Recruitment Of Ascidians Research Articles

Recruitment patterns of the solitary ascidian Phallusia nigra Savigny, 1816 on artificial substrates submerged in the central Red Sea, Saudi Arabia

Abstract The solitary ascidian Phallusia nigra is commonly found on hard substrates along the Jeddah coastal waters of the central Red Sea. In this study, the recruitment pattern of P. nigra on artificial substrates was assessed in relation to their type, surface color and orientation. The results showed a higher recruitment rate of the ascidian species on concrete and dark panels. The abundance of the ascidian on test panels varied between the four seasons. The orientation (vertical or horizontal) of the panels did not show any major difference in the recruitment. Significant effects of light intensityon the recruitment of P. nigra were observed on test panels, with higher abundance on panels submerged in the shade. In conclusion, this study clearly indicates the importance of the type and color of substrates in the recruitment of ascidians on artificial materials.

Disentangling settlement responses to nutrient-rich contaminants: Elevated nutrients impact marine invertebrate recruitment via water-borne and substrate-bound cues

Anthropogenic contaminants, including nutrient enrichment, frequently alter environmental conditions in marine systems and affect the development of communities on hard-substrata. Biofilms can influence the settlement of marine invertebrates and hence impact on the structure of fouling communities. Few studies have examined bacteria, invertebrates and nutrient-rich contaminants in concert, with none yet to examine the effects of nutrient-rich contaminants on both biofilms and the recruitment of sessile invertebrate communities in-situ to ascertain the mechanistic basis behind observed impacts. Biofilm treatments were allowed to develop under manipulated environmental conditions of either ambient or enriched nutrient levels. Enrichment conditions were elevated via slow-release fertiliser and invertebrate recruitment was prevented during initial biofilm development. Biofilm treatments (including a no film control) were then subject to either ambient or enriched water-borne nutrients (in a fully-factorial design) during a period of invertebrate colonisation in the field. Effects of nutrient-rich contaminants on invertebrate recruitment were observed as changes to community composition and the abundances of taxonomic groups. Communities on no biofilm control treatments differed from those with pre-developed biofilms. Naturally developed biofilms promoted recruitment by all organisms, except barnacles, which preferred nutrient-enriched biofilms. Water-borne nutrients increased the recruitment of ascidians and barnacles, but suppressed bryozoan, serpulid polychaete and sponge recruitment. The direct and indirect impacts observed on biofilm and invertebrate communities suggest that increasing nutrient levels via nutrient-rich contaminants will result in structural community shifts that may ultimately impact ecosystem functioning within estuaries.

A short note on heavy cunjevoi growth observed on commercial scallops (Pecten fumatus)

ABSTRACTCommercial scallops (Pecten fumatus) were collected from Bass Strait, Australia from 41 dredge tows. Of these, four dredges undertaken in February 2016 at 46 m depth returned scallops that were covered by ascidians of the Pyura stolonifera species complex, commonly known as cunjevoi. There were no obvious signs of immediate ill health in the scallops, with meat being assessed as normal quality and all scallops requiring force to separate the shells. Ascidian-encrusted scallops were significantly smaller, and previous tows in the same location ten and eight months earlier returned far fewer scallops with clean shells and no signs of ascidians. This suggests that both both scallop and ascidian recruitment and growth occurred during the period between sampling events. Future research combining laboratory experiments and field observations is recommended to understand this relationship and its potential impacts on scallop populations.

Impact of seawater temperature on growth and recruitment of invasive fouling species at the global scale

AbstractEpibenthic fouling communities are dominated by invasive species that are globally distributed and can have substantial ecological and economic impacts in coastal habitats. Little is known about inter‐specific differences in life history strategies that cosmopolitan invasive species employ to acquire space and succeed in invaded habitats. The goal of this study was to examine the impact of seawater temperature on recruitment and growth of several cosmopolitan fouling species including the tunicates Botrylloides violaceus, Botryllus schlosseri and Diplosoma listerianum, as well as the bryozoans Bugula neritina and Watersipora subtorquata. To do this, the iBARGE (Invasive Bryozoan and Ascidian Recruitment and Growth Experiment) program was developed, utilizing a global network of collaborators to examine patterns over a broad geographic scale and a wide range of naturally varying seawater temperatures. This project produced a data set of thousands of photographs from 18 marinas in five countries in summer 2014 and 2015, allowing for recruitment and growth to be tabulated at a variety of temperatures. Thermal growth curves were established for five invasive species, and growth was compared among temperatures across sites, revealing a significant thermal effect. Recruitment was linked to temperature, with generally higher recruitment at warmer seawater temperatures and the highest peak recruitment values for the bryozoan Bugula neritina. Temperature also changed the relative importance of growth and recruitment for several species. These results paint a complex picture of the interactions among invasive fouling species as they relate to seawater temperature.

Distinct community dynamics at two artificial habitats in a recreational marina

Man-made facilities along coastlines modify water circulation and sedimentation dynamics which can affect the structure of marine benthic and pelagic communities. To test how environmental heterogeneity associated with a recreational marina affects the structure of the fouling community and the benthic-pelagic link, we conducted an experiment in which predation effects on recruitment and community structure were assessed in two artificial habitats: inside the marina, an area of calm waters and often disturbed by boating activity, and the breakwater, a more hydrodynamic area. Using visual censuses and video footages we also described the predation pressure and the identity of predators on the two areas. Inside the marina, the recruitment of ascidians and serpulids, but not of bryozoans, was restricted in some occasions, possibly due to reduced water circulation. Predation, mainly by the silver porgy fish Diplodus argenteus, reduced the survivor of didemnid ascidians on both areas, but predation intensity was 40 times higher in the breakwater than inside the marina. While the two artificial habitats did not necessarily support distinct communities, low recruitment coupled to weak predation inside the marina, a less dynamic environment, likely imply lower resilience and more susceptibility to disturbance.

