Pedro M. Anastácio

Population Biology and Production of the Red Swamp Crayfish Procambarus clarkii (Girard) in the Lower Mondego River Valley, Portugal

ABSTRACT The population of Procambarus clarkii from the lower Mondego River valley, Portugal, was studied for 13 months. Population structure was analyzed and 7 cohorts were identified. The main recruitment period occurred from the second half of October to the end of November, but juveniles were found throughout the year. Tracking recognizable cohorts along size-frequency distributions from successive sampling dates allowed an estimation of growth parameters in order to calibrate a growth model incorporating seasonal adjustments. Average growth rate was estimated at 1.16 mm of total length per week. Production was estimated at 27.22 g m-2 per year, the average biomass at 5.4 g m-2, and the P/B ratio at 5.03. Females outnumbered males throughout the year and the average sex ratio was 0.24.

Shifts in aquatic macroinvertebrate biodiversity associated with the presence and size of an alien crayfish

To investigate the effects of Procambarus clarkii on macroinvertebrate diversity, we conducted a mesocosm experiment simulating small pools in rice field pads after the rice season. We hypothesized that crayfish predation would negatively impact macroinvertebrate diversity, and the magnitude of this impact should vary with the size of P. clarkii. We conducted a short-term mesocosm experiment to determine macroinvertebrate diversity in the presence of three size classes and in the absence of crayfish, as well as the diet composition of crayfish from the three size classes. At the end of the experiments, the diet of crayfish was composed of the most available taxa (Culicidae, Chironomus, Tanytarsini and Orthocladinae). These results also show evidence that, in confined areas, crayfish are important predators of major rice pests such as rice Chironominae larvae. Macroinvertebrate diversity was negatively affected by crayfish presence, but the effect was inversely proportional to crayfish size. The highest diversity index was obtained in the absence of P. clarkii, and juvenile crayfish significantly reduced macroinvertebrate diversity. Thus, the impact of P. clarkii on aquatic macroinvertebrates is size dependent and may be relevant in small pools formed in rice field pads from early autumn to late winter. Overall, our findings suggest that the negative effects of P. clarkii on macroinvertebrate diversity may be particularly strong in local natural assemblages confined to puddles of water or small ponds in wetland areas.

Impact of crayfish densities on wet seeded rice and the inefficiency of a non-ionic surfactant as an ecotechnological solution

In order to compare the effects of crayfish (Procambarus clarkii) on rice production, with and without the use of a non-ionic surfactant (Genapol OX-80) at a concentration of 0.005%, 12 enclosures at 1 m2 containment area were built in each of two experimental fields. Crayfish densities used in the experiment were: 0, 1, 3, and 5 adult crayfish per m−2. In each field, at harvest time, five randomly chosen areas of 1 m−2 were also sampled for rice, infestants and sediment characteristics. Additionally, the number of filled grains per panicle, the percentage of empty grains and the 100 grains weight were determined. One of the experimental fields was used as the treatment (field T) and another one as the control (field C), and no statistically significant differences (p>0.05, Mann–Whitney U test) were found between them. No perceptible reduction in crayfish damaging effects was observed after the use of the surfactant in field T. Results of an ANOVA performed on the effects of crayfish density on rice production at each field were statistically significant (p<0.05). There was a total destruction (100%) of rice in the enclosures with densities of 3 and 5 crayfish m−2. Some infestant macrophytes survived at 3 crayfish m−2 in both fields and at 5 crayfish m−2 in field C. At lower densities (1 crayfish m−2) the average decrease in grain production attributable to crayfish was 41.61%. Results provided data to calibrate a management model and suggested that the surfactant is not effective in field conditions.

Integrated production of crayfish and rice: a management model

Abstract The introduction of the Louisiana Red Swamp Crayfish is another example of a non-native species causing damage to the natural balances within a region. In the Mondego river valley (Northern Portugal) the species is considered a pest and is assumed to cause considerable damage to the rice production due to burrowing. Up to now, it has been treated with xenobiotic chemicals. This is undesirable since the species is also used as human food source and it is of economical importance to the region. Modelling has been applied as a ecotechnological tool to identify future strategies for the simultaneous harvesting of both rice and crayfish within the same fields. The available data indicates that a restocking program is needed in order to maintain population numbers from year to year when crayfish are harvested or a surfactant is used to reduce crayfish activity. The development of the model is included in the scope of a general project with the goal to reduce damages in the rice fields and to implement crayfish production.

Processes and patterns of plant destruction by crayfish: effects of crayfish size and developmental stages of rice

Interference by crayfish on the establishment of rice plants was evaluated in this study. Two experiments were performed in outdoor containers with wet-seeded rice. The purpose of the first experiment was to determine if crayfish size has a significant impact on plant destruction. Two different scales of habitat size were analysed. The second experiment was designed to determine the influence of crayfish on different developmental stages of rice and to obtain data on the type of destruction caused by crayfish. Remaining dry weight, number and dry weight of the rice seedlings (intact + damaged) and number and dry weight of the seeds (intact + damaged) were quantified in the first experiment. The second experiment quantified: (1) number of viable seeds or seedlings, (2) dry weight of the remaining rice biomass; (3) number of viable seeds; (4) number of non-viable seeds; (5) height of any damaged seedlings, (6) number of seedlings damaged, (7) height of intact seedlings, and (8) number of intact seedlings. Our findings indicate that: increasing crayfish size results in larger negative effects on rice plant establishment; and consumption is the most important cause of destruction although the effect is reduced as plants grow. Crayfish left only a very small portion of the seedlings intact at 3 and 6 days of plant development. Thus, practical implications for management are that any crayfish control mechanisms being used are expected to be particularly effective during the first 6 days of rice growth.

