Positive Scope For Growth Research Articles

Resilience against the impacts of climate change in an ecologically and economically significant native oyster

Climate change is acidifying and warming our oceans, at an unprecedented rate posing a challenge for marine invertebrates vital across the globe for ecological services and food security. Here we show it is possible for resilience to climate change in an ecologically and economically significant oyster without detrimental effects to the energy budget. We exposed 24 pair-mated genetically distinct families of the Sydney rock oyster, Saccostrea glomerata to ocean acidification and warming for 4w and measured their resilience. Resilience was identified as the capacity to defend their acid-base balance without a loss of energy available for Scope for Growth (SFG). Of the 24 families, 13 were better able to defend their acid-base balance while eight had no loss of energy availability with a positive SFG. This study has found oyster families with reslience against climate change without a loss of SFG, is an essential mitigation strategy, in a critical mollusc.

CO2-induced pH reduction increases physiological toxicity of nano-TiO2 in the mussel Mytilus coruscus

The increasing usage of nanoparticles has caused their considerable release into the aquatic environment. Meanwhile, anthropogenic CO2 emissions have caused a reduction of seawater pH. However, their combined effects on marine species have not been experimentally evaluated. This study estimated the physiological toxicity of nano-TiO2 in the mussel Mytilus coruscus under high pCO2 (2500–2600 μatm). We found that respiration rate (RR), food absorption efficiency (AE), clearance rate (CR), scope for growth (SFG) and O:N ratio were significantly reduced by nano-TiO2, whereas faecal organic weight rate and ammonia excretion rate (ER) were increased under nano-TiO2 conditions. High pCO2 exerted lower effects on CR, RR, ER and O:N ratio than nano-TiO2. Despite this, significant interactions of CO2-induced pH change and nano-TiO2 were found in RR, ER and O:N ratio. PCA showed close relationships among most test parameters, i.e., RR, CR, AE, SFG and O:N ratio. The normal physiological responses were strongly correlated to a positive SFG with normal pH and no/low nano-TiO2 conditions. Our results indicate that physiological functions of M. coruscus are more severely impaired by the combination of nano-TiO2 and high pCO2.

Scope for growth of juvenile Cortez oyster, Crassostrea corteziensis fed isocaloric diets prepared with microalgae and cereal flours

We evaluated the effect of nine isocaloric diets prepared with a mixture of microalgae alone ( Tisochrysis lutea + Chaetoceros calcitrans + Ch. gracilis ; 1:1:1) and different combinations of the algal mixture and cornstarch or wheat flour, on the Scope for Growth (SFG) of Cortez oyster Crassostrea corteziensis juveniles (7.2 ± 1.1 mm shell length). A total 15,000 spat was acclimated to the experimental diets for 30 days at 21oC, prior SFG determinations. Consumed energy, absorbed energy, and SFG decreased with a corresponding decrease in the proportion of live microalgae in the diet. Oysters fed the microalgal diet showed significantly increased physiological activity in all parameters except absorption efficiency. Oysters fed diets containing up to 50% dry feedstuff showed positive SFG values but these were significantly lower than SFG shown in oysters fed microalgae alone. Oysters fed diets containing ≥75% dry feedstuff showed negative SFG. These results suggest that cereals can be used as complementary food or C. corteziensis spat in hatchery operations, provided replacement of microalgae is kept below 50%.

Physiological energetics and biogeographic range limits of three congeneric mussel species

Closely related species with different physiological tolerances and distributions make ideal systems for documenting range shifts in response to a changing climate. Mytilus edulis, M. trossulus, and M. galloprovincialis are sibling species of marine mussels with distinct biogeographical ranges that are correlated with sea surface temperatures. We determined the scope for growth of these three species at a range of temperatures to determine if energetics could predict their distributions. Scope for growth (SFG) represents energy available for growth and/or reproduction above that necessary for maintenance requirements. The SFG of M. galloprovincialis, the species known to inhabit the warmest habitats, was shifted towards warmer temperatures compared to the other two species, remaining positive until nearly 30 °C. M. edulis, a cold-temperate species, maintained a positive SFG up to 23 °C. M. trossulus, a boreal species, generally was not able to maintain a positive SFG above 17 °C. The warm end of each species' range correlated strongly with the point at which that species' SFG became negative in summer and fall. Energetics at cold temperatures did not predict the cold end of the species' ranges, as there was no clear SFG advantage to explain the dominance of M. trossulus in cold habitats. As sea surface temperatures continue to warm with climate change, the energetics of these three species provide a basis for developing mechanistic models predicting future distribution and productivity changes in mussel populations.

