Effect of temperature and water activity on in vitro germination of Monilinia spp.

Aims:  This study evaluated the effect of temperature (0–38°C) and water activity ( a _w: 0·87–0·99) on the lag phase prior to germination and the percentage of germination over time for Monilinia laxa , Monilinia fructicola and Monilinia fructigena .
Methods and Results:  More than 80% of viable conidia germinated at 25°C and 0·99 a _w within 2 h for M. fructicola and M. fructigena and 4 h for M. laxa . There was no germination at 38°C, and all three Monilinia spp. germinated at 0°C. At the lowest a _w (0·87), none of the Monilinia spp. was able to germinate at any of the incubation temperatures studied. Whereas at 0·90 a _w, conidia were only able to germinate at 15, 25 and 30°C for the three species studied, except for M. fructicola at 15°C. In contrast, at 0·95, 0·97 and 0·99 a _w, germination occurred at all studied temperatures less 38°C. Generally, the lag phase was longer at low levels of a _w (0·90–095), and differences were more evident as temperatures were far from the optimum (0–5°C).
Conclusions:  Germination and lag phase period were markedly influenced by temperature and a _w, and in general when conditions of temperature and a _w were suboptimal, the lag phase was longer and the percentage of germination was lower.
Significance and Impact of the Study:  Knowledge of the germination requirements of this fungus is important in order to understand their behaviour in natural situations and to provide baseline data required for the construction of new prediction models. Our study might be used to develop a predictive model to understand and control the disease caused by Monilinia spp.     

Determination of optimal growth parameters for the bioincising fungus Physisporinus vitreus by means of response surface methodology

Aim:  To evaluate the influence of water activity ( a _w), temperature and pH on the radial growth and lag phase of Physisporinus vitreus (E-642), a basidiomycete was used in the biotechnological process of bioincising.
Methods and Results:  Radial growth was monitored for 20 days on malt extract agar medium. Five levels of a _w (0·998, 0·982, 0·955, 0·928, 0·892) were combined with three incubation temperatures (10, 15, 20°C) and three pH values (4, 5, 6). Data analyses showed a highly significant effect of a _w and temperature ( P <  0·0001) and a significant effect of pH ( P <  0·05). The radial growth rate and lag phase of P. vitreus were very sensitive to a _w reduction. Although P. vitreus was able to grow at all the selected temperatures and pH values, the lag phase increased with decreasing a _w and growth became inhibited at a _w = 0·955. Optimal conditions for growth of P. vitreus were a _w = 0·998, 20°C and pH 5. The response surface model provided reliable estimates of these growth parameters and confirmed a greater dependence on a _w than on temperature or pH under in vitro conditions.
Conclusions:  Low levels of a _w can prevent growth of P. vitreus , so wood moisture content should be adjusted accordingly.
Significance and Impact of the Study:  Implementation of these results should contribute towards the optimization and efficiency of bioincising.     

Modelling the growth of Weissella cibaria as a function of fermentation conditions

Aims:  To investigate the effect of pH, water activity ( a _w) and temperature on the growth of Weissella cibaria DBPZ1006, a lactic acid bacterium isolated from sourdoughs.
Methods and Results:  The kinetics of growth of W. cibaria DBPZ1006 was investigated during batch fermentations as a function of pH (4·0–8·0), a _w (0·935–0·994) and temperature (10–45°C) in a rich medium. The growth curve parameters (lag time, growth rate and asymptote) were estimated using the dynamic model of Baranyi and Roberts (1994. A dynamic approach to predicting bacterial growth in food. Int J Food Microbiol 23, 277–294). The effect of pH, a _w and temperature on maximum specific growth rate (μ_max) were estimated by fitting a cardinal model. μ_max under optimal conditions (pH = 6·6, a _w = 0·994, T  = 36·3°C) was estimated to be 0·93 h⁻¹. Minimum and maximum estimated pH and temperature for growth were 3·6 and 8·15, and 9·0°C and 47·8°C, respectively, while minimum a _w was 0·918 (equivalent to 12·2% w/v NaCl).
Conclusions:  Weissella cibaria DBPZ1006 is a fast-growing heterofermentative strain, which could be used in a mixed starter culture for making bread.
Significance and Impact of the Study:  This is the first study reporting the modelling of the growth of W. cibaria , a species that is increasingly being used as a starter in sourdough and vegetable fermentations.     

