Changes in the abundance and distribution of sav along Florida’s springs coast: a comparison based on aerial photography acquired in 1992 and 1999

More bang for your buck: multiple defensive roles of sponge triterpene glycosides

Julia Kubanek,¹* Kristen E. Whalen,² Sebastian Engel,² Sarah R. Kelly,² Timothy P. Henkel,² William Fenical,³ and Joseph R. Pawlik.^{2 1}Georgia Institute of Technology, School of Biology, Atlanta, GA 30332-0230, USA; ²University of North Carolina at Wilmington, Center for Marine Science, Wilmington, NC 28403, USA; ³Scripps Institution of Oceanography, Center for Marine Biotechnology and Biomedicine, La Jolla, CA 92037-0204, USA.

Despite high nutritional value and a lack of physical defenses, most marine sponges appear to be minimally affected by predators, competitors, and fouling organisms, possibly due to sponge chemical defenses. In the last fifteen years, several triterpene glycosides have been isolated from sponges, but their ecological or physiological roles are largely unknown. We tested triterpene glycosides from Erylus formosus and Ectyoplasia ferox, Caribbean sponges belonging to two different orders, in field and laboratory assays for effects on fish feeding, attachment by potential biofilm-forming bacteria, fouling by invertebrates and algae, and overgrowth by neighboring sponges. Formoside and other triterpene glycosides from Erylus formosus deterred predation, microbial attachment, and fouling by invertebrates and algae. Triterpene glycosides from Ectyoplasia ferox were found to be antipredatory and allelopathic. Thus, triterpene glycosides in these sponges appear to have multiple ecological functions. Tests with different triterpene glycosides at several concentrations indicated that small differences in molecular structure affect ecological activity.

Getting over the hump: barriers to dispersal and the northward spread of asexual populations of the genus Mastocarpus in the Atlantic and Pacific

Janet Kübler and Steve Dudgeon. Department of Biology, California State University, Northridge, CA 91330-8303, USA.

It is often assumed that asexual populations, being free of the need to find mates, can disperse farther and faster than sexually reproducing populations. One would expect this pattern to be even more pronounced for taxa with heteromorphic alternation of generations that include a slow-growing crustose phase in the sexual life cycle. Difference in the rate of postglacial recolonization of the temperate north after the last ice age might, hypothetically explain the more northerly distributions of asexual populations in numerous taxa. If asexual populations could recolonize the north more quickly, the appearance of a geographic barrier to dispersal during recolonization should be reflected in their current distributions. We use existing and new data for the geographic distributions of sexual and asexual variants of Mastocarpus papillatus in the Pacific and Mastocarpus stellatus in the Atlantic to test this hypothesis. We used logistic regression to determine where along their respective coasts mixed populations switch from predominantly one life history type to the other. In the case of M.papillatus, the outflow of freshwater into the Pacific from San Francisco Bay may be a recent dispersal barrier. Similarly, the English Channel may inhibit northward dispersal of M. stellatus from the Atlantic coast of Iberia to the British Isles.


Physiology in the field: large and small-scale gradients of photosynthetic performance in fucoid algae

M. Lamote,^1,2 Y. Lemoine,² and L. E. Johnson.¹* ¹G.I.R.O.Q., Université Laval, Québec, G1K 7P4, Canada; ²Laboratoire de cytophysiologie végétale et Phycologie, Université de Lille I, 59575 Villeneuve d’Ascq, France.

