Differences in feeding on algae and bacteria by temperate and ...
1200 V
1100
Ii
0
, 1000
T..
C,
tke
a, 900 E • 800
700
8 18 24 32 40 48 Days Feeding
Figure 2. Increase in total length and differentiation of 32-day-old bipinnaria larvae under different food regimes. Total length values represent means and standard deviations of two or three replicates per treatment, with 15-20 larvae measured per replicate. Sibling larvae were reared on diets consisting of either Dunaliella tertiolecta at 104 per milliliter (A), bacteria at 106 per milliliter (•), or no added particulate food (LI). All were in seawater filtered through a 0.2 micrometer pore-size membrane filter. (p.m denotes micrometer.)
Differences in feeding on algae and bacteria by temperate and antarctic sea star larvae J.S. PEARSE, I. BOSCH, V.B. PEARSE, and L.V. BASCH Institute of Marine Sciences University of California, Santa Cruz Santa Cruz, California 95064
Many abundant and widespread animals of shallow antarctic seas have pelagic, planktotrophic larvae (Pearse, McClintock, and Bosch 1991). Morphologically similar larvae in temperate seas presumably feed on phytoplankton (Strathmann 1987). Nearshore waters of the Antarctic, however, are extremely ohgotrophic during much of the year (Rivkin 1991), and few phytoplankton cells are available to feeding larvae most of the time. In particular, one of the most characteristic species in nearshore antarctic waters, the asteroid Odontaster validus, spawns in late winter, and the resulting planktotrophic larvae are present in early spring (Pearse and Bosch 1986; Bosch, Pearse, and Basch 1990), months before the summer bloom of phytoplankton. Preliminary experiments suggested that these and other feeding larvae of antarctic invertebrates can ingest bacteria, which in polar seas generally have higher and more equable densities 170
Bosch, I., J.S. Pearse, and L.V. Basch. 1990. Particulate food and growth of planktotrophic sea star larvae in McMurdo Sound, Antarctica. Antarctic Journal of the U.S., 25(5), 210-212. Colwell, S.J., and D.T. Manahan. 1988. A comparison of the transport rates by marine invertebrate larvae of monosaccharides and alanine from seawater. American Zoologist, 28, 131A. Manahan, D.T. 1991. Personal communication. Manahan, D.T., F.M. Shilling, J.R. Welborn, and S.J. Colwell. 1990. Dissolved organic material in seawater as a source of nutrition for invertebrate larvae from McMurdo Sound, Antarctica. Antarctic Journal of the U.S., 25(5), 206-208. Pearse, J.5., I. Bosch, VB. Pearse, and LV. Basch. 1991. Differences in feeding on algae and bacteria by temperate and antarctic sea star larvae. Antarctic Journal of the US, 26(5). Pechenik, J.A., and N. Fisher. 1979. Feeding, assimilation, and growth of mud snail larvae, Nassarius obsoletus, on three different algal diets. Journal of Experimental Marine Biology and Ecology, 38, 57-80. Rivkin, R.B., I. Bosch, J.S. Pearse, and E.J. Lessard. 1986. Bacterivory: A novel feeding mode for asteroid larvae. Science, 223, 1311-1314. Rivkin, R.B., M.R. Anderson, and D.E. Gustafson Jr. 1991. Ingestion of phytoplankton and bacterioplankton by polar and temperate echinoderm larvae. Antarctic Journal of the U.S., 26(5). Simon, M., and F. Azam. 1989. Protein content and protein synthesis rates of planktonic marine bacteria. Marine Ecology Progress Series, 51, 201-213.
