Influence of canopy-forming algae on temperate sponge assemblages

<p>Changes in the distributions of organisms not only alter community composition and food web structure, but also can initiate important changes at the ecosystem level. Understanding the interactions between biotic and abiotic factors affecting species’ distribution patterns in temperate habitats is important for predicting responses to future environmental change. Sponges are important members of temperate rocky reefs assemblages that are influenced by a number of abiotic factors including water movement, light regime, inclination and stability of the substratum, as well as complex ecological interactions. The aim of this thesis was to investigate the interactions between sponges and macroalgae on shallow-water rocky reefs of Wellington, New Zealand, assessing if the distribution patterns of sponges are independent of algal populations. I used a combination of surveys, and manipulative field and laboratory experiments to explore the existence of interactions (positive or negative) between sponges and macroalgae and also to explore the effect of environmental factors on the distribution and abundance of temperate sponges. My first objective was to determine if the spatial distribution patterns of sponges are independent of macroalgae distribution and abundance at different sites on the Wellington south coast (Chapter 2). The results showed that abundance of most sponge species were strongly correlated with inclination, which supports previous studies in the northern hemisphere suggesting that sponge abundance and algal abundance are negatively correlated. In contrast, only a few sponge species were positively correlated with algal abundance. I then explored the positive interactions occurring between some sponges species and the presence of canopy-forming algae (Chapter 3). Results from this chapter suggest the canopy of Ecklonia radiata facilitates the existence of some sponge species such as Crella incrustans on vertical rocky walls. The removal of Ecklonia canopy led to a community dominated by turf algae, which corresponded with a decrease in sponge abundance and richness. My results suggest that the Ecklonia canopy facilitates the presence of some sponge species and allows their coexistence with turf algae underneath the canopy and also by altering immediate physical factors that may be detrimental for some sponge species. To further explore the existence of sponges and understory algae, I used an experimental approach (Chapter 4) to investigate the effect of the brown alga Zonaria turneriana on Leucetta sp. and also mechanisms involved in the interactions. However results from this chapter provided no evidence to support previous hypotheses that understory algae negatively affect sponges. In the last data chapter (Chapter 5), I studied sponges inhabiting different habitats in order to test if environmental variation affects the abundance and diversity of microorganisms, hence having the potential to affect the distribution and abundance of these species The stability observed in bacterial communities among specimens occupying different habitats suggests that environmental variation occurring in those habitats does not affect the stability of the community, and hence most likely does not radically alter the metabolism of these sponges. Although environmental factors such as light and sediment may have an effect on early sponge stages, other environmental (e.g. nutrients, temperature, wave action) and biotic factors, are more likely to influence the growth, survival and distribution of sponges on temperate rocky reefs. In summary, temperate sponge assemblages are strongly influenced by interactions between a number of abiotic and biotic factors. The outcomes of the ecological interactions are controlled by environment (e.g. influence of inclination on competition between sponges and understory algae) and at the same time, biological interactions (e.g. facilitation) can moderate the influence of abiotic factors such as light, sedimentation and wave action, thus facilitating the coexistence between sponge and macroalgae underneath the Ecklonia canopy. My thesis makes a significant contribution to our knowledge of temperate subtidal ecology, in terms of the effects of biotic and abiotic factors on sponge assemblages and also improves our knowledge of temperate patterns of sponge and macroalgal interactions. Finally, my thesis highlights the importance of small-scale environmental variation in influencing the structure and diversity of sponge assemblages and also increase our understanding of temperate rocky reefs sponges, especially on the less studied sponge assemblages occurring in Ecklonia stands on vertical rocky walls.</p>

