Blondeau, J.

Brandt, M.

Calnan, J.

Kadison, E.

Nemeth, R.

Smith, T.

Taylor, M.

English

Aquatic Commons

 Proceedings of the 63rd Gulf and Caribbean Fisheries Institute     November 1 - 5, 2010   San Juan, Puerto Rico 
 
Reef Fish Recruitment to Low and High Diversity Banks in the Northwestern Gulf of Mexico 
 
LYNNE S. WETMORE* and JAY R. ROOKER 
Department of Marine Biology, Texas A&M University at Galveston, Galveston, Texas 77551 USA. 
*scubageek17@gmail.com 
 
ABSTRACT 
 Natural banks represent the only naturally occurring hard-bottom structured habitat on the continental shelf in the 
Northwestern Gulf of Mexico and as such, may represent critical habitat for reef-associated fish species.  However, the relative 
nursery values and functional roles of different natural bank types for reef fish in the Gulf are currently unknown.  In 2009, we 
conducted monthly (May-Sept) visual surveys on SCUBA to quantify the density and diversity of reef fish recruits on two mid-shelf 
low coral diversity banks (Sonnier, Stetson) and two shelf-edge high coral diversity banks (East and West Flower Gardens). Overall 
fish density was highest at the two low diversity banks , and density, species richness (S), and Shannon diversity (H’) were 
significantly higher at Stetson than any of the other study sites.  Analysis of similarities (ANOSIM) was used to compare fish 
assemblage structure among bank types, and pairwise comparisons showed significant differences in reef fish communities between 
low diversity and high diversity banks but no significant differences within a given bank type.  Furthermore, significant differences 
in the densities of specific trophic guilds among study sites suggests that habitat partitioning may occur between bank types, 
particularly for upper-level trophic groups (i.e. piscivores, carnivores).  Overall, preliminary analysis of the 2009 data suggests that 
both bank types support large and diverse communities of reef fish recruits and that high coral diversity and low coral diversity 
banks may support distinct fish assemblages and trophic community structures.  
 
KEY WORDS: Natural banks, reef fish, community structure 
 
 
Reclutamiento de Peces Coralinos en Bancos de Baja y Alta Diversidad  
del Noroeste del Golfo de México 
 
PALABRAS CLAVE:  Bancos de baja y alta diversidad, peces coralinos, reclutamiento 
 
 
Recrutement de Poissons Coralliens aux Banques de Basse et Haute Diversité  
au Nord-Ouest du Golfe du Mexique 
 
MOTS CLÉS:  Banques de basse et haute diversité, poisons coralliens, recrutement 
 
INTRODUCTION 
Although recruitment to many systems present in the 
eastern Gulf have been studied (e.g., Allman and Grimes 
2004, Fitzhugh et al. 2005), the relative value of putative 
nursery areas for reef fishes in other regions have not been 
well documented or characterized, including mid-shelf and 
shelf-edge reef banks in the northwestern Gulf.  This is 
particularly alarming because many ‘overfished’ stocks 
require these habitats to successfully complete their life 
cycles, and changes in the quality or quantity of these reef 
s may lead to declines in survival during early life 
(settlement or nursery period).  In addition, these habitats 
may be lost or degraded by coastal development and 
fishing activities before their value as essential fish habitat 
(EFH) is even assessed.  
Several low and high diversity banks are present in 
mid and outer shelf environments in the northwestern Gulf 
(Rezak et al. 1985).  These natural banks range from low 
coral diversity banks with hydrocorals (i.e., Millepora) and 
sparsely distributed individual coral colonies (Sonnier 
Bank, Stetson Bank) to high coral diversity banks covered 
with hermatypic corals (East and West Flower Garden 
Bank).  Since the aforementioned banks represent the only 
naturally occurring structured habitat on the continental 
shelf in the northwestern Gulf of Mexico, they represent 
critical habitat of reef-associated species (Dennis and 
Bright 1988).  Moreover, the complexity afforded by these 
habitats likely enhances early life survival by reducing 
predation-mediated mortality and enhancing prey availabil-
ity (Rooker et al. 1997).  If this assumption is valid, 
survival and recruitment success of certain reef-dependent 
species will be linked to the distribution, abundance, and 
general condition of reefs.  In response, these banks 
potentially play a critical role sustaining marine fisheries 
throughout the Gulf. 
Here, we comprehensively examined recruitment to 
both low and high diversity banks in the northwestern 
Gulf.  Visual SCUBA surveys were used to quantify the 
density and diversity of juvenile reef fishes present on two 
low coral diversity mid-shelf (Sonnier, Stetson) and two 
high coral diversity shelf-edge (East and West Flower 
Garden) banks.  Spatial and temporal variability in overall 
reef fish community structure were examined during 2009, 
and associations between specific trophic guilds, bank 
    Wetmore, L.S. and J.R. Rooker  GCFI:63   (2011) Page 231 
types and habitat variables were also assessed.  Unfortu-
nately, data on recruitment to these natural banks and their 
potential role as nurseries is incomplete, and additional 
information on the causes of population change for reef 
fish populations in the Gulf is needed to enhance conserva-
tion of low diversity and high diversity reef habitats.  
 
