Sucessão ecológica em parcelas orgânicas de madeira, macroalgas e em carcassas de baleia no mar... por Angelo Fraga Bernardino - Versão HTML
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individual parcels spanning a broad range of sizes (1 - 1000 kg) to the seafloor (Wolff
1979, Smith 1983, C. Smith personal observations during >100 submersible and
remotely operated vehicle dives off California and Hawaii).
It is long recognized that food falls at the deep-sea floor can contribute to beta
diversity in deep-sea by creating patches of organic enrichment and chemical or
physical disturbance (Stockton & DeLaca 1982, Smith & Hamilton 1983, Smith 1985,
1986, Grassle & Morse-Porteous 1987, Snelgrove & Smith 2002). However, patterns
of succession resulting from the arrival of kelp and wood falls, and the identity of
their characteristic species remain essentially unstudied along the bathyal Californian
slope. Such information is essential to understanding the recycling of different types
of organic parcels (e.g., sunken kelp paddies, logs) on the continental slope and their
roles in maintaining biodiversity in the deep northeast Pacific (Snelgrove et al. 1992,
Snelgrove et al. 1996, Snelgrove & Smith 2002).
The effects of small-scale, low intensity disturbances on deep-sea infaunal
communities, resulting from algal enrichment and scavenger disturbance, have been
evaluated in a number of deep-experiments; these disturbances produce modest
increases on species diversity (Levin & Smith 1984, Snelgrove & Smith 2002).
However, substantial organic enrichment of deep-sea sediments (e.g., from
macroalgae, wood falls, diatom detritus, and whale falls) can cause dramatic
population enhancement of opportunistic and sulfophilic species (e.g. capitellid and
dorvilleid polychaetes, leptostracans and cumaceans; (Turner 1977, Smith 1986,
Grassle & Morse-Porteous 1987, Snelgrove et al. 1994, Smith et al. 2002, Smith &
Baco 2003). Community patterns in organic-rich sediments around whale falls
resemble the classic spatial succession described along organic-enrichment gradients
in shallow-water [e.g., (Pearson & Rosenberg 1978)] with very low diversity and
extremely high densities of opportunistic polychaetes species adjacent to the whale
fall, moderate macrofaunal enhancement and species diversity at intermediate
distances, and low abundances and high diversity in the background community
(Smith et al. 2002, Smith & Baco 2003). During later stages of succession, deep-sea
whale falls also support substantial assemblages of animals with chemoautotrophic
endosymbionts, producing reducing habitats ecologically similar to vents and seeps
(Smith & Baco 2003, Treude et al. 2009).
Large wood and kelp parcels also have the potential to produce intense
organic enrichment and reducing habitats in deep-sea sediments. Deep-sea wood falls
are initially processed by wood-boring xylophagainae bivalves (Turner 1977, Wolff
1979, Distel & Roberts 1997, Turner 2002, Voight 2007b) which may broadcast
organic-rich fecal material onto surrounding sediments (Turner 1977), potentially
creating organic and sulfide-rich sediments. The breakdown of large kelp
accumulations at the deep-sea floor also has the potential to create organic and
sulfide-rich sediment patches against an oligotrophic background (Vetter 1994, 1996,
Vetter & Dayton 1998).
While deep-sea wood and kelp falls are common on regional scales, temporal
patterns of infaunal community succession around large wood and kelp parcels
remain very poorly studied. Thus, the contribution of wood- and kelp-fall
communities to beta diversity in the deep sea, and their relationship to deep-sea
reducing assemblages (e.g., vent, seep and whale-fall communities) cannot be
evaluated. In this study, we investigated macroinfaunal structure for over 5 years
around experimentally implanted kelp and wood parcels in the bathyal NE Pacific to
test the following hypotheses:
1) Large wood and kelp falls exhibit distinct patterns of infaunal macrobenthic
community succession, promoting beta diversity in the deep sea;
2) There is little species overlap between sediment communities around large
wood and kelp parcels and other reducing habitats (whale falls, seeps and
vents) at similar depths in the deep sea.
2.2. Materials and Methods
Study site, deployments and sampling
Experimental implantations of kelp and wood parcels were conducted near
well-studied whale falls off southern California (Smith & Baco 2003) (Fig. 1.1). In
particular, wood and kelp parcels were implanted on the flat sediment-covered floor
of Santa Cruz Basin (SCrB), California (~33° 27’ N, 119° 22’W, 1670 m depth,
bottom temperature ~4°C, bottom-water oxygen concentration 260 µM (Treude et al.