Changes in Escherichia coli O157:H7 numbers during holding on excised lean, fascia and fat beef surfaces at different temperatures

Aim:  To investigate changes in Escherichia coli O157:H7 numbers on excised beef carcass surfaces over 72 h at different temperatures.
Methods and Results:  Excised lean meat, fascia and fat were inoculated with E. coli O157:H7 and held in an environmental chamber for 72 h, at air speed 0·5 m s⁻¹, relative humidity (RH) 90%, and temperatures 4, 8 and 12°C. On lean, pathogen counts increased significantly at 12°C. On fascia, significant reductions in counts occurred at 4 and 8°C. Pathogen numbers were significantly reduced on fat at 4, 8 and 12°C (64 h). Counts on fat were significantly less at all temperatures, compared to lean or fascia and surface water activity, a_w, decreased significantly over time on fat at 4°C. Significant decreases in surface pH values were recorded on all meat substrates.
Conclusions:  The survival of E. coli O157:H7 varied in relation to the meat substrate and the holding temperature. Reductions in counts on fat surfaces appeared to be related to low surface a_w values. No relationship between pathogen survival and surface pH was established.
Significance and Impact of the Study:  The use of excised meat pieces in an environmental cabinet offers a more flexible approach to determining the use of different chilling regimes in the production of safe meat.     

Survival of Salmonella on refrigerated chicken carcasses and subsequent transfer to cutting board

Objective:  To determine the effect of refrigeration time and temperature on Salmonella cell numbers on inoculated chicken carcasses and their transfer to a plastic cutting board.
Methods and Results:  The survival of Salmonella on chicken skin and the transfer to a plastic cutting board when exposed to different refrigeration temperatures (2, 6 or 8°C) for 9 days were the two main issues on which this work focused. Two scenarios were carried out to ascertain these effects: carcasses treated with a decontaminating acetic acid solution and untreated carcasses. All of the contaminated carcasses remained contaminated after 9 days of refrigeration. However, on untreated samples, while Salmonella numbers increased almost 1·5 log at 8°C, the pathogen numbers decreased about 1 log at 2 and 6°C. On acid-treated samples, cell numbers slightly decreased at all of the temperatures studied. Temperature did not affect salmonellae transfer to the cutting board, but time did. Acid decontamination increased cell numbers transferred to the cutting board compared with untreated samples.
Conclusion:  Proper refrigeration at low temperatures did not allow Salmonella numbers to rise, regardless of which carcasses had been, or had not been, acid treated. Despite the fact that the rate of transfer was not affected by temperature, the acid treatment detached Salmonella cells from the chicken skin and, therefore, the probability of greater cross-contamination should be studied further.
Significance and Impact of the Study:  The results of this study may provide better information about the refrigeration conditions for fresh chicken storage and also determine if these, along with acetic acid decontamination of broiler chicken, would affect the pathogen transfer to a cutting board.     

