Joseph J. Taylor

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.

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).

Population genetics of a marine bivalve, Pinctada maxima, throughout the Indo‐Australian Archipelago shows differentiation and decreased diversity at range limits

Intraspecific genetic diversity governs the potential of species to prevail in the face of environmental or ecological challenges; therefore, its protection is critical. The Indo‐Australian Archipelago (IAA) is a significant reservoir of the worlds marine biodiversity and a region of high conservation priority. Yet, despite indications that the IAA may harbour greater intraspecific variation, multiple‐locus genetic diversity data are limited. We investigated microsatellite DNA variation in Pinctada maxima populations from the IAA to elucidate potential factors influencing levels of genetic diversity in the region. Results indicate that genetic diversity decreases as the geographical distance away from central Indonesia increases, and that populations located towards the centre of P. maximas range are more genetically diverse than those located peripherally (P < 0.01). Significant partitioning of genetic variation was identified (FST = 0.027; RST = 0.023, P < 0.001) and indicates that historical biogeographical episodes or oceanographic factors have shaped present population genetic structure. We propose that the genetic diversity peak in P. maxima populations may be due to (i) an abundance of suitable habitat within the IAA, meaning larger, more temporally stable populations can be maintained and are less likely to encounter genetic bottlenecks; and/or (ii) the close proximity of biogeographical barriers around central Indonesia results in increased genetic diversity in the region because of admixture of genetically divergent populations. We encourage further genetic diversity studies of IAA marine biota to confirm whether this region has a significant role in maintaining intraspecific diversity, which will greatly assist the planning and efficacy of future conservation efforts.

Assessment of artificial substrates for collection of hatchery-reared silver-lip pearl oyster (Pinctada maxima, Jameson) spat

This paper reports on three experiments in which artificial substrates were assessed for the collection of hatchery-reared silver-lip (or gold-lip) pearl oyster, Pinctada maxima (Jameson), spat. In the first experiment, pediveliger larvae were settled onto collectors made from a variety of materials: curved PVC slats; polypropylene rope; a combination of PVC slats and polypropylene rope; and monofilament nylon. After 37 days, the rope and the combined PVC slat and rope collectors had significantly higher numbers of spat (P<0.05) than either nylon or PVC slat collectors. In a second experiment, PVC slat collectors were placed in a larval settlement tank in either a horizontal or vertical orientation. Significantly greater numbers of spat (P<0.001) were observed on horizontally positioned PVC slat collectors than on collectors positioned vertically. Regardless of orientation, the concave surface of PVC slats had significantly higher (P<0.001) numbers of spat than the convex surface. In the third experiment, collection of P. maxima spat was compared between PVC slats with or without an epifloral biofilm. Significantly more (P<0.001) spat attached to PVC slats with a biofilm than clean PVC slats. These results indicate that the choice of collector material, the surface orientation of collectors and method of collector preparation can optimise the collection of hatchery-reared P. maxima spat.

Inducing detachment of silver-lip pearl oyster (Pinctada maxima, Jameson) spat from collectors

A number of stress factors were assessed for their potential to induce detachment of silver-lip (or gold-lip) pearl oyster (Pinctada maxima, Jameson) spat from spat collectors. The factors assessed were: increased salinity to 40 parts per thousand (ppt) or 45 ppt, reduced salinity to 30 ppt or 25 ppt, raised (to pH 10) and reduced (to pH 4) pH and exposure to air. All treatments promoted significantly greater (P 0.05) in the proportion of detached spat. Spat that had detached in the treatment baths within the first hour began to re-attach during the second hour. With the exception of the pH 10 and air exposure treatments, detached spat in all treatments had firmly re-attached and had apparently adapted to the new environmental conditions after 24 h. Survival of spat left exposed to these treatments for 24 h was 100% as was the survival of spat exposed to air for up to 6 h. No mortality was recorded for any treatment 24 h after the spat were returned to control sea water.

Effects of mesh covers on the growth and survival of silver-lip pearl oyster (Pinctada maxima, Jameson) spat

Spat of the silver-lip (or gold-lip) pearl oyster, Pinctada maxima, were re-settled onto PVC slats at a mean density of 340 per 100 cm². Spat had a mean (±s.e.) dorso-ventral shell height and antero-posterior shell length of 1.2±0.3-mm and 1.8±0.5-mm, respectively. The PVC slats were either left exposed (control) or covered with a mesh sleeve of varying aperture sizes (0.75, 1.5 or 3.0-mm) before being transferred to an ocean-based suspended nursery culture system. After two weeks of nursery culture, there was no significant difference (P>0.05) among the number of spat retained on the covered slats; however, all covered slats had significantly greater (P 0.05). This probably resulted from fish and other predators preferentially attacking the larger individuals. There was no advantage in using sleeves with a mesh size small enough to retain dislodged spat. The majority of dislodged spat in the 0.75-mm and 1.5-mm mesh sleeves perished when they fell into the corners of the sleeve whereas most dislodged individuals were small enough to fall through the 3.0-mm mesh sleeve. A 3.0-mm mesh is appropriate to house spat of the size used in this study. Smaller mesh sizes, while not affecting survival, fouled more rapidly and resulted in reduced spat growth.