Ecological co-benefits from sea cucumber farming: Holothuria scabra increases growth rate of seagrass

Abstract

Sea cucumber aquaculture is increasing in extent and importance throughout the Indo-Pacific region, supplying a luxury seafood market in Asia. In this context, the grow-out of hatchery-bred juveniles in community-farmed pens is proving to be a viable model, providing increased income security and alternative livelihood options to resource-limited communities. Here, we report a study of the impacts of such sea cucumber farming on the growth of seagrass (a favourable habitat for the animals) at a village-scale aquaculture site in southwest Madagascar. Using experiments, we found that the presence of the hatchery-bred sea cucumber Holothuria scabra (sandfish), at stocking densities of 300 g m-2 (similar to the density used in the farmed pens, but relatively high for natural populations), resulted in a large (~30%), statistically significant increase in the leaf extension rate of the locally dominant seagrass species Thalassia hemprichii. However, the other dominant seagrass species, Cymodocea serrulata, did not significantly change its leaf extension rate in the presence of H. scabra. Since seagrass is a globally important coastal habitat, supporting high biodiversity, carbon sequestration, shoreline stability and nursery grounds for commercial and small-scale fisheries, the positive effect of H. scabra farming on the growth rate of at least one dominant seagrass species implies potential important ecological co-benefits. These co-benefits of H. scabra farming are likely to be relevant across the tropical Indo-Pacific coastlines, where this species is cultured.

Abundance modulates the ecosystem functional contributions of two sympatric Caribbean sea cucumbers

“…Some sea cucumber species can cause changes in sediment grain size, potentially through calcium carbonate dissolution and sediment abrasion during digestive processes ( Hammond, 1981 ; Schneider et al, 2011 ). Additionally, sea cucumbers excrete inorganic nitrogen as ammonium (NH 4 + ), providing a nitrogenous source for benthic microalgae ( Mukai et al, 1989 ; Uthicke & Klumpp, 1998 ; Uthicke, 2001a ), macroalgae ( Felaco, Olvera-Novoa & Robledo, 2020 ) and seagrass ( Wolkenhauer et al, 2010 ; Arnull et al, 2021 ). For example, in the Indo-Pacfic, field enclosures with high densities of the sea cucumber Holothuria scabra resulted in a 30% increase in seagrass leaf extension rate compared to low-density enclosures ( Arnull et al, 2021 ).…”

“…Additionally, sea cucumbers excrete inorganic nitrogen as ammonium (NH 4 + ), providing a nitrogenous source for benthic microalgae ( Mukai et al, 1989 ; Uthicke & Klumpp, 1998 ; Uthicke, 2001a ), macroalgae ( Felaco, Olvera-Novoa & Robledo, 2020 ) and seagrass ( Wolkenhauer et al, 2010 ; Arnull et al, 2021 ). For example, in the Indo-Pacfic, field enclosures with high densities of the sea cucumber Holothuria scabra resulted in a 30% increase in seagrass leaf extension rate compared to low-density enclosures ( Arnull et al, 2021 ). Owing to their high densities in some habitats, sea cucumber populations have the potential to contribute a consistent ‘press’ of ammonium within marine systems ( Allgeier, Burkepile & Layman, 2017 ).…”

Catch and Trade of Sea Cucumbers in Getafe, Bohol, Philippines

“…The significance of conserving sea cucumbers was emphasized. A recent study mentioned that the high density of some sea cucumber species like Holothuria scabra could provide protection, conservation, and even enhance the seagrass habitats (10) . Moreover, sea cucumbers are known as the seas' bioturbators and recyclers.…”

Effects of sea cucumber fishing on tropical seagrass productivity

“…In particular, sea cucumbers are thought to promote the growth of seagrass, though this relationship is tenuous. In cage experiments, both the exclusion of sea cucumbers (i.e., simulating a fishery) and the addition of sea cucumbers (i.e., simulating aquaculture) have generated mixed results: while higher sea cucumber densities were sometimes associated with higher seagrass growth rates, these differences only occurred in certain years (Wolkenhauer et al, 2010) or in certain seagrass species and sites (Arnull et al, 2021). Although this alludes to the potential consequences of reducing sea cucumber populations through fishing, it remains difficult to predict the large‐scale and long‐term effects of these human‐induced changes with so much variability even within individual studies and in the absence of nutrient contributions from other animal sources.…”