Faunal associations with drifting macrophytes and wrack accumulations in the nearshore of South ...

247 Pages·2015·2.42 MB·English

by  Ryan Baring

Faunal associations with drifting macrophytes and wrack
accumulations in the nearshore of South Australian sandy
beaches

Ryan J. Baring
BSc. Mar Biol (Hons), Flinders University

A thesis submitted for the degree of Doctor of Philosophy (PhD)
School of Biological Sciences, Faculty of Science and Engineering
Flinders University
September 2014
Table of Contents
Summary .................................................................................................................................. iii
Declaration.............................................................................................................................. vii
Statement of contribution..................................................................................................... viii
Acknowledgements .................................................................................................................. x

Chapter 1: General Introduction ........................................................................................... 1
1. Drifting macrophytes in coastal ecosystems ………………………………………………. 1
2. Study background: Patchiness in time and space of drifting macrophytes …………………6
3. Macroinvertebrate assemblages associated with drifting macrophytes ……………….........7
4. Fish assemblages associated with drifting macrophytes ……………………………………9
5. Trophic interactions associated with drifting macrophytes ………………………………..12
6. Source to sink: The drift pathway ……………………………………………………........14
7. Aims of this project ………………………………………………………………………..18
Chapter 2: Steps for establishing precise estimates of floral and faunal distributions in
patchy marine habitats: an example from nearshore marine environments ……………20
1. Introduction ………………………………………………………………………………..20
2. Methods ……………………………………………………………………………............27
3. Results ………………………………………………………………………………..........33
4. Discussion ……………………………………………………………………..…………..44
5. Conclusion …………………………………………………………………………….......48
Chapter 3: Storm versus calm: variation in fauna associated with drifting macrophytes
in sandy beach surf zones …………………………………………………………………..50
1. Introduction ………………………………………………………………………………..50
2. Methods ……………………………………………………………………………..……..54
3. Results ……………………………………………………………………………………..61
4. Discussion ………………………………………………………………………….……...74
5. Conclusion …………………………………………………………………………………81
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Chapter 4: Trophic structure within surf-zone wrack accumulations at sandy
beaches ………………………………………………………………………………………83

1. Introduction …………………………………………………………………………..........83
2. Methods ……………………………………………………………………………………88
3. Results ………………………………………………………………………………..........94
4. Discussion …………………………………………………………………………..........110
5. Conclusion …………………………………………………………………………..........118
Chapter 5: Drift dynamics of natural versus artificial seagrass at various distances from
shore and initial colonisation by invertebrates and fish ………………………………...120
1. Introduction ………………………………………………………………………………121
2. Methods ……………………………………………………………………………..........124
3. Results ……………………………………………………………………………………134
4. Discussion …………………………………………………………………………..........155
5. Conclusion ………………………………………………………………………………..164
Chapter 6: General Discussion …………………………………………………………....166
1. Key findings ……………………………………………………………………………...167
2. Key areas for future research ……………………………………………………………..179
3. Management implications ……………………………………………………..…………180
4. Conclusion ………………………………………………………………………………..182

References ………………………………………………………………………………….185
Appendices …………………………………………………………………………………203

