This presentation describes a series of experiments designed to study the biology and fisheries of decapod crustaceans in the Western Mediterranean in the framework of research programmes carried out by Instituto de Ciencias del Mar (CSIC) in Barcelona. The results have been used to highlight the importance of bio-ecological studies on commercial species in instituting fisheries management programmes. A series of examples are used to demonstrate how integrating knowledge of the effects of biological and ecological aspects (growth, reproduction, migrations, aggregations, environmental factors, sexual dimorphism, behaviour, etc.) in the fisheries, is essential to avoid sampling errors and errors in stock assessment. Finally, potential directions for future research in this area are discussed.

The farming of freshwater crayfish (astaciculture) is mainly carried out in the southern states of the USA, and in Australia and Europe. Production levels vary with climate but are in the region of 40 000 to 60 000 tonnes per annum. In addition, at least an equivalent amounts is harvested from the wild, particularly in North America, China, Australia, Kenya, Turkey and Europe. Crayfish farming is usually either of an extensive (ranching) or semi-intensive nature, intensive methods being infrequent, except for the rearing of juveniles for stocking (or restocking of natural waters depleted of crayfish). As crayfish do not have larvae and are polytrophic, they are relatively easy to rear, although fecundity is much lower when compared with other cultured crustaceans. At least 85% of world production is based on the red swamp crayfish, Procambarus clarkii, mainly from Louisiana and other southern USA states, but also from China, Kenya and Spain, where it has been introduced. In Australia, three species are of aquacultural importance, the yabbie, Cherax destructor; the marron, C. tenuimanus; and the red claw, C. quadricarinatus. Some very large production units have been built but none have lived up to their promise. The red claw is thought to have considerable aquacultural potential, but, being a tropical species, needs warm water for good growth. In Europe, the only endemic species cultured to any extent is the noble crayfish, Astacus astacus, mainly as juveniles for restocking. It fetches a higher price than other crayfish. The North American signal crayfish, Pacifastacus leniusculus, has been introduced to most European countries, but farmed production is relatively low. About 98% of crayfish consumed in Europe come from extensive systems or the wild harvest. European crayfish markets were upset by the collapse of the Turkish crayfishery (based on Astacus leptoductylus) due to overfishing and disease in the mid-1980s. The environmental impact of crayfish farming is most noticeable in Europe. Crayfish plague, introduced from North America last century, has devastated populations of the native species in many countries. Its spread has been exasperated by the translocation of foreign crayfish (and probably by fish) for aquacultural purposes. In addition, introduced crayfish frequently escape into the wild and form large populations, often in direct competition with native species. Burrowing and prolific species, such as P. clarkii, can also do considerable environmental damage.

For centuries, several species of prawns and crabs have been raised from wild-caught juveniles in coastal brackish-water fish ponds in various countries of south east Asia. The Indonesian "tambaks" are well known examples of such traditional practices. In western countries, since the turn of the century, advances of marine biology and fast increase of marine fisheries enabled the development of large-scale production and release of larval stages of American and European lobsters in a fruitless attempt to restock natural populations. After the Second World War, the increasing demand for crustaceans in United States and Japan was satisfied by opening new prawn fisheries all over the world. A major breakthrough was achieved with the development of hatchery technologies for the penaeid prawn Penaeus japonicus (Hudinaga, 1942 in Japan) and the caridean prawn Macrobrachium rosenbergii (Ling, 1969 in Malaysia), which occurred during the first decades of the second half of this century. Together with the increasing market demand in developed countries for sea food, this led to a considerable interest of both public agencies and private investors in marine shrimp and prawn culture. In western countries, a large number of pioneering commercial ventures, often based on assumptions not scientifically founded, failed. Nevertheless, the aquaculture production of prawns mainly based on wild-caught juveniles increased in South-East Asia and Central America during the 1980s. This overall positive trend should not hide important failures which occurred at a local scale, such as the Taiwanese crisis of 1988 due principally to environmental degradation, resulting in severe disease problems and a near collapse of the farming activity. Following the early period of hatchery technology development, the major scientific achievements were related to food requirements and formulation of compound diets for larvae, juveniles and adults and to a better knowledge of diseases caused by bacteria and several viruses which have been identified from hatcheries and intensive farming ponds. Additional new technological advances have emerged from recent research in the fields of physiology (endocrinology) and genetics. By far, the major part of the world production of marine crustaceans relies on penaeid prawns and, to a lesser extent, on Macrobrachium species. However, some other species of marine crustaceans have potential for aquaculture.

