved in this study compare well with similar studies. Gelatin-acacia microcapsules containing marine oils are a suitable means for HUFA enrichment of Artemia; they allow inexpensive enrichment diets to be made on-site and may offer a cheaper alternative to commercial enrichment preparations.

Effects of stocking density on growth and survival of early juvenile silver-lip pearl oysters, Pinctada maxima (Jameson), held in suspended nursery culture

This study investigated the effects of stocking density on the growth and survival of juvenile silver-lip (or gold-lip) pearl oysters, Pinctada maxima. Spat were resettled onto PVC slats (75 × 500 mm2) and held in suspended nursery culture for 6 weeks at four stocking densities: ten juveniles per slat (1.3 juveniles per 100 cm2); 50 juveniles per slat (6.7 juveniles per 100 cm2); 100 juveniles per slat (13.3 juveniles per 100 cm2) and 150 juveniles per slat (20 juveniles per 100 cm2). Best survival was recorded at a stocking density of ten juveniles per slat (80 ± 4.36%, mean ± s.e.) which was significantly higher than the other densities tested (P 0.05). Best growth, measured as wet weight, shell length and shell height, was shown at a density of ten juveniles per slat, where wet weight and shell length were significantly greater than at any other stocking density (P 0.05). The ratio of shell height to shell length was also influenced by stocking density. Differences between the shell height:shell length ratios were significant between all stocking densities (P 0.05).

Fouling and predation; how do they affect growth and survival of the blacklip pearl oyster, Pinctada margaritifera, during nursery culture?

This paper reports on 5 experiments conducted to assess the effect of cleaning regime and predation on growth and survival of blacklip pearl oyster (Pinctada margaritifera) juveniles in north Queensland, Australia. P. margaritifera juveniles with a mean (±SE) dorso-ventral shell height (DVH) of 4.5 ± 0.1 mm were placed into plastic mesh trays and cleaned either every 4 or 8 weeks or left uncleaned for 16 weeks. Cleaning regime had a significant effect on growth and survival (P < 0.005). Lowest DVH (16.2 ± 1.0) was shown by oysters in uncleaned trays during 16 weeks compared to oysters in cleaned trays; however, there was no significant difference in DVH between oysters held in trays cleaned every 4 (19.4 ± 1.2) or 8 weeks (21.2 ± 0.8). In contrast lowest survival was shown by oysters held in trays that were cleaned every 4 weeks (30 ± 5%), but no differences were noted between oysters cleaned every 8 weeks (63 ± 4%) and oysters that were left uncleaned for 16 weeks (75 ± 8%). Predators of P. margaritifera in northern Australia included crabs, stomatopods, flatworms, gastropods and fish. The stomatopod, Gonodactylus falcatus, was the most destructive predator with individuals consuming in excess of 20 juvenile pearl oysters per week. The leather jacket, Paramonocanthus japonicus, did not kill pearl oysters, but trimmed the margin of oysters shells significantly reducing DVH when compared to control groups cultured without fish. Removing predators monthly had a significant effect on growth of pearl oysters compared to oysters in non-inspected trays; however monthly inspection of culture trays did not significantly improve oyster survival.

Effects of Varying Dietary Fatty Acid Composition on Growth and Survival of Seahorse, Hippocampus Sp., Juveniles

Three commercially available fatty acid enrichment emulsions (DC Selco, DC DHA Selco and DC Super Selco) were used to enrich Artemia nauplii fed to seahorse, Hippocampus sp. fry. The emulsions varied in their n-3 highly unsaturated fatty acid (HUFA) composition. Total n-3 HUFA content ranged from 200 to 450 mg g-1 between the three emulsions while levels of eicosapentaenoic acid (EPA, 20 : 5n-3) and docosahexaenoic acid (DHA, 22 : 6n-3) ranged between 47–220 and 80–190 mg g-1, respectively. Survival and growth of seahorses at the end of the 30 day growth trial were greater in treatments receiving enriched Artemia. Seahorses receiving Artemia enriched with DC DHA Selco and DC Super Selco showed significantly (p < 0.05) greater mean survival (71.6 ± 6.0% and 78.3 ± 6.0%, respectively) than those receiving unenriched Artemia (48.3 ± 6.0%). Mean standard length was also significantly greater (p < 0.05) in fry fed DC DHA Selco and DC Super Selco enriched Artemia (20.2 ± 0.3 and 19.7 ± 0.3 mm, respectively) compared to those fed unenriched Artemia (18.1 ± 0.3 mm). The results show that dietary n-3 HUFA are essential for optimal growth and survival of Hippocampus sp. and, based on the fatty acid compositions of the enriched Artemia used in this study, indicate that the level of dietary DHA supporting optimal growth and survival is greater than 9.3 mg DHA g-1 dry weight.

Growth and fatty acid composition of Pacific oyster (Crassostrea gigas) spat fed a spray-dried freshwater microalga (Spongiococcum excentricum) and microencapsulated lipids

Abstract Pacific oyster ( Crassostrea gigas ) spat were fed for 28 days on either a 100% ration of spray-dried freshwater microalga Spongiococcum excentricum , or an 80% ration of S. excentricum and 20% gelatin-acacia microcapsules (GAM) containing various lipid sources. Replacement of S. excentricum with any lipid significantly increased the ash free dry weight (AFDW) of spat. GAM containing squid oil or mixtures of squid oil and either coconut oil, corn oil, or linseed oil produced spat with significantly higher AFDW than GAM containing vegetable oils only. Spat fed a live reference diet ( Chaetoceros muelleri ) had significantly higher AFDW than spat fed any of the S. excentricum /GAM-diets. There was no correlation between AFDW of spat and the energy content of GAM, however, AFDW was positively correlated with levels (% of total fatty acids) of the fatty acids 20:5 n − 3 and 22:6 n − 3 in GAM. The fatty acid profile of spat generally reflected that of the diet after 28 days and unfed spat retained high % levels of 20:5 n − 3 and 22:6 n − 3, indicating the importance of these fatty acids for spat growth.

Growth of blacklip pearl oyster (Pinctada margaritifera) juveniles using different nursery culture techniques.

This study was based on blacklip pearl oyster (Pinctada margaritifera) juveniles, that were hatchery-reared and 8 months old. They were held for 5 months in suspended culture using five culture techniques: in 24-pocket juvenile panel nets (PN24); enclosed within 5-mm plastic mesh ‘inserts’ placed in the pockets of eight-pocket adult panel nets (PN8); in 5-mm plastic mesh inserts without being placed into panel nets (INSERT); in plastic mesh trays (55×30×10 cm) with lids (TRAY); and by ‘ear’ hanging (EAR). Survival was high during the experiment and ranged from 100% in PN24 and PN8 to 90.6% for the INSERT treatment. Juveniles held in 24-pocket nets (PN24) and ear-hung juveniles showed the greatest growth during the experiment, and had significantly greater dorso-ventral height (DVH) and wet weight (WW) than oysters in all other treatments (P EAR>TRAY>PN8>INSERT.