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HomeMy WebLinkAboutBrown Tide Blooms Perturb Coastal Marine EcosystemEstuaries Vo~. 10, NO. 4, p. 264-290 Dec~mber 1987 Recurrent and Persistent Brown Tide Blooms Perturb Coastal Marine Ecosystem ELIZABETH M. COSPER WILLIAM C. DENNISON EDWARD J. CARPENTER V. MONICA BRICELJ JAMES G. MITCHELL SUSAN H. KUENSTNER Marine Sciences Research Cen~er State University' of ,X~' Yor~ DAVID COLFLESH MAYNARD DEWEY Anatomical Sciences State Universit.¥ of New York Stony Brook, New York 11794 ABSTRACT: Throughout the summers of 1985 and 1986 a small (2-$ am diameter), previously undescribed chrysophyte bloomtni monosF~:ifically (> 10' cells 1- ') in Long Island embayments. The bloom colored the water dark brown, decimated eelgrass b~ls through decreased light penetration and caused starvation (tissue weight loss) and recruitment failure of commercially important bay ~callop populations. These perturbations portend long- term changes in subtidal communities. Similar and concurrent blooms in bays of Rhode Island and New Jersey suggest a meteorological component of the environmental conditions promoting bloom formation. Culture exper- iments with isolates of the microalga suggest the presence of stimulator)' growth factors in the bloom seawater. Introduction Many coastal embayments of Long Island ex- perienced algal blooms of a small (2-3 ~m) mi- croalga during the summers of 1985 and 1086 that were unprecedented in their persistence (~6 months) and cell density (>10° I-~). Virtually monospecific blooms occurred throughout many of the inland embayments of Long Island (Fig. 1) and were popularl) called the brown tide due to the resulting water color. Reports of similar and concurrent brown tide blooms in Narragansett Bay, Rhode Island and Barnegat Bay, New jersey have been made (Olsen 1986: Sieburth et al. 1986). Historically, small microalgae generally have been found to dominate the phytoplankton bio- mass and productivity in Long Island embayments such as Great South Bay (Lively et al. 1983) and the Peconic Bays (Bruno et al. 1983) during the summer. The brown tide blooms were unique due to the extreme dominance of a single, previously unidentified species throughout the summers of both 1985 and 1986. Usually the small forms ob- served are diverse and composed of many species of diatoms, chlorophytes, cryptomonads and small ~ 1987 Estuarr~e ReSearch Federation 284 flagellates (Bruno et al. 1983: Lively et al. 1983). Primary productivity rates for these bays during this time are extremely high and do not appear to be limited by nutrient availability since inorganic nutrient levels remain relatively high (Bruno et al. 1983: Lively et al. 1983). The dense algal blooms decreased light pene- tration and, thus, reduced the extent of eelgrass (Zostera marl,n) beds. Eelgrass can grow onb to approximately the Secchi disc depth (Dennison 1987) which, during the algal bloom, was less than 1 m. The 1985 bloom coincided with the spawning period (June-July) of commercially valuable bay scallops (Argopectea irradinas irradiaa~0 io the Pe- conic and Gardiner's bays. These bays contribute more than 80~ of New York State's bay scallop harvest, and the bloom resulted in massive recruit- ment failure of the 1985 year-class. In order lo document the extent, nature and causes of these unusual blooms, studies were initiated during the summer of 1985. Investigations were also con- ducted to document the impacts of these blooms on the coastal ecosystems, particularl) on the scal- lop populations and eelgrass beds. 0160-8347/87/040284-07501.50/0 "Brown Ti~e" Blooms 285 GARDINERS lO nout miles )AY RB PECONIC BAYS ~0~ \S~~t~O BP GREAT SOUTH BAY Fig. 1. Embayments on Long Island affected (shaded areas) by brown tide blooms during 1985 and 1986. (lslip Marine. l M: Blue Point, BP; Reeves Ba), RB; New Suffolk, NS) Methods and Materials Aerial overflights of Long Island bays (provided by the New York Air National Guard and the Suf- folk Count)' Police) and photographic documen- tation (by R. G. Rowland and W. C. Dennison) were utilized several times during the summers of 1985 and 1986 to determine the extent and duration of the blooms. In addition, four field collection sites-- Islip Marina (IM) and Blue Point (BP) in Great South Bay, and Reeves Bay (RB) and New Suffolk (NS) in the Peconlc Bays (Fig. 1)--were sampled on approximately a weekly basis during the sum- mer months and less frequently at other times. Surface