Frequently, population ecology of marine organisms uses a descriptive approach in which their sizes and densities are plotted over time. This approach has limited usefulness for design strategies in management or modelling different scenarios. Population projection matrix models are among the most widely used tools in ecology. Unfortunately, for the majority of pelagic marine organisms, it is difficult to mark individuals and follow them over time to determine their vital rates and built a population projection matrix model. Nevertheless, it is possible to get time-series data to calculate size structure and densities of each size, in order to determine the matrix parameters. This approach is known as a “demographic inverse problem” and it is based on quadratic programming methods, but it has rarely been used on aquatic organisms. We used unpublished field data of a population of cubomedusae Carybdea marsupialis to construct a population projection matrix model and compare two different management strategies to lower population to values before year 2008 when there was no significant interaction with bathers. Those strategies were by direct removal of medusae and by reducing prey. Our results showed that removal of jellyfish from all size classes was more effective than removing only juveniles or adults. When reducing prey, the highest efficiency to lower the C. marsupialis population occurred when prey depletion affected prey of all medusae sizes. Our model fit well with the field data and may serve to design an efficient management strategy or build hypothetical scenarios such as removal of individuals or reducing prey. TThis This sdfsdshis method is applicable to other marine or terrestrial species, for which density and population structure over time are available.
A lot of confusion (over the last 90 years) surrounds the naming of the Californian carybdeid population, sighted near La Jolla and Santa Barbara, since its first description by Stiasny in 1922. The specimens were first identified as Carybdea rastonii and later as Carybdea marsupialis but the identification was doubted by several scientists. To clear up the confusion, specimens of the Californian population were compared to specimens of all known carybdeid species. This comparison revealed that the Californian population represents an undescribed carybdeid species, named Carybdea confusa n. sp., being identified by the combination of the following characters: Gastric phacellae (single rooted, single stemmed), velarial canals (2 velarial canal roots/octant; canals multiple-branched with rounded tips) and pedalial canal (knee bend with thorn-like appendage).
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