Predator and prey: the role of the round goby Neogobius melanostomus in the western Baltic

Different studies on the position of the non-indigenous species Neogobius melanostomus within the coastal food web of the Pomeranian Bay (western Baltic) were performed, resulting in a quantitative and qualitative species list of prey organisms found in the stomachs of the invader and an estimation concerning the importance of round goby as prey for different resident predators. It seems that the colonization process is not fully completed yet, but the results reveal that the species is already established in the food web 16 years after the first observation within the study area. The results show that N. melanostomus feed upon a wide range of different resident organisms. While a direct predation effect on native fish species appears rather unlikely, indirect effects such as competition cannot yet be excluded. In addition, our results reveal an ontogenetic diet shift and that the round goby itself already serves as an important prey for piscivorous fish and seabirds. Finally, we formulate different hypotheses based on our results which will require further research.     

Early life-history processes and their implications for the invasion of the barnacle Balanus glandula

As invasions become increasingly prevalent, it is important to understand how spread may be moderated by environmental conditions. This study considered the effect of location and changing substratum temperature on the early life-history processes of the alien barnacle Balanus glandula and its native comparator, Chthamalus dentatus, along the South African coast. Using settlement plates of different colours, temperature was manipulated to assess settlement, mortality, recruitment and growth of the two species. These variables were tracked over 10 weeks using repeat photography. Unexpectedly, there was no evidence of an effect of temperature on early life-history processes of either species. Settlement by the two barnacles was spatially segregated, with B. glandula occurring only on the West Coast where it is the dominant intertidal barnacle, while C. dentatus settled only on the South Coast, which has only recently been invaded by the alien. Despite this, it was notable that the relative settlement of B. glandula on rock was higher than that of C. dentatus. However, the lack of mortality of the native resulted in comparable levels of recruitment among the species. Nonetheless, the propensity of B. glandula to settle sporadically, coupled with fast growth, suggests that the invader may still possess the ability to become dominant along the newly invaded South Coast. This study highlights that measurements of early life-history parameters may not adequately predict the future range and impacts of alien species unless interpreted within the broader context of the nature of the recipient region and species-specific traits of the invader.     

Diversity of uncultured microorganisms associated with the seagrass Halophila stipulacea estimated by restriction fragment length polymorphism analysis of PCR-amplified 16S rRNA genes.

The diversity of microorganisms associated with the leaves of the seagrass Halophila stipulacea in the northern Gulf of Elat was examined by culture-independent analysis. Microorganisms were harvested by a sonication treatment for total-community genomic DNA isolation. Oligonucleotides complementary to conserved regions in the 16S rRNA-encoding DNA (rDNA) of bacteria were used for PCR amplification. The 16S rDNA PCR products were subcloned and further characterized by a restriction fragment length analysis termed ARDRA (amplified rDNA restriction analysis). These analyses were carried out after reamplifying the cloned fragments with two primers binding symmetrically to the plasmid immediately on both sides of the cloned insert. Computer-aided clustering was performed after separate restriction analysis with enzymes HinfI and HpaII. By this method, 103 cloned 16S rDNA fragments were clustered into a total of 58 different groups. Sequence analysis of clones with an identical ARDRA pattern confirmed that members of an ARDRA group were closely related to each other. The sequenced clones were found to be affiliated with a marine snow-associated plastid-like rRNA clone and with a marine Hyphomonas strain, respectively. The method applied in this study could be useful for the routine study of other microbial communities of interest.     

Reproduction in Seagrasses: Pollen Development in Thalassia hemprichii, Halophila stipulacea and Thalassodendron ciliatum

The general features of pollen morphogenesis in three marinemonocotyledons, Thalassia hemprichii, Halophila stipulacea andThalassodendron ciliatum, are described in this paper. Thalassia disperses spherical trinucleate pollen grains. Inthis genus simultaneous cytokinesis generally produces an isobilateraltetrad of microspores, but linear and T-shaped configurationsalso occur, together with configurations intermediate betweenisobilateral and T-shaped. Partitioning is followed by a phaseof cellular degeneration affecting one or two, never more, membersof the tetrad. Subsequent development of the surviving, functionalmicrospores does not differ essentially from the pattern ofmorphogenesis in terrestrial flowering plants. Halophila disperses strings of four reniform trinucleate pollengrains contained in a mucilaginous moniliform tube. These ariseby successive transverse partitioning of an elongate mothercell and the linear unit so formed is maintained throughoutpollen development. The tetrad tube substance originates inthe tapetal periplasmodium and deposition begins soon aftermeiosis. Thalassodendron disperses filiform trinucleate pollen grains.The characteristic form of the pollen in this genus is attainedduring post-meiotic growth and differentiation, as in othergenera belonging to the same family. This contrasts with thesituation in seagrasses belonging to the Zosteraceae where thefiliform shape is established before meiosis. Precocious divisionof the microspore nucleus in Thalassodendron launches the binucleatepollen phase soon after the spores separate from the tetrad.The division precedes the vacuolate period; again, this is afeature of the family. In Thalassia the tapetal periplasmodium is progressively transformedinto thecal slime. In Thalassodendron and Halophila the periplasmodialresidue forms a superficial coating on the pollen wall and tetradtube. These products could be implicated in attachment and recognitionof the pollen at the stigma surface. Thalassia hemprichii, Halophila stipulacea, Thalassodendron ciliatum, seagrasses, pollen development     

