Charles F. Boudouresque

Fishing, trophic cascades, and the structure of algal assemblages : evaluation of an old but untested paradigm

Removal of important predators by fishing can result in trophic cascades and indirect effects on marine benthic communities. Indirect effects are especially evident when prey populations released from predation by fishing have the ability to modify entire benthic communities as do sea urchins Sea urchins have been shown to dramatically alter the underwater landscape by grazing, by converting stands of large erect algae into coralline barrens. In the western Mediterranean, a recent extension of coralline barrens into areas formerly dominated by erect algal assemblages has been attributed to release of predation on sea urchins by overfishing. Most suggestions concerning the transition form erect algeal assemblages to coralline barrens, however, have been speculative, and little descriptive and experimental work has been carried out to verify the hypothesis that fish predation on sea urchins (and its subsequent release by overfishing) drives this transition. Here we critically review the literature concerning the effect of fishing on sea urchin populations and its subsequent maintenance of different algal assemblages in the Mediterranean. The extant data cannot refute the fishes as important predators model. but we argue that other processes trecruitment, pollution, disease, large-scale oceanographic events, sea urchin harvesting, food subsidies, and availability of shelters) may also be important in regulating the structure of Mediterranean algal assemblages.

Climate change effects on a miniature ocean: the highly diverse, highly impacted Mediterranean Sea

Little doubt is left that climate change is underway, strongly affecting the Earths biodiversity. Some of the greatest challenges ahead concern the marine realm, but it is unclear to what extent changes will affect marine ecosystems. The Mediterranean Sea could give us some of the answers. Data recovered from its shores and depths have shown that sea temperatures are steadily increasing, extreme climatic events and related disease outbreaks are becoming more frequent, faunas are shifting, and invasive species are spreading. This miniature ocean can serve as a giant mesocosm of the worlds oceans, with various sources of disturbances interacting synergistically and therefore providing an insight into a major unknown: how resilient are marine ecosystems, and how will their current functioning be modified?

Are the Mediterranean waters becoming warmer? Information from biological indicators

The authors are biologists specializing in benthos or ichthyofauna survey. They have worked in marine protected areas or in other littoral zones of the Mediterranean Sea for a long time. The use of SCUBA diving as a sampling method allows them a great knowledge of the benthos and ichthyofauna. Charles-Francois Boudouresque is vice-chairman of the Benthos Committee of the CIESM, and chairman of the scientific committees of the National Park of Port-Cros and of the Natural Regional Park of Corsica (marine reserve of Scandola). The other authors are members of these scientific committees

Ecology of Paracentrotus lividus

Paracentrotus lividus is an incredibly oppommistic generalist, with a very wide range of adaptive responses to environmental conditions. It can do everything and anything. This chapter presents a short overview of the ecology of Paracentrotus lividus. Paracentrotus lividus is a rather large sea urchin that can reach 7.5 cm. In spite of its popular name, the color is highly variable: black–purple, purple, red–brown, dark brown, yellow–brown, light brown or olive green. In the most of its geographical range, either in past or present times and on a regular or occasional basis, its gonads have been appreciated as seafood or it has been intensely harvested. This chapter also gives a deeper understanding of its distribution and habitat, food and feeding, movement and migration, morality, diseases, growth, and reproduction cycles.

Regression of Mediterranean seagrasses caused by natural processes and anthropogenic disturbances and stress: a critical review.

Seagrass meadows are considered to be among the most important marine ecosystems, with regard to both ecology and biodiversity and for the services they provide. Seven species occur in the Mediterranean Sea: Posidonia oceanica (the most common in the open sea), Cymodocea nodosa (particularly common in the eastern basin), Ruppia cirrhosa, R. maritima, Zostera marina and Zostera noltii (mainly in estuaries and brackish lagoons), and Halophila stipulacea (introduced from the Red Sea). Seagrass regression may be due to natural processes and/or natural or anthropogenic disturbances and stress. It can also be due to long-term climate trends, e.g., the post-Last Glacial Maximum rise in sea-level, the Little Ice Age (LIA) cooling and the post-LIA warming, resulting in possible misinterpretation. Human-induced losses of P. oceanica have been mainly related to coastal development, pollution, trawling, fish farming, moorings, dredging, dumping and introduced species. All other seagrasses have also undergone more or less dramatic regression events. In fact, accurate data are generally of very local value and they are lacking for most of the Mediterranean Sea. In the absence of a reliable baseline, some widely cited cases of regression are questionable. Relatively healthy P. oceanica meadows, whose limits have changed little since the 1950s, may thrive in highly anthropized areas. In addition, the decline of one species can benefit another, so that the overall seagrass balance may remain unchanged (e.g., Cymodocea replacing Posidonia). However, to conclude that everything is for the best would be erroneous. First, the lack of data supporting the general regression hypothesis does not invalidate the hypothesis. Indisputably dramatic seagrass losses have been documented (e.g., P. oceanica and Z. marina). Second, the Posidonia regression is irreversible at human scales, while other seagrasses can rapidly recover, and the expansion of some seagrasses (e.g., Cymodocea) cannot counterbalance, in terms of ecosystem services, the decline of the P. oceanica meadows. Third, human pressure (demography, tourism, etc.) on Mediterranean seagrass ecosystems is destined to strongly increase in the coming decades. Finally, the rise in sea-level due to global climate change will automatically induce a withdrawal of the lower limit of seagrass meadows whenever the limit is beyond the compensation depth. So the regression trend observed in Mediterranean seagrasses, even if it proves to be currently weaker than postulated, will significantly increase and become a major concern in the future. There is therefore an urgent need for the adoption of a set of efficient indicators and the setting up of a robust comparative baseline in order to draw up an accurate assessment of the losses and, for seagrasses other than Posidonia, possible gains at Mediterranean scale. In addition, seagrasses and seagrass habitats should be granted legal protection and, where such protection already exists, it should be implemented.