<p>Coral reefs across the globe are in decline due to multiple threats including overexploitation, pollution, coastal development, climate change and ocean acidification. Much research has focused on the effects of these threats on hard corals while their impacts on other important benthic invertebrate groups have been overlooked. Sponges are a diverse and abundant component of coral reef communities in the Indo-Pacific that play important functional roles on reefs including nutrient cycling, linking primary and secondary production, reef bioerosion and spatial competition. Consequently, changes in the abundance and distribution patterns of sponges can affect overall reef ecosystem function. Understanding the factors that control sponge distribution patterns is therefore essential for the successful prediction and mitigation of the effects of current threats to reef systems. Sponge distributions are known to be affected by a number of abiotic factors such as wave action, sedimentation and water flow, but the role of biological factors such as predation and competition is less clear. The primary aim of my thesis was to determine the effects of predation on the distribution and abundance of sponge assemblages in the Wakatobi Marine National Park (WMNP), SE Sulawesi, Indonesia. My first objective (chapter 2) was to identify the major spongivores in the Wakatobi using surveys and behavioural observations of key invertebrate (nudibranchs and starfish) and vertebrate taxa (fish). I then adopted a statistical modelling approach (chapter 3) to examine associations between sponges and a suite of abiotic and biological factors, including spongivore abundance, across nine sites in the WMNP. The results of this analysis showed that although sponge assemblage composition was weakly associated with spongivore abundance, sedimentation is more likely to have a greater impact on sponge abundance and distribution patterns. I found that degraded sites were characterized by low diversity sponge assemblages dominated by a single sediment tolerant species Lamellodysidea herbacea. In order to explore the relationship between sponges and spongivore abundance further, I used an experimental approach (chapter 4), establishing a caging experiment to examine the effect of excluding predators on reef slope sponge assemblages. The caging experiment did not reveal any effects of predator exclusion on sponge abundance or diversity. In the last data chapter (chapter 5), I focus on sub-lethal predation effects on sponges and examine the extent and impact of partial predation on the Indo-Pacific giant barrel sponge Xestospongia testudinaria. Video observations of fish predation and measurements of barrel sponge regeneration rates were used to model the impacts of predation on barrel sponges. In summary, a combination of observational, modelling and experimental approaches were used in order to determine the impact of fish predation on Indo-Pacific sponge assemblages. Spongivory does not appear to have a major influence on the abundance and distribution of reef sponges but is an important trophic link in reef ecosystems. Ecologically important sponge species, such as the giant barrel sponge X. testudinaria, are exposed to intensive partial predation and future changes in predation intensity could have consequences for the fitness of these species. Finally, my work suggests that changes on reefs such as increases in sedimentation could produce a shift from coral dominated to lower diversity sponge dominated communities.</p>

Although coral reef health across the globe is declining as a result of anthropogenic impacts, relatively little is known of how environmental variability influences reef organisms other than corals and fish. Sponges are an important component of coral reef fauna that perform many important functional roles and changes in their abundance and diversity as a result of environmental change has the potential to affect overall reef ecosystem functioning. In this study, we examined patterns of sponge biodiversity and abundance across a range of environments to assess the potential key drivers of differences in benthic community structure. We found that sponge assemblages were significantly different across the study sites, but were dominated by one species Lamellodysidea herbacea (42% of all sponges patches recorded) and that the differential rate of sediment deposition was the most important variable driving differences in abundance patterns. Lamellodysidea herbacea abundance was positively associated with sedimentation rates, while total sponge abundance excluding Lamellodysidea herbacea was negatively associated with rates of sedimentation. Overall variation in sponge assemblage composition was correlated with a number of variables although each variable explained only a small amount of the overall variation. Although sponge abundance remained similar across environments, diversity was negatively affected by sedimentation, with the most sedimented sites being dominated by a single sponge species. Our study shows how some sponge species are able to tolerate high levels of sediment and that any transition of coral reefs to more sedimented states may result in a shift to a low diversity sponge dominated system, which is likely to have subsequent effects on ecosystem functioning.

Habitat associated differences in temperate sponge assemblages:: the importance of chemical defence

Sponges comprise a diverse and important benthic invertebrate group in many ecoregions, being a dominating compo nent in the Antarctic communities. Based on two piston cores from the Admiralty Bay, West Antarctica, we isolated the sponge spicules from the sediments and compared the sub-fossil sublittoral sponge assemblage with the Recent sponge fauna of this area. In addition, we performed statistical analysis to compare the species composition from and within each core. While no significant shifts in the composition of sponge assemblages along the cores were noticed, our study revealed a noteworthy distinction between the documented sponge species in the area and those identified based on loose spicules within the sediment. The sedimentological record appeared to capture more sponge species than identified in contemporary faunistic studies. Out of the 27 sponge taxa recognized in the sediment, merely seven were confirmed as presently inhabiting the area. Of the remaining 20 taxa, several were documented in nearby regions such as Maxwell Bay or South Shetland Islands in general, but 12 species had not been previously recorded in this locality or its adjacent areas. Conversely, the sediments did not indicate the presence of nine modern species previously reported in this area. We attribute these discrepancies to various factors, including the potential oversights in recognizing sponges characterized by small size, fragility, or encrusting habits during faunistic studies. In cases where the certain taxa lack a fossil record, we suggest that the simplicity of their spicule types made the recognition in sediments challenging. In summary, our findings underscore that Admiralty Bay remains substantially understudied in terms of sponge species inhabiting this area, highlighting the need for further comprehensive studies in this region.

