Is surface orientation a determinant for colonisation patterns of vagile and sessile macrobenthos on artificial reefs?

In order to examine how substratum colonisation can affect community structure, a 1-year study was conducted at the Faro/Ancão artificial reef (Algarve, Portugal). In the study of hard substratum communities, motile species are usually neglected and only the conspicuous species are taken into account. Therefore, the development of vagile and sessile components of the epibiotic community were analysed separately. Differences between assemblages on horizontal surfaces, but not on vertical surfaces, were detected. Multivariate analysis detected differences in macrobenthic community structure either considering sessile or motile components. However, significant differences were only detected for vagile fauna. Moreover, this study suggests that for hard substratum communities, analysis of the vagile fauna is important and should be taken into account in the functioning of the artificial raft.     

Is surface orientation a determinant for colonisation patterns of vagile and sessile macrobenthos on artificial reefs?

In order to examine how substratum colonisation can affect community structure, a 1-year study was conducted at the Faro/Ancao artificial reef (Algarve, Portugal). In the study of hard substratum communities, motile species are usually neglected and only the conspicuous species are taken into account. Therefore, the development of vagile and sessile components of the epibiotic community were analysed separately. Differences between assemblages on horizontal surfaces, but not on vertical surfaces, were detected. Multivariate analysis detected differences in macrobenthic community structure either considering sessile or motile components. However, significant differences were only detected for vagile fauna. Moreover, this study suggests that for hard substratum communities, analysis of the vagile fauna is important and should be taken into account in the functioning of the artificial raft.     

Community Structure of Fishes and Habitat Complexity on a Tropical Rocky Shore

The relationship between the variables of reef fish community structure (fish richness, fish diversity and total number of fishes) and those of habitat complexity (total surface area, substratum diversity, topographic complexity, number of holes, percent cover of turf algae, zoanthids, millepores, massive corals, bare rock, encrusting calcareous algae, urchins, other sessile organisms and Sargassum) were examined on three different rocky shores (FA, FB and FT) at Arraial do Cabo, a tropical region located on Brazilian southeastern coast (23° S, 42° W). Fish abundance and vertical distribution were assessed by a visual census technique using strip transects. Percentage cover of benthic organisms and other substratum types were calculated by replicated transects using a chain laid down on the substratum. Topographic complexity was determined by the chain link method and number of holes were estimated by direct counts on replicated transects. More than 91 fishes belonging to 37 families were seen in all study sites during one year of visual census effort. FA and FB sites had similar fish community structure and habitat complexity characteristics, while FT showed different habitat characteristics and higher fish diversity and richness, plus total number of fishes. Vertical distribution of fishes along the rocky shores studied seemed to be predictable and was determined by factors such as feeding habits and behavior, availability of refuges and social interactions. The habitat variables that best explained the higher diversity and number of fishes observed in FT site were total surface area of rocky shores and the abundance of benthic sessile invertebrates; these conditions were typical of rocky shores more exposed to wave surge.     

Development of a subtidal epibenthic community: factors affecting species composition and the mechanisms of succession

Summary Macroinvertebrate grazers and temporal variability were found to strongly influence species composition of communities that developed subtidally on plexiglas panels. On panels exposed to the naturally high densities of sea urchins and sea stars, only grazer-resistant algal crusts, a diatom/blue-green algal film and short-lived filamentous algae became abundant. On those panels protected from grazers, however, other algae and sessile invertebrates were also common. Both the effects of grazing and the abundance of individual taxa differed on panels immersed at different times of the year.Resident species also affected subsequent recruitment. Some colonists were found more frequently on panels with established communities than on recently immersed plates. Others became more abundant on younger than on older panels. Considerable small-scale spatial variation in the abundance of species was also found among panels within treatments and appeared to persist throughout the 13 months of the study.I suggest that since the interactions that determine which mechanisms are important in succession occur between individuals (generalized here to species), not between successional stages, factors such as those examined that can determine which species will interact, indirectly determine the mechnaisms that are important in the development of a community. Models that deal with interactions between successional stages may lack the detail neccessary to predict or explain changes in species composition in diverse communities.     

