Relative abundances of the five most common taxa in benthic samples from four habitats (one with two microhabitats) at three times during the day. Each habitat and time was sampled on two days and these replicates are placed one above the other. 

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... ENTHIC AND P LANKTONIC S AMPLES .—The number of taxa recognized in the benthic samples was 30. The five most numerous taxa constituted 83.3% of the 11,642 individuals counted; in decreasing order (with percent of individuals) were harpacticoid copepods (58.6), nematodes (7.6), ostracods (5.9), foraminifers (5.9) and polychaetes (5.3). Calanoid copepod fragments represented 0.05% of the total and cyclopoid copepods represented 0.59%. With the exception of the high samples in the high spur and groove zone, harpacticoids dominated all samples (Fig. 1). The high samples were more variable than the others with two having large numbers of nematodes and three having large numbers of ostracods. Even in these samples, harpacticoids were the single most numerous group with one exception: in row 1, column 4 (R1C4) of Figure 1 where nematodes constituted 40% of the sample compared to 37% for harpacticoids. The number of taxa recognized in the plankton samples was 48. The five most numerous taxa constituted 95.8% of the 32,488 individuals counted; in decreasing order (with percent of individuals) were calanoid copepods (82.6), cyclopoid copepods (9.5), eggs (2.1), mysids (1.1) and foraminifers (0.5). Harpacticoid copepods represented 0.28% of the total. The plankton samples were more variable than the benthic samples both between habitats and over time. With the exception of the pavement zone, most samples were dominated by calanoid and cyclopoid copepods (Fig. 2). The variation over time was considerable, occasionally with complete dominance by one group such as cyclopoid copepods (82.4% of R4C2 in Fig. 2) or calanoid copepods (98.5% of R2C5 in Fig. 2). This temporal variability was most pronounced during 7 and 8 March when there was a striking aggregation of the oceanic calanoid copepod, Acartia spinata . The percent of calanoid copepods in the samples those days (Fig. 2) was 97.6 (R1C4), 95.1 (R5C4) and 98.5 (R2C5). The aggregation dispersed on 8 March and the percents dropped as the day progressed with the early, mid and late day samples from the low spur and groove zone being 98.5 (R2C5), 87.3 (R4C5) and 67.0 (R6C5). The density dropped from 103,744 individuals per tow in the morning to 7309 at midday, whereas cyclopoids remained steady with 592 in the morning and 619 at midday. Calanoid densities during the aggregation averaged 60,226 individuals per tow as compared to 1468 for the remaining tows in the high and low spur and groove zones. It is also notable that the only days in which calanoids were abundant in the pavement zone were 6 March and 9 March (R5C1 and R4C1 in Fig. 2, respectively), the day before and the day after the aggregation was apparent in the two spur and groove zones. Sampling did not occur in the pavement zone on 7 and 8 March. During the aggregation, calanoid copepods were denser in high than in low samples in the high spur and groove zone. The two high tows on 7 March averaged 38,467 calanoids whereas the two low tows averaged 788 calanoids. This pattern held at other times but was not a result of sampling bias because other organisms, such as mysids and isopods, were denser in low tows (Fig. 3). The two points in the upper right corner of Figure 3 represent calanoid densities during the aggregation when the high-low difference was greatest (high-low ratios 103 and 33.3 as compared with a range of 0.99 to 7.71 for the other times). Unlike calanoids, cyclopoid and harpacticoid copepods were not more abundant in high tows but larvaceans and eggs were (Fig. 3). The density of all plankton combined was greater in the high tows (high-low ratios = 1.43 0.20 SE for tows taken when there was no calanoid aggregation). The average overlap of the planktonic and benthic samples was 0.11. This figure masks the unusual nature of the pavement zone, however. Because the plankton sample in this zone was taken with a stationary net in contact with the substrate (see Methods), the plankton sample is probably intermixed with some benthic organisms. This was evident in the average similarities of the benthic and plankton samples in the different zones: for the pavement zone the value was 0.23 whereas it was 0.08 for the other zones combined (P < 0.0001, m = 6, n = 24, Mann-Whitney Test). The real overlaps were lower than reported here because many groups were recognized only to order, thus failing to distin- guish between planktonic and benthic species; the three groups for which this was most evident (with their average benthic and planktonic percents were: Isopoda (2.4, 3.9), Fora- minifera (6.1, 13.8), and Ostracoda (4.9, 1.5). G UT S AMPLES .