Four parcels of wood and kelp were experimentally deployed at a mean water
depth of 1670 m in the SCrB (Fig. 1.1, point A; Table 2.1), approximately 100 m
from an experimental 30-ton whale carcass (Smith & Baco 2003, Treude et al. 2009).
Wood parcels were deployed in October 1999 and May 2002 (Table 2.1). Kelp
parcels were deployed in May 2002 and July 2002 (Table 2.1). Each kelp parcel
consisted of ~100 kg (4-5 whole plants) of fresh Macrocystis pyrifera contained in a
5-cm stretch mesh nylon net bag with one kelp holdfast protruding from the bag to
facilitate sampling of kelp associated fauna; Fig. 2.1). The wood parcels consisted of
~200 kg of untreated Douglas fir ( Pseudotsuga menziesii) with four small, 2-kg wood
packages inside a 2.5-cm stretch mesh nylon net bags attached to the upper surface
Figure 2.1 A. Kelp parcel deployed at Santa Cruz Basin after 0.25 y on the sea floor. Notice
the presence of a whitish bacterial mat over the sediment neaby the parcel. Dark sediments
around it represent sulfide rich sediments. B. 200Kg wood parcel that has been deployed at
SCrB for two years. Small wood packs inside 2.5cm mesh net nylon bags are attached on the
top of the parcel. C. Detail showing the presence of bacterial mats nearby the kelp falls at 0.25 y.
Kelp and wood parcels were sampled using the Remotely Operated Vehicle
(ROV) Tiburon during three cruises on board of the RV Western Flyer (Table 2.1).
Kelp parcels were sampled at 0.25 and 0.5 years after deployment, while wood
parcels were sampled at 0.5, 1.8, 3 and 5.5 y after deployment (Table 2.1). Sampling
occurred around distinct parcels for each time interval; because parcels were located
within several hundreds meters of one another on the homogenous basin floor, we
assumed that all fall types were bathed in the same larval pool, i.e., location effects
were modest compared to treatment effects. At all sites, three randomly located
transects radiating outward from the treatment were sampled, collecting tube cores (7
cm diameter, 10 cm deep) at 0 m, 0.5 m, 1.0 m and 2.0 m from the parcel.
Background samples (17 replicate tube cores) were additionally collected in 2002,
2004 and 2005 at random locations of 9-100 meters away from any parcel, allowing
averaging of temporal patterns in the background Santa Cruz Basin. Tube cores were
immediately sectioned into 0-1, 1-5 and 5-10 cm horizons and fixed in 4% buffered
formaldehyde-seawater solution until laboratory analysis, or frozen at -20oC for
organic carbon analysis in laboratory.
Table 2.1. Drop and sampling date from organic parcels artificially deployed at SCrB. Note
that each wood and kelp parcels were sampled on distinct cruises, thus representing
community succession on several time scales. Background cores were collected at three
different cruises (see text).
Parcel type /
Sampling date/ ROV dive
Oct. 25, 2002/TD 494
Wood (CRS 397)
Mar. 1, 2005/TD 827
Oct. 24, 2002/TD 492
Wood (CRS 800)
Mar. 1, 2004/TD 652
Kelp (CRS 799)
Oct. 25, 2002/TD 493
Kelp (CRS 806)
Oct. 22, 2002/TD 489
2002/ TD 490, 502, 505
2004/ TD 655
2005/ TD822, 823, 824
Laboratory and data analysis
In the laboratory, macrobenthic samples were sieved on a 300-µm sieve,
stained with Rose Bengal, sorted and identified to the lowest attainable taxonomic
level. Metazoan trophic group classification was made according to (Kukert & Smith
1992). Sediment samples for organic carbon and nitrogen analysis were acidified to
remove carbonates by repeated additions of sulfurous acid (8 % v/v) until no
effervescence was observed (Verardo et al. 1990) and then analyzed using a Perkin-
Elmer 2400 CHN Elemental Analyzer, with a limit of detection of 1 mg and 1.2 mg
for C and N, respectively, while the precision was 0.3 % and 0.4 % for C and N,
respectively. CHN standards were made with acetanilide and blanks were made of
both non-acidified and acidified cups, both giving minor signals of TOC and TN.
