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The information published annually by the National Science Foundation on its Graduate Research Fellowship Program (GRFP) awardees was used to create an Awardees in Ocean Sciences (AOS) data set. This data set shows that women have been successful in receiving the fellowship award in the ocean sciences, receiving an overall 69% of the awards from 1996 through 2021 (458 women among 659 awardees). Women comprised at least 50% of awardees in the six ocean sciences disciplines listed as GRFP subfields of study. The highest percentages of awards to women (72%) were in biological oceanography and marine geology/geophysics, followed by marine biology and chemical oceanography (69%), physical oceanography (67%), and ocean engineering (61%). Women were successful both as undergraduate applicants (69% of undergraduate awardees) and as graduate applicants (71% of graduate awardees). We estimate that GRFP women awardees made up 17.8% of the women obtaining doctoral degrees in oceanography from 2017 to 2021, compared with GRFP men awardees comprising 8.5% of the male doctoral recipients for the same period. Our analysis suggests future directions for study of GRFP awardees and highlights the need for data that would help inform community outreach to underserved student populations.

The National Science Foundation plans to decrease its Graduate Research Fellowship Program (GRFP) awards, which support graduate students pursuing degrees in science, technology, engineering, and mathematics (STEM) and STEM education fields, to only 1600 in upcoming competitions ([ 1 ][1]). No supporting evidence or rationale has been provided. Such cuts would likely have a disproportionate effect on women and underrepresented minorities. After the doubling of fellowships to 2000 awards in 2010, women and underrepresented minorities made substantial and sustainable gains that have grown over time ([ 2 ][2]). In the 2018 GRFP competition, nearly 58% of awardees were women, and 23% (461 individuals) identified as underrepresented minorities ([ 3 ][3]). A 20% cut in new fellowships risks narrowing the participation of these groups in the U.S. scientific workforce, especially in STEM leadership roles. Cutting the number of GRFP awards poses a threat to U.S. leadership in science and innovation. It signals to the “best and brightest” ([ 4 ][4]) U.S. citizens that their talents are valued less in the STEM workforce than in lucrative fields such as management or finance. Although the U.S. population grew by 5.8% between 2010 and 2018 ([ 5 ][5]), the number of awards has remained at 2000 for the past 10 years. This would be defensible from a policy standpoint if employment in science and engineering sectors were flat; however, such employment is steadily rising ([ 6 ][6]). The United States should be increasing federal fellowships for its citizens, not decreasing them. We urge NSF and elected leaders to cancel the cuts. GRFP recruits a diverse pool of talented early-career STEM students from a broad range of scientific fields, educational institutions, geographic regions, and economic circumstances. However, sustaining this public good demands publicly available data and a thoughtful approach to the mix of federal funding mechanisms used to support graduate students. We call for experts in graduate education and STEM workforce development to convene and consider evidence-based policies for nurturing student-centered research and innovation in the United States ([ 7 ][7]). 1. [↵][8]NSF, Graduate Research Fellowship Program Solicitation: NSF 19-590 (2019); [www.nsf.gov/pubs/2019/nsf19590/nsf19590.pdf][9]. 2. [↵][10]1. G. Muller-Parker, 2. S. E. Brennan, 3. E. C. Jones , GradEdge: Insights Grad Educ Res. 9, 4 (2020). [OpenUrl][11] 3. [↵][12]NSF, “NSF announces Graduate Research Fellowships for 2018,” News Release 18-022 (2018); [www.nsf.gov/news/news\_summ.jsp?cntn\_id=245024][13]. 4. [↵][14]1. R. B. Freeman , “Investing in the best and brightest: Increased fellowship support for American scientists and engineers” (Brookings Discussion Paper 2006-09, 2006). 5. [↵][15]U.S. Census Bureau, “Monthly population estimates for the United States: April 1, 2010 to December 1, 2020 (NA-EST2019-01)” (2019); [www.census.gov/data/tables/time-series/demo/popest/2010s-national-total.html#par\_textimage\_2011805803][16]. 6. [↵][17]National Science Board Science and Engineering Indicators, U.S. S&E workforce: Definition, size, and growth (2018). 7. [↵][18]National Academies of Sciences, Engineering, and Medicine, Graduate STEM Education for the 21st Century (The National Academies Press, Washington, DC, 2018). [1]: #ref-1 [2]: #ref-2 [3]: #ref-3 [4]: #ref-4 [5]: #ref-5 [6]: #ref-6 [7]: #ref-7 [8]: #xref-ref-1-1 "View reference 1 in text" [9]: http://www.nsf.gov/pubs/2019/nsf19590/nsf19590.pdf [10]: #xref-ref-2-1 "View reference 2 in text" [11]: {openurl}?query=rft.jtitle%253DGradEdge%253A%2BInsights%2BGrad%2BEduc%2BRes.%26rft.volume%253D9%26rft.spage%253D4%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [12]: #xref-ref-3-1 "View reference 3 in text" [13]: http://www.nsf.gov/news/news_summ.jsp?cntn_id=245024 [14]: #xref-ref-4-1 "View reference 4 in text" [15]: #xref-ref-5-1 "View reference 5 in text" [16]: http://www.census.gov/data/tables/time-series/demo/popest/2010s-national-total.html#par_textimage_2011805803 [17]: #xref-ref-6-1 "View reference 6 in text" [18]: #xref-ref-7-1 "View reference 7 in text"

