Hybridization within the species complex of the scleractinan coral Montastraea annularis

The morphologically variable reef coral previously known as Montastraea annularis (Ellis and Solander, 1786) has recently been separated into three species based on differences in morphology, behavior, allele frequencies and some life-history traits of Panamanian specimens. To further investigate the proposed reclassification and its conformity to the biological species concept we conducted reciprocal intra- and inter- specific fertilization experiments with gametes from each of the three species on Florida reefs. With one exception, self-fertilization rates were very low or zero. Within-species crosses resulted in production of planulae, as did all inter-species (hybrid) crosses, but there was much variation in fertilization success within each type of cross. In an experiment with separated gametes, hybrid crosses between M. annularis and M. franksi produced more larvae than within-species crosses for each species. Hybridization crosses between M. faveolata and the other two species produced fewer larvae than did within- M. faveolata crosses in the experiment with separated gametes, but many larvae resulted when the hybridizations were performed by mixing entire gamete bundles. Additional observations showed that M. franksi had 20% larger eggs and fewer eggs per gamete bundle than did the other two species and that it consistently spawned 1 to 1.5 h before the others, a potential temporal barrier to hybridization. These results indicate that there is no inherent pre-zygotic barrier to cross-fertilization among the three morphological species, although post-zygotic survival and fertility remain to be determined. The adherence of the proposed reclassification to the biological species concept requires further examination. Received: 16 April 1997 / Accepted: 17 June 1997     

Distribution and ecology of leptocephali of the congrid eel, Ariosoma scheelei, around Sulawesi Island, Indonesia

A survey for leptocephali around Sulawesi Island in the central Indonesian Seas during May 2001 found that the leptocephali of the congrid eel, Ariosoma scheelei, were present in all seven areas that were sampled. A total of 551 leptocephali (22–166 mm TL) were collected, and A. scheelei was by far the most abundant species of leptocephali collected during the survey. The wide range of sizes in most areas indicated that spawning had occurred during a period of several months in many different areas, although the exact spawning locations were not determined. The larger size classes were more abundant in all areas except in Tomini Bay on the northeast side of Sulawesi Island. The highest catch rates were observed at the eastern edge of the Java Sea and to the north in the Celebes Sea near Makassar Strait. Premetamorphic leptocephali were also collected in surface samples at 11 stations (N=62), but metamorphosing leptocephali (N=86) were only caught in IKMT tows that fished from the surface to about 200 m. Metamorphosing leptocephali were collected primarily at two stations in the Java Sea and Makassar Strait where a surface layer of lower-salinity water was detected. Their total lengths (105.3–153.3 mm) and the largest premetamorphic individuals suggested that this species can reach maximum sizes of about 165 mm before beginning to metamorphose. It is hypothesized that this species may be abundant in the Indonesian Seas region and that it has ecological traits such as large size at recruitment and a small size at reproduction that have made it successful in many regions of the Indo-Pacific.     

Morphology of<Emphasis Type="Italic"> Ecklonia radiata</Emphasis> (Phaeophyta: Laminarales) along its geographic distribution in south-western Australia and Australasia

Ecklonia radiata (C. Ag.) J. Agardh is a common macroalga on reefs in the warm-temperate parts of the southern hemisphere. It is a dominant habitat-former and as such has a strong structuring effect on associated algal assemblages. Morphological variation in E. radiata potentially affects its interactions with the surroundings and contributes to confusion about its taxonomy. We quantified the magnitude of morphological variation in fully developed E. radiata sporophytes across Australasia and tested the hypotheses that E. radiata has different morphology at different locations and that the degree of morphological difference depends on spatial distances among locations. A total of 11 morphological characters were sampled from 11 locations along the Australian coastline from Kalbarri in Western Australia to Sydney in New South Wales as well as from Doubtful Sound, New Zealand. Most morphological characters varied considerably from one location to another. For example, the average (±SE) thallus length was 135.2±12.5 cm in Kalbarri and only 69.7±5.5 cm in Sydney. There were no consistent spatial patterns of variation among individual morphological characters, and, generally, variations among individual characters were poorly correlated (-0.5< R<0.5). This suggests that individual morphological characters develop independently of each other in response to processes operating at different spatial scales. Multivariate measures of morphology were found to be different among some locations and similar among others (-0.37=Clarke's  R=1), but there was no correlation (Spearman's R=0.08) between morphological similarity and distance between locations. Consequently, our results do not support clinal variation in E. radiata morphology. Rather, they suggest the presence of discrete morphologically different populations, in which the morphology at any one location reflects multiple forcing factors operating on different morphological characters at different spatial scales.     

