Growth estimates of Caribbean reef sponges on a shipwreck using 3D photogrammetry

Lauren K Olinger,Alexander R Scott,Steven E Mcmurray,Joseph R Pawlik

doi:10.1038/s41598-019-54681-2

Lauren K Olinger, Alexander R Scott + Show 2 more

Open Access

https://doi.org/10.1038/s41598-019-54681-2

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Abstract

The growth rates and ages of many benthic marine organisms are poorly understood, complicating our understanding of ecosystem change. This is particularly true for sponges, which are morphologically diverse and lack indicators of annual growth. In this study, we used emerging technologies to measure volume, surface area, and approximate age of 16 sponge species on the Tibbetts shipwreck off Cayman Brac, Caribbean Sea. Photogrammetry was used to determine the volume of individual sponges on the wreck surface, and a time series of YouTube videos was amassed in order to approximate the greatest possible age of the sponges as 8.74 y. Applying the volume measurements to an existing growth equation for the Caribbean sponge Aiolochroia crassa yielded age estimates of 5.2–10.4 y for the largest individuals of the 16 species. Specific growth rates were then calculated for 7 species from the Tibbetts and 8 species from a second shipwreck (Spiegel Grove, Key Largo, FL). Subsequent growth forecasts from these 15 species corroborate a resource trade-off between growth and the production of chemical defenses. Shipwrecks and other anthropogenic structures can be an important source of demographic information for benthic organisms, provided that certain assumptions about their provenance and history can be met.

Highlights

A better understanding of marine ecosystem function and change requires knowledge of the demographics of the organisms that make up marine communities
The three individuals with the greatest surface area (SA) belonged to the massive lobate species Verongula rigida (SA = 19,262 cm2) and V. gigantea (SA = 18,884, 18,137 cm2), and the three individuals with the smallest surface area belonged to P. walpersi (SA = 383, 1,270 cm2) and Aiolochroia crassa (SA = 1,340 cm[2]; Table 1, Fig. 2)
Basic demographic information about many benthic marine organisms is lacking because these organisms do not generate indicators of annual growth, such as the density bands found in the mineralized skeletons of some corals or the otoliths of many fishes

Summary

Introduction

A better understanding of marine ecosystem function and change requires knowledge of the demographics of the organisms that make up marine communities. Past approaches to measuring volume and surface area have included displacing subject organisms in water[3,4] and wrapping organisms with paraffin wax or tinfoil[5,6] These traditional methods require destructive (and often fatal) removal of the organism from the substratum, limiting replicates and precluding repetitive time-series measurements. We generated 3D models using photogrammetry to measure the volume and surface area of individual sponges growing on the Tibbetts shipwreck, located off the west coast of Cayman Brac, in the Caribbean Sea. Publicly-available footage of this shipwreck, posted on YouTube by recreational divers and professional photographers, allowed us to define the earliest date of sponge recruitment, from which we approximated the age of the largest individuals. We calculated and compared specific growth rates for the most abundant sponge species from the Tibbetts wreck to those from the Spiegel Grove wreck (Key Largo, FL), whose displacement volumes were previously measured[4]

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