FISHERY BULLETIN: VOL. 81, NO. 3 



accounted for the relatively high abundance of 

 polychaetes in Ojo de Liebre (Fig. 4). The few in- 

 faunal crustaceans (Fig. 4) also were small species 

 and individuals <6 mm in length vs. 20 mm for typi- 

 cal Bering Sea individuals). Although A. agassizi was 

 a relatively large benthic crustacean for the lagoons 

 of Baja California, this species was much smaller 

 than A. macrocephala from the Bering Sea (Fig. 



6). 



Samples from the channel and eelgrass habitats in 

 each lagoon were lumped for Figures 4 and 5, but in- 

 faunal abundance and biomass were highest in the 

 eelgrass beds. When Laguna Manuela and Estero 

 Coyote were considered together with the three calv- 

 ing lagoons (Fig. 1), the overall infaunal biomass was 

 24.3 ± 0.9 g/m 2 (± SD; n = 45). Infaunal biomass in 

 eelgrass habitats was 35.9 ± 2.7 g/m 2 (n = 21) and 

 was only 13.2 ± 1.6 g/m 2 (n = 24) in the channels. 

 This difference was highly significant (P < 0.001; 

 Mann Whitney U test). 



All the lagoon entrances were surveyed in the pre- 

 sent study except San Ignacio. Qualitative sampling 

 of the infaunal and epifaunal invertebrates revealed 



600 1 



_i 

 < 



O 



9400 

 > 



200- 



Ampelisca agassizi 

 SonOuintin -Jon, 1981 

 n = 1452 (from 3 cores) 



1.6 1.8 28 3.2 4.0 "5.5 

 -1.8 -28 -32 -40 -48 -60 



SIZE IN mm 



7 9 II 13 15 

 SIZE IN mm 



18 20 23 25 



FIGURE 6. — Length-frequency histograms of .-1 macrocephala 

 collected from a variety of stations in the Bering Sea and of . \ 

 agassizi from San Quintin. Ampelisca macrocephala populations 

 were dominated by recently released young in summer samples 

 (molt stages I and II). Most A. agassizi were preadult individuals 

 from a midwinter population. 



very low numbers and biomass. Quantitative core 

 samples taken at the entrance of Laguna Ojo de Lie- 

 bre substantiated these observations (only 14 g/m 2 ). 



The biomass of potential benthic prey was extreme- 

 ly low outside the lagoon entrances as well. Benthic 

 invertebrate communities were surveyed outside the 

 Scammon's Lagoon complex between Laguna 

 Manuela and Guerrero Negro (Fig. 1). The infauna 

 were sampled at two water depths (9 and 17 m) and 

 in areas that were likely to harbor well-developed in- 

 faunal populations. The substrate was a coarse, 

 mobile sand at each depth. When the depths were 

 combined, the infaunal biomass was 2.7 ± 3.3 g/m 2 

 (SD; n — 8). This was considerably lower than the low 

 biomass recorded from the lagoon channels (P 

 < 0.0001 ; Mann Whitney U test). A dense concentra- 

 tion (100-200/m 2 ) of the heart urchin, Lovenia cor- 

 diformis, was not included in the biomass figures 

 because this species is not a potential prey for gray 

 whales. Our experiences along other wave-exposed 

 coasts (Oliver et al. 1980) indicate that unobserved 

 patches of dense infaunal prey probably do not occur 

 in offshore habitats. 



No large zooplankton, including euphausiids and 

 galatheid crabs, were seen by divers in the offshore 

 habitats, in the lagoons, or in the lagoon mouths 

 (Norris et al. in press). 



In addition to the plankton, conspicuous mobile 

 epifauna were not abundant at the lagoon entrances 

 or anywhere in the lagoons, either on reefs or over the 

 soft sediments. Several groups of the mysid crusta- 

 cean, Mysidopsis californica, were observed near 

 eelgrass beds, but these patches were rare, covered a 

 relatively small area (10 to 20 m 2 ), and did not con- 

 tain a large number of individuals. Small groups of 

 shrimp were even rarer. 



The calving and adjacent noncalving lagoons in the 

 southern part of Baja California had highly dynamic 

 sedimentary environments. We observed tidal 

 currents of 2 to 3 kn in several lagoons. Sediments 

 were primarily coarse sand and gravel (see Phleger 

 and Ewing 1962), and surface structures indicated 

 highly mobile substrates. These structures included 

 broken shell debris and ripple marks as large as 1 m in 

 height. Surprisingly, these structures were not re- 

 stricted to the lagoon mouth. For example, large 

 lunate ripples (length about 10 m, height 30 cm) oc- 

 curred in the channel of Estero Norte, an arm of the 

 extreme back lagoon in Ojo de Liebre. These ripple 

 marks were more than 10 m wide, were highly mobile, 

 and changed direction with the tide. Unlike the more 

 southerly lagoons, we encountered relatively fine 

 sands and silts in San Quintin. Similar differences 

 between the sedimentary habitats in San Quintin 



518 