Seasonal non-indigenous species succession in a marine macrofouling invertebrate community

We report results from a 2-year study on the succession pattern of macrofouling assemblages in the Taranto Sea, an important alien species hotspot in the Mediterranean Sea. Four sets of PVC panels were used as macrofouling collectors; each unit was installed at a different time (April 2013, July 2013, October 2013 and January 2014) and then surveyed quarterly for 1 year. The macrofouling community consisted of 93 sessile invertebrate species, of which 16 were NIS and five were cryptogenic. In both years non-indigenous species (NIS) recruitment occurred mainly in the quarter July/October in concert with the settlement of pioneer autochthonous species. This recruitment is independent of immersion time, occurring on both bare substrates and on previously colonized panels. This increase in NIS coverage is influenced by the development stage of the community, suggesting that NIS grow better without potential competitors. Two sets of NIS were distinguished. The first included abundant ascidians, serpulids, and bryozoans that are structuring components of early communities when favorable conditions exist (i.e. a lack of competitive autochthonous species). After settlement, these species are unable to develop in later-stage communities. The second set of NIS was composed of sabellid worms that settle in early and late communities but, unlike the other NIS, are able to persist and become dominant in late macrofouling communities independent of seasonal changes.     

Reef fish community structure in the Tropical Eastern Pacific (Panamá): living on a relatively stable rocky reef environment

We compared the community structure of reef fish over different physical complexities in 12 study zones of Bahía Honda, Gulf of Chiriquí (BH-GCH), Tropical Eastern Pacific (TEP), Panama, aiming at an analysis of the importance of the physical structure provided by corals, rocks and benthic sessile organisms. This was the first region that emerged in the Isthmus of Panama; it exhibits the oldest benthic fauna and has constant conditions in terms of temperature and salinity. Two hundred and eighty-eight visual fish censuses were conducted on 48 benthic transects from February to July 2003. One hundred and twenty-six fish species of 44 families were found. Plankton feeding pomacentrids and labrids along with haemulids that feed on mobile invertebrates were the most abundant, particularly in shallow areas. Fourteen species showed size-segregations between zones, suggesting ontogenetic migrations (smaller fishes in shallow high-complexity zones, larger-sized fishes in deeper habitats). Highly mobile and site-attached genera were abundant in most shallow, wave-exposed zones particularly on exposed rocky substrates. Planktivores were the most abundant, followed by carnivores, feeders on mobile invertebrate and piscivores. Herbivores and feeders on sessile invertebrate were lower in abundance. Species richness exceeds that of any other studied region close to the mainland in the TEP and correlates with substrate diversity, increasing size-heterogeneity of holes and structural complexity. Species diversity increases with habitat complexity and benthic diversity. It seems that water current strength, tides and waves which select for swimming, play an important role in the community organization. The study region has been proposed as a refuge-centre in the TEP, where reef fishes that evolved on coral reefs have shifted their distribution onto rocky reef habitats.     

Reassessing the spatial relationship between sponges and macroalgae in sublittoral rocky bottoms: a descriptive approach

Because sublittoral sponges of temperate areas are usually more abundant at sites with low algal abundance, there is the widespread notion that macroalgae out-compete and displace sponges to habitats less suitable for algal proliferation. In this study, based on 292 sampling quadrats, we collected a total of 87 demosponge species and examined the level at which sponge distribution pairs with a variety of alga-dominated and animal-dominated habitats occurring in three zones located across a marked in-bay/out-bay environmental gradient. We found significant differences in sponge biomass, richness and diversity between the 18 habitats considered in the three zones, with abundance, richness and diversity being significantly higher in caves, vertical surfaces and overhangs out of the bay than in the remaining habitats. The cluster analysis and the unconstrained ordination consistently reflected the in-bay/out-bay environmental gradient. These analyses also revealed that the taxonomic distribution of sponge abundance is independent of the algal occurrence in the habitat, being more related to between-zone differences than to between-habitat differences. This trend was corroborated when the role of depth, algal abundance and substratum inclination in explaining total sponge abundance and diversity was examined by canonical correspondence analysis, regression analysis and mean comparisons. These analyses pointed to substratum inclination, rather than to algal abundance, as the factor explaining most variation in distribution of sponge abundance. These results, when discussed in the context provided by the outcome of other studies concerned with the spatial distribution of the sessile benthos in rocky temperate communities, strongly suggest a need to re-examine the idea that spatial distribution of sublittoral sponges largely results from competition with macroalgae.     

