Delphine Nourisson

Seasonal variation in the orientation of Talitrus saltator on a Mediterranean sandy beach: an ecological interpretation

The amphipod Talitrus saltator (Montagu 1808), diffused on the Mediterranean and Eastern Atlantic coasts, displays physiological and behavioural adaptations to life on sandy beaches. To avoid dehydration, sandhoppers burrow in moist sand near the water’s edge during the day in the warmest seasons. When displaced, they can navigate to this safe zone using a sun compass and several additional mechanisms, both universal and local, an adaptive behaviour named ‘zonal recovery’. In this study, we analysed the effects of several variables on the talitrids’ orientation behaviour to highlight the relevance of the local cues and analyse the behavioural variation with relation to the ecology of sandy beaches. In different seasons for 2 years, orientation experiments were made on T. saltator sub-populations, at three sites of an extended sandy beach, differing in shoreline sedimentary dynamics; the main environmental, climatic and individual variables known to influence talitrid orientation were registered during each experimental session. The statistics of circular distributions were calculated and a multiple regression analysis adapted to angular data was performed, to highlight the scaling triggered by environmental conditions. The results showed that seasonal climatic variables played a primary role, adaptively modifying the sandhoppers’ behaviour. A significant interaction with the site (the chosen sites differed for sedimentary dynamics) was observed as well. A high behavioural plasticity appears to guarantee to T. saltator a good adaptation (both as abundance and geographical spreading) to life on sandy beaches, which are notably unstable environments.

Characterisation of a Tunisian coastal lagoon through hyperspectral underwater irradiance

North African coastal lagoons are unique ecosystems that often suffer degradation due to human activities. Therefore, monitoring methods are required to identify stressors and assist with the management of these valuable and often understudied ecosystems. A synthetic indicator of water ecological quality would be desirable for regular monitoring of these ecosystems under pressure. In 2008 an optical procedure was developed and applied in Ghar El Melh, a Tunisian lagoon which has been increasingly impacted by pollutant loading, especially from agriculture. In situ hyperspectral irradiance was measured at several stations, from which the apparent optical properties (AOPs), namely the irradiance attenuation coefficient K(λ) and the reflectance ratio R(λ), were obtained in order to relate them to water composition, in terms of light-attenuating substances (LASs). The significant relationships observed between R and LAS values enabled the application of a hyperspectral optical classification, which effectively highlighted threatened sectors of the lagoon. The pattern of differing water quality across the lagoon system that was derived from the hyperspectral classification agreed well with that obtained from a conventional optical classification that included AOPs and LASs. We suggest that hyperspectral analysis and classification is a useful monitoring tool for the assessment of change in coastal lagoons, and perhaps also in other shallow-water ecosystems.

Monitoring changes in sandy beaches in temperate areas through sandhoppers' adaptations

Sandhoppers (Amphipoda, Talitridae) are keystone species of sandy beach ecosystems in temperate areas. Several traits have been studied and proposed as bioindicators of impacts on sandy beaches, at individual (physiology and behaviour), population (life cycle, abundance, population dynamics and structure, morphometry and fluctuating asymmetry) and species (genetic structure and variation) levels. Sandy beaches, where these species spend their whole life cycle, are dynamic environments, subject to periodic changes (night-day, tides and seasons), as well as to impacts that may cause erosion or accretion of the littoral zone. The first response of an animal to potentially injuring factors is shown by its avoidance behaviour regarding the potential stress. This behaviour may be a rapid escape reaction, shown by single individuals, the whole or part of the population. Activity rhythms, changes in zonation, burrowing, escape reactions, orientation towards the optimal zone on the beach, are all adaptations to environmental changes, increasing the survival chances of the individuals and populations that express such behaviours. In this paper we present case studies of the talitrid species’ behavioural adaptations related to natural and human impacts on sandy beaches in the Mediterranean: (1) erosion/accretion dynamics of a Tyrrhenian beach in central Italy (Maremma Regional Park), and (2) increasing urbanisation on a beach in north-western Morocco (Oued Laou river mouth). The best behavioural adaptation was shown by the populations from more stable coastlines. For the survival value of rapid and possibly anticipatory responses to stressful factors, behavioural variation may be proposed as an early-warning indicator of environmental changes. The adaptation at higher levels (population and species) may reflect, on the one hand, the evolvability of the species and, on the other hand, the changeability of the environment. Adaptations at population level may be used as bioindicators of past changes over generations and evolutionary times.

Locomotor activity rhythm of Talitrus saltator (Crustacea, Amphipoda) on a progradating sandy beach

ABSTRACT In the Maremma Natural Park (Grosseto, Italy), the Collelungo beach exhibits a clear morphodynamics gradient, resulting in a severe erosion to a gradual accretion along the shoreline. Here, three sub-populations of the sandhopper Talitrus saltator (Montagu) (Crustacea, Amphipoda) were studied to highlight eventual intra- and inter-population variation of the endogenous locomotor rhythm. Individual activity recordings were carried out for 21 days in constant darkness and controlled temperature and humidity conditions. The variation of the free-running period was analysed at individual and sub-population levels, and the dependence on intrinsic (individual features) and extrinsic (habitat of origin and season) factors was analysed. A seasonal variation was highlighted, related to the seasonal spontaneous activity of the species. In summer and autumn, a significant correlation between the behavioural variation in the sub-populations (period and definition of the period) and beach physical parameters (slope and width) defined the dependence of the behavioural gradient on the environmental gradient. The observed relationship may represent an adaptation to the local coastline dynamics, suggesting the importance of a plastic behaviour as adaptive response to a variable environment.