A sixth-level habitat cascade increases biodiversity in an intertidal estuary

Area of Science:

• Marine Ecology
• Community Ecology
• Biodiversity Research

Background:

• Habitat cascades, where one species creates habitat for another, are well-documented for two co-occurring species.
• The theoretical potential for longer, multi-species habitat cascades remains largely unexplored in natural systems.
• Understanding complex habitat interactions is crucial for marine biodiversity conservation.

Purpose of the Study:

• To document and analyze a multi-level habitat cascade beyond the typical two-species model.
• To investigate the role of species traits and interactions in structuring complex habitat cascades.
• To interpret the habitat cascade as a habitat-formation network.

Main Methods:

• Correlative analysis of attached inhabitants with the size and biomass of biogenic hosts in the Avon-Heathcote Estuary, New Zealand.
• Identification of predictable sequences of habitat-formation (attachment space).
• Manipulative experiments to test the regulatory role of key habitat-forming species.

Main Results:

• Documented a sixth-level habitat cascade initiated by the bivalve Austrovenus, involving seaweeds (Ulva, Gigartina) and snails (trochids).
• Observed increased facilitation strength with larger seaweed frond size, accumulated seaweed biomass, and accumulated shell biomass.
• Experimental evidence confirmed seaweed and trochid abundance as key regulators of the cascade.

Conclusions:

• Long habitat cascades, extending beyond two species, are significant drivers of biodiversity.
• The strength of these cascades is influenced by the abundance and traits of higher-order habitat-formers.
• Such complex cascades are likely common in marine benthic and old forest systems where species attachment is facilitated.