The development of sessile epifaunal communities in Kylesalia,Kilkieran bay (west coast of Ireland)

Test panels, which were suspended horizontally at three sites in a shallow inlet on the west coast of Ireland, were sampled monthly over a period of one year to investigate the development of epifaunal communities. In addition, the current regime and sedimentation at these sites were measured. The deposited materials, of high organic value, may enhance the food supply to the sessile organisms through resuspension. Heavy deposition at one site interrupted the study. At the other two sites, however, the experiment was not affected. At one site, initial settlement by colonial bryozoans, followed by solitary ascidians, was noted on the panels over the period studied. In the competition for space, the dense aggregations during settlement, the relative large size, and the rapid growth of these solitary animals may occlude the colonization by colonial bryozoan mats underneath. At the other site, a more diversified community with co-existence of many sedentary polychaete and colonial bryozoan species was recorded on the panels. The continuing availability of free space on the panels suggests that the development of sessile communities at this site may be hindered by the relatively slow current flow and heavy deposition and resuspension. Whilst differences in community development were observed on the panels at these two sites, it would be difficult, through such a short study period, to ascertain whether stable climax states had been reached.     

Convergence of community composition during secondary succession on Zokor rodent mounds on the Tibetan Plateau

Aims The community succession theory is much debated in ecology. We studied succession on Zokor rodent mounds on the Tibetan Plateau to address several fundamental questions, among them: (i) During secondary succession, does the community composition converge towards one community state or multiple states depending on the initial colonization? (ii) Do mound communities located in different background communities exhibit different assembly trajectories?Methods In a sub-alpine meadow, we investigated a total of 80 mound communities at several successional stages in three different background communities resulting from different management histories and compared their changes in species composition. The distribution of plant communities over time was analyzed with quantitative classification and ordination methods. The co-occurrence patterns of species were evaluated at each successional stage, and the degree of convergence/divergence among communities was obtained by calculating two beta-diversity indices.Important findings During secondary succession, species richness of mound communities changed over time, and this change was dependent on the background community. Five life-form groups exhibited different dynamic patterns in species richness and plant cover. Community composition and the degree of species co-occurrence between communities increased over time since disturbance. There was much variation in species composition at earlier stages of succession, but communities on older mounds became more similar to each other and to their surrounding vegetation over the course of secondary succession. Post-disturbance succession of Zokor mound communities transitioned from 'multiple alternative states' to 'background-based deterministic community assembly' over time. Tradeoffs between competition and colonization, as well as the characteristics of different life-forms and mass effects within a limited species pool are the mechanisms responsible for convergence of mound communities.     

Natural succession of macroalgal-dominated epibenthic assemblages at different water depths and after transplantation from deep to shallow water on Spitsbergen

In the current study, we investigated the primary succession of seaweeds over different time periods at different water depths. Furthermore, we followed the succession of field-grown benthic communities of different successional age, developing on ceramic tiles, prior to and after transplantation from 8 to 0.5 m water depth. The transplantation simulated changes associated with the break up of sea-ice cover, e.g. light regime or wave exposure. For this purpose, we transplanted 12 and 21-month old communities, grown at 8 m water depth, together with a set of sterile tiles, onto rafts, floating in 0.5 m water depth. Our results describe for the first time the succession of macroalgal communities in the Arctic and give important insights into the effect of disturbance of differently aged communities. The primary succession at 0.5 m water depth was mainly driven by Bacillariophyta and filamentous green algae like Urospora sp. and Ulothrix implexa. Twelve-month old communities at 8 m water depth are dominated by members of the Ectocarpales (Phaeophyceae), like Pylaiella littoralis, P. varia, and Ectocarpus siliculosus and the green alga U. implexa, whereas the 21-month old community showed a higher cover of the green algal class Ulvophyceae and sessile invertebrates. After transplantation to near surface conditions, species composition of the communities changed, but this effect was differently strong between communities of different age.     

