New Zealand Journal of Marine and Freshwater Research abstracts
Effects of beach erosion on abundance and distribution of toheroa (Paphies
ventricosa) at Bluecliffs Beach, Southland, New Zealand
Michael P. Beentjes
Glen D. Carbines
Andrew P. Willsman
National Institute of Water and Atmospheric Research Limited
P.O. Box 6414
Dunedin, New Zealand
email: m.beentjes@niwa.co.nz
Abstract Data on abundance, distribution, and size structure
of toheroa (Paphies ventricosa) on Bluecliffs Beach, Southland, New
Zealand from 42 surveys (1966 to 2005) are presented. Toheroa abundance declined
from over 2 million adults in the mid 1960s to c. 80 000 by 1990 and since
then has remained low but relatively stable. The decline mirrors that of other
toheroa populations throughout New Zealand. Recent recruitment was highly variable
but low compared with historical levels in the 1960s. Length frequency distributions
are characteristically bimodal with a strong adult mode and a juvenile mode
of variable strength, with relatively few toheroa of intermediate size. The
distribution is related to mortality and growth characteristics of Bluecliffs
Beach toheroa. Spatial distribution of adult toheroa has progressively changed
over the last 40 years—historical distribution included the entire beach and toheroa
were most dense just east of the Rowallan Burn. Since 1997, they have been aggregated
into one large bed just west of the Rowallan Burn. Toheroa showed intertidal
size zonation with small juveniles near high water and larger toheroa near mid
to low water. Beach profile surveys were carried out in 1997, 2001,
and 2005 to assess the dynamics of beach geomorphology and erosion. The surveys
indicated a net loss of sand from the beach between 1997 and 2005, exposing
underlying gravel and cobble substrates, and a general erosion of the vegetated
dunes. Aerial photos from 1947 reveal that Bluecliffs Beach was homogeneous
sand substrate—significant
erosion and loss of sand began in the mid 1980s and only c. 54% of the beach
surface is now fine/coarse sand. Our results indicate that distribution and abundance
of toheroa on Bluecliffs Beach is related to the amount and distribution of sand
on the beach. If the erosion continues with loss of sand habitat, the toheroa
population may be at risk of collapsing.
Keywords toheroa; Paphies ventricosa; bivalve;
Bluecliffs Beach; Te Waewae Bay; abundance; spatial distribution; size distribution;
survey; substrate; erosion
New Zealand Journal of Marine and Freshwater Research, 2006, Vol. 40:
439–453
0028–8330/06/4003–0439 © The Royal Society
of New Zealand 2006
M06013; Online publication date 14 July 2006. Received 17 March 2006;
accepted 20 June 2006
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