View
3
Download
0
Category
Preview:
Citation preview
FLOATING SEAWEED AS EPHEMERAL
NEUSTONIC HABITATDrijvend zeewier als efemeer neustonisch habitat
Sofie Vandendriessche
The neustonic zone and its inhabitants
Neuston s.l.: all plants and animals inhabiting the surface layer of oceans and seas
Pleuston = organisms whose bodies project at least partly into the air (Physaliaphysalis = Portuguese-Man-of-War; the water bug Halobates sp.) Neuston s.s. = organisms that live underneath the water surface film (e.g.Janthina sp. = purple bubble raft snail)
Sampling: neuston net that partly projectsabove and below the water surface=> Neuston s.l.
www.jochemnet.de
FLOATING SEAWEED AS EPHEMERAL NEUSTONIC HABITAT
? ? ?
The neustonic zone and its inhabitants
Harsh environment:high temperature variation high UV irradiation high light levels inhibit photosynthesis exposed to wave actionmarine and aerial predators contaminants (heavy metals, hydrocarbons)
The neustonic layer: considerably different living conditions compared to deeperlayers
Rich environment:High dissolved oxygen contentIntensive absorption of solar radiationHigh nutrient supply
airial precipitationanimal excreta and remainscolloidal and dissolved organic matter
Floating tar
Foam
Whale carcass
Rich fauna displaying adaptive strategies to reduce stress (e.g. pigmentation, floating devices)
Floating objects
Why do neustonic organisms concentrate near floating objects?
Availibility of a surface for attachmentProvision of shelter from predatorsPresence of a food source
Substitution of the seabedSpawning substrate and nursery areaMeeting point for the formation and maintenance of schoolsCleaning station
Possibility for dispersal via rafting
Small-scale spatial variation in neuston: local accumulations of organisms
< winds and currents, which create surface slicks, fronts, upwelling zones and windrows
< presence of floating structures (seaweed, wood, plastic debris, buoys, pumice,...)
Floating objects
Song Ye et al, 1991 – Minchin, 1996 - Jokiel, 1989 – Thiel, 2003 - Barnes & Fraser, 2003
Low food valueHigh survival time
High food valueLow survival time
High food valueHigh survival time
Natural Man-made
Tar pellets, plastic, rubber, rope, nylon nets, bottles
Less photodegradableResurfaceNo grazing
Tar from natural seepsVolcanic pumice
SeedsLogsseagrass
seaweed
GrazingDegradationpneumatocysts
Grazing Degradation
FLOATING SEAWEED AS EPHEMERAL NEUSTONIC HABITAT
?
Pelagic Sargassum versus ephemeral seaweed aggregations
Sargassum natans & S. fluitans in the Atlanticocean
Fully adapted to a permanently pelagic life
Rich fauna :
- Specialised / endemic e.g. Histrio- Opportunists: juvenile fish, invertebrates, young turtles looking for food and shelter
Multi-species
aggregates of detached intertidal and subtidal seaweed branches
< fragmentation due to storms, grazing damage & seasonal release of plant parts
limited longevity => ephemeral
Associated fauna
www.bigelow.org
Ephemeral rafts of floating seaweed
Fauna on seaweed rafts (Thiel & Gutow, 2005)
Species composition of seaweed-associated fauna
4 categories influences
1) Inhabitants of attached seaweeds2) Inhabitants of cast-up seaweed3) Subtidal, benthic and epibenthic species4) Planktonic and neustonic species
Clump sizeSpatial and temporal variationRaft age (succession)Seaweed species compositionDisturbance and exchange between clumps
Objectives and thesis outline
Ecological impact of floating seaweeds as ephemeral habitats in the North Sea?
Influence of floating seaweed on the richness and composition of the neuston
Analysis of the environmental and biological factors structuring the seaweed-associated invertebrate community
Effect of increased prey concentration on the presence, abundance and behaviour of fishes and birds
Seaweed raft longevity and potential as dispersal vector
I.
Chapter 2. Floating seaweed in the neustonic environment: a case study from Belgian coastal waters
II.
Chapters 3 - 4. Food and habitat choice in floating seaweed clumps: the obligate opportunistic nature of the associated macrofauna & Sources of variation in floating seaweed associated macro-invertebrates
III.
