Crassostrea is a genus of true oysters family Ostreidae containing some of the most important oysters used for food. Some species in the genus have been moved to the genus Magallana. Extant species include: . The genome of Crassostrea gigas now Magallana gigas has been recently sequenced revealing an extensive set of genes that enable it to cope with environmental stresses. From Wikipedia, the free encyclopedia.
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A type of platform, known as a table, is now being used for mangrove oyster farming. The present study has the following main objectives: to identify and catalogue the ichthyofauna colonizing the Crassostrea rhizophorae farming platforms; to evaluate ecological aspects, such as the possible correlation between the physical and chemical variables for water quality and the occurrence of the ichthyofauna; and to observe the differences in the fish species found during tidal variations.
Specimens were identified and quantified using the linear-transect, visual census methodology. The ichthyofauna observed comprised 3, individuals belonging to 28 species and 20 families. Of the 28 species found in the area studied, 14 were marine transients, 12 marine dependent, and only 2 permanent residents. A significant association was observed between the abundance of 11 species and the physical and chemical variables studied.
Based on these results, it may be concluded that the platforms act as artificial reefs for the ichthyofauna, being colonized by at least 28 species, and providing protection from predators as well as a source of food and a reproductive substrate.
A ictiofauna avistada compreendeu 3. Oyster farming has been on the increase worldwide, mainly in the last few decades. In Brazil, the first commercial farming methods appeared in The platforms used for oyster farming serve as artificial reefs oyster reefs , which may be defined as structures intentionally deployed on the seabed to influence biological or physical processes Seaman, The oyster reefs provide numerous and important ecosystem features which have only recently been documented and quantified, in part because of the short history of the recognition of these reefs as important habitats for fish Peterson et al.
Fish represent the most important group colonizing the oyster farm platform area. These animals have adapted to the peculiar conditions of the estuary environment Haedrich, ; Day et al.
Knowledge of the ichthyofauna of the oyster reefs is needed, as this ecosystem has only recently been recognized as a fish habitat. This study has several main objectives: to identify and catalogue the ichthyofauna colonizing the Crassostrea rhizophorae mangrove oyster farm platforms; to classify the species according to period of residence in the estuary; to evaluate ecological aspects, such as possible associations between the physical and chemical variables of water quality with the occurrence of the ichthyofauna during tidal variations; and to determine the vertical distribution of the species inhabiting the oyster farm platforms.
This region includes the estuary of the Jaguaribe River, whose clay soil substrate makes it more suitable for farming oysters on the platforms known as tables Quayle, The oyster farming areas, which were installed in June , are to be found near Canto da Barra, 6. Recently, there has been an increase in the human presence of this area, especially during the summer, and on weekends and holidays Fig. The specimens were identified and quantified in situ using the linear transect visual census methodology Bortone et al.
This technique requires a diver to swins parallel to and on one side of a transect line 50 m length and at a distance of one meter from it, while identifying and counting the number of individual specimens per species encountered within this one-meter-wide zone parallel to the transect.
Samples whose species could not be identified in the field e. The species were listed according to Nelson , based on their evolutionary relationships. For the measurement of salinity, a portable manual sodium-chloride refractometer model SR1 Aquatic Ecosystems Inc.
Water transparency in the estuary was measured twice, using Secchi discs tied to a bathymetric cable at 10 cm intervals. The temperature was measured using a thermometer with a mercury column and bulb, readings being taken from the moment of the immersion of the thermometer in the water until the temperature measured became stable. The following values were calculated: the absolute abundance AA , which is the number of individuals of a species present; the relative abundance RA corresponds to the quotient of the absolute abundance of each species and the total abundance sum of all individuals , multiplied by ; the absolute frequency AF relates to the number of visits on which a certain species was encountered; and the relative frequency RF which is the quotient of the absolute frequency and the number of visits, multiplied by Diversity measures, using Diversity software, were employed.
The following indices were applied: the Shannon diversity index H' and the Pielou evenness index J. The ichthyofauna observed comprised 3, individuals belonging to 28 species, 24 genera and 20 families. Of these, 13 are of commercial value as fish for human consumption and 3 as ornamental fish Table 1. The vertical distribution of some species of fish inhabiting the oyster farming platform area is illustrated in Figure 2.
A total of individuals were observed during the flood tide Table 2 , when Lutjanus apodus,Sphoeroides testudineus,Eugerres brasilianus and Abudefduf saxatilis were the most abundant and frequent. The most abundant families were the Lutjanidae, Tetraodontidae, Gerreidae and Pomacentridae, in that order.
A larger number of specimens 2, were observed during the ebb tide Table 2 , there being great abundance of the following species: Atherinella brasiliensis,Cetengraulius edentulus,Sphoeroides testudineus and Lutjanus apodus. The most abundant families were the Atherinidae, Engraulidae, Tetraodontidae and Lutjanidae. The ecological classification of the species according to the literature Moura et al.