A few top-ranked macrofaunal organisms at representative stages of
community succession on kelp and wood parcels were selected for stable isotope
analysis. Individuals were sorted using methanol-cleaned forceps and specimens were
rinsed and cleaned in DI water. Calcareous shelled organisms were decalcified with
phosphoric acid and placed in pre-weighed tin cups for overnight drying (35-40 ºC).
Multiple individuals of single species were combined in one sample to make up the
necessary dry weight of 0.5-2 mg for analysis. Samples were combusted in a
Eurovector elemental analyzer and resulting N2 and CO2 gases were separated by gas
chromatography and admitted into an IRMS mass spectrometer for determination of
15N/14N and 13C/12C ratios (reproducibility: ±0.5 ‰ for δ15N and ±0.2 ‰ for δ 13C).
Macrofaunal C-isotopic ratios were measured against a Pee Dee Belemnite (PDB)
standard for δ13C and atmospheric nitrogen for δ15N. Results are expressed as delta (δ)
notation representing the relative difference between sample and standard, where δX
(‰) = [(Rsample/Rstandard)-1] x 103, where R=15N/14N or R=14C/13C.
Macroinfaunal organisms were fixed in 4% formaldehyde solution, potentially
introducing artifacts in stable isotope values, although shifts in carbon isotope ratio
are usually small compared to the wide natural C variability in marine food sources
(Fry & Sherr 1989, Edwards et al. 2002, Sarakinos et al. 2002). In this study, we
corrected for preservation artifacts by adding 1‰ to δ 13C (Baco-Taylor 2002,
Sarakinos et al. 2002, Demopoulos et al. 2007). Trophic shift boxes from potential
organic matter sources at kelp and wood parcels helped to determine potential food
sources (Fry 2006). Trophic changes of 3 ‰ were added to the range of δ15N values
obtained for each organic matter source (DeNiro & Epstein 1978, Minagawa & Wada
1984, Fisher et al. 1994). Species that exclusively use a particular source for nutrition
are expected to fall within the appropriate trophic-shift box. Isotope values from kelp
plants were obtained from the published literature (Page et al. 2008). A multi-source
mixing model was used to calculate proportional contributions of each primary
organic matter source (i.e.: kelp, wood, sedimentary organic carbon and bacterial mats
growing on sulphidic sediments around treatments) to the benthic food web
[IsoSource software; (Phillips & Gregg 2003)]. This model examines all possible
combinations of each source contribution (0-100%) in small increments (e.g., 1%),
where the combinations that best fit to the observed species isotope signature are
considered feasible (Phillips & Gregg 2003). A mixing polygon was drawn around
fauna samples, with polygon apices representing end members for each organic
matter source (Demopoulos et al. 2007). Mixing contributions were calculated for
consumers that fit within the mixing polygon, using a priori faunal corrected (i.e.
trophic fractionation) isotope measurements for each trophic group (Kukert & Smith
1992, Phillips & Gregg 2003, Demopoulos et al. 2007). We assumed a δ15N
fractionation of 3‰ for omnivores, deposit feeders and “other” trophic levels (Fry
1988, 2006, Demopoulos et al. 2007). Statistical tests to detect differences on the
contribution of organic sources to the fauna were performed using the IsoError
software (Phillips & Gregg 2001).
Statistical analyzes on sediment organic content were examined with Student t
test of means or Kruskal-Wallis, when the number of replicates allowed. Patterns of
faunal abundance, faunal similarity and diversity were compared among distances and
time for each treatment type. Total densities around treatments and in ambient
sediments were examined with One-Way ANOVA if normality of variances was
present. If homogeneity of variances was not attained, a non-parametric Kruskal-
Wallis test was performed. For significant ANOVA and Kruskal-Wallis results, post-
hoc tests were used to examine difference in means [statistical package BioEstat
(Zar 1996)]. Species diversity was evaluated for pooled replicate cores at each
distance sampled (n=1-4) due to the low density of metazoans. Hulbert’s rarefaction
curves (ESn) were used to compare species diversity between treatments. ESn gives an
estimative of the number of species that would be found in a given number of
individuals, interpolated from the number of species collected in each sample
assuming a random distribution of individuals within samples (Hulbert 1971).
Although this index tends to overestimate within-sample diversity, it is widely use to
compare deep-sea samples of different sizes (Levin et al. 2001). Values of ESn were
compared at n=10, n=25 and n=50, where possible. Near treatment samples were
compared at higher n values, because these samples contained higher abundances and
were particularly interesting as they were directly influenced by the treatments.