water samples were collected for phyto- plankton counts and identification. Chlorophyll a analyses and primary productivit)' estimates were made along with measurements of temperature, salinity by refractometer, and Secchi disc depth. Microscopic enumeration and identification of phytoplankton were performed using Lugols and formalin-fixed samples (Lively et al. 1983). An in- verted microscope and an epifluorescent micro- scope were used with DNA-specific fluorescent stains and light filter sets to distinguish different species and groups of microalgae. The brown tide organism was recognized b) the presence of its red- fluorescing, cup-shaped chloroplast plus the shape of its nucleus after staining with the fluorochrome DAPI, Other phytoplankton and codominants, mainly the small diatom, Minutocellus polynorpbu~, were recognized by the distinctive shape of their nuclei and chloroplasts, and cyanobacteria such as S?ecbococcus were recognized by their orange flu- orescence under green-light excitation. Water samples were size fractionated, by passing water through 5-~m nucleopore filters and 10- #m nitex screens, so as to compare productivity and phytoplankton biomass levels of different au- totrophic size groups (<5 ~m, < 10 $~m. whole). Fluorometric measurements of chloroph)ll a were performed on 90cA acetone extracts using methods of Strickland and Parsons (1972). Estimates of pro- ductivity, using the uptake of '4C-HCOs during short-term incubations 00:00-14:00 h under nat- ural sunlight, were determined (Stricklaud and Parsons 1972) in duplicate at three light levels (100, 33, and 2~ ambient light). Incubations were ter- minated b)' filtration onto 0.22-~m Millipore fil- ters. The filters were dried in a desiccator over- night in scintillation vials and counted in a Packard TriCarb 300C scintillation counter after the ad- dition of Aquasol. Depth profiles of ~4C uptake rates were constructed and then were integrated down to the Iq light depth (approximately the photic zone) and expressed as mg C m : h-h Cal- culat ions were made to estimate the potential turn- over rate of photic zone carbon by assuming a C:Chl a = 45 (Parsons et al. 1977). During the summer of 1986 isolates of t he brown tide were established in unialgal culture as de- scribed in Cosper (1987), using standard isolation and culture techniques (Guillard 1973: McLachlan 1973). Growth rates of cultures were determined microscopically using daily hemacytometer counts. 286 E.M. Cosper et al. Fig. 2. Scanning electron micrograph of the brown tide species at x:SO,O00 magnification. Samples for scanning electron microscopy were fixed in glutaraldeh)de, filtered onto nylon filters, postfixed with osmium, dehydrated in acetone, critical-point dried and mounted on stubs for anal- ysis in a jOEL EX 1200 electron microscope. Eelgrass (Zostera mari~ia L.) surveys were con- ducted in August 1986 in Great South Bay and the Peconic Bays using SCUBA techniques. Water depth transects throughout Great South Bay and the Peconic Bays were spaced approximately' 5 km apart starting south of Islip Marina (IM) at Fire Island Inlet and heading east out to Gardiner's Bay (Fig. 1): locations were determined with shore sightings and Loran. Three sampling stations were located along each transect. Eelgrass shoot density' was estimated from five randomly' selected 0.0625 or 0.25 me quadrats. Subsamples of the eelgrass leaf canopy' were randomly selected, dried (90 *C: 48 h) and weighed. Eelgrass leaf biomass estimates were obtained from the product of shoot density' and leaf dry' weight per shoot. In addition to the three stations along each transect, the maximum depth penetration of eelgrass was ascertained by swimming beyond the deepest growing plants. The area capable of supporting eelgrass growth in the bay's was calculated by determining the bay bottom areas between mean Iow water level and the pre- bloom and postbloom maximum depth penetra- tion of eelgrass. Prebloom depth penetration was determined using the report of.Jones and Schubel (1978) along with field observations made in 1984. Postbloom depth penetration was determined us- ing the 1986 depth transects. For measurements of particle retention efficien- cy, adult scallops or mussels were individually placed in a beaker containing 1.5 I of seston collected during the bloom, artificially enriched with cul- tured Thalassiosira weissflogii (11 ~m in equivalent spherical diameter) at 23 *C. This diatom was cho- sen since Mohlenberg