—The number of taxa recognized in the gut samples was 33 and the number of items identified in the samples ranged from 59 to 586 per five fish. The five most numerous taxa constituted 84.3% of the 8000 individuals counted; in decreasing order (with percent of individuals) were harpacticoid copepods (79.1), calanoid copepods (5.5), ostracods (4.7), tanaids (2.1) and cyclopoid copepods (1.9). When combined, copepods constituted 61 to 96% of the food items in the 42 five-fish gut samples. A. greenfieldi, A. paula and A. aspera guts averaged >80% harpacticoid copepods in all habitats whereas A. spinosa contained an average of 18.6% harpacticoids (Fig. 4). Con- versely, A. spinosa guts averaged 46.3% calanoid copepods whereas the other species averaged <3% in all habitats. All copepods in all fish species ranged from 84.5 to 90% on average. For benthic and gut samples, Ivlev’s index of electivity indicates that harpacticoids are actively selected by all species except A. spinosa (P = 0.02, Sign test) whereas isopods are actively rejected by all species except A. spinosa (Table 1). The apparent preference of A. spinosa for isopods is misleading because the isopods consumed by that species are of planktonic origin and therefore not represented in the benthic samples used in this analysis. Ostracods are selected in all cases except the high spur and groove zone, and polychaetes and nematodes are selected against in all cases. For plankton and gut samples, Ivlev’s index of electivity indicates that A. spinosa does indeed select isopods whereas none of the other species do (P = 0.02, Sign test, Table 2). In addition, all the species have very few calanoids in their guts relative to their abundance in the water column but A. spinosa , while having fewer calanoids than the water column, has a considerably lesser reduction than the other species. A. spinosa fed primarily on plankton whereas the other three species fed primarily on benthos (Fig. 5). For all taxa, the gut-plankton overlap was 0.56 for A. spinosa and 0.09 for the other species combined (t = 14.2, df = 40, P < 0.0001). In contrast, the gut-benthos overlap was 0.29 for A. spinosa and 0.56 for the other species combined (t = 8.29, df = 40, P < 0.0001). There is a positive correlation of percent calanoids in the plankton tows and in the A. spinosa guts (Spearman rank correlation = 0.9, one-tailed P = 0.042, n = 5). Based on copepods, gut contents reflected an increasing planktonic proportion as samples were taken from greater distances from shore (Fig. 6). Fish from the pavement zone, which is on the backreef, had many fewer calanoids and cyclopoids relative to harpacticoids than fish taken from the forereef. A. spinosa guts were very different from the others with a planktonic to benthic copepod ratio of 3.5 as compared with 0.02 (range 0.006 to 0.03) for the other species on the forereef. The mean number of items in the guts at early, mid and late day were 156, 250 and 166 per five fish. The mean number of items varied with fish species, so the numbers were expressed as percents (with the highest value on a given day = 100%) to give equal weight to each species. Mean percents for early, mid and late day were 62, 95 and 66 (F = 10.3, df = 2,39, P = 0.0003, ANOVA). The reason for a significantly greater number of food items at midday is unclear. M ETABOLIC R ATES .—The data presented include four species of Acanthemblemaria and two species of Emblemariopsis . A seventh species, Acanthemblemaria maria , was represented by only two specimens and is omitted from the analysis. For each species, the O 2 consumption rate vs live weight showed a straight line relationship (Fig. 7, Table 3). The weight of the fishes varied by more than an order of magnitude (11 to 220 mg), yet the O 2 consumption rates fell into three groups based on comparisons of the slopes of O con- 2 sumption vs weight: (1) A. spinosa, E. pricei and E. ruetzleri had steep slopes (0.34 ...