The phone rang in my university office. “I'm pleased to tell you that we're funding your grant,” the program officer at the U.S. National Science Foundation (NSF) told me. I was elated. I'd spent years trying to win support for my project on sea anemones—and now I could actually do the work. But hours later, I received another call—also from NSF, responding to an application I had filed 4 months earlier. “We'd like to offer you the job as program director,” said the caller. The choice before me was stark: I could continue on my academic path, or take a leap into a very different career. ![][1] ILLUSTRATION: ROBERT NEUBECKER > “My job at NSF filled the void I felt in my academic work.” Eighteen years earlier, I'd started my faculty position eager to launch my research exploring symbiotic relationships in marine organisms. But over time, I'd become more interested in mentoring students and serving as a catalyst to help others reach their goals. When I looked back on a 4-year NSF-funded research project studying coral bleaching in the Bahamas, I realized that the most rewarding aspect of it wasn't the research; it was the impact the project had on the 18 undergraduates I took into the field with me. I'd seen them transformed by the opportunity to go beyond the classroom and get hands-on experience doing research, and I'd felt I made a difference in their lives. I had also started to feel I could have a bigger impact working outside of academia. A few years earlier, I'd taken a 2-year hiatus from my faculty job to serve as a rotating program officer at NSF, working on ocean education programs. I wanted to see how NSF worked from the inside so that I could help launch research programs at my predominantly undergraduate institution. When I went back to my faculty position, I was full of ideas about how I could help my university take advantage of NSF's programs. But my department chair told me to focus on my classes and normal faculty duties. I felt deflated. So the same month I applied for the grant, I also applied for a job overseeing NSF's fellowship program for graduate students. When both came through, I had a tough choice to make. Most of my colleagues advised me to stay in academia, where I had a satisfying job teaching and mentoring students. But my gut told me to take a chance and try something new—so I accepted the job offer. It wasn't an easy transition. My skill set and experiences were firmly rooted in academia, and at times I wondered whether I had what it takes to be an effective program director. But eventually, I realized that my academic experiences were assets to capitalize on, not obstacles to surmount. Teaching large classes had honed my communication skills, which proved essential when speaking with NSF's leadership team and the broader research community. Working with diverse students on class projects gave me the confidence to lead strong teams centered on common goals. I could also empathize with the academics I worked with and help them navigate the ins and outs of NSF. Best of all, my job at NSF filled the void I felt in my academic work. As a professor, I had an impact on scores of students each year. Now, I felt I was making a difference for the thousands of students who applied to the program each year—for instance, by revising the application materials to be more inclusive and by training reviewers to take a broader view of applicants' qualifications. I celebrated the fellows' successes as if I were their adviser. After 10 years at the agency, I retired this past May. If I'd stayed in academia, I would have maintained some status as a professor emeritus. But now, when I search for my name on NSF's staff directory, it's gone—as if I no longer exist. So, I remind myself why I chose the government: to enable others, especially students, to make new scientific discoveries and to chart their own—hopefully fulfilling—career paths. [1]: /embed/graphic-1.gif

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).

