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Accumulations of green macroalgae (green tides) are becoming increasingly common in many coastal habitats and substances released by these blooms may impact other organisms. In the northeastern Pacific, a dominant contributor to green tides is Ulvaria obscura, an alga that produces dopamine which affects a variety of physiological processes and can trigger metamorphosis in marine invertebrates. Eggs, embryos, and larvae of Pacific oysters (Crassostrea gigas) and sand dollars (Dendraster excentricus) were exposed to U. obscura exudates and dopamine to determine how exposure affects fertilization, development, and morphology. Exposing eggs to these compounds had no significant effect on fertilization of C. gigas and limited impact on D. excentricus, relative to unexposed controls. Early embryos exposed to the compounds developed successfully, but the resulting C. gigas veligers had larger shells and the D. excentricus gastrulae had shorter archenterons. When exposed to dopamine, C. gigas veligers had smaller shells, while larval arms of D. excentricus were significantly shorter relative to unexposed controls. Results indicate that compounds released by U. obscura affect development differently between invertebrate species and among developmental stages. The stage-specific responses likely result from changes in structure and metabolic activity at different life history stages, as well as changes in the localization and function of dopamine and dopamine receptors that occur during larval development. The changes in larval morphology and function induced by compounds released by marine macroalgae could ultimately impact the ability of larvae to feed and survive.

Because planktonic invertebrate larvae may be food-limited, anything that increases feeding and digestive efficiency should increase the chances of larval survival to metamorphosis. As light directly enhances both feeding and digestion in some planktonic heterotrophic protists, we hypothesize that similar processes might occur in the larvae of marine invertebrates. We studied the direct effects of light on feeding and development in sea urchin larvae (Strongylocentrotus droe- bachiensis, S. franciscanus and sand dollar Dendraster excentricus). Larvae were placed in 12:12 h light:dark cycles or in complete darkness and ingestion rates were measured. We monitored larval morphology during the first 2 to 3 wk of development and tested for light-related differences. Short- term changes in light regime had no effect on feeding rates. However, larvae of all 3 species showed longer-term diel feeding patterns with ingestion rates generally higher during daylight hours. These patterns persisted in S. franciscanus larvae even when larvae were held in complete darkness for 3 d. Larvae of D. excentricus exposed to natural light cycles developed longer arms usually associated with food limitation; those held in darkness had significantly shorter arms. The developing juvenile structures (i.e., rudiments) of S. droebachiensis larvae exposed to light were significantly smaller than those of larvae held in continuous darkness, suggesting that light may have negative effects on larval growth and development. Measuring the effects of light on feeding and growth may clarify the behaviors of invertebrate larvae during their critically important planktonic period.

The solitary ascidian Corella injutu is a com- mon fouling organism in many areas of Puget Sound and the San Juan Archipelago, Washington, USA. Despite its abun- dance, it is conspicuously absent from areas that receive direct sunlight. Previous work suggests that ascidians in unshaded habitats can be overgrown and killed by algal overgrowth. In this study, we tested the hypothesis that UV irradiation contributes to C. inflatu distribution by killing individuals exposed to direct sunlight. To test this, we exposed C. infuta embryos, larvae, juveniles, and adults to UV irradiation and measured the responses. We also tested for UV-absorbing compounds in larvae, juveniles, and adults. In the laboratory, UV significantly damaged all life stages; the earliest stages were most vulnerable. A 3-week UV exposure significantly shortened adult life span. Juve- niles suffered 100% mortality after only 3 days. Tadpole larvae decreased settlement and metamorphosis after I day of UV exposure, and embryos exhibited developmental abnormalities after only 30 minutes of exposure. None of the life-history stages had apparent UV-absorbing com- pounds. Given the vulnerability of this species to UV, we suggest that its unique life-history traits (i.e., time of spawn- ing, brooding behavior, length of larval life) help it persist in its preferred habitat and avoid dispersal into inappropri- ate, UV-exposed areas.

The ascidian Corella inflata (Chordata, Ascidiacea) is common in many areas of Puget Sound, Washington, USA. However, it occurs only in habitats where it is protected from direct sunlight. Previous experiments with artificial lights showed that UV irradiation kills all life stages of this animal. The effects of natural sunlight exposure (measuring survival of adults, juveniles, larvae, and embryos) were compared. We partitioned the light spectrum to separate the effects of UVB, UVA, and visible light (PAR). Natural sunlight severely damaged C. inflata. Adults and juveniles died after 2-5 d. Exposed embryos failed to develop normally and larvae did not settle. As expected, UVB had significant effects, but pronounced effects were also seen when the animals were exposed to longer wavelengths alone (UVA and PAR). Thus, the distribution of C. inflata may be determined largely by exposure to light. Understanding the basic ecology of this species requires consideration of its vulnerability to sunlight damage and the effects of UVB, UVA, and PAR.

