RESULTS
The total MaxN over time increased from 56 (±9) in 2002 to 82 (±17) in
2018, an average increase of 46.4% (Chi = 0.003, df = 1, 209, p 0.003;\(R^{2}=0.038;\text{Fig.\ }1a).\) Similarly, species richness also
increased over time from a mean of 10 (±1) to 18 (±0.8) (an 80%
increase) (Chi = < 0.001, df = 1, 209, p < 0.001,\(R^{2}=0.338;\text{Fig.\ }1b\)).
The probability of occurrence of tropical fishes from all trophic guilds
combined increased over time (Chi = < 0.001, df = 1, 1948, p
< 0.001, \(R^{2}=0.051\)). When broken down into trophic
guilds, three of the four guilds for tropical fishes showed a
significant increase in probability of occurrence over time -
herbivores, piscivores and invertivores - while planktivores showed no
change (Fig 2a; SI T1). Temperate fish also increased overall (Chi =
< 0.001, df = 1, 2598, p < 0.001, \(R^{2}=0.006\))
with a significant increase for piscivores and invertivores and no
change for herbivores (Fig 2b, SI Table 1). There was, however, a
significant decline in temperate planktivorous fishes (Fig. 2b; SI Table
1).
Out of 110 species, we identified 26 that individually showed
significant changes in probability of occurrence over time (GLMM slope
estimates and p-values in supplementary Table 2) (Fig.3). Most of these
species (22 out of 26) increased in probability of occurrence through
time, and this included both tropical and temperate affiliated species
(Fig. 3). However, we also identified 4 temperate-associated species
that significantly declined over time: the planktivore Atypicthys
strigatus (Fig. 4; Chi < 0.001, slope estimate (Year) =
-0.036; df = 1,48; \(R^{2}=0.100\)), the invertivoresOphthalmolepis lineolata (Fig. 3; Chi < 0.001, slope
estimate (Year) = -0.025; df = 1,48; \(R^{2}=0.886\)) andPictilabrus laticlavius (Fig. 3; Chi < 0.001, slope
estimate (Year) = -0.006; df = 1,48; \(R^{2}=0.522\)) and the
piscivore Dinolestes leweni (Fig. 3; Chi < 0.001, slope
estimate (Year) = -0.004; df = 1,48; \(R^{2}=0.794\)).
As a proxy for ecological niche space, body shape of all fish species
present in the community was modelled using geometric morphometrics
analysis. The complete list of Voronoi area size and distance to
community weighted mean for each species are given in supplementary
Table 2. Figure 4 shows a visual representation of the relative body
shape analysis for each trophic guild. Species that showed a significant
probability change (species labelled by picture) were randomly placed
within their respective groups, with no obvious group outliers (Species
not labelled).
Each species’ distance to the community weighted mean (CWM) and their
Voronoi area derived from the morphometric model were tested as possible
explanatory variables for change in probability of occurrence over time.
Neither distance (\(F_{1,75}\)=0.102, p= 0.75) nor area (log(area):\(F_{1,\ 75}\)=0.50, p=0.482) in trait space were significant predictors
of occurrence.