Resistance of Enterobacter sakazakii (Cronobacter spp.) to environmental stresses

Aim:  To gain a better understanding of the survival and persistence of Enterobacter sakazakii in severe environments.
Methods and Results:  We evaluated the resistance of Ent. sakazakii to various environmental stresses, including heating, drying, water activity ( a _w), and pH. The resistance of Ent. sakazakii to heat varies widely among strains. Most tested strains of Ent. sakazakii exhibited unusual resistance to dry stress, which depends on drying media. Growth of most strains occurred within 24 h at 37°C when the initial a _w of the medium was adjusted to 0·94 with sucrose or sodium chloride. The minimum pH for growth within 24 h at 37°C was 3·9 or 4·1 for most strains tested. Additionally, there did not appear to be any relationship between resistance to stresses and biofilm-forming ability in Ent. sakazakii planktonic cells.
Conclusions:  These results indicate that Ent. sakazakii is much more resistant than other Enterobacteriaceae to environmental stresses. Moreover, it is likely that Ent. sakazakii has cross-resistance to dry and thermal stresses.
Significance and Impact of the Study:  The findings of this study will contribute to an improved understanding of the survival and behaviour of Ent. sakazakii , which will lead to improved strategies for preventing outbreaks of Ent. sakazakii infection.     

The Effect of Water Activity on the Growth and Respiration of Pseudomonas fluorescens

The growth rate of Pseudomonas fluorescens was greater and continued at lower water activity ( a _w) values when glycerol controlled the a _w of glucose minimal medium than when the a _w was controlled by NaCl and sucrose. Growth was not observed below 0·945, 0·970 and 0·964 a _w when glycerol, sucrose and NaCl respectively controlled the a _w. The catabolism of glucose, Na lactate and DL-arginine as measured by respirometry was completely inhibited at a _w values greater than the minimum for growth when the a _w was controlled with NaCl. When the a _w was controlled with glycerol, catabolism of the three substrates continued at a _w values significantly below the a _w for growth on glucose. Catabolism of glucose in the presence of sucrose occurred at a level below the minimum growth a _w but catabolism of the other two substrates ceased at a _w values greater than the minimum growth a _w. Arrhenius plots between 10° and 34°C of the growth rate in glucose minimal medium at 0·98 a _w showed that the order of inhibition was sucrose > NaCl > glycerol. The order of inhibition differed when Arrhenius plots of catabolism of glucose was examined between 10° and 34 °C, namely NaCl > sucrose > glycerol. The mechanism of action of solutes controlling a _w is discussed.     

Intrinsic rate of population increase of Amitus fuscipennis MacGown and Nebeker (Hym., Platygasteridae) according to climatic conditions and bean cultivar

Data on adult longevity, reproduction and intrinsic rate of population increase of insect parasitoid Amitus fuscipennis MacGown and Nebeker (Hym., Platygasteridae) were obtained under different climatic conditions on two bean cultivars. The insect host was the greenhouse whitefly Trialeurodes vaporariorum (Westwood) (Hom., Aleyrodidae). On cv. Chocho, at 19°C, 75 ± 5% RH and at 22°C, 70 ± 5% RH, mean longevity of adult Amitus females on the host insect was 9.3 and 5.7 days; mean fertility was 64.1 eggs and 52.7 eggs; and r_m values were 0.102 day^–1 and 0.144 day^–1 for the respective conditions. On cv. ICA-Pijao, at 19°C, 75 ± 5% RH, mean longevity was 15.2 days; mean fertility was highest (162.8 eggs); and r_m value was 0.117 day^–1. The r_m values of Amitus were higher than those of its host under the same test conditions. This parasitoid may therefore be a suitable candidate for use in inoculative or seasonal inoculative control programs against T. vaporariorum .     

Effect of heat treatment on Cronobacter spp. in reconstituted, dried infant formula: preparation guidelines for manufacturers