Larvae of many shallow-water marine invertebrates show phototactic behaviors which may allow them to exercise some control over their positions in the water column. Such behavior should be useful only in regions where light provides a consistent directional cue and might not, therefore, be expected in species found exclusively in deep water where light levels are extremely low. In this paper, we investigated larval phototactic responses in two barnacle and one prosobranch gastropod species that occur epifaunally on tropical, bathyal sea urchins. Newly released larvae of the gastropod Pelseneeria sp. did not respond to light but Stage I nauplii of both barnacle species (Verruca floridana and Paralepas pedunculata) showed strong positive phototaxis at light intensities greater than 2.66 μmol m−2s−1. Larvae are expected to encounter the threshold intensities at depths no greater than 90 m in Caribbean waters. As both barnacle species were collected at much greater depths, phototaxis (at least in the early larvae) should have little effect. The ability to detect and respond to light may foreshadow functional photoresponses in later larvae that move to shallower depths. Alternatively, the presence of photoreceptors and light responses may be interpreted as evidence that these barnacles, which now reside in the deep sea, may have originated in shallow water.

Swimming and nonswimming tadpole larvae of the ascidian Ecteinascidia turbinata Herdman were followed in situ by divers to determine whether swimming affects larval dispersal. Swimming affected neither dispersal direction nor time spent in the water column. However, the dispersal rates and distances of swimming larvae were significantly lower than those of nonswimming larvae. Potential paths of larval dispersal were modeled with subsurface drogues. Movements of both swimming and nonswimming larvae differed consistently from surface flo w direction in these shallow (1.0–1.5 m) waters, indicating that caution should be used in modeling larval dispersal with drogues, particularly when larvae do not consistently remain in surface waters. In our south Florida study site, E. turbinata colonies were present only on unanchored mangrove prop roots and survival of colonies transplanted into surroundings habitats was very low. Drogue paths demonstrated that currents could potentially carry E. turbinata between mangrove islands, but behavior of the larvae suggests that dispersal is generally very localized with larvae settling near colonies from which they were released. This behavior differs dramatically from that reported for E. turbinata larvae in a more homogeneous habitat in the northern Gulf of Mexico. The short-distance dispersal of swimming tadpole larvae inthis study may represnt a local adaptation to favor recruitment near parental habitats and to prevent advection to inappropriate sites. Long-distance exchange between isolated islands probably occurs through rafting of adult colonies on fragmented mangrove roots rather than through larval dispersal.

We manipulated live sponges in Belize, Central America, Big Pine Key, Florida (USA), and Indian River lagoon, Florida (USA) in summer/autumn, 1988. At each location, live sponges of three species were placed within 0.5 cm of ceramic tiles. Tiles with synthetic sponges positioned in the same manner and tiles with no sponges served as controls. Of 26 recruiting species analyzed, only one (Sponge sp. 6 — Indian River) was inhibited by living sponges. Four species (Perophora regina — Belize;Aiptasia pallida — Big Pine Key; andCrassostrea virginica andAscidia nigra — Indian River) recruited in greater numbers in the presence of sponges, suggesting that some larvae may be attracted rather than repelled by sponge allelochemicals. Allelopathic effects were less important than small-scale flow effects and patchy larval supply in determining recruitment patterns on surfaces adjacent to sponges.

In the coastal waters of Florida (USA) tadpole larvae of the colonial ascidian Ecteinascidia turbinata contain chemicals which make them unpalatable to planktivorous juvenile pinfish Lagodon rhomboides. Experiments demonstrate that the bright organe color of E. turbinata tadpoles is aposematic. Fish that have recently tasted larvae of E. turbinata will not attack the palatable tadpoles of Clavelina oblonga when the latter are dyed organe to resemble larvae of E. turbinata. Tadpoles of E. turbinata that have been mouthed and rejected by fish generally survive to complete a normal metamorphosis. Individual selection explains the evolution of aposematic coloration in E. turbinata better than kin selection. The identity of the defensive chemical is unknown. The unpalatable substance in larvae of E. turbinata is removed by dialysis, indicating that it has a molecular weight less than 14000 d. Larvae are not acidic, nor is the active substance denatured by doiling.

Gut analyses of five ascidian species from the San Juan Islands, Washington, Chelyosoma productum Stimpson, Pyura haustor (Stimpson), Ascidia callosa Stimpson, Boltenia villosa (Stimpson) and Styela gibbsii (Stimpson) and five species from the Atlantic coast of Florida, Herdmania momus (Savigny), Ascidia curvata (Traustedt), Ascidia nigra (Savigny), Molgula occidentals Traustedt and Styela plicata (Lesueur), indicate that solitary ascidians consume a variety of invertebrate larvae. Analysis of plankton samples collected near aggregations of live ascidians and near mimic aggregations, however, indicate that the ascidians are not significantly depleting the local supplies of larvae. Temporal and spatial patchiness in larval supply combined with selective feeding by the ascidians and escape responses of larvae are invoked to explain the lack of small scale depletion effects.