Impact of Terrestrial-Derived Sedimentation on Temperate Rocky Reef Communities

Abstract

Accelerated anthropogenic pressures on the world's oceans demand an improved understanding of the connectivity between terrestrial and marine environments in order to ensure its economic and ecological viability in the future. Sedimentation as a result of terrestrial runoff can cause significantly changes in ecosystem structure and functioning through changes in rates of colonisation and development, through changes in succession, and indirectly through changes in species interactions. Te Whanganui - A - Hei Marine Reserve spans a natural gradient of sedimentation as a result of the Whitianga Harbour and Purangi Estuary. This environmental gradient is enhanced during and shortly after rainfall events that occur multiple times throughout the year significantly increasing the levels of suspended and deposited sediment in the reserve. This study demonstrated a change in community structure along this naturally variable sedimentation gradient with species with more robust body forms or those that can preempt open space more effectively more abundant at sites continually subjected to higher levels of sedimentation. This observed difference in community structure could be due partly to the development of the community which showed an inverse relationship between rate of colonisation and differences in the succession of organisms along this gradient of natural sedimentation. The response of individuals to increases in sedimentation will have a significant effect on species interactions. This study demonstrates the response of four species of different taxon to variable sedimentation. The macroalga Sargassum sinclairii, the sponge Tethya aurantium, the mussel Perna canaliculus and the crab Petrolisthes elongatus all responded negatively to increases in sedimentation. The response of each species was related to different constituents of sedimentation (e.g., suspended sediment, deposited sediment, turbidity, organic content). This study increases our understanding of the processes related to sedimentation and how temperate subtidal coastal ecosystems respond. The gained knowledge is essential for predictive and more effective management.