Chapters 5 -6. Hiding and feeding in floating seaweed: floating seaweed as possible refuges or feeding grounds for fishes & Seabirds foraging at floating seaweeds in the Northeast Atlantic
IV.Chapter 7. Floating seaweed and the influences of temperature, grazing and clump size on raft longevity – a microcosm study
Hiding and feeding in floating seaweed: floating seaweed clumps as possible refuges and feeding
grounds for fishes
Floating seaweed clumps as refuges or feeding grounds for fishes
Wide variety of fish taxa are attracted to floating structures
Plastic debris, floating seaweeds, wood, jellyfish, FAD’s, animal remainse.g. Safran & Omori, 1990; Davenport & Rees, 1993; Moser et al, 1998, Masuda & Tsukamoto, 2000; Castro et al, 2002; Jacquemet, 2004; Thiel & Gutow, 2005a; Thiel & Gutow, 2005b
Fish community most diverse underneath seaweeds (Fedoryako, 1989):increased diversity due to the substantial increase in habitat complexity of the pelagic environment due to the presence of these seaweeds Kingsford (1995)
AIMS:describe species composition and behaviour of fish associated with
floating seaweedscomparing neustonic data with those obtained from seaweed samplessize distributions and diets of the fishesstructuring factors influencing species composition
Provision of food, shelter, a visual orientation point, passive transport, ...
Gathering data: sampling along the Belgian coast
Dip net samples
Seaweed-associated fish
Neuston net samples
Neustonic fish
length rangeSP SU AU WI (cm)
Ammodytes tobianus /Hyperoplus lanceolatus
Arnoglossus laterna ∎ 0,5 1Belone Belone ∎ 0,9 - 3,7 69
Chelon labrosus ∎ ∎ ∎ 0,3 - 3,8 1591Ciliata mustela ∎ ∎ 0,4 - 3,6 405
Clupea harengus /Sprattus sprattus/
Engraulis encrassicolusCottidae sp. ∎ ∎ ∎ 0,2 - 1,2 290
Echiichthys vipera ∎ 0,4 - 1,6 45Hippocampus guttulatus ∎ 2,9 - 3,5 2
Labrus bergylta ∎ 0,6 - 1,1 2Merlangius merlangus ∎ 0,6 - 4,1 10
Pleuronectidae sp. ∎ ∎ 0,7 - 1,3 3Pollachius pollachius ∎ 3,2 1
Pollachius virens ∎ 2,5 1Scophthalmus maximus ∎ ∎ 1,6 - 2,1 4
Solea solea ∎ ∎ ∎ ∎ 0,3 - 0,8 14Syngnathus acus ∎ ∎ ∎ 2,9 - 5,5 7
Syngnathus rostellatus ∎ ∎ ∎ ∎ 1,0 - 5,7 28Trachurus trachurus ∎ ∎ 0,3 - 4,2 258
0,4 - 9,3 2257∎ ∎ ∎ ∎
# caught
∎ ∎ ∎ ∎ 0,3 - 12,2 884
Significant seasonal differences
MDS of neustonic fish data (sqrt transformation, Bray-Curtis similarity): black triangles = summer samples, white triangles =autumn samples, crosses = spring samples, squares = winter samples
Stress: 0,13
large variability in the summer samples (average similarity: 34), compared to the other seasons (average similarity au: 64, wi: 54, sp: 60).
No effects of sampling station and presence of small amounts of floating seaweed and debris
Neustonic fish
Length range # caughtSP SU AU WI (cm)
Belone belone ∎ 4.0 1Blennidae ∎ 1 – 1.2 2
Callionymus lyra ∎ - 1Chelon labrosus ∎ ∎ 0.7-2.8 202Ciliata mustela ∎ ∎ 1.0 - 4.0 147
Cottidae ∎ 0.8 – 1.7 13Cyclopterus lumpus ∎ ∎ ∎ ∎ 0.6 – 4.9 97Entelurus aequorius ∎ ∎ ∎ 13.6 - 15 6
Gobiidae ∎ 1.1 – 1.2 2Merlangius merlangus ∎ 3.4 1
Nerophis lumbriciformis ∎ 5 1Pollachius pollachius ∎ 2.3 – 2.6 11
Pollachius virens ∎ 2.3 1Syngnathus acus ∎ 7.4 - 14.4 2
Syngnathus rostellatus ∎ 3.7 – 12.2 7Trachurus trachurus ∎ 0.7 – 4.3 147
Stress: 0,01
Chelon labrosus
Cyclopterus lumpus
Ciliata mustela Trachurus trachurus
Groups based on dominant fish species
pattern of the fish data compared to the environmental data: seaweed volume, relative abundances of the seaweed constituents per sample, surface water temperature and salinity, distance to shore, atmospheric pressure and humidity, densities of seaweed-associated macrofauna
