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 July 2022 the first 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 11 different taxa of marine life were observed. In total 41 different families and/or species of marine life were found. The highest number of species was observed on the sandy bottom, followed by the granite sprinkler layer and finally the marble sprinkler layer (29, 26 and 21 respectively). The amount of individuals or colonies per still shows the highest number in the granite layer (4.2), followed by the marble layer (3.65) and the sandy bottom (2.84).
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. A total of twelve fish species were found: six benthic species and six pelagic species. No relation between stone type (G or M) and fish community composition was found based on the species composition. Three out of the four species that varied between locations were found both in location 2 and 3, which were located further offshore. The three-spined stickleback, which is considered an estuarian species, was only detected in location 1 (closest to shore).
Since the layers have been deployed recently (2021) further evolution of the communities might diverge in upcoming years. The planned surveys in 2023 and 2024 might give insight in the developments of this still fairly young habitats.