Different environmental variables predict distribution and cover of the introduced red seaweed Eucheuma denticulatum in two geographical locations

Abstract

In this study we examined abiotic and biotic factors that could potentially influence the presence of a non-indigenous seaweed, Eucheuma denticulatum, in two locations, one outside (Kane’ohe Bay, Hawai’i, USA) and one within (Mafia Island, Tanzania) its natural geographical range. We hypothesized that the availability of hard substrate and the amount of wave exposure would explain distribution patterns, and that higher abundance of herbivorous fishes in Tanzania would exert stronger top–down control than in Hawai’i. To address these hypotheses, we surveyed E. denticulatum in sites subjected to different environmental conditions and used generalized linear mixed models (GLMM) to identify predictors of E. denticulatum presence. We also estimated grazing intensity on E. denticulatum by surveying the type and the amount of grazing scars. Finally, we used molecular tools to distinguish between indigenous and non-indigenous strains of E. denticulatum on Mafia Island. In Kane’ohe Bay, the likelihood of finding E. denticulatum increased with wave exposure, whereas on Mafia Island, the likelihood increased with cover of coral rubble, and decreased with distance from areas of introduction (AOI), but this decrease was less pronounced in the presence of coral rubble. Grazing intensity was higher in Kane’ohe Bay than on Mafia Island. However, we still suggest that efforts to reduce non-indigenous E. denticulatum should include protection of important herbivores in both sites because of the