Physical conditions experienced during low tide may affect the performance of intertidal algae thereby contributing to their patterns of distribution. Québec rocky shores are dominated by three fucoid algae Ascophyllum nodosum, Fucus vesiculosus, Fucus distichus, which can form distinct zones. We investigated the photosynthetic activity of various stages of these algae as measured by pulse-amplitude modulated (PAM) fluorometry under a variety of different meteorological regimes, including the sunny and windy conditions that exacerbate thallus dehydration. For adult plants, photosynthesis continued for several hours after emersion before photoinhibition (i.e., reduced photosynthetic efficiency, Fv/Fm) was observed. Differences among species corresponded with their position on the shore with adults of the lowest distributed species, F. distichus, showing the quickest and most dramatic evidence of photoinhibition, especially under sunny-windy conditions. Early stages (3 wk-old) of all species responded more quickly than adult stages, and no differences were seen among the different species, suggesting possible ontogenetic shifts in their response to environmental conditions. More fine-scale measurements on F. distichus showed that photosynthesis is highly sensitive to vertical position on the shore and appears to be determined by rates of evaporation. Because desiccation is controlled by environmental conditions, differences in recruitment observed between different tidal heights and different years may depend on the variation in the frequency, timing, and duration of particularly stressful meteorological conditions that reduce growth and survival.

An ecophysiological approach to understanding patterns of nitrate reduction

in estuarine macroalgae

Julien Lartigue¹* and Tim D Sherman.^{2 1}University of South Alabama, Department of Marine Sciences; LSCB-25, Mobile, Alabama 36688-0002, USA, and Dauphin Island Sea Lab, 101 Bienville Blvd, Dauphin Island, AL 36528, USA; ²University of South Alabama, Department of Biological Sciences, LSCB-124, Mobile, Alabama 36688-0002, USA.

In estuaries, freshwater input can lead to substantial changes in the amount and form of inorganic nitrogen available to macroalgae. Whether macroalgae are able to translate this pulsed supply of inorganic nitrogen, especially nitrate, into production depends on how quickly rates of nitrate assimilation can be increased. In turn, the assimilation of nitrate is rate-limited by the reduction of nitrate to nitrite by the enzyme nitrate reductase (NR). A novel NR activity assay developed for use in the laboratory and field was employed to determine if Enteromorpha sp. (Chlorophyceae) and Gelidium sp. (Rhodophyceae) from Mobile Bay, AL are able to access pulses of nitrate entering the estuary. Seasonal field measurements demonstrated that NR activity increases as much as 3-fold following pulses of less saline, nitrate-rich water. However, other environmental factors, including temperature and light, were also significant predictors of NR activity. Surprisingly, NR activity was not completely inhibited in the presence of appreciable amounts of ammonium, although NR activity and ammonium had a significant negative correlation. Physiological factors, such as internal nutrient stores and protein levels, were not correlated to NR activity. Laboratory experiments on Enteromorpha sp. demonstrated that NR activity begins to increase when nitrate becomes available and peaks after approximately 3 hr, while nitrate uptake rates slowly decline as internal stores of nitrate increase. Following nitrate pulses, NR activity remains elevated for at least 12 hr, even in nitrate-depleted waters. To date, this work indicates that estuarine Enteromorpha sp. and Gelidium sp. are able to take up and reduce nitrate when delivered in pulses. Furthermore, external, environmental factors (i.e. water column nutrients), rather than internal, physiological factors (i.e. internal nutrient stores) are more influential in determining rates of nitrate reduction.


Fertilization success on a surface brooding gorgonian

Howard R. Lasker.* Department of Biological Sciences, University at Buffalo, Buffalo, NY 14260, USA.

In the Bahamas, the Caribbean gorgonian Pseudopterogorgia elisabethae spawns during 3-5 day periods after the new moon during November and December. Female colonies release eggs that remain on the surface of the colony. Eggs are fertilized on the surface, develop over several days after which time the planulae are washed off by wave and current action. Male spawning has not been directly observed. Among other surface brooding species distance between males and females can be a critical factor affecting the successful fertilization of released eggs and low fertilization rates have been observed in nature. However, fertilization among P. elisabethae eggs was high during spawning in December 2001 regardless of local colony density. Eggs were collected from 18 different P. elisabethae colonies on San Salvador Is. in the Bahamas and inspected for signs of development as an assay of fertilization. Over the 5 days that spawning was observed, 88% of the 15,214 collected eggs had initiated development. Fertilization success was lowest on the first and last days of spawning but even on those days was sometimes greater than 50%. Eggs collected from different colonies had differing levels of fertilization success but that pattern best correlates with which days the colony spawned. There was no apparent relationship between fertilization rate and local (with 2 m) population density. One of the highest fertilization rates occurred on a colony that only had 3 other colonies within 2 m and all three were over 1 m away from the colony. Male density ultimately will have some affect on fertilization rates, but at the densities found on San Salvador close proximity was not required to assure fertilization.


