Lagoon ecosystems: peculiarities of the species, spatial and trophic structure of macrobenthos (Kandalaksha bay, White sea)

Изучены видовое разнообразие, пространственная и трофическая структура макробентосных сообществ сублиторали и нижних горизонтов литорали в 5-ти лагунных экосистемах Кандалакшского залива Белого моря. Всего в исследованных экосистемах было обнаружено 52 вида бентосных беспозвоночных животных и 6 видов морских трав и водорослей. В сублиторали наибольшим видовым разнообразием, общей плотностью и биомассой макробентоса характеризуется наиболее открытая к морю лагуна, расположенная на выходе из кутовой области Кислой губы, а наименьшим - наиболее закрытая и заиленная лагуна Никольской губы, где преобладали солоноватоводные и морские эвригалинные виды. Промежуточное положение занимали лагуна Ермолинской губы, лагуна, расположенная рядом с Ершовским озером и лагуна на Зеленом мысу. В нижней литорали общие показатели структуры сообщества макробентоса (общая плотность, биомасса и в меньшей степени видовое разнообразие) в отличие от сублиторали увеличивались от менее зарегулированных и открытых экосистем к более закрытым системам. Исключением является лагуна Никольской губы, значительное заиление которой приводит к существенному уменьшению видового разнообразия и снижению общей плотности и биомассы сообщества макробентоса. The species diversity, spatial and trophic structure of macrobenthos communities in the sublittoral and lower littoral horizons in five lagoon ecosystems of the Kandalaksha Bay of the White Sea have been studied. In total, 52 species of benthic invertebrates and 6 species of sea grasses and algae were found in the studied ecosystems. In the sublittoral zone, the highest species diversity, total density and biomass of macrobenthos is characterized by the lagoon most open to the sea, located at the exit from the innermost area of Kislaya Bay. The lowest diversity is found in the most closed and silted lagoon of Nikolskaya Bay, where brackish water and marine euryhaline species predominated. The lagoon of the Ermolinskaya Bay, the lagoon located next to the Ershov Lake and the lagoon on Cape Verde hold an intermediate position. In the lower littoral zone, the general indicators of the structure of the macrobenthos community (total density, biomass, and, to a lesser extent, species diversity), in contrast to the sublittoral one, increased from less regulated and open ecosystems to more closed systems. An exception is the lagoon of Nikolskaya Bay, the significant siltation of which leads to a significant decrease in species diversity and a decrease in the total density and biomass of the macrobenthos community.