Sponges are a major component of benthic ecosystems across the world and fulfil a number of important functional roles. However, despite their importance, there have been few attempts to compare sponge assemblage structure and ecological functions across large spatial scales. In this review, we examine commonalities and differences between shallow water (<100 m) sponges at bioregional (15 bioregions) and macroregional (tropical, Mediterranean, temperate, and polar) scales, to provide a more comprehensive understanding of sponge ecology. Patterns of sponge abundance (based on density and area occupied) were highly variable, with an average benthic cover between ~1 and 30%. Sponges were generally found to occupy more space (percentage cover) in the Mediterranean and polar macroregions, compared to temperate and tropical macroregions, although sponge densities (sponges m-2 ) were highest in temperate bioregions. Mean species richness standardised by sampling area was similar across all bioregions, except for a few locations that supported very high small-scale biodiversity concentrations. Encrusting growth forms were generally the dominant sponge morphology, with the exception of the Tropical West Atlantic, where upright forms dominated. Annelids and Arthropods were the most commonly reported macrofauna associated with sponges across bioregions. With respect to reproduction, there were no patterns in gametic development (hermaphroditism versus gonochorism), although temperate, tropical, and polar macroregions had an increasingly higher percentage of viviparous species, respectively, with viviparity being the sole gamete development mechanism reported for polar sponges to date. Seasonal reproductive timing was the most common in all bioregions, but continuous timing was more common in the Mediterranean and tropical bioregions compared to polar and temperate bioregions. We found little variation across bioregions in larval size, and the dominant larval type across the globe was parenchymella. No pattens among bioregions were found in the limited information available for standardised respiration and pumping rates. Many organisms were found to predate sponges, with the abundance of sponge predators being higher in tropical systems. While there is some evidence to support a higher overall proportion of phototrophic species in the Tropical Austalian bioregion compared to the Western Atlantic, both also have large numbers of heterotrophic species. Sponges are important spatial competitors across all bioregions, most commonly being reported to interact with anthozoans and algae. Even though the available information was limited for many bioregions, our analyses demonstrate some differences in sponge traits and functions among bioregions, and among macroregions. However, we also identified similarities in sponge assemblage structure and function at global scales, likely reflecting a combination of regional- and local-scale biological and physical processes affecting sponge assemblages, along with common ancestry. Finally, we used our analyses to highlight geographic bias in past sponge research, and identify gaps in our understanding of sponge ecology globally. By so doing, we identified key areas for future research on sponge ecology. We hope that our study will help sponge researchers to consider bioregion-specific features of sponge assemblages and key sponge-mediated ecological processes from a global perspective.

ABSTRACTPhotosynthesis/photon flux density (PFD) relationships were compared among some of the major components of sparse algal turfs (green endoliths, red crusts, red filaments, Crouania, Sphacelaria)/ from Tague Bay forereef St. Croix, U.S. Virgin Islands. Algal turfs grazed by the sea urchin Diadema antillarum were 2–10 times more productive per unit chl a than when not grazed by sea urchins. The maximum rate of net photosynthesis (Pnetmax) and saturation PFDs, but not the slope of the light‐limited portion of the curve (α), differed significantly among the algal turf components examined. The hypothesis that increased biomass‐specific primary productivity results from shifts in algal community structure was not supported because the maximum difference in photosynthesis between algal components was only a factor of two, and the less productive components were relatively more abundant under grazing. In the understory, green endoliths exhibited higher α and lower Pnetmax, suggesting shade adaptation. Photon flux density measurements taken with a fiber optic microprobe within the algal turfs indicated that photosynthesis of basal portions of algal filaments and red crusts are light‐limited in ungrazed algal turfs. As self‐shading changes with grazer‐mediated canopy removal, algal sublayers will contribute differentially to whole turf primary productivity.