Background replicate cores (n=17) from 2002, 2004 and 2005 were combined to
calculate a composite diversity from the background community; with confidence
limits calculated from pooled cores. From rarefaction “knots” obtained in each pooled
sample, a one-tailed 95% confidence interval was calculated using the T distribution.
Diversity curves were then compared to the background confidence curve in order to
test for statistical differences on diversity (Smith 1986). Additionally, Pielou’s
evenness values ( J’) is given to provide further information on community structure
(Clarke & Warwick 2001). The relative abundance of trophic guilds at each period
sampled was integrated by distance in order to increase the power of statistical
analyzes. Samples from 0 m and 0.5 m were compared against the background in
order to evaluate changes in trophic structure nearby our treatments; and examined
with ANOVA or Kruskal-Wallis.
Cluster analyses and non-metric multi-dimensional scaling (MDS) based on
species-abundance data from standardized quantitative samples (PRIMER v6, (Clarke
& Gorley 2006); were used to compare community structure across distance and time.
Square-root transformations were used prior to multivariate analysis in order to
balance the importance of common and rare species (Clarke & Warwick 2001).
Clustering and ordination analyses were often combined to verify mutual consistency.
Analysis of similarities (ANOSIM) was performed on standardized quantitative
samples to determine significant differences between groups (distance and time) and
dissimilarity percentages identified species contributions to these patterns (SIMPER
analysis, (Clarke & Warwick 2001).
In order to determine the level of species overlap between kelp, wood and
other reducing habitats, we restricted our direct comparisons to relatively abundant
species (i.e., over 1% rel. ab. at any treatment type) collected nearby our treatments
(i.e. 0 to 0.5 meters) and that were not sampled in ambient sediments (i.e. total of 17
background cores from 2002, 2004 and 2004). We excluded rare species (less than
1% rel. abundance) from our comparisons in order to account for difficulties in
taxonomic identification and undersampling biases. Comparisons of species overlap
with other published studies were carried out at the genus and species level in order to
account for differences in taxonomic identification between studies.
Sedimentary organic carbon and nitrogen at kelp and wood parcels
After 0.25 years, percent organic carbon (TOC) in surface sediments near kelp
falls was only 0.5% above background levels, with a spatial decrease in sedimentary
TOC from 0 m to 1m (Fig. 2.2). After 0.5 years, the TOC levels at 0 meters was
significantly higher than 0.5 meters away (t=-11.045, d.f.=2, p=0.008), although no
significant temporal increase in TOC was observed at 0 meters (Fig. 2.2). The
combined TOC content in nearest 0-0.5 meters from the kelp falls at 0.5 y was
significantly higher than 0.25 y and background sediments (Kruskal-Wallis, H=7.833,
d.f.=2, p=0.02). Sedimentary percent organic nitrogen (TON) was also slightly
elevated near kelp parcels at 0.25 y, with significant differences from 0.5 meters and
background sediments (t=6.05, d.f.=5, p=0.0018; Fig. 2.2). Sedimentary C/N ratios
confirm the presence of relatively labile (i.e., nitrogen-rich) material at 0 m after 0.25
y. C/N ratios were significantly lower at 0.25 y at 0 meters than all other distances
and background sediments (t=-15.94, d.f.=4, p<0.01; Fig. 2.2).
Sedimentary TOC and TON around wood parcels resembled those in
background levels at 0.5 and 1.8 y after deployment (Fig. 2.2). However, by the 3 y,
surface sediments adjacent to wood parcels had become massively enriched in organic
enrichment, with TOC 3-6 times higher than background values (t=17.37, d.f.=1,
p<0.001; Fig. 2.2). In addition, C/N ratios were extremely high (up to 82.9 C:N;
t=52.49,d.f.=1, p<0.001) compared to all other distances sampled, suggesting
enrichment from relatively refractory woody material. Mean TOC and C/N ratios in
surface sediments near wood falls were still well above ambient levels after 5.5 y
(Fig. 2.2). In addition, percent organic nitrogen was depressed in surface sediments
near the wood parcel to distances of 2 m after 5.5 y (ANOVA, F=61.64, d.f.=1,
p=0.0005), suggesting that low C/N ratio woody organic material had spread some
distance from the wood parcel (Fig. 2.2).
