Abstract
Tennet constructed a first pilot of eco-friendly cable crossings in Hollandse Kust (zuid): the pilot area contains a top layer of marble instead of granite which commonly used. In the researched area both types of sprinkler layers are present. The general research question for this project is:
Do eco-friendly cable crossings (pilot design) have a higher biodiversity and/or abundance of reef (associated) species, compared to the conventional design both on the crossing works and in the direct vicinity (~10-20 m)?
The research question requires 2 different approaches for several species-groups:
1. Drop-cam (benthic sessile and slow-moving species, lots of detail)
2. Metabarcoding of environmental eDNA (semi-quantitative, highly sensitive for detection of all classified fish species)
In June 2023 the second survey (of three successive years) was performed, and the brief results are reported in this note.
Drop-cam survey: The dropcam system was acquiring video footage during a controlled drift over the sprinkler layers. At each location footage was acquired of the substrate (granite, marble or sand) which was analyzed off site for biodiversity (semi-quantitative). In this study 13 different taxa of marine life were observed. In total 47 different families and/or species of marine life were found. In 2023 the highest number of species was observed on the granite sprinkler layer, followed by the marble sprinkler layer and the sandy layer (39, 27 and 27 respectively). The amount of individuals or colonies per still shows the highest number in the Marble layer (33.55), followed by the granite layer (32.55) and the sandy bottom (6.85).
Metabarcoding of environmental eDNA: Fish community assessment in the vicinity of the underwater cables was assessed with environmental DNA analysis. The fish species were identified using 12S and 16S mitochondrial genomic markers. For each marker gene (12S and 16S) two primer sets were used, one fish optimized and one shark/ray optimized primer set.
The sequencing analysis yielded a total of eleven fish species, five benthic species and six pelagic. Sand goby (Pomatoschistus minutus) was the only species that was consistently found on only one substrate type (marble). Other species were detected on both substrates or just once on a single substrate. Atlantic mackerel (Scomber scombrus) and sand-eel (Ammodytes spec.) were only detected in the location furthest offshore (location 3).
Since the layers have been deployed in 2021 further evolution of the communities might diverge in upcoming years. The surveys in 2022, 2023 and 2024 might give insight in the developments of this still fairly young habitats.