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 μm(3) ) 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.

The sea anemone Anthopleura elegantissima is a common member of intertidal communities along the west coast of North America, and can experience extended periods of increased temperature during summertime low tides. Internal body temperatures of emersed individuals of A. elegantissima were monitored in a laboratory wind tunnel and in the field, and factors influencing the anemones’ thermal experience were examined. Larger body size and aggregation with conspecifics slowed body temperature increases in controlled wind tunnel conditions. In the field, anemones in the interior of an aggregation stayed cooler than those on the edges, and microhabitat features related to light exposure and surface orientation overshadowed any direct effects of body size. In the warmest month only (July), aggregations of A. elegantissima were significantly larger at the upper limit of their distribution than they were at the mid and lower limits, suggesting aggregation in high intertidal zones may be a behavioral response to desiccation and temperature stress. As this sea anemone can host multiple species of symbiotic algae with different thermal tolerances, the ability to slow body heating may affect the type of algae hosted and thus the potential contribution of this abundant anemone to primary production in the intertidal zone.

We evaluated the seasonal stability of two algal symbiont populations in the temperate intertidal sea anemone Anthopleura elegantissima on San Juan Island, Washington, where the relatively thermally tolerant dinoflagellate Symbiodinium muscatinei coexists with the less thermally tolerant chlorophyte Elliptochloris marina. Random collection of anemones along repeatedly sampled transects over four seasons and three shore heights revealed S. muscatinei to be the dominant symbiont, with E. marina mostly limited to anemones in the lower intertidal zone. At the lowest shore height sampled (+0.2 m), the proportion of E. marina was between 40% and 50% of the total symbiont population throughout the year. Symbiont distribution patterns persisted despite considerable seasonal variation in aerial exposure, temperature, irradiance, nutrients, and phytoplankton concentration, as well as a high potential for symbiont shuffling, with mixed-symbiont assemblages occurring in 51% of all anemones sampled. Symbiont density in anemones also changed little despite three- to fourfold-higher division frequencies of both symbionts during July and November. Although the intertidal zonation of these symbionts was stable over an annual period, we predict that their spatial distributions will be responsive to longer-term environmental change, and anticipate that this anemone symbiosis will be a useful and highly tractable barometer for future climate change, with this study serving as a baseline. A diverse array of shallow-water cnidarians, including sea anemones, corals, jellyfish, and hydroids, engage in endosymbioses with phototrophic dinoflagellates (Symbiodinium spp.) that translocate photosynthetic products to their host. Many of these symbioses exhibit plasticity with respect to both the population density and genetic identity of the dinoflagellate partner, allowing them to exploit a wide range of conditions that vary spatially and temporally. In tropical systems, where cnidarian symbioses are particularly well studied, many hosts show depth-related differences in symbiont density and physiology, and also undergo predictable seasonal fluctuations in symbiont density and physiology that are correlated with environmental conditions (Fitt et al. 2000; Warner et al. 2002). In

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).

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 μm(3) ) 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.

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 (P(max) 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 per thousand ((13)C) and 5 per thousand ((15)N) enriched and zoochlorellate anemone tissue was 6 per thousand ((13)C) and 8 per thousand ((15)N) 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.

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.

