Kerry B. Clark

CHLOROPLAST SYMBIOSIS IN A NON-ELYSIID MOLLUSC, COSTASIELLA LILIANAE MARCUS (HERMAEIDAE: ASCOGLOSSA (=SACOGLOSSA): EFFECTS OF TEMPERATURE, LIGHT INTENSITY, AND STARVATION ON CARBON FIXATION RATE

The hermaeid ascoglossan slug Costasiella lilianae possesses functional symbiotic chloroplasts derived from its algal food, Avrainvillea nigricans. Symbiotic plastids continued to fix carbon after 65 days starvation, though efficiency of fixation declined about 87%. Chlorophyll level did not decline during this period.Degeneration of symbiotic plastids involved swelling and delamination of thylakoids, increase in electron density of plastids, and decrease in pyrenoid electron density. Plastids within single cells degenerate at about the same time, suggesting that individual cells phagocytize the entire complement of plastids during a brief period.Temperature strongly influenced carbon fixation, both in rate of net fixation and in production of alcohol-insoluble photosynthates. The optimum temperature for fixation was 25°C. Photosynthetic rate exhibited saturation at about 500 µ\g=elunate\ (microeinsteins). m-2 · s-1 and substantial fixation occurred at intensities as low as 25 µ\g=elunate\ · m-2 · s-1. No...

A COMPARISON OF EGG SIZE, CAPSULE SIZE, AND DEVELOPMENT PATTERNS IN THE ORDER ASCOGLOSSA (SACOGLOSSA) (MOLLUSCA: OPISTHOBRANCHIA)

Data on egg size, capsule size, development type, and the presence and nature of albumen are summarized for 32 species of Ascoglossa, including new data on 23 species from Florida and the Caribbean. Lower limits of egg sizes for Ascoglossa with lecithotrophic and capsular development were substantially lower than limits reported for other opisthobranchs, probably because of the use of albumen as nutrient reserves in species with extended development. Capsule size is a more accurate predictor of development type than egg size. The use of albumen as a nutrient resource is associated with a relatively high plasticity of development.

Seasonal variation in standing crop of the seagrassSyringodium filiforme and associated macrophytes in the Northern Indian River, Florida

Seasonal variation in the standing crop of the seagrassSyringodium filiforme and its associated macrophytes was studied in a northern basin of the Indian River, a large mesohaline lagoon in central Florida, near the northern distributional limit ofS. filiforme. The minimum standing crop occurred from February through April and the maximum in September. Two other seagrasses,Halodule wrightii andHalophila engelmannii, together with a drift algal community, occurred in the study quadrat, but were not major components of the macrophytic system. The formation of sizeable sandy patches within Indian River seagrass beds is partially due to the burrowing activities ofLimulus polyphemus. Thermal stresses associated with the northern geographicalS. filiforme range may contribute to this phenomenon by restricting annual production, hence limiting patch regrowth.

Effects of temperature on carbon fixation and carbon budget partitioning in the zooxanthellal symbiosis of Aiptasia pallida (Verrill)

Abstract Effects of temperature on carbon fixation rates and partitioning between Aiptasia pallida (Verrill) and its symbiotic alga Symbiodinium microadriaticum Freudenthal were examined by 14C incubation studies. Total fixation varied strongly with temperature, with an optimum of 32 °C. More photosynthate was translocated to the host at 12 °C (82%) than at 27 °C (63%). Partitioning among three fractions (alcohol soluble, ether soluble, and alcohol/ether insoluble) varied with temperature in Aiptasia pallida, but not in the alga. Relative partitioning between host and alga increased with time in favor of A. pallida when maintained at 12 °C, but absolute levels of translocation to the host did not change; however, photosynthate retention by the alga did decline substantially. Total fixation declined by ≈ 80% after 10 days at 12 °C. Turnover rates of fixed carbon also varied with temperature, as determined by pulse-chase studies, and the effect varied for the different fractions. These results suggest that zooxanthellae are less thermally adaptable than their hosts, and may be especially susceptible to low temperatures. Thermal effects on biochemical partitioning may have great importance in relation to growth and reproduction of animal hosts of zooxanthellae and the viability of the symbiotic relationship. These effects, combined with the pronounced effect of temperature on total photosynthate production, probably play a major role in limitation of zooxanthellal symbioses to warm waters.

Effects of temperature on products of symbiotic chloroplasts in Elysia tuca Marcus (opisthobranchia: ascoglossa)

The effect of temperature on carbon fixation of symbiotic chloroplasts in the tropical ascoglossan Elysia tuca Marcus was analyzed and compared with that of the alga Halimeda discoidea Decaisne, which serves as food and plastid source for Elysia tuca. Maximum autotrophic carbon fixation for E. tuca occurred at 15°C, and for Halimeda discoidea, at 20°C. The net fixation rate was higher for Elysia tuca than for Halimeda discoidea, suggesting that CO2 transport by the animal host is an important factor stimulating photosynthetic rate. Temperature also controlled relative production of alcohol-soluble and insoluble components. This effect may control the fate of autotrophically-fixed carbon compounds, possibly determining whether these are used for maintenance metabolism or somatic growth. This hypothesis may partially explain the greater abundance of plastid symbioses in the tropics. Similar effects may operate in zooxanthellal symbioses.