Figure 2.2. Upper panels: Mean (+ 1 SE) TOC and TON in surface sediments (0-2 cm)
around kelp parcels. C/N ratios are shown in text format, with upper and lower values representing 0.25- and 0.5 y averages, respectively. Horizontal parallel lines demark average
%TOC/TON (± 1 SE) of background sediments and C/N ratio (in Italics). Lower panels: Temporal variability on TOC and TON in surface sediments (0-2 cm) around wood parcels
(± 1 SE when n >1). C/N ratios are shown for 0 m and background samples only (in text format).
Macrofaunal density, composition and patterns of succession
Spatial and temporal patterns of species composition and trophic structure
indicate that kelp falls dramatically influenced infaunal communities over short
spatial scales (< 1 m) for at least 0.5 y. At 0.25 y, macroinfaunal abundance within
0.5 m of kelp parcel was significantly enhanced by ~5–fold relative to background
sediments (Fig. 2.3A). This pattern persisted relative unchanged after 0.5 y (Kruskal-
Wallis, H =24.05; d.f.=8, p=0.002; Fig. 2.3A - Inset). At distances of over 0.5 meters
from the kelp, macroinfaunal abundance remained near ambient levels at both 0.25
and 0.5 y (Fig. 2.3A).
Dorvilleid polychaetes and cumaceans dominated sediments within 0.5 m of
kelp falls after 0.25 y and 0.5 y, but were rare in ambient sediments (Fig. 2.3B). The
four top-ranked species at 0.25 y constituted over 88% of all individuals at 0 m, and
dorvilleids and cumaceans represented over 36 and 34 % of the total macrofauna,
respectively (Table 2.2, Fig. 2.4). At 0.5m, cumaceans still responded for over 55%
of all macrofaunal individuals at 0.25 y (Fig. 2.3B, Fig. 2.4). At distances of ≥ 1 m
from the kelp parcels at 0.25 y, background species dominated the infaunal
community. At 0.5 y, cumaceans and dorvilleids still dominated the macrofaunal
community at a distance of 0 m, with background species becoming abundant at
distances ≥ 0.5 m form the kelp (Fig. 2.4, Table 2.2). The rapid increase in abundance
of the two species of cumaceans ( Cumella sp. A and Cumacean sp. K) and the
dorvilleid Ophryotrocha sp. A within 0.5 m from the kelp treatments suggests this
species are opportunistically responding to enrichment and disturbance conditions
(Grassle & Grassle 1974, Pearson & Rosenberg 1978). The cumacean species that
responded to the kelp enrichment in this study were not typically encountered in our
background communities, but they colonize enrichment experiments in deep-sea
regions, including fish and whale-falls in the NE Pacific (Smith 1986, Snelgrove et al.
1996, Smith et al. in prep).
Figure 2.3. A. Mean macrofauna abundance at 0.25- and 0.5-y kelp parcels deployed in SCr
Basin. The solid black line denotes the average background density (± 1SE, dotted line).
Inset: A posteriori multiple comparisons based on Kruskal-Wallis test (H=24.05, p<0.001).
Groups not underscored by a common line are statistically different at p<0.05. No significant
difference was found between 0.25- and 0.5-y at the same distance. B. Abundance of top-
ranked species at 0.25 y (top panel) and 0.5 y (bottom panel) kelp parcels.
The dominance of a Ophyotrocha sp. A and the two cumacean species,
lowered species evenness ( J’) and diversity nearby kelp treatments, at both times
sampled (Table 2.3). At 0 m, species dominance was significantly higher than
background sediments during both periods sampled (Kruskal-Wallis, H= 12.96, d.f.=
4, p=0.01). Species diversity (ESn) increased from 0.25 y to 0.5 y within 0.5 meters of
kelp parcels (Table 2.3, Fig. 2.5). At 0.25 y, rarefaction diversity was significantly
lower within 0.5 m of the kelp treatments, if compared to background samples (Fig.
2.5). At 0.5 y, diversity increased towards background sediments at distance of over
0.5 m, but diversity was still significantly depressed at the 0 m macroinfaunal
community (Fig. 2.5). The diversity changes around kelp treatments suggest that
although areas nearby the parcels were being negatively affected by the enrichment
and disturbance conditions after 0.5 y, the macrofauna in sediments over 0.5 m had
returned to background conditions.
