Conference: “Host variety enhances diversity: the role of multiple secondary habitat-forming seaweeds in facilitating estuarine invertebrate communities”

New Zealand Marine Science Society conference (NZMSS) 2017, University of Canterbury, New Zealand

10-nzmss-2017 2

Alfonso Siciliano, Mads S. Thomsen, David R. Schiel

Abstract

Shell-forming molluscs are primary habitat-forming species that affect the structure of invertebrate assemblages in sedimentary estuaries. Importantly, their shells provide hard substratum that seaweeds attach to, and these seaweeds can subsequently provide secondary habitat to epibiontic invertebrates, giving rise to habitat cascades. Here we hypothesized that (1) invertebrate communities depend on the identity and density of morphologically different seaweeds (Gracilaria chilensis vs. Ulva sp.), (2) these invertebrates have different host-specificities related to the ecological differences between seaweeds, (3) results are consistent across latitudes and (4) invertebrate community structure depends on whatever primary and secondary habitat-formers are alive or dead (mimics). The first two hypotheses were tested in surveys and experiments run seasonally. There were consistent significant effects of both seaweed species-identity and density, but the results from the experiment was less conclusive. A regional survey in 13 estuaries tested the third hypothesis, confirming the results from the local survey. Finally, a field experiment confirmed hypothesis four demonstrating that live habitat-formers have higher diversity than mimics, suggesting that secondary habitat-formers may provide trophic subsidies for invertebrates. In concert, these results show that habitat cascades are common in increasing biodiversity in estuaries of the South Island of New Zealand.

Conference: “Habitat cascade destroyed in the Kaikoura earthquake”

New Zealand Marine Science Society conference (NZMSS) 2017, University of Canterbury, New Zealand

07-nzmss-2017

Mads S. Thomsen, Isis Metcalfe, Alfonso Siciliano, Tommaso Alestra, Stacie Lilley, Shawn Gerrity, David R. Schiel

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Abstract

It is well-described how anthropogenic activities and natural disaster can destroy primary habitat-forming species, like seagrasses, corals and kelps. However, less research and conservation effort has focused on how these types of disturbances affect associated secondary habitat-formers, like epiphytes, and animals depending on biogenic habitat. In this talk we will first introduce the concept of habitat cascades with examples from New Zealand rocky shores and compare them to habitat cascades from other ecosystems. We will then show that intertidal primary (fucoid hosts) and secondary (seaweed epiphytes) habitat-formers and their inhabitants (small mobile invertebrates) have been decimated on reef along a 100km swathe of coastline that were uplifted by 1-6m by the recent 7.8mW Kaikoura earthquake. Finally, we will discuss potential cascading ecological effects, future scenarios for natural recovery and whether restoration is a viable option to speed up the recovery of habitat cascades on these degraded reefs.

Paper: “Recreational diving and its effects on the macroalgal communities of the unintentional artificial reef Zenobia shipwreck (Cyprus)”

paper-2-siciliano-et-al-2016

Siciliano Alfonso, Jimenez Carlos, Antonis Petrou

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Abstract

The ecological role of shipwrecks as artificial reefs is well established and often is prime and exclusive destinations for diving tourism. But they are also extremely delicate and sensitive environments. For this reason, the impact of recreational diving on shipwrecks should be taken in consideration since diver’s experience can strongly affect their associated benthic communities. The aim of this study was to verify the impact of anthropogenic activities (scuba divers) on the macroalgal coverage, here considered as indicator of physical disturbance, on the modern shipwreck Zenobia, in Cyprus (east Mediterranean Sea). Divers behaviour was investigated in the wreck and the macroalgal coverage was determined (photo-quadrat method) in three areas differently exposed to physical contact of divers. Our results suggest that diving is having a significant negative effect on the macroalgae coverage of the shipwreck, especially in areas subject to high levels of use (e.g., meeting stations) when compared to control sites in the same wreck. Divers’ behaviour and popular dive routes at the wreck are factors associated to the observed decrease in macroalgae benthic cover. It is important that relevant stakeholders utilizing the Zenobia wreck agree on basic management planning in order to protect and enhance the wreck’s biodiversity. In addition, this study provides for the first time evidence of ecological deterioration of one of the most emblematic shipwreck of the Mediterranean Sea.

Conference: “Effects of seaweeds, nutrients and sedimentation on seagrass and seagrass-associated fauna”

Annual Biology Conference (ABC) 2016, University of Canterbury, New Zealand

08-abc-conference-2016

Alfonso Siciliano, Mads S. Thomsen, David R. Schiel

X

Abstract

Seagrasses are marine plants that take up nutrients, stabilize sediments, increase habitat complexity and thereby also increase biodiversity of sedimentary coastal ecosystems. Seagrasses also facilitate seaweeds that can become entangled around seagrass leaves and stems. However, relatively little is known about interactions between entangled seaweeds and seagrass, their effects on seagrass-associated invertebrates and if their interactions are modified by abiotic conditions, like nutrient and sedimentation levels. We aimed to test the hypotheses that (i) seaweeds have negative effects on seagrass (competing for limited resources) but positive effect on invertebrate biodiversity (by increasing habitat-complexity), across seasons in the Avon-Heathcote estuary, (ii) that similar processes occur in other estuaries, and (iii) that the magnitude of effects increases with increasing levels of inorganic nutrients and sediments. To test the first two hypotheses, we collected cores from the Avon-Heathcote estuary and from six other estuaries. To test the third hypothesis, we manipulated nutrient and sedimentation levels in two field-experiments. Preliminary data analysis supports our hypotheses: seaweeds had negative impact on seagrass but positive effects on the abundance of many invertebrates. We also found that enhanced sediments, but not nutrients, had strong negative impact on seagrass with cascading negative impacts on the invertebrate community.

