Abstract
In order to study the segregated distribution of the three most abundant jellyfish species in the southern Gulf of Mexico, a total of 85 stations were sampled during an oceanographic cruise from 19 May to 18 June 2006. Trawling took place from surface to a maximum depth of 200 m, using a Bongo net with a 61 cm mouth diameter and 333 and 500 μm mesh sizes. Temperature and salinity were recorded. Samples were preserved in 4% formalin, neutralized with sodium borate, and changed to 70% ethylic alcohol after 24 hours for conservation. The jellyfish data were standardized to 100 m3 of filtered water. A total of 10,610 jellyfish were collected from the 333 μm mesh size net, of which eight species represented 88.49% of the total density: Aglaura hemistoma, Liriope tetraphylla, Nausithoe punctata, Clytia hemisphaerica, Persa incolorata, Obelia spp., Clytia folleata and Eutima gracilis. The former three species are the subject of this study. The results obtained indicate that the high density areas of these three species have a segregated distribution. Segregation values (White’s index) recorded between pairs of specie were very high: L. tetraphylla - A. hemistoma, 0.88; L. tetraphylla - N. punctata, 0.86 and A. hemistoma - N. punctata, 0.84. The spatial distribution of the high density areas of these species fits well with the three hydrodynamically different areas: A. hemistoma in Campeche Bank, L. tetraphylla on the Campeche and Tabasco shelves and N. punctata in Campeche Bay. This spatial distribution pattern corresponds to their main habitat and reproductive habits of the species, as well as the influence of the hydrodynamics that dominate each area.
Highlights
Jellyfish are planktonic invertebrates that are distributed mainly in marine and coastal environments [1] [2]
The results obtained in this study indicate that, notwithstanding the wide distribution of these three species in the southern Gulf of Mexico, their high density areas have a segregated distribution (Figure 3), as was confirmed by the high values obtained with the segregation index (Table 2)
It can be understood that the distribution of each species varies depending on oceanographic events and his own biology, which necessarily implies an appropriate availability of food for individual and population growth
Summary
Jellyfish are planktonic invertebrates that are distributed mainly in marine and coastal environments [1] [2]. A general estimation is that there are approximately 40,000 marine and freshwater species They are a successful group as a result of their abundance in a wide variety of aquatic environments. Their geographical distribution ranges from polar to tropical areas and in the water column they live from the surface to depths of 2000 m [3] [4]. Their relevance lies in the part they play in trophic chains as predators, mainly at the top levels of the chains, with a diet that includes from diatoms and dinoflagellates to fish eggs and larvae, and practically all zooplanktonic groups [5]-[9]. An important aspect of these organisms is that they tend to form blooms which, more than being beneficial to some groups of predators, generally constitute a bother, stopping up water inputs at nuclear plants or invading tourism areas
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