RELATIONSHIPS BETWEEN WAVE DISTURBANCE AND ZONATION 



OF BENTHIC INVERTEBRATE COMMUNITIES ALONG A SUBTIDAL 



HIGH-ENERGY BEACH IN MONTEREY BAY, CALIFORNIA 



John S. Ouver, Peter N. Slattery, Larry W. Hulberg, and James W. Nybakken' 



ABSTRACT 



Benthic marine invertebrate communities were organized along a gradient of wave-induced substrate 

 motion on the subtidal high-energy beach in Monterey Bay, California. Two general zones were 

 distinguished from 6 to 30 m of water. A shallow zone (<14 m) contained sediments that were 

 commonly disrupted by wave activity and it was primarily occupied by small, mobile, deposit-feeding 

 peracarid and ostracod crustaceans. Patterns of crustacean morphology and mobility were related to 

 their depth zonation. Few animals lived in permanent tubes or burrows in the crustacean zone. Wave 

 disturbance decreased with increasing water depth, while the numbers of sessile and semisessile 

 species, commensal animals, and suspension or selective- surface-deposit feeders increased. The deeper 

 zone ( > 14 m) was dominated by polychaete worms living in relatively permanent tubes and burrows. A 

 variety of descriptive-correlative evidence indicates that community zonation is strongly influenced by 

 wave- induced bottom disturbance. The evidence includes: 1) a fxjsitive correlation between water 

 depth and the numbers of tube dwellers, burrow dwellers, and conunensal animals which apparently 

 cannot establish or maintain papulations in shifting sediments; 2) other depth and thus substrate 

 disturbance related natural history patterns; 3) a positive correlation between the strength of wave 

 activity and the width and depth limits of the faunal zones ( i.e., when wave disturbance is more intense, 

 the crustacean zone ends and the polychaete zone begins in deeper water); 4) a correspondence between 

 the largest decrease in polychaete population size and the season and location of greatest wave activity 

 (winter months at the shallowest station); and 5) a marked similarity between community zonation 

 along a depth-dependent gradient of oscillatory substrate motion (gently sloping sandflats) and the 

 zonation along a constant depth gradient of creeping substrate motion ( submarine canyon ridge ) . Other 

 explanations are inconsistent with these biological patterns and, thus, wave disturbance is apparently 

 the major physical process affecting community zonation. 



Sedimentary environments are dynamic and 

 strongly influenced by water currents and the 

 physical and biological properties of the sediment. 

 These animal-sediment relations have become a 

 major focus of benthic community studies since 

 the pioneering work of Sanders (1958, 1960) and 

 Rhoads and Young (1970) and were recently re- 

 viewed by Rhoads (1974) and Gray (1974). This 

 previous work was primarily restricted to wave- 

 protected embayments where deposition and re- 

 suspension of fine sediments is a major process. In 

 contrast, the open-coastal environment is com- 

 monly subjected to oceanic swell which has a 

 dramatic effect on substrate motion (e.g., Komar 

 1976). Although sediment scour and motion are 

 major sedimentary processes affecting the shallow 

 parts of most continental shelves, little is known 



'Moss Landing Marine Laboratories, P.O. Box 223, Moss 

 Landing, CA 95039. 



about their effect on the establishment and 

 maintenance of soft-bottom communities. 



The large areal scale of gradients in wave-in- 

 duced bottom disturbance and the corresponding 

 community patterns are difficult to manipulate 

 experimentally. However, potential relationships 

 between wave disturbance and community zona- 

 tion can be explored by a posteriori correlations 

 and by a priori use of "natural experiments" 

 (sensu Cody 1974). While communities are often 

 organized along gradients of environmental vari- 

 ability ( Whittaker 1962, 1967; Mills 1969; Nichols 

 1970), the complex interactions between physical 

 and biological regulatory processes are rarely un- 

 derstood. The descriptive and experimental 

 studies in the marine rocky intertidal habitat are 

 an important exception (e.g., Connell 1961; Day- 

 ton 1971; Ricketts et al. 1972; Stephenson and 

 Stephenson 1972; Paine 1974; Lubchenco and 

 Menge 1978). This study has two primary objec- 

 tives: to describe the zonation of benthic inverte- 



Manuscript accepted November 1979. 

 fishery BULLETIN: VOL. 78. NO. 2, 1980. 



437-- 



