PARENT SESSION
Oral Session # 63: Marine Ecology II: Communities, Barnacles, and Clams.
Presiding: RA Feagin
Thursday, August 7. 8:00 AM to 11:30 AM, SITCC Meeting Room 101.
Scaling top-down effects: Can variable recruitment and fish predation explain meso-scale mussel distribution?
Rilov, Gil*,1, 1 University of Canterbury, Christchurch, New Zealand, New Zealand
ABSTRACT- Rocky intertidal community structure can vary across wave-exposure and biogeographical scales. Differences may also occur at regional meso-scales (1-10s kms), and may be driven by nearshore oceanographic conditions that affect nutrient and larvae supply (bottom-up effects). In New Zealand, it has been suggested that upwelling conditions on the west coast enhance top-down predation effects, while on the east coast both effects are weak and macro predators (seastars and whelks) are rare. However, there is considerable localized variation. Within 2 km of shoreline on the east coast are sites with different mussel cover, species abundance and size structure. Sites surrounded by sand and with no adjacent subtidal reefs (+S-ST) had high mussel cover and plenty of small mussels. On sites with no sand and with subtidal reefs (-S+ST), small mussels were rare in the low shore. Using a comparative-experimental approach, I demonstrate that large mobile predators (probably fish) can have strong and rapid predation effects on small mussels in the low shore; there, most mussels transplanted were removed within a day in plots unprotected from such predators, while slower mortality was evident in the mid shore. There was a strong and rapid predation effect on two sites (-S+ST), and no such effect on +S-ST sites. Orders-of-magnitude differences in recruitment rates among sites were also found, with the high values comparable to those measured in the west coast. Fish can be important predators on small intertidal mussels, and can thus play a major role in shaping mussel distribution and populations structure, especially where recruitment is relatively poor or sporadic. I suggest that highly localized oceanographic, biotic and demographic differences may account for site-to-site variation. This work is part of the PISCO/Mellon projects.
Key words: mussel, fish, intertidal, predation