Low matching coefficient (0.23): only part of biotic structure explained
Seaweed-associated fish
Seaweed-associated fish
Harpacticoida L. holsatus MG G. crinicornis /G. locustaI. baltica H. varians PL Idotea sp. JP. longicornis MG C. maenas MG L. holsatus JAphididae S. marina A. swammerdamiP. elegans PL Jassa sp. ChironomidaeI. emarginata T. tergipes
Cyclopterus lumpus
0204060
0,5-1 1-1,5 1,5-2 2-2,5 2,5-3 3-3,5 3,5-4 4-4,5 4,5-5
length class (cm)
# in
divi
dual
s
Ciliata mustela
-150-100-50
050
100
0 - 0,5 0,5 - 1 1 - 1,5 1,5 - 2 2 - 2,5 2,5 - 3 3 - 3,5 3,5 - 4
length class (cm)
# in
divi
dual
s
Chelon labrosus
-150
-100
-50
0
50
100
0 - 0,5 0,5-1 1-1,5 1,5-2 2-2,5 2,5-3 3-3,5 3,5-4
length class (cm)
# in
divi
dual
s
Trachurus trachurus
-150
-100
-50
0
50
0 - 0,5 0,5 - 1 1 - 1,5 1,5 - 2 2 - 2,5 2,5 - 3 3 - 3,5 3,5 - 4 4 - 4,5
length class (cm)
# in
divi
dual
s
Syngnathus rostellatus
-15
-10
-5
0
5
1 - 1,5 2,5 - 3 4-4,5 5,5-6 7-7,5 8,5-9 10-10,5 11,5-12
length class (cm)
# in
divi
dual
s
Black: seaweed fishGrey: neustonic fish
Seaweed-associated fish: size-frequency distributions
Numerical percentage
0%
20%
40%
60%
80%
100%
1,5 - 2 2 - 2,5 2,5 - 3 3 - 3,5 3,5 - 4
le ngt h c la ss (cm)
L. ho lsatus MG unid ent . Crab larvae Gammarus sp .
Calano id a sp . Harp actico id a sp . I. b alt ica
fish egg A. swammerdami G. crinico rnis / G. locus tares t
• First-year juveniles
• Highest Fulness index (0 – 18.3), positively correlated with length of the fish• Shift in dominant prey with increasing length: Liocarcinus holsatus megalopae, calanoid and harpacticoid copepods and small gammarid amphipods (mainly Gammarus sp. juveniles) in the smallest length class Idotea baltica, fish eggs, calanoids and large gammarid amphipods (Gammarus locusta and G. crinicornis) in the larger length classes
Stomach analyses of 5 fish species: Cyclopterus lumpus
Stomach analyses of 5 fish species
TRACHURUS TRACHURUSNume ric a l pe rce nt a ge
0%
20%
40%
60%
80%
100%
2 - 2,5 2,5 - 3 3 - 3,5 3,5- 4
lengt h c la sse s
L. holsa t us Z Ca la noida sp. Ha rpa c t ic oida sp.
P a la e monida e sp. Z Cypris Biva lvia
P odon sp. Mysida ce a sp. Na uplius
Nume ric a l pe rc e nt age
0%
20%
40%
60%
80%
100%
2 - 2,5 2,5 - 3 3 - 3,5
le ngt h c la sse s
Ca la noida sp. Ha rpa c t ic oida sp. P a la emonidae sp. P L
P a la e monida e sp. Z Cypris P le urobrac hia pile us
Ga mma rus sp.
Neuston Seaweed
SYNGNATHUS ROSTELLATUS< 8 cm : only calanoid copepods
> 8 cm from seaweed samples also ingested harpacticoid copepods and crab megalopae
Seaweed fish: calanoid (N%: 95) and harpacticoid copepods (N%: 3.9), dipteraninsects (N%: 0.6).Neustonic fish: Calanoid copepods (N% >99); Dipteran insects and cypris larvae were rarely found; harpacticoid copepods were absent
CILIATA MUSTELA Nume ric a l pe rce nt a ge
0%
20%
40%
60%
80%
100%
2 - 2,5 2,5 - 3 3 - 3,5
le ngt h c la sse s
L. holsa t us MG Ca la noida sp. f ish e gg
P la t he lmint he s Ammodyt ida e sp.
Nume ric a l pe rce nt a ge
0%
20%
40%
60%
80%
100%
2,5 - 3 3 - 3,5 3,5 - 4
le ngt h c la sse s
L.holsa t us MG Cala noida sp. inve rt ebra t e egg
f ish e gg Harpac t icoida sp. Ga mma rus sp.
re st
Neustonic fish: Calanoida, fish eggs and, as they grow, they start feeding on larger prey items like crab megalopae. Seaweed-associated fish: more variable, also comprises harpacticoid copepods, small gammaridamphipods and invertebrate eggs (probably from isopods and amphipods).
