Brian L. Bingham

Rapid Assessment Survey for exotic organisms in southern California bays and harbors, and abundance in port and non-port areas

In recent decades, the world has witnessed an array of harmful invasions by exotic marine organisms. To provide the public and policymakers with better information on the status of exotic species in southern California waters, and to assess differences between port and non-port areas, a Rapid Assessment Survey of selected habitat types in sheltered waters between San Diego and Oxnard was conducted in the summer of 2000. The objectives included comparing the prevalence of exotic species among habitats and regions and between recent and past surveys; obtaining reference data for future assessments of changes in invasion status and the effectiveness of prevention or control efforts; detecting new invasions; and documenting significant range extensions. Twenty-two sites were sampled to include the three major commercial port areas in southern California, non-port-area marinas and lagoon sites. Sampling included dock fouling and adjacent soft-bottom benthos, nearby intertidal sites, and selected subtidal lagoon habitats. Samples were collected by a variety of manual techniques. Sixty-nine of the species collected are exotic, including representatives from two algal divisions and six invertebrate phyla. Ascidians are especially well-represented (14 exotic species) and widely occurring, and some bivalves and bryozoans also occur very widely. The numbers and proportions of exotic taxa were not significantly greater in port areas than in non-port areas.

Larval behavior of the ascidian Ecteinascidia turbinata Herdman; an in situ experimental study of the effects of swimming on dispersal

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.

Influence of sponges on invertebrate recruitment : a field test of allelopathy

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.

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.

EPIBIOTIC SPONGES ON THE SCALLOPS CHLAMYS HASTATA AND CHLAMYS RUBIDA : INCREASED SURVIVAL IN A HIGH-SEDIMENT ENVIRONMENT

The small free-swimming scallops, Chlamys hastata and Chlamys rubida , are frequently encrusted by the sponges Mycale adhaerens and Myxilla incrustans . It is unclear why this association exists. We hypothesized that living on scallop valves increases sponge survival by reducing the effects of sediment accumulation. Scallops were collected to measure correlations between sediment load and encrusting sponge mass. In the laboratory, the survival of sponges on living scallops and empty scallop valves was measured. Time-lapse video was used to quantify spontaneous swimming and clapping of C. hastata. In the field, both scallop size and sponge mass were significantly greater in high turbidity sites. In the laboratory, sponges on empty scallop valves experienced near complete mortality after five weeks. Manually clearing sediments increased survival but did not duplicate the high survival of sponges on living scallops, which regularly swam or clapped their valves.

Light Cycles and Gametogenesis in Three Temperate Ascidian Species

Many temperate ascidians reproduce seasonally but the factors controlling their gametogenic cycles have not been experimentally demonstrated. I tested the effects of daylength on gametogenesis in three ascidians (Boltenia villosa, Styela gibbsii, and Chelyosoma productum) by exposing animals to normal or reversed light cycles and measuring gonad and oocyte sizes. Under a normal cycle, all species followed patterns reported for field populations. B. villosa showed evidence of continuous reproduction; S. gibbsii and C. productum spawned primarily in the spring (though a secondary mid-winter spawn may also have occurred in S. gibbsii). Altering the light cycle demonstrated that the gametogenic cues differ in these three species. Gametogenesis in B. villosa and S. gibbsii was largely unaffected by a reversed light treatment but the cycle of C. productum was dramatically changed. Even in C. productum, however, the gametogenic cycle was not completely reset in the 12-month experiment. This suggests that other factors (e.g., temperature, endogenous rhythms) contribute to gametogenic control. Longer-term experiments are needed to establish the relative importance of light cycle in these species. Additional key words: tunicates, reproduction, seasonality, synchrony, daylength Synchronous spawning is critical for marine invertebrates that release gametes into the water column and rely on currents for fertilization. Water temperature, light, phytoplankton abundance, lunar cycle, and presence of conspecifics all may cue populations to synchronize spawning and maximize fertilization (reviewed by Giese & Kanatani 1987; see also Starr et al. 1990, 1991; Tyler et al. 1992). For such cues to be effective, however, some earlier signal must entrain gametogenic cycles so that gonads contain viable sperms and full-grown oocytes or ova when the spawning cue arrives. Laboratory experiments have shown that gonad growth and maturation cycles in some marine invertebrates are affected by temperature or food abundance (reviewed by Giese & Pearse 1974; see also Babcock et al. 1986; Franz 1986; Tyler 1988; Tyler & Young 1992; Tyler et al. 1992; Beauchamp 1993). Some of the clearest evidence for extrinsic control of gametogenesis, however, comes from experimental studies with light. For example, gametogenic cycles of polychaetes (Olive & Pillai 1983; Fong & Pearse 1992a,b), a cephalopod (Richard 1967), seastars (Pearse & Eernisse 1982; Pearse & Beauchamp 1986; Pearse & Walker 1986; Pearse et al. 1986a; Xu & Barker 1990), sea urchins (Pearse et al. 1986b; McClintock & Watts 1990), and a cephalochordate (Fang et al. 1989) have been altered or completely reset by simple modifications of the light cycle. Giese & Kanatani (1987) suggest that daylength may be a fairly general gametogenic cue, but to date, only a few species in a few phyla have been studied. In this paper, I report on the first test for such effects in ascidians (phylum Chordata, subphylum Urochordata). Millar (1952, 1958) and Berrill (1975) suggested that temperature controls gametogenesis in ascidians. At temperate latitudes where annual temperature fluctuations are large and predictable, gametogenic cycles could cue to temperature changes. In tropical waters where temperatures remain quite constant, absence of the temperature cue could lead to non-seasonal reproduction. Consistent with this hypothesis, temperate ascidian species often show highly seasonal reproduction (reviewed by Millar 1971; Berrill 1975) while continuous reproduction has been demonstrated for some tropical species (Goodbody 1961, 1963). However, temperature control of ascidian gametogenesis has never been tested experimentally, and Svane & Young (1989) suggest that daylength should also be considered. The hypothesis that light controls reproductive seasonality can accommodate continuously reproducing tropical species since annual changes in daylength This content downloaded from 207.46.13.129 on Sun, 26 Jun 2016 07:01:17 UTC All use subject to http://about.jstor.org/terms

Ultraviolet Radiation and Distribution of the Solitary Ascidian Corella inflata (Huntsman)

The solitary ascidian Corella inflata is a common fouling organism in many areas of Puget Sound and the San Juan Archipelago, Washington, USA. Despite its abundance, 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. inflata distribution by killing individuals exposed to direct sunlight. To test this, we exposed C. inflata 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. Juveniles suffered 100% mortality after only 3 days. Tadpole larvae decreased settlement and metamorphosis after 1 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 compounds. Given the vulnerability of this species to UV, we suggest that its unique life-history traits (i.e., time of spawning, brooding behavior, length of larval life) help it persist in its preferred habitat and avoid dispersal into inappropriate, UV-exposed areas.

Effects of sponge encrustation on the swimming behaviour, energetics and morphometry of the scallop Chlamys hastata

The effect of sponge encrustation on swimming ability of Chlamys hastata was determined by investigating swimming behaviour, scallop morphometry, and energy expended during swimming with and without commensal epibionts. Scallops swam significantly longer after sponge encrustation was removed from their shells, but no significant differences were detected in swimming elevation or distance. Scallops with sponge encrustation showed no adductor muscle hypertrophy or changes in shell morphometry compared to scallops without encrustation. However, C. hastata did exhibit scaling relationships associated with maximizing swimming efficiency. Specifically, shell width and adductor muscle mass were positively allometric with shell height, while shell mass was negatively allometric with shell height. Scallops increased their energy expenditure (both aerobic and anaerobic) during valve-clapping, but no significant difference was detected between unencrusted (43·0 μmol adenosine triphosphate [ATP] consumed during a two min escape swim) and sponge-encrusted (40·0 μmol ATP) scallops. Scallops in both treatments derived 86% of the energy used for swimming from anaerobic sources. The lack of substantial differences between scallops with and without commensal sponges is partially explained by the observation that even heavy sponge encrustation increases the immersed weight of the scallop by only 5%. The presence of a sponge encrustation does not appear to inhibit swimming by this scallop species.

Solar damage to the solitary ascidian, Corella inflata

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.

Thicker host tissues moderate light stress in a cnidarian endosymbiont

SUMMARY The susceptibility of algal–cnidarian holobionts to environmental stress is dependent on attributes of both host and symbiont, but the role of the host is often unclear. We examined the influence of the host on symbiont light stress, comparing the photophysiology of the chlorophyte symbiont Elliptochloris marina in two species of sea anemones in the genus Anthopleura. After 3 months of acclimation in outdoor tanks, polyp photoprotective contraction behavior was similar between the two host species, but photochemical efficiency was 1.5 times higher in A. xanthogrammica than in A. elegantissima. Maximum relative electron transport rates, derived from rapid light curves, were 1.5 times higher in A. xanthogrammica than in A. elegantissima when symbionts were inside intact tissues, but were not significantly different between host species upon removal of outer (epidermis and mesoglea) tissue layers from symbiont-containing gastrodermal cells. Tissues of A. xanthogrammica were 1.8 times thicker than those of A. elegantissima, with outer tissue layers attenuating 1.6 times more light. We found no significant differences in light absorption properties per unit volume of tissue, confirming the direct effect of tissue thickness on light attenuation. The thicker tissues of A. xanthogrammica thus provide a favorable environment for E. marina – a relatively stress-susceptible symbiont – and may explain its higher prevalence and expanded range in A. xanthogrammica along the Pacific coast of North America. Our findings also support a photoprotective role for thicker host tissues in reef corals that has long been thought to influence variability in bleaching susceptibility among coral taxa.