Aim:  To explore safe guidelines for manufacturers and consumers to prepare, handle and store dry infant formula (DIF) to protect infants against Cronobacter spp.
Methods and Results:  Selected strains (2.45, FSM 293, ATCC-12868, FSM-271) screened from 68 strains of Cronobacter spp . were used to study growth and survival in commercial DIF. Prototype growth patterns in Enterobacteriaceae enrichment broth (EEB) containing a cocktail comprised of ATCC 12868, ATCC 29004, ATCC 29544 and ATCC 51329 showed a rapid increase in cell count (2·0 log₁₀ to 6·2 log₁₀ CFU ml⁻¹). Infant formula provided a better protective environment for the cells of Cronobacter strains than did buffered peptone water . Experiments on survival in inoculated (10⁴–10⁶ CFU ml⁻¹) reconstituted infant formula (RIF), preparation temperature, the effect of preparation volume (one-serving or two-serving) and effect of storage at room temperature for up to 10 h provided information to develop consumer guidelines for DIF preparation and handling.
Conclusions:  Reconstituted DIF in water at >70°C in larger volumes, minimizing storage time before feeding and storing unused reconstituted formulate at <4°C, may reduce the risk of Cronobacter infection in infants.
Significance and Impact of the Study:  Meningitis, necrotizing enterocolitis and bacteremia in premature babies has been linked to contaminated milk powder and DIF; better handling practices may improve the safety of these foods for neonates.     

Effect of water activity and temperature on growth and fumonisin B1 and B2 production by Fusarium proliferatum and F. moniliforme on maize grain

S. MARIN, V. SANCHIS, I. VINAS, R. CANELA AND N. MAGAN. 1995. The effect of different water activities ( a _w, 0.968, 0.956, 0.944, 0.925) and temperature (25°C and 30°C) on colonization and production of fumonisin B₁ (FB₁) and B₂ (FB₂) on sterile layers of maize by Fusarium proliferatum and F. moniliforme isolates was determined over periods of 6 weeks. Generally, both F. moniliforme and F. proliferatum grew faster with increasing a _w and best at 30°C. All three isolates produced more FB 1 than FB₂ regardless of a _w or temperature. Very little FB₁ and FB₂ were produced at 0.925 a _w, with maximum produced at 0.956 and 0.968 a _w at both temperatures tested. Most FB₁ and FB₂ were produced by F. moniliforme (25N), followed by F. proliferatum isolates (73N and 131N). At all a _w levels and both temperatures there was an increase in FB₁ and FB₂ concentration with time. Statistical analyses of a _w, temperature, time, two- and three-way interactions showed some significant differences between isolates and FB₁ and FB₂ production.     

Predictive assessment of ochratoxin A accumulation in grape juice based-medium by Aspergillus carbonarius using neural networks

Aims:  To study the ability of multi-layer perceptron artificial neural networks (MLP-ANN) and radial-basis function networks (RBFNs) to predict ochratoxin A (OTA) concentration over time in grape-based cultures of Aspergillus carbonarius under different conditions of temperature, water activity ( a _w) and sub-inhibitory doses of the fungicide carbendazim.
Methods and Results:  A strain of A. carbonarius was cultured in a red grape juice-based medium. The input variables to the network were temperature (20–28°C), a _w (0·94–0·98), carbendazim level (0–450 ng ml⁻¹) and time (3–15 days after the lag phase). The output of the ANNs was OTA level determined by liquid chromatography. Three algorithms were comparatively tested for MLP. The lowest error was obtained by MLP without validation. Performance decreased when hold-out validation was accomplished but the risk of over-fitting is also lower. The best MLP architecture was determined. RBFNs provided similar performances but a substantially higher number of hidden nodes were needed.
Conclusions:  ANNs are useful to predict OTA level in grape juice cultures of A. carbonarius over a range of a _w, temperature and carbendazim doses.
Significance and Impact of the Study:  This is a pioneering study on the application of ANNs to forecast OTA accumulation in food based substrates. These models can be similarly applied to other mycotoxins and fungal species.     

