Diel vertical migration of seagrass-associated benthic invertebrates: A novel escape mechanism that provides an allochthonous input of seagrass-based production to coral reef resident predators.

摘要

Diel Vertical Migration (DVM) is the term used to describe the well documented phenomenon of marine and aquatic zooplankton migration from deeper, poorly lit, waters to shallower waters after sunset and their subsequent return before sunrise. While the qualitative documentation of benthic emergence seems well established in many ecosystems, few studies have assessed the importance of nocturnal re-dispersal of marine benthic invertebrates. The occurrence of DVM has been documented for a variety of organisms living in a diverse array of benthic habitats including aquatic insects, seagrass meiofauna, some polychaetes, and many crustaceans. When taken together, the results of these unrelated studies indicate that DVM by benthic organisms is much more widespread than current thinking would allow.; In this dissertation, I provide the first quantitative evaluation of a heretofore undocumented link between coral reef and seagrass communities at two geographically separated sites in the Florida Keys National Marine Sanctuary. Using multiple sampling techniques and laboratory experiments I document the intense (often exceeding 1000 individuals per m2 per night) nocturnal emergence of seagrass-associated benthic invertebrates. Furthermore, I experimentally demonstrate that the mechanism influencing this nocturnal emigration is an active behavioral choice made by these invertebrates seeking to avoid nocturnally foraging, small, coral reef consumers. Once in the water column, these benthic invertebrates become entrained in local currents and are unable or unwilling to alter their horizontal positions, become homogenized throughout the water column, and are passively transported by the current, potentially over long distances. Finally, through gut contents and stable isotope analysis, I found that this seagrass-associated production can subsidize the diets of coral reef-resident fish (e.g., those fish that remain on the coral reef during the day and at night). Overall, this study documents the probable importance of the transfer of seagrass-based production, via passive deposition of benthic invertebrates, to coral reef residing consumers, and consequently adds another step in understanding the importance of cross-habitat energy exchanges in determining the productivity and structure of the seagrass-coral reef trophic food web.