The contributions of habitat structure and larval supply to broad-scale recruitment variability in a temperate zone, seagrass-associated fish

Abstract

The contribution of habitat structure and larval supply to broad-scale spatial variability in recruitment of a temperate zone, seagrass associated fish, Sillaginodes punctata (Cuvier and Valenciennes), was investigated in Port Phillip Bay, Australia, from September to November, 1994. Replicate artificial seagrass beds were placed at five sites over a 50 km section of coastline, and artificial and adjacent natural seagrass were sampled approximately fortnightly for Sillaginodes punctata recruitment. Significant differences in recruitment amongst sites were apparent for both natural and artificial seagrass. A small but significant effect of habitat was detected where more recruits occurred in artificial relative to natural seagrass at sites with longer plant stems in the natural seagrass. The contribution of larval supply to spatial variability in recruitment was investigated by sampling natural seagrass, and concomitantly sampling the plankton immediately offshore for pre-settlement larvae. There was no significant correlation between larval abundances and recruitment, or between habitat structure and recruitment, over nine sites. We hypothesise that the high spatial variability in recruitment attributable to location is probably related to a combination of factors. These factors may include variation in larval supply, and also variation in the physical exposure of the location that influences mortality and movement of recruits in the early post-settlement stage.