Habitat-associations of turban snails on intertidal and subtidal rocky reefs.

Patchiness of habitat has important influences on distributions and abundances of organisms. Given the increasing threat of loss and alteration of habitats due to pressures associated with humans, there is a need for ecologists to understand species' requirements for habitat and to predict changes to taxa under various future environmental conditions. This study tested hypotheses about the generality of patterns described for one species of marine intertidal turban snail for a different, yet closely-related species in subtidal habitats along the coast of New South Wales, Australia. These two closely-related species live in similar habitats, yet under quite different conditions, which provided an opportunity to investigate how similar types of habitats influence patterns of distribution, abundance and size-structure in intertidal versus subtidal environments. For each species, there were similar associations between biogenically structured habitat and densities. The intertidal species, Turbo undulates, were more abundant, with greater proportions of small individuals in habitats formed by the canopy-forming alga, Hormosira banksii, the solitary ascidian, Pyura stolonifera or the turfing red alga, Corallina officinalis compared to simple habitat (bare rock). Similarly, more Turbo torquatus were found in biogenically structured subtidal habitat, i.e. canopy-forming algae, Ecklonia radiata, mixed algal communities ('fringe'), or turfing red algae (Corallina officinalis and Amphiroa aniceps) than where habitat is simple (barrens). Small T. torquatus were more abundant in areas of turf and 'fringe', while large snails were more abundant in areas of kelp and barrens. These patterns were found at each location sampled (i.e. eight intertidal and two subtidal rocky reefs) and at all times of sampling, across each environment. This study highlighted the consistent influence of biogenically structured habitats on the distribution, abundance and size-structure of intertidal and subtidal turban snails and forms a basis for increasing the understanding of the potential underlying processes causing such patterns

Number of quadrats and site(s) sampled in the Sydney Region, NSW, Australia on each intertidal rocky-shore from North to South.⁺

+<p>Mona Vale (33°40′33.46″S, 151°18′23.51″E), North Narrabeen (33°42′23.44″S, 151°17′18.1″E), Tamarama (33°53′52.8″S, 151°16′4.8″E), Cronulla – north and south (34°3′26.78″S, 151°9′7.88″E), Era (151°04′E, 34°09′S), Coal Cliff (34°14′0″S, 150°58′0″E) and Bulli Point (34°19′59.23″S, 150°55′7.14″E; see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0061257#pone-0061257-g001" target="_blank">Figure 1</a>). All locations are on the open-coast with medium to heavy exposure to waves.</p>✓<p>indicates the habitat sampled.</p

Analyses of the proportion of small (and thus, large) <i>T. undulatus</i> in intertidal, structured habitats at each location and time of sampling.⁺

+<p>Due to the limited number of snails in unstructured habitat, they were not analysed.</p>**<p><i>P</i><0.01,</p>***<p><i>P</i><0.001 and – denotes no data available.</p

Mean density of <i>Turbo undulatus</i> on intertidal rocky reefs.

<p>Mean density (+ S.E.; <i>n</i> = 8) of <i>T. undulatus</i> in areas of (a) <i>Hormosira</i> (black bars; quadrat 0.25 m²) and non-<i>Hormosira</i> (white bars), (b) <i>Pyura</i> (dark grey bars; quadrat 0.04 m²) and non-<i>Pyura</i> (white bars) and (c) <i>Corallina</i> (<i>n</i> = 6; quadrat 0.25 m², grey bars) and non-<i>Corallina</i> (white bars), at each location and at each time of sampling. In areas of unstructured habitat (e.g. non-<i>Hormosira</i>), mean density of individuals are presented above the columns, where needed, due to the small number of individuals.</p

Mean density of <i>Turbo torquatus</i> on subtidal rocky reefs.

<p>Mean density (+ S.E.; <i>n</i> = 7) of <i>T. torquatus</i> in 5×1 m transects in each of three representative sites of each habitat at Cape Banks at (a) time 1 and (b) time 2.</p

Analyses of densities of <i>T. torquatus</i> among subtidal habitats at (a)⁺Cape Banks during each time of sampling and (b)⁺⁺Cape Banks and Bare Island.

+<p>Habitat, fixed 4 levels, Site, random, nested in Habitat, 3 levels, <i>n</i> = 7 and (b).</p>++<p>Cape Banks and Bare Island; Location, random 2 levels, Habitat, fixed, orthogonal, 3 levels, Site, random, nested in (Location x Habitat), <i>n</i> = 7. One site of each type of habitat was removed randomly from Cape Banks, for each time of sampling to be comparable with Bare Island.</p>a<p>Variances were heterogeneous and were stabilised, where possible, using a forth root transformation (X^0.25). Significant differences in means were compared using Student-Newman-Keuls (SNK) tests. NS denotes not significant,</p>*<p><i>P</i><0.05,</p>**<p><i>P</i><0.01,</p>***<p><i>P</i><0.001. For SNK comparisons: B, barrens; K, kelp; F, fringe; T, turf.</p>X<p>Denotes <i>post-hoc</i> pooling, <i>P</i>>0.25. New <i>F</i>-values are given for those tested against the pooled term.</p>X<p>Tested against Si(Lo x Ha), Lo x Ha and Residual.</p

Analyses of the proportion of small (and thus, large) <i>T. torquatus</i> in structured and unstructured habitats on subtidal rocky reefs at each location and time of sampling.⁺

+<p>** <i>P</i><0.01 and *** <i>P</i><0.001.</p

Map of locations studied.

<p>Map of locations studied.</p

Intra-specific variation in movement and habitat connectivity of a mobile predator revealed by acoustic telemetry and network analyses

Few studies have considered linkages of mobile predators across large spatial scales despite their significant and often critical role in maintaining ecosystem function and health. The bull shark (Carcharhinus leucas) is a large, widespread coastal predator capable of undertaking long-range movement, but there is still limited understanding of intra-regional differences in movement and habitat connectivity across latitudes within the same coastline. This study used acoustic telemetry data and network analyses to investigate long-range movements, residency patterns and seasonal habitat linkages of sub-adult and adult C. leucas along the east coast of Australia. Our results revealed that C. leucas tagged in Sydney Harbour were mainly present within this temperate estuary in summer and autumn; the rest of the year individuals were detected in tropical and subtropical habitats from southern and central Queensland. In contrast, the detection probability of C. leucas tagged in the Townsville Reefs (central Great Barrier Reef) peaked in spring, with a portion of the tagged population migrating south during the summer months. Differences in residency time between tagging locations were also detected, as all C. leucas tagged in Sydney Harbour were absent between June and November, but 35% of the tropical-reef tagged population remained resident year-round. Network analyses complemented these findings by revealing different seasonal habitat use between regions, thus highlighting complex seasonal-habitat linkages of C. leucas along the coast. Our findings support the hypothesis that the timing, duration, and drivers involved in the long-range movements and connectivity of sub-adult and adult C. leucas vary between latitudinal regions, most likely driven by the interaction between seasonal temperature changes, foraging and reproduction