Can giant clam (Tridacna squamosa) populations be restored on Singapore's heavily impacted coral reefs?

• 1. Giant clams have been a sustainable resource for millennia, but unregulated harvesting has led to local extinctions within the Indo‐Pacific region. Giant clam mariculture can produce large numbers of juveniles for restocking wild populations where natural recruitment is low or absent.
• 2. Singapore is surrounded by more than 60 small islands, many with fringing reefs. These reefs, however, experience increased turbidity and sedimentation resulting from massive coastal development projects and regular dredging of shipping lanes.
• 3. Seven reefs off Singapore's southern islands were surveyed (9670 m²) for giant clams. Also, an experiment was conducted to determine the growth of Tridacna squamosa reared in aquaria under three light treatments: ～50% ambient photosynthetically active radiation (PAR); ～25% ambient PAR; and ～12% ambient PAR. Finally, 144 clams (T. squamosa) were transplanted to four reefs around Singapore to study survival and growth in a heavily impacted environment.
• 4. A total of 23 adult clams from three species were found during the survey, representing a mean density of 0.24 per 100 m². Most clams were found at Raffles Lighthouse, Singapore's ‘best’ reef. No juvenile clams were encountered. In the aquarium experiment, clam growth was significantly different among the three light treatments, with growth greatest in the ～50% ambient PAR treatment. Of the 144 transplanted clams, 116 (80.6%) were recovered after 7 months. All specimens had increased in size, with growth rates among reefs ranging from 3.3 mm month^?1 (SD=1.3 mm) to 4.8 mm month^?1 (SD=1.6 mm).
• 5. Results suggest that, despite high levels of sedimentation and turbidity on Singapore's reefs, giant clams can survive and grow well. Restocking efforts using maricultured clams may be effective in enhancing the dwindling local populations. It is not clear, however, whether a self‐sustaining community can be established as high sedimentation may hinder larval settlement and survival.

Copyright © 2007 John Wiley & Sons, Ltd.     

Dietary habits of grazers influence their suitability as biological controls of fouling macroalgae in ex situ mariculture

The dietary habits of the sea urchin Salmacis sphaeroides and the gastropod Trochus maculatus in ex situ mariculture were examined. Fouling algal assemblages on terracotta tiles were exposed to the grazers and compared. Except for Day 0, the assemblages on Days 2, 13 and 27 differed significantly across treatments. S. sphaeroides rapidly consumed most algae, leaving an assemblage dominated by turf algae and bare tile. T. maculatus primarily fed on green filamentous algae, resulting in an even distribution of other algal functional groups, while control tiles were dominated by green filamentous algae. Using three representative fouling algae species (Bryopsis corymbosa, Hypnea spinella and Lobophora variegata), the consumption rates of both grazers and dietary preferences of S. sphaeroides were examined through a single‐diet and a choice experiment respectively. The single‐diet experiment revealed differential algal consumption rates for S. sphaeroides (H. spinella = B. corymbosa > L. variegata) and T. maculatus (B. corymbosa > H. spinella = L. variegata). The choice experiment showed that S. sphaeroides preferred H. spinella over the other two species. These experiments highlighted the importance of understanding the dietary habits of grazers as this has direct implications on their effectiveness as biological controls of fouling macroalgae in mariculture.     

Characterisation ofFusarium oxysporum isolated from carnation in Australia based on pathogenicity,vegetative compatibility and random amplified polymorphic DNA (RAPD) assay

Isolates ofF. oxysporum collected from symptomless carnation cuttings from Australian carnation growers properties, together with isolates from national collections, were screened for pathogenicity and grouped according to vegetative compatibility and random amplified polymorphic DNA (RAPD) patterns. The collection of 82 Australian isolates sorted into 23 different vegetative compatibility groups (VCGs). Of 69 isolates tested for pathogenicity, 24 were pathogenic to carnations, while the remaining 45 were non-pathogenic. All pathogenic isolates were within two VCGs, one of which was also compatible with an isolate obtained from an international culture collection, and which is known to represent VCG 0021 and race 2. Race status of the two pathogenic VCGs remains unknown. The RAPD assay revealed distinct DNA banding patterns which could distinguish pathogenic from non-pathogenic isolates as well as differentiate between isolates from the two pathogenic VCGs.