1000 cr = 100 Cr ;i 10 w I— z
LU LU
0.1
0.01
1000 D00 ALGAL CELLS/ML Figure 1. Feeding rates of bipinnarias of Odontaster validus and Asterina miniata on algal cells (Dunaliella tertiolecta) at four concentrations. Data given as means ±1 standard deviation for four replicates (standard deviation was smaller than symbol for Asterma). Rates were estimated by feeding the larvae carbon-14-labeled algal cells and determining the amount of label in the larvae and the food. The larval label (plotted as "cell equivalents") represents food ingested and assimilated over the course of the feeding experiment (6 hours for 0. validus, 3 hours for A. miniata) as well as food in the gut at the end of the experiment. Our "cell equivalents" would equal total cells ingested only if assimilation efficiency was 100 percent and respiration was negligible; actual ingestion rates were about three times higher for A. miniata. (ML denotes milliliter. HR denotes hour.) ANTARCTIC JOURNAL
than phytoplankton, and which might provide an additional source of nutrition for larvae (Rivkin et al. 1986). We report here that the larvae of 0. validus can ingest and assimilate both algal and bacterial cells, while the morphologically similar larvae of Asterina miniata, an asteroid common along the temperate shores of western North America, can utilize algae but not bacteria. Feeding rates on laboratory-cultured algal cells were concentration-dependent for bipinnarias of both Odontaster validus and Asterina ininiata, ranging from about 20- to 100-fold greater for A. miniata than for 0. oalidus, depending on cell concentration (figure 1). Feeding rates on laboratory-cultured bacteria for bipinnarias of 0. validus were similarly concentration-dependent (figure 2). The middle concentration of bacteria used (lOS cells per milliliter) was roughly equivalent to ambient concentrations in McMurdo Sound at that season (November/December) (Rivkin 1991); parallel studies indicate that bipinnarias of 0. validus are able to ingest both phytoplankton and bacteria collected from the field as well (Rivkin, Anderson, and Gustafson, Antarctic Journal, this issue). There was no measurable feeding, however, by bipinnarias of A. miniata on bacteria at 106 cells per milliliter, the highest concentration examined for 0. oalidus, and a level comparable to ambient concentrations for these larvae at our temperate site (Monterey Bay, California). Autoradiographs revealed activity in the gut cells of bipinnarias of 0. validus fed bacteria labeled with tritiated thymidine, confirming digestion and assimilation of the ingested bacteria (figure 3). Similar patterns of activit y were seen in
fs
50 pm
'0
'•'
loop Figure 3. Autoradiograph (below) and photomicrograph (above) of nearly adjacent 0.8 micrometer-thick sections of a bipinnaria of Odontaster validus fed bacterial cells labeled with tritiated thymidine (see figure 2); note intense activity over gut cells, confirming digestion and assimilation. (S denotes stomach. gm denotes micrometer.)
I >
(I)
Iz LU —J
10
>
0 LU -j —J
LU
0
'I,, BACTERIAL CELLS/ML
Figure 2. Feeding rates of bipinnarias of Odontaster validus on bacterial cells at three concentrations. In parallel experiments with bipinnarias of Asterina miniata there was no demonstrable feeding on bacteria at 106 cells per milliliter. Data given as means ± 1 standard deviation for three replicates. Rates were estimated by feeding the larvae bacterial cells labeled with tritiated thymidine and determining the amount of label in the larvae and the food. The data are corrected for direct uptake of tritiated thymidine; uptake of label was reduced by adding unlabeled thymidine to the seawater. The larval label (plotted as "cell equivalents") represents food ingested and assimilated over the course of the feeding experiment (6 hours), as well as food in the gut at the end of the experiment. Our "cell equivalents" would equal total cells ingested only if assimilation efficiency was 100 percent and respiration was negligible. (ML denotes milliliter. HR denotes hour.) 1991 REVIEW
autoradiographs of bipinnarias of both 0. validus and A. ininiata fed carbon-14-labeled algal cells. There was negligible activity in the gut or other tissues of bipinnarias of A. ininiata fed bacteria labeled with tritiated thymidine, as in those of either species provided with equivalent amounts of dissolved tritiated thymidine in 0.2 micrometer-filtered seawater. These experiments complement our findings from the 19891990 season at McMurdo suggesting that larvae of 0. validus develop equally well in the laboratory when fed either algae, bacteria, or fractionated plankton (Bosch, Pearse, and Basch 1990). Those findings were largely confirmed and expanded upon with experiments done during the 1990-1991 season at McMurdo; the larvae do equally well whether fed bacteria or a range of concentrations of algae. In contrast, the morphologically near-identical larvae of A. miniata failed to develop when provided only bacteria, and their development and growth was very sensitive to both type and amounts of algae provided. There appear to be fundamental differences in the feeding capabilities of bipinnaria larvae of 0. validus and A. minicita. How the bacteria are captured and ingested by antarctic larvae—but not by temperate larvae—and whether they provide an important source of nutrition to antarctic larvae remain to be determined. 171
This research was supported by National Science Foundation grants DPP 88-20132 and 88-18354 to R.B. Rivkin and J.S. Pearse, respectively. We thank D.E. Gustafson, Jr., M.R. Anderson, R.B. Rivkin, and the staff of Antarctic Support Associates for assistance and logistic support at McMurdo, and G.W. Allison, A.J. Doif, S.D. Erickson, L.M. Gutierrez, and the staff of the Joseph M. Long Marine Laboratory for assistance and logistic support at Santa Cruz.