METHODS 
 
Field Surveys 
Fish assemblages associated with low diversity 
(Sonnier, Stetson) and high diversity (East and West 
Flower Garden) banks were evaluated during five cruises 
conducted in May, June, July, August, September of 2009. 
Visual surveys were conducted by pairs of divers on 
SCUBA as 5 m x 2 m band transects, with all individual 
fish observed within the transect area quantified by species 
and age class.  Sampling effort ranged from 10 - 12 
transects at each bank per sampling trip with a total of 251 
total transects conducted over the course of the study.  East 
Flower Garden Bank (EFGB) and West Flower Garden 
Bank (WFGB) were sampled during all five survey months 
(May-Sept), Stetson Bank  was sampled during four survey 
months (June-Sept), and Sonnier Bank was sampled twice 
in May and September. 
 
Spatial and Temporal Variability in Community 
Structure 
Estimates of mean overall density, species richness 
(S), Pielou’s evenness (J'), and Shannon diversity (H') were 
calculated and a one-factor analysis of variance (ANOVA) 
was used to test for differences among study sites.  
Normality was tested with a Shapiro-Wilk test and a 
posteriori differences among means were detected with a 
Tukey’s HSD test with an alpha level of 0.05.  Estimated 
mean densities of specific trophic guilds were also 
calculated, with ANOVA and Tukey’s HSD used to detect 
differences among study sites. 
Fish assemblage data were analyzed with the Plym-
outh Routines in Multivariate Ecological Research 
(PRIMER) statistical package (Clarke and Warwick 2001).  
Densities were ln-transformed to down-weight the 
abundant species and to retain information regarding some 
of the less abundant species.  A Bray-Curtis similarity 
matrix was then computed among all samples using density 
data.  Two-factor non-metric multi-dimensional scaling 
(MDS) models were computed for each survey month to 
visualize similarities and dissimilarities in fish assemblage 
structure among banks and survey months.  Stress coeffi-
cients (residual modeling error) of 0.2 were treated as 
critical values to test goodness-of-fit of a given MDS 
model in two dimensions (Clarke and Warwick 2001).  A 
stepwise data reduction procedure in PRIMER, BV-STEP, 
was performed with a Spearman rank correlation coeffi-
cient of 0.95 as the threshold to determine which species 
explained the majority of the variability in assemblage 
structure.  The analysis of similarities (ANOSIM) permuta-
tion procedure was used to test for differences in fish 
assemblage structure among banks and survey months 
(Clarke and Warwick 2001).  To assess species-specific 
contributions, Similarity Percentages (SIMPER) was used 
as the post-hoc analysis to indicate the contribution of a 
particular species to the overall fish assemblage structure 
among banks and survey months (Clarke and Warwick 
2001).  
 