Trophic interactions of marine sponges

<p>Marine communities in the Anthropocene are changing rapidly with potentially severe consequences for ecosystem functioning. Recently, there has been increased interest in the ecological role of sponges, particularly on coral reefs, driven by evidence that sponges may be less affected by this period of environmental change than other benthic organisms. The Sampela reef system in the Wakatobi Marine National Park, Indonesia, is an example of a reef that has shifted to sponge dominance following a decline in hard corals and an increase in sponge density. Previous research suggests that the Sampela reef system may support a greater abundance of spongivorous fishes relative to surrounding reefs, however, uncertainties remain regarding spongivore identity and predated sponges. In addition, little is known about how shifts towards sponge dominance affect the trophic structure of reefs. The primary aim of my thesis was to investigate sponge trophic interactions to gain insight into the way sponge-dominated reefs of the future might function. This information is essential to predict the broader functional consequences of increasing sponge dominance on reefs in the Anthropocene. In my first data chapter, I measured the functional impact of spongivorous fishes by quantifying sponge biomass consumption on Wakatobi reefs. Video analysis identified 33 species from 10 families of reef fish grazing on Xestospongia spp., although 95% of bites were taken by only 11 species. Gut content analysis indicated that Pygoplites diacanthus and Pomacanthus imperator were obligate spongivores and Pomacanthus xanthometopon, Zanclus cornutus and Siganus punctatus regularly consumed sponges. In situ feeding observations revealed that sponges from the family Petrosiidae are preferred by P. diacanthus and Z. cornutus. Spongivores were estimated to consume 46.6 ± 18.3 g sponge 1000 m- 2 of reef day-1 and P. diacanthus had the greatest predatory impact on sponges. While estimates provided here are conservative and likely underestimate the true magnitude of spongivory on Indo-Pacific coral reefs, this chapter provides the first known estimate of reef wide sponge biomass consumption. Comparisons with published data estimating coral consumption by Chaetodontids in the Pacific suggests that biomass transferred through both pathways is similar in magnitude. Hence spongivory is an important, yet overlooked, trophic pathway on Indo-Pacific reefs. In my second data chapter, I developed genetic methods to identify sponges from the stomach contents of spongivorous angelfishes sampled in my first chapter. A range of primers and associated predator-blocking primers targeting the 18S rDNA gene were designed and tested on extracts of sponge and spongivore DNA. Sequences were successfully amplified from 14 sponges spanning 6 orders of Porifera, with the majority of samples identified belonging to the order Haplosclerida. This study is the first to successfully sequence sponges from the gut contents of spongivorous fishes. Sequence data indicated that Pygoplites diacanthus consumed sponges with considerable chemical defences and exhibited significant dietary plasticity within the Porifera phylum, similar to observations of angelfishes in the Caribbean and the eastern Pacific. In my third data chapter, I used stable isotope analysis to investigate differences in consumer niche widths and trophic diversity on the sponge-dominated Sampela reef system in comparison to an adjacent, higher quality reef. I measured the stable isotope ratios of coral reef fish representing different functional feeding groups, prey items and basal carbon sources at both sites. I used isotope data to calculate the trophic position and isotopic niches of each species and performed interspecific and inter-site comparisons. The fish assemblage had a significantly lower mean trophic position at the sponge-dominated site and the majority of species had wider isotopic niches, in accordance with optimal foraging theory which supports expansion in niche widths when per capita prey is low. The fish assemblage sampled at the sponge-dominated site used a significantly lower range of resources, had lower trophic diversity and obtained more carbon from benthic production than fish from the higher quality reef site. Results indicate a simpler trophic structure at the sponge-dominated site characterised by fish with more similar diets. Whilst trophic niche expansion may facilitate population survival in the short term, it can be expected to lead to intensified competition for increasingly scarce resources. In my final data chapter, I investigated niche partitioning and organic matter contributions to co-occurring temperate sponges. I sampled the stable isotope ratios of five abundant sponge species at 10 m and 30 m at two sites at opposing ends of Doubtful Sound, Fiordland. I also used an ROV to opportunistically sample sponges at depths >50 m and measured stable isotope ratios of picoplankton (</p>