References Bosch, I., J.S. Pearse, and L.V. Basch. 1990. Particulate food and growth of planktotrophic sea star larvae in McMurdo Sound, Antarctica. Antarctic Journal of the U.S., 25(5), 210-212.
Density, energy content, and chemical activity of three conspicuous antarctic benthic marine invertebrates JAMES B. MCCLINTOCK and MARC SLATTERY Department of Biology University of Alabama at Birmingham Birmingham, Alabama 35294-1107
JOHN HEINE and JAMES WESTON Moss Landing Marine Laboratories Moss Landing, California 95039-3304
The shallow marine benthic community in Antarctica is thought to be structured primarily by physical factors such as ice scour and anchor ice at depths less than 15-30 meters (Dayton et al. 1969; Dayton et al. 1974; Pearse, McClintock, and Bosch 1991). At deeper depths, biological factors such as competition and predation are considered to be more important in regulating the distribution and abundance of benthic invertebrates (Dayton et al. 1974). The extent to which chemical bioactivity may mediate such processes as competition and predation within the antarctic benthic community has received little attention (McClintock et al. 1990). The present study documents the abundance (numbers and energetic density) and bioactivity of body tissues of three macroinvertebrates which collectively constitute a conspicuous component of the benthic fauna of McMurdo Sound, Antarctica. This work is a portion of a larger program investigating the chemical ecology of antarctic marine invertebrates. The long-term goals of this program are to examine the incidence of bioactivity in sessile and sluggish antarctic marine invertebrates, to isolate and identify bioactive chemicals, and to evaluate the role of bioactive compounds as feeding deterrents, antifouling agents, and/or compounds that inhibit overgrowth. 172
Pearse, J.S., and I. Bosch. 1986. Are the feeding larvae of the commonest antarctic asteroid really demersal? Bulletin of Marine Science, 39, 477-484. Pearse, J.S., J.B. McClintock, and I. Bosch. 1991. Reproduction of antarctic benthic marine invertebrates: Tempos, modes, and timing. American Zoologist, 31, 65-80. Rivkin, R.B. 1991. Seasonal patterns of planktonic production in McMurdo Sound, Antarctica. American Zoologist, 31, 5-16. Rivkin, RB., I. Bosch, J.S. Pearse, and E.J. Lessard. 1986. Bacterivory: A novel feeding mode for asteroid larvae. Science, 223, 1311-1314. Rivkin, RB., M.R. Anderson, and D.E. Gustafson, Jr. 1991. Ingestion of phytoplankton and bacterioplankton by polar and temperate echinoderm larvae. Antarctic Journal of the U.S., 26(5). Strathmann, R.R. 1987 Larval feeding. In A.C. Giese, J.S. Pearse, VB. Pearse (Eds.), Reproduction of marine invertebrates (Vol. 9). Pacific Grove, California: Blackwell/Boxwood Press.