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Summary
The research in this thesis identifies and addresses some of the knowledge gaps
surrounding the role that detached and drifting macrophytes play as habitat and potential food
resources in the nearshore of sandy beaches. So far, very little research has been conducted in
southern Australia to investigate if important detached macrophytes are to nearshore
production. This is surprising considering the large volumes that regularly accumulate as
wrack in the surf zone and on sandy beaches, and in some cases wrack is a semi-permanent
feature. Very few beach management programs have considered the role of drifting
macrophytes and wrack accumulations in coastal ecosystems, which is concerning when
beach cleaning or wrack harvesting procedures are in place. Beach cleaning can occur up to
multiple times a week along metropolitan Adelaide beaches, particularly during the warmer
months. In South Australia, the amounts of wrack removed from beaches varies with
approximately 50-110 tonnes of algae and 3000 tonnes of seagrass per year from the South
East region of the state (PIRSA 2007).
To establish efficient sampling designs for investigating drifting wrack and associated
fauna in surf zones of sandy beaches, I undertook a carefully-planned pilot study to establish
optimal-precision estimates for sampling macroinvertebrates and ichthyofauna. I investigated
the precision of the mean for various numbers of sub-samples and replicates of seine nets to
establish a larger sampling program. The pilot study showed that the processing time for
individual seine-net samples could be reduced by 50 % using sub-sampling compared to
double the amount of time taken to process the whole sample and the time taken to process
replicate seine net samples could be reduced by 25 %, while maintaining acceptable
precision. The pilot study and exploratory approaches used in Chapter 2 were essential for
establishing precise estimates of flora and fauna associated with very patchy habitats, such as
wrack in sandy-beach surf-zones.
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The effects of regular storms on drifting marine macrophytes, consequent
accumulation of wrack (i.e. seagrass or macroalagae or both) and associated fauna in beach
surf zones across three different regions was investigated. Results showed that the influence
of storms may be more pronounced in sheltered coastal waters compared to more exposed
coastlines, where biota could have adaptations to persist in larger swell conditions. Regional
differences were more obvious than the impact of weather, with distinct macrophyte and
macroinvertebrate species richness, abundances and assemblages occurring in each region.
Fish were less aligned to the regional patterns identified for wrack or invertebrates. This
study also showed that beach morphology, specifically grain size and beach slope, may be
important to the ecology of surf zones. The new knowledge about the ecology of faunal
associations in nearshore waters during storm and calm weather in multiple regions highlights
the importance of surf-zone wrack as habitat for many fauna.
A separate study was undertaken to investigate possible trophic pathways associated
with wrack accumulations, which are little understood, particularly where wrack
compositions vary or where wrack is a semi-permanent feature in sandy-beach surf-zones. In
this study, I sampled the gut contents of fish and analysed the δ13C and δ15N stable isotope
signatures of fish, macroinvertebrates and macrophytes. Results showed that fish may be
using wrack as habitat but are likely to be foraging widely over multiple habitats away from
wrack accumulations. More evidence exists that some invertebrates such as grazers may be
using wrack accumulations for both habitat and food. Although preliminary, this study
identified baselines for trophic pathways associated with wrack accumulations in these
sandy-beach surf-zones, which can be applied to more directed studies in future. More
directed studies of specific trophic pathways, other food sources and fauna in nearby habitats
(e.g. benthic fauna) would provide better understanding of the trophic pathways within wrack
accumulations and also linkages between wrack accumulations and nearby habitats.
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Previously, no studies had investigated the surface drift dynamics of detached
seagrass. Existing studies have mainly focused on larger macroalgae such as kelps or fucoids
in open-ocean systems, rather than along sheltered coastlines. Here, the trajectories of
detached natural and artificial seagrass were investigated to establish the drift pathways and
short-term colonisation of fauna to drifting macrophytes close to shore. Various release
distances from shore in gulf waters in South Australia were compared. Tagged seagrass
generally travelled in the same direction as tides but patterns were variable across sampling
days and different distances from shore. Many tagged seagrass units released close to shore
were stranded on beaches after six hours but the eventual stranding of drifting macrophytes
further offshore was more difficult to quantify.
The colonisation of macroinvertebrates and fish to tagged seagrass was compared to
fauna found from in situ drifting (natural) macrophytes. The results of the drifting
macrophyte study also showed that colonisation by fish to drifting macrophytes are more
likely to be for habitat, rather than food. Also, more macroinvertebrates may colonise drifting
macrophytes at distances closer to shore, possibly due to shallower depths and thus increased
proximity of source habitats. This study provides further knowledge about macrophyte drift
dynamics, the short-term colonisation of fauna and habitat function along nearshore
coastlines. This is essential for further understanding of the ecological significance of
allochthonous material arriving on shorelines.
The research in this thesis was strategically planned to investigate and better
understand the dynamic movement of nearshore drifting macrophytes, their arrival into surf
zones and the fauna that utilise the drifting material as habitat and a food resource. This thesis
had an equal amount of research effort placed on the study of macrophytes,
macroinvertebrates and fish across multiple regions that were variously dominated by
macroalgae and/or seagrasses. The research encompasses some of the few studies anywhere
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where much wrack in the surf zone is from seagrasses. Information gained from this research
will be useful for future investigation of the ecological function and management of
nearshore ecosystems, particularly where processes such as beach cleaning occur. Future
management of allochthonous inputs such as wrack in the nearshore zone is particularly
important in southern Australia where it has received no attention in previous beach
management programs.

