Lipid biogeochemistry of plankton, settling matter and sediments in Trinity Bay, Newfoundland. I. Lipid classes

PII:

Org. Geochem. Vol. 29, No. 5±7, pp. 1531±1545, 1998 # 1998 Elsevier Science Ltd. All rights reserved Printed in Great Britain S0146-6380(98)00176-4 0146-6380/98 $ - see front matter

Lipid biogeochemistry of plankton, settling matter and sediments in Trinity Bay, Newfoundland. I. Lipid classes CHRISTOPHER C. PARRISH* Ocean Sciences Centre and Department of Chemistry, Memorial University of Newfoundland, St. John's, NF, Canada A1C 5S7 AbstractÐSeawater, settling particles and sediments were sampled in Trinity Bay, a fjord-like bay on the east coast of Newfoundland, to determine the nature and rates of lipid inputs. At the height of the spring bloom, diatom triacylglycerol storage increased in response to lowered nitrate and silicate concentrations. This was followed by increased concentrations of phospholipids which coincided with biomass increases in dino¯agellates and zooplankton. Sediment trap results from 50±100 m show that planktonic lipids appear to be transferred with little alteration through the water column to benthic and demersal food webs. Fluxes are high, especially in spring, and incorporation into the food web seems to be very ecient with little loss through burial in the sediments. Much higher lipid concentrations are seen in sediments closer to shore where terrestrial plants are likely to be an important contributor to the lipids. The sediment trap results also show that the use of poisons can cause an overestimation of ¯uxes of some acyl lipid classes, while leaching during deployment may cause an underestimation of ¯uxes of most lipid classes. # 1998 Elsevier Science Ltd. All rights reserved Key wordsÐlipids, phytoplankton, zooplankton, particulate matter, sediments, cold coastal northwest Atlantic

INTRODUCTION

In most fjord-like systems, the spring phytoplankton bloom is the largest annual event in terms of carbon dynamics (Wassmann, 1991). Spring blooms occur because of the uncoupling of primary production and grazing by zooplankton and they have major e€ects on food webs and the export of carbon from the photic zone (Legendre, 1990). During the bloom period, large quantities of intact diatom cells may settle out (Davies and Payne, 1984). The rapid sedimentation of such ungrazed material (Smetacek, 1985) provides a pulse of easily metabolizable organic carbon that may be largely assimilated by benthic macrofauna (Fitzgerald and Gardner, 1993). The remaining material undergoes various bacterial, chemical and physical diagenetic transformations before and during burial in the sediments (Henrichs, 1992). Lipids are an important carbon-rich product of the spring bloom that are relatively easily metabolizable. These compounds have a very high energy value and are thus important fuels in marine ecosystems (Lee et al., 1971). Certain components of lipids such as polyunsaturated fatty acids are also essential nutrients for animal survival and growth (Takeuchi, 1997). The study of lipid biogeochemistry in the cold waters o€ the east coast of *To whom correspondence should be addressed. Tel.: +1709-737-3225; Fax: +1-709-737-3220; E-mail: [email protected]

Newfoundland is timely given current problems with ground®sh stocks (Gomes et al., 1995; Hutchings and Myers, 1994) and the increasing interest in aquaculture in this area. A study of lipid biogeochemistry to the west of Newfoundland, at the same latitude but far into the heart of the continent, revealed a variety of water column inputs from vascular plants, pollution and marine plankton (Colombo et al., 1996a). Little of the marine material survived early diagenesis down to 35 cm depth in the sediments with most losses occurring between 150 m in the water column and 0±3 cm in the sediments (Colombo et al., 1997). In this study, cruises were undertaken in Trinity Bay, Newfoundland, to sample seawater, sedimenting material and sediments in order to determine the sources and rates of current and historical lipid inputs to Trinity Bay. Trinity Bay is a large fjordlike bay which historically had an abundance of spawning cod in both its inner and outer reaches during the months of May and June (Hutchings et al., 1993). The seasonal nature of primary production in this area with its mid-latitude light regime, in combination with the area's subpolar oceanographic climate zone makes it particularly interesting for studying marine lipids. The seasonality of the food supply can lead to high levels of lipid storage in marine fauna, and low temperatures may necessitate increased unsaturation in phospholipid fatty acids (Clarke, 1983). We have found high levels of polyunsaturation in membrane and storage

1531

1532

C. C. Parrish

lipids in benthic organisms living in Newfoundland waters (Parrish et al., 1996). Polyunsaturated fatty acids are essential fatty acids required for normal membrane structure and function, especially at low temperatures (Hazel et al., 1991). The cold ocean temperatures also mean that during the spring bloom in this area, zooplankton and bacterial activity are low (Pomeroy et al., 1991), thus facilitating the delineation of the production and transfer of algal lipids in this ecosystem. METHODS