Context 2

... ENTHIC AND P LANKTONIC S AMPLES .—The number of taxa recognized in the benthic samples was 30. The five most numerous taxa constituted 83.3% of the 11,642 individuals counted; in decreasing order (with percent of individuals) were harpacticoid copepods (58.6), nematodes (7.6), ostracods (5.9), foraminifers (5.9) and polychaetes (5.3). Calanoid copepod fragments represented 0.05% of the total and cyclopoid copepods represented 0.59%. With the exception of the high samples in the high spur and groove zone, harpacticoids dominated all samples (Fig. 1). The high samples were more variable than the others with two having large numbers of nematodes and three having large numbers of ostracods. Even in these samples, harpacticoids were the single most numerous group with one exception: in row 1, column 4 (R1C4) of Figure 1 where nematodes constituted 40% of the sample compared to 37% for harpacticoids. The number of taxa recognized in the plankton samples was 48. The five most numerous taxa constituted 95.8% of the 32,488 individuals counted; in decreasing order (with percent of individuals) were calanoid copepods (82.6), cyclopoid copepods (9.5), eggs (2.1), mysids (1.1) and foraminifers (0.5). Harpacticoid copepods represented 0.28% of the total. The plankton samples were more variable than the benthic samples both between habitats and over time. With the exception of the pavement zone, most samples were dominated by calanoid and cyclopoid copepods (Fig. 2). The variation over time was considerable, occasionally with complete dominance by one group such as cyclopoid copepods (82.4% of R4C2 in Fig. 2) or calanoid copepods (98.5% of R2C5 in Fig. 2). This temporal variability was most pronounced during 7 and 8 March when there was a striking aggregation of the oceanic calanoid copepod, Acartia spinata . The percent of calanoid copepods in the samples those days (Fig. 2) was 97.6 (R1C4), 95.1 (R5C4) and 98.5 (R2C5). The aggregation dispersed on 8 March and the percents dropped as the day progressed with the early, mid and late day samples from the low spur and groove zone being 98.5 (R2C5), 87.3 (R4C5) and 67.0 (R6C5). The density dropped from 103,744 individuals per tow in the morning to 7309 at midday, whereas cyclopoids remained steady with 592 in the morning and 619 at midday. Calanoid densities during the aggregation averaged 60,226 individuals per tow as compared to 1468 for the remaining tows in the high and low spur and groove zones. It is also notable that the only days in which calanoids were abundant in the pavement zone were 6 March and 9 March (R5C1 and R4C1 in Fig. 2, respectively), the day before and the day after the aggregation was apparent in the two spur and groove zones. Sampling did not occur in the pavement zone on 7 and 8 March. During the aggregation, calanoid copepods were denser in high than in low samples in the high spur and groove zone. The two high tows on 7 March averaged 38,467 calanoids whereas the two low tows averaged 788 calanoids. This pattern held at other times but was not a result of sampling bias because other organisms, such as mysids and isopods, were denser in low tows (Fig. 3). The two points in the upper right corner of Figure 3 represent calanoid densities during the aggregation when the high-low difference was greatest (high-low ratios 103 and 33.3 as compared with a range of 0.99 to 7.71 for the other times). Unlike calanoids, cyclopoid and harpacticoid copepods were not more abundant in high tows but larvaceans and eggs were (Fig. 3). The density of all plankton combined was greater in the high tows (high-low ratios = 1.43 0.20 SE for tows taken when there was no calanoid aggregation). The average overlap of the planktonic and benthic samples was 0.11. This figure masks the unusual nature of the pavement zone, however. Because the plankton sample in this zone was taken with a stationary net in contact with the substrate (see Methods), the plankton sample is probably intermixed with some benthic organisms. This was evident in the average similarities of the benthic and plankton samples in the different zones: for the pavement zone the value was 0.23 whereas it was 0.08 for the other zones combined (P < 0.0001, m = 6, n = 24, Mann-Whitney Test). The real overlaps were lower than reported here because many groups were recognized only to order, thus failing to distin- guish between planktonic and benthic species; the three groups for which this was most evident (with their average benthic and planktonic percents were: Isopoda (2.4, 3.9), Fora- minifera (6.1, 13.8), and Ostracoda (4.9, 1.5). G UT S AMPLES .