Survey of deep-dwelling red coral (<Emphasis Type="Italic">Corallium rubrum</Emphasis>) populations at Cap de Creus (NW Mediterranean) |
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Authors: | Sergio Rossi Georgios Tsounis Covadonga Orejas Tirma Padrón Josep-Maria Gili Lorenzo Bramanti Núria Teixidó Julian Gutt |
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Institution: | (1) Institut de Ciència i Tecnologia Ambientals (Universitat Autònoma de Barcelona), Edifici Cn Campus UAB, 08193 Cerdanyola del Vallés (Barcelona), Spain;(2) Institut de Ciències del Mar (CSIC), Passeig Marítim de la Barceloneta 37-49, 08003 Barcelona, Spain;(3) Department of Biology (Zoology), University of Pisa, Via Volta 6, 56126 Pisa, Italy;(4) Centre d’Océanologie de Marseille, CNRS, UMR 6540 DIMAR, Station Marine d’Endoume, Rue de la Batterie des Lions, 13007 Marseille, France;(5) Alfred Wegener Institut for Polar and Marine Research, Columbusstr., 27568 Bremerhaven, Germany |
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Abstract: | The distribution and population structure of the eurybathic gorgonian Corallium rubrum were studied off Cap de Creus (Costa Brava, Northwestern Mediterranean Sea). Red coral is endemic to the Mediterranean Sea
and the adjacent NE Atlantic coast, where it has been over exploited for centuries. This study presents, the first quantitative
data on the spatial distribution and structure of a population extending between 50 (common SCUBA limits) and 230 m depth,
and compared it with shallow populations previously studied in the same area. Different remotely operated vehicles (ROV) and
two methodological approaches were employed during four cruises between 2002 and 2006: 1-Extensive surveys: sea to coast transects
in which red coral density and patch frequency were recorded; 2-Intensive surveys, in which parameters describing colony morphology
were recorded. Most of the hard substrate between 50 and 85 m depth was inhabited by red coral colonies, showing a patch frequency
of 8.3 ± 7.9 SD patches per 100 m-transect (total transect area: 34 m2), and within-patch colony densities of 16–376 colonies m−2 (mean of 43 ± 53 colonies m−2). Below 120 m depth red coral was less abundant, and rather than forming dense patches as in shallow water, isolated colonies
were more common. The population structure differed between sites that are easily accessible to red coral fishermen, and remote
ones (both at similar depth, 60–80 m), as colonies in easily accessible locations were smaller in height and diameter, and
showed a less developed branching pattern. At shallower locations (10–50 m depth) the population structure was significantly
different from those at deeper locations, due to the heavy harvesting pressure they are exposed to in the shallows. Twenty-five
to forty-six percentage of the deeper colonies were taller than 6 cm, while only 7–16% of the shallow water colonies exceeded
6 cm colony height. Forty-six to seventy-nine percentage of the colonies in deeper waters were large enough to be legally
harvested, while only 9–20% of the shallow water colonies met the 7 mm legal basal diameter to be collected. The branching
pattern was also better developed in deeper colonies, as up to 16% of the colonies showed fourth order branches, compared
to less than 1% of the shallow water colonies (of which 96% consisted of only one single branch). The results thus confirm
that C. rubrum populations above 50 m depth are exposed to a higher harvesting intensity than deeper populations in the same area. |
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