Gisèle Muller-Parker

The effects of temperature and light on two algal populations in the temperate sea anemone Anthopleura elegantissima (Brandt, 1835)

The effects of temperature (13 °C and 20 °C) and irradiance (low light (LL) = 10 μmol/m2/s; high light (HL) = 137 μmol/m2/s) on the population density of two symbiotic algae in the tentacle region of the intertidal sea anemone Anthopleura elegantissima (Brandt) were examined in this study. Anemones contained zooxanthellae (brown anemones), zoochlorellae (green anemones), or a mixture of both algae (mixed anemones). Temperature and light have different effects on zooxanthellae and zoochlorellae, resulting in changes in the algal complement of A. elegantissima. High temperature caused a significant decrease in the density of zoochlorellae over 25 days (in green anemones: −32 and −20 algae/μg tentacle protein per day under HL and LL, respectively) and a reduction in algal mitotic index (from 15% to < 5% cells dividing after 6 days). Low light caused a significant increase in the density of zooxanthellae over 25 days (in brown anemones: +15 and +20 algae/μg tentacle protein per day at 13 °C and 20 °C, respectively). Overall, temperature had a greater effect than light on the population density of algae in the tentacles of A. elegantissima; the percent change in zoochlorellae density in tentacles of anemones held at 20 °C was significantly less (in green anemones, −69%) than changes obtained with all other symbiont-temperature interactions. Zooxanthellae and zoochlorellae in mixed anemone tentacles showed the same population density response to the treatments as zooxanthellae and zoochlorellae in brown and green anemones, respectively. Population densities of both algal symbionts are regulated by temperature and light, and the relative abundance of each alga in a host anemone may be shifted with changes in these environmental factors.

Nutritional Role of Two Algal Symbionts in the Temperate Sea Anemone Anthopleura elegantissima Brandt

The intertidal sea anemone Anthopleura elegantissima in the Pacific Northwest may host a single type of algal symbiont or two different algal symbionts simultaneously: zooxanthellae (Symbiodinium muscatinei) and zoochlorellae (green algae; Trebouxiophyceae, Chlorophyta). A seasonal comparison of zooxanthellate and zoochlorellate anemones showed stable symbiont population densities in summer and winter, with densities of zoochlorellae about 4 times those of zooxanthellae. Photosynthesis-irradiance curves of freshly isolated symbionts show that the productivity (Pmax cell) of freshly isolated zooxanthellae was about 2.5 times that of zoochlorellae during July; comparable rates were obtained in other months. Models of algal carbon flux show that zoochlorellae may supply the host with more photosynthetic carbon per unit anemone biomass than zooxanthellae supply. Zooxanthellate anemone tissue was 2‰ (13C) and 5‰ (15N) enriched and zoochlorellate anemone tissue was 6‰ (13C) and 8‰ (15N) enriched over their respective symbionts, suggesting that zoochlorellate anemones receive less nutrition from their symbionts than do zooxanthellate individuals. The disparity between predicted contributions from the algal carbon budgets and the stable isotopic composition suggests that short-term measures of algal contributions may not reflect actual nutritional inputs to the host. Isotopic data support the hypothesis of substantial reliance on external food sources. This additional nutrition may allow both algae to persist in this temperate intertidal anemone in spite of differences in seasonal photosynthetic carbon contributions.

CHANGES IN THE ULTRASTRUCTURE OF SYMBIOTIC ZOOXANTHELLAE (SYMBIODINIUM SP., DINOPHYCEAE) IN FED AND STARVED SEA ANEMONES MAINTAINED UNDER HIGH AND LOW LIGHT1

The ultrastructure of symbiotic dinoflagellates (Symbiodinium sp., zooxanthellae) in the sea anemone Aiptasia pallida Verrill was examined in well‐fed or starved (up to 120 days) anemones maintained under two light levels (5 and 50 μmol · m−2· s−1). Cell size of zooxanthellae was not affected by feeding history; however, both light and feeding history affected the relative cell volume of chloroplasts, lipids, and vacuoles. Stereological analysis of transmission electron micrographs showed that algae in low‐light starved anemones had 10 times as much lipid (17.4% of cell volume) as those in well‐fed anemones under the same light conditions (1.8%). The lipid content of algae from anemones in high light increased from 15.4% in well‐fed anemones to 30.1% in starved anemones. The starch content of zooxanthellae in low‐light anemones was law (4.1%) and not affected by feeding history, while the starch content of zooxanthellae in high‐light anemones was greater (10.7%), with some differences among groups. Algal photoacclimation to low light included an increase in chloroplast relative volume from 17% (in well‐fed high‐light anemones) to 33% in well‐fed low‐light anemones. Starvation of the host resulted in a significant decrease in chloroplast volume in zooxanthellae in anemones at both light levels. Morphometry provides quantitative confirmation of biochemical and physiological data on zooxanthellae, because the changes in zooxanthellae with starvation of the host are consistent with other indicators of nutrient limitation of zooxanthellae of A. pallida held without food for long periods of time.