Environmental change is commonly considered as a driver for the extinction of rare species. This belief, long established on land, may not apply to marine species. Dramatic environmental change in the shallow marine ecosystems of Kos, an island in the Aegean (east Mediterranean Sea) caused algal reefs to shift to sponge reefs. Among the sponge species that gained supremacy on Kos reefs, the Mediterranean endemic Ircinia retidermata was previously a rare species. Comparing surveys carried out in 1981 and 2013 by the same method (time-based visual census along random paths by scuba diving), in the same sites, by the same people, showed that I. retidermata increased its overall abundance by one order of magnitude, and expanded its occurrence to all the habitats examined. This outcome contradicts the current common belief that rare species in semi-enclosed seas are prone to extinction. Besides being the state preceding final extinction, rarity could represent the source of variation that marine ecosystems need in order to face environmental change. However, for many marine invertebrates, and especially sponges, inferred rarity may simply be the result of insufficient investigation. This study represents an attempt to assess change with time in a rare sponge species’ abundance using visual census by scuba diving.

Despite numerous ecological studies with mosquitoes, it remains unclear what environmental factors are the most important determinants of structure, species richness, and abundance of mosquito assemblages. In the current study, we investigated relations between these characteristics of mosquito larvae assemblages and environmental factors in a large set of different habitats. Particular objectives were (1) to rank the factors regarding their explanatory power, and (2) to quantify the contribution of major sets of factors such as habitat spatial/hydrological (H), water physico-chemical (W), and aquatic vegetation characteristics (V). Variance partitioning and forward selection based on ordinations and multiple regressions were applied to the data set on 79 water-bodies in southwestern Siberia covering a wide gradient of environmental characteristics and diverse mosquito assemblages. The results showed that richness and abundance inter-correlated poorly (r2 = 0.21), and assemblage structure, richness, and abundance depended on different sets of predictors. Explanatory importance of the three sets of environmental factors differed among the three assemblage variables: H, W, and V had equal importance for assemblage structure, while richness and abundance depended on H and V more than on W. The study showed that contradiction between the aims of conservation (support biodiversity) and mosquito control (reduce mosquito abundance) can be avoided, as relevant environmental factors can be used to define habitats with high richness and low abundance (i.e., high conservation value and low nuisance and disease transmission risk) for conservation activities, and conversely for control measures.

The Mesoamerican Reef is the second largest coral reef in the world and has experienced a 50% loss of coral coverage in recent decades. Due to the high biodiversity of marine life that depend on the Mesoamerican Reef, identifying drivers of coral loss is crucial. This study was designed to assess the relationship between the presence of yellow band disease (YBD) and white plague type-II (WPII) on stony corals with environmental (water depth) and biological stressors (abundance of sponges in close proximity) in the reef surrounding the Bay Islands, Honduras. Both radial and parallel transect survey techniques were used to quantify the abundance of seven sponge species within a one-meter radius of Orbicella species and Montastraea cavernsoa. The strongest predictor of coral health was the abundance of Callyspongia plicifera, followed by Svenzea zeai, in close proximity to diseased coral. A weak, but positive, correlation between poriferan abundance and the presence of disease lesions on coral was observed. However, no significant relationship of disease prevalence with water depth was observed. Additionally, no differences in the prevalence of disease lesions between four species of native stony corals were observed. These findings suggest coral species are equally susceptible to bacterial pathogens, but that close association with poriferans may increase the transmission and persistence of harmful bacteria in coral reef ecosystems.

Marine biology,marine ecology,Phytoplankton, marine algae, zooplankton, nekton, benthos, corals and coral reefs, ecology, zoogeography and systematics, primary production and experimental work on ecosystem including energy flow at different trophic levels, population dynamics and theoretical models, recycling of matter, influence of environmental factors on metabolic activity, marine microbiology, mariculture and experimental work on propagation of cultivable species, biology of fishes, marine reptiles, sea birds and mammals, physical, chemical, geological and meteorological features of the environments related to marine biology, marine environmental damage caused by pollution and engineering works, underwater observations, conservation of living resources, modifications in methodology and techniques and development of new apparatus related to marine sciences

Sponges are important components of high-latitude benthic communities, but their diversity and abundance in algal-dominated rocky reefs has been underestimated because of the difficulty of in situ identification. Further, the influence of canopy-forming algae on sponge richness has been poorly studied in southern high-latitude rocky reefs compared to other latitudes. Here, we quantified taxon richness of sponges in algae-dominated rocky reefs at three sites in the western Antarctic Peninsula (62–64° S) and two sites in the Magellan region (53° S). We found higher sponge richness at sites in Antarctica (15) than in Magallanes (8), with Antarctic sponge richness higher than that reported for Arctic algal beds and similar to that reported for temperate regions. Estimated sponge richness at our Antarctic sites highlights diverse sponge assemblages (16–26 taxa) between 5 and 20 m that are typically dominated by macroalgae. Our results suggest that sponge assemblages associated with canopy-forming macroalgae on southern high-latitude reefs are more diverse than previously thought.