CRISP (crayfish and rice integrated system of production): 2. Modelling crayfish (Procambarus clarkii) population dynamics

Abstract An ecological sub-model of crayfish ( Procambarus clarkii ) population dynamics is presented for integration into the CRISP (crayfish and rice integrated system of production) series of models. The present structure is directed towards simulation of crayfish population responses under different human interventions, namely different capture rates. The crayfish population was subdivided into seven age classes of 80 days, each one constituting a state variable. The increase in weight for each 80-day period was considered dependent on the temperature, the oxygen level and the water level. Mortality was assumed to be dependent on the dry weight of the crayfish and regulated by the total crayfish biomass. Food, water and oxygen content of the water were considered to be non limiting. Total crayfish biomass and total wet weight of crayfish captures were very sensitive to both the temperature for maximum growth and the mortality rates. Our most optimistic simulation, with a 50% decrease in the mortality rates, resulted in a fourfold increase in captures, from 230 to 917 kg ha −1 per year. Without capture, a value of 121 kg ha −1 was simulated for the average crayfish biomass, which is close to the 124 kg ha −1 obtained with crayfish capture. Our simulated average crayfish biomass was approximately 120 kg ha −1 in a natural situation, which lies inside the reported ranges from areas at approximately the same latitude.

Predicting the impact of climate change on the invasive decapods of the Iberian inland waters: an assessment of reliability

In an effort to predict the impact of climate change on the distribution of existing invasive species, niche-based models (NBMs) are being increasingly used to make forecasts. Here, we investigate the reliability of these models in predicting future climatic suitability for 4 invasive decapods of the Iberian Peninsula: Cherax destructor, Eriocheir sinensis, Pacifastacus leniusculus and Procambarus clarkii. From an ensemble of forecasts generated by 5 distinct algorithms (generalized linear models, artificial neural networks, support vector machines, random forests and alternating decision trees), we calculated consensus predictions for current conditions and 3 future time periods (2030, 2050 and 2080) under low and high scenarios of greenhouse gas emissions. Three criteria were examined to infer the robustness of the forecasts: ability to predict current distributions, inter-model variability and degree of environmental extrapolation. Our results indicate an overall decline in climatic suitability for the 4 invaders as time progresses. However, we also identified highly distinct levels of predictive uncertainty among species. Good indicators of reliability were found for Procambarusclarkii and Pacifastacusleniusculus, whereas the predictions for C. destructor showed low predictive performance, low inter-model agreement and wide areas of environmental extrapolation. For E. sinensis, the models also showed high variability with respect to areas projected to lose climatic suitability. Overall, our results highlight the need to consider and evaluate multiple sources of uncertainty when using NBM predictions for invaders under current and future conditions.

Surfactant (Genapol OX-80) toxicity to Selenastrum capricornutum

A non-ionic surfactant (Genapol OX-80) was proposed as a means of reducing destructive crayfish activity in rice. In order to study the toxicity of this product on algae, a test in accordance to the ISO 8692 protocol (1989) was performed. The growth inhibiting effect of the pure formulation of Genapol OX-80 was studied on Selenastrum capricornutum in the concentration range of 0.01-1.0 mg/l. The result indicated a 72 h EC50-value of 0.5 mg/l. The suggested field concentration of approximately 50 mg/l is therefore two orders of magnitude above the algal EC50-value. From our findings it is expected that the impact on the rice field algae will not be negligible.

A model for amphipod (Talitrus saltator) population dynamics

Abstract This study provides a population dynamics model for one of the most common species ( Talitrus saltator ) in sandy beaches. Sensitivity analysis showed that in the model the abundance of T. saltator is deeply affected by variations in the minimum recruitment day length, the minimum temperature at recruitment, and the period between recruitments. The mortality rate, as expected, also had a profound effect on model performance. The abundance (IST, ind m −1 ) of T. saltator was most sensitive to the initial number of individuals in age class 5 (ca. 4 months old) and least sensitive to the initial number in age class 9 (ca. 8 months old). Data used for the calibration of the model were obtained in the Lavos beach in central Portugal. The model is based on differential equations and it was constructed using Stella simulation software. Five different model versions were tested corresponding to different modes of recruitment that could fit the data. It was found that the best model was obtained when considering reproduction dependent on temperature and photoperiod and occurring on a semi-lunar basis. Two out of the five different model versions tested gave a good statistical performance. Only one of these two model versions makes an effective use of causality mechanisms. This was also the model with the best intercept and slope of the simulated vs. observed regression equation. The other statistically satisfactory model used continuous reproduction between two dates. These dates do not match a photoperiod threshold. The final model version (e) may serve as a useful tool, when used alone or when coupled with other models. One of its uses could be in assessing the effects of human actions upon a sandy beach ecosystem.

CRISP (crayfish and rice integrated system of production): 1. Modelling rice (Oryza sativa) growth and production

A ecological sub-model for rice growth, adapted to the culture processes used in the lower Mondego river valley (Portugal), is presented. The structure of the model is based on the production of carbohydrates by the photosynthesis. Parallel structures were used to simulate the development stage of the crop, and the tillering process. The model is composed of 11 state variables, 14 forcing functions, 22 rate processes, 9 parameters and 17 switches, regulatory processes and calculated values. Simulations were performed for periods ranging from January 1995 to October 1996. During this period the simulation results were compared with data on aerial rice biomass and also on the tiller density. In addition, the simulated final rice production parameters were compared with the observed values for both years. It can be stated that the model performs well in what regards prediction of final production parameters but it underestimated rice biomass during the growth period. Although at this stage the model is mainly directed towards research, the final purpose is the management of crayfish and rice production. In order to achieve this aim, it will be necessary to couple several sub-models.