Grazing patterns in Siphonaria gigas (Mollusca,Pulmonata) on the rocky Pacific coast of Panama

The pulmonate limpet Siphonaria gigas is the most abundant molluscan grazer in the mid zone on rocky, wave-exposed shores of the Pacific coast of Panama. Erect macroalgae and sessile invertebrates are rare; crustose algae cover ～90% of the rock. The relative abundance of a common blue-green algal crust (Schizothrix calcicola?) is negatively correlated with Siphonaria's abundance. Large-scale removals of the limpet cause rapid increases in percent cover of Schizothrix and concomitant decreases in other crusts, but no changes in the abundance of erect algae or sessile invertebrates. Removing Siphonaria also (1) increases recruitment of crustose algae and barnacles onto new rock and plexiglass substrata, and (2) decreases the abundance of a calcified form of Schizothrix. Harsh conditions during daytime low tides and foraging by fishes at high tide control the microdistribution of most of this region's mobile and sessile benthic organisms. Wave action and substratum heterogeneity modify these constraints: Siphonaria is rare or absent in sheltered areas, especially on homogeneous surfaces, and is most abundant at wave-exposed sites. However, at extremely wave-beaten sites, Siphonaria and other benthic consumers are rare and ineffective. Crustose algae are reduced in abundance and space is dominated by erect macroalgae and/or barnacles. These normally rare species can outcompete crusts only when thermal or desiccation stress and the effects of benthic consumers and fishes are drastically reduced.     

The non-native solitary ascidian Ciona intestinalis (L.) depresses species richness

Non-native ascidians are a dominant feature of many sessile marine communities throughout the world and may have negative effects on species diversity. We tested effects of the non-native Ciona intestinalis on the sessile invertebrate community in San Francisco Bay, where it occurs in dense aggregations. In particular, we compared species richness between PVC panels from which C. intestinalis were experimentally removed to panels with naturally dense C. intestinalis growth, using fouling panels of four sizes (between 49 cm² and 1177 cm²) to measure the effect of C. intestinalis recruitment on species-area relationships. We initially deployed 120 fouling panels (30 of each size) at a site known to have dense populations of C. intestinalis, assigning these to three different treatments: (1) Experimental removal, whereby new recruits of C. intestinalis were removed on a weekly basis, pulling panels out of the water for a short time period to do so; (2) Manipulated control, whereby panels were removed from the water each week (as in the experimental removal) but without C. intestinalis removal; and (3) Unmanipulated control, which remained in the water throughout the experiment. After 4 months, all of the panels were collected and analyzed to estimate species richness and relative abundance (percent cover) of sessile invertebrates and of C. intestinalis. Across all panels, species richness was negatively correlated with C. intestinalis abundance. The removal of C. intestinalis produced communities with significantly higher species richness than the controls. The overall species composition of treated and control panels was also distinctly different, with many species occurring more often in the absence of C. intestinalis, while others occurred more often on C. intestinalis-dominated panels. These data suggest that C. intestinalis both depress local species diversity and alter community assembly processes to fundamentally change sessile community composition.     

Looking for long-term changes in hydroid assemblages (Cnidaria,Hydrozoa) in Alboran Sea (South-Western Mediterranean): a proposal of a monitoring point for the global warming

In the last 20–30 years, the temperature of the Mediterranean Sea has increased and global warming is allowing the establishment of tropical-affinity species into more temperate zones. Sessile communities are particularly useful as a baseline for ecological monitoring; however, a lack of historical data series exists for sessile marine organisms without commercial interest. Hydroids are ubiquitous components of the benthic sessile fauna on rocky shores and have been used as bio-indicators of environmental conditions. In this study on the benthic hydroid assemblages of the Chafarinas Islands (Alboran Sea, South-Western Mediterranean), we characterized the hydroid assemblages, identified the bathymetric gradients, and compared them with a previous study carried out in 1991. Hydroid assemblages showed a significant difference both between year and among depths. Furthermore, eight species not present in 1991 were found, including two possible new species and the tropical and subtropical species Sertularia marginata. Due to its strategic position at the entrance of the Mediterranean and the existence of previous data on hydroid assemblages, the Chafarinas Islands are proposed as a possible monitoring point for entrance of Atlantic tropical species into the Mediterranean Sea.     

