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Reproductive biology of four Diplodus species Diplodus vulgaris, D. annularis, D. sargus sargus and D. puntazzo (Sparidae) in the Gulf of Tunis (central Mediterranean)
- N. Mouine, P. Francour, M.H. Ktari, N. Chakroun-Marzouk
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- Journal:
- Journal of the Marine Biological Association of the United Kingdom / Volume 92 / Issue 3 / May 2012
- Published online by Cambridge University Press:
- 13 July 2011, pp. 623-631
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The reproductive features of four commercially important species of the Diplodus genus were studied in the Gulf of Tunis to contribute to better fisheries management on the local scale. The study was specifically aimed to estimate sex-ratio and size at first maturity, to determine spawning season, to analyse hepatic and muscular energy reserve changes and to highlight possible regional difference over the Diplodus geographical distribution. A total of 570 Diplodus vulgaris (two-banded seabream), 428 Diplodus annularis (annular seabream), 350 Diplodus sargus sargus (white seabream) and 218 Diplodus puntazzo (sharpsnout seabream) were collected from the commercial catches of the artisanal fleet between October 2004 and June 2006. Male:female ratio was initially skewed in favour of females for the four Diplodus species and especially among larger-sized individuals. Length and age at first maturity was 17.4 ± 0.2 cm total length (TL) (4 years) for D. vulgaris, 9.7 cm TL (2 years) for D. annularis, 21.0 ± 0.3 cm TL (4 years) for D. s. sargus, 21.5 ± 0.2 cm TL (3 years) for D. puntazzo and a recommendation is made for the increasing of the captured length. According to the monthly succession of gonad maturity stages and the yearly gonadosomatic index (GSI) fluctuation, the spawning season of Diplodus species present a temporal succession along the year. The two-banded seabream has a winter spawning period, the white seabream is mainly a spring spawner, the annular seabream spawns essentially in summer months and the spawning of sharpsnout seabream takes place in autumn. Generally, hepatosomatic index presented an inverse trend to GSI in relation to the breeding activity. The condition factor showed significant monthly variations affected by the sexual cycle of the Diplodus species.
Trophic cascades in benthic marine ecosystems: lessons for fisheries and protected-area management
- J.K. PINNEGAR, N.V.C. POLUNIN, P. FRANCOUR, F. BADALAMENTI, R. CHEMELLO, M.-L. HARMELIN-VIVIEN, B. HEREU, M. MILAZZO, M. ZABALA, G. D'ANNA, C. PIPITONE
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- Journal:
- Environmental Conservation / Volume 27 / Issue 2 / June 2000
- Published online by Cambridge University Press:
- 10 May 2002, pp. 179-200
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An important principle of environmental science is that changes in single components of systems are likely to have consequences elsewhere in the same systems. In the sea, food web data are one of the few foundations for predicting such indirect effects, whether of fishery exploitation or following recovery in marine protected areas (MPAs). We review the available literature on one type of indirect interaction in benthic marine ecosystems, namely trophic cascades, which involve three or more trophic levels connected by predation. Because many indirect effects have been revealed through fishery exploitation, in some cases we include humans as trophic levels. Our purpose is to establish how widespread cascades might be, and infer how likely they are to affect the properties of communities following the implementation of MPAs or intensive resource exploitation. We review 39 documented cascades (eight of which include humans as a trophic level) from 21 locations around the world; all but two of the cascades are from shallow systems underlain by hard substrata (kelp forests, rocky subtidal, coral reefs and rocky intertidal). We argue that these systems are well represented because they are accessible and also amenable to the type of work that is necessary. Nineteen examples come from the central-eastern and north-eastern Pacific, while no well-substantiated benthic cascades have been reported from the NE, CE or SW Atlantic, the Southern Oceans, E Indian Ocean or NW Pacific. The absence of examples from those zones is probably due to lack of study. Sea urchins are very prominent in the subtidal examples, and gastropods, especially limpets, in the intertidal examples; we suggest that this may reflect their predation by fewer specialist predators than is the case with fishes, but also their conspicuousness to investigators. The variation in ecological resolution amongst studies, and in intensity of study amongst systems and regions, indicates that more cascades will likely be identified in due course. Broadening the concept of cascades to include pathogenic interactions would immediately increase the number of examples. The existing evidence is that cascade effects are to be expected when hard-substratum systems are subject to artisanal resource exploitation, but that the particular problems of macroalgal overgrowth on Caribbean reefs and the expansion of coralline barrens in the Mediterranean rocky-sublittoral will not be readily reversed in MPAs, probably because factors other than predation-based cascades have contributed to them in the first place. More cascade effects are likely to be found in the soft-substratum systems that are crucial to so many large-scale fisheries, when opportunities such as those of MPAs and fishing gradients become available for study of such systems, and the search is widened to less conspicuous focal organisms such as polychaetes and crustaceans.