Fish larvae association in a Mexican Caribbean bay

Interannual ichthyoplankton variation, was analyzed in Bahía de la Ascensión, Mexico, during December of four consecutive years (1994-1997). A total of 32 families, 35 genera and 21 species of fish larvae were identified. The most abundant fish larvae were the Gobiidae followed by the Callionymidae, Clupeidae and Tetraodontidae. Larval diversity was low when compared with other periods ("dry" and "rainy"). Three spatial associations (internal, medium and external) were found in December 1994 and 1995. In 1996-1997, stations of the inner and outer parts of the bay were mixed. The dominant families characterized most of the faunal associations. Egg density was highest in the external zone of the bay, whereas larvae were most abundant in the inner area. Major factors affecting the fish larval assemblages during December (1994-1997) in Bahía de la Ascensión seem to be related to the nursery areas location and to the tropical fishes reproductive period.     

Phylogenetic Analysis of Bacterial Communities Associated with Leaves of the Seagrass Halophila stipulacea by a Culture-Independent Small-Subunit rRNA Gene Approach

Abstract The phylogenetic diversity of the bacterial community associated with leaves of the marine plant Halophila stipulacea in the northern Gulf of Elat was examined by 16S rRNA gene (rDNA) sequence analyses of a clone library. For 59 clones corresponding to 51 ARDRA (amplified rDNA restriction analysis) groups, the sequence of ∼1 kb was determined, and the fraction of the corresponding ARDRA groups of the leaf library was calculated. The class Proteobacteria was represented by 62.6% of the clone sequences. Most sequences originated from members of the γ-subclass (27.3%), affiliated with members of the genera Pseudomonas, Vibrio, Marinomonas, Oceanospirillum, and other marine groups. Affiliation to the α-subclass was determined for 24.2% of the sequences. They were related to the genera Hyphomonas, Roseobacter, Ruegeria, and Rhizobiaceae. Several α-proteobacterial sequences were distantly related to known sequences. Only 4% of the clone sequences were related to β-Proteobacteria. Additionally, 7.1% of the sequences possibly belonged to the class Proteobacteria, but branched deeply from known subclasses. Several sequences were affiliated to members of the orders Verrucomicrobiales and Planctomycetales, the Holophaga/Acidobacterium phylum, and chloroplasts of marine diatoms. Received: 20 March 1999; Accepted: 13 August 1999; Online Publication: 2 March 2000     

rDNA analysis of the Red Sea seagrass,Halophila, reveals vicariant evolutionary diversification

The effects of opening the Suez Canal as a connection between the Red Sea and the Mediterranean Sea were reported for a number of marine species. However, the evolutionary origin of the seagrasses in the Red Sea and the linking population genetics of seagrasses between the Arabian Sea, the Gulf of Aden, the Red Sea and the Mediterranean Sea have not yet been investigated in detail. The invasion of Halophila stipulacea Asch. from the Red Sea into the Mediterranean Sea after the opening of the Suez Canal was already recorded. We hypothesize that Halophila ovalis populations in the Red Sea developed through long-term historical processes such as vicariant evolutionary diversification. Seagrass samples were collected along the Egyptian coastline of the Red Sea and analysed by the molecular marker ITS. The sequences were compared with published ITS sequences from seagrasses collected in the whole area of interest. In this study, we reveal the linking population genetics, phylogeography and phylogenetics of two dominant seagrass species, Halophila stipulacea and Halophila ovalis, among species collected in the Red Sea and worldwide. The results indicate that the Red Sea Halophila ovalis populations do not group to Halophila ovalis worldwide, and Halophila major, Halophila ovalis collected worldwide and Halophila ovalis collected at the Red Sea are sister clades. Hence, vicariant evolutionary diversification for Halophila ovalis may occur in the Red Sea.     

