Effects of Reef Proximity on the Structure of Fish Assemblages of Unconsolidated Substrata

Abstract

Fish assemblages of unconsolidated sedimentary habitats on continental shelves are poorly described when compared to those of hard substrata. This lack of data restricts the objective management of these extensive benthic habitats. In the context of protecting representative areas of all community types, one important question is the nature of the transition from reefal to sedimentary fish assemblages. We addressed this question using Baited Remote Underwater Videos (BRUVs) to assess fish assemblages of sedimentary habitats at six distances from rocky reefs (0, 25, 50, 100, 200, and 400 m) at four sites in subtropical eastern Australia. Distance from reef was important in determining fish assemblage structure, and there was no overlap between reef sites and sedimentary sites 400 m from reef. While there was a gradient in assemblage structure at intermediate distances, this was not consistent across sites. All sites, however, supported a mixed ‘halo’ assemblage comprising both reef and sediment species at sampling stations close to reef. BRUVs used in conjunction with high-resolution bathymetric and backscatter spatial data can resolve differences in assemblage structure at small spatial scales (10s to 100s of metres), and has further application in unconsolidated habitats. Unless a ‘reef halo’ assemblage is being examined, a minimum of 200 m but preferably 400 m distance from any hard substrate is recommended when designing broader-scale assessments of fish assemblages of sedimentary habitats.

Habitat structural complexity metrics improve predictions of fish abundance and distribution

“…The positive influence of surface rugosity on the abundance of piscivores and sediment infauna predators may relate to the influence on their prey. Piscivores may benefit from surface rugosity because it increases the availability of their prey; while sediment infauna predators may find a habitat with more patches of sand around reef edges has higher abundance of their prey, compared to sandy areas further away from reefs, and also provides quicker access to shelter (Schultz et al 2012). The negative influence of surface rugosity on herbivores likely relates to advantages Table 4.…”

“…Understanding relationships between habitat complexity and fish assemblages, as surrogates for biodiversity patterns, will benefit management planning, especially as high-resolution seabed terrain data become available (Ierodiaconou et al 2007, Todd andKostylev, 2011). High-resolution data is capable of capturing heterogeneity across multiple spatial extents and therefore should be incorporated into spatial ecology and conservation planning, as suggested in other studies (Valentine et al 2007, Vanderklift et al 2007, Schultz et al 2012). This study demonstrated that high-resolution surface rugosity is a useful measure that explained on average 16% of the variance in fish abundance, whereas the mean amount of variance explained by the main predictor of interest in ecological studies is typically between 2.5-5.4% (Møller and Jennions 2002).…”

“…In the context of fish, ecologically relevant extents are those that influence key ecological processes, such as predation. Fish assemblages can change substantially across habitats and spatial extents, even across tens of meters in reefs (Vanderklift et al 2007, Schultz et al 2012, Fulton et al 2016. Important ecological processes, such as herbivory, can vary spatially at sub-meter resolution (Ferrari et al 2012b).…”

Depth and Medium-Scale Spatial Processes Influence Fish Assemblage Structure of Unconsolidated Habitats in a Subtropical Marine Park

“…However, preliminary BRUVs data, both from an examination of the effects of proximity to reef on fish assemblages [30], and from haphazard deployment across the SIMP (Malcolm, unpublished data), suggest a substantially different suite of species to those found on rocky reefs.…”

Relationships between the spread of Caulerpa filiformis and fish communities on temperate rocky reefs

“…A dummy variable with a species value of 1 was added to each sample, for all analyses, to account for undefined values as a result of the absence of fishes along some RVCs (Monk et al ., ). All univariate analyses outlined below were based on Euclidian distance (Schultz et al ., ) and all multivariate analyses on Bray‐Curtis distance measures. Monte‐Carlo P ‐values (Anderson, ) were used for all analyses both univariate and multivariate where there was an insufficient number of unique permutations for estimates of P ‐values.…”