The mutualistic relationship between corals and their dinoflagellate endosymbionts is a key factor in the evolutionary success of hermatypic (reef building) corals. The endosymbiotic algae benefit corals in numerous ways that have contributed to the long term persistence of coral reefs over geologic time. In this chapter we review ecological and physiological aspects of the interactions between corals and their symbiotic algae in light of recent advances in our knowledge of the diversity of these symbionts. While the role of symbiont diversity in promoting coral survival during environmental bleaching events has been a major focus of recent research, its importance in other physiological and ecological contexts such as inorganic nutrient dynamics and photosynthetic carbon fluxes has received much less attention. We suggest that cost-benefit analysis is a useful approach to examine these symbioses in the context of environmental change and human impacts upon corals and coral reefs. Weighing the costs versus the benefits of the symbiotic association under specific environmental perturbations has potential for use as an indicator of the health of not only corals but indeed the whole coral reef ecosystem. Drastic changes in the stability of the symbiosis, evidenced by changes in the ratio of zooxanthellae to animal biomass in corals, may turn out to be a useful diagnostic indicator of stresses to coral reefs. By using new tools developed to assess the stability of the symbiosis, we may be better able to understand and predict the effects of future stressors and perturbations that threaten these beautiful reef ecosystems.

Echinoderms are major predators of anemones in temperate ecosystems. The fate of two algae, zooxanthellae and zoochlorellae, after their host anemone (Anthopleura elegantissima Brandt) was consumed by the leather star Dermasterias imbricata Grube was determined in experiments conducted in July and August 2004. Productivity, photosynthetic pigments, and mitotic index (percent of cells dividing) were used as indicators of algal health; algae released after leather stars consumed their host were compared with algae freshly isolated from anemones. Two types of waste products contained algae: pellets resulting from extraoral digestion, and feces. Zooxanthellae and zoochlorellae isolated from these waste products were photosynthetic, although to different extents. For algae from feces and pellets, light-saturated photosynthetic rates (Pmax) were 85 and 13%, respectively, of Pmax of freshly isolated zooxanthellae; and were 20 and 46%, respectively, for zoochlorellae. The photosynthetic pigments and mitotic index (percent of dividing cells) were not altered by the feeding activities of the leather star. These results show that algae released by seastar predation on their hosts remain viable, and are hence available for establishing symbioses in A. elegantissima and other potential hosts.

The aeolid nudibranchAeolidia papillosa is an important predator on the sea anemone Anthopleura elegantissima, a host to two kinds of endosymbiotic algae: zooxanthellae and zoochlorellae. The possible influence of the algae on the nudibranch's predatory response to this anemone was examined in a laboratory study. In chemosensory experiments, the nudibranch detected and chose anemone scent over a seawater control, but in both chemosensory and feeding experiments showed no preference for zooxanthellate or zoochlorellate anemones. Ingestive conditioning on zooxanthellate or zoochlorellate anemones had no effect on choice of these two anemone types in chemosensory experiments. Comparisons of the productivity and photosynthetic pigments of algae obtained from nudibranch feces and from anemones show that both algae survive passage through the nudibranch gut. The productivity of fecal zooxanthellae was 1.6X greater than that of zooxanthellae freshly isolated from anemones, although the chlorophyll a content of fecal zooxanthellae was reduced. The productivity and amount of pigments were the same for zoochlorellae in nudibranch feces and freshly isolated from anemones. Comparing fecal and isolated algae, there was no significant difference in the percentage of zooxanthellae in the process of cell division. However, the percentage of dividing cells was 2.6X higher in fecal than in freshly isolated zoochlorellae (18% and 6.9% respectively). Although the endosymbiotic algae do not make their host more or less attractive to the nudibranch, this predator may play an important role in maintaining the symbiotic relationship of Anthopleura elegantissima with zooxanthellae and zoochlorellae by providing viable algae in its feces as a source for the anemone host.