Post-settlement predation on ascidian recruits: predator responses to changing prey density

To understand factors contributing to sessile marine species mortality, we assessed the role of two species of small predaceous neogastropods (Mitrella lunata and Anachis lafresnayi) on mortality patterns of different species of ascidian recruits. By using the functional response approach (i.e., predator response to variations in prey density) we obtained comparative information on the survival and potential local persistence patterns of several species of ascidians common to southern New England, USA, coastal waters. In addition, we were able to compare the influence of the predators on ascidian species which were relatively recent invaders (e.g., last ~30 yrs or less) into southern New England from those species which have been resident in the region for more than a century. Ascidian recruits examined included both solitary (Ciona intestinalis, Styela clava, Molgula manhattensis, Ascidiella aspersa) and colonial (Botryllus schlosseri, Botrylloides violaceus and Diplosoma listerianum) forms. Collectively, our studies indicated that the predators displayed fairly generalized predation patterns and neither species readily consumed Botrylloides recruits. When ascidian recruit densities were manipulated over a 1 to 3 order of magnitude range, predator consumption rates differed between prey species. Proportional mortality was prey density independent (Type I functional response) when Anachis was preying on Styela, Ciona, Botrylloides and Diplosoma and when Mitrella was foraging on Diplosoma. Mortality was inversely prey density dependent (Type II functional response) when Anachis was feeding on Molgula and Mitrella was feeding on Styela, Ciona and Botryllus recruits. Low prey density mortality rates, suggestive of a Type III functional response, were observed when Anachis was feeding on Ascidiella and Botryllus and when Mitrella was feeding on Molgula recruits. Collectively, results indicate that, for the most part, the predators are capable of effectively controlling the prey regardless of naturally occurring variations in ascidian recruitment densities.

Ascidian recruitment patterns on an artificial reef in Eilat (Red Sea)

Although ascidians are conspicuous members of the fouling community not much is known regarding their recruitment patterns in coral reefs. A 1-year study was carried out along the Red Sea coast of Israel to examine the effects of season and spatial distribution on ascidian recruitment to artificial marine structures. In general, autumn and spring were characterized by higher coverage with a significantly higher percentage of cover of Didemnum granulatum in autumn and higher numbers of Herdmania momus in spring. These species contributed the most to similarity between treatments consequently setting the pattern for each group (colonial and solitary). Halocynthia spinosa had significantly higher numbers during winter and Phallusia nigra was absent in spring and winter. H. momus showed a preference for horizontal surfaces. P. nigra and Ascidia cannelata showed a preference for floating units. It is concluded that the ascidian recruitment patterns are species-specific and vary between seasons, orientation and position on the substrata and in the water column.

Predation on early ontogenetic life stages and its effect on recruitment into a marine epifaunal community

In a New England (USA) subtidal hard-substrate community, 2 species of very small gas- tropods, Anachis lafresnayi and Mitrella lunata, prey on several species of newly settled ascidians. Pre- liminary expenments indicated that this predation drastically changes ascidian recruitment patterns. In order to examine this phenomenon more fully, an extensive series of field expenments using artificial substrates was performed over a 2 yr period between 1991 and 1992. In 1992, weekly experiments were conducted over the complete recruitment season between July and October. Comparisons of the exper- iments were made to test for any weekly or annual variation m the effect of these micro-predators on recruitment. Results demonstrated that the predators (1) were fairly specific in their prey preferences, (2) could eliminate prey species regardless of their settlement density, (3) switched prey in response to changes in prey species abundance, and (4) affected recruitment throughout the entire settlement sea- son. These results indicate that processes affecting post-settlement life stages contribute significantly to the overall dynamics of communities and must be considered along with the much better docu- mented effects of larval supply, adult predators, and physical disturbance.

Recruitment and development of epibioses on artificial and cleared substrata at two sites in Gullmarsfjorden on the Swedish West Coast

Abstract Recruitment and community development on artificial and natural scraped-off substrata were compared between two sites at a depth of 15m in Gullmarsfjorden on the Swedish west coast. The sites are separated by a distance of about 9 km. At each site, three asbestos panels were suspended freely from an aluminium rod in the water column away from the vertical rock wall. Three similar panels were hung against the rock wall. Additionally, three 0.25 m2 areas ofrock wall were cleared ofliving organisms and three similar areas were left undisturbed as controls. The experiment was performed twice. Panels, scraped-off areas and controls were monitored by stereophotography. Recruitment and community development among treatments were quantitatively and qualitatively different between sites. Within sites, recruitment and community development differed between artificial substrata and cleared natural substrata. At the exp.sed site, however, panels positioned on the rock wall were colonized by the same annual ascidians as the scraped-off areas. Recruitment to both artificial and natural substrata was by settling larvae as lateral growth and migration from adjacent organisms did not occur. Established assemblages in the control areas were relatively persistent during the experiments and did not receive any substantial recruitment of the annual ascidians Ascidiella scabra and Ciona intestinalis, which otherwise influenced the community structure on the panels and cleared natural substratum. Cionarecruited more heavily on panels away from the rock wall and Ascidiellaon panels against the rock wall and cleared natural substratum. This pattern is explained by differential settlement rather than the effects of predation and dislocation. Recruitment of ascidians was found to be synchronous at the two stations.