Lifting back the waters: Marine geophysics provides new insights into the uThukela Banks Marine Protected Area

Abstract

Using the first high-resolution geophysical data set collected from the uThukela Banks Marine Protected Area (MPA), we reveal a plethora of hitherto unknown or poorly resolved seabed features. In tandem with several remotely operated vehicle dives, we improve on the previous National Biodiversity Assessment map for the area and reveal a more complex picture of the seabed geology and geomorphology on which the MPA is predicated. The upper slope (-120 m and deeper) is dominated by small canyons, gullies and rills that occasionally extend to the shelf edge and form a series of slumps. Suspected cold-water corals were imaged on the interfluves of the Thukela Canyon. The mid to outer shelf (-60 to -100 m) is mostly rocky, and is composed of Pliocene-age siltstones for the most part. Aeolianite shorelines are found at depths of 60 m and 100 m, in which palaeo-lagoons and parabolic aeolian dune systems are also preserved. These features provide habitat for mesophotic corals and demersal fishes. Overlying and abutting hard rock substrates are unconsolidated sandy sediments that are mobilised by the inshore movement of the Agulhas Current. An inshore mud belt characterised by pockmarks associated with free gas expulsion is mapped for the first time. A well-developed palaeo-drainage pattern is also revealed, posing exciting new opportunities for the study of benthic communities associated with palaeo-estuaries and lagoons now exposed at the seabed. Several new habitats, both inside and out of the MPA boundaries, should form the basis for future research within the MPA, in addition to informing expansions of the MPA.

The value of multibeam bathymetry in marine spatial planning in South Africa: A review

“…This MPA has not received much attention in terms of high-resolution MBES mapping despite encompassing an extensive subaqueous delta 58,59 and multiple reef complexes noted for high biodiversity 52 . Green et al 34 recently carried out an extensive MBES survey, providing new insights into higher-resolved geomorphology within the uThukela Banks MPA. This extensive survey showed the value of incorporating geological data into informing MPA management (and therefore, MSP).…”

“…Of the 41 MPAs within South Africa's EEZ, none is covered entirely by MBES data, with relatively limited (or focused) coverage where data do exist (e.g. uThukela MPA 34 ). However, demarcation based on rich biodiversity, even without marine geological context, is testament to the work of researchers from marine subdisciplines (biological and physical oceanography), with qualitatively described marine habitats in the literature (cf.…”

“…To date, our knowledge (from MBES) of the structural properties of the uThukela Banks MPA seabed is limited (e.g. focused multibeam bathymetry 34 ). Given that South Africa's MSP management framework is still in its early years of implementation, the current framework is likely subject to revision and fine-tuning for application in future marine spatial plans.…”

“…31 There are 41 MPAs (total area 5.4%) within South Africa's EEZ 32 , defined on ecosystem conservation and/or socio-economic objectives, but only a fraction of these MPAs are associated with the high-resolution geospatial context provided by MBES data (e.g. Protea Banks MPA 33 , the uThukela MPA 34 and Cape Canyon MPA 35 ). The management, protection and monitoring of the oceanic resources and services that are not holistically understood pose significant challenges (e.g.…”