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Reproduction of two non-commercial sea urchins (Echinodermata: Echinoidea) in the Mombasa Marine National Park, Kenya
Samyn, Y. (1995). Reproduction of two non-commercial sea urchins (Echinodermata: Echinoidea) in the Mombasa Marine National Park, Kenya. MSc Thesis. Vrije Universiteit Brussel: Brussel. 134 pp.
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| Beschikbaar in | Auteur |
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Documenttype: Doctoraat/Thesis/Eindwerk
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Echinoidea [WoRMS]; Echinothrix calamaris (Pallas, 1774) [WoRMS]; Echinothrix diadema (Linnaeus, 1758) [WoRMS]
Marien/Kust |
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| Abstract |
The reproductive pattern of two non-commercial exploited sea urchins, Echinothrix diadema (Linnaeus, 1758) and E. calamaris (Pallas, 1774), originating from the Mombasa Marine National Park in Kenya, was examined. Evidence was found that E. calamaris spawns around every full moon, and that the animals are in close gametogenic synchrony. For E. diadema a lunar pattern could not be found per se, but is probably also characteristic for this species. It is argued that for E. diadema a lunar pattern in reproduction exists, but that the M.M.N.P. population displays this pattern very poorly. Such a highly synchronized pattern probably was not necessary before the creation of the Park, considered the high sea urchin density and the low number of competitive and predatory fishes that were present at that moment. Synchronized spawning probably was not necessary to maximize the reproductive output at that moment. However, comparative studies on morphogenic characters such as body size, CaCC>3 -index and Aristotle's lantern, revealed clear differences between E. diadema individuals originating from a fished site and an unfished site. A moderately fished site in the reserve showed intermediate morphogenic values. It is argued that the M.M.N.P. population of E. diadema has a higher population density, which arised before the creation of the Park, i.e. before fishing restriction, than can nowadays be supported by the available food. I argue that the E. diadema population in the M.M.N.P. in the years to come will or allocate more resources to its reproduction -a negative test growth will be the consequence, thus the animals will become smaller - or it will not change its reproductive strategy and the population density will drop to "pristine environment-levels”. E. calamaris differs from E. diadema in two ways. First, the populationdensity of E. calamaris in the M.M.N.P. is much smaller then the one for E. diadema. Second, E. calamaris has a totally different behavior. Comparative studies on the same morphogenic characters as with E. diadema showed no differences between individuals originating from the Reserve (restrictive fishing) and the Park (fishing prohibited). E. calamaris does not experience food shortage as much as E. diadema due to its lower population density and its different behavior. I argue that E. calamaris also kept the same reproductive strategy as before the creation of the Park, and that the population will persist unchanged in the new 'Parkenvironment', because this strategy covers the needs for survival. |
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