Fungi of the Bay of Fundy

During the spring and summer of 1979, 48 species of geofungi and several sterile, unidentified fungi were isolated from two off-shore stations on the Bay of Fundy, Canada. Isolations were made from subsurface water and surface slicks on 6 agar media including one containing hexadecane, and from subsurface water baited with hemp seeds. Numbers of fungi were 10 to 100 times higher than those reported for other offshore stations and similar to those reported for a saltmarsh outflow. Species isolated during a high freshwater flow largely corresponded to a typical soil flora. Species isolated during a reduced freshwater flow were either marine in character or noted for association with area littoral seaweeds. Three fungi (Cladosporium cladosporioides, Trichoderma viride, and Gliocladium rosium) were tested for growth on media of increasing salinity. Growth was measured by dry weight production, pH drop and glucose used in liquid culture. C. cladosporioides showed responses typical of a marine fungus, T. viride of a terrestrial fungus and G. roseum was intermediate. The results are discussed in relation to the role of geofungi in the sea.     

Ecology of a corallivorous gastropod,<Emphasis Type="Italic"> Coralliophila abbreviata</Emphasis>, on two scleractinian hosts. II. Feeding,respiration and growth

Coralliophila abbreviata is a corallivorous gastropod that has been observed to cause large feeding scars on reef-building corals on Floridian and Caribbean reefs. We detected differences in the population structure (length-frequency distribution and sex ratios) of C. abbreviata populations living on two coral host taxa, Acropora palmata and Montastraea spp., in the Florida Keys in a previous study. We hypothesize that diet (host) has a major influence on snail population structure and, thus, we characterize metabolism, feeding and growth for snails residing on these coral taxa. Here, we present results of a reciprocal transplant experiment demonstrating that the taxon of the host influences snail growth rates, as indicated by changes in shell and body tissue weight. Regardless of the host from which they were drawn, snails resident on A. palmata grew faster than those resident on Montastraea spp. Thus, diet influences snail population structure. However, the tissue of Montastraea spp. provides more N and C per area of tissue than that of A. palmata. Respiration rates and tissue composition of snails collected from the two host taxa did not differ. Therefore, snails feeding on Montastraea spp. should have to consume less tissue per day to satisfy their metabolic requirements compared to snails feeding on A. palmata. Feeding rates for snails on A. palmata were measured in the laboratory over 48 h (1–9 cm² coral tissue snail⁻¹ day⁻¹) and estimated from feeding scars observed in the field (weekly mean rate of 1.07 cm² coral tissue snail⁻¹ day⁻¹). The lack of definition of snail feeding scars on Montastraea spp. required the calculation of coral tissue consumption rates based on estimated minimum carbon requirements. Calculated feeding rates for C. abbreviata were 0.13–0.88 cm² coral tissue day⁻¹ snail⁻¹, when feeding on Montastraea spp., and 0.44–3.28 cm² coral tissue day⁻¹ snail⁻¹, when feeding on A. palmata. The calculated range for the latter is consistent with measured rates. Thus, C. abbreviata exhibits high variation in growth parameters in response to environmental variability and/or food source. At mean levels of snail density on reefs off Key Largo, Fla., 20% of A. palmata colonies lose between 1.32 and 9.84 cm² tissue day⁻¹, while 50% of Montastraea spp. colonies lose between 1.04 and 7.04 cm² tissue day⁻¹. Together with published coral tissue regeneration rates, these results suggest that if sustained, such rates of predation could have a serious effect on the viability of these coral populations on Florida's reefs.     