Table 2.2. Mean density per core (38.5 cm-2) and relative abundances of top 5 ranked
macrofaunal species at 0 m and 0.5 m from kelp parcels, and background sediments in SCr
Basin. (P) Polychaeta, (Cr) Crustacea, (M) Mollusca.
Figure 2.4. Macro-infauna composition around kelp parcels at 0.25 y (a) and 0.5 y (b) in SCr
Basin. Bkgd - Background fauna from SCr Basin in 2002, 2004 and 2005 (n=17 cores).
Table 2.3. Diversity indices from kelp parcels and background sediments at SCrB. Mean
number of individuals (M) per core (38.5cm-2 ± 1SE). J’-Pielou eveness index, ESn- Expected number of species at 10, 25 and 50 individuals (inside brackets) per sample.
ES 25 (50)
Figure 2.5. Rarefaction diversity for Kelp macrofauna 0.25 y and 0.5 y.
Trophic-group analysis revealed large changes adjacent to kelp parcels (i.e., ≤
0.5 m) after 0.25 – 0.5 y. At 0.25 y, the high abundance of dorvilleids and cumaceans
dramatically increased the proportion of omnivores (OMNI, Kruskal-Wallis,
H=6.836, d.f.=2, p=0.02) and the “other” trophic group (Kruskal-Wallis, H=16.624,
d.f.=2, p<0.01) within 0.5 meters from the treatments (Fig. 2.6). The augmented
number of “other” trophic group at 0 m was still significant after 0.5 y (p<0.01; Fig.
2.6). Surface deposit feeders (SDF) were slightly depressed nearby kelp parcels
compared to background sediments, but no significant trend was observed (Fig. 2.6).
In addition, sub-surface deposit feeders (SSDF) were wholly absent adjacent to kelp
parcels (0 m) after 0.25 -0.5 yr (Kruskal-Wallis, H=5.70, d.f.=1, p=0.018; Fig. 2.6).
This suggests that sub-surface deposit feeders were particularly affected by the
physical and organic disturbances in sediments nearby the kelp parcels. Trophic
differences between 0.25 and 0.5 y at 0.5 m suggests recovery towards background
conditions at 0.5 y, with an increase in the importance of SDF accompanied by a
strong decrease in the “other” trophic group (Fig. 2.6). The elevated number of
omnivores and “other” trophic guilds are consistent with the opportunist species that
colonized sediments and possibly with the augmented amount of detritus within 0.5 m
from the treatments. Complete abundance and relative contribution of species at kelp
parcels are presented in Appendix 2A.
Figure 2.6. Percentage of total abundance in trophic groups at 0.25 y and 0.5 y kelp parcels
at SCr Basin. OMNI-Omnivores, Carnivores and Scavengers; SDF-Surface deposit feeders;
SSDF-Sub-surface deposit feeders, Other- Trophic groups not determined (see methods).
Wood parcels also exhibited dramatic effects on macrofaunal community
structure in space and time. The sediment near the wood parcels accumulated a
massive number of Xylophaga washingtonia recruits during the first 0.5 – 3 years
(Fig. 2.7A), presumably resulting from settling response to available wood substrate
nearby. Brooder species of Xylophaga present on the wood parcels may have been the
source of juveniles that rained down to the sediments after 0.5 y (Voight 2007a). The
Xylophaga bivalves never attained adult size within the sediments, although adults
were present on the wood parcels from 0.5 y onward. Thus, Xylophaga represents a
sink population resulting from mass effects of the wood parcel (Leibold et al. 2004).
Because Xylophaga appear to represent sink populations in the sediment community
derived from mass effects of the wood parcels, we also evaluated macrofaunal
community patterns with Xylophaga removed from the analyses. At 0.5 y, mean
macrofaunal abundance, without Xylophaga, was significantly higher at 0 m than in
background sediments; at further distances macrofaunal abundances resembled
background levels (Fig. 8B; Kruskal-Wallis test, H=27.98, d.f.=13, p=0.03).
Macrofaunal densities around the wood parcels were significantly elevated at 0 m
after 1.8 y (ANOVA, F=12.906, d.f.=3, p=0.003), dropping to background levels by
0.5 m from the parcels (Fig. 2.7B). At subsequent sampling times (3.0 and 5.5 y),
macrofaunal abundance progressively increased adjacent to the parcels, reaching very
high numbers (15,100 ± 2400 ind.m-2) at 0 m after 5.5 y (p<0.001; Fig. 2.7B).
