Prado, E.; Cristobo, J.; Rodríguez-Basalo, A.; Ríos, P.; Rodríguez-Cabello, C.; Sánchez, F. (2021). In situ Growth Rate Assessment of the Hexactinellid Sponge Asconema setubalense Using 3D Photogrammetric Reconstruction. Frontiers in Marine Science. 8: 612613.
We describe the first application of a non-invasive and novel approach to estimate the
growth rate of Asconema setubalense (Porifera, Hexactinellida) through the use of 3D
photogrammetric methodology. Structure-from-Motion techniques (SfM) were applied
to videos acquired with the Politolana ROTV in the El Cachucho Marine Protected Area
(MPA) (Cantabrian Sea) on three different dates (2014, 2017, and 2019) over six years.
With these data, a multi-temporal study was conducted within the framework of MPA
monitoring. A complete 3D reconstruction of the deep-sea floor was achieved with
Pix4D Mapper Pro software for each date. Having 3D point clouds of the study area
enabled a series of measurements that were impossible to obtain in 2D images. In
3D space, the sizes (height, diameter, cup-perimeter, and cup-surface area) of several
A. setubalense specimens were measured each year. The annual growth rates recorded
ranged from zero (“no growth”) for a large size specimen, to an average of 2.2 cm
year?1 in cup-diameter, and 2.5 cm year?1 in height for developing specimens. Von
Bertalanffy growth parameters were estimated. Taking into account the size indicators
used in this study and based on the von Bertalanffy growth model, this sponge reaches
95% maximum size at 98 years of age. During the MPA monitoring program, a high
number of specimens disappeared. This raised suspicions of a phenomenon affecting
the survival of this species in the area. This type of image-based methodology does
not cause damage or alterations to benthic communities and should be employed in
vulnerable ecosystem studies and MPA monitoring