Ammonium enhancement of dark carbon fixation and nitrogen limitation in zooxanthellae symbiotic with the reef coralsMadracis mirabilis andMontastrea annularis

The nutrient status (limitation vs sufficiency) of dinoflagellates (zooxanthellae) symbiotic with reef corals in Bermuda was assessed in 1989 and 1990 by measuring the enhancement of dark carbon fixation with 20 μM ammonium by isolated symbionts. A colony ofMadracis mirabilis was kept in the laboratory and fed daily or starved for one month. Symbionts from fed portions of the colony had ammonium-enhancement ratios (NH4dark+; SWdark;SW=seawater without added ammonium) similar to those of the original field population (1.2 to 1.3). Ammonium-enhancement ratios increased with starvation of the host (x≧1.7) as did values forVD′:VL [(ammonium dark rate-seawater dark rate): light rate in seawater]. Both parameters indicated decreasing nitrogen sufficiency of the algae when the host was not fed, but starvation appeared to affect these algae less than symbionts of sea anemones. Field samples of zooxanthellae fromM. mirabilis (Three Hill Shoals and Baileys Bay Flats) yielded results similar to those for fed corals, but those taken from Baileys Bay Flats in May 1990 yielded exceptionally high values for enhancement (>3) andVD′:VL indicating pronounced nitrogen limitation at the time of sampling. We sampled zooxanthellae from populations ofMontastrea annularis at 8 m (Three Hill Shoals) and 24 m (Soldiers Point) depths. Enhancement andVD′:VL values for zooxanthellae from the 8 m corals were density-dependent: symbionts from corals with “normal” symbiont densities displayed the most nitrogen limitation (enhancement values=1.4 to 2.0), while those from bleached corals with lower density exhibited enhancement andVD′:VL values typical of nitrogen-sufficient algae. Symbionts isolated from the 25 m corals yielded the highest values, and appeared to exhibit the least nitrogen-sufficiency for this species.

Phylogenetic Placement of "Zoochlorellae" (Chlorophyta), Algal Symbiont of the Temperate Sea Anemone Anthopleura elegantissima

At northern latitudes the sea anemones Anthopleura elegantissima and its congener A. xanthogrammica contain unidentified green chlorophytes (zoochlorellae) in addition to dinophytes belonging to the genus Symbiodinium. This dual algal symbiosis, involving members of distinct algal phyla in one host, has been extensively studied from the perspective of the ecological and energetic consequences of hosting one symbiotic type over the other. However, the identity of the green algal symbiont has remained elusive. We determined the phylogenetic position of the marine zoochlorellae inhabiting A. elegantissima by comparing sequence data from two cellular compartments, the nuclear 18S ribosomal RNA gene region and the plastid-encoded rbcL gene. The results support the inclusion of these zoochlorellae in a clade of green algae that form symbioses with animal (Anthopleura elegantissima), fungal (the lichen genus Nephroma), and seed plant (Ginkgo) partners. This clade is distinct from the Chlorella symbionts of Hydra. The phylogenetic diversity of algal hosts observed in this clade indicates a predisposition for this group of algae to participate in symbioses. An integrative approach to the study of these algae, both within the host and in culture, should yield important clues about how algae become symbionts in other organisms.

ELLIPTOCHLORIS MARINA SP. NOV. (TREBOUXIOPHYCEAE, CHLOROPHYTA), SYMBIOTIC GREEN ALGA OF THE TEMPERATE PACIFIC SEA ANEMONES ANTHOPLEURA XANTHOGRAMMICA AND A. ELEGANTISSIMA (ANTHOZOA, CNIDARIA)(1).

Symbiotic green algae from two species of intertidal Pacific sea anemones, Anthopleura elegantissima and Anthopleura xanthogrammica, were collected from the northeastern Pacific coast of North America across the known range of the symbiont. Freshly isolated Anthopleura symbionts were used for both morphological and molecular analyses because Anthopleura symbiont cultures were not available. Light and transmission electron microscopy supported previous morphological studies, showing the symbionts consist of spherical unicells from 5 to 10 μm in diameter, with numerous vesicles, and a single bilobed chloroplast. Pyrenoids were not seen in LM, but a thylakoid‐free area was observed in TEM, consistent with previous findings. Many algal cells extracted from fresh anemone tissue were observed in the process of division, producing two autospores within a maternal cell wall. The morphology of the green symbionts matches that of Elliptochloris Tscherm.‐Woess. Molecular phylogenetic analyses of the nuclear SSU rDNA and the plastid encoded gene for the large subunit of RUBISCO (rbcL) support the monophyly of these green algal symbionts, regardless of host species and geographic origin. Phylogenetically, sequences of the Anthopleura symbionts are nested within the genus Elliptochloris and are distinct from sequences of all other Elliptochloris spp. examined. Given the ecological and phylogenetic distinctions among the green algal symbionts in Anthopleura spp. and the named species of Elliptochloris, we designate the green algal symbionts as a new species, Elliptochloris marina (Trebouxiophyceae, Chlorophyta).