Analysis of ribosomal ITS1 sequences indicates a deep divergence between Rhodactis (Cnidaria: Anthozoa: Corallimorpharia) species from the Caribbean and the Indo-Pacific/Red Sea

This paper explores the implications of ribosomal ITS1-sequence analysis for evolutionary relationships between four species of corallimorphs which are morphologically very similar but have distinct distributions. The analyses highlight the unreliability of morphological criteria in establishing systematic relationships amongst tropical corallimorphs. Both parsimony and distance methods of phylogenetic analysis strongly support a deep divergence between the Caribbean species Rhodactics sanctithoma and the three morphologically-related species R. howesii and R. indosinensis from the Indo-Pacific and R. rhodostoma from the Red Sea. The analyses also strongly support a closer relationship between the Red Sea species, R. rhodostoma, and one of the Indo-Pacific species, R. howesii, than between these two and the second Indo-Pacific species, R. indosinensis. The first of these results is presumably a consequence of the closure of the Central American Seaway, the event which led to the separate development of Atlantic and Indo-Pacific coral faunas. However, the lack of detailed distribution data represents a major barrier to reconstructing the evolutionary history of the genus.     

Ecological energetics of the seaweed zone in a marine bay on the Atlantic coast of Canada. III. Energy transformations by sea urchins

An energy budget was constructed for a population of the sea urchin Strongylocentrotus droebachiensis in the nearshore area of St. Margaret's Bay, Nova Scotia, Canada. Of the 6 age classes identified, ages 1+and 2+accounted for about 1/2 the population energy flow. Population production efficiencies were: production/assimilation=0.28, production/consumption=0.04 to 0.13, and production/biomass=0.80. Although S. droebachiensis was the dominant herbivore in the seaweed bed, it utilized only 1 to 7% of seaweed production. As with other populations of sea urchins, however, it had a proportionately greater influence on seaweed biomass, and also presumably production, by clearing seaweed from large areas of substrate and maintaining it clear. Loss of dissolved organic matter, the only term in the energy budget not measured, was estimated by substracting the other terms in the energy budget from consumption. In laboratory individuals, this ranged from 40 to 80% of absorption (consumption-faeces). A critical review of energy budgets for 6 other species of marine benthic grazers also revealed large amounts of energy unaccounted for that might be attributed to loss of dissolved organic matter.Contribution to the International Biological Program CCIBP 192Bedford Institute Contribution.     

A spatial gradient in the potential reproductive output of the sea mussel <Emphasis Type="Italic">Mytilus californianus</Emphasis>

Spatial variation in reproductive output from different populations within a region could have important consequences for recruitment, and cascading effects on populations and communities of marine species, but is rarely examined over meso-scales (i.e., tens to hundreds of kilometers). In this study, reproduction in the dominant mid-intertidal mussel, Mytilus californianus, was examined from sites spanning Point Conception, California over a 6-month period (March–August 2000). There was a dramatic geographic pattern in the relationship between size and potential reproductive output that was qualitatively similar across all 6 months sampled. Increases in allocation to reproductive tissue with increasing body size occurred at all sites, but the slope nearly doubled at sites south of Point Conception compared to northern sites. The spatial variation in size-specific reproductive output, coupled with additional spatial gradients in mussel density and size distributions, combined to increase total reproductive output by over eightfold at southern relative to northern sites. This study highlights the need to explicitly examine spatial patterns of reproductive output at these meso-scales, in order to better understand connectivity and source–sink dynamics in marine systems.