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Declaration
I certify that this thesis does not incorporate without acknowledgement any material
previously submitted for a degree or diploma at any university; and to the best of my
knowledge and belief it does not contain any material previously published or written by
another person except where due reference is made in the text.

Ryan Baring

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Statement of Contribution

This thesis was prepared as a series of manuscripts (Chapters 2-5) which are either in the
process of being, or will in the future be, submitted to various scientific journals. Prof. Peter
Fairweather and Dr Rebecca Lester, as my primary supervisors, provided conceptual and
methodological input throughout the writing of this thesis. Dr Charlie Huveneers as my
secondary supervisor assisted with input into drafting of some chapters at the later stages of
writing.
Chapter 2 will be submitted in the near future to a methods based journal, which is yet to be
decided. This manuscript is co-authored by my supervisors, Prof. Peter Fairweather, who
provided assistance to me with conceptual design, data analyses and editing the manuscript,
and Dr Rebecca Lester, who also provided assistance with the writing of R script and
subsequent data analyses. I reviewed the literature and undertook all field data collection,
laboratory processing and species identification, data analyses and manuscript preparation.
My proportional contribution to this manuscript was 85 %, Dr Rebecca Lester contributed 10
% and Prof. Peter Fairweather contributed 5 %. .
Chapter 3 has been published in Journal of Experimental Marine Biology and Ecology (see
Baring et al. 2014) . This manuscript is co-authored by my supervisors, Prof. Peter
Fairweather and Dr Rebecca Lester, who provided assistance with conceptual design, data
analyses and editing the manuscript. I reviewed the literature and undertook all field data
collection, laboratory processing and species identification, data analyses and manuscript
preparation. My contribution to this manuscript was 90 %, and Prof. Peter Fairweather and
Dr Rebecca Lester contributed 5 % each.
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Chapter 4 will be submitted in the near future to Estuaries and Coasts. This manuscript is co-
authored by my supervisors, Prof. Peter Fairweather and Dr Rebecca Lester, who provided
assistance with conceptual design, data analyses and editing the manuscript. Dr Charlie
Huveneers provided advice with editing of the manuscript. I undertook all field data
collection, laboratory processing, data analyses and manuscript preparation. My contribution
to this manuscript was 89 %, with Prof. Peter Fairweather and Dr Rebecca Lester contributed
5 % each and Dr Charlie Huveneers 1 %.
Chapter 5 will be split into two manuscripts in the near future, with one manuscript focusing
upon the drift movement of detached macrophytes and the second manuscript focusing on
colonisation and biological interactions with associated fauna offshore. The two manuscripts
will be submitted to Estuarine, Coastal and Shelf Science and Marine Ecology Progress
Series, respectively. These manuscripts will be co-authored by my supervisors, Prof. Peter
Fairweather and Dr Rebecca Lester, who provided assistance with conceptual design, data
analyses and editing the manuscript. I undertook all field data collection, laboratory
processing, data analyses and manuscript preparation. My contribution to this manuscript was
90 %, and Prof. Peter Fairweather and Dr Rebecca Lester contributed 5 % each.

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