Resource-partitioning in a degraded coral reef: a case study from Eilat, Gulf of Aqaba
by Julian Lilkendey, Michael Meares and Armagan Sabetian
Leibniz Centre for Tropical Marine Research(ZMT) | Auckland University of Technology (AUT) | Auckland University of Technology (AUT)
Herbivores play an integral functional role as mediators of primary productivity, exerting top-down control on benthic algal production. In return, bottom-up effects of “turf wars” play an important role on the availability of resources for competing herbivores. Little is known, however, about the effects of reef degradation on resource-partitioning and interspecific competition in this ecological guild. In a severely degraded coral reef in Eilat (Israel, Gulf of Aqaba) we conducted remote underwater stereo-video surveys to compare the expression of grazing behaviours (bite rates, bite distances, grazed substrate) between two closely related herbivorous fishes. Here we show that reef degradation had a significant impact on the foraging behaviour of two surgeonfish species of similar functional roles; while bristletooth surgeonfish Ctenochaetus striatus mainly grazed nearby detritus on dead coral substrate, yellowtail surgeonfish Zebrasoma xanthurum preferentially fed on filamentous turf algae which covered rocks and rubble at greater distances. However, depending on the availability of grazable substrate, both model species showed opposing adjustments of their bite rates. This compensation mechanism may be responsible for the observed balance in biomass distribution between the two species. Closely examining feeding strategies in sympatric herbivorous fishes facilitates our understanding of fine-scale specialization, competition for resources, and habitat use in coral reefs. Species with similar functional traits may have an adaptive capacity in the way they exploit resources to compensate for anthropogenic disturbances to their ecosystem.
Extractive Taxonomies: Untangling Networked Knowledge Flows in Zanzibar’s Shell Economy
by Theresa Schwenke and Rapti Siriwardane-de Zoysa
ZMT | ZMT
Gleaning on Zanzibar is conducted for subsistence and for the local and tourist industry. The gleaning activities minimize the population sizes. For the local human population on Zanzibar increasing effort is required to gain decreasing amounts of food or income. A variety of gastropods and bivalves are present on Zanzibar’s coast. Some are harmful or even poisonous. Gleaners need to possess specific knowledge on species abundance and what they can safely collect. As the shell gleaning, processing and usage locally and their global implications are complex in terms of livelihood, social, economic and ecological sustainability the question arises: From which sources do different actors involved in Zanzibar’s shell economy gain their knowledge and how do they make sense of, utilize and communicate these “learned taxonomies”? Therefore we investigate a) perceptions on marine organisms presently harvested (and those in the past); b) why certain species are harvested and not others; c) how differentiation and classification between marine organisms occur. In the scope of the MariTA project, we identified and interviewed actors involved in shell gleaning, processing, selling and buying on Zanzibar. We provide first results on 1) Who is involved in Zanzibar’s shell economy, 2) What actors have access to what source and kind of knowledge? 3) Which actors are in contact? 4) What forms of knowledge are transferred? and 5) How do actors define and perceive their own and the roles of other actors within the emerging shell gleaning, processing and usage network? Increasing our understanding of the shell gleaning economy on Zanzibar and their interacting actors will help to enhance and make communication and knowledge flows more transparent for governing social, economic and ecological sustainability.
Dissection of a complex trait: quantitative analysis of reef fish colour pattern
by Floriane Coulmance, Oscar Puebla, Derya Akkaynak, Yann Le Poul and Owen McMillan
Leibniz Centrefor Tropical Marine Research | Leibniz Centre for Tropical Marine Research (ZMT) / OldenburgUniversity | Harbor Branch Oceanographic Institution | München University | Smithsonian Tropical Research Institute
Colour pattern plays a fundamental role in the ecology and evolution of a variety of organisms. This is particularly true for coral reef fishes that live in a highly visual environment and display a stunning diversity of colour patterns. Nevertheless, reef fish colour pattern is a highly complex trait and has not yet been analysed with fully quantitative approaches. Here, I present a pipeline for the objective and quantitative analysis of colour pattern in reef fishes and apply it to the hamlets, a group of Caribbean reef fishes that is characterised by spectacular variation in colour pattern, as a proof of principle. My analysis is based on >1000 photographs of 113 live specimens from 13 species and 4 populations that were taken in situ in a standardised way. Images were colour-standardised with a custom MATLAB script and aligned with a novel machine learning algorithm that uses a combination of landmarks and Bézier curves. This approach allows to conduct pixel-by-pixel comparisons of all photographs for the quantitative analysis of both colour and pattern. In addition, the entire genomes of the 113 samples were sequenced. The combination of these two datasets will allow to dissect the genomic bases of colour pattern variation with unprecedented resolution.