Changes in Macroalgal Communities in the Vicinity of a Mediterranean Sewage Outfall After the Setting Up of a Treatment Plant

Benthic macroalgal communities of the upper rocky sublittoral were studied in 1995-1996 in the vicinity of the Marseille (Mediterranean, France) sewage outfall, 8 years after the setting up of a wastewater treatment plant and compared to a previous study carried out in 1972-1974. The number of taxa has increased, a clear stational and seasonal gradient of differentiation of the vegetation appeared, and a turf of ephemeral species is taking place of Corallina elongata at sites close to the outfall. These changes may be due to a decrease in pollutant load, the discharge of ferric chlorates used in the treatment process. However, the overall change is much less conspicuous than that described for deeper soft bottom communities, in particular the Cystoseira amantacea community is not still restored. Biological traits of this species (short distance dispersal) and the nature of most pollutants removed from the effluent (solids and organic matter) may explain this phenomenon.

Blitzkrieg in a marine invasion: Caulerpa racemosa var. cylindracea (Bryopsidales, Chlorophyta) reaches the Canary Islands (north-east Atlantic)

On the basis of morphological and genetic studies (rDNA ITS1, 5.8S, ITS2, and a 18S rDNA intron), we confirm here that Caulerpa racemosa var. cylindracea (Sonder) Verlaque, Huisman et Boudouresque, a southwestern Australian taxon recently introduced into the Mediterranean Sea also occurs in the Canary Islands. This is the first report of C. racemosa var. cylindracea in the Atlantic. It was observed for the first time in the Canary Archipelago in 1997–1998. The speed and regional scale of expansion (north Atlantic Ocean and the Mediterranean Sea) of this invasive species appear to be among the most dramatic ever recorded. The possible outcome of this introduction in the Atlantic is discussed.

Aquatic bird populations as possible indicators of seasonal nutrient flow at Ichkeul Lake, Tunisia

Lake Ichkeul is fed in autumn and winter by 7 main freshwater oueds (rivers) which create an overflow towards the mediterranean sea. Conversely, seawater enters the lake after the end of the rainy season. Thus, strong inverse variations occur twice a year both in water depth and salinity level, with a major hydraulic flow to the sea between October and January.Waterbirds exploit the lake (ca 50 species belonging to 13 families) with a marked seasonal variation in specific richness and diversity; in winter, population size (200 000 ducks, coots and geese) and biomass are much higher: 92.2% of the trophic impact occurs between October and March, because of both numbers and size of the wintering birds. The bird community is phytophagous for 96.2% of its annual biomass.The data, related to the hydraulic regime of the lake, support the hypothesis of an energetic input (N and P) which is mostly linked to the freshwater flow and an export brought about by migrating birds and the harvesting of fish. Nutrients would be a limiting factor for both plant and animal communities, Ichkeul being an atypic (rather oligotrophic) mediterranean lake. New dams around the lake (for drinking and irrigation water) are changing drastically this energetic balance and will lead to an important loss of the main characteristics of the lake, making Ichkeul an ordinary man-managed wetland.

Sargassum muticum begin to invade the mediterranean

Abstract In the Mediterranean, the Japanese brown alga Sargassum muticum (Yendo) Fensholt is no longer confined to the relatively closed Thau lagoon (France), but is spreading along the Languedoc open-sea coasts: 11 new localities, from Grau du Roi (Gard) to Port-la-Nouvelle (Aude), are mentioned.

An ecosystem-based approach to assess the status of a Mediterranean ecosystem, the Posidonia oceanica seagrass meadow.

Biotic indices, which reflect the quality of the environment, are widely used in the marine realm. Sometimes, key species or ecosystem engineers are selected for this purpose. This is the case of the Mediterranean seagrass Posidonia oceanica, widely used as a biological quality element in the context of the European Union Water Framework Directive (WFD). The good quality of a water body and the apparent health of a species, whether or not an ecosystem engineer such as P. oceanica, is not always indicative of the good structure and functioning of the whole ecosystem. A key point of the recent Marine Strategy Framework Directive (MSFD) is the ecosystem-based approach. Here, on the basis of a simplified conceptual model of the P. oceanica ecosystem, we have proposed an ecosystem-based index of the quality of its functioning, compliant with the MSFD requirements. This index (EBQI) is based upon a set of representative functional compartments, the weighting of these compartments and the assessment of the quality of each compartment by comparison of a supposed baseline. The index well discriminated 17 sites in the north-western Mediterranean (French Riviera, Provence, Corsica, Catalonia and Balearic Islands) covering a wide range of human pressure levels. The strong points of the EBQI are that it is easy to implement, non-destructive, relatively robust, according to the selection of the compartments and to their weighting, and associated with confidence indices that indicate possible weakness and biases and therefore the need for further field data acquisition.