Sea pens and bamboo corals in Skagerrak and the Norwegian trench

Abstract

ABSTRACT This study presents the distribution and abundance of key species of the vulnerable marine ecosystems (VMEs) ‘Coral gardens’ and ‘Sea pen and burrowing megafauna’ in Skagerrak and the Norwegian trench. It is based on 543 bycatches from 2017–2021, and 35 ROV dives from 2016-2017. Bycatches were used to indicate distribution and relative abundance of the VME key species while ROV observations provided information on colony densities, associated fauna and damages. Four sea pen species were recorded. Funiculina quadrangularis and Kophobelemnon stelliferum were widely distributed and most abundant below 200 meters. The few records of Pennatula phosphorea were mainly from shallower than 100 meters, and the rare Balticina finmarchica primarily occurred below 200 meters. The ROV videos confirmed the pattern from the bycatches, however, colony densities were much higher, and the sea pen Virgularia mirabilis recorded in high abundances was not present in bycatches. The coral garden key species Isidella lofotensis, endemic to Norway, had a restricted area of occurrence confirmed by both methodologies. The restricted distribution makes it particularly vulnerable. Fishing activities overlap with the VMEs distribution and the observations of sea pen skeletons and the coral predatory anemone Ptychodactis patula are indicative of pressure from bottom trawl fishing. KEY POLICY HIGHLIGHTS ‘Sea pen and burrowing megafauna’ is a widely distributed VME in Skagerrak and the Norwegian trench, an area with intense bottom trawling. Recorded sea pen species show different distribution patterns, and vulnerability should be evaluated at species level. There is an immediate need for protection of the VME ‘Coral Garden’ represented by the bamboo coral Isidella lofotensis and mapping and monitoring is necessary to evaluate ecological status. Trawl bycatches provide valuable information on VMEs, but the precision on position and abundance of colonies is low compared with visual mapping, and trawling is a threat to the VMEs.