Effects of gastropods on sediment characteristics in mangroves
by Niklas Reinhardt1,2, Fiona MacKay3,4, Steven Weerts5, Martin Zimmer1,2,7 and Véronique Helfer1
Authors‘ affiliations:
1 Department of Ecology, Leibniz Centre for Tropical Marine Research, Bremen, Germany
2 University of Bremen, Faculty 02 Biology/Chemistry, Bremen, Germany
3 Oceanographic Research Institute, South African Association for Marine Biological Research, Durban, South Africa
4 School of Life Sciences, University of KwaZulu-Natal, Durban, South Africa
5 Coastal Systems Research Group, Council for Industrial and Scientific Research, South Africa
6 Department of Zoology and Coastal Research Unit of Zululand, University of Zululand, South Africa
7 IUCN SSC-Mangrove Specialist Group
Molluscs in mangroves are ecologically important because they are found on multiple consumer levels. As an important mollusc class, gastropods often occur in high densities across the intertidal and vertically on trees and similar structures in mangroves. Despite their significance in mangrove ecosystems, their ecological role is poorly understood. Here, we investigate the effects of the truncated mangrove snail, Cerithidea decollata, on sediment characteristics, such as sediment respiration, organic matter content and quality, and sediment grain size, by means of an enclosure-exclosure experiment in an Avicennia marina forest at the east coast of KwaZulu-Natal, South Africa. Three different treatments (no snails, ambient density = 16 individuals/0.318 m², high density = 32 ind./ 0.318 m²) were applied. While we found no significant effects of snail’ density on sediment respiration or organic matter content, we observed a significant increase in the percent sand in the upper sediment layer over time, at high densities. Likely, C. decollata mucus induces sediment grains to bind together into larger particles whilst detritus-feeding. We therefore postulate that snails can help stabilize mangrove sediments and possibly help in counteracting erosion. These snails may therefore contribute to the ecosystem service that mangroves provide as coastal defenses.
Diversity in fish intestine morphology: drivers and use in functional studies
by Mattia Ghilardi, Nina M. D. Schiettekatte, Jordan M. Casey, Simon J. Brandl, Samuel Degregori, Alexandre Mercière, Fabien Morat, Yves Letourneur, Sonia Bejarano and Valeriano Parravicini
Reef Systems Research Group, Department of Ecology, Leibniz Centre for Tropical Marine Research (ZMT),Fahrenheitstraße 6, 28359 Bremen, Germany | PSL Université Paris: EPHE-UPVD-CNRS, USR3278CRIOBE, 66860 Perpignan, France | PSL Université Paris: EPHE-UPVD-CNRS, USR3278 CRIOBE, 66860Perpignan, France | PSL Université Paris: EPHE-UPVD-CNRS, USR3278 CRIOBE, 66860 Perpignan,France | Department of Ecology and Evolutionary Biology, University of California Los Angeles, LosAngeles, United States | PSL Université Paris: EPHE-UPVD-CNRS, USR3278 CRIOBE, 66860 Perpignan,France | PSL Université Paris: EPHE-UPVD-CNRS, USR3278 CRIOBE, 66860 Perpignan, France | UMRENTROPIE (UR-IRD-CNRS-IFREMER-UNC), LabEx « Corail », Université de la Nouvelle-Calédonie, BPR4, 98851 Nouméa Cedex, New Caledonia | Reef Systems Research Group, Department of Ecology,Leibniz Centre for Tropical Marine Research (ZMT), Fahrenheitstraße 6, 28359 Bremen, Germany | PSLUniversité Paris: EPHE-UPVD-CNRS, USR3278 CRIOBE, 66860 Perpignan, France
Trait-based approaches are increasingly used in ecosystem functioning studies. However, trait-function relationships are often supported by weak empirical evidence, undermining the strength of these approaches. Digestion and nutrient assimilation remain challenging functions to characterise using traits. In fishes, this is commonly achieved using intestine length. Although there is consensus on the relationship between fish intestine length and species’ diets, evolutionary and environmental forces have shaped a great diversity of intestine morphologies that is not captured by length alone.
