Here’s a cool recent paper from Cesar Megina and colleagues: Harbours as marine habitats: hydroid assemblages on sea-walls compared with natural habitats. Megina et al. compared communities of hydroids in harbors and natural rocky habitats along the southern coast of Spain.
Quick interlude – if you’re wondering what hydroids are, here’s a good overview. They’re essentially colonies that grow in a vast variety of shapes, sizes and structures. The colonies are comprised of lots of little polyps, but often have a medusoid phase as well, like a jellyfish.
OK, back to the story… Cesar Megina and colleagues from Spain and Italy sampled hydroids at multiple harbors and natural rocky sites on the Iberian Peninsula. They found that hydroid assemblages in harbors tended to be comprised of species that formed small colonies and put a higher proportion of their energetic effort towards reproduction. Conversely, the hydroid species growing in natural rocky habitats away from cities tended to be those that form large colonies, put proportionally less effort into their reproductive stage, and have a greater capacity for competition with other benthic organisms for space.
Harbors also tended to support a higher proportion of non-indigenous hydroid species. This is a finding that has been extended across multiple taxa and in several other parts of the world (I’ll post soon about a recent paper on this subject from the Pacific Northwest).
Megina et al. note that they were surprised to find high species richness of sessile hydroids in harbors in southern Spain. As the field of urban marine ecology expands, it would be interesting to see whether this is a finding that carries over to other parts of the world.