Sanitation of faeces from source-separating dry toilets using urea

Aim:  To develop a reliable and simple method to produce safe fertilizers from human excreta using urea for sanitation of faeces.
Methods and Results:  Urea was added to faecal matter (17% dry matter) at concentrations of 0·5–2% (w/w) and inactivation of Salmonella enterica subspecies 1 serovar Typhimurium (Salm. Typhimurium), Enterococcus spp . and the Salm. Typhimurium bacteriophage 28B was monitored at 14, 24 and 34°C. Urea additions enhanced inactivation and inactivation rates were positively related to increasing NH₃ (aq) concentration and temperature. Salm. Typhimurium was the most sensitive of the organisms studied, while Enterococcus spp. showed more persistence, especially at lower temperatures. The bacteriophage was the most resistant organism studied.
Conclusions:  Salmonella reduction levels that meet requirements for safe reuse of faeces as fertilizer (i.e. 6 log₁₀ reduction) can be achieved for 1% urea within 2 months at 14°C or within 1 week at 24°C and 34°C.
Significance and Impact of the Study:  The relationships between organism inactivation rates and temperature, ammonia and pH were identified. Urea treatment proved to be a robust and efficient option for safe recycling of plant nutrients.     

Survival and growth of Cronobacter species (Enterobacter sakazakii) in wheat-based infant follow-on formulas

Aims:  To determine the survival and growth characteristics of Cronobacter species ( Enterobacter sakazakii ) in infant wheat-based formulas reconstituted with water, milk, grape juice or apple juice during storage.
Methods and Results:  Infant wheat-based formulas were reconstituted with water, ultra high temperature milk, pasteurized grape or apple juices. The reconstituted formulas were inoculated with Cronobacter sakazakii and Cronobacter muytjensii and stored at 4, 25 or 37°C for up to 24 h. At 25 and 37°C, Cronobacter grew more (>5 log₁₀) in formulas reconstituted with water or milk than those prepared with grape or apple juices ( c. 2–3 log₁₀). The organism persisted, but did not grow in any formulas stored at 4°C. Formulas reconstituted with water and milk decreased from pH 6·0 to 4·8–5·0 after 24 h, whereas the pH of the formulas reconstituted with fruit juices remained at their initial pH values, c. pH 4·8–5·0.
Conclusions:  Cronobacter sakazakii and C. muytjensii can grow in reconstituted wheat-based formulas. If not immediately consumed, these formulas should be stored at refrigeration temperatures to reduce the risk of infant infection.
Significance and Impact of the Study:  The results of this study will be of use to regulatory agencies and infant formula producers to recommend storage conditions that reduce the growth of Cronobacter in infant wheat-based formulas.     

Intergenerational acclimation in aphid overwintering

Abstract.  1. When first instar nymphs and adults of the grain aphid Sitobion avenae (Fabricius) (Hemiptera: Aphidiae) were maintained in long-term cultures (>6 months) at 20 °C and 10 °C, the LT₅₀ decreased from −8 and −8.8 °C to −16.0 and −13.5 °C, respectively.
2. When aphids from the 20 °C culture were transferred to 10 °C, there was a progressive increase in cold tolerance through three successive generations. Transfer of newly moulted pre-reproductive adults reared at 10 °C for three generations back to 20 °C resulted in a rapid loss of cold hardiness in their nymphal offspring.
3. In all generations reared at 10 °C, first born nymphs were more cold hardy than those born later in the birth sequence. The LT₅₀ of nymphs produced on the first day of reproduction in the first, second and third generations maintained at 10 °C were −14.8, −17.0 and −16.6 °C, respectively. Thereafter, nymphal cold hardiness decreased over the subsequent 14 days of reproduction in each generation at 10 °C with mean LT₅₀ values of −10.3, −12.6 and −14.8 °C, respectively. By contrast, the cold tolerance of first born nymphs of aphids reared continuously at 20 °C did not differ in comparison with later born siblings. The LT₅₀ of adult aphids was also unaffected by ageing.
4. The ecological relevance of these findings is discussed in relation to the overwintering survival of aphids such as S. avenae .     

