Summary

This document examines density and biomass of fish communities inside and outside the boundaries of the Hind Bank Marine Conservation District (MCD) and Virgin Islands Coral Reef National Monument (VICRNM).

Trophic groups

Density

Mean and variance of fish density (#/100m2) for trophic groups of interest across sites.
Trophic Group MPA Location Mean Density SD n SEM
all fish MCD IN 154.84 110.37 31 19.82
all fish MCD OUT 129.27 100.39 30 18.33
all fish VICRNM IN 239.19 165.22 31 29.67
all fish VICRNM OUT 175.47 130.15 30 23.76
herbivores MCD IN 40.39 19.00 31 3.41
herbivores MCD OUT 36.50 19.01 30 3.47
herbivores VICRNM IN 65.10 35.74 31 6.42
herbivores VICRNM OUT 74.80 42.56 30 7.77
piscivores MCD IN 3.68 2.21 31 0.40
piscivores MCD OUT 4.63 3.84 30 0.70
piscivores VICRNM IN 6.45 7.40 31 1.33
piscivores VICRNM OUT 10.00 24.33 30 4.44
Mean fish density (#/100m^2^) for trophic groups of interest across sites. Error bars represent mean ± SE.

Mean fish density (#/100m2) for trophic groups of interest across sites. Error bars represent mean ± SE.

Herbivores, while present at all sites, were found at higher densities around the VICRNM than the MCD. Piscivores were present at most sites in low densities.

Biomass

Mean and variance of fish biomass (kg/100m2) for trophic groups of interest across sites.
Trophic Group MPA Location Mean Biomass (kg) SD n SEM
all fish MCD IN 6.57 4.69 31 0.84
all fish MCD OUT 10.19 8.83 30 1.61
all fish VICRNM IN 10.47 9.85 31 1.77
all fish VICRNM OUT 9.47 11.71 30 2.14
herbivores MCD IN 2.65 2.38 31 0.43
herbivores MCD OUT 2.74 2.42 30 0.44
herbivores VICRNM IN 2.44 2.99 31 0.54
herbivores VICRNM OUT 2.08 1.98 30 0.36
piscivores MCD IN 1.63 1.80 31 0.32
piscivores MCD OUT 3.82 5.94 30 1.08
piscivores VICRNM IN 2.33 3.39 31 0.61
piscivores VICRNM OUT 4.67 9.01 30 1.65
Mean fish biomass (kg/100m^2^) for trophic groups of interest across sites. Error bars represent mean ± SE.

Mean fish biomass (kg/100m2) for trophic groups of interest across sites. Error bars represent mean ± SE.

Lionfish

Density

Mean and variance of lionfish density (#/100m2) across sites.
MPA Location Mean Density SD n SEM
MCD IN 0.97 1.02 31 0.18
MCD OUT 0.63 1.00 30 0.18
VICRNM IN 0.32 1.30 31 0.23
VICRNM OUT 0.20 0.61 30 0.11
Mean lionfish density (#/100m^2^) across sites. Error bars represent mean ± SE.

Mean lionfish density (#/100m2) across sites. Error bars represent mean ± SE.

lionDensAnova <- aov(TotalNumber ~ MPA * InOut, 
                     data = filter(dl, ScientificName=="Pterois volitans"))
summary(lionDensAnova)
##              Df Sum Sq Mean Sq F value Pr(>F)   
## MPA           1   8.93   8.926   8.668 0.0039 **
## InOut         1   1.59   1.592   1.546 0.2162   
## MPA:InOut     1   0.34   0.342   0.332 0.5655   
## Residuals   118 121.51   1.030                  
## ---
## Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1
TukeyHSD(lionDensAnova, which ="MPA")
##   Tukey multiple comparisons of means
##     95% family-wise confidence level
## 
## Fit: aov(formula = TotalNumber ~ MPA * InOut, data = filter(dl, ScientificName == "Pterois volitans"))
## 
## $MPA
##                  diff        lwr        upr     p adj
## VICRNM-MCD -0.5409836 -0.9048463 -0.1771209 0.0039002

Lionfish densities were not significantly different inside and outside MPAs (p=0.2), but were significantly higher around the MCD (inside and outside) than around the VICRNM (p<0.01). This may be due to the fact that the MCD is deeper and has a higher rugosity than the VICRNM, which may be a more attractive habitat for lionfish.