Benthic invertebrate recolonization of small-scale disturbances in the littoral zone of a subtropical Florida lake

Construction of spawning beds by the exotic cichlid fish, Sarotherodon aurea, produces numerous small-scale disturbances in shallow Florida lakes. Two experimental methods were used to simulate these disturbances (containers filled with defaunated sediment and disturbed natural substratum) and to determine benthic invertebrate recolonization patterns and rates.Recolonization of experimental containers was rapid and densities of macroinvertebrates reached equilibrium with the control habitat by Day 6 following disturbance. However, Chironomidae and miscellaneous taxa usually were more abundant (p < 0.05) in the experimental containers, and Oligochaeta always were more abundant (p < 0.01) in the control. Species of the planktonically dispersed insects either attained equilibrium rapidly or showed significantly higher densities in the experimental containers (i.e. opportunistic species).In the second experimental approach, disturbance of natural substratum removed 91% of the benthic invertebrates. The common species of chironomids reached equilibrium by Day 6 but the two predominant oligochaetes, Limnodrilus and Pristina, reached equilibrium at 9 and 15 days respectively. For the entire community, similarity on Day 6 was 87.1% and over the remainder of the sample period averaged 86.8%. Chironomid instar analyses showed significantly higher proportions of early instars in the disturbed patch indicating that colonization is principally by younger organisms. Thus, small-scale disturbance in freshwater benthic communities may be more important in ordering the biomass or age-group structure than the numerical abundance.     

Biofouling communities on test panels coated with TBT and TBT-free copper based antifouling paints

Abstract

Formation of biofouling communities on the surfaces of steel panels coated with two different TBT-free copper-based and one TBT-based antifouling paint was examined following submersion for periods of 3, 6, 9 and 12 months in Kastela Bay, Croatia. Test panels coated with Shopprimer and anticorrosive paint were used as control panels. Thirty five taxa of benthic algae and 32 taxa of benthic animals were found. Diatomeae dominated by frequency and abundance on test panels coated with antifouling paints, while the animal species Serpula vermicularis, Mytilus galloprovincialis and Balanus amphitrite amphitrite dominated the fouling communities on control panels. On panels protected by antifouling paints, low values of biomass were found compared to the very high values associated with control panels.     

Biofouling communities on test panels coated with TBT and TBT-free copper based antifouling paints

Formation of biofouling communities on the surfaces of steel panels coated with two different TBT-free copper-based and one TBT-based antifouling paint was examined following submersion for periods of 3, 6, 9 and 12 months in Kastela Bay, Croatia. Test panels coated with Shopprimer and anticorrosive paint were used as control panels. Thirty five taxa of benthic algae and 32 taxa of benthic animals were found. Diatomeae dominated by frequency and abundance on test panels coated with antifouling paints, while the animal species Serpula vermicularis, Mytilus galloprovincialis and Balanus amphitrite amphitrite dominated the fouling communities on control panels. On panels protected by antifouling paints, low values of biomass were found compared to the very high values associated with control panels.     

Testing the impact of Remotely Operated Vehicle (ROVs) camera angle on community metrics of temperate mesophotic organisms: A 3D model-based approach