Survival of Staphylococcus aureus and enterotoxin A in glassy and rubbery states of gelatin

About 1% of Staphylococcus aureus cells survived the production of gelatin sheets containing nutrient broth. Those cells which survived showed no evidence of injury. Growth occurred in rubbery state gelatin with a _w values of 0.98 and 0.93; viability decreased during storage at a _w values of 0.89, 0.62 and 0.36 but there was little loss of viability in gelatin at an a _w of 0.25 over 27 d storage at 26°C. Assays for enterotoxin A detected no synthesis of new toxin but no loss in pre-formed toxin. The results suggest that high levels of Staph. aureus and its toxins should be excluded from glassy and rubbery state food products in order to prevent illness.     

Roles of endothermy in niche differentiation for ball-rolling dung beetles (Coleoptera: Scarabaeidae) along an altitudinal gradient

Abstract.  1. An analysis of whether niche differentiation in ball-rolling dung beetles can be explained by the way in which they regulate their body temperature was conducted.
2.  A priori assumptions were: (i) if thermoregulation affects niche partitioning, sympatric species must have different endothermic strategies that minimise encounters; or, alternatively (ii) if two co-occurring species show the same thermoregulation pattern and their flight periods overlap, they might be avoiding competition by exhibiting different resource preferences or different food relocation behaviour.
3. The ball-rolling dung beetles studied showed a hierarchical structure based on the species' endothermic capacity, measured as temperature excess [ T _ex= difference between body temperature ( T _b) and ambient temperature ( T _a)]. Those with a high T _ex (10–15 °C) were located exclusively at altitudes >1000 m a.s.l. On the coastal plains, species with a high T _ex were restricted to flying at night when the T _a was lower. Species with a lower T _ex (less than 10 °C higher than T _a) were found in the coastal plains zone.
4. Where there was sympatry with similar trophic habits, the species involved showed very different thermal niches, and where there was significant overlap of thermal niches between sympatric species, trophic habits of species were very different.
5. The results suggest that it is possible to use the concept of the thermal niche as a tool to explain interspecific interactions and the spatial distribution of species.     

The Effect of Water Activity and the aw Controlling Solute on Spore Germination of Bacillus stearothermophilus

The germination of spores of Bacillus stearothermophilus was studied in nutrient broth in relation to the water activity ( a _w) of the medium, the nature of the a _w controlling solutes glycerol, sucrose, KCl, and NaCl, and temperature. Quantitation of germination was based on the change of the phase-bright spore to phase-dark. Activation of spores was by exposure to 100°C/10 min in a medium of the same composition as that used for germination.
Of the four solutes used, sucrose proved most inhibitory to germination, especially in the upper part of the temperature range 38-75°C, glycerol was the most favourable whereas KCl and NaCl, whose effect was almost identical, occupied an intermediate place. The glycerol effect became more pronounced as the a _w of the medium decreased towards 0.960, becoming inhibitory thereafter.
The solute effect on spore germination followed a pattern that related to the class of solute, i.e. electrolyte or non-electrolyte, and its cell penetration characteristics.
Solute penetration during heat activation and germination was considered as the major germination factor and was associated with the osmoregulation mechanism within the spore proposed recently as the basis of spore dormancy and resistance.     

Combined effect of organic acids and supercritical carbon dioxide treatments against nonpathogenic Escherichia coli, Listeria monocytogenes, Salmonella typhimurium and E. coli O157:H7 in fresh pork