However, macrofaunal enhancement was limited in a spatial scale, with slight
increases after 1.8 – 5.5 y at 0.5 m, at all time points, and background levels of
abundance at > 1 m from parcels even at 5.5 y, when abundances at 0 m were 15
times background levels (Fig. 2.7B).
At the species level, Cumacean sp. K dominated macrofaunal assemblages
adjacent to wood parcels after 0.5 y, although three background species ( Monticellina
sp. A, Chaetozone sp. D and Cossura rostrata) remained among the 5 dominant
species (Fig. 2.8, Table 2.4). By 1.8 y, Ophryotrocha sp. A (a dorvilleid) and
ampharetid polychaetes dominated assemblages at 0 - 0.5 m, with cumaceans also
abundant at 0.5 m (Table 2.4); at further distances, background polychaetes continued
to dominate (Fig. 2.8). By 3.0 y, dorvilleids (two species of Ophrytotrocha) had
achieved very high densities at 0 m, representing over 40% of the macrofauna (Fig.
2.8, Table 2.4) and the chemoautotrophic-symbiont-containing mytilid Idas
washingtonia was first encountered at the wood parcels (Table 2.4). At 5.5 y,
dorvilleids ( Ophryotrocha and Parougia) and two species of ampharetids dominated
the macrofauna at 0 m, with very high abundances (Table 2.4, Fig. 2.8); Cumacean
sp. K, was also abundant. None of the dorvilleids, ampharetids and cumaceans were
collected in the background community, or even off distances of 2 m from the wood
falls. This, plus their larger response to kelp parcels suggest that they are
opportunistic species, or may be wood associated species enhanced by mass effects
(Leibold et al. 2004) from the adjacent wood parcels.
Figure 2.7. Temporal variability on macroinfaunal abundance at the wood parcels (Average
± 1SE). A. Xylophaga recruits included; B. Xylophaga not included. The solid black line and
shadowing represent the average background (100m) abundances (± 1SE).
Figure 2.8. Sediment macrofaunal composition at the wood parcels deployed at SCr Basin. a.
0.25 y, b. 1.8 y, c. 3 y, d. 5.5 y.
Table 2.4. Mean density per core (38.5 cm-2) and relative abundances of top 5 ranked
macrofaunal species at 0m and 0.5m at wood parcels and background fauna at SCr Basin.
The total percentage of top ranked species is given below each list. (P) Polychaeta, (Cr) Crustacea, (M) Mollusca.
The increase in macrofaunal density at 0 m from 0.5 y to 5.5 y was followed
by a significant decrease on community evenness in the latter period ( J’, ANOVA,
F=8.384, d.f.=3, p=0.001, Table 2.5), resulting from higher densities of opportunist
species. At the other periods, J’ was always within background levels (Table 2.5).
Rarefaction diversity demonstrates a clear temporal pattern adjacent to wood parcels.
At 0.5 y, rarefaction diversity adjacent to the wood parcel falls above background
levels (Table 2.5, Fig. 2.9); diversity then progressively declines at 0 m from 1.8 to
5.5 y (Table 2.5, Fig. 2.9). The diversity curve at 5.5 y falls well below all other
curves and is significantly lower than background (Fig. 2.9).
Table 2.5. Average number of individuals (M) per core (38.5cm-2 ± 1SE), Pielou’s species evenness (J’) and expected diversity around wood parcels deployed at SCr Basin. Expected
number of species E(Sn) estimated from 10 and 25 individuals (ES25 inside brackets).
Figure 2.9. Hulbert’s rarefaction plot detailing the temporal variability on macroinfaunal
diversity at the wood parcels (0 meters only).
Functional group analysis also indicated dramatic wood parcel effects on the
adjacent macrofaunal community, increasing in intensity from 0.5 – 5.5 y. At 0.5 y,
the dominant trophic groups were largely typical of ambient sediments, although at 0
m the importance of the “others” group slightly increased due to the presence of the
apparently opportunistic Cumacean sp. K (Fig. 2.10). By 1.8 y, omnivores at 0 m had
increased to 26%, and rose to 50% of the macrofauna at 3.0 - 5.5 y (Fig. 2.10). After
3 y, the omnivores within 0.5 m from wood falls were significantly more numerous
than the 0.5 y community and the background sediments (Kruskal-Wallis, H=12.19,
d.f.=4, p=0.016). SDF’s were relatively abundant during the whole period analyzed
(over 30%), with ampharetids being dominant nearby the parcels and cirratulids in
background sediments. Subsurface deposit feeders usually represented less than 1% of
the infauna at 0 m during all periods (Fig. 2.10). Complete abundance and distribution
of species at wood parcels are presented in Appendix 2B.
