EFFECTS OF BOUNDARY-LAYER FLOW ON THE SETTLEMENT OF ORGANISMS 

 ONTO FLAT PLATES: PRELIMINARY RESULTS FROM CROSS SEAMOUNT 



L. S. Mullineaux, C. A. Butman, and C. M. Fuller 

 Dept. of Ocean Engineering 

 Woods Hole Oceanographic Institution 

 Woods Hole, MA 02543 



ABSTRACT 



Boundary-layer flow conditions may influence the supply of 

 invertebrate larvae to benthic habitats, and their behavior 

 during settlement. The response of larvae of deep-water, 

 encrusting organisms to different flow conditions was 

 investigated by deploying two thicknesses of settlement plates on 

 the summit of Cross Seamount, central north Pacific (410 m water 

 depth). Currents were measured 1.8 m above the study site during 

 the 48-day experiment. These measurements were combined with 

 dissolution rates of alabaster disks and previous laboratory 

 flume studies to describe the flow patterns expected over the 

 settlement plates. Settlement of organisms (mostly benthic 

 foraminif ers ) onto 1-cm-thick Lexan plates was significantly 

 greater than onto 0.15-cm thick plates, possibly because of 

 advantageous settlement environments in eddies formed at the 

 edges of thick plates. Ferromanganese coated plates were also 

 deployed to see if larvae actively selected substrates similar to 

 their natural habitat. 



INTRODUCTION 



The initial settlement of larvae can be an important stage 

 in structuring benthic communities, especially those living on 

 hard substrates (Osman, 1977; Underwood, Denley and Moran, 1983; 

 Grossberg, 1982; Keough, 1984a; Connell, 1985; Gaines and 

 Roughgarden, 1985; Gaines, Brown and Roughgarden, 1985). In many 

 habitats, early colonists determine subsequent successional 

 events, and the species composition may be more strongly 

 influenced by larval settlement than by competition or predation 

 (e.g. Keough, 1984b). 



Field and laboratory experiments on settlement onto sediment 

 (Eckman, 1983; Butman, Grassle and Webb, submitted) and onto hard 

 substrates (Crisp, 1955; Christie, 1973; DeWolf, 1973; Munteanu 

 and Maly, 1981; Wethey, 1985) have suggested that the boundary- 

 layer flow regime can have a major effect on transport and 

 settlement of larvae and other propagules. The temporal and 

 spatial scales of these types of investigations often determine 

 the relative importance of hydrodynamic and other processes 

 affecting larval settlement (Butman, 1986; 1987). Although very 

 little is known about settlement of deep-sea larvae, it is 



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