Sampling area Trinity Bay is one of several large fjord-like bays on the Atlantic coast of Newfoundland (Fig. 1). It is about 100 km long and 30 km wide, with a maximum depth of about 590 m and a sill depth of 240 m. Very little is known about the sedimentology of Trinity Bay. However, a study of the sedimentary history of nearby Bonavista Bay (Fig. 1) has been performed (Cumming et al., 1992). Bonavista Bay is blanketed by a veneer of unconsolidated sediments and postglacial sediments are thickest in the deep basins. Similarly, not much is known about the circulation and hydrography of Trinity Bay. The one published study of the physical oceanography of Trinity Bay (Yao, 1986) looked at the responses of currents to wind forcing during the summer. The direction of the mean current was found to be incoming on

the northwest side and outgoing on the southeast side. The wind direction was generally along the axis of the bay and when it blew out of the bay, there was upwelling on the northwest side of the bay and downwelling on the southeast side. The circulation and hydrography of nearby Conception Bay (Fig. 1) has, however, been better studied (deYoung and Sanderson, 1995). In Conception Bay the seasonal cycles of temperature (ÿ1.6 to 13± 178C) and salinity (31±32.5 psu) were found to closely follow those on the adjacent shelf where icemelt has an important in¯uence on salinity. Tidal currents were found to be weak as was the general circulation and vertical mixing. Seawater sampling Stations (Table 1) were located along a transect from the center of Trinity Bay to the Southwest Arm (St-7±St-12), just o€ the town of Clarenville (H-9), and in a transect (T-1±T-4) leading towards the town of Trinity (Fig. 1). CTD casts and seawater sampling were conducted at nearly all stations. A Seabird CTD with a SeaTech ¯uorometer was used, and water samples were collected with Niskin or GO-Flo bottles. All stations visited were coastal marine with surface water salinities ranging from 31.6±32.3 psu. Plankton samples During the spring blooms of 1995 and 1996, thirty-nine horizontal and vertical net-tow samples

Fig. 1. Station locations on the southeast coast of the island of Newfoundland.

Lipid class biogeochemistry of Trinity Bay

1533

Table 1. Station locations, depths, and samples taken over the period June 1994±May 1997 Dates sampled Depth (m)

Net-tows (0±100 m)

Nutrients (15±100 m)

Sediment traps (50±100 m)

Sediment sample type (49±363 m)

Trinity Bay ± Southwest Arm St-7 48 08.2 53 22.0

363

48 05.7

53 31.7

224

St-10 St-11

48 04.6 48 03.8

53 35.0 53 37.8

260 314

Jun±Jul 94, Jul 94±Apr 95, May 97 Jun±Jul 94, Jul±Oct 94, Apr 95, May 97 ± ±

core core

St-12

48 02.1

53 42.2

260

Apr±May 95, Mar±Jun 96 Apr±May 95, Mar±Jun 96 ± May 95, Mar±Jun 96 ±

core

St-9

Apr±May 95, Mar±June 96 Apr±May 95, Mar±June 95 ± May 95, Mar±Jun 96 ±

±

core

Hickman's Harbour ± Clarenville H-1 48 05.0 53 43.8 H-2 48 05.6 53 44.3 H-3 48 05.2 53 44.4 H-4 48 04.8 53 45.3 H-6 48 05.1 53 50.3 H-7 48 05.4 53 53.3 H-8 48 07.6 53 54.9 H-9 48 09.8 53 57.0

67 49 66 83 56 53 57 59

± ± ± ± ± ± ± Mar±Apr 96

± ± ± ± ± ± ± Mar±Apr 96

± ± ± ± ± ± ± ±

core grab grab core grab core core core

Trinity Bay ± Trinity transect T-1 48 18.9 53 17.6 T-2 48 19.9 53 18.5 T-3 48 21.2 53 19.9 T-4 48 22.7 53 21.4

143 116 36 30

± ± ± ±

± ± ± ±

Station

Latitude (8N)

Longitude (8W)

Apr Apr Apr Apr

95 95 95 95

(20 mm mesh) were taken. These samples were taken during the months of March to June from stations St-7, St-9, St-11, H-9 and T-1±T-4 (Table 1). Horizontal tows were conducted at 2 knots for 10 min at the chlorophyll maximum determined from the CTD cast. Vertical tows were from 100 m to the surface. Plankton in the cod end were poured into pre-washed plastic bottles and kept on ice. In the laboratory, subsamples were taken for lipid and weight determination and for preservation with 1 ml Lugol's iodine followed by 1 ml 10% bu€ered formaldehyde. Samples for lipid and weight determination were ®ltered onto pre-combusted glass®bre ®lters (Whatman GF/C) and those used for dry weight and ash free dry weight determinations were then washed with 5 ml of 3% ammonium formate to remove the salt. These pre-weighed ®lters were then dried at 708C for 16±18 h and reweighed. They were then combusted at 4508C for 16±20 h and weighed again. Filters for lipid determinations were placed directly in chloroform and stored under nitrogen at <ÿ208C until extraction. Floristic analyses were performed on 200 ml of the preserved samples which were observed under 200  magni®cation with an inverted Zeiss compound microscope. Biovolumes were calculated using an ocular micrometer and appropriate geometric shapes. The net-tows collected mainly phytoplankton, but zooplankton, especially copepod nauplii were often present as well. Samples of settling matter Taut-wire sediment trap moorings were deployed in Trinity Bay at a nearshore station (St-9) in 224 m

Apr Apr Apr Apr

95 95 95 95

core

of water and at an o€shore station (St-7) in 363 m of water. Trap frames were set at 50, 75, and 100 m below surface, with four 10 cm diameter, 60 cm high PVC collectors per depth. They were deployed continuously from 21/6/94 to 20/4/95, and then again from 26/5/97 to 29/5/97. Traps were recovered and redeployed so that twenty-one samples were obtained representing collection periods approximating to summer 1994, summer/fall 1994, fall 1994/winter 1995, early spring 1995, and late spring 1997. One liter of 40 ppt NaCl solution was poured into the bottom of each trap before deployment, and the remainder of the trap was then gently ®lled with seawater. In April 1995 and May 1997, 5±6 g of HgCl2 was added to the salt solution that was poured into one of the collectors at each depth. On recovery the traps were covered as soon as they were on board, and the particles in the sediment tubes were allowed to settle for at least 30 min before draining o€ most of the water in the tubes through a 20 mm screen. The remaining water containing the settled particles was then collected in pre-washed plastic bottles and stored on ice. Any material caught on the screen was washed back into the sample containers. In the laboratory, samples were carefully decanted and then resuspended in a known volume of 1 mm-®ltered seawater. Subsamples were then taken for particulate lipid determination, weight determination and preservation as in the case of the plankton samples. Any swimmers caught on the Whatman GF/C ®lters were carefully removed with forceps. In May 1997, in addition to sampling the particulate matter, the ®ltrate

