Implications of Sponge Biodiversity Patterns for the Management of a Marine Reserve in Northern Australia

Abstract

Marine reserves are becoming progressively more important as anthropogenic impacts continue to increase, but we have little baseline information for most marine environments. In this study, we focus on the Oceanic Shoals Commonwealth Marine Reserve (CMR) in northern Australia, particularly the carbonate banks and terraces of the Sahul Shelf and Van Diemen Rise which have been designated a Key Ecological Feature (KEF). We use a species-level inventory compiled from three marine surveys to the CMR to address several questions relevant to marine management: 1) Are carbonate banks and other raised geomorphic features associated with biodiversity hotspots? 2) Can environmental (depth, substrate hardness, slope) or biogeographic (east vs west) variables help explain local and regional differences in community structure? 3) Do sponge communities differ among individual raised geomorphic features? Approximately 750 sponge specimens were collected in the Oceanic Shoals CMR and assigned to 348 species, of which only 18% included taxonomically described species. Between eastern and western areas of the CMR, there was no difference between sponge species richness or assemblages on raised geomorphic features. Among individual raised geomorphic features, sponge assemblages were significantly different, but species richness was not. Species richness showed no linear relationships with measured environmental factors, but sponge assemblages were weakly associated with several environmental variables including mean depth and mean backscatter (east and west) and mean slope (east only). These patterns of sponge diversity are applied to support the future management and monitoring of this region, particularly noting the importance of spatial scale in biodiversity assessments and associated management strategies.

Patterns of Sponge Biodiversity in the Pilbara, Northwestern Australia

“…Taxonomic resolution of those OTUs remains a work in progress. The high species richness observed for northern tropical Australia highlights the immense significance of the Australian continental shelf as a habitat for marine sponges, with numerous biodiversity hotspots reported [3,4,19,26,27]. Presently the Pilbara stands out in northwestern Australia, with the number of sponge species recorded in this study much higher than in the neighbouring Kimberley (342 species, based on a similar historic study, [46]), although this difference may lessen with sampling programs presently being undertaken in the latter region.…”

“…Recent heating events caused coral bleaching and mortality, but local coral species are also known from other areas [44]. However, for sponges the risk of losing not only local communities, but endemic species, to disturbance events is considerably larger, which needs to be taken into consideration for management priorities [4,19,88,89]. To ensure the sustained occurrence of these habitat forming communities, the species rich and rapidly changing bioregions, Pilbara Nearshore and Offshore, should be assessed for marine protection.…”

“…When only described species were considered (n = 172), a similar pattern in species occurrence was seen, with about half of the species occurring only in one bioregion (Figure 3b). Sediment-dwelling, endopsammic sponges displayed a notable diversity, with 51 Oceanapia spp., 19…”

“…Sponge populations and communities generally lack effective management, to the extent that they have been defined as a 'neglected group' [17,18]. Two recent publications have examined sponge biodiversity patterns in northern Australia with a management perspective [4,19]. Worldwide, only a handful of monitoring projects have included sponges in their surveys and programs [20][21][22].…”

Assessing the Potential of Sponges (Porifera) as Indicators of Ocean Dissolved Si Concentrations

“…According to Figure 4, lithistid taxa are more likely to be found at <60 µM dSi, with the greatest relative frequency at <20 µM and <1,000 m. Some of them are known to build reef-like formations in habitats where dSi availability is low relative to that reported for the Hexactinosida reef-like builders (Maldonado et al, 2015a,b). Hypersilicified species lithistid (e.g., Leiodermatium spp) also cohabit with members of sponges without siliceous skeletons (i.e Dictyoceratida, Dendroceratida, and Verongiida) (Przeslawski et al, 2014(Przeslawski et al, , 2015 in relatively shallow habitats of northern Australia, with dSi concentrations <5 µM, exposed to strong tidal currents, high turbidity, and substantial sediment mobility (Przeslawski et al, 2011). As suggested by Maldonado et al (2015b), some lithistid species seem to benefit from heavy sediment deposition, and patterns of local circulation that might deliver food and Si in pulses.…”