Abstract: Several studies have demonstrated the negative effects of clearcutting on terrestrial plethodontid salamander populations. However, none has experimentally compared clearcutting with multiple alternative timber‐harvest methods. Using a randomized, replicated design, we compared the short‐term effects ( 1–4 years after harvest ) of clearcutting to effects of leavetree, group selection, and two shelterwood cuts on terrestrial salamanders in the southern Appalachian Mountains of Virginia and West Virginia ( U.S.A. ). Treatment plots were 2 ha each. We also compared salamander age class ( percent juvenile ), fecundity ( percentage of females carrying eggs and average number of eggs per gravid female ), size of gravid females, and species composition and diversity between treatments with canopy removal ( cut ) and those without canopy removal ( uncut ). All treatments with canopy removal had significantly fewer salamanders than the control treatment, but salamander abundances on alternative treatments with canopy removal did not differ significantly from salamander abundances on the clearcuts. There were no significant differences between cut and uncut treatments in the proportion of females that were gravid or in the average number of eggs in gravid females; however, gravid Plethodon cinereus females weighed more on the cut treatments and gravid Desmognathus ochrophaeus females weighed more on uncut treatments. There were no significant differences between cut and uncut treatments in the proportion of the sample that was juvenile, except in the largest species tested, P. glutinosus, which had a significantly higher proportion of juveniles in the uncut treatments. We conclude that initial declines in terrestrial plethodontid abundance caused by timber harvesting may be minimized across the landscape by concentrating high‐intensity timber harvesting ( clearcutting ) in small areas ( a few hectares in size ).

Sponges constitute one of the most diverse and abundant animal groups in the marine tropical benthos especially in coral reefs, though poorly studied to species level. The aim of this study is to characterize the sponge community along a depth gradient at Isla Larga (Parque Nacional San Esteban, Venezuela) fringe reef. Net and total sedimentation, roughness index, sponge species richness, density and proportion of the bottom covered by sponges, were evaluated at seven depths (1, 3, 6, 9, 12, 15, 18 m), 17 species were identified grouped in 10 demosponges families. The highest densities and coverage corresponded to 6 m of depth (6.03ind/m2; 11%), that coincides with the lowest net sedimentation and highest substrate heterogeneity. Most abundant species were Desmapsamma anchorata, Amphimedon erina and Scopalina rueztleri. Principal component analysis divided this community in three zones according to depth. The shallow zone of the reef (1 and 3 m), where wave force and high irradiance exert a constant stress sponges, shows the lowest density and coverage by sponges. In contrast, medium depth (6, 9 y 12 m) and deep zone (15 y 18 m) with lower light and sedimentation levels seem to enhance sponge growth and survival that are reflected on the higher densities and coverage of sponges.

AimIn this study, we investigated whether environmental factors can effectively control the spatial distribution of various benthic algae and examined the critical ecological impacts of algae on corals across the South China Sea (SCS). Relationships between benthic algae and environmental factors were assessed, and potential ecological impacts of algae on coral communities were evaluated across spatial scales.LocationA total of 104 sites at 12 coral reefs in four coral reef regions (CRRs) of the SCS (latitude range of 9–22° N).TaxaTurf algae, macroalgae (including fleshy macroalgae and Halimeda), crustose coralline algae (CCA), coral and juvenile coral.MethodsUsing diver‐based surveys (2015–2018), we investigated four CRRs with different reef distance to mainland (RDM) across the SCS. We obtained field data on benthic algal composition and cover, coral cover and diversity, and juvenile coral density. We also measured and collected the environmental factors (including seawater environmental parameters and reef fish diversity).ResultsThe cover of turf algae and CCA gradually decreased and increased, respectively, with an increase in RDM, which had a strong relationship with the gradually changing environmental factors. Random forest models suggested that nutrients, reef fish diversity, seawater transparency and temperature were the most important factors for predicting turf algae and CCA cover. Linear regression analyses showed a significant relationship between the turf algae, macroalgae, and CCA covers, and juvenile coral density.Main conclusionsOur results showed that gradually changing environmental factors were correlated with the spatial distributions of turf algae and CCA. However, the natural biophysical relationships between macroalgae and environmental factors may be disrupted by turf algal overgrowth and nutrient subsidies. Increases in all benthic algal groups significantly impacted coral recruitment, highlighting the critical role of benthic algae in determining the recovery trajectory of the Indo‐Pacific reefs that are threatened by human activities.