Sediment selection in juvenile plaice and its behavioural basis

148

132

Little is known about the relative influence of landscape structure on the spatial distribution and abundance of marine organisms. To address this problem, we applied landscape ecology concepts and methods, together with conventional sampling techniques and path analysis, to test alternative hypotheses of linkages between marine nekton and landscape structure in Moreton Bay, Queensland (Australia). We quantified substratum structure at 3 spatial scales: (1) whole landscape mosaic (10s of hectares); (2) habitat type (benthic class) (100s m 2 to hectares) and (3) within-patch scale (cm 2 to m 2 ). Substratum structure at all scales was important for assemblage density and number of species, with the landscape structure of individual habitat types explaining more of the spatial variation than either within-patch structure or the structure of the whole landscape mosaic. Density and the number of species of seagrass residents were strongly influenced by landscape composition quantified as the proportion of all seagrass habitat (r 2 = 0.40 and 0.48 respectively) and the proportion of long-leaved Zostera capricorni (r 2 = 0.34 and 0.30 respectively) seagrass in the landscape. An abrupt decline in assemblage density and number of species was evident at < 20% seagrass cover. More species of fish used mangroves with adjacent continuous seagrass beds than mangroves with adjacent patchy seagrasses or unvegetated sandflats. Several species of fish using mangroves at high tide were more strongly influenced by the spatial configuration of mangrove patches and the composition of adjacent substratum than the internal structure of mangrove patches. The study highlights the need for a hierarchical landscape approach when investigating animal-environment relations in marine landscapes.

Section: Influence Of Within-patch Structurementioning

confidence: 99%

Linking fish and prawns to their environment: a hierarchical landscape approach

Pittman

McAlpine²,

Pittman³

2004

148

132

“…While some species, such as yellowfin sole Pleuronectes asper and plaice P. platessa, show little sizerelated sediment preference (Moles & Norcross 1995, Gibson & Robb 2000, other species, such as starry flounder Platichthys stellatus, winter flounder Pseudopleuronectes americanus, Pacific halibut Hippoglossus stenolepis and northern rock sole Lepidopsetta polyxystra, exhibit shifts in sediment preference during their first year (Moles & Norcross 1995, Stoner & Ottmar 2003. For species demonstrating ontogenetic shifts, smaller juveniles generally prefer finer sediments than do larger juveniles and adults.…”

Section: Introductionmentioning

confidence: 99%

Behavioral mechanisms underlying the refuge value of benthic habitat structure for two flatfishes with differing anti-predator strategies

Ryer¹,

Stoner²,

Titgen³

2004

109

Juvenile flatfish habitat is usually modeled on the basis of sediment grain-size, depth and temperature. Recent evidence indicates that some juvenile flatfishes associate with emergent structures such as sponge, shell and other biogenic and bed-form features of otherwise low-relief shelf habitats. In laboratory experiments we examined the habitat preference and effects of habitat structure upon predation vulnerability of sub-yearling (Age-0) Pacific halibut Hippoglossus stenolepis and northern rock sole Lepidopsetta polyxystra. When given the choice between bare sand or sand with 16% sponge coverage, halibut demonstrated strong preference for sponge, while rock sole showed no preference. Larger Age-2 halibut (used as predators in the subsequent experiment) also preferred sponge, but this preference declined with increasing hunger. When allowed to forage for Age-0 flatfishes in either bare sand or sponge, predators consumed more prey in sand and consumed more Age-0 halibut than rock sole. We were able to determine which behavioral processes in the predator-prey interaction were modified by the presence of habitat structure. Predator-prey encounter rates decreased in the sponge habitat as predator search was impeded: predators paused more frequently and swam more slowly to maneuver through the sponges. Sponges also tended to hinder the pursuit of prey. Rock sole utilized stereotypic flatfish defense-mechanisms, relying upon immobility, burial and crypsis, and were less likely to flush at a predator's approach than halibut. Halibut have a less developed ability to mimic sediments, but a deeper/narrower body that confers greater swimming speed, and were more likely to flush as a predator approached. Once they had flushed and were pursued by a predator, halibut were more likely to escape than were rock sole. These experiments support an accumulating body of evidence that emergent structure, in otherwise low-relief benthic habitats, may play an important role in the ecology of some juvenile flatfishes. Removal of emergent structure by towed fishing gear and other anthropogenic and/or natural disturbance may influence patterns of distribution for juvenile halibut, as fish redistribute to less preferred habitat, and may decrease survival rates through increased losses to predation.

“…On the other hand, slipper limpets transform their benthic habitat not only through the accumulation of pseudofaeces and fine sediment during filter-feeding, but through the way in which individuals assemble in colonies by attachment to each other, creating stacks that reach up into the water column (Thieltges et al 2003) and spread across the sea floor reducing available area of soft-bottom subtrate. Flatfishes appear to prefer habitats which offer homogeneous bottom sediments suitable for burying in (Gibson & Robb 2000). This behaviour is considered to reduce predation risk and provide shelter from strong currents, and may also serve to conserve their energy by reducing their activity and metabolic rate.…”

Section: Possible Explanations Of Negative Effectmentioning

confidence: 99%

“…1). The relationships between the physical properties, bathymetry (Gibson 1997) and sediment texture (Millner & Whiting 1990, Gibson & Robb 2000, which are known to influence the spatial distribution of juvenile sole (Le Pape et al 2003a), and the densities of slipper limpet populations and sole densities were studied. Generalised linear models were used to identify the respective effects of these factors, and especially to quantify the effects of the slipper limpet invasion on YOY sole, assuming delta distribution for juvenile sole by coupling binomial model testing for the presence of YOY sole with a lognormal distribution for density when these YOY were known to be present.…”

Section: Introductionmentioning

confidence: 99%

Effect of an invasive mollusc, American slipper limpet Crepidula fornicata, on habitat suitability for juvenile common sole Solea solea in the Bay of Biscay

Pape¹,

Guérault²,

Désaunay³

2004

This study describes the effect of an invasive mollusc, the slipper limpet Crepidula fornicata, on the distribution and abundance of young-of-the-year sole Solea solea in coastal nursery areas, based on beam-trawl surveys in the Bay of Biscay (France) over a 3 yr period (2000 to 2002). As habitat suitability for juvenile sole varies according to bathymetry and sediment structure, these factors and the density of the slipper limpet were used as descriptors in generalised linear models of habitat suitability to characterise the distribution of juvenile sole. The models were based on a delta distribution, coupling a binomial model testing for the presence of juvenile sole with a log-normal distribution for density when juveniles were known to be present. These linear models were used to quantify the effect of the presence and density of the slipper limpet on the density of young-of-the-year sole in nursery habitats. Despite large variability in the data set, this quantitative approach emphasised the negative role of the mollusc on juvenile sole density in the Bay of Biscay. There was no apparent effect of the slipper limpet on the extent of the sole nursery grounds, but the density of young-of-the-year sole was significantly lower where this invasive species was established. The negative effect of this invasive species on nursery habitat capacity and sole stock recruitment is discussed.