Three common groups of marine invertebrates that are known to harbor bioactive compounds in temperate and tropical latitudes are the tunicates, soft corals and nernerteans (Faulkner 1984, 1986; Kern 1985). The solitary tunicate Cnemidocarpa verrucosa, the alcyonean soft coral Alcyonium paessleri, and the large nemertean worm Parborlasia corrugatus are polar representatives of these groups and are common in McMurdo Sound. To determine the relative abundance of each species, we placed a minimum of three 20-meter transect lines on the benthos using scuba at depths ranging from 15 to 30 meters (C. verrucosa was examined at Danger Slope; A. paessleri and P corrugatus were examined at Arrival Heights). We counted the numbers of individuals occurring within 1 meter of each transect, and we determined the mean sizes of individuals within the population by collecting a haphazard subsample of individuals and measuring their wet weight. To determine the energetic content of the tissues, subsamples of body components (C. verrucosa) or whole body tissues (A. paessleri and P corrugatus) were lyophilized, weighed, and ground into a fine powder. We conducted biochemical measurements following the protocol of Lawrence (1973). Energetic composition of tissues was measured indirectly using energy-conversion factors. The energy content of an intact individual was calculated by multiplying the energy content of the tissue (in kilojoules per gram of dry weight) by the total dry weight of the individual. Energy population density values were estimated for each species by multiplying the energy content of a mean-sized individual by the mean number of individuals per square meter. The energetic compositions and numerical and energetic densities are presented in table 1. In terms of kilojoules per gram of tissue dry weight, these values are generally higher than those reported by Dayton et al. (1974) for 19 species of antarctic sponges. When averaged over the entire study area, the mean population energetic density values were low compared to some species of large sponges. Nonetheless, all three species show clumped or aggregated distributions (Slattery et al. 1990; Heine et al. 1991; McClintock et al. 1991), resulting in higher population energy densities in some areas. Individual and population-level energy contents, lack of conspicuous morphological defenses, and sessile or sluggish nature make these species potentially attractive prey for predatory invertebrates or fish. ANTARCTIC JOURNAL
1100
Ii
0
, 1000
T..
C,
tke
a, 900 E • 800
700
8 18 24 32 40 48 Days Feeding
Figure 2. Increase in total length and differentiation of 32-day-old bipinnaria larvae under different food regimes. Total length values represent means and standard deviations of two or three replicates per treatment, with 15-20 larvae measured per replicate. Sibling larvae were reared on diets consisting of either Dunaliella tertiolecta at 104 per milliliter (A), bacteria at 106 per milliliter (•), or no added particulate food (LI). All were in seawater filtered through a 0.2 micrometer pore-size membrane filter. (p.m denotes micrometer.)
Differences in feeding on algae and bacteria by temperate and antarctic sea star larvae J.S. PEARSE, I. BOSCH, V.B. PEARSE, and L.V. BASCH Institute of Marine Sciences University of California, Santa Cruz Santa Cruz, California 95064
Many abundant and widespread animals of shallow antarctic seas have pelagic, planktotrophic larvae (Pearse, McClintock, and Bosch 1991). Morphologically similar larvae in temperate seas presumably feed on phytoplankton (Strathmann 1987). Nearshore waters of the Antarctic, however, are extremely ohgotrophic during much of the year (Rivkin 1991), and few phytoplankton cells are available to feeding larvae most of the time. In particular, one of the most characteristic species in nearshore antarctic waters, the asteroid Odontaster validus, spawns in late winter, and the resulting planktotrophic larvae are present in early spring (Pearse and Bosch 1986; Bosch, Pearse, and Basch 1990), months before the summer bloom of phytoplankton. Preliminary experiments suggested that these and other feeding larvae of antarctic invertebrates can ingest bacteria, which in polar seas generally have higher and more equable densities 170