While Remotely Operated Vehicle (ROV) technologies have rapidly increased our understanding of deeper water mesophotic ecosystems, there are some inherent problems in their use when estimating the abundance of sessile benthic organisms. Specifically, for rocky and coral reefs there has been recent debate about the importance of the angle of the ROV camera to the substrate, which is difficult to standardise, and how variation in this angle might impact abundance estimates and therefore our ability to detect change in mesophotic ecosystems. Here we simulated a series of 3D rocky temperate mesophotic communities based on real data with three different levels of habitat complexity (high, medium, and low). We ‘sampled’ these communities in a virtual space varying the angle of the camera to the substrate, to assess the influence of camera angle on percent cover estimates and overall benthic community composition. We found that increases in the ROV to substrate angle overestimated the percent cover (per degree of camera angle) of gorgonians (large: R² = 0.16; small: R² = 0.18), tubular sponges (R² = 0.11), and ascidians (R² = 0.05–0.13), and underestimated the abundance of Crustose Coraline Algae (R² = 0.1, likely due to shading) in the most complex habitats. While we also found some significant differences in the overall benthic community and data dispersion for the more complex habitats, angle explained only a small amount of total variation (<6%) and significant dispersion was only found between 0- and 50-degree angles in high and medium complexity habitats. We conclude that while ROV to surface angle should be a consideration when sampling deep water reefs, its influence on standard measurements that we estimate with photography is likely to be low, and restricted to errors in the abundance of organisms with a high ratio of height to planar projection area (e.g., gorgonians).     

Impacts and negative feedbacks in community recovery over eight years following removal of habitat-forming macroalgae

The decline or loss of habitat-forming species has affected rocky shore marine communities worldwide. Many short-term studies have documented the initiation of cascading effects due to canopy losses of macroalgae, but relatively few studies have followed recovery dynamics over many years. Here, we show that the experimental removal of a dominant intertidal fucoid in southern New Zealand had numerous community effects up to 8 years later. Even though the dominant fucoid returned to a nearly closed canopy, there remained many differences between disturbed and control communities. The disturbed treatments had lower plant density and biomass of the dominant fucoid, fewer species and more turfing coralline algae than controls. Plots with press disturbances were more affected than those with pulse disturbances. The negative feedback of turfing algae on the recovery of fucoid recruitment resulted in effects on cover and diversity in the wider community being evident after 8 years. We discuss the feedbacks between fucoids, benthic turfing algae and community recovery and argue that if biodiversity impacts on marine rocky reefs are to be understood, the role of non-trophic interactions in structure, function and dynamics must be better delineated.     

Night-time lighting alters the composition of marine epifaunal communities

Marine benthic communities face multiple anthropogenic pressures that compromise the future of some of the most biodiverse and functionally important ecosystems in the world. Yet one of the pressures these ecosystems face, night-time lighting, remains unstudied. Light is an important cue in guiding the settlement of invertebrate larvae, and altering natural regimes of nocturnal illumination could modify patterns of recruitment among sessile epifauna. We present the first evidence of night-time lighting changing the composition of temperate epifaunal marine invertebrate communities. Illuminating settlement surfaces with white light-emitting diode lighting at night, to levels experienced by these communities locally, both inhibited and encouraged the colonization of 39% of the taxa analysed, including three sessile and two mobile species. Our results indicate that ecological light pollution from coastal development, shipping and offshore infrastructure could be changing the composition of marine epifaunal communities.     

Mechanisms of successional dynamics: Consumers and the rise and fall of species dominance

Insight into potential mechanisms of succession following disturbance to an ecological community can be gained by considering processes that contribute to the rise (colonization, interactions with established species) and demise (differential mortality) of specific stages within the successional sequence. Most successional theories focus on the rise to dominance, assuming demise is the result of competition, but other factors can cause differential mortality among species, including physical disturbance, senescence, and consumers. In rocky intertidal communities on the coast of Washington state, USA, gaps in mussel beds exhibit a succession from predator-susceptible to predator-resistant species following disturbance, suggesting that differential consumption by mobile species may play an important role in the demise of early succession species and the eventual dominance of the mussel Mytilus californianus. Experimental manipulation of a dominant species earlier in succession, the blue mussel Mytilus trossulus, demonstrated that this species inhibits the invasion of M. californianus in the absence of predators. Experimental manipulation of predatory snails (Nucella emarginata and Nucella canaliculata), which feed heavily on M. trossulus but not M. californianus, greatly increased the rate at which M. californianus invaded gaps. These results and those of other studies indicate that consumers frequently have important effects on the dynamics of succession in benthic marine systems, and might also play a role in other settings.