Effectiveness of ecomodules in increasing aquatic biodiversity and bioproductivity in a port environment.

Abstract

Abstract In early spring of 2018, so called ecomodules were attached to support piles of jetties within the polyhaline part of the port of Rotterdam. The objective of the ecomodules is to increase bioproductivity and biodiversity of the port basins and waterways, by ‘greening’ nautical infrastructure structures, which would otherwise support few species. An ecomodule consists of a coated steel construction of 1 meter wide and 4 meters high to which elements of structural diversity that facilitate the settlement and growth of organisms can be attached. About a quarter of the ecomodule protrudes above the water level at low tide, the other part is permanently under water. Five different types (I to V) of ecomodules have been tested. Ecomodules with: (I, cups, reference) tidal cups and a subtidal concrete reference slab, (II, ropes) used nylon hawsers with a diameter of 12 cm, (III, drainage pipes) drainage pipes sheathed with polypropylene with a diameter of 12,5 cm, (IV, fender hulas) bundles of thin nylon threads (untangled used hawsers), and (V roots) strands with 3 mm thick nylon strings with a length of 40 cm each. Monitoring of the ecomodules took place in the summers of 2018 and 2019. The biofouling on all ecomodules was zonate both inter- and subtidal. Different types of seaweed were found of which Ulva spec. occurred on all ecomodules while the large seaweed Fucus vesiculosus (Bladder wrack) only occurred on type II and IV. Amongst the macrofauna some groups/species clearly (co-)dominated the different types of ecomodules: barnacles and Crassostrea gigas (Pacific oysters) on type I, ascidians on type I, II, III and IV, hydrozoans on type II, III and V, bryozoans on type IV, while with a coverage of nearly 100% Mytilus edulis (Blue mussel) dominated type V. The ecomodules with elements of structural diversity vs the concrete reference plate scored higher on both biodiversity and bioproductivity. The total number of macrofaunal species found on the ecomodules ranged from 23 to 39 in order from lowest to highest number on respectively type, I (concrete reference plate), IV, V, II, III. The wet biomass on the ecomodules ranged from 5225 gr.m-2 to 80096 gr.m-2 in order from lowest to highest weight on respectively type, I (concrete reference plate), IV, III, II, V. We conclude that ecomodules can be an effective means to increase biodiversity and biomass in an aquatic environment consisting to a large extent of artificial structures, such as a port. An ideal ecomodule was designed based on the findings of the experiment and will be applied to mooring posts in a new project.