CHELON LABROSUS
Stomach analyses of 5 fish species
Neustonic fish community Seaweed-associated fish community
Mainly seasonally structured Low matching coefficient with environmental data, seaweed composition, associated macrofaunal densities
Fish do not select their seaweed clumps
Individuals captured from below floating seaweeds are often larger than conspecifics from open waters (Kingsford, 1992)
Chelon labrosus Cyclopterus lumpus, Trachurus trachurus, Ciliata mustela: effect of species interactions (competition, territorialism)?
Obvious in all species, especially Ciliata mustela and Syngnathus rostellatus
protection and/or food enhance growth OR floating seaweeds are colonised by larger individuals
Conclusions
Cylopterus lumpus:
only found in seaweed samples, majority of ingested prey consists of seaweed-associated fauna (gammarid amphipods, idoteid isopods, crab megalopae, postlarval prawns, harpacticoids)
weedpatch specialist: closely associated resident
Ciliata mustela & Trachurus trachurus
larger individuals in seaweed clumps, ingestion of seaweed associated macrofauna (limited proportion of diet)
visitors – residents
Chelon labrosuscomparable size as in neuston, very limited feeding on associated fauna
(only harapacticoids)visitors
Syngnathus rostellatus
recruitment from neuston or carried with seaweed
Conclusions
“Floating seaweeds can be regarded as temporary and unpredictablehabitats shared between several fish species (mainly juveniles) that use
them for different reasons and with variable intensity.”
Introduction
Variations in seabird distribution:
Large scale Environmental heterogeneity due to physical oceanographic processes
Pervasive anthropogenic disturbance
Patchiness Species-specific responses to the environmente.g. surface features can provide resting grounds or additional food
Fronts, internal wavesFloating objects such as plastic, cuttlebones, seaweed
Are there seabirds that are frequently observed in association with ephemeral seaweed patches?
Are these associations feeding mode dependent?
database analysis
ESAS – European Seabirds at Sea
Seabird observations collected and coded using standardised survey techniques
Used data from North Sea, period 1979 -2000Specific coding for associations birds and surface phenomena
Floating seaweeds as sources of small-scale patchiness in seabirds
0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
Ster
cora
rius
skua
Ster
cora
rius
pom
arin
usSt
erco
rari
uspa
rasi
ticus
Ster
cora
rius
long
icau
dus
Laru
shyp
erbo
reus
Laru
sarg
enta
tus
Laru
sfus
cus
Laru
scan
usLa
rusm
arin
usLa
rusr
idib
undu
sLa
rusm
inut
usRi
ssa
trid
acty
laPu
ffinu
sgra
vis
Puffi
nusg
rise
usPu
ffinu
spuf
finus
Hyd
roba
tesp
elag
icus
Fulm
arus
glac
ialis
Mer
guss
erra
tor
Ster
na p
arad
isae
aSt
erna
sand
vice
nsis
Ster
na h
irun
doPo
dice
pscr
ista
tus
Gav
iaar
ctic
aG
avia
stel
lata
Alca
tord
aFr
ater
cula
arct
ica
Sula
bass
ana
Phal
acro
cora
xca
rbo
Phal
acro
cora
xar
isto
tele
sU
ria
aalg
eC
epph
usgr
ylle
Mel
anitt
ani
gra
Mel
anitt
afu
sca
Som
ater
iam
ollis
sim
a
Parasitism, scavenging, opportunistic surface feeding
Surface-seizing, pursuit-plunging, pursuit-diving (shallow dives)
Surface feeding, dive down to 5-10 m
Deep diving, pelagic and bottom feeding
Diving, benthos feeding
Freq
. of o
ccur
renc
e % Most common behaviour:
surface peckingActively searchingPursuit plunging
Arctic TernSurface pecking, actively searching and dipping => dipping and surface pecking
Sandwich Tern:Actively searching & deep plunging
Common Tern:Actively searching, pursuit diving & scavenging =>surface pecking and
dipping
Floating seaweeds as sources of small-scale patchiness in seabirds
Other clues about the association seabirds – floating seaweeds from literature:
Terns: plunge-diving in vicinity of floating seaweeds in Canada (Parsons, 1986)
Roosting and foraging in South Africa and Sargasso Sea (Tree & Klages, 2004, Haney, 1986)
Fulmars: Idotea metallica in diet (Furness & Todd, 1984)
Pecking on North Sea debris (Cadée, 2002)
Cormorants: Pick up floating debris from sea-surface (Tasker et al, 2000)
Cyclopterus lumpus in diet (Lilliendahl & Solmundsson, 2006)
Common scooters and eiders: mainly benthos feeders, but also feed on seaweed-associated organisms
Some seabirds are attracted to floating seaweeds
Mostly plunge-diving or surface feeding
Profit from increased prey concentration
The increased structural complexity and food supply in floating seaweeds temporarily enhance foraging conditions for some seabirds depending on their preferred prey and foraging strategy small-scale patchiness
Recommended