Darcy J. Lonsdale

Latitudinal Differentiation in Copepod Growth: An Adaptation to Temperature

We demonstrate the presence of significant differentiation in development rate, adult body length, and stomatic growth rate in the estuarine harpacticoid copepod Scottolana canadensis (Willey) collected from a broad range of latitudes (27°—43° N) and reared in the laboratory for several generations under the same conditions (15 g salts per 1000 g seawater, and 15°, 20°, 25°, or 28°C). The changing pattern of differential growth with increased temperature suggests local adaptation to maximize scope for growth under prevailing temperatures conditions; northern—derived individuals grew faster at low but not at high temperatures. See full-text article at JSTOR

A review of the causes, effects, and potential management of harmful brown tide blooms caused byAureococcus anophagefferens (Hargraves et sieburth)

Brown tides caused by the harmful algaAureococcus anophagefferens abruptly appeared in some coastal embayments of the northeastern United States (Rhode Island, New York) in 1985. Since then, brown tides have vanished from some bays, chronically reoccurred in others, and recently have exhibited an apparent southern expansion into new regions (e.g., New Jersey, Delaware, Maryland, and Virginia). Brown tides have also recently been detected across the Atlantic Ocean in South Africa. Although blooms ofA. anophagefferens have no known direct, negative effects on human health, they are considered harmful because of their detrimental effects on estuarine organisms, such as suspension feeders (scallops and hard clams) and submerged aquatic vegetation. The selective effect of blooms on pelagic grazers (zooplankton and shellfish) is likely to affect food webs and biodiversity within affected ecosystems. Recent findings indicate brown tides occur in shallow estuaries with long residence times and high salinities (> 25‰). These estuarine characteristics may foster the accumulation of algal biomass and a nutrient environment (high dissolved organic matter and low dissolved in organic nitrogen) as well as a low light regime that encourages rapid cellular growth ofA. anophagefferens. A lack of sufficient grazing control by benthic and pelagic suspension feeders during the initiation phase of blooms is also implicated in brown tide development.

Latitudinal differentiation in embryonic duration, egg size, and newborn survival in a harpacticoid copepod

We demonstrate significant genetically based differentiation in embryonic duration (h), egg size (µm3), and newborn survival (number/h) in the harpacticoid copepod, Scottolana canadensis (Crustacea), taken from a broad range of latitudes (°N) and reared in the laboratory for several generations under the same conditions. Egg development times of the northern-derived (ME) individuals were significantly longer at all test temperatures, and thus did not demonstrate compensation at low temperature. Maine development times may be due to the larger egg size.

Composition and seasonality of zooplankton of North Inlet, South Carolina

The zooplankton of the North Inlet estuary near Georgetown, South Carolina, was collected bi-weekly from January 1974 to August 1975 (20 months) at four stations. Zooplankton numbers ranged from 377 to 84,414 m−3 (\(\bar X\)=9257 m−3) and biomass from 640 to 140,169 μg dry weight m−3 (\(\bar X\)=16,178 μg dry weight m−3). The major peak in the density of zooplankton occurred between April and July both years.

Abundance and distribution of phototrophic and heterotrophic nano- and microplankton in the southern Ross Sea

Phototrophic and heterotrophic nanoplankton (PNAN, HNAN; 2–20mm protists) and microplankton (PMIC, HMIC; 20–200mm protists and micrometazoa) are major taxa involved in partitioning carbon and energy within the pelagic food web. In the Ross Sea, Antarctica, plankton biomass appears to be controlled by the seasonal recession ofthe sea ice and the f ofthe Ross Sea polynya during the short austral spring-summer period. During four cruises in 1996–1997 within the southern Ross Sea as part of the US JGOFS program, we determined the abundances and biomasses ofphototrophic and heterotrophic nanoplankton and microplankton primarily along a transect at 76130 0 S. The colonial prymnesiophyte Phaeocystis antarctica (excluding mucus carbon) contributed significantly to community structure during both non-bloom and bloom periods (B25% and 90%, respectively, ofmicrobial biomass). However, shif ts occurred both seasonally and spatially between a diatom/heterotrophic dinoflagellate and a colonial P. antarctica-dominated assemblage. While nanoplankton biomass varied o50% during any particular cruise, PNAN and HNAN biomass ranged more than three orders ofmagnitude among the f our cruises (0.1–359 and 1.5–268 mmol C m � 2 , respectively). Cruise averages ofPMIC biomass ranged f rom 2.5 to 530 mmol C m � 2 , and a maximum biomass of1530 mmol C m � 2 was observed during the bloom ofcolonial P. antarctica in summer. Average heterotrophic biomass was o30% ofthe total microbial biomass (excluding bacteria) from early austral spring through summer. This value rose to E87% in autumn following the decline and disappearance of P. antarctica. The contribution oftotal nano- and microplankton biomass to POC in the upper 60 m over the three sampled seasons varied from 7% to 52.4% with an overall average of 21.8% for all four cruises which is comparable to contributions of these assemblages in other oceans even with the strong seasonal dominance of P. antarctica. r 2001 Elsevier Science Ltd. All rights reserved.