RESULTS AND DISCUSSION 
There appeared to be some distinct bank-specific 
trends in overall fish density and diversity indices.  Density 
was significantly higher at Stetson than at the other three 
banks examined, and both species richness (S) and 
Shannon diversity (H’) were significantly higher at Stetson 
and significantly lower at Sonnier, with intermediate values 
at EFGB and WFGB (ANOVA; Tukey’s HSD, p < 0.05) 
(Figure 1).  Evenness did not differ significantly among 
bank types.  This result was somewhat unexpected, as 
Sonnier and Stetson are most similar to each other in 
habitat type and should theoretically have more similar fish 
assemblages but instead showed the greatest differences 
between sites.  The two high diversity shelf edge banks 
show the expected trend, being statistically similar in all 
four indices.  It is notable that Sonnier was the only study 
site not located within the boundaries of the Flower Garden 
Banks National Marine Sanctuary and thus, the lower 
richness and diversity values of this site may represent 
something of a reserve effect. 
Analyses comparing species composition rather than 
overall density and diversity values did show distinct 
separations between high diversity and low diversity bank 
fish communities.  Assemblage structure varied among 
banks (ANOSIM; Global R = 0.421, p < 0.05) and among 
survey months (ANOSIM; Global R = 0.197, p < 0.05) 
over the period investigated in this study.  When combined 
across survey months, pairwise comparisons showed 
significant differences in fish assemblage structure between 
high diversity (East and West Flower Garden) and low 
diversity (Sonnier and Stetson) banks (p < 0.05 for all 
comparisons), but were similar within high and low 
diversity banks (p > 0.05).  Figure 2 shows the MDS plots 
of all transects with natural groupings of similar assem-
blage composition of high diversity banks contrasted with 
the low diversity banks.  Results of SIMPER analysis 
identified bluehead, threespot damselfish, Spanish hogfish, 
and sunshinefish as the most important species structuring 
the high diversity banks.  In contrast, cocoa damselfish, 
purple reeffish, and dusky damselfish were most influential 
in determining fish assemblage structure on the low 
diversity reefs. Bluehead accounted for 63% and 62% to 
the total species contribution within each of the high 
diversity banks (East and West Flower Garden, respective-
ly) (Figure 2).  Likewise, the low diversity banks of 
Sonnier and Stetson were dominated by the cocoa damsel-
 Page 232  63rd Gulf and Caribbean Fisheries Institute  
fish, with total contributions at 64% and 49%, respectively.  
Species assemblage structure was most similar among all 
banks in June compared to other survey months.  Signifi-
cant temporal differences were only found when June was 
contrasted with July (p < 0.05), but was similar when 
compared to May, August, and September (p > 0.05).  
Species assemblage structure between high and low 
diversity banks was significantly different during all 
months (p < 0.05 for all comparisons), with density 
differences of bluehead contributing most to survey month 
differences. 
For trophic analyses, all species observed in the study 
were classified into one of six feeding categories based on 
their published dietary preferences in the literature (Table 
1).  Comparisons of trophic guild density across study sites 
showed strong evidence of habitat partitioning, particularly 
among the upper level predatory trophic groups (Figure 3). 
Four of six trophic guilds showed significant differences 
across study sites (ANOVA, p < 0.05), and in the two 
groupings where highly significant (p < 0.0001) differences 
were found, there was a clear division between low 
diversity and high diversity bank types, with both lower 
level carnivores and herbivores showing significantly 
higher densities at both Sonnier and Stetson.  The only 
trophic group with higher observed mean densities at the 
high diversity banks was the piscivore group, which was 
also the only group absent from Stetson.  The relatively 
low overall densities and patchy distribution of the large 
groupers that made up this trophic group (characteristic of 
upper level predators) prevented the trend from showing 
statistical significance.  However, it is important to 
recognize the non-numerical ecological important of such 
species and it is conceivable that their presence or absence 
may be driving differences across the other two predatory 
groups through competitive interactions or predation. 
Densities of smaller carnivores were significantly lower at 
banks where larger groupers were encountered on tran-
sects, and only one single species of smaller carnivores was 
even regularly observed at banks where large groupers 
were present. 
Associations between specific trophic guilds and bank 
types provide further evidence that high and low diversity 
banks have different functional roles in determining fish 
assemblage structure.  Futhermore, the relative densities of 
the piscivore and carnivore trophic guilds suggests that low 
vs. high diversity bank types may be particularly critical in 
structuring the assemblages of the higher level predatory 
fish species that are generally targeted and managed as 
fisheries.  The results of this study indicate that both types 
of banks support large, diverse fish assemblages, but 
suggest that each bank type (high diversity or low diversi-
ty) may be associated with a distinct fish assemblage and 
trophic structure that appear to remain consistent even 
across fairly large geographical distances.  Furthermore, 
analysis of specific trophic guilds appears to suggest 
differences in the functional role and relative nursery value 
of high and low coral diversity banks in the northwestern 
Gulf.  Including 2010 data in this analyses will expand our 
sample size and allow us to further examine these trends. 
However, it is apparent that the different ecological roles of 
these two bank types need to be taken into account for 
informed ecosystem-based management efforts. 
 
 
 
 
 
Figure 1.  Mean species density, richness (S), evenness 
(J'), and Shannon diversity (H') indices at each bank.  
Error bars represent one standard error. P-values denote 
analyses that showed significant differences among 
banks (ANOVA), and lowercase letters denote bank 
groupings based on post-hoc tests (Tukey). Bank codes: 
EFGB = East Flower Garden Bank; WFGB = West 
Flower Garden Bank; SON = Sonnier Bank; STET = 
Stetson Bank. 
    Wetmore, L.S. and J.R. Rooker  GCFI:63   (2011) Page 233 
ACKNOWLEDGEMENTS 
 I would like to give a special thanks to all of the faculty, 
students and staff at Texas A&M who assisted with the field research and 
data analysis for this project, as well as the crew of the M/V Fling and the 
NOAA Flower Garden Banks National Marine Sanctuary Office. This 
research was supported by funding from the Gulf of Mexico Fisheries 
Management Council. 
 