Bosch, I., J.S. Pearse, and L.V. Basch. 1990. Particulate food and growth of planktotrophic sea star larvae in McMurdo Sound, Antarctica. Antarctic Journal of the U.S., 25(5), 210-212. Colwell, S.J., and D.T. Manahan. 1988. A comparison of the transport rates by marine invertebrate larvae of monosaccharides and alanine from seawater. American Zoologist, 28, 131A. Manahan, D.T. 1991. Personal communication. Manahan, D.T., F.M. Shilling, J.R. Welborn, and S.J. Colwell. 1990. Dissolved organic material in seawater as a source of nutrition for invertebrate larvae from McMurdo Sound, Antarctica. Antarctic Journal of the U.S., 25(5), 206-208. Pearse, J.5., I. Bosch, VB. Pearse, and LV. Basch. 1991. Differences in feeding on algae and bacteria by temperate and antarctic sea star larvae. Antarctic Journal of the US, 26(5). Pechenik, J.A., and N. Fisher. 1979. Feeding, assimilation, and growth of mud snail larvae, Nassarius obsoletus, on three different algal diets. Journal of Experimental Marine Biology and Ecology, 38, 57-80. Rivkin, R.B., I. Bosch, J.S. Pearse, and E.J. Lessard. 1986. Bacterivory: A novel feeding mode for asteroid larvae. Science, 223, 1311-1314. Rivkin, R.B., M.R. Anderson, and D.E. Gustafson Jr. 1991. Ingestion of phytoplankton and bacterioplankton by polar and temperate echinoderm larvae. Antarctic Journal of the U.S., 26(5). Simon, M., and F. Azam. 1989. Protein content and protein synthesis rates of planktonic marine bacteria. Marine Ecology Progress Series, 51, 201-213.
1000 cr = 100 Cr ;i 10 w I— z
LU LU
0.1
0.01
1000 D00 ALGAL CELLS/ML Figure 1. Feeding rates of bipinnarias of Odontaster validus and Asterina miniata on algal cells (Dunaliella tertiolecta) at four concentrations. Data given as means ±1 standard deviation for four replicates (standard deviation was smaller than symbol for Asterma). Rates were estimated by feeding the larvae carbon-14-labeled algal cells and determining the amount of label in the larvae and the food. The larval label (plotted as "cell equivalents") represents food ingested and assimilated over the course of the feeding experiment (6 hours for 0. validus, 3 hours for A. miniata) as well as food in the gut at the end of the experiment. Our "cell equivalents" would equal total cells ingested only if assimilation efficiency was 100 percent and respiration was negligible; actual ingestion rates were about three times higher for A. miniata. (ML denotes milliliter. HR denotes hour.) ANTARCTIC JOURNAL
than phytoplankton, and which might provide an additional source of nutrition for larvae (Rivkin et al. 1986). We report here that the larvae of 0. validus can ingest and assimilate both algal and bacterial cells, while the morphologically similar larvae of Asterina miniata, an asteroid common along the temperate shores of western North America, can utilize algae but not bacteria. Feeding rates on laboratory-cultured algal cells were concentration-dependent for bipinnarias of both Odontaster validus and Asterina ininiata, ranging from about 20- to 100-fold greater for A. miniata than for 0. oalidus, depending on cell concentration (figure 1). Feeding rates on laboratory-cultured bacteria for bipinnarias of 0. validus were similarly concentration-dependent (figure 2). The middle concentration of bacteria used (lOS cells per milliliter) was roughly equivalent to ambient concentrations in McMurdo Sound at that season (November/December) (Rivkin 1991); parallel studies indicate that bipinnarias of 0. validus are able to ingest both phytoplankton and bacteria collected from the field as well (Rivkin, Anderson, and Gustafson, Antarctic Journal, this issue). There was no measurable feeding, however, by bipinnarias of A. miniata on bacteria at 106 cells per milliliter, the highest concentration examined for 0. oalidus, and a level comparable to ambient concentrations for these larvae at our temperate site (Monterey Bay, California). Autoradiographs revealed activity in the gut cells of bipinnarias of 0. validus fed bacteria labeled with tritiated thymidine, confirming digestion and assimilation of the ingested bacteria (figure 3). Similar patterns of activit y were seen in
fs
50 pm
'0
'•'
loop Figure 3. Autoradiograph (below) and photomicrograph (above) of nearly adjacent 0.8 micrometer-thick sections of a bipinnaria of Odontaster validus fed bacterial cells labeled with tritiated thymidine (see figure 2); note intense activity over gut cells, confirming digestion and assimilation. (S denotes stomach. gm denotes micrometer.)