The potentially lethal bleaching of invertebrates through loss of their algal symbionts is a major global conservation issue; cnidarians in such interactions could potentially withstand environmental change by having multiple symbiotic partners whose physiologies vary with critical field parameters such as temperature and light. Spatial variation in symbiont distributions in the field is a strong indicator of such potential. We show that, in an association between an abundant temperate sea anemone and its two endosymbionts, the dinophyte Symbiodinium muscatinei (zooxanthellae) and an unidentified green alga (zoochlorellae), densities and ratios of anemones’ symbionts change along a light gradient generated by intertidal caves in Washington state. In the laboratory, the photosynthetic performance of zooxanthellate anemones exceeded that of zoochlorellate anemones under high irradiance levels (.100 mmol quanta m 22 s 21 ). Further, field sampling revealed that caves are divided into three distinct regions based on anemones’ algal complements: a brown region of zooxanthellate anemones near the mouth of the cave, a green region of zoochlorellate anemones in the middle of the cave, and a white region of algae-free anemones near the back of the cave. These data, together with field reciprocal transplant experiments showing algae-free anemones’ ability to regrow algae consistent with local physical conditions, suggest that algal performance (vs. host selection) determines observed variation in these symbioses. Our results support the idea that temperate, as well as tropical, host‐symbiont associations can respond plastically to environmental change. Our data also suggest that intact symbioses in adult hosts are surprisingly stable; bleaching may be required in rearranging host‐symbiont associations.

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.

The Minorities in Marine Science Undergraduate Program (MIMSUP) is an academic program at Western Washington University's 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 t...

The phaeophyte alga Desmarestia munda (Order Desmarestiales) concentrates sulfuric acid (H2SO4) in cell vacuoles. The primary function of the accumulated acid in the alga's life history is unknown. To investigate if sulfuric acid works as a chemical defense, grazing by the sea urchin herbivore Strongylocentrotus droebachiensis on D. munda was compared to grazing on four common non-acidic phaeophyte algae (Alaria marginata, Laminaria saccharina, Costaria costata, and Nereocystis luetkeana) in multiple-choice feeding preference experiments. Both fed and starved urchins discriminated among algae; N. luetkeana and L. saccharina were consumed preferentially to D. munda and A. marginata. Fed urchins consumed a smaller quantity of A. marginata and D. munda than the starved urchins (15–28% less). The lack of preference for D. munda was not correlated with the presence of polyphenolic compounds or with nitrogen concentration. A. marginata had a high polyphenolic concentration (0.8% DM, dry mass) compared to that of the other four algae (0.08–0.24% DM). The nutritional content (C:N ratio and percent nitrogen) of the five algae ranged from 10.8 to 16.2 and from 2.08 to 3.55, respectively, but was not correlated with food choice by the urchins. Sulfuric acid made up nearly 16% DM of D. munda tissue and the pH of homogenized tissues averaged 1.99 pH units. Sulfuric acid, added to prepared food to provide a range of pH values from 1.9 to 6.2 pH units, deterred feeding by urchins at pH values ≤3.5 pH units. This result provides direct evidence that sulfuric acid at concentrations found in algal tissues deters grazing by S. droebachiensis. Therefore, acid accumulation in D. munda provides an important ecological defense against grazing by this herbivore.

