Many of the invertebrates that live on seamounts spend the majority of their lives firmly attached to the bottom or crawling slowly across it. But for most there is a planktonic larval stage at the beginning of their lives, a time to swim or to be swept along in the currents that flow around and between seamounts. With this freedom comes great peril. Set loose in the vastness of the deep sea, the larvae have just several hours to perhaps a few months to find a suitable place to settle down, metamorphose, and spend the rest of their lives. Research into the reproductive and dispersal strategies employed by seamount organisms is still in its infancy. A number of physical and biological variables appear to affect the dispersal of seamount larvae. One is maturity at release. Some sponges fertilize their eggs internally, and release fully developed larvae. Others discharge their eggs and sperm, and fertilization and larval development take place in the open sea. A second variable is current flow. Some seamounts are swept by strong currents that flow around and over them with only modest disruptions. Others develop a complex current flow that spirals up and then sinks down above their summits. These current patterns may change seasonally. In this activity, you will explore how fertilization behavior and current flow influence the dispersal of sponge larvae. |
Watch the paired animations below to see how larval behavior varies with current patterns and with the timing of fertilization. Then answer the questions that follow. |
Critical ThinkingHow might the geologic history of a seamount or seamount chain influence the larval dispersal strategy practiced by its inhabitants? Check Answer
Scientists seek to understand and explain how the natural world works. Many of the questions raised in this endeavor have no absolute answers. Seamounts are undersea volcanoes. Many of them form close to plate boundaries, where geologic activity is frequent and often violent. Their first inhabitants would predominately be creatures that have traveled some distance. While eruptions and earthquakes and other types of sudden and severe activity are common, seamount faunas will be repeatedly established, obliterated, and then reestablished from distant sources. Organisms that spread their larvae widely will be most likely to colonize and then to produce surviving offspring. Over time, as tectonic activity eases, habitats become more persistent and more restrictive larval strategies become viable as well. |