and Riisgard (1975) have shown that pectinids retain particles greater than 6-7 gm with 100cA efficiency. Gentle stirring main- tained algae in suspension but prevented the re- suspension of biodeposits. Mean experimental con- centrations (calculated as the geometric mean of algal densities before and after grazing) were ~379,000 cells mi-~ of Aureococcus anorexeffere~s and 3,300 cells ml-~ of T. weissflogii. Retention ef- ficiency of A. anorexefferens was calculated as the clearance rate of this alga (1.6 to 3.2 #m size frac- tion) relative to that of T. weissflogii (8-16 gm size fraction) x 100. Clearance rates (volume swept clear of particles per unit time) were determined from the change in algal concentrations following a fixed feeding interval (Coughlan 1969). Particle concentrations of 30-40 mi samples were deter- mined using an electronic particle counter (Coulter Counter, Model TA II). Results and Discussion Transmission electron inicroscopy (Carpenter and Cosper 1986) showed this microalga is a pre- viously undescribed species and similar to the chrysophyte species tentatively' desighated Aureo- coccus a~wrexefferens, which also bloomed in Nar- ragansett Bay', Rhode Island in 1985 (Sieburth et al. 1986). Scanning electron microscopy (Fig. 2) revealed irregular coccoid cells with a shrface in- dentation and a coating of globular material. In 1985 the bloom was first noticeable in earlx June and p~rsisted to late September, reappeare~l in April 1986, reaching densities of > 10* cells I-~ within several weeks, and persisted into November at densities of 10~ cells I- ~. The brown tide was not only' the species that was dominant in terms of cell number, but also the one that contributed >80% of total cellular phytoplankton volume throughout most of the bloom period (Fig. 3) except for two sampling dates in May and July' ~'hen there were inexplicable decreases. Primary' productivity rates of 200 to 400 mg C m-e h-~ were measured in Great South Bay and the Peconic Bays during the summer of 1986, consistent with previously doc- umemed high rates of productivity during the sum- mcr months (Bruno et al. 1983; Lively et al. 1983). Estimates of carbon turnover rates ranged from 3.5 to 13 h. The <10 t~m fraction of the phyto- plankton, generally' dominated by' the brown tide organism, often contributed >90c~ to total pho- tosynthetic activity throughout the bloom period (Table 1). Abundance of the bloom organism dur- ing the summer remained at ~ 10* cells I- ~ or slight- 70- o D~,T E Fig. $. Percent of total cellular phytoplankton volume con- tributed b~ the brown tide during the summer of 1986 for weekly, int~*rx'als sampled at Blue Point (BP). ly less, and chlorophyll a levels were relatively nor- mal for these bays during the summer months at levels of ~ 10-25 ug I-~ (Bruno et al. 1983; Lively et al. 1983). Changes in phytoplankton biomass, thus, did not reflect the rapid rates of turnover estimated from the productivity experiments. Since dailx sinking rates of such a small microalga would be s~nall (Smavda 1971) and flushing of the bays is on the order ~f weeks (Hard)' 1976: Lively et al. 1983), neither of these factors could account for such constant population densities. Closely coupled grazing, probably by microzooplankton, most like- ly served as a control mechanism. Rapid growth rates (three divisions d-}) of iso- lates (Cosper 1987) have been obtained in labo- rator)' cultures under optimum conditions, consis- tent with the high productivity estimates for field popu at ons. This microalga grows minimally in standard media used for culturing marine microa - gae, f/2 enriched lnstant Ocean Sea Salts (EIO) (McLachlan 1973), while f/2 media made from natural filtered seawater (from bloom affected areas) gives maximal growth rates. Substitution of sodium glycerophosphate for inorganic phosphate at equivalent phosphate levels to the f/2 EIO me- dia enhanced growth to 709~ of growth in natural seav,'ater media indicating that specific organic nu- trients are required for rapid growth of this species. This suggests that there are growth inducing fac- tors in the bloom water. The role of light availability in controlling growth and depth distribution of eelgrass has been eluci- dated with in situ manipulation experiments (Den- nison and Alberte 1982, 1985), transplant exper- iments (Dennison and Alberte 1986) and carbon balances (Dennison 1987). These studies demon- strated that light availability controls the maximum depth