1534

C. C. Parrish

was also sampled for dissolved lipids in two of the collectors on each frame. Sediment samples Core and grab samples were collected at stations St-7±St-12, and in a cruise track (Fig. 1) from the mouth of Hickman's Harbour (H-1) along the Northwest Arm to just o€ the town of Clarenville (H-9): stations H-1±H-4, and stations H-6±H-9 (Table 1). Samples were taken with a 30 cm boxcorer, immediately put on ice and then frozen on returning to land (Pulchan et al., 1997). Prior to extraction, samples were dried in the dark at 308C and then homogenized with a mortar and pestle (Favaro et al., 1996). Lipids were extracted in dichloromethane±methanol (9:1) in a Soxhlet extractor for 24 h. For most of the cores, samples from only the top two cm were extracted; however, for cores from stations St-7, H-1 and H-9, samples were taken from the entire 30 cm core, so that there were eight samples per core. In all, the lipids in thirty-®ve core and grab samples were extracted. Subsamples from the cores taken at St-7, H-1 and H-9 were dated using 210 Pb (Schell, 1982). Lipid class analyses Filters from net-tow and sediment trap samples were extracted in chloroform±methanol using a modi®ed Folch procedure (Parrish, 1998). The May sediment trap ®ltrates were placed in 1 l separatory funnels and extracted with 20 ml of chloroform. The pH was adjusted to pH 2 and the water was extracted again with 2  10 ml of chloroform. All extracts were combined and concentrated under nitrogen. Lipid classes in the extracts from the nettow samples, the particulate and dissolved sediment trap samples, and the core and grab samples were separated by thin layer chromatography on Chromarods-SIII (Parrish, 1987a). The lipid class bands were quanti®ed by passing the rods through the ¯ame ionization detector of an Iatroscan MK V. Inorganic nutrient analyses Between June 1994 and June 1996, 101 samples were collected for silica, orthophosphate and nitrate + nitrite determinations. Samples were collected between 15 and 100 m at stations St-7±St-11, H-9, and four stations in a transect leading into Trinity Harbour. They were ®ltered through a 0.45 mm cellulose acetate ®lter and measured in an EnviroFlow 3500 nutrient analyzer (Perstorp Analytical, Wilsonville, OR). Of the samples collected, 38 had nitrite determined independently. The average coef®cient of variation for three determinations of each of the major nutrients was 3.4±3.6%. The average coecient of variation for three determinations of nitrite concentrations was 6.1%. The higher variability here re¯ects the much lower concentrations

observed for nitrite in comparison with the other nutrients. Nitrite concentrations were approximately 1% of the average nitrate + nitrite concentrations. RESULTS AND DISCUSSION

Plankton During the spring blooms of 1995±1997, the maximum in situ ¯uorescence was observed in May, with the o€shore station (St-7) showing higher values than those nearer to shore. Floristic analyses of a net-tow sample from the o€shore station in May 1996 revealed that the centric diatom, Chaetoceros sp., was the major contributor to the algal biomass. This particular tow was taken after we recorded a maximum in situ ¯uorescence equivalent to about 11.5 mg mÿ3 of chlorophyll a, which was the highest value we determined in three years of CTD casts in Trinity Bay. Figure 2 shows the average nutrient and lipid concentrations from St-7 to St-11 during the 1996 spring bloom. The data from the three stations were similar during that period: there were very few statistically signi®cant concentration gradients in the transect. Where this did occur, the concentrations increased from St-7 to St-11. Orthophosphate concentrations at 15 m increased, on average, by 64% in going from St-7 to St-11 over the four months. This coincided with a consistent but small decrease in salinity of 0.2±0.3 psu. One of the major rivers in the area, which drains into Hickman's Harbour on Random Island, had silica, orthophosphate and nitrate + nitrite concentrations of 6.3, 0.46, and 3.3 mM respectively. The 15 m water temperature at station 7 was ÿ0.58C at the beginning of the sampling period in 1996 and the ¯uorescence maximum was at 25 m. By the end of the sampling period the 15 m temperature had risen to 6.88C and the ¯uorescence maximum was below the thermocline at 57 m. During this time, the average nitrate + nitrite and silicate concentrations at 15 and 50 m had dropped continuously (Fig. 2). The mean nitrate + nitrite concentrations at 15 m showed the largest observed di€erence during the 1996 bloom, where June concentrations were only 6% of the March concentrations. From April to June, total lipid concentrations increased and there was a peak in triacylglycerol proportions in May (Fig. 2). In June, phospholipids became a much more important component of the continually increasing lipid concentrations. This results in a sequence of increasing triacylglycerol concentrations followed by increasing phospholipid concentrations after the bloom, and it represents a switch in the nature of plankton lipids from those associated with storage to those associated with membranes. Increases in phospholipid concentrations have also been observed in suspended par-

Lipid class biogeochemistry of Trinity Bay

1535

Fig. 2. Nutrient concentrations in bottle samples, and lipid concentration and lipid class composition of net-tow samples during the 1996 spring bloom in Trinity Bay. Horizontal tows were conducted at the chlorophyll maximum and vertical tows were from 100 m to the surface. TG: triacylglycerol; PL: phospholipid. The data represent the mean2S.D. of three stations (St-7, St-9, St-11) in a transect from the center of the bay.

