Fish feeding and dynamics of soft-sediment mollusc populations in a coral reef lagoon

A 2 yr field experiment conducted in 2 locations in seagrass meadows within Everglades National Park, Florida Bay, tested the hypothesis that variations in physical structure of experimental shelters ('casitas') would affect abundance and composition of the predator guild and, in turn, that these predators would then have measurable and commensurate impacts on the nearby benthic community. Experimental structures (casita frame, mesh-roof casita and full-roof casita) were successful in attracting and aggregating predators as hypothesized, with those structures providing more overhead cover attracting significantly more predators. Although many predators, including the numerically dominant spiny lobster Panulirus argus, preyed heavily on or included molluscs in their diets, no significant impacts of predation by spiny lobsters and finfishes on the abundance and species richness of the molluscan assemblage were observed. Regional differences in prey abundance and richness were significant, yet predator effects were similar between locations. Significant location differences in prey abundances, therefore, did not result from differential impacts of prey consumption by casita-associated predators. Predation effects by spiny lobsters and various species of finfishes in Florida Bay were dispersed over time and space and predation was not the primary structuring mechanism for the gastropod and bivalve assemblages in these seagrass and macroalgal habitats. Measurable differences between prey populations in the 2 study locations probably reflect differences in habitat heterogeneity, spatial and temporal variability in predator and prey abundances and distributions, overall high diversity of benthic prey, and ontogenetic shifts in diet and habitat use by predators, all which tend to buffer predatory impacts.

Section: Discussionmentioning

confidence: 99%

Predation in subtropical soft-bottom systems: spiny lobster and molluscs in Florida Bay

Nizinski¹

2007

“…They support a diverse suite of infaunal and epibenthic invertebrates and fishes that are specialized for life on sand (Jones 1984, St John et al 1989, Jones et al 1990, Adams & Ebersole 2002. In addition, many reef-dwelling fishes initially recruit into sandy habitats before migrating onto reefs (Shulman 1984, 1985, Adams & Ebersole 2002 or actively forage over sand as adults (Jones et al 1991(Jones et al , 1992. This suggests that there are important ecological linkages between reef and sand habitats on coral reefs.…”

Section: Introductionmentioning

confidence: 99%

Habitat structure, disturbance and the composition of sand-dwelling goby assemblages in a coral reef lagoon

Syms¹,

Jones²

2004

Self Cite

Coral reef lagoons and back reef areas are composed more of sand than hard reef habitat. They support a diverse mix of fishes, including species restricted to sandy habitats and those dependent on both hard and soft substrata. However the resident assemblages associated with sand and the factors affecting their distribution and abundance are poorly understood. Here we examine spatial co-variation in the abundance of burrowing goby assemblages and habitat characteristics in the lagoon at Lizard Island (Great Barrier Reef). The aim was to identify which key habitat-variables should be incorporated into models to predict the structure of sand-dwelling fish communities. We focused on 10 common sand goby species from 7 genera: Amblyeleotris, Cryptocentrus, Ctenogobiops and Vanderhorstia (associated with burrows constructed by alpheid shrimps), and Amblygobius, Oplopomus and Valenciennea (free-living, burrowing species). Spatial patterns were examined by stratifying the lagoon into 6 recognizable habitat zones, and conducting visual transects in replicate sites within each zone. The abundance of all goby species encountered and habitat variables (depth, distance from reef, topography, disturbance of different types, sediment composition) were recorded in each transect. Habitat characteristics and fish abundance, diversity and species composition differed markedly among habitat types and sites within habitats. There was a strong association between sites grouped according to habitat characteristics and goby assemblage. These changes reflected species-specific responses to different combinations of habitat variables and their interactions. All habitat variables measured were at least partially correlated, either positively or negatively, with the abundance of some of the species. Depth, distance from consolidated reef, sediment composition and the level of disturbance were particularly important. Our study indicates that sandy habitats, although superficially uniform, support highly structured fish communities influenced by a wide range of factors.KEY WORDS: Gobiidae · Soft-sediment · Disturbance · Tropical fish · Habitat association · Lagoon Resale or republication not permitted without written consent of the publisher

“…Posey & Ambrose 1994, Langlois et al 2006), but not always, indicating that other influences might often be more important (e.g. Jones et al 1992, Barros 2005.…”

Section: Introductionmentioning

confidence: 99%

Proximity to reef influences density of small predatory fishes, while type of seagrass influences intensity of their predation on crabs

Vanderklift

How²,

Wernberg³

et al. 2007

The magnitude of the influence that predators exert on their prey is partly determined by factors that influence the density and behaviour of predators, and partly by factors that influence the survival of prey in the presence of predators. We tested whether the presence of reefs influences the density of small predatory fishes inhabiting seagrass meadows, and the intensity of predation by these fishes on tethered crabs, by taking measurements at increasing distances from 10 rocky reefs at 2 locations separated by several hundred km. We also tested whether these variables were influenced by type of seagrass by comparing patterns yielded in meadows dominated by Amphibolis spp. and Posidonia sinuosa, 2 seagrasses with different morphological and architectural characteristics. The densities of small predatory fishes declined rapidly with increasing distance from reefs, with significantly lower densities 30 m from reefs than immediately adjacent to reefs. Densities > 300 m from reefs were generally not significantly different to densities 30 m from reefs. However, the survival of tethered crabs showed no consistent trend associated with distance from reefs. Type of seagrass was not a significant influence on the density of small predatory fishes, but did influence the survival of tethered crabs: those in Amphibolis spp. meadows were 3.1× more likely to be eaten than those in P. sinuosa meadows. These patterns were consistent between locations. Our results suggest that over landscape scales (hundreds of metres) reefs are an important influence on abundance of small predatory fishes, but not on the intensity of predation on crabs. Differences in the intensity of predation between the 2 seagrass species are likely due to their dissimilar morphological and architectural characteristics.