penetration of eelgrass and controls eelgrass "Brown T~" Blooms 287 TABLE 1. Photosynthesis (mgcarb°n m-~ h-~) in the < 10 um phytoplankton fraction as a percent of the total from the four sites (see Fig. 1) in Long Island bays (Islip Marina, IM; Blue Point, BP: Reeves Bay, RB; New Suffolk, NS) in 1986. June 19 ** 777t ** ** June 26 ** ** 79~ 78q Jul} 9 997t 957t ** ** Jul) 15 ** ** 100/q 100~ Jub 22 937~ 959~ ** ** August 5 ** ** 1007~ 100/~ August 12 1007~ 91~ ** ** September 18 ** ** 947t 87~ October ] 3 ** ** 96~ 959~ Indicates dates that s~tes were not sampled. growth in deeper portions of its distribution. Sur- veys of eelgrass beds were performed to assess the potential impact of the dense algal blooms, which decreased light penetration. The Secchi depths were less than I m (50-60 cm) throughout the bloom periods in contrast to several meters found during the summer months in previous years in these coastal embavments (Bruno et al. 1983: Live- ly et al. 1983). ThJe increased attenuation of light during the brown tide blooms is not a consequence of increased absorption of light by .chloroph)'ll a, since concentrations remained at levels similar to those of previous years. Increased scattering of light due to the small size of this particular phytoplank- ton species (Jerlov 1968: Morel 1987) is most likel) the cause of the severe reduction in light penetra- tion. This decreased light penetration led to a sub- stantial reduction in eelgrass biomass and depth distribution (Fig. 4), which resulted in large areas of Great South Ba) (50 km~) and the Peconic Bays {65 kin:) that were not capable of supporting eel- grass growth. These areas represent ~557r of the prebloom area capable of supporting eelgrass growth. Eelgrass beds are crucial to Long Island's shallow water ecosystems, since the)' influence sedimenta- tion patterns, nutrient cycling and water flow, and serve as nurseries for man) species of finfish and shellfish (Phillips and McRoy 1980). Recruitment of bay scallops and postsettlement survix al is linked to the hydrodynamics of eelgrass meadows (Eck- man 1987) and results in a close association be- tween eelgrass and scallops (Thayer and Stuart 1974). Eelgrass requires years to decades for re- cover)' from large-scale mortality, as occurred in the 1930's (Rasmussen 1977). Long Island bay scallops spawn in their first year and experience mass, senescent mortality during the winter of their second )'ear. Postspawning aduh, during 1985 (1984 cohort) sho~'ed a 769~ reduc- 288 E. M Casper et aL EELGRAS$ L;AF BIOMAS$(g/m~') 0 ~00 200 300 400 500 4 Pre-bJoom; Peconic Bays Pre-bloom~Great South Bay Post- bloom; Peconic Boys 0---(3 Post-bloom;GreatSouth Bo Fig. 4. Leaf biomass of eelgrass (Zostera marl~la) vs. water depth before and after the ! 98.5-198§ algal blooms. Eelgrass biomass ~,as measured in October 1084 (prebloom) and August 1986 (post bloom) for Peconic Baxs (4 l°00.$'N, 72°18.7'W)and Great South Bax (40°42 6'N: 72°.58.§'¥,')· Preb}oom data f'or Great South Ba) gere obtained from Jones and Schubel (1978). tion in mean adductor muscle dry weight relative to the previous .~ear (Bricelj et al. 1987). Mortality rates of this year-class were not documented. Sur- vivors, however, showed rapid recovery in muscle · ,,.'eights (three-fold increase during September) af- ter the bloom subsided, so that tissue weights sur- passed those of the 1983 cohort by earl)' October (Bricelj et al. 1987). Thus, New York State landings of bav scallops in 198.5, although Iow, remained about' 58c~ of landings averaged over the previous four-year period (New York State, Department of Envi(onmemal Conservation, Landings File, 1985). Experiments with scallops held in cages in situ indicated that about 307r of the population poten- tially survived to a second spawning in june 1986 (Bri~relj et al. 1987). Natural restocking was pre- cluded, however, by recurrence of the bloom in the summer of 1986. Transplant programs of hatchery-reared seed into Long Island's embay- ments were initiated in the fall of 1986 (Rose 1987). Grazing experiments revealed that bay scallops retained the brown tide cells with a mean efficiency 1.0- 0.8- 0.6. 0,2' 1.0 0.6 1.2 0 (Vxn) . BAY ~1,0 ~'~1, ~ 51,0 81.0' ~,7 ~6,~ ~ MUSSEL 2.0 3.2 5.0 8.0 12.7 20.2 32 Particle diameter (/~m) : :Before grozing;o--.oAfter grazing Fig. 5. Particle biomass (~olume x concentration) mi ' of a mixed suspension of the bro'~ n tide (2 gm in equix alem spher- ical diameter, ESD). and Tbaln~do~ira u,e~s~flo~ii (1 I ~m in ESD). vs. particle diameter, before and after grazing by a represen- tative bay scallop and blue mussel. Retention et.