ticulate matter after blooms in Bedford Basin, Nova Scotia (Parrish, 1987b). Between May and June, the concentration of phospholipids in Trinity Bay increased eight to twelve-fold. This indicates an increase in numbers of planktonic species other than diatoms at this time, as diatom membrane synthesis is likely to be attenuated at the low nutrient concentrations prevalent at the end of the bloom (Parrish and Wangersky, 1987). Floristic analyses and fatty acid data strongly suggest that dino¯agellates may be the major contributors to the increase (Budge and Parrish, 1998). Planktonic fauna may also be involved, but for them to be a major contributor would require a recycling of phosphorus and nitrogen from other constituents of the diet to animal phospholipids at this time. Floristic analyses

indicated that while zooplankton had become a signi®cant component of the biomass at this time, the dino¯agellate Ceratium sp. was by far the major contributor to the biomass in June. Overall, thirty-nine 20 mm mesh net-tow samples were taken during the spring blooms of 1995 and 1996. The value for these samples of 4 23% for total lipid as a proportion of dry weight (Table 2) encompasses the range of 1.8±6.9% given by Parsons et al. (1961) for diatoms. In comparison with the sediment trap material, the net-tow samples were characterized by having higher organic contents and total lipid contents as a proportion of total particulate material (Table 2). However, total lipid as a proportion of particulate organic matter, the proportions of neutral and

1536

C. C. Parrish

Table 2. Composition of net-tow, sediment trap and core/grab samples from Trinity Bay, NF, 1994±1997. All proportions are in percent; data are mean 2S.D., n = 15±39. Net-tow samples were taken from stations St-7, St-9, St-11, H-9 and T-1±T-4 during the months of March to June; n = 31±39. Sediment trap samples were collected year-round at stations St-7 and St-9; n = 18±21. Core and grab samples were collected at stations St-7±St-12, stations H1±H-4, and stations H-6±H-9; n = 30±35 Net-tows POM/TPM TL/TPM TL/POM Neutral lipids/TL Polar lipids/TL LI HI

57.3* 2 13.5 3.8*2 3.2 4.2*2 3.6 66.0* 2 12.9 34.0* 2 12.9 15.3* 2 10.6 24.2* 2 14.8

Sediment traps Cores and grabs 45.8$ 2 15.8 1.6$ 2 1.4 4.4*2 5.4 61.7* 2 12.9 38.3* 2 12.9 15.6* 24.1 29.7* 28.2

15.6% 27.9 0.1% 20.1 0.7$ 20.4 30.5$ 213.9 69.5$ 213.9 7.6$ 25.2 53.2$ 223.1

POM: particulate organic matter (ash free dry weight); TPM: Total particulate matter (dry weight); TL: total lipid (sum of Iatroscan determined lipid classes); Neutral lipids: hydrocarbons, wax and steryl esters, ketones, triacylglycerols, free fatty acids (FFA), alcohols (ALC), sterols, diacylglycerols; Polar lipids: monoacylglycerols, acetone-mobile polar lipids, phospholipids; LI: lipolysis index (FFA + ALC/acyl lipids + ALC); HI: hydrolysis index (FFA + ALC/neutral acyl lipids + ALC). *$%Means with di€erent symbols are signi®cantly di€erent (P < 0.05) from one another (ANOVA, Tukey test).

polar lipids, and the breakdown indicators were not signi®cantly di€erent in the two types of samples over the sampling period. The lipolysis index (LI: Parrish et al., 1995) shows lipid breakdown as a proportion of total acyl lipids while the hydrolysis index (HI: Weeks et al., 1993) shows breakdown as a proportion of neutral acyl lipids. The similarity in these indices and the lipid proportions in the two sample types suggests planktonic lipids were transferred with little alteration through the water column to the sediment traps. This is supported, in part, by the lack of signi®cant di€erences in proportions of half of the individual lipid classes measured (Table 3). This in turn suggests that di€erences in organic matter and lipids on a dry weight basis (Table 2) result from higher proportions of inorganic material in the sediment trap samples.

While the overall picture for lipids suggests strong similarities between net-tow and sediment trap material, some of the details are di€erent. Half the lipid class proportions were signi®cantly di€erent (Table 3) even though proportions of total neutral and polar lipids remained similar in the net-tow and sediment trap samples (Table 2). Those classes that were di€erent changed by a factor of about two. This represents some shifting in the proportions of the classes that make up the neutral and polar lipids, due either to transformations in planktonic material entering the traps or to the arrival of material not caught by a 20 mm mesh net-tow. As suggested by Fig. 2, Table 4 con®rms that there was a strong temporal variability in the lipid content and composition of plankton during the spring blooms in 1995 and 1996. Total lipid increased by a factor of two in May and June by comparison with March and April (Table 4). This increase coincides with a doubling in the proportions of all acyl lipid classes except wax and steryl esters and phospholipids, and with a signi®cant increase in sterol composition (Table 5). The overall increase in triacylglycerol content again con®rms the May 1996 peak in triacylglycerols in the Trinity Bay transect (Fig. 2) as being a general late bloom phenomenon in the Trinity Bay area. This increase is probably related to inorganic nutrients. The average nutrient concentrations in the top 50 m of the water column for both years were signi®cantly di€erent in early and late spring with silica and nitrate + nitrite concentrations showing the greatest decrease. Diatoms have been shown to increase triacylglycerol synthesis when the supply of nitrate or silicate is low (Parrish and Wangersky, 1987, 1990; Roessler, 1990). The increase in breakdown indices as the blooms progressed (Table 4) can be attributed to an

