yVhite croakers (Genyonemus lineatus) were captured only on the east 

 side and an unidentified species of rockfish was captured only on the 

 south side. 



7. Natural Bottom Survey Results . 



Figure 3 shows the location of the natural bottom transect and . 

 sampling stations for sediment infauna. Dominant epibiota (organisms 

 on the surface of rocks or sediments) and substrate type encountered 

 along this transect are shown in Figure 21. In general, the deeper 

 areas of the transect, which are representative of the natural bottom 

 existing before the island was constructed, are predominantly sedi- 

 mentary (sandy silt grading into silty sand in the shoreward direc- 

 tion). On the basis of diver observations, it may be stated that the 

 biomass, numbers, and variety of epibiota encountered visually over 

 natural bottom areas are much lov;er than that of epibiota oberved on 

 the rock revetments of the island. Although rocky areas exist in the 

 shallower parts of the transect, the biota they support was observed 

 to be of lower abundance and variety than the biota occurring at 

 corresponding depths on the island. The macrophytic algae band is 

 broader over the transect than on the island; however, zonation in 

 general is much less distinct over the natural bottom transect than 

 over the island's revetments. A more detailed account of biota and 

 habitat types observed along this transect is provided in Appendix E. 



The results of analysis of the sedimentary infauna samples are 

 summarized in Table 4 (data on grain-size distributions for the two 

 sediments sampled are given in App. F). A total of 62 species was 

 encountered in the six samples. Disregarding sample 4 (a part of 

 which was lost), polychaetes accounted for 35 percent of the wet 

 weight biomass and 50 percent of the taxa present in the samples 

 taken collectively. 



Diversity, as represented by Simpson's Index, was relatively 

 uniform and high, averaging about 0.93 for the five complete samples. 

 These high numbers reflect the relatively even distribution of 

 individuals among the species present and the fact that the propor- 

 tion of total individuals accounted for by any single species is 

 small in these samples. 



The biomass values, which averaged approximately 0.7 gram per 

 sample, convert to approximately 14 grams per 0.25 square meter of 

 sedimentary bottom. Even considering the added contribution of 

 epifaunal biomass, the quantitative samples indicate that the biomass 

 of natural bottom habitats is much lower overall than that of the 

 rock revetments of the island (see Tables D-1 and D-2) . Also, the 

 number of species encountered during limited sampling of natural 

 bottom areas is much less than recorded on the rock habitats of the 

 island. 



58 