Increased heavy metal and nutrient contamination does not increase fluctuating asymmetry in the seagrass Halophila ovalis

Fluctuating asymmetry (random differences between symmetric structures, FA) is one of the stress indices used recently to assess a subtle effect of environmental degradation on organisms and is expected to increase under stress conditions. In this study, we developed an original technique of measuring FA in seagrass, Halophila ovalis. We analysed five metric and meristic characters on leaves of the seagrass from a polluted and several control locations in a lagoon in Eastern Australia. The seagrass was sampled from three sites at each location. The analyses revealed significant spatial heterogeneity of samples in fluctuating asymmetry with the highest variability was observed among sites. There was no increase in FA of H. ovalis from polluted location. Possible explanations suggest that whether existing concentrations of heavy metals do not cause developmental stress in seagrass or their effect is compensated or even surpassed by effect of uncontrolled factors.     

Magnitude of within-patch variation in seagrass Halophila ovalis growth affected by adjacent Thalassia hemprichii vegetation

Seagrass beds in South-east Asia sometimes consist of a mosaic of different species in monospecific patches. We examined whether the magnitude of within-patch variation in the seagrass Halophila ovalis is affected by the presence or absence of surrounding vegetation consisting of another seagrass species Thalassia hemprichii in an intertidal flat in Thailand waters. We measured biomass and growth rates of H. ovalis at the edges and centers of two different types of patches: (i) H. ovalis patches adjoining T. hemprichii vegetation (HT patches), and (ii) H. ovalis patches adjoining unvegetated sand flats (HS patches). Furthermore, we examined the possible effects of interspecific interactions on the growth of H. ovalis by experimentally removing adjoining T. hemprichii at the edges of HT patches. The biomass of H. ovalis was greater at the patch centre than the patch edge in both types of patches. For the growth rate of H. ovalis, significant interactions were detected between patch types and positions in patches. The difference in growth was significant and more than 4-fold between edges and centers of the HS patches, whereas the growth was not significantly different between edges and centers of the HT patches. The removal of T. hemprichii did not significantly affect the growth rate of H. ovalis at the edge of the HT patches. These findings demonstrate that the magnitude of within-patch variation in H. ovalis growth is affected by the conditions of adjoining habitats. However, any effects of local competition with T. hemprichii on H. ovalis growth were not evident in this short-term manipulative experiment.     

Harpacticoid copepods associated with the seagrass Halophila ovalis in the Ashtamudi Estuary,south-west coast of India

A temporal study of harpacticoid copepod populations associated with the seagrass Halophila ovalis was undertaken in the Ashtamudi Estuary, south-west coast of India. A total of 19 species representing 8 families was recorded in this assemblage. Harpacticoids formed 7.52% of the total phytal meiofauna. At the species level, harpacticoids exhibit parallel assemblages with phytal zones, found in other localities.     

Patterns of seagrass macrobenthic biodiversity in the warm-temperate Knysna estuarine bay,Western Cape: a review

Aquatic Ecology - Knysna estuarine bay in South Africa's Garden Route National Park is that country's most significant estuarine system for biodiversity and conservation value. One...     

Juvenile settlement,survivorship and in situ growth rates of four species of Caribbean damselfishes in the genusStegastes

Synopsis FourStegastes species were visually censused to determine seasonality and size of juvelines at settlement as well as their survival and growth rates. The census was performed weekly from September 1987 to March 1991 in southwest Puerto Rico. All species had a settlement pulse during September–October. The threespot damselfish,S. planifrons, appeared to have the strongest site fidelity, longest survivorship and slowest growth of the four species. The cocoa damselfish,S. variabilis, and the bicolor damselfish,S. partitus, had similar patterns of site fidelity, life expectancy and growth rates, but these two species differed in being the most and least abundant, respectively. The beaugregory,S. leucostictus, occurred second in abundance but included the least number of new settlers. This species displayed poor site fidelity, a characteristic which probably influenced calculations indicating poor survivorship, life expectancy and growth relative to its congeners. Similarities and differences in these characteristics, as well as in the habitat preferences displayed by these four fishes, may contribute to their abilities to coexist in the same area.     