Table 3. Lipid class composition of net-tow (n = 39), sediment trap (n = 21) and core/grab (n = 35) samples from Trinity Bay, NF, 1994±1997. All proportions are in percent; data are mean 2 S.D., n = 21±39

Hydrocarbons Wax/steryl esters Methyl esters Ketones Triacylglycerols Free fatty acids Alcohols} Pink pigment} Sterols Diacylglycerols Acetone-mobile polar lipids Phospholipids

Net-tows

Sediment traps

Cores and grabs

2.5* 23.2 30.6* 217.3 1.1 2 1.9 0.0* 20.0 11.5* 28.0 12.3* 29.6 2.0* 22.4 0.0* 20.0 2.8* 21.7 3.3 2 2.6 9.3* 26.3 24.6* 214.9

5.1$ 25.6 22.0* 211.7 1.5 2 1.7 0.0*20.1 9.0*25.0 8.9*23.1 4.5$ 21.6 0.6$ 21.0 7.3$ 22.4 2.7 2 1.7 24.5$ 28.5 14.0$ 28.1

7.3$ 2 6.8 2.3$ 2 2.0 1.0 21.6 2.1$ 2 2.1 4.6$ 2 2.8 1.4$ 2 1.3 4.4$ 2 2.1 0.0*2 0.0 4.3% 2 2.4 3.2 22.4 46.7% 2 8.7 22.8* 2 8.2

All data were tested for normality and equal variance. Where these tests failed, either a Dunn's test or a Mann±Whitney Rank Sum test was performed. *$%Means with di€erent symbols are signi®cantly di€erent (P < 0.05) from one another (ANOVA, Tukey test). }ALC consisted usually of two or more peaks in core samples. }HPLC revealed this to be a peridinin-like pigment.

Lipid class biogeochemistry of Trinity Bay

1537

Table 4. Temporal comparisons of net-tow, sediment trap and core sample compositions in Trinity Bay, NF, 1994±1997. All proportions are in percent; data are mean 2S.D., n = 2±22. Abbreviations are explained in Table 2 Net-tows

POM/TPM TL/TPM TL/POM Neutral/TL Polar/TL LI HI

Sediment traps

Cores

early spring}

late spring}

summer6

fall/winter

surface$$

sub-surface%%

55.4 213.0 2.5*2 2.4 3.1*2 3.2 65.6 212.3 34.4 212.3 11.5* 2 6.6 19.6* 2 12.8

61.82 14.2 5.5*2 3.3 5.7*2 3.6 66.62 14.0 33.52 14.0 20.3* 2 12.8 30.1* 2 15.5

37.3* 218.4 2.5* 21.6 7.5* 26.8 69.7* 29.5 30.3* 29.5 16.5 24.5 26.0* 27.4

54.2*2 5.6 0.9* 20.5 1.7* 21.1 51.0*2 8.4 50.0*2 8.4 14.5 23.4 34.6*2 6.6

23.4 211.3 0.3 20.2 1.4* 20.3 27.9 211.7 72.1 211.7 5.3 21.1 37.5 23.1

20.72 7.1 0.2 20.1 0.8*2 0.3 21.2 210.1 78.8 210.1 5.3 21.5 65.7 225.9

}March and April; n = 22. }May and June; n = 9±17. 6May±October; n = 8±12. July±April; n = 9. $$The ®rst two cm of the cores from stations H1 and H9 only; n = 2. %%The remainder of the cores from the same two stations; n = 14. *Means are signi®cantly di€erent (P < 0.05, t-test).

increase in the proportion of free fatty acid (Table 5). The lack of an increase in alcohol content points to the breakdown of acyl lipids other than wax esters. Since there are no other acyl lipid classes which decrease signi®cantly, and since diacylglycerols and acetone-mobile polar lipids increase signi®cantly, it is possible that triacylglycerols are in fact a major source of these free fatty acids. Monoacylglycerols can be an important component of the acetone-mobile polar lipids and, together with diacylglycerols and free fatty acids, are the products of lipase activity on triacylglycerols. Settling particulate matter Fluxes of material into the sediment traps increased by an order of magnitude in the spring (Fig. 3). For most of the year, the biomass in the traps was dominated by algal detritus and crus-

tacean appendages, but in the spring centric diatoms such as Biddulphia sp. and Coscinodiscus sp. became much more important contributors. Faecal pellets were minor components of the detritus in all samples examined. The results from the sediment trap work show that the total particulate matter and particulate organic matter data are similar to those of a comparable study in nearby Conception Bay (Redden, 1994), although the ranges are larger. For example, particulate organic matter ¯uxes ranged from 0.08± 4.63 g mÿ2 dÿ1 in Trinity Bay compared with spring values of 0.17±2.15 g mÿ2 dÿ1 that can be calculated for Conception Bay (Redden, 1994). After conversion of organic mass to organic carbon using a factor of 0.294 calculated from the data of Redden (1994), the mean ¯ux in Trinity Bay was 359 mg C mÿ2 dÿ1 with a range of 24± 1361 mg C mÿ2 dÿ1 (Fig. 3). These calculated or-

Table 5. Temporal comparisons of lipid class composition in net-tow, sediment trap and core samples from Trinity Bay, NF, 1994±1997. All proportions are in percent. Data are mean 2S.D., n = 2±22 Net-tows

Hydrocarbons Wax/steryl esters Methyl esters Ketones Triacylglycerols Free fatty acids Alcohols Pink pigment Sterols Diacylglycerols Acetone-mobile polar lipids Phospholipids

