Well known reasons why sea urchins migrate according to studies are:
(1) The juveniles outgrew their hiding places and migrated to the seagrass beds.
(2) Diet shift (e.g. juveniles eating coraline algae/detritus to adults that are able to consume seagrass blades)
(3) Aggregation-formation in order to increase reproductive success/protection from predators
My data shows that there is an increase in density of adult tropical sea urchin Tripneustes gratilla in the shallow-water seagrass beds in certain times of the year and this coincides with the spawning season. I'm suspecting that the juveniles come out of their cryptic habitats and migrate to the seagrass beds. I'm wondering if indeed sea urchins go to shallow-water to spawn or they just go there in order to feed because they have already reached adult size? Also, if they indeed spawn in the shallow seagrass beds, would this increase fertilization rate (seagrass habitat is more complex and may provide additional protection)?
Thank you for your help!
It is unlikely that seagrass habitats would affect fertilization rate any more or less than any other habitat (e.g. coral or seaweed dominated habitats). Fertilisation rate is dependent on the proximity of spawning adults and water flow, which determines the density of sperm and eggs. There are many papers which have examined this issue, most recently in the context of ocean acidification.
For example:
Byrne, M., et al. (2010). "Sea urchin fertilization in a warm, acidified and high pCO2 ocean across a range of sperm densities." Marine Environmental Research 69(4): 234-239.
Levitan, D. R., et al. (1992). "How Distribution and Abundance Influence Fertilization Success in the Sea Urchin Stronglocentrotus franciscanus." Ecology 73(1): 248-254.
Sea urchins can congregate in shallow water to spawn. However it is unlikely that the depth of the water is important, rather water flow, i.e. some sea urchins move into areas with some water flow possibly as a way to increase the dispersal of their gametes and resulting larvae. For example here in Australia, Tripneustes gratilla and other mobile marine invertebrates have been seen aggregating on the highest points on subtidal rocky reefs to spawn.
You might want to try digging these two papers up;
Nichols D, Bishop GM, Sime AAT (1983) The effects of depth and exposure on gonad production in the sea urchin, Echinus esculentus from sites around the British Isles. Prog Underw Sci 8:61–71
Nichols D, Sime AAT, Bishop GM (1985) Growth in populations of the sea urchin Echinus esculentus L. (Echinodermata: Echinoidea) from the English channel and firth of Clyde. J Exp Mar Biol Ecol 86:219–228
- Badges
- Science topic
- Similar topics
- Chemistry
- Biochemistry