Habitat surrounding patch reefs influences the diet and nutrition of the western rock lobster

This study investigated the influence of the spatial arrangement of habitat patches on the diet and nutrition of a common reef-associated generalist consumer, the western rock lobster Panulirus cygnus. Stable isotopes (C-13/C-12 and N-15/N-14) and gut contents were used to assess diet and nutrition of lobsters collected from 8 shallow patch-reef sites on the lower west coast of Australia in April and October 2005. A distance-based linear model indicated that the predominant benthic habitat surrounding a reef (seagrass or macroalgae/sand-dominated) was an important source of variation in diet and nutrition, explaining significant (p < 0.01) variation in isotope signatures and gut contents of 52.7 and 7.0%, respectively. Mobile invertebrates, sessile filter feeders, coralline algae and seagrass were consumed by lobsters from all sites, but sessile filter feeders (sponges and colonial ascidians) were consumed in significantly greater volumes (p < 0.05) at macroalgae/sand-dominated sites (21.16 +/- 3.0%) than at seagrass-dominated sites (<= 6.1 +/- 1.08%). A modified mass balance mixing model (IsoSource), which factored in C:N ratios of food sources and lobster-specific delta C-13 and delta N-15 discrimination values, was used to determine the contribution of food sources to lobster nutrition. Articulated coralline red algae were an important source, especially from sites dominated by macroalgae and sand contributing 22-72% to nutrition. Bait potentially contributes up to similar to 30% of lobster muscle nutrition and therefore may also play an important nutritional role for lobsters in areas where lobster potting occurs. Macroalgae, rather than seagrass, appears the most likely autochthonous energy source driving P. cygnus production in shallow coastal waters; however, seagrass plays an important role as habitat for lobster prey.