Sediment traps

Cores

early spring*

late spring$

summer%

fall/winter}

surface}

sub-surface6

3.6** 24.0 38.0** 217.8 0.8** 22.2 0.0 2 0.0 8.7** 25.7 8.3** 25.1 2.2 2 2.8 0.0 2 0.0 2.4** 22.0 1.8** 21.3 6.8** 25.1 27.42 10.8

1.2** 2 0.9 20.9**2 10.9 1.5** 2 1.4 0.0 20.0 15.2**2 9.1 17.6**2 11.5 1.7 21.6 0.0 20.0 3.3** 2 1.0 5.2** 2 2.7 12.6**2 6.3 20.9 218.7

3.0 2 1.2 29.5** 28.6 0.8** 21.5 0.0 2 0.1 9.9 2 5.9 9.7 2 3.2 4.5 2 1.8 1.0** 21.2 8.6** 22.0 2.7 2 1.6 21.82 9.1 8.7** 22.8

8.0 2 7.8 12.1**2 6.5 2.4** 21.5 0.0 2 0.0 7.7 2 3.4 7.8 2 2.9 4.6 2 1.4 0.0** 20.0 5.5** 21.5 2.7 2 1.9 28.2 26.3 21.0**2 7.4

4.6 2 2.4 5.7 2 7.4 0.3 2 0.4 1.4 2 1.6 5.5 2 3.6 1.9 2 1.0 2.9 2 0.2 0.0 2 0.0 3.1 2 0.6 2.6 2 2.1 44.9 28.1 27.2 23.7

5.7 2 7.5 1.4 2 0.5 0.6 2 1.0 1.1 2 1.2 2.6 2 1.5 1.5 2 0.8 3.2 2 1.1 0.0 2 0.0 2.8 2 1.6 2.3 2 2.2 50.82 6.2 28.02 7.7

All data were tested for normality and equal variance. Where these tests failed, a Mann±Whitney Rank Sum test was performed. *March and April; n = 22. $May and June; n = 17. %May±October; n = 12. }July±April; n = 9. }The ®rst two cm of the cores from stations H1 and H9 only; n = 2. 6The remainder of the cores from the same two stations; n = 14. **Means are signi®cantly di€erent (P < 0.05, t-test).

Fig. 3. Fluxes of total particulate matter, particulate organic carbon and total lipids, and organic content (%) of particles settling at stations 7 and 9 in Trinity Bay. Organic mass was converted to organic carbon using a factor of 0.294 calculated from the data of Redden (1994). TPM: total particulate matter; POC: particulate organic carbon; N/A: not available. Data are mean2S.D., n = 1±4 traps.

1538 C. C. Parrish

Lipid class biogeochemistry of Trinity Bay

ganic ¯uxes are comparable to, although generally higher than, those of Hargrave (1995) and Colombo et al. (1996b) for various other coastal regions and continental shelf areas of eastern Canada. These converted data are also comparable to, but again on the high side of, those of highly productive Norwegian fjords (Wassmann, 1991; Reigstad et al., 1995). Total lipid sedimentation rates in Trinity Bay, along with those for particulate matter and particulate organic matter, were higher than in the North Atlantic (De Baar et al., 1983; Kortzinger et al., 1994), and in April and May, the rates increased to a level more typical of a highly productive oceanic upwelling region (Wakeham et al., 1984). At this time, ¯uxes of phospholipids were at their highest, reaching a maximum of 7.4 mg mÿ2 dÿ1, which indicates massive transport of membrane material through the water column. The highest ¯ux of triacylglycerol (9.2 mg mÿ2 dÿ1) was also observed during this period, indicating storage of energy in bloom organisms. All the triacylglycerol ¯uxes measured in late spring, together with some of those observed during summer, summer/fall, and early spring in Trinity Bay, were higher than those reported for various oceanic regions, including the Peru upwelling region (Wakeham et al., 1984). The proportions of free fatty acids were at their lowest during the bloom with values as low as 4.7%, re¯ecting a relative lack of acyl lipid degradation at that time. Fluxes of free fatty acids and another indicator of degradation, free aliphatic alcohols, were highest in the summer/fall samples reaching maxima of 3.8 and 1.3 mg mÿ2 dÿ1 respectively. The high alcohol ¯ux suggests degradation of zooplanktonderived wax esters and chlorophylls was greatest then. The changes in lipid concentrations in settling material in the water column re¯ect the same changes in lipid concentrations in plankton during the bloom (Table 4). Thus, material settling out at the end of the bloom has higher total lipid concentrations than at other times of the year. It is for this reason that ¯uxes of lipids do not show the large seasonal signal that is seen in the total particulate matter ¯uxes or the particulate organic matter ¯uxes (Fig. 3). Thus, ¯uxes remain quite high during the summer so that benthic and demersal food webs continue to have a source of fresh lipidrich material in the post-bloom period. This may be important for higher trophic level species such as cod, crab, ¯ounder and plaice. Accuracy of ¯ux estimates In descending from a trap depth of 50 to 100 m below surface, half the ¯uxes showed a small continuous downward trend indicating that there were few problems with the sediment trap data in terms of the entry of resuspended or advected material.