Figure 2.10. Trophic group patterns at the wood parcels implanted at SCr Basin. OMNI-
Omnivores, Carnivores and Scavengers; SDF-Surface deposit feeders; SSDF-Sub-surface
deposit feeders, Other-Trophic groups not determined.
MDS patterns of faunal distribution at Kelp and Wood parcels
Nonmetric Multidimensional Scaling (MDS) analyses further elucidate
successional patterns in space and time around the kelp and wood parcels. At kelp
falls, 0 m samples from 0.25 and one replicate from 0.5 y separated strongly from all
other distances (Fig. 2.11, Two-way ANOSIM R= 0.358, P=0.001). The top-ranked
species at 0 m accounted for over 70% of the dissimilarity from the other samples at
both time intervals (SIMPER). All other samples from 0.5 m to background, clustered
with each other at 0.25 and 0.5 y, with no distinct difference between them (Fig. 2.11,
ANOSIM). Overall, highest dissimilarities in sediments nearby kelp falls and
background communities resulted from the dominance of apparently opportunistic
species adjacent to the kelp fall at 3 months, and the low background densities of
Figure 2.11. Multidimensional scaling plot (MDS) of macrofaunal communities (>300µm) at
Kelp (top panel) and Wood (bottom panel) parcels on SCr Basin. Grouped symbols denote
stronger similarity among samples (see text).
At wood parcels, the MDS also revealed marked spatial and temporal patterns
(Two-way ANOSIM, p<0.01). At 0.5 y and 1.8 y, all samples generally grouped
together with no evident difference between treatments and background communities
(Fig. 2.11, ANOSIM). A dramatic shift in macrofaunal community structure was
indicated at 0 m at 3 y and persisted to 5.5 y (Fig. 2.11, ANOSIM, R= 0.319, P=
0.001). The top ranked macrofaunal species (including apparently opportunistic
dorvilleids in the genus Ophryotrocha) at these two later periods accounted for over
20% of the spatial dissimilarity among samples (SIMPER). Pairwise comparisons
revealed a lower degree of dissimilarity between 5.5 y and the two first periods
sampled, suggesting that macrofaunal community structure by 5.5 y may have been
recovering towards background conditions (ANOSIM).
These results confirm our first hypothesis, that kelp and wood falls promote
very distinct patterns of macrobenthic community succession. The dynamics of
dominant species were distinct between kelps and wood, with kelps promoting early
changes (scales of 1-3 months) on community composition, which lowered local
diversity in the short scale as a result of a massive colonization by a few omnivore
species (cumaceans and dorvilleids). On the other hand, dominant species altered
community structure around wood parcels only after 1 – 2 years, but the duration of
the organic enrichment promoted significant changes for over 5 years. A higher
number of species colonized sediments around wood falls, likely as a consequence of
increased food availability, but the fauna became less diverse with time as densities of
opportunist species increased.
Stable isotope analysis at Kelp and Wood parcels
Potential primary organic matter sources at kelp and wood falls include kelp
and wood biomass, sedimentary matter from deposited phytoplankton, and biomass
from chemoautotrophic sulfur-oxidizing bacteria utilizing sulfide emitted from kelp or
wood parcels. Kelp biomass (Macrocystis pyrifera) had the highest δ 13C and δ15N
isotope values from all primary organic sources (Table 2.6). Sediment organic carbon
and wood fragments had very similar isotope signatures (Table 2.6), which were
consistent with previous studies in the basin (Baco-Taylor 2002). Mats of sulfur-
oxidizing chemoautotrophic bacteria growing on whale skeletons off southern
California had δ 13C signatures similar to the other organic sources but with the lowest
δ15N values compared to the other sources (Table 2.6). Isotope signatures from sulfur-
oxidizing bacteria can have a much wider isotopic range due to variable inorganic C
sources (Ruby et al. 1987).
Table 2.6. Stable isotope values from primary organic matter sources used in this study. End
members values were used in the mixing model calculations in order to account for maximum
environmental variability. Values in delta notation.
Page et al.,