Effects of sea urchin(Evechinus chloroticus)grazing in Dusky Sound, Fiordland, New Zealand

Abstract

Evechinus chloroticus (Val.) is known to be an important grazer of subtidal barren habitats in northern New Zealand but its role in structuring rocky reef communities at colder southern localities is poorly understood. The present study was prompted by a proposal for the establishment of an E. chloroticus fishery in Dusky Sound, Fiordland, New Zealand. To determine the ecological importance of E. chloroticus in Dusky Sound, sea urchins were experimentally removed from shallow fucoid fringe (upper zone), mid-depth barrens (middle zone), and deeper algal meadow (lower zone), at eight sites and compared with a paired set of eight control sites. Two years of continuous removal of E. chloroticus resulted in conspicuous changes to the algal community at all depth zones examined. The density of fucoid algae (Carpophyllum spp., Sargassum spp., Cystophora spp., and Landsburgia quercifolia) increased mostly in the upper and middle zones, although smaller increases were also observed in the lower zone. Changes in cover of herbaceous, turfing and crustose algae observed in the middle and lower zones were larger than in the upper zone. Density increases of the kelp Ecklonia radiata were observed mainly in the lower zone, although still important in the middle zone. These results show that E. chloroticus can have a strong influence on the structure of algal assemblages in Dusky Sound hence the development of an E. chloroticus fishery in this area should be treated with caution.

Persistence of the exotic kelp Undaria pinnatifida does not depend on sea urchin grazing

“…The depth of our experimental removals (7 to 12 m) may have influenced the response of native canopy-forming species. Experimental removal of sea urchins in a New Zealand study has demonstrated that colonisation of large brown algae was much slower in a deeper zone (6.5 to 11.5 m) compared with 2 shallower zones (0 to 3.5 m and 3.5 to 6.5 m) (Villouta et al 2001).…”

The other 93%: trophic cascades, stressors and managing coastlines in non-marine protected areas

“…However, where urchins are abundant in patches in the south, their effects are similar to those in northern New Zealand and elsewhere. For example, Villouta (2000) and Villouta et al (2001) found that two years of continuous removal of sea urchins in Dusky Sound, Fiordland, resulted in increases in fucoid algae, mostly in shallow depths. This confirmed the nature of a strong urchinÁmacroalgae interaction in cold temperate New Zealand, and the strongest and unequivocal part of the tritrophic relationship between predators, urchins and macroalgae.…”

A novel interaction between nutrients and grazers alters relative dominance of marine habitats

“…These results demonstrate a novel interaction between nutrients (bottom-up control) and grazing pressure (top-down control), which are fundamental to predictions about management of human activities that continue to reduce densities of herbivores and increase nutrient availability on temperate coasts. KEY WORDS: Grazing · Top-down · Bottom-up · Eutrophication · Turf-forming algae Resale or republication not permitted without written consent of the publisher Connell 2002, Vanderklift & Kendrick 2004) compared with eastern Australia (Fletcher 1987, Andrew & Underwood 1993 and other parts of the world (Scheibling et al 1999, Villouta et al 2001. The interactive effects of nutrients and grazers on coasts with few grazers are not well understood, and these coasts would seem to be most vulnerable to increases in nutrient concentration because of a lack in consumer pressure, yet there is little information to challenge or support this concern.…”