Physiological energetics and gross biochemical composition of the ascidian Styela clava cultured in suspension in a temperate bay of Korea

The ascidian Styela clava has recently become a common species for suspended aquaculture in Korea. Because of the ecological and commercial importance of this species, it is important to understand seasonal variations in its physiological energetics and gross biochemical composition. The purpose of this study was to determine fundamental biological traits for the cultivation of S. clava. Physiological processes (food consumption, feces production, ammonia excretion and respiration), and gross biochemical composition (protein, lipids, and carbohydrates) of the ascidian were measured monthly from April 2008 to April 2009 under in situ environmental conditions in a mariculture region on the temperate coast of Jindong Bay, Korea. Changes in the physiology and somatic growth of S. clava were largely influenced by seasonal variation in water temperatures. The reduced importance of food availability in explaining their physiological adjustments seems to be due to low seston concentrations in water column of the bay. Seasonal variations in the ingestion and respiration rates of the ascidians were mismatched, resulting in an energy imbalance (i.e. an increased metabolic energy cost and lowered ingestion rate; and vice versa). This mismatched activity resulted in negative scope for growth (SFG) values during spring–summer, followed by rapid exhaustion of energy reserves and flesh weight loss. Weight loss during this period was also related to spring spawning. During autumn–winter, the ascidians had a positive SFG as a result of decreased oxygen consumption and elevated ingestion rates, showing accumulation of nutrient reserves and weight gain. The ascidians showed positive SFG, even in cold conditions below 12 °C in the present study. In this respect, an autumn–winter culturing period is recommended to maximize ascidian production in long-line suspended culture under the natural environmental conditions occurring in the study area.

Effect of salinity and temperature on feeding physiology and scope for growth of an invasive species ( Brachidontes pharaonis - MOLLUSCA: BIVALVIA) within the Mediterranean sea

The Indo-Pacific mytilid Brachidontes pharaonis (Bivalvia, Fischer 1870) offers an excellent model for the study of “Lessepsian migration” and the successive colonization at new Mediterranean locations. This species in out competing indigenous bivalves is particularly well adapted to Mediterranean conditions and this is likely due to biological characteristics and physio-ecological plasticity. In the present paper, we report on clearance rate (CR), respiration rate (RR) and Scope for Growth (SFG) of B. pharaonis collected from a Western Sicilian pond (Southern Tyrrhenian, MED). Physiological variables were determined in response to a range of temperatures from 11 ° to 20 °C and a broad range of salinities from 15 to 60 psu. Salinity and temperature had a significant influence on CR of B. pharaonis as there was a general reduction in CR with a decline in temperature from 20 °C to 11 °C and declining salinity from 37 to 15 psu. RR showed a general temperature dependent relationship with highest RR at 20 °C. SFG showed negative values at lowest salinity of 15 psu at all tested temperatures. SFG values were generally the highest at 45 psu (at 11 °C and 20 °C), although SFG showed a maximum at 37 psu at 15 °C. SFG values were positive over the broadest range of salinities (25 to 60 psu) at 20 °C. The plasticity of the physiological rates demonstrated that B. pharaonis had the capacity to maintain positive SFG and tolerate a wide range of temperature/salinity conditions. Possible implications of high physiological plasticity of B. pharaonis in competing against indigenous bivalves are discussed.

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.

The effects of salinity on the physiological ecology of Choromytilus chorus (Molina, 1782) (Bivalvia : Mytilidae)

Choromytilus chorus frequently occurs in the estuaries of southern Chile, an environment that subjects it to changing ambient salinities. The effect of different salinities on the physiological processes of C. chorus was measured at 15, 18, 24 and 30‰ and at 12 °C. Scope for growth and net growth efficiency were used as physiological stress indices. Filtration rate was greater and similar at the two higher salinities (24 and 30‰), decreased at 18‰ and was considerably reduced at 15‰. Assimilation efficiency was high (≈ 80 %) and independent of both body weight and salinity. Oxygen uptake was also reduced by low salinity. There were no significant differences between weight exponents or between elevations when standard metabolism was compared at the three higher salinities. However, when the lowest salinity was included in the analysis, significant differences were observed. The energy lost due to excretion was very low at all salinities. The lowest value obtained at 15‰ was associated with the pronounced valve closure shown at this salinity, resulting in a build up of ammonia in the mantle cavity and body tissue and an inhibition in the production of NH 4. Scope for growth in C. chorus of given size was similar between 24 and 30‰ salinity and always positive in this range. Low feeding activity and a relatively high metabolic rate at the lower salinities resulted in a negative scope for growth for the larger animals at 18‰ and for all the size classes at 15‰ salinity. The stress imposed on C. chorus by low salinity was also reflected in a decreased net growth efficiency ( K 2). The data suggest that the growth rate as well as the degree to which this species can penetrate estuaries is partially determined by the amount of time which the mussels are able to spend in positive scope for growth under the estuarine conditions of reduced and fluctuating salinities.