1539

The integrity of the lipids in the sediment traps seems to have been well conserved as evidenced by breakdown indices which were not signi®cantly di€erent from those in net-tow samples (Table 2), and the low proportion of bacterial markers (Budge and Parrish, 1998). This is likely due to the use of a hypersaline layer and to temperatures at trap depths being sub-zero at the time of deployment and recovery for all cruises except one. At all times the measured temperatures were between ÿ1.6 and +0.68C. A solution of 5±6 g/l HgCl2 in 40 ppt NaCl solution was also tested as a poison in two short-term spring deployments. As expected from the observations of Lee et al. (1992), the poisoned samples had many more swimmers which had to be removed. However, there were few signi®cant di€erences in any of the variables we measured in poisoned and unpoisoned traps. Where there were signi®cant di€erences, the values in the poisoned traps were usually higher, sometimes several fold higher. Subsamples from one poisoned trap had a wax and steryl ester ¯ux that was as much as eight times higher than the ¯uxes of wax and steryl esters in the remaining traps on the same frame (Fig. 4). This was the highest observed di€erence; however, the variable most commonly observed to be signi®cantly higher in poisoned traps was the free fatty acid ¯ux, which was higher in three of the seven poisoned samples. This suggests that in at least one poisoned sample we had not removed all the swimmers or parts thereof, and that acyl lipid breakdown can appear to be higher in poisoned traps. This again is consistent with Lee et al. (1992), who suggest that swimmers can greatly a€ect the ¯ux and composition of organic matter in poisoned traps and that they may decrease the e€ectiveness of the poison at inhibiting microbial activity. By contrast with possible increases in ¯uxes caused by swimmers, leaching of material in the bottom of the trap may cause serious underestimations of ¯uxes (Kortzinger et al., 1994). We found quite high and variable concentrations of dissolved lipids (346 2 220 mg/l) in trap water whose salinity had not changed appreciably between deployment and recovery. The amount of dissolved lipids in the bottom of the traps was usually about one third that of particulate lipids. Given our small sample size (6) and the variability in the data, we were not able to discern any di€erences between unpoisoned and poisoned traps, although the ratio of dissolved to particulate lipids was consistently higher in the poisoned traps. This may relate again to the added input of swimmers to these traps (Lee et al., 1992). In addition to con®rming the high and variable fatty acid dissolution observed by Kortzinger et al. (1994), we can also con®rm their ®nding of a higher proportion of free fatty acids undergoing dissolution than total fatty acids. The proportion of free

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C. C. Parrish

Fig. 4. Lipid class ¯uxes in unpoisoned and poisoned (5±6 g/l HgCl2) traps deployed in April 1995 and May 1997. Data are shown for only the lipid classes which had signi®cant di€erences between unpoisoned and poisoned traps on more than one frame. WE/SE: wax/steryl esters; TG: triacylglycerols; FFA: free fatty acids; ST: sterols; PL: phospholipids. Data are mean2 S.D., n = 1±3.

fatty acids in the dissolved fraction of sediment trap material was signi®cantly higher than in the particulate fraction, while the proportions of wax and steryl esters and triacylglycerols were signi®cantly lower (Fig. 5). The lack of signi®cant di€erences between poisoned and unpoisoned dissolved samples suggests the di€erent proportions are a

function of lipid class solubility rather than microbial lipase activity, but again it is dicult to be sure because of the variability. Sediments The results from 210 Pb dating of the three cores revealed very di€erent sedimentary environments

Lipid class biogeochemistry of Trinity Bay

1541

Fig. 5. Lipid class proportions in dissolved and particulate matter from traps deployed in May 1997. HC: hydrocarbons; WE/SE: wax/steryl esters; KET: ketones; TG: triacylglycerols; FFA: free fatty acids; ALC: alcohols; PIG: peridinin-like pigment; ST: sterols; DG: diacylglycerols; AMPL: acetonemobile polar lipids; PL: phospholipids. Data are mean 2S.D., n = 6 traps.

for the three stations in terms of ¯uxes and mixing. The top 6 cm of the core at H-1 accumulated in 68 years, while the top 28 cm of the core at H-9 accumulated in 74 years. The data for St-7 suggested an extremely mixed sediment core resulting from bioturbation. The median concentration of lipids between 0 and 2 cm in the cores was 0.7 mg/g dry weight. Total lipid concentrations in the surface sediments (Fig. 6) were not signi®cantly lower (P > 0.05) in Trinity Bay (St-7±St-10) than in the Northwest and Southwest Arms. However, the highest concentrations were observed near the communities of Hickman's Harbour (H-1), Lady Cove (H-6), Clarenville (H-9), and Southport (St-11) each of which is in the vicinity of a river. This suggests the possibility of signi®cant anthropogenic or terrestrial in¯uence on the sediments. Hydrocarbon concentrations are also higher at these stations (Fig. 6), and comparisons with nalkane data (Favaro, 1998) and phenol data (Pulchan, 1998) suggest that terrestrial plants were a major source for at least the hydrocarbons in these sediments. Hydrocarbons are a major component of surface waxes in terrestrial plants and insects (Gurr and James, 1971), and n-alkanes are typically a higher proportion of land-derived or-

ganic matter than of algae (Bourbonniere and Meyers, 1996). The organic content and lipid composition of the cores was very di€erent to that observed in the nettow and sediment trap samples (Tables 2 and 3). There are several possible causes for these large di€erences, but given that they occur at sub-zero temperatures in an environment where bacterial and zooplankton activity are low during the spring bloom (Pomeroy et al., 1991), near bottom diagenetic processes are likely to dominate (Colombo et al., 1996c). Sediment trap studies by Redden (1994) in Conception Bay show settling rates of 20±23 m/d during the Newfoundland spring bloom. Thus particles at stations 7 and 9 would settle from 100 m to the bottom in only 6±11 days. During this period, the bacteria would be preferentially attacking the algal carbohydrates and proteins (Harvey et al., 1995). Harvey et al. give a turnover time of 44 days for lipids at 198C, so that at sub-zero temperatures, the turnover time would be more like 176 days based on chemical kinetics. Thus only about 5% of the lipids would be consumed in the water column. This itself could be a maximal proportion as bacterial numbers are low during the Newfoundland spring bloom (Pomeroy et al., 1991).

