Understanding/unravelling carotenoid excited singlet states.

Carotenoids are essential light-harvesting pigments in natural photosynthesis. They absorb in the blue–green region of the solar spectrum and transfer the absorbed energy to (bacterio-)chlorophylls, and thus expand the wavelength range of light that is able to drive photosynthesis. This process is an example of singlet–singlet excitation energy transfer, and carotenoids serve to enhance the overall efficiency of photosynthetic light reactions. The photochemistry and photophysics of carotenoids have often been interpreted by referring to those of simple polyene molecules that do not possess any functional groups. However, this may not always be wise because carotenoids usually have a number of functional groups that induce the variety of photochemical behaviours in them. These differences can also make the interpretation of the singlet excited states of carotenoids very complicated. In this article, we review the properties of the singlet excited states of carotenoids with the aim of producing as coherent a picture as possible of what is currently known and what needs to be learned

Comparative effects of temperature on suspension feeding and energy budgets of the pearl oysters Pinctada margaritifera and P. maxima

This study assessed the effects of seasonal temperatures on suspension feeding, related physiological parameters and energy budgets in 2 pearl oysters, Pinctada margaritifera and P. maxima. Pearl oysters that were acclimatised at approximately 19, 23, 28 and 32°C in the field were tested in the laboratory at these temperatures. Clearance rate (CR), absorption efficiency (ae), absorbed energy (AE), respired energy (RE), excreted energy (EE) and the value of (AE - RE) were significantly affected by temperature. They usually increased with increasing temperature. ae, RE, EE and the value of (AE - RE) differed significantly between the pearl oyster species. P. margaritifera had a significantly higher CR than P. maxima at 19°C. P. maxima had higher ae than P. margaritifera at 28 and 32°C. As a result, P. margaritifera had greater AE than P. maxima at 19°C, but the latter species had greater AE at 32°C. Temperature significantly affected the RE of P. margaritifera over a wider temperature range (19 to 32°C) than P. maxima (19 to 23°C). However, interspecific differences in RE were only significant at 32°C. P. maxima had significantly higher EE at 32°C than P. margaritifera, although this energy accounted for a very small portion of AE (<5%). P. maxima exceeded P. margaritifera in Scope for Growth [SFG = (AE - RE) - EE] at 32°C, but the latter species had greater SFG at 19°C. These results agree with observations of the occurrence of P. margaritifera at higher latitudes and lower temperature habitats. The temperature effects on suspension feeding, related physiological parameters and SFG indicate that there will be marked seasonal variations in growth in both species in environments where water temperatures vary seasonally. In bioenergetic terms, the optimum temperature ranges for these pearl oysters are approximately 23 to 28 and 23 to 32°C for P. margaritifera and P. maxima, respectively

Comparative effects of microalgal species and food concentration on suspension feeding and energy budgets of the pearl oysters Pinctada margaritifera and P. maxima (Bivalvia: Pteriidae)

This study aimed to determine the influence of microalgal species and food concentration on various physiological parameters and Scope for Growth (SFG) in adults of 2 pearl oysters, Pinctada margaritifera and P. maxima. Clearance rate, pseudofaecal production rate, absorption efficiency, respiration rate and excretion rate were determined over a range of food concentrations using 2 microalgal diets, Tahitian Isochrysis sp. (T-Iso) and Dunaliella primolecta at 28°C. Clearance, pseudofaecal production and respiration rates were significantly affected by microalgal diet. From these results, and because of the higher energy content of T-Iso, pearl oysters feeding on T-Iso had maximum values of SFG that were 1.5 to 2.1 times higher than when feeding on D. primolecta. Clearance rate and absorption efficiency were significantly related to food concentration as negative exponential relationships (p < 0.001). Generally, pseudofaecal production, respiration and excretion rates were significantly related to food concentration as positive linear relationships (p < 0.005). Optimal food concentrations for maximum SFG for P. margaritifera and P. maxima were 1 to 2 mg 1-1 and 2 to 3 mg l-¹, respectively. P. maxima was better adapted to a wider range of food concentrations. P. maxima maintained positive SFG up to 9 mg l-¹ food concentration when feeding on T-Iso and up to 7 mg l⁻¹ when feeding on D. primolecta, while equivalent values for P. margaritifera were 7 mg l⁻¹ and 5 mg l⁻¹, respectively. These results are in accordance with P. maxima occurring in a wider range of habitats than P. margaritifera, and experiencing greater concentration ranges of suspended particulate matter

Feeding adaptations of the pearl oysters Pinctada margaritifera and P. maxima to variations in natural particulates

