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>

Early line and hook fishing at the Epipaleolithic site of Jordan River Dureijat (Northern Israel)

Nineteen broken and complete bone fish hooks and six grooved stones recovered from the Epipaleolithic site of Jordan River Dureijat in the Hula Valley of Israel represent the largest collection of fishing technology from the Epipaleolithic and Paleolithic periods. Although Jordan River Dureijat was occupied throughout the Epipaleolithic (~20–10 kya the fish hooks appear only at the later stage of this period (15,000–12,000 cal BP). This paper presents a multidimensional study of the hooks, grooved stones, site context, and the fish assemblage from macro and micro perspectives following technological, use wear, residue and zooarchaeological approaches. The study of the fish hooks reveals significant variability in hook size, shape and feature type and provides the first evidence that several landmark innovations in fishing technology were already in use at this early date. These include inner and outer barbs, a variety of line attachment techniques including knobs, grooves and adhesives and some of the earliest evidence for artificial lures. Wear on the grooved stones is consistent with their use as sinkers while plant fibers recovered from the grooves of one hook shank and one stone suggest the use of fishing line. This together with associations between the grooved stones and hooks in the same archaeological layers, suggests the emergence of a sophisticated line and hook technology. The complexity of this technology is highlighted by the multiple steps required to manufacture each component and combine them into an integrated system. The appearance of such technology in the Levantine Epipaleolithic record reflects a deep knowledge of fish behavior and ecology. This coincides with significant larger-scale patterns in subsistence evolution, namely broad spectrum foraging, which is an important first signal of the beginning of the transition to agriculture in this region.