Aims:  To evaluate the effectiveness of organic acids and supercritical carbon dioxide (SC-CO₂) treatments as well as their combined effect for the reduction of nonpathogenic Escherichia coli and three pathogenic bacteria in fresh pork.
Methods and Results:  The different treatment conditions were as follows: (i) treatment with acetic (1%, 2% or 3%) or lactic acid (1%, 2% or 3%) only, (ii) treatment with SC-CO₂ at 12 MPa and 35°C for 30 min only and (iii) treatment with 3% acetic or lactic acid followed by treatment with SC-CO₂. Within the same organic acid concentration, the lactic and acetic acid treatments had similar reductions. For the combined treatment of lactic acid and SC-CO₂, micro-organism levels were maximally reduced, ranging from 2·10 to 2·60 log CFU cm⁻² ( E. coli , 2·58 log CFU cm⁻²; Listeria monocytogenes , 2·60 log CFU cm⁻²; Salmonella typhimurium , 2·33 log CFU cm⁻²; E. coli O157:H7, 2·10 log CFU cm⁻²).
Conclusions:  The results of this study indicate that the combined treatments of SC-CO₂ and organic acids were more effective at destroying foodborne pathogens than the treatments of SC-CO₂ or organic acids alone.
Significance and Impact of the Study:  The combination treatment of SC-CO₂ and organic acids may be useful in the meat industry to help increase microbial safety.     

Freezing and desiccation tolerance of imbibed canola seed

Depending on the environmental conditions, imbibed seeds survive subzero temperatures either by supercooling or by tolerating freezing-induced desiccation. We investigated what the predominant survival mechanism is in freezing canola ( Brassica napus cv. Quest) and concluded that it depends on the cooling rate. Seeds cooled at 3°C h⁻¹ or faster supercooled, whereas seeds cooled over a 4-day period to −12°C and then cooled at 3°C h⁻¹ to−40°C did not display low temperature exotherms. Both differential thermal analysis and nuclear magnetic resonance (NMR) spectroscopy confirmed that imbibed canola seeds undergo freezing-induced desiccation at slow cooling rates. The freezing tolerance of imbibed canola seed (LT₅₀) was determined by slowly cooling to −12°C for 48 h, followed with cooling at 3°C h⁻¹ to −40°C, or by holding at a constant −6°C (LD₅₀). For both tests, the loss in freezing tolerance of imbibed seeds was a function of time and temperature of imbibition. Freezing tolerance was rapidly lost after radicle emergence. Seeds imbibed in 100 μ M abscisic acid (ABA), particularly at 2°C, lost freezing tolerance at a slower rate compared with water-imbibed seeds. Seeds imbibed in water either at 23°C for 16 h, or 8°C for 6 days, or 2°C for 6 days were not germinable after storage at −6°C for 10 days. Seeds imbibed in ABA at 23°C for 24 h, or 8°C for 8 days, or 2°C for 15 days were highly germinable after 40 days at a constant −6°C. Desiccation injury induced at a high temperature (60°C), as with injury induced by freezing, was found to be a function of imbibition temperature and time.     

Using infrared thermography to assess seasonal trends in dorsal fin surface temperatures of free-swimming bottlenose dolphins (Tursiops truncatus) in Sarasota Bay, Florida

The temperature differential (Δ T ) between a body surface and the environment influences an organism's heat balance. In Sarasota Bay, FL, where ambient water temperature ( T _w) ranges annually from 11° to 33°C, Δ T was investigated in a resident community of bottlenose dolphins ( Tursiops truncatus ). Dorsal fin surface temperatures ( T _dfin) were measured on wild, free-swimming dolphins using infrared thermography. Field and laboratory calibration studies were also undertaken to assess the efficacy of this non-invasive technology in the marine environment. The portability of infrared thermography permitted measurements of T _dfin across the entire range of environmental temperatures experienced by animals in this region. Results indicated a positive, linear relationship between T _dfin and T _w ( r ²= 0.978, P < 0.001). On average, T _dfin was 0.9°C warmer than T _w across seasons, despite the 22°C annual range in T _w. Changes in integumentary and vascular insulation likely account for the stability of Δ T _{dfin − w} and the protection of core temperature ( T _core) across seasons. The high thermal conductivity of water may also influence this Δ T . The use of infrared thermography is an effective, non-invasive method of assessing dorsal fin skin surface temperatures (±1°C) across large numbers of wild, free-swimming dolphins throughout their thermally dynamic aquatic environment.