Focusing on coral reef fishes as a model group, we investigate the drivers of inter- and intraspecific variability in intestine morphology. Using a dataset encompassing 142 species and 31 families collected in three locations in French Polynesia, we test whether phylogeny, body size, trophic level, and geographic location predict three intestinal morphological traits: intestine length, diameter, and surface area.
We demonstrate that phylogeny, body size, and trophic level explain most of the interspecific variability in fish intestine morphology. Despite the high degree of phylogenetic conservatism, the flexibility of the intestine allowed adaptive convergent evolution through adjustments in both intestine length and diameter. Further, we show intraspecific variability in intestinal traits across geographic location, revealing that fishes may independently adjust one or more intestinal traits to adapt to local conditions.
We conclude that intestine surface area may be the most appropriate trait to characterise inter- and intraspecific patterns in intestine morphology, and we posit that it may be a more suitable trait to apply in functional studies than intestine length. Furthermore, the high predictive accuracy of our models highlight their potential application in macroecological studies. Lastly, our results are critical in the understanding of two ecosystem services provided by fish which are affected by intestine morphology: nutrient cycling and inorganic carbon cycling.
Poster
Do the trees matter? – Exploring spatial patterns of chemo- and biodiversity in mangrove forests
by Jonas Geburzi, Mondane Fouqueray, Ulf Mehlig, Martin Zimmer and Véronique Helfer
Department ofEcology, WG Mangrove Ecology, Leibniz-Centre for Tropical Marine Research, Bremen, Germany | SoilScience, TUM School of Life Sciences, Technical University of Munich, Weihenstephan, Germany |Instituto de Estudos Costeiros, Universidade Federal do Pará, Campus Bragança, Brazil | Department ofEcology, WG Mangrove Ecology, Leibniz-Centre for Tropical Marine Research, Bremen, Germany |Department of Ecology, WG Mangrove Ecology, Leibniz-Centre for Tropical Marine Research, Bremen,Germany
Little is known about spatial patterns and the drivers of organic matter (OM) quantity and quality, as well as that of biodiversity in mangrove ecosystems. Yet, such patterns are likely to exist considering the variety of biotic and abiotic gradients that are present throughout mangrove forests. Here, we aim at evaluating the effect of the ecosystem-engineering mangrove trees, as those are likely to influence the surrounding sediment by, e.g., their root system, canopy structure and the chemical composition of their leaf litter. Resolving the influence of different mangrove tree species on chemo- and biodiversity is of particular interest for knowledge-based ecosystem protection and restoration.
We will combine chemical and biological approaches to explore the influence of mangrove tree species on sediment characteristics and the composition and diversity of their associated micro- and macrobiota. To this end, we collected sediment samples from monospecific stands of the tree species Rhizophora mangle, Avicennia germinans and Laguncularia racemosa, from ten sites distributed over a mangrove forest in northern Brazil. The chemical analyses will assess the quantity and quality of the organic matter by, e.g., stepwise combustion (OM recalcitrance) and pyrolysis-gas chromatography mass spectrometry (py-GCMS; OM metabolomic fingerprinting), along with nutrient, C and N contents. The biological analyses will decipher the sediment community composition and diversity using sedimentary environmental DNA (sed-eDNA) metabarcoding, targeting major taxonomic groups: bacteria and archaea, protists, metazoans, and fungi.
This study will provide deep insights into distribution patterns of OM quantity and quality and biodiversity, how they are influenced by the species composition of the mangrove forest, and how they potentially influence each other. The results of this study will provide a sound basis for conservation planning and ecosystem design.