Facilitation cascades create a predation refuge for biodiversity in a novel connected habitat

Lanham B.S., AGB Poore, PE Gribben
Ecosphere 11(4) (2020) e03053

Communities structured via facilitation cascades whereby one habitat-forming species promotes a ‘secondary’ habitat-forming species with synergistic effects on biodiversity are increasingly documented. Habitat-formers can also extend the realized niche of other habitat-forming species by facilitating their recruitment into novel environments across heterogeneous landscapes. However, further understanding of whether secondary habitat-formers in these novel environments differ in their structure or support different communities from those settled in their natal habitat is required. Here, we investigated if abiotic and biotic conditions in a novel connected habitat influence biodiversity within a secondary habitat-former facilitated outside its natal habitat. We contrasted the morphology of the habitat-forming alga, Sirophysalis trinodis, and its associated fish and epifaunal community occurring on rocky reef (natal habitat) and on nearby a biogenic hard substrate, live clam shells (novel habitat) in soft-sediments. The algae on clams had a different morphology to those on the rocky shore and supported increased abundance of some epifaunal species. A reciprocal transplant experiment of S. trinodis individuals among habitats found that differences in the abundance of epifauna were explained by the increased abundance and consumption rates of predatory fish on the reef habitat compared to soft-sediment habitats, and not by differences in algal morphology between habitats. We demonstrate that facilitation promotes a secondary habitat-former into a novel habitat, which then enhances the abundance of associated epifauna by providing a predation refuge. This study contributes to a small but growing body of research demonstrating landscape scale effects of facilitation cascades, and that basal habitat-formers can extend the realized niche of secondary habitat-formers and their associated communities.


Altered fish community and feeding behaviour in close proximity to boat moorings in an urban estuary

Lanham B.S., A Vergés, LH Hedge, EL Johnston, AGB Poore
Marine Pollution Bulletin 129 (2018) 43-51

Coastal urbanization has led to large-scale transformation of estuaries, with artificial structures now commonplace. Boat moorings are known to reduce seagrass cover, but little is known about their effect on fish communities. We used underwater video to quantify abundance, diversity, composition and feeding behaviour of fish assemblages on two scales: with increasing distance from moorings on fine scales, and among locations where moorings were present or absent. Fish were less abundant in close proximity to boat moorings, and the species composition varied on fine scales, leading to lower predation pressure near moorings. There was no relationship at the location with seagrass. On larger scales, we detected no differences in abundance or community composition among locations where moorings were present or absent. These findings show a clear impact of moorings on fish and highlight the importance of fine-scale assessments over location-scale comparisons in the detection of the effects of artificial structures.


Beyond the border: effects of an expanding algal habitat on the fauna of neighbouring habitats

Lanham B.S., PE Gribben, AGB Poore
Marine Environmental Research 106 (2015) 10-18

The impacts of novel habitat-forming organisms on associated fauna have been difficult to predict, and may affect the fauna of neighbouring habitats due to changes in the spatial configuration of habitat patches of differing quality. Here, we test whether the localised expansion of a native habitat-forming macroalga, Caulerpa filiformis, on subtidal reefs can affect the abundance of fauna associated with a neighbouring macroalgal habitat. C. filiformis was a functionally distinct habitat for fauna, and the total abundance of epifauna associated with the resident alga, Sargassum linearifolium, was reduced at some sites when in close proximity to or surrounded by C. filiformis. Experimental manipulation of habitat configuration demonstrated that the low abundance of gastropods on S. linearifolium when surrounded by C. filiformis was likely explained by C. filiformis acting as a physical dispersal barrier for mobile fauna. Changes to the spatial configuration of novel and resident habitats can thus affect the abundance of fauna in addition to the direct replacement of habitats by species undergoing range expansions or increasing in abundance.