The economic aspects of marine crustacean aquaculture should be considered together with those of the fishing industry: market prices are rather similar, depending on the quality of the product. The balance between market demand and production is an important constraint which, in turn, establishes the success of prawn farming. Since the early 1980s, crustacean aquaculture has increased tremendously in both Asiaand America: the world production for 1991 approximated 700,000 tons, with more than 600,000 tonsfrom penaeid prawn culture.

Bien que la chitine soit synthétisée par un grand nombre d'espèces animales, unicellulaires ou métazoaires, appartenant notamment aux groupes zoologiques de la lignée des Coelomates Spiralia, la production de chitine en milieu marin est essentiellement due aux Crustacés. Une étude comparée des quelques données analytiques disponibles a permis de tenter de calculer les valeurs de biomasse et de production de chitine dans quelques grands types d'écosystèmes marins, et d'évaluer ainsi l'importance quantitative de la chitine dans les cycles biogéochimiques du carbone et de l'azote. Les principales données actuellement disponibles concernent le plancton de la baie de Calvi (Corse) en Méditerranée, le krill arctique et antarctique, une population de langoustes des côtes de l'Afrique du Sud, et les communautés benthiques infralittorales à algues photophiles des côtes rocheuses de la Corse. Dans tous les cas, la production de chitine a pu être estimée à environ 1g par an et par m2 de substrat rocheux ou de surface océanique. Sur base de ces valeurs de production et de l'étendue relative des principaux écosystèmes marins, la productiontotale annuelle de chitine par les crustacés marins a été évaluée à ± 2,3 milliards de tonnes.

This paper develops briefly four examples illustrating the use of crustaceans as experimental animals in the field of metabolic and transport physiology. In cells of euryhaline crabs, organic substances such as free amino acids contribute much more than inorganic ions to osmotic adaptation, a feature that is now realized to be of general importance in living organisms. Anhydrobiotic and anaerobically dormant embryos of the brine shrimp Artemia provide very convenient models to study cellular control of metabolic depression. Studies on amphibious crabs have highlighted the constraints imposed upon gas exchange and acid-base balance by the very contrasted properties of oxygen and carbon dioxide in water and in air. Finally, the blood oxygen transport system of decapod crustaceans has been a model of choice to demonstrate the significance of an increased oxygen affinity for adaptation to environmental hypoxia. These examples illustrate the role played in the past as well as the great future potential of crustaceans as experimental animal models for general studies in Comparative Physiology.

The toxicity of sewage sludge to adult and larval Sand shrimp, Crangon crangon, and larval brine shrimp Artemia salina, was studied. Temporal changes in toxicity, ammonia and pH of sewage sludge in seawater were determined. The feasibility of sediment choice bioassays using adult Crangon were examined. The 24 h LC50 of sewage sludge at 20 °C was 0.4% sludge for Crangon larvae, and 10.0% for Artemia larvae. Toxicity to Crangon larvae decreased with decreasing ammonia and increasing pH as sludge decayed over 7 days. In adult Crangon, a dose response with greater variation at < 3% sewage sludge (wet volume in seawater) was found. For adult Crangon at 10 °C, the LT50 at 1% sludge was 80-90 h and 96 h LC50 0.8-1.7% sludge. No clear differences were apparent between 96 h LC5O's in static and 24 h renewal tests. Adult Crangon avoided sediments mixed to concentrations of 6.25% and 10% sewage sludge, but buried at similar frequencies in uncontaminated and 1.57% sludge sediments. In addition to possible chemical effects from ammonia and other sewage sludge components (e.g. metals, organochlorines, hydrocarbons), sludge solids may have physical effects on Crustacea. Bioaccumulation is possible if persistent contaminants occur in the sludge. From estimated field concentrations of sewage sludge, and the results of this and other toxicity studies, lethal effects at sewage sludge disposal sites are believed unlikely. However, further sediment studies (longer-term, life-cycle, bioaccumulation, and mesocosm) are required to evaluate the role of sediment tests in understanding the effects of sewage sludge on benthic Crustacea.