Development and Application of a Monoclonal-Antibody Technique for Counting Aureococcus anophagefferens, an Alga Causing Recurrent Brown Tides in the Mid-Atlantic United States

ABSTRACT A method was developed for the rapid detection and enumeration of Aureococcus anophagefferens, the cause of harmful algal blooms called “brown tides” in estuaries of the Mid-Atlantic United States. The method employs a monoclonal antibody (MAb) and a colorimetric, enzyme-linked immunosorbent assay format. The MAb obtained exhibits high reactivity with A. anophagefferens and very low cross-reactivities with a phylogenetically diverse array of other protists and bacteria. Standard curves are constructed for each 96-well microtiter plate by using known amounts of a preserved culture of A. anophagefferens. This approach allows estimation of the abundance of the alga in natural samples. The MAb method was compared to an existing method that employs polyclonal antibodies and epifluorescence microscopy and to direct microscopic counts of A. anophagefferens in samples with high abundances of the alga. The MAb method provided increased quantitative accuracy and greatly reduced sample processing time. A spatial survey of several Long Island estuaries in May 2000 using this new approach documented a range of abundances of A. anophagefferens in these bays spanning nearly 3 orders of magnitude.

Effects of Zooplankton Grazing on Phytoplankton Size-Structure and Biomass in the Lower Hudson River Estuary

The impact of mesozooplankton (>210 μm, mostly adult copepods and late-stage copepodites) and micrometazoa (64–210 μm, mostly copepod nauplii) on phytoplankton size structure and biomass in the lower Hudson River estuary was investigated using various14C-labeled algal species as tracers of grazing on natural phytoplankton. During spring and summer, zooplankton grazing pressure, defined as %=mg C ingested m−2 h−1/mg C produced m−2 h−1 (depth-integrated rates)×100, on total phytoplankton ranged between 0.04% and 1.9% for mesozooplankton and 0.1% and 6.6% for micrometazoa. The greatest grazing impact was measured in fall when 20.2% and 44.6%, respectively, of the total depth-integrated primary production from surface water phytoplankton was grazed. Mesozooplankton exhibited some size-selective grazing on phytoplankton, preferentially grazing the diatomThalassiosira pseudonana over the larger diatomDitylum brightwelli, but this was not found for micrometazoa. Neither zooplankton group grazed on the dinoflagellateAmphidinium sp. We conclude that metazoan zooplankton have a minimal role in controlling total phytoplankton biomass in the lower Hudson River estuary. Differences in the growth coefficients of various phytoplankton size-fractions—not grazing selectivity—may be the predominant factor explaining community size-structure.

Growth rate and reproductive differences in a widespread estuarine harpacticoid copepod (Scottolana canadensis)

We demonstrate the presence of significant genetically based differentiation in growth rate (μg dry weight d-1) and reproductive traits (percent reproductive females and mean clutch size μg dry weight-1) among females of an harpacticoid copepod (Crustacea),Scottolana canadensis (Willey), taken from a broad range of latitudes and reared in the laboratory under the same conditions. As temperature increases (15°–25° C), the growth rate of southern-derived copepods continues to increase, while that of northern-derived copepods levels off or decreases. Southern-derivedS. canadensis also have a higher percentage of reproducing females at high temperature (25°C) when rations (cells ml-1) are reduced, while northern-derived females are at an advantage at low temperature (15°C). Both life-history traits indicate local adaptation to maximize scope for growth and reproduction at prevailing temperatures. The data support our hypothesis that evolution has occurred to maximize feeding minus metabolic energy expended, and that this maximization requires changes in feeding efficiency with differing temperatures.

Lectin binding to surface glycoproteins on coullana spp. (copepoda: Harpacticoida) can inhibit mate guarding

We tested the hypothesis that surface glycoproteins found on Coullana spp. are important signals in contact mate‐recognition. Female copepodites (mostly molt‐stage V) of Coullana canadensis (Maryland) and Coullana sp. (Florida) were treated with 0.1 mg ml−1 of four lectins that represent a variety of carbohydrate affinities. The females were then washed and exposed to males. Binding of some lectins significantly reduced the ability of males to recognize potential mates and initiate precopulatory mate guarding. Other lectin treatments had no significant effect on this behavior. These data show that surface glycoproteins on female Coullana spp. are important mating signals for males in the recognition of conspecifics. Our results also suggest that differences in chemical signals among these sibling species may have evolved.

Linking phytoplankton community composition with juvenile-phase growth in the Northern QuahogMercenaria mercenaria (L.)

This study examined whetherMercenaria mercenaria (L.) (quahog) growth is influenced by variability in phytoplantkon community composition in the waters of Long Island, New York. Field studies conducted during 1999 and 2000 compared juvenile quahog growth and phytoplankton assemblages between West Sayville (WS), an embayment in Great South Bay along Long Island’s south shore where quahog landings have recently declined, and Oyster Bay (OB), an embayment on Long Island’s north shore where quahog landings are still high. Quahogs grew better at OB than WS during both study years. Centric diatoms were typically the dominant phytoplankton species at OB, and pennate diatoms and dinoflagellates characterized WS. At WS, the phytoplankton community consisted of heterotrophic dinoflagellates during a brown tide in 2000 and pennate diatoms afterward. Nanoflagellates were abundant (105–106 cells ml−1) at WS throughout the summer of 2000. Multiple regression analysis revealed a significant effect of site and temperature on individual clam biomass during both years, but brown tide was only significant during 2000. Biomass comparisons of dominant phytoplantkon taxa with laboratory physiology studies showed that 0B, with its abundance of centric diatoms, likely represented a more nutritional diet for quahogs than pennate diatoms, which were abundant at WS. Small flagellates, which were common at WS, may also have been important for sustaining growth during some months. Variability in plankton assemblages between OB and WS likely represented two distinct, diets that were critical influences on clam growth.