LITERATURE CITED 
Allman, R.J. and C.B. Grimes.  2004.  Temporal and spatial dynamics of 
spawning, settlement, and growth of gray snapper (Lutjanus griseus) 
from the West Florida shelf as determined from otolith microstruc-
tures. Fisheries Bulletin 100:391-403. 
Bohnsack, J.A. et al.  1999.  Baseline data for evaluating reef fish 
populations in the Florida keys, 1979-1998. National Marine 
Fisheries Service Technical Memo NMFS-SEFSC-427. 
Clarke, K.R. and R.M. Warwick.  2001.  Changes in Marine Communi-
ties: An Approach to Statistical Analysis and Interpretation, 2nd 
Edition. PRIMER-E Ltd, Plymouth, United Kingdom. 
Dennis, G.D. and T.J. Bright.  1988.  Reef fish assemblages on hard 
banks in the northwestern Gulf of Mexico. Bulletin of Marine 
Science 43:280-307. 
Fitzhugh, G.R., C.C. Koenig, and F.C. Coleman.  2005.  Spatial and 
temporal patterns in fertilization and settlement of young gag 
(Mycteroperca microlepis) along the west Florida shelf. Bulletin of 
Marine Science 77:377-396. 
Newman, M.J.H., G.A. Paredes, E. Sala, and J.B.C. Jackson.  2006. 
Structure of Caribbean coral reef communities across a large 
gradient of fish biomass. Ecology Letters 9(11):1216-1227. 
 
Rezak, R., T.J. Bright, and D.W. McGrail.  1985.  Reefs and Banks of the 
Northwestern Gulf of Mexico. John Wiley & Sons, Inc., New York, 
New York USA. 259 pp. 
Rooker, J.R., Q.R. Dokken, C.V. Pattengill, and G.J. Holt.  1997.  Fish 
assemblages on artificial and natural reefs in the Flower Garden 
Banks National Marine Sanctuary, U.S.A. Coral Reefs 16:83-92. 
 
Figure 2.  Multi-dimensional scaling plots of fish assemblages surveyed on 
high diversity (East and West Flower Garden = EFGB & WFGB, respectively) 
and low diversity (Sonnier, Stetson) banks in the northwestern Gulf of Mexico 
from monthly surveys (May to September, 2009).  July surveys are only 
shown in the combined plot due to limited surveys that only occurred at EFGB 
and WFGB. Stress coefficients represent goodness-of-fit criteria. 
 Page 234  63rd Gulf and Caribbean Fisheries Institute  
Figure 3.  Overall mean densities of each feeding guild at each study site. 
Densities are reported as the number of individual fish per square meter.  Error 
bars represent one standard error. P-values denote feeding guilds that showed 
significant differences in density among banks (ANOVA), and lowercase letters 
denote bank groupings based on post-hoc tests (Tukey). 
Table 1.  Description of major categories used for trophic guild analysis (derived from Bohnsack 
et. al. 1999 and Newman et. al. 2006). 
 Trophic Categories 
  
Predators 
  
Piscivores 
  
  
Higher level predators, feed almost exclu-
sively on fish 
  
e.g. black grouper 
  
Carnivores 
  
Lower level generalist predators, feed on 
smaller benthic invertebrates and fish 
  
e.g. rock hind 
  
Invertivores 
  
Lower level predators, feed almost exclusive-
ly on mobile benthic invertebrates 
  
e.g. tomtate 
  
1˚  & 2˚ 
Consumers 
  
Planktivores 
  
Feed on small zooplanktonic organisms, 
forage midwater and often form schools 
  
e.g. bluehead wrasse 
  
Sessile Grazers 
  
Feed on sedentary benthic organisms such 
as coral, sponges, tunicates, etc. 
  
e.g. queen angelfish 
  
Herbivores 
  
  
Primary consumers, feed on algae, plant 
material, and detritus 
  
e.g. yellowtail damsel 


Reef fish Community Differences among the U.S. Virgin Islands and Implications for Management.

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Reef fish Community Differences among the U.S. Virgin Islands and Implications for Management.

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