Trophic interactions of marine sponges

<p>Marine communities in the Anthropocene are changing rapidly with potentially severe consequences for ecosystem functioning. Recently, there has been increased interest in the ecological role of sponges, particularly on coral reefs, driven by evidence that sponges may be less affected by this period of environmental change than other benthic organisms. The Sampela reef system in the Wakatobi Marine National Park, Indonesia, is an example of a reef that has shifted to sponge dominance following a decline in hard corals and an increase in sponge density. Previous research suggests that the Sampela reef system may support a greater abundance of spongivorous fishes relative to surrounding reefs, however, uncertainties remain regarding spongivore identity and predated sponges. In addition, little is known about how shifts towards sponge dominance affect the trophic structure of reefs. The primary aim of my thesis was to investigate sponge trophic interactions to gain insight into the way sponge-dominated reefs of the future might function. This information is essential to predict the broader functional consequences of increasing sponge dominance on reefs in the Anthropocene. In my first data chapter, I measured the functional impact of spongivorous fishes by quantifying sponge biomass consumption on Wakatobi reefs. Video analysis identified 33 species from 10 families of reef fish grazing on Xestospongia spp., although 95% of bites were taken by only 11 species. Gut content analysis indicated that Pygoplites diacanthus and Pomacanthus imperator were obligate spongivores and Pomacanthus xanthometopon, Zanclus cornutus and Siganus punctatus regularly consumed sponges. In situ feeding observations revealed that sponges from the family Petrosiidae are preferred by P. diacanthus and Z. cornutus. Spongivores were estimated to consume 46.6 ± 18.3 g sponge 1000 m- 2 of reef day-1 and P. diacanthus had the greatest predatory impact on sponges. While estimates provided here are conservative and likely underestimate the true magnitude of spongivory on Indo-Pacific coral reefs, this chapter provides the first known estimate of reef wide sponge biomass consumption. Comparisons with published data estimating coral consumption by Chaetodontids in the Pacific suggests that biomass transferred through both pathways is similar in magnitude. Hence spongivory is an important, yet overlooked, trophic pathway on Indo-Pacific reefs. In my second data chapter, I developed genetic methods to identify sponges from the stomach contents of spongivorous angelfishes sampled in my first chapter. A range of primers and associated predator-blocking primers targeting the 18S rDNA gene were designed and tested on extracts of sponge and spongivore DNA. Sequences were successfully amplified from 14 sponges spanning 6 orders of Porifera, with the majority of samples identified belonging to the order Haplosclerida. This study is the first to successfully sequence sponges from the gut contents of spongivorous fishes. Sequence data indicated that Pygoplites diacanthus consumed sponges with considerable chemical defences and exhibited significant dietary plasticity within the Porifera phylum, similar to observations of angelfishes in the Caribbean and the eastern Pacific. In my third data chapter, I used stable isotope analysis to investigate differences in consumer niche widths and trophic diversity on the sponge-dominated Sampela reef system in comparison to an adjacent, higher quality reef. I measured the stable isotope ratios of coral reef fish representing different functional feeding groups, prey items and basal carbon sources at both sites. I used isotope data to calculate the trophic position and isotopic niches of each species and performed interspecific and inter-site comparisons. The fish assemblage had a significantly lower mean trophic position at the sponge-dominated site and the majority of species had wider isotopic niches, in accordance with optimal foraging theory which supports expansion in niche widths when per capita prey is low. The fish assemblage sampled at the sponge-dominated site used a significantly lower range of resources, had lower trophic diversity and obtained more carbon from benthic production than fish from the higher quality reef site. Results indicate a simpler trophic structure at the sponge-dominated site characterised by fish with more similar diets. Whilst trophic niche expansion may facilitate population survival in the short term, it can be expected to lead to intensified competition for increasingly scarce resources. In my final data chapter, I investigated niche partitioning and organic matter contributions to co-occurring temperate sponges. I sampled the stable isotope ratios of five abundant sponge species at 10 m and 30 m at two sites at opposing ends of Doubtful Sound, Fiordland. I also used an ROV to opportunistically sample sponges at depths >50 m and measured stable isotope ratios of picoplankton (</p>

Flooding affects food web structure and basal sources supporting fish guilds in a subtropical wetland and shallow lake

Aquatic ecosystems exchange nutrients and organic matter with surrounding terrestrial ecosystems, and floods import allochthonous material from riparian areas into fluvial systems. We surveyed food web components of a wetland and shallow lake in a subtropical coastal region of Brazil to examine how community trophic structure and the entrance of allochthonous material into the food web were affected by floods. Stable isotope analysis was performed for samples of terrestrial and aquatic basal production sources and aquatic animals to trace the origin of organic matter assimilated by aquatic animals and estimate vertical trophic positions and food chain length. Lake and wetland trophic structures were compared for cool/wet and warm/dry seasons. Food web structure was hypothesized to differ based on hydrology, with the more stable lake having greater food web complexity, and seasonal flooding resulting in greater allochthonous inputs to the aquatic food web. We compared spatial and temporal variation in assemblage trophic structure using an adapted isotopic ellipse approach that plots assemblage elements according to δ13C on the x-axis and estimated TP on the y-axis. Lake trophic structure was more complex with longer food chains compared to that of the wetland. A greater contribution from terrestrial resources to animal biomass was observed in the wetland during the cool/wet period, and food chains in both habitats tended to be longer during the cool/wet period. Findings supported the hypothesis of greater assimilation of allochthonous sources during floods and greater trophic complexity in the more hydrologically stable system.