## 3 Results
### Chemical Defence  
Four bacterial isolates were applied in anti-bacterial settlement inhibition bioassays, in order to quantify antifouling activity on eelgrass. The defence strength against the different isolates varied, but it was always particularly low in May and June (Figure 2) and in the later month P. dokdonensis was even attracted and not deterred (Figure 2D). The defence strength increased in all four cases significantly from June to July and remained stable or decreased non-significantly until November (Repeated measures ANOVA, Table 2A-D). The mean defence activity against all four isolates basically exhibited the same pattern (Repeated measures ANOVA, Table 3A and Figure 3A) and it was significantly lower in May than in July and August and significantly lower in June than in any other month. The mean surface concentrations of rosmarinic acid were highest in September, but differences among months were not significant (Figure 3B, repeated measures ANOVA, Table 3B). Rosmarinic acid concentrations and defence strength were not significantly correlated (r = \(-\)0.2967, \(p\) = 0.1252). \begin{table}
\begin{tabular}{c c c c c c c} \hline  & & **SS** & **DF** & **MS** & **F** & \(p\) \\ \hline A & Intercept & 172,931,151 & 1 & 172,931,151 & 81.22 & 0.0029 \\  & Error & 6,387,136 & 3 & 2,129,045 & & \\  & Month & 79,883,772 & 6 & 13,313,962 & 19.02 & \textless{}0.0001 \\  & Error & 12,596,887 & 18 & 699,827 & & \\ \hline B & Intercept & 54,269,905 & 1 & 54,269,905 & 79.12 & 0.0030 \\  & Error & 2,057,806 & 3 & 685,935 & & \\  & Month & 8,559,980 & 6 & 1,426,663 & 5.76 & 0.0017 \\  & Error & 4,461,122 & 18 & 247,840 & & \\ \hline C & Intercept & 177,998.3 & 1 & 177,998.3 & 46.37 & 0.0065 \\  & Error & 11,517.0 & 3 & 3839.0 & & \\  & Month & 34,337.6 & 6 & 5722.9 & 1.92 & 0.1316 \\  & Error & 53,516.4 & 18 & 2973.1 & & \\ \hline \end{tabular}
\end{table} 
Table 1: Repeated measures ANOVA of A: bacterial fouling pressure (measured as bacterial density on glass slides; see Figure 1A); B: bacterial density on _Z. marina_ (see Figure 1B); C: bacterial density on _Z. marina_ relative to bacterial fouling pressure (see Figure 1C) in different months. \begin{table}
\begin{tabular}{c c c c c c c} \hline  & & **SS** & **DF** & **MS** & **F** & \(p\) \\ \hline A & Intercept & 5.7717 & 1 & 5.7717 & 4604.62 & \textless{}0.0001 \\  & Error & 0.0038 & 3 & 0.0013 & & \\  & Month & 0.0441 & 6 & 0.0073 & 2.67 & 0.0492 \\  & Error & 0.0494 & 18 & 0.0027 & & \\ \hline B & Intercept & 0.4503 & 1 & 0.4503 & 2517.79 & \textless{}0.0001 \\  & Error & 0.0005 & 3 & 0.0002 & & \\  & Month & 0.0425 & 6 & 0.0071 & 13.06 & \textless{}0.0001 \\  & Error & 0.0098 & 18 & 0.0005 & & \\ \hline C & Intercept & 7.8046 & 1 & 7.8046 & 7108.19 & \textless{}0.0001 \\  & Error & 0.0033 & 3 & 0.0011 & & \\  & Month & 0.0933 & 6 & 0.0155 & 8.93 & 0.0001 \\  & Error & 0.0313 & 18 & 0.0017 & & \\ \hline D & Intercept & 0.5419 & 1 & 0.5419 & 68.50 & 0.0037 \\  & Error & 0.0237 & 3 & 0.0079 & & \\  & Month & 0.2952 & 6 & 0.0492 & 5.97 & 0.0014 \\  & Error & 0.1483 & 18 & 0.0082 & & \\ \hline \end{tabular}
\end{table} 
Table 2: Repeated measures ANOVA of chemical defence of _Z. marina_ against A: _B. aquamaris_; B: _A. stellipolaris_; C: _L. rosea_; D: _P. dokdonensis_. Within-measures factor was the month of sampling. Figure 3: Seasonal variation of (**A**) the mean antisettlement activity of propan-2-ol surface extract from _Z. marina_ against four different bacteria (_B. aquimaris_, _A. stellipolaris_, _L. rosea_, and _P. dokdonensis_) and (**B**) rosmarinic acid concentrations on _Z. marina_ surfaces. (Mean \(\pm\) SD, n = 4). In (**A**) increasingly negative values indicate increasing activity strength. Months that are significantly different ([PERSON]’s post hoc test, \(p\) < 0.05) are marked by different letters. Figure 2: Seasonal variation of the antisettlement activity of propan-2-ol surface extract from _Z. marina_ against (**A**) _B. aquimaris_; (**B**) _A. stellipolaris_; (**C**) _L. rosea_, and (**D**): _P. dokdonensis_ (mean \(\pm\) SD, n = 4).