Paper: “A sixth-level habitat cascade increases biodiversity in an intertidal estuary”

paper-1-thomsen-et-al-2016

Mads S. Thomsen, Thomas Hildebrand, Paul M. South, Travis Foster, Alfonso Siciliano, Eliza Oldach, David R. Schiel

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Abstract

Many studies have documented habitat cascades where two co-occurring habitat-forming species control biodiversity. However, more than two habitat-formers could theoretically co-occur. We here documented a sixth-level habitat cascade from the Avon-Heathcote Estuary, New Zealand, by correlating counts of attached inhabitants to the size and accumulated biomass of their biogenic hosts. These data revealed predictable sequences of habitat-formation (= attachment space). First, the bivalve Austrovenus provided habitat for green seaweeds (Ulva) that provided habitat for trochid snails in a typical estuarine habitat cascade. However, the trochids also provided habitat for the non-native bryozoan Conopeum that provided habitat for the red seaweed Gigartina that provided habitat for more trochids, thereby resetting the sequence of the habitat cascade, theoretically in perpetuity. Austrovenus is here the basal habitat-former that controls this “long” cascade. The strength of facilitation increased with seaweed frond size, accumulated seaweed biomass, accumulated shell biomass but less with shell size. We also found that Ulva attached to all habitat-formers, trochids attached to Ulva and Gigartina, and Conopeum and Gigartina predominately attached to trochids. These “affinities” for different habitat-forming species probably reflect species-specific traits of juveniles and adults. Finally, manipulative experiments confirmed that the amount of seaweed and trochids was important and consistent regulators of the habitat cascade in different estuarine environments. We also interpreted this cascade as a habitat-formation network that describes the likelihood of an inhabitant being found attached to a specific habitat-former. We conclude that the strength of the cascade increased with the amount of higher-order habitat-formers, with differences in form and function between higher and lower-order habitat-formers, and with the affinity of inhabitants for higher-order habitat-formers. We suggest that long habitat cascades are common where species traits allow for physical attachment to other species, such as in marine benthic systems and old forest.

Conference: “Epiphytism as key driver of biodiversity in canopy-forming seaweeds-dominated systems”

11th International Temperate Reefs Symposium (ITRS) 2016, University of Pisa, Italy

06-itrs-2016

Alfonso Siciliano, Mads S. Thomsen, David R. Schiel

X

Abstract

It is well established that host species that are morphologically and genetically different can support different epibiotic species, and that these differences can support different invertebrate communities. However, no studies have tested the opposite hypothesis of whether morphologically similar congeneric hosts support similar epibiota and have similar cascading effects on invertebrate communities. This hypothesis was tested with mensurative and manipulative experiments using three conspecific, morphologically similar marine seaweed hosts: the canopy-forming fucoids Cystophora torulosa, C. scalaris, and C. retroflexa. In the mensurative experiment, hosts, epiphytes and associated invertebrate communities were sampled and enumerated from 4 tide-pools (>1 m apart), at 2 reefs (>1 km apart) and 4 sites (>100 km apart). In two follow-up manipulative experiments, defaunated hosts, epiphytes and epiphytes’ mimics were combined and transplanted to shared tide pools and the epifaunal recolonization was quantified. Both experiments suggest that epiphytism increases abundances and richness of invertebrates, across host species, epiphyte species, sites, regions, and experimental methods, demonstrating its key role in sustaining the epifaunal community. However, the experiments reject the initial hypothesis since congeneric and morphologically similar hosts appear to support a different epifauna and having different cascading effects.

Conference: “Cascading effects of epiphytism associated with co-occurring congeneric hosts”

New Zealand Ecological Society conference (NZES) 2015, University of Canterbury, New Zealand

03-nzes-conference-2015

Alfonso Siciliano, Mads S. Thomsen, David R. Schiel

X

Abstract

It is well established that host species that are morphologically and genetically different can support different epibiotic species, and that these differences can support different invertebrate communities. However, no studies have tested the opposite hypothesis of whether morphologically similar congeneric hosts support similar epibiota and have similar cascading effects on invertebrate communities. This hypothesis was tested with mensurative and manipulative experiments using three conspecific, morphologically similar marine seaweed hosts: the canopy-forming fucoids Cystophora torulosa, C. scalaris, and C. retroflexa. In the mensurative experiment, hosts, epiphytes and associated invertebrate communities were sampled and enumerated from 4 tide-pools (>1 m apart), at 2 reefs (>1 km apart) and 4 sites (>100 km apart). In two follow-up manipulative experiments, defaunated hosts, epiphytes and epiphytes’ mimics were combined and transplanted to shared tide pools and the epifaunal recolonization was quantified. Both experiments suggest that epiphytism increases abundances and richness of invertebrates, across host species, epiphyte species, sites, regions, and experimental methods, demonstrating its key role in sustaining the epifaunal community. However, the experiments reject the initial hypothesis since congeneric and morphologically similar hosts appear to support a different epifauna and having different cascading effects.