Automatically link to entries in rich text field
How about just using the replace filter?

{% set text = "A small boat surrounds a large ​island​​" %}

{% set linkedText = text|replace({'boat':'&lt;a href="/whatever"&gt;boat&lt;/a&gt;'}) %}

{{ linkedText|raw }}&lt;br&gt;&lt;br&gt;


That works.  

In theory there should be a way to do it with parseRefs too, but my initial test isn't working yet:

{% set refText = text|replace({'boat':'&lt;a href="{entry:11102:}"&gt;boat&lt;/a&gt;'}) %}

{% set parsedText = refText|parseRefs %}

{{ parsedText|raw }}


...which leaves an unparsed ref tag so far.  I'm just heading out of the office but maybe a simple replace as above is enough to get you started?