During the ebb tide, The water quality variables salinity, transparency, temperature and dissolved oxygen were measured at a distance of 1 m from the oyster farm area. The values for salinity varied, when the tide was in flood, from 35 to 42 ppt, and, when the tide was ebb, from 31 to 38; the temperature during the flood tide varied from Dissolved oxygen during the flood tide varied from 4.
The diversity indices obtained for the ichthyofauna colonizing the oyster reefs during the flood tide were, for the Shannon diversity index H' , 2. It was observed in the ebb tide that the salinity and temperature were the parameters that presented the greatest variations. The species Abudefduf saxatilis, Labrisomus nuchipinnis, Eucinostomus melanopterus and Chaetodipterus faber presented a positive association with the variable salinity, while Needles Hemirhamphus sp.
Haemulon aurolineatum showed a high correlation with temperature, while marine dependent species Centropomus spp. In the flood tide, the salinity and transparency were the parameters that presented the greatest changes.
Nevertheless, the majority of species showed some correlation with temperature Eucinostomus melanopterus, Labrisomus nuchipinnis and Lutjanus apodus. The marine dependent species, Chaetodipterus faber and Centropomus spp. The marine dependent needles Hemirhamphus sp. Eugerres brasilianus was the only species that presented a correlation with transparency.
Abudefduf saxatilis, Haemulon aurolineatum and Sphoeroides testudineus did not show any close relationship with the water parameters during the flood tide. The present study suggests that two years is a sufficient period of time to transform a simple structure, like an oyster farming platform, into an artificial reef. These structures were capable of attracting at least 3, individuals belonging to 28 different species of fish, despite the low visibility of the Jaguaribe estuary.
A total of minutes of diving time was required to obtain these results. The diversity indices have been used by ecologists in studies of the structure of fish communities to facilitate the description of ecological characteristics and allow for comparison between different areas Moring, It is also believed that the oyster farming platforms are being used by some species as a nursery area Peterson, , given the abundance of fingerlings found, Abudefduf saxatilis and Haemulon aurolineatum ; specimens of some species were found of less than 2 cm in length.
The oyster reef also functions as a feeding ground. The especially high abundance of the estuary resident species Sphoeroides testudineus in the present results may be explained by the fact that it is a potential oyster predator Pauly, The presence of species that commonly inhabit rocky beds e. This would certainly not be the case for the species mentioned above, because the specimens used as samples were small between about 10 and 15 cm , or at least, young. However, fish of the Lutjanidae and Haemulidae families, for example, have been reported as undertaking feeding migrations on a daily basis, using established routes and having a fixed schedule in terms of time of day , traveling distances of more than 1 km Nagelkerken et al.
More marine visitor species e. Oliveira argued that marine visitors are capable of tolerating a great variation in salinity and represent a majority of the species. Contrary to common belief Griffiths, , marine visitors were usually found in smaller numbers in the estuaries, when the salinity was relatively high flood tide.
According to Griffiths , the present study showed that four non-resident species utilized in CCA, Abudefduf saxatilis, Labrisomus nuchipinnis, Eucinostomus melanopterus and Chaetodipterus faber , were associated with salinity in the ebb tide, when this parameter is higher than it is in the flood tide.
Taking into consideration the number of species and the abundance of species of fish encountered, in addition to the different tide levels, it may be concluded that the values obtained during the ebb tide are greater than those for the flood tide. This may be attributed to the fact that, at lower tide levels, a large number of fish congregate in a smaller volume of water, increasing the probability of their being encountered.
This corroborates the suggestion of Morrison et al. The species Atherinella brasiliensis,Bagre marinus,Bothus sp. During the ebb tide, unpredictable changes in the environmental variables occur: salinity decreases as temperature increases several degrees, owing to the smaller volume of sea water, when the tide is low and the surface of the water is nearer the bed Levinton, For this reason, resident species such as Atherinella brasiliensis and Sphoeroides testudineus are the most highly "adapted" euryhaline and eurythermic to these adverse conditions.
With regard to water transparency visibility and dissolved oxygen, the needles species Hemirhamphus sp. This is the case of the marine dependent Eugerres brasilianus , that is influenced by this parameter in the flood tide.
The levels of dissolved oxygen are important for the distribution of species, although only needles Hemirhamphus sp. Some marine species suffer stress when levels of dissolved oxygen fall to less than or equal to 4. Such a low value, however, was not encountered in the course of this research project, suggesting that the fish were inhabiting an environment with a satisfactory saturation level 4. Even though the time period covered by this research project was insufficient to evaluate the degree of dependence of the fish on this oyster reef, more than 3, specimens, belonging to almost 30 species were registered, 7.
It may be suggested that the majority of the species registered, although classified as marine visitors, are adapted to the estuarine conditions. It was discovered that the species had a tendency to adapt to the variations in the parameters of the water whitin the tidal range.
On the basis of these results obtained over seven months, it may be concluded that Crassostrea rhizophorae oyster farm platforms act as an artificial reef for colonizing ichthyofauna, providing shelter, protection from predators, and a supply of food, as well as a safe place to reproduce. Joseph Nelson University of Alberta, Canada for their invaluable suggestions.
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Crassostrea rhizophorae (Guilding, 1828)