The tropical pearl oysters Pinctada margaritifera (Linnaeus) and P. maxima Jameson are suspension feeders of major economic importance. P. margaritifera occurs in coral reef waters characterised by oligotrophy and low turbidity. P. maxima habitats are generally characterised by high terrigenous sediment and nutrient inputs, and productivity levels. These differences in habitat suggest that P. margaritifera will feed more successfully at low food concentrations, while P. maxima will cope with a wider range of food concentrations and more silty conditions. The effect of varying concentrations of natural suspended particulate matter (SPM) on clearance rate (CR), pseudofaeces production, absorption efficiency (abs.eff.), respired energy (RE) and excreted energy (EE) was determined for P. margaritifera and P. maxima. The resultant scope for growth (SFG) was determined and related to habitat differences between the oysters. There was no selective feeding on organic particles in either species. P. margaritifera had higher CR at low SPM concentration (<2 mg l⁻¹), while P. maxima had higher CR under turbid conditions (SPM: 13-45 mg l⁻¹). The latter species produced less pseudofaeces in relation to its filtration rates; consequently, this species ingested more SPM than P. margaritifera. P. maxima had positive SFG over a wider range of SPM concentrations (up to 30-40 mg l⁻¹) while P. margaritifera maximised SFG under low SPM conditions (<3 mg l⁻¹). Thus feeding responses and energy balance reflected the typical habitats of each species. P. margaritifera retained smaller particles than P. maxima, enabling it to consume a wider particle size range of SPM at low food levels. P. maxima was adapted to its environments of greater SPM load through greater ingestion rates and higher digestive ability. The optimum SPM concentrations and particle size range for P. margaritifera (SPM < 5 mg l⁻¹, size > 3 µm) and P. maxima (SPM = ca 3 to 15 mg l⁻¹, size > 4 µm) may be used for selection of optimum pearl culture sites

Effects of body size on suspension feeding and energy budgets of the pearl oysters Pinctada margaritifera and P. maxima

This study compared suspension feeding, assimilation efficiency, respiration and excretion, and energy budgets (= scope for growth, SFG) in relation to body size in 2 pearl oysters, Pinctada margaritifera and P. maxima, at a low food concentration (ca 5000 cells m1⁻¹ Tahitian Isochrysis galbana). Clearance rate (CR), respiration rate (R) and ammonia excretion rate (E) were strongly correlated with body size (p < 0.001) in both species, with exponents of 0.60 and 0.61 (CR), 0.44 and 0.56 (R), and 0.64 and 0.78 (E), respectively, for P. margaritifera and P. maxima. CR did not differ significantly between the species, but absorption efficiency, which was unrelated to size, was significantly greater in P. maxima (57.5 vs 51%, p < 0.05). There was, however, no significant difference in absorbed energy (AE) between the species. Respired energy (RE) and excreted energy (EE) as proportions of AE were significantly lower (p < 0.01) in P. maxima of 0.1 g dry soft tissue wt (ca 36 mm shell height, SH). The former was 0.36 compared to 0.58 in P. margaritifera of the same size. Thus, P. maxima of 0.1 g dry soft tissue wt exceeded P. margaritifera of the same size in SFG, which accords with the former species' more rapid early growth. Both species of pearl oysters have a high ability to acquire energy under low phytoplankton conditions. Both species are exceptional bivalves in terms of energy fluxes, with clearance rates of 50 to 100 l h⁻¹ in large oysters of 150+ mm SH. They show among the highest CR, R, E and SFG values recorded for bivalves (using 1 g dry soft tissue wt as a standard size). The largest giant clam, Tridacna gigas, is one tropical bivalve with comparable SFG. It, however, is dependent on energy from autotrophy as well as heterotrophy to achieve its high SFG

The pearl oysters, Pinctada maxima and P margaritifera, respond in different ways to culture in dissimilar environments

Growth, Condition Index (CI) and survival of the pearl oysters, Pinctada maxima and R margaritifera, were measured in three size groups of oysters over 14 months at two dissimilar environments in the Great Barrier Reef lagoon. These were the Australian Institute of Marine Science (AIMS) in a mainland bay and Orpheus Island Research Station (OIRS) in coral reef waters. Temperature, suspended particulate matter (SPM) and particulate organic matter (POM) were monitored during the study. Temperature at AIMS fluctuated more widely than at OIRS both daily and seasonally, with annual ranges 20-31 degrees C and 22-30 degrees C, respectively. Mean SPM concentration at AIMS (11.1 mg l(-1)) was much higher than at OIRS (1.4 mg l(-1)) and fluctuated widely (2-60 mg l(-1)). Mean POM level was also substantially higher at AIMS, being 2.1 mg l(-1) compared with 0.56 mg l(-1) at OIRS. Von Bertalatiffy growth curve analyses showed that P. maxima grew more rapidly and to larger sizes than P. margaritifera at both sites. For the shell height (SH) of R maxima, growth index phi'=4.31 and 4.24, asymptotic size SHinfinity = 229 and 205 mm, and time to reach 120 mm SH (T-(120))= 1.9 and 2.1 years at AIMS and OIRS, respectively. While for P margaritifera, phi'=4.00 and 4.15, SHinfinity = 136 and 157 mm, and T-(120) = 2.5 and 3.9 years at AIMS and OIRS, respectively. R maxima had significantly lower growth rates and lower survival of small oysters during winter compared with summer. There were, however, no significant differences between the two sites in growth rates of P. maxima and final Cl values. In contrast, P. margaritifiera showed significant differences between sites and not seasons, with lower growth rates, survival of small oysters, final Cl values and asymptotic sizes at AIMS. The winter low temperatures, but not high SPM at AIMS, adversely affected P. maxima. Conversely, the high SPM levels at AIMS, but not temperature, adversely affected P. margaritifera. This was in accordance with earlier laboratory-based energetics studies of the effects of temperature and SPM on these two species. P maxima has potential to be commercially cultured in ca. > 25 degrees C waters with a wide range of SPM levels, including oligotrophic coral reef waters with appropriate particle sizes. It is possible to culture R margaritifera in turbid conditions, but its poor performance in these conditions makes commercial culture unlikely. (c) 2005 Elsevier B.V. All rights reserved