I >
(I)
Iz LU —J
10
>
0 LU -j —J
LU
0
'I,, BACTERIAL CELLS/ML
Figure 2. Feeding rates of bipinnarias of Odontaster validus on bacterial cells at three concentrations. In parallel experiments with bipinnarias of Asterina miniata there was no demonstrable feeding on bacteria at 106 cells per milliliter. Data given as means ± 1 standard deviation for three replicates. Rates were estimated by feeding the larvae bacterial cells labeled with tritiated thymidine and determining the amount of label in the larvae and the food. The data are corrected for direct uptake of tritiated thymidine; uptake of label was reduced by adding unlabeled thymidine to the seawater. The larval label (plotted as "cell equivalents") represents food ingested and assimilated over the course of the feeding experiment (6 hours), as well as food in the gut at the end of the experiment. Our "cell equivalents" would equal total cells ingested only if assimilation efficiency was 100 percent and respiration was negligible. (ML denotes milliliter. HR denotes hour.) 1991 REVIEW
autoradiographs of bipinnarias of both 0. validus and A. ininiata fed carbon-14-labeled algal cells. There was negligible activity in the gut or other tissues of bipinnarias of A. ininiata fed bacteria labeled with tritiated thymidine, as in those of either species provided with equivalent amounts of dissolved tritiated thymidine in 0.2 micrometer-filtered seawater. These experiments complement our findings from the 19891990 season at McMurdo suggesting that larvae of 0. validus develop equally well in the laboratory when fed either algae, bacteria, or fractionated plankton (Bosch, Pearse, and Basch 1990). Those findings were largely confirmed and expanded upon with experiments done during the 1990-1991 season at McMurdo; the larvae do equally well whether fed bacteria or a range of concentrations of algae. In contrast, the morphologically near-identical larvae of A. miniata failed to develop when provided only bacteria, and their development and growth was very sensitive to both type and amounts of algae provided. There appear to be fundamental differences in the feeding capabilities of bipinnaria larvae of 0. validus and A. minicita. How the bacteria are captured and ingested by antarctic larvae—but not by temperate larvae—and whether they provide an important source of nutrition to antarctic larvae remain to be determined. 171
This research was supported by National Science Foundation grants DPP 88-20132 and 88-18354 to R.B. Rivkin and J.S. Pearse, respectively. We thank D.E. Gustafson, Jr., M.R. Anderson, R.B. Rivkin, and the staff of Antarctic Support Associates for assistance and logistic support at McMurdo, and G.W. Allison, A.J. Doif, S.D. Erickson, L.M. Gutierrez, and the staff of the Joseph M. Long Marine Laboratory for assistance and logistic support at Santa Cruz.
References Bosch, I., J.S. Pearse, and L.V. Basch. 1990. Particulate food and growth of planktotrophic sea star larvae in McMurdo Sound, Antarctica. Antarctic Journal of the U.S., 25(5), 210-212.
