DOI: 10.5061/dryad.g1jwstqvj
title: Habitat traits and predation interact to drive abundance and body size patterns in macroalgae associated fauna

description: Habitat-forming organisms provide three-dimensional structure that
 supports abundant and diverse communities. Variation in the morphological
 traits of habitat-formers will therefore likely influence how they
 facilitate associated communities, either via food and habitat
 provisioning, or by altering predator-prey interactions. These mechanisms,
 however, are typically studied in isolation and thus we know little of how
 they interact to affect associated communities. In response to this, we
 used naturally occurring morphological variability in the alga Sargassum
 vestitum to create habitat units of distinct morphotypes to test whether
 variation in the morphological traits (frond size and thallus size) of S.
 vestitum, or the interaction between these traits, affect their value as
 habitat for associated communities in the presence and absence of
 predation. We found morphological traits did not interact, instead having
 independent effects on epifauna that were negligible in the absence of
 predation. However, when predators were present, habitat units with large
 fronds were found to host significantly lower epifaunal abundances than
 other morphotypes, suggesting large frond alga provided low-value refuge
 from predators. The presence of predators also influenced the size
 structure of epifaunal communities from habitat units of differing frond
 size suggesting the refuge value of S. vestitum was also related to
 epifauna body size. This suggests that habitat-formers may chiefly
 structure associated communities by mediating size-selective predation,
 and not through habitat-provisioning. Furthermore, these results also
 highlight that habitat traits cannot be considered in isolation, for their
 interaction with biotic processes can have significant implications for
 associated communities.
description: To test whether habitat unit size (i.e., algal biomass/thallus
 size) interacted with frond size diversity (small, large and mixed mean
 frond size) to affect the abundance and size structure of associated
 communities, we created and deployed five types of habitat units: a single
 branch with small fronds, a single branch with large fronds, two branches
 with small fronds, two branches with large fronds and a unit with one
 branch with small fronds and one branch with large fronds (hereafter
 ‘mixed frond’ in text and ‘mix’ in plots).    To test
 how variation in algal morphology and predation risk structure epifaunal
 communities, we used an orthogonal design with predation risk (three
 levels) and habitat unit morphology (three levels, as only double-branched
 habitat units were used); with 6 replicates for each combination
 level. After five days, all algae were retrieved by
 snorkelling.  Each branch was collected separately by removing cage (if
 present), then the cable tie at the attachment point and quickly placing
 each branch of the habitat unit in a jar underwater (i.e., for
 double-branched habitat units branches were placed in separate jars). Back
 in the laboratory, all jars were stored in the refrigerator (~2 °C) until
 processing (maximum three days). Digital zooplankton scanner technology
 was then used to count and measure (total body length: µm) all
 epifauna.
description: **Title of Dataset:** "Habitat traits and predation interact to drive
 abundance and body size patterns in associated fauna". ***
 **"HabitatUnit\_MorphologyData.csv"** Dataset of morphology
 traits for the seaweed, *Sargassum vestitum,* used to create habitat units
 of specific morphotypes to test for the relative influence of frond size
 and thallus size in structuring the invertebrate communities associated
 with seaweed in the presence and absence of predators.   Column name
 descriptions 1. “Caging treatment” = the caging treatment that strand of
 algae was exposed to; “full” = fully caged treatment where predators were
 excluded; “none” = uncaged treatment where predators had full access to
 habitat units; “half” = open cages used as a cage control for the
 experiment.  “Single” = single strand habitat units that were used to test
 for the effect of thallus size on invertebrate communities and were
 excluded from the caging experiment. 2. “Patch\_ID” = unique identifier
 for each patch used to deploy habitat units (four habitat units were
 deployed per patch) 3. “Sample\_ID” = unique identifier for each habitat
 unit.  First character represents caging treatment (F – full cage, N =
 uncaged, H = open cage); second character is meaningless; third character
 represent frond size (S = small; L = large); forth character is used to
 distinguish between replicates within treatments. 4. “Sample\_ID2” =
 unique identifier for each strand.  First character represents caging
 treatment (F – full cage, N = uncaged, H = open cage); second character is
 meaningless; third character represent frond size (S = small; L = large);
 forth character is used to distinguish between habitat unit replicates
 within treatments; firth character is used to distinguish between
 individual strands used in double strand habitat units. 5. “herbivory” =
 binary value (Y/N) of whether habitat units experienced herbivory during
 the experiment 6. “Epiphytes” = if epiphytes were present at the
 conclusion of the experiment 7. “Alga\_biomass” = weight of algal strand
 in grams 8. “Alga\_surface\_area” = surface area of algal strand in
 mm<sup>2</sup> 9. “Frond\_ID” = identifies individual fronds
 (10 in total) taken from each strand for morphological trait measurement
 10. "F\_Area" = frond area in mm<sup>2</sup> 11.
 "F\_Perim" = frond perimeter in mm<sup>2</sup> 12.
 "F\_length" - maximum length of frond in
 mm<sup>2</sup> **“Epifauna\_BodySizeData.csv”** Dataset of
 body length measurements for each individual macroinvertebrate that
 colonised habitat units. Column name descriptions 1. “Patch\_ID” = unique
 identifier for each patch used to deploy habitat units (four habitat units
 were deployed per patch) 2. “Caging treatment” = the caging treatment that
 strand of algae was exposed to; “full” = fully caged treatment where
 predators were excluded; “none” = uncaged treatment where predators had
 full access to habitat units; “half” = open cages used as a cage control
 for the experiment. 3. “Sample\_ID” = unique identifier for each habitat
 unit.  First character represents caging treatment (F – full cage, N =
 uncaged, H = open cage); second character is meaningless; third character
 represent frond size (S = small; L = large); forth character is used to
 distinguish between replicates within treatments. 4. “Branch ID” = Unique
 identifier to distinguish between individual strands used in double strand
 habitat units. 5. “Org\_ID” – Identifies individual invertebrates from
 each community. 6. “Taxa” = taxonomic classification (usually down to
 order only). 7. “Len\_micro” = maximum body length measurement of
 individual in micrometres. **Sharing/access Information** Was data derived
 from another source? No