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C. C. Parrish

Fig. 6. Total lipid and hydrocarbon content (mg/g dry weight) of sur®cial sediments. The data represent the mean2 S.D. of three analyses of grab samples or samples from the top two cm of the cores.

At the trap sites in Trinity Bay (St-7 and St-9), the concentrations of total lipids in the surface sediments were in the range 0.4±0.5 mg/g (Fig. 6). When compared with a year round average of 16.4 mg/g in the sediment trap material (Table 2) this suggests a 97% loss of lipids occurred between 100 m in the water column and 0±2 cm in the sediments. This year round average is signi®cantly higher (P = 0.001) than the 14.2 22.1 mg/g observed for settling particles in the Laurentian Trough in May and July (Colombo et al., 1996b). However, the lipid concentration in the sediments at stations 7 and 9 is signi®cantly lower (P = 0.004) than the average of 1.15 2 0.28 mg/g that can be calculated for the top two cm of sediments in this similar environment (Colombo et al., 1996c). Thus, the 35-fold di€erence between concentrations in settling particles and surface sediments is very high

in comparison with the Laurentian Trough, where the di€erence was twelve-fold on average. This suggests a greater uptake of lipids in benthic and demersal food webs in Trinity Bay, and it may be related to the relative proportions of terrestrial material settling in the two environments. Colombo et al. (1996b) estimate that about half the carbon ¯ux in the Laurentian Trough is of terrigenous origin, while Budge and Parrish (1998) indicate that almost all the acyl lipid ¯ux in Trinity Bay is of marine origin. In any case, the high degree of bioturbation in the core at the center of this bay points to the presence of a very active benthic community there. Budge and Parrish (1998) give further evidence for the eciency of this community in that polyunsaturated fatty acid concentrations are at least two orders of magnitude lower in sediments by comparison with settling particles.

Lipid class biogeochemistry of Trinity Bay

Lipid concentrations remained low (0.2±0.5 mg/g dry weight) throughout the 30 cm core from the center of Trinity Bay. Using either the accumulation rate at H-1 or H-9, this suggests there have been few major changes in biogeochemical cycling of lipids in Trinity Bay for at least the past half century. This time period encompasses the historical maximum in 1968 of catches of Atlantic cod in Newfoundland waters (Hutchings and Myers, 1994).

1543

The total lipid pro®les for H-1 and H-9 show a decreasing trend with depth with a subsurface peak at H-1 (Fig. 7). The maxima in total lipids again match quite well with the hydrocarbon data, and the pro®les are very similar to those for terrestrial plant compounds from the same cores (Favaro, 1998; Pulchan, 1998). Terrestrial plants are thus likely to be an important contributor to lipids in nearshore sediments where the spatial and temporal distribution of terrestrial plant compounds is

Fig. 7. Pro®les of total lipid and hydrocarbon content (mg/g dry weight) in sediment cores from stations H-1 and H-9. Data are mean2S.D., n = 3. Dates were obtained from 210 Pb data.

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C. C. Parrish

strongly in¯uenced by wood cutting practices around Trinity Bay. The decrease in hydrocarbon concentrations between 1983 and 1994 at H-9, which is repeated in the phenol data and the terrestrial n-alkane data, occurs when there is an increase in total lipids (Fig. 7) and organic carbon (Pulchan, 1998). This suggests the increases may not have been related to inputs from terrestrial plants at this time. Again, anthropogenic in¯uences are a possibility as H-9 is adjacent to Clarenville, which is the major town in the region.

CONCLUSIONS

(1) In 1995±1997 the spring diatom bloom in Trinity Bay reached a peak in May. At this time triacylglycerol storage increased in response to lowered nitrate and silicate concentrations. This was followed by increased concentrations of phospholipids which coincided with biomass increases in dino¯agellates and zooplankton. (2) Plankton lipids appear to be transferred with little alteration through the water column to benthic and demersal food webs. Fluxes are high compared with values in the literature, especially in spring, and incorporation into the food web seems to be very ecient with little loss through burial in the sediments. (3) The use of poisons in sediment traps can cause an overestimation of some acyl lipid classes; however, leaching into the hypersaline layer may cause an underestimation of ¯uxes of hydrocarbons, alcohols, sterols, diacylglycerols, acetone-mobile polar lipids, phospholipids, and especially free fatty acids. (4) Only 3% of the lipid ¯ux through the water column in the center of Trinity Bay is preserved in the sediments. The preserved lipids consist largely of polar lipids. Much larger concentrations are preserved closer to shore in the vicinity of the major rivers and of the few towns in the area. Terrestrial plants are likely to be an important contributor to lipids in nearshore sediments. AcknowledgementsÐI wish to thank the captains and crews of the F. R. V. Shamook, the R. V. Karl and Jackie II, the M. V. Nain Banker, and the Baccalieu Endeavour. I also thank Jeanette Wells for technical support in all analytical aspects of this work, Jack Foley for help with the moorings, Dennis Short for ¯oristic analyses, Jerry Pulchan for collecting the core samples, Yvette Favaro for providing sediment extracts, Jack Cornett for the 210 Pb dates, and Betty Hat®eld for the pigment analysis. I am grateful to an anonymous reviewer, Ray Thompson, Don Deibel and Sue Budge for helpful comments which improved the manuscript, and to Ali Aksu and Brad deYoung for discussions of sedimentology and physical oceanography. This work was funded through Environment Canada's Tri-Council Eco-Research Program.

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