BROAD THERMAL TOLERANCE OF THE SYMBIOTIC DINOFLAGELLATE SYMBIODINIUM MUSCATINEI (DINOPHYTA) IN THE SEA ANEMONE ANTHOPLEURA ELEGANTISSIMA (CNIDARIA) FROM NORTHERN LATITUDES1

The sea anemone Anthopleura elegantissima (Brandt) hosts two species of symbiotic dinoflagellates, known as zooxanthellae, which coexist within the host at southern latitudes only. One of these species, Symbiodinium muscatinei LaJeunesse et Trench, has a broad latitudinal distribution, occurring in intertidal anemones from Washington state to Southern California. To investigate whether high thermal tolerance contributes to the ability of S. muscatinei to inhabit anemones from northern and southern regions, the upper thermal tolerance limit for photosynthesis of symbionts in northern (48°24′ N) populations of A. elegantissima was determined by subjecting anemones to a gradual increase in temperature from 12°C to 30°C over a 10‐week period. Light‐saturated photosynthetic rates of isolated zooxanthellae were the same over the range of 12°C–24°C and declined significantly at 26°C, which is 14°C and 5°C above average summertime seawater temperatures in northern Puget Sound and Southern California, respectively. At 28°C, zooxanthellae isolated from the anemones, and those expelled by their hosts, exhibited extremely low rates of photosynthesis and highly reduced chl content. The photosynthetic rates and chl content of expelled zooxanthellae were lower than those of retained zooxanthellae. The high thermal tolerance of S. muscatinei isolated from northern populations of anemones supports the broad latitudinal distribution of this symbiont, allowing it to coexist with S. californium (#383, Banaszak et al. 1993 ) in southern populations of anemones.

LOW THERMAL LIMIT OF GROWTH RATE OF SYMBIODINIUM CALIFORNIUM (DINOPHYTA) IN CULTURE MAY RESTRICT THE SYMBIONT TO SOUTHERN POPULATIONS OF ITS HOST ANEMONES (ANTHOPLEURA SPP.; ANTHOZOA, CNIDARIA)1

Symbiodinium californium (#383, Banaszak et al. 1993 ) is one of two known dinoflagellate symbionts of the intertidal sea anemones Anthopleura elegantissima, A. xanthogrammica, and A. sola and occurs only in hosts at southern latitudes of the North Pacific. To investigate if temperature restricts the latitudinal distribution of S. californium, growth and photosynthesis at a range of temperatures (5°C–30°C) were determined for cultured symbionts. Mean specific growth rates were the highest between 15°C and 28°C (μ 0.21–0.26 · d−1) and extremely low at 5, 10, and 30°C (0.02–0.03 · d−1). Average doubling times ranged from 2.7 d (20°C) to 33 d (5, 10, and 30°C). Cells cultured at 10°C had the greatest cell volume (821 μm3) and the highest percentage of motile cells (64.5%). Growth and photosynthesis were uncoupled; light‐saturated maximum photosynthesis (Pmax) increased from 2.9 pg C · cell−1 · h−1 at 20°C to 13.2 pg C · cell−1 · h−1 at 30°C, a 4.5‐fold increase. Less than 11% of daily photosynthetically fixed carbon was utilized for growth at 5, 10, and 30°C, indicating the potential for high carbon translocation at these temperatures. Low temperature effects on growth rate, and not on photosynthesis and cell morphology, may restrict the distribution of S. californium to southern populations of its host anemones.

Increasing Diversity in the Marine Sciences Through the Minorities in Marine Science Undergraduate Program

The Minorities in Marine Science Undergraduate Program (MIMSUP) is an academic program at Western Washington Universitys Shannon Point Marine Center (SPMC) that seeks to increase the representation of minority individuals in the marine sciences. For the past 13 years, groups of students have spent two 10-week quarters at SPMC studying marine science, doing independent research, and developing the skills needed for success as marine scientists/educators. Program elements include formal coursework in marine science, supervised independent research, training in up-to-date field and laboratory investigative techniques, experience developing scientific and personal job-related skills, and introduction to the career options open to marine scientists. Results indicate that the program is impacting the career paths of student participants; program alumni seek advanced education and pursue careers in the marine and environmental sciences. MIMSUP introduces underrepresented students to the marine sciences, helps them develop greater confidence in their potential, and prepares them for successful careers in this field.