Detailed visual seabed survey at drilling site 7218/11-1

Table of Contents
PREFACE ................................ ................................ ................................ ................................ ..........................4
1 INTRODUCTION ................................ ................................ ................................ ................................ .............5
1.1BACKGROUND................................ ................................ ................................ ................................ ...................5
1.2SUMMARYOFPREVIOUSURVEYSATDARWIN................................ ................................ ................................ .........5
1.2.1Baselinesurvey2011................................ ................................ ................................ ............................. 5
1.2.2Additionalstudies2012................................ ................................ ................................ .........................6
1.3AIMSANDCHALLENGES FORPRESENTSURVEY................................ ................................ ................................ ..........7
2 MATERIALSANDMETHODS................................ ................................ ................................ ..........................8
2.1VESSELANDNAVIGATION................................ ................................ ................................ ................................ .....8
2.2ROV,VIDEOANDSTILLIMAGES................................ ................................ ................................ ............................. 8
2.3SURVEYTRACKANDWAYPOINTS................................ ................................ ................................ ..........................10
2.4OBSERVATIONLOGSANDEVENTLOGGING................................ ................................ ................................ .............11
2.4.1Stepstakento addresschallenges................................ ................................ ................................ .......11
2.4.2Eventlogging................................ ................................ ................................ ................................ .......12
3 ABOUTSPONGESANDCHALLENGES FORASSESMENT................................ ................................ ...............13
3.1OSPARHABITATCLASSIFICATI ONOFSPONGES ................................ ................................ ................................ .......13
3.2SPONGESIN THESOUTH-WESTERNBARENTSEA................................ ................................ ................................ ....13
3.3ABOUTSPONGES IN GENERAL................................ ................................ ................................ .............................. 16
3.4RED-LISTEDSPONGES ................................ ................................ ................................ ................................ ........18
3.5SPONGESASECOSYSTEMENGINEERS ................................ ................................ ................................ ....................19
4 ABUNDANCEQUANTIFICATIONCHALLENGES - CASESTUDYSALINA,JUKSAANDDARWIN.........................21
4.1GENERAL................................ ................................ ................................ ................................ ........................21
4.2CURRENTAPPROACHES – ASSESSINGCOVERAGE ................................ ................................ ................................ .....22
5 RESULTSANDDISCUSION................................ ................................ ................................ ...........................25
5.1GENERALOBSERVATIONS ................................ ................................ ................................ ................................ ...25
5.2SEAFLOORCONDITIONS................................ ................................ ................................ ................................ .....26
5.2.1Sedimentcomposition................................ ................................ ................................ .........................26
5.2.2Litter andotherhumanimpacts................................ ................................ ................................ ..........26
5.2.3Seashorealgaeandfishfalls................................ ................................ ................................ ................27
5.3DISTRIBUTIONMAPSANDSELECTED IMAGES................................ ................................ ................................ ..........27
5.3.1Generaloverview................................ ................................ ................................ ................................ . 27
5.3.2Plotsof spongedistributionanddensity................................ ................................ .............................. 28
5.3.3Overallassessmentof spongedensitiesat the Darwinsite................................ ................................ . 36
5.3.4Integratedassessment – baselinesurveyanddetailedsitesurvey................................ ......................37
5.3.5Dominantspongespeciesrecordedin the currentsurvey................................ ................................ ...38
5.3.6Trawltracks................................ ................................ ................................ ................................ .........44
5.3.7Generalimpressions(images)................................ ................................ ................................ ..............45
5.4ENVIRONMENTALCOSTSANDBENEFITSFORDISCHARGESCENARIOS ................................ ................................ ............48
5.4.1Dischargescenarios................................ ................................ ................................ ............................. 48
5.4.2Depositionscenariosrelatedto areaof impactto sponges................................ ................................ . 50
5.4.3Comparativeassessment ................................ ................................ ................................ .....................56
5.5ASSESSINGVULNERABILI TYOFSPONGEASSEMBL AGESTODRILLINGDISCHARGES ................................ ............................ 56
5.5.1What do sensitivityandvulnerabilitymean?................................ ................................ .......................56
5.5.2Ongoingandplannedexperimentalandin situ workon assessingsensitivityof spongesto drilling
cuttings................................. ................................ ................................ ................................ ........................57
6 REFERENCES ................................ ................................ ................................ ................................ .................58
APPENDICES ................................ ................................ ................................ ................................ ....................60
Detailed site survey at PL531 Darwin
Akvaplan-niva AS Rapport 6051 - 1