In this review, we seek to develop new insights about the nature of algal-sea anemone symbioses by comparing such associations in temperate and tropical seas. Temperate seas un- dergo pronounced seasonal cycles in irradiance, temperature, and nutrients, while high irradi- ance, high temperature, and low nutrients are seasonally far less variable in tropical seas. We compare the nature of symbiosis between sea anemones ( = actinians) and zooxanthellae (Sym- biodinium spp.) in both regions to test tropical paradigms against temperate examples and to identify directions for future research. Although fewer anemone species are symbiotic in tem- perate regions, they are locally dominant and ecologically important members of the benthic community compared to the tropics. Zooxanthella densities tend to be lower in temperate anemones, but data are limited to a few species in both temperate and tropical seas. Zooxanthella densities are far more stable over time in temperate anemones than in tropical anemones, suggesting that temperate symbioses are more resistant to fluctuations in environmental parameters such as irradiance and temper- ature. Light-saturated photosynthetic rates of temperate and tropical zooxanthellae are similar, but temperate anemone hosts receive severely reduced carbon supplies from zooxanthellae during winter months when light is reduced. Symbiont transmission modes and specificity do not show any trends among anemones in tropical vs. temperate seas. Our review indicates the need for the following: (1) Investigations of other temperate and tropical symbiotic anemone species to assess the generality of trends seen in a few "model" anemones. (2) Attention to the field ecology of temperate and tropical algal-anemone symbioses, for example, how symbioses function under seasonally variable environmental factors and how zooxanthellae persist at high densities in darkness and winter. The greater stability of zooxan- thella populations in temperate hosts may be useful to understanding tropical symbioses in which bleaching (loss of zooxanthellae) is of major concern. (3) Study of the evolutionary history of symbiosis in both temperate and tropical seas. Continued exploration of the phylo- genetic relationships between host anemones and zooxanthella strains may show how and why zooxanthellae differ in anemone hosts in both environments.

The mosshead sculpin Clinocottus globiceps (Girard, 1857) feeds on the sea anemone Anthopleuru elegantissima that contains two different algal endosymbionts, zooxanthellae and zoochlorellae. During laboratory feeding experiments, the sculpin selectively fed on the tentacles of zooxanthellate anemones over those of zoochlorellate and algae-free anemones. Zoochlorellae passed through the fish gut unharmed while zooxanthellae were degraded. The productivity of zooxanthellae in the fish feces (0.20 ± 0.13 pg C cell−1 h−1) was significantly lower (93% less) than that of zooxanthellae freshly isolated from anemones (3.14 ± 0.52 pg C cell−1 h−1), whereas the productivity of fecal zoochlorellae was the same as that of freshly isolated zoochlorellae (1.21 ± 0.15 pg C cell−1 h−1). The chlorophyll content (Chl a and c) of zooxanthellae was reduced by 50% after passage through the fish gut while the chlorophyll content of zoochlorellae (Chl a and b) did not change. Selective predation on zooxanthellate anemones confers several ecological advantages to zoochlorellate anemones and to zoochlorellae, most notably predator avoidance and dispersal of viable zoochlorellae that may serve as a source of symbionts for other anemones. By influencing the outcome of predator-prey interactions involving their hosts, symbiotic algae may have broader ecological roles in benthic communities than previously described.

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.

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.

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 (NH 4dark + ; 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 forV D′:V L [(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 Bailey's Bay Flats) yielded results similar to those for fed corals, but those taken from Bailey's Bay Flats in May 1990 yielded exceptionally high values for enhancement (>3) andV D′:V L 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 (Soldier's Point) depths. Enhancement andV D′:V L 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 andV D′:V L 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.

The nutrient status of algae symbiotic with marine invertebrates is controversial. We assessed the nitrogen status of zooxanthellae symbiotic with the sea anemone Aiptasia pallida using NH,+ enhancement of dark C fixation; enhancement increases with N limitation in other microalgae. Freshly isolated symbionts obtained from laboratory populations of known feeding history and from field populations were assayed: NH,+ enhancement depended on the nutritional history of the host anemones. Zooxanthellae from well-fed laboratory populations showed little enhancement of dark 14C fixation by NH,+, while mean dark enhancement ratios (NH,’ rates: seawater rates) exceeded 2.3 for zooxanthellae from anemones unfed for l-6 weeks. Photosynthetic rates of the isolated algae declined with starvation. V,,, : V,, an index which includes both dark NH,+ enhancement and photosynthesis, increased markedly with time since feeding. Three of four field samples of A. pallida yielded zooxanthellae with dark enhancement ratios similar to those of fed laboratory populations; I’,. : V, values were somewhat higher. Symbionts from anemones collected on a fourth date had a mean enhancement ratio of 2.88, and I’,,. : V, values similar to those from laboratory anemones that had not fed for l-2 weeks, indicative of increased N limitation.