Assessing Processing Waste from the Sea Urchin (Centrostephanus rodgersii) Fishery as an Organic Fertilizer

Abstract

The longspined sea urchin, Centrostephanus rodgersii, is a climate-driven pest species in south-eastern Australia. The harvest of this species is highly encouraged and in Tasmania, the existing fishery is expanding resulting in a large amount of waste that needs disposal. Research into use of waste products as inputs for organic or biodynamic farming systems can help reduce costs of disposal and keep the industry profitable; by sustaining or incrementing sea urchin harvest the industry can assist in their control. In the current study, urchin waste was dried and finely ground to a powder and applied to tomato plants in a greenhouse to examine the effect on growth and productivity. Urchin waste powder (UWP) had a mineral composition of Ca (40 g 100 g−1), Mg (1.7 g 100 g−1), P (0.03 g 100 g−1), Fe (19.34 mg kg−1) and B (38 mg kg−1), a pH 8.06 in water and an Electrical Conductivity (EC) value of 7.64 dSm−1. Seven different treatment rates of UWP (0.3%; 0.5%; 0.8%; 1%; 2%; 3%; 5%), were added to 10 replicate pots containing 4 kg nutrient-poor potting mix planted with tomato (Variety K1) seedlings. Plant growth, yield, quality attributes and mineral content of tomato were measured under UWP treatments with comparison against a Hoagland solution control. UWP influenced tomato growth and productivity proportional to the quantity applied, however, the Hoagland solution control had a significantly greater yield. Potting mix pH increased from 6.8 to 7 and higher available P was detected in potting mix receiving higher rates of UWP. No phytotoxic effects were detected. The highest UWP treatment matched the Hoagland control in fruit quality and nutritional composition. Processing waste from the sea urchin fishery has potential as organic fertiliser or amendment providing plant-available Ca and some microelements such as Boron.

Sea urchin roe quality within urchin barrens and improvement through kelp restoration

“…In our study, sea urchins from all urchin barren areas were observed to have kelp in their guts at some sampling events and drift kelp was observed throughout barren control areas on numerous occasions, particularly following storm events (authors' personal observations). All barrens in this study were near deeper kelp forests, and these observations support that there are significant drift kelp subsidies into urchin barrens, as has been previously suggested (Cole, 1993; Elsmore, 2021; Grime et al, 2023; Kelly et al, 2012) or demonstrated (Campus, 2021). Most of the time, the gut contents of sea urchins from barrens were classified as full or very full, suggesting high food availability, even in the absence of growing kelp.…”

“…Sea urchins within barrens generally have low GSI values, leading fishermen to typically avoid harvesting these areas (James et al, 2007; Teck et al, 2018; Worthington & Blount, 2003). However, this is not universal, as harvest of some species occurs within and on the margins of barrens (Campus, 2021; Cresswell et al, 2023; Lee et al, 2021). Therefore, understanding the variability in sea urchin GSI across habitats is key to understanding if, when, and where urchins may be in harvestable condition within barrens.…”