—The number of taxa recognized in the gut samples was 33 and the number of items identified in the samples ranged from 59 to 586 per five fish. The five most numerous taxa constituted 84.3% of the 8000 individuals counted; in decreasing order (with percent of individuals) were harpacticoid copepods (79.1), calanoid copepods (5.5), ostracods (4.7), tanaids (2.1) and cyclopoid copepods (1.9). When combined, copepods constituted 61 to 96% of the food items in the 42 five-fish gut samples. A. greenfieldi, A. paula and A. aspera guts averaged >80% harpacticoid copepods in all habitats whereas A. spinosa contained an average of 18.6% harpacticoids (Fig. 4). Con- versely, A. spinosa guts averaged 46.3% calanoid copepods whereas the other species averaged <3% in all habitats. All copepods in all fish species ranged from 84.5 to 90% on average. For benthic and gut samples, Ivlev’s index of electivity indicates that harpacticoids are actively selected by all species except A. spinosa (P = 0.02, Sign test) whereas isopods are actively rejected by all species except A. spinosa (Table 1). The apparent preference of A. spinosa for isopods is misleading because the isopods consumed by that species are of planktonic origin and therefore not represented in the benthic samples used in this analysis. Ostracods are selected in all cases except the high spur and groove zone, and polychaetes and nematodes are selected against in all cases. For plankton and gut samples, Ivlev’s index of electivity indicates that A. spinosa does indeed select isopods whereas none of the other species do (P = 0.02, Sign test, Table 2). In addition, all the species have very few calanoids in their guts relative to their abundance in the water column but A. spinosa , while having fewer calanoids than the water column, has a considerably lesser reduction than the other species. A. spinosa fed primarily on plankton whereas the other three species fed primarily on benthos (Fig. 5). For all taxa, the gut-plankton overlap was 0.56 for A. spinosa and 0.09 for the other species combined (t = 14.2, df = 40, P < 0.0001). In contrast, the gut-benthos overlap was 0.29 for A. spinosa and 0.56 for the other species combined (t = 8.29, df = 40, P < 0.0001). There is a positive correlation of percent calanoids in the plankton tows and in the A. spinosa guts (Spearman rank correlation = 0.9, one-tailed P = 0.042, n = 5). Based on copepods, gut contents reflected an increasing planktonic proportion as samples were taken from greater distances from shore (Fig. 6). Fish from the pavement zone, which is on the backreef, had many fewer calanoids and cyclopoids relative to harpacticoids than fish taken from the forereef. A. spinosa guts were very different from the others with a planktonic to benthic copepod ratio of 3.5 as compared with 0.02 (range 0.006 to 0.03) for the other species on the forereef. The mean number of items in the guts at early, mid and late day were 156, 250 and 166 per five fish. The mean number of items varied with fish species, so the numbers were expressed as percents (with the highest value on a given day = 100%) to give equal weight to each species. Mean percents for early, mid and late day were 62, 95 and 66 (F = 10.3, df = 2,39, P = 0.0003, ANOVA). The reason for a significantly greater number of food items at midday is unclear. M ETABOLIC R ATES .—The data presented include four species of Acanthemblemaria and two species of Emblemariopsis . A seventh species, Acanthemblemaria maria , was represented by only two specimens and is omitted from the analysis. For each species, the O 2 consumption rate vs live weight showed a straight line relationship (Fig. 7, Table 3). The weight of the fishes varied by more than an order of magnitude (11 to 220 mg), yet the O 2 consumption rates fell into three groups based on comparisons of the slopes of O con- 2 sumption vs weight: (1) A. spinosa, E. pricei and E. ruetzleri had steep slopes (0.34 ...