Larval settlement preferences and post-settlement survival of the threatened Caribbean corals Acropora palmata and A. cervicornis

The settlement specificity of two threatened Caribbean corals, Acropora palmata and A. cervicornis, was tested by measuring their rates of larval metamorphosis in response to crustose coralline algae (CCA) and other substrata. In the no-choice experiments, the coral larvae were placed in six treatments: filtered seawater (FSW), a fragment of biofilmed dead skeleton of A. palmata, or a fragment of one of four species of CCA (Hydrolithon boergesenii, Porolithon pachydermum, Paragoniolithon solubile, and Titanoderma prototypum). Within each CCA treatment, there were three different substrata on which to settle and metamorphose: (1) the CCA surface, (2) the rock under the CCA, or (3) the plastic dish. The 5-day-old larvae of both A. palmata and A. cervicornis had similar rates of total metamorphosis (all substrata combined) in every treatment (excluding FSW) even in the absence of CCA. However, there were differences in larval behavior among the CCA species since the larvae settled and metamorphosed on different substrata in the presence of different CCA species. In the no-choice experiments the larvae of both corals had higher rates of metamorphosis on the top surfaces of H. boergesenii and/or T. prototypum than on P. pachydermum. In the choice experiments, the coral larvae were offered two species of CCA in the same dish. When given a choice, both species of coral larvae had more settlement and metamorphosis on the surface of H. boergesenii or T. prototypum or clean rock than onto the surface of P. solubile. After 6 weeks in the field, transplanted A. palmata recruits had approximately 15% survival on both T. prototypum and H. boergesenii, but A. cervicornis recruits only survived on T. prototypum (13%). Some, but not all, CCA species facilitated the larval settlement and post-settlement survival of these two threatened corals, highlighting the importance of benthic community composition for successful coral recruitment.     

Fitness costs of butterfly oviposition on a lethal non-native plant in a mixed native and non-native plant community

Non-native plants may be unpalatable or toxic, but have oviposition cues similar to native plants used by insects. The herbivore will then oviposit on the plant, but the offspring will be unable to develop. While such instances have been described previously, the fitness costs at the population level in the wild due to the presence of the lethal host have not been quantified, for this or other related systems. We quantified the fitness cost in the field for the native butterfly Pieris macdunnoughii in the presence of the non-native crucifer Thlaspi arvense, based on the spatial distributions of host plants, female butterflies and eggs in the habitat and the survival of the larvae in the wild. We found that 2.9 % of eggs were laid on T. arvense on average, with a survival probability of 0, yielding a calculated fitness cost of 3.0 % (95 % confidence interval 1.7–3.6 %) due to the presence of the non-native in the plant community. Survival probability to the pre-pupal stage for eggs laid on two native crucifers averaged 1.6 % over 2 years. The magnitude of the fitness cost will vary temporally and spatially as a function of the relative abundance of the non-native plant. We propose that the fine-scale spatial structure of the plant community relative to the butterflies’ dispersal ability, combined with the females’ broad habitat use, contributes to the fitness costs associated with the non-native plant and the resulting evolutionary trap.     

Exploring the impact of a non-native seed predator on the seed germination of its non-native host

Biological Invasions - Novel interactions between introduced and native species commonly occur and can even be predicted from existing native interactions in a certain area. However, novel...     

Monsoonal and lunar variability in microzooplankton abundance and community structure in the Terusan mangrove creek (Malaysia)

This study documents the monsoonal and lunar effects on species composition and abundance of microzooplankton in a tropical estuary. We investigated microzooplankton abundance in relation to the various environmental and biotic parameters, sampled in the Matang mangrove (Malaysia) from April 2013 to February 2014. A total of 39 microzooplankton taxa comprising four major groups, i.e. loricate ciliates (37.72%), aloricate ciliates (29.46%), dinoflagellates (24.33%) and meroplanktonic nauplii (8.49%) were identified. The loricate ciliates were the most diverse group with 31 taxa recorded. Four major species of loricate ciliates were identified, i.e. Tintinnopsis beroidea, Tintinnopsis rotundata, Stenosemella avellana and Tintinnidium primitivum, while Strombidiidae and Strobilidiidae dominated the aloricate ciliates. Although small loricate ciliates were ubiquitous, redundancy analysis shows marked shifts in microzooplankton community structure, from one that was dominated by loricate ciliates during the drier SW monsoon, to aloricate ciliates at the onset of the wet NE monsoon, and then to dinoflagellates towards the end of the drier NE monsoon period. These shifts were associated with rainfall, dissolved inorganic nutrients, salinity, temperature and microbial food abundance. There was no clear lunar effect on abundance of microzooplankton except for Favella ehrenbergii and copepod nauplii, which were more abundant during neap than spring tides.