Behavior of grouped spiny lobsters, Palinurus argus, under attack by piscine predators, Balistes capriscus

Kari L. Lavalli,¹* William F. Herrnkind,² Michael Childress,³ and Andrew Evans.^{1 1}Department of Biology, Southwest Texas State University, 601 University Drive, San Marcos, TX 78666, USA; ²Department of Biological Science, Florida State University, Tallahassee, FL 32306-1100, USA; ³Department of Biological Sciences, Clemson University, Clemson, South Carolina 29634, USA.

Mesocosm experiments at the Keys Marine Laboratory were performed to investigate the effects of predatory triggerfish, Balistes capriscus, on the grouping and defensive behavior of free-roaming spiny lobsters, Panulirus argus in 2000. Lobsters in groups of 1, 3, 5, 10, and 20 were exposed to 5 triggerfish after acclimation to mesocosm conditions for 1-2 hours. Group sizes were observed every 5 min for 3 hours. Lobsters showed a bimodal distribution in group size and were found commonly as either 1-3 individuals or >3, >7, and >15 individuals for 5, 10, and 20 lobsters, respectively. Examination of distributions per hour revealed that lobsters formed fewer large groups initially, but coalesced into larger groups as the number of fish attacks increased over time. The point at which an individual lobster was subdued and killed influenced the overall pattern of group size distributions, such that larger groups were formed shortly after the death of a lobster. These results indicate that (a) predator presence strongly influences the development of lobster defensive rosettes, and (b) increased exposure to attacking fish drives the development of larger and larger rosettes of lobsters. Behavioral interactions were also videotaped and scored to determine the type and frequency of lobster counter-attack measures during fish attacks. The behavioral data was further analyzed to determine frequency differences between attack countermeasures by single lobsters and by individual lobsters remaining within a group. These data will be discussed with regard to the benefits of group living.


Spatial displacement of the snail Melampus bidentatus by a sympatric salt marsh snail

Sarah Lee* and Brian Silliman. Department of Ecology and Evolutionary Biology, Brown University, Providence, RI 02912, USA.

The role that biotic interactions such as competition and habitat amelioration play in structuring salt marsh plant communities has been the subject of much exploration. Few studies, however, have examined the importance of interspecific interactions in determining the distribution of salt marsh animals. Here, we examined the possibility that the distribution of the snail Melampus bidentatus in salt marshes on Sapelo Island, Georgia, was limited by direct (i.e., competition) or indirect (through habitat alteration) interactions with another abundant gastropod, Littoraria irrorata. Cages were used to determine the effects of shading and Littoraria densities on the abundance of Melampus. Choice experiments were conducted in the lab to ascertain whether Melampus avoided cues present in Littoraria mucus. Under natural conditions, both snails were rare in the low marsh, with Littoraria and Melampus dominating middle and high marsh, respectively. In the middle marsh, removal of Littoraria and light reduction significantly increased densities of Melampus. Adding Littoraria in the high marsh significantly decreased Melampus densities, and the choice experiment demonstrated that Melampus used mucus cues to avoid Littoraria. Although Littoraria clearly are not the only determinants of of Melampus distribution, our results suggest that Melampus avoid high densities of Littoraria. This behavior is likely evoked by both a reduction in the shade canopy due to Littoraria grazing and by cues present in Littoraria mucus. These preliminary analyses suggest that interspecific interactions play an important role in structuring the macroinvertebrate community in these marshes.


Crab predation prevents the successful reestablishment of sea urchins in Maine

Amanda V. Leland* and Robert S. Steneck. University of Maine, Darling Marine Center, 193 Clark’s Cove Rd., Walpole, ME 04573, USA.