Biomass

Mean and variance of lionfish biomass (kg/100m2) across sites.
MPA Location Mean Biomass (kg) SD n SEM
MCD IN 0.31 0.43 31 0.08
MCD OUT 0.14 0.31 30 0.06
VICRNM IN 0.09 0.48 31 0.09
VICRNM OUT 0.07 0.19 30 0.04
Mean lionfish biomass (kg/100m^2^) across sites. Error bars represent mean &plusmn; SE.

Mean lionfish biomass (kg/100m2) across sites. Error bars represent mean ± SE.

Lionfish biomass showed a similar pattern to density across locations.

Groups of interest

Density

Mean fish density (#/100m^2^ &plusmn; SE) across sites for all lionfish and other groups of interest, separated by MPA and inside/outside MPA boundaries. Groups were adapted from Green et al (2012).

Mean fish density (#/100m2 ± SE) across sites for all lionfish and other groups of interest, separated by MPA and inside/outside MPA boundaries. Groups were adapted from Green et al (2012).

While it appears there might be a difference in large-bodied predator density between MPAs, the difference was not significant (see ANOVA table below).

##                Df Sum Sq Mean Sq F value Pr(>F)
## MPA             1    0.1 0.06675   2.526  0.112
## InOut           1    0.0 0.01028   0.389  0.533
## MPA:InOut       1    0.0 0.00501   0.190  0.663
## Residuals   14392  380.3 0.02643

Biomass

Mean fish biomass (kg/100m^2^ &plusmn; SE) across sites for all lionfish and other groups of interest, separated by MPA and inside/outside MPA boundaries. Groups were adapted from Green et al (2012).

Mean fish biomass (kg/100m2 ± SE) across sites for all lionfish and other groups of interest, separated by MPA and inside/outside MPA boundaries. Groups were adapted from Green et al (2012).

There seems to be no relationship between density or biomass of lionfish and small-bodied prey fish, potential lionfish predators, or other functional groups. At the time of these recent surveys, lionfish density has had no clear direct or indirect impacts on native fish populations, although here was large variation in the density and biomass of each of these groups across sites.

While there was no significant difference in large-bodied predator density between MPAs, there was a significantly higher biomass of large-bodied predators outside MPAs than inside (see ANOVA table below).

##                Df    Sum Sq Mean Sq F value Pr(>F)  
## MPA             1 1.600e+04   15999   0.173 0.6774  
## InOut           1 4.346e+05  434620   4.702 0.0301 *
## MPA:InOut       1 9.330e+02     933   0.010 0.9200  
## Residuals   14392 1.330e+09   92439                 
## ---
## Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1

Families

Mean fish family biomass (kg/100m^2^ &plusmn; SE) across sites, separated by MPA and inside/outside MPA boundaries.

Mean fish family biomass (kg/100m2 ± SE) across sites, separated by MPA and inside/outside MPA boundaries.

There was higher biomass of several fish families inside VICRNM than other areas, including Acanthuridae (surgeonfishes), Balistidae (triggerfish), Haemulidae (grunts), Mullidae (goatfish), and Pomacanthidae (angelfish).

Species Richness

Mean and variance of species richness across sites.
MPA Location Mean Richness SD n SEM
MCD IN 18.77 4.91 31 0.88
MCD OUT 20.87 5.14 30 0.94
VICRNM IN 20.42 5.38 31 0.97
VICRNM OUT 21.23 4.42 30 0.81

##              Df Sum Sq Mean Sq F value Pr(>F)
## MPA           1   31.5   31.51   1.272  0.262
## InOut         1   64.4   64.39   2.601  0.109
## MPA:InOut     1   12.5   12.46   0.503  0.479
## Residuals   118 2921.8   24.76

Fish species richness was not significantly different across MPAs, nor across boundaries near an MPA.