Density, energy content, and chemical activity of three conspicuous antarctic benthic marine invertebrates JAMES B. MCCLINTOCK and MARC SLATTERY Department of Biology University of Alabama at Birmingham Birmingham, Alabama 35294-1107
JOHN HEINE and JAMES WESTON Moss Landing Marine Laboratories Moss Landing, California 95039-3304
The shallow marine benthic community in Antarctica is thought to be structured primarily by physical factors such as ice scour and anchor ice at depths less than 15-30 meters (Dayton et al. 1969; Dayton et al. 1974; Pearse, McClintock, and Bosch 1991). At deeper depths, biological factors such as competition and predation are considered to be more important in regulating the distribution and abundance of benthic invertebrates (Dayton et al. 1974). The extent to which chemical bioactivity may mediate such processes as competition and predation within the antarctic benthic community has received little attention (McClintock et al. 1990). The present study documents the abundance (numbers and energetic density) and bioactivity of body tissues of three macroinvertebrates which collectively constitute a conspicuous component of the benthic fauna of McMurdo Sound, Antarctica. This work is a portion of a larger program investigating the chemical ecology of antarctic marine invertebrates. The long-term goals of this program are to examine the incidence of bioactivity in sessile and sluggish antarctic marine invertebrates, to isolate and identify bioactive chemicals, and to evaluate the role of bioactive compounds as feeding deterrents, antifouling agents, and/or compounds that inhibit overgrowth. 172
Pearse, J.S., and I. Bosch. 1986. Are the feeding larvae of the commonest antarctic asteroid really demersal? Bulletin of Marine Science, 39, 477-484. Pearse, J.S., J.B. McClintock, and I. Bosch. 1991. Reproduction of antarctic benthic marine invertebrates: Tempos, modes, and timing. American Zoologist, 31, 65-80. Rivkin, R.B. 1991. Seasonal patterns of planktonic production in McMurdo Sound, Antarctica. American Zoologist, 31, 5-16. Rivkin, RB., I. Bosch, J.S. Pearse, and E.J. Lessard. 1986. Bacterivory: A novel feeding mode for asteroid larvae. Science, 223, 1311-1314. Rivkin, RB., M.R. Anderson, and D.E. Gustafson, Jr. 1991. Ingestion of phytoplankton and bacterioplankton by polar and temperate echinoderm larvae. Antarctic Journal of the U.S., 26(5). Strathmann, R.R. 1987 Larval feeding. In A.C. Giese, J.S. Pearse, VB. Pearse (Eds.), Reproduction of marine invertebrates (Vol. 9). Pacific Grove, California: Blackwell/Boxwood Press.
Three common groups of marine invertebrates that are known to harbor bioactive compounds in temperate and tropical latitudes are the tunicates, soft corals and nernerteans (Faulkner 1984, 1986; Kern 1985). The solitary tunicate Cnemidocarpa verrucosa, the alcyonean soft coral Alcyonium paessleri, and the large nemertean worm Parborlasia corrugatus are polar representatives of these groups and are common in McMurdo Sound. To determine the relative abundance of each species, we placed a minimum of three 20-meter transect lines on the benthos using scuba at depths ranging from 15 to 30 meters (C. verrucosa was examined at Danger Slope; A. paessleri and P corrugatus were examined at Arrival Heights). We counted the numbers of individuals occurring within 1 meter of each transect, and we determined the mean sizes of individuals within the population by collecting a haphazard subsample of individuals and measuring their wet weight. To determine the energetic content of the tissues, subsamples of body components (C. verrucosa) or whole body tissues (A. paessleri and P corrugatus) were lyophilized, weighed, and ground into a fine powder. We conducted biochemical measurements following the protocol of Lawrence (1973). Energetic composition of tissues was measured indirectly using energy-conversion factors. The energy content of an intact individual was calculated by multiplying the energy content of the tissue (in kilojoules per gram of dry weight) by the total dry weight of the individual. Energy population density values were estimated for each species by multiplying the energy content of a mean-sized individual by the mean number of individuals per square meter. The energetic compositions and numerical and energetic densities are presented in table 1. In terms of kilojoules per gram of tissue dry weight, these values are generally higher than those reported by Dayton et al. (1974) for 19 species of antarctic sponges. When averaged over the entire study area, the mean population energetic density values were low compared to some species of large sponges. Nonetheless, all three species show clumped or aggregated distributions (Slattery et al. 1990; Heine et al. 1991; McClintock et al. 1991), resulting in higher population energy densities in some areas. Individual and population-level energy contents, lack of conspicuous morphological defenses, and sessile or sluggish nature make these species potentially attractive prey for predatory invertebrates or fish. ANTARCTIC JOURNAL