~ciency o! the brown tide (se~' text) is calculated from the relative decline of "small" and "large" algae. of only 36.1% (SE = 4.0; n = 24), while mussels' mean retention efficiency for Aureococcu~ was 59.3~ (SE = 2.9: n -- 27). A representative example of the particle size-frequency distribution before and after grazing is shown for each bivalve species in Fig. 5. Starvation, reflected in weight loss of tissues. occurs whenever the absorbed ration fails to bal- ance the animal's metabolic energ) expenditure. Even 36~ retention of brown tide could potentiall5 result in a net energ5 gain at high bloom concen- trations, and additional explanations are needed to account for the observed tissue weight losses of scallops. Furthermore, although mussels are rela- tively more efficient in retaining the bloom cells, populations of3L edulis in Narragansett Ba), Rhode Island, experienced mortalities >95c~ during the bloom (Trace) 1985). Therefore, inefficient reten- tion of small particles (<3-6 ~m) by the animal's gills cannot alone account for the impact of the "Brown T~e" Blooms 289 brown tide on suspension-feeding bivalves. Possi- ble mechanisms currently being investigated are toxicity effects, reduced ingestion rates (concen- tration-dependent depression of clearance rates and/or rejection of filtered algae as pseudofeces), reduced absorption effqciencies at high particle loads, and/or poor nutritional value of the brown tide. The concomitant appearance of the brown tide over a wide geographic range in noncontiguous bodies of water, Narragansett Bay, Rhode Island and Long Island embayments as well as Barnegat Bay' in New Jersey may indicate a meteorological component to the environmental conditions pro- moting bloom formation. Rainfall data obtained from Brookhaven National Laboratory', Upton, Long Island indicated that for the first year of the bloom (1985), rainfall was the third lowest annual level in the last 37 yr and in 1986, annual levels were again well below average. Six years of tide gauge data from Great South Bay', supplied by' the Suffolk County' Department of Public Works, Waterways, Division, Yaphank, Long Island, in- dicates that sea level elevations during 1985 and 1986 were substantially' lower than earlier in the decade, and as a result, the flushing rate of Great South Bay would have decreased (Vieira 1986). Mean sea lex'el (MSL) between January and May' in 1984 was 66cA of MSL for the same months in 1981, ~¥hile in 1985 and 1986 the percentages were 46~ and 62cA, respectively. A trend of decreasing sea level, attaining a minimum in 1985, coincided with the first year of the bloom. The great reduc- tion in rainfall, in spite of the lowered flushing from coastal waters, led to elevated salinities in the bay': measurements during the summer for all sites and dates sampled, with only' one exception at Islip Marina (IM), were above 25%c and close to 30~/,x, while in previous years they' have been generally' 25~ (Lively et al., 1983). Hox¥ these conditions could promote the brown tide blooms needs fur- ther evaluation. Recurrence of the brown tide in future years cannot be accurately' predicted with current infor- mation and understanding. The brown tide has reappeared in restricted Long Island embayments during the summer of 1987 and further research is ongoing. Chrysophyte species can form cysts as a stage of their life history', and if the brown tide species produces cysts which overwinter in shallow embayments and reseed the pelagic zone during the spring, this might enhance the recurrence of blooms in certain areas, similar to recurrent di- noflagellate red tides (Anderson et al. 1982). The occurrence of the brown tide two years in succes- sion has already' severely perturbed Long Island's coastal ecosystems. Reestablishment of bay' scallop populations in Long Island waters will depend on successful restocking of decimated areas, but the efforts could be inhibited by the loss of eelgrass habitat. ACKNOWLEDGMENTS Research supported by Suffolk Count), New York: Ne~ York State Sea Grant: Marine Sciences Research Center of the State University of New York: and The Living Marine Resources Institute bf the State of Ne~, York. 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Received for cousideratio~. August 27, 1987 Accepted for publication. Noaember 16. 1987