Green sea urchins (Strongylocentrotus droebachiensis) have been extirpated by overfishing in vast areas of the Gulf of Maine over the last 15 years. We examined the hypothesis that the reintroduction of adult urchins can aid in population recovery. In two separate trials (August 2000 and April/May 2001), we relocated 3000 adult urchins to each of 9 sites in an area where urchins were once abundant but are now depleted. In both trials, urchin abundance declined dramatically in the latter part of August and early part of September, when large migratory crabs (Cancer borealis) invaded the area. These crabs were significantly larger and more abundant at all relocation sites in August and September 2001 than they had been prior to or after that period. In addition, crabs were significantly more abundant at urchin relocation sites than control sites during this time suggesting that crab predators were actively seeking urchin prey. We propose that serial overfishing of multiple trophic levels in coastal Maine may have relaxed crab population controls so that they may maintain this system free of herbivores.


Analysis of genetic variation in mtMSH in the genus Leptogorgia (Cnidaria: Octocorallia) and implications for studying population structure

Andrea LePard* and Scott C. France. Department of Biology, University of Charleston, SC, Charleston, SC, USA.

The mitochondrial genome is often used in analyses of genetic structure because of its usefulness at a variety of taxonomic levels. Previous studies of octocorals have shown little intraspecific variation within the mitochondrial genome. However, mtMSH (mitochondrial MutS homolog, a putative mismatch repair gene), a marker unique to octocorals, has shown relatively high-levels of variation between species. The objectives of this study are to determine if mtMSH will be a variable marker on the intraspecific level. To test this hypothesis, we analyzed mtMSH DNA sequences of the octocoral Leptogorgia virgulata from the U.S. east and Gulf coasts, which we expected would be divided into subpopulations due to isolation by distance.

We have sequenced the entire mtMSH gene (≈3000 bp) in Leptogorgia virgulata, L. hebes, and L. chilensis. We have found little variation within the genus and no intraspecific variation in mtMSH within these three species. We also sequenced the non-coding region (NCR) between COI and COII and found the same result. Lack of intraspecific variation within the sequenced mitochondrial DNA regions could be a result of several processes. If the product of mtMSH is functional in mismatch repair, it would lower mutation rate in mitochondrial DNA, which would eliminate possible variation. High levels of gene flow between populations would also account for low variation. We are now looking at nuclear gene regions to evaluate these alternate hypotheses.

Can trophic interactions drive salt marsh succession? Using restoration and invasion research to untangle the trophic web

L. Levin,¹* T. Talley,¹ P. McMillan,¹ C. Neira,¹ G. Mendoza,¹ S. Moseman,¹ C. Forder,¹ C. Whitcraft,¹ C. Currin,² R. Michener.^{3 1}Integrative Oceanography Division, Scripps Institution of Oceanography, La Jolla, CA 92093-0218, USA; ²National Ocean Service, 101 Pivers Island Road, Beaufort, NC 28516, USA; ³Boston University Stable Isotope Lab, Department of Biology, 5 Cummington St., Boston, MA 02215, USA.

Fundamental interest in maintaining healthy wetlands has focused attention on ecosystem function. The key salt marsh trophic support functions appear straightforward, but detailed trophic webs are difficult to infer when one cannot determine what organisms are assimilating. We employed direct gut content observations, natural abundance stable isotopic analyses, and C-13 tracer studies to evaluate macrofaunal successional shifts in faunal trophic structure as vascular vegetation cover developed in a created Spartina foliosa marsh in Mission Bay, California. Results from this and related studies suggest that bottom-up processes (changing microalgae/detritus availabilities) generate transitions in marsh macrofauna from insect-dominated to annelid-dominated communities in the restored marshes of southern California. Spartina (alterniflora-foliosa) hybrid invasion on unvegetated tidal flat habitat in San Francisco Bay appears to drive a similar successional scenario, but with different macrofaunal players. These studies exemplify the potential for invasion and restoration sites to provide large-scale "experiments" that elucidate determinants of wetland structure and function.

Reproductive isolation among the Montastraea annularis species complex

Don R. Levitan¹* and Nancy Knowlton.^{2 1}Department of Biological Science, Florida State University, Tallahassee, FL 32306-1100; e-mail [e-mail]; ²Marine Biology Research Division, Scripps Institution of Oceanography, La Jolla, CA 92093; e-mail [e-mail].

There is an ongoing discussion on the nature of species and speciation in corals. Many coral species spawn simultaneously, have compatible gametes, and perhaps hybridize intermittently. Three western Atlantic corals, Montastraea annularis, M. faveolata, and M. franksi all spawn sympatrically on the same evenings after the full moons of late summer and early fall. There has been a controversy as to whether these taxa are truly different species and in particular, given their pattern of spawning, whether they are reproductively isolated. Here we report on laboratory studies of gamete compatibility and field studies of spawning times, gamete dispersal, and fertilization success in both Panama and the Bahamas over multiple years. The results indicate that temporal differences in spawning, sperm aging, egg dispersal, and gametic incompatibility act in various combinations among the three species to render hybrid fertilization unlikely.


Distribution of Tritonia sp., a tritoniid opisthobranch, on a Bahamian patch reef

Cynthia L. Lewis,* Meredith A. Dorner,* and Evelyn Luna. Buffalo Undersea Reef Research, Department of Biological Sciences, State University of New York at Buffalo, Buffalo, NY, 14260, USA; telephone [phone].

Small tritoniid opisthobranchs, probably Tritonia hamnerorum, were observed on both Gorgonia flabellum and G. ventalina along the seaward portion of a patch reef off Rocky Point, San Salvador, Bahamas. Although both the gorgonian species and the nudibranchs were clumped, the gorgonians were distributed around the reef while the nudibranchs were observed only on the seaward side of the reef. G. ventalina colonies were significantly larger and more abundant than G. flabellum. Nudibranchs showed no significant preference for one species of gorgonian over the other based on either the number of colonies or total surface area of the gorgonians in the transects where the nudibranchs were observed. Nudibranchs were only observed on colonies with a surface area smaller than 0.35 m². Among colonies containing Tritonia, no relationship was found between the size of the gorgonian and the number of tritoniid nudibranchs present. The number of tritoniid nudibranchs observed on individual sea fans varied between two consecutive days.


Patterns of benthic community structure and differential recruitment in Narragansett Bay, Rhode Island (USA)

Emily L. Lindsey,* Andrew H. Altieri, and Jon D. Witman. Department of Ecology and Evolutionary Biology, Brown University, Providence, RI 02912, USA.

Preliminary research has revealed distinctive patterns in the faunal composition of benthic communities in Narragansett Bay, RI, and suggests that differences in recruitment of benthic snails (Crepidula plana and C. fornicata) and mud crabs (Dispanopeus [Neopanope texana] sayi) correlates with the presence of blue mussel (Mytilus edulis) beds. The large-scale Mytilus recruitment in spring 2000 allowed us to test the hypothesis that predator (D. sayi) recruitment tracks prey density in this system. Crepidula and Dispanopeus recruits were collected on settlement brushes at eight subtidal (4m -5m MLW) sites in Narragansett Bay. The study sites were distinguished by flow regime. Presence of Mytilus was assumed to correlate positively with flow. “Low flow” sites had 0%-0.13% live mussel cover. “High flow” sites had 17%-61% live mussel cover. Crepidula densities were nearly ten times higher on average at sites where mussels were absent. Average densities of mud crab recruits were more than twice as high at sites where mussels were absent. These results indicate that recruitment of Dispanopeus sayi correlates positively with Crepidula recruitment and inversely with the presence of Mytilus edulis and/or flow intensity, and suggest a predator-prey relationship between D. sayi and C. spp. Additional research to test prey preference of mud crabs for Crepidula vs. Mytilus is being conducted to elucidate the underlying causes of these observed patterns.


Catastrophic disturbance, ecosystem degradation, and population phase shifts in Chesapeake Bay

Romuald N. Lipcius* and Rochelle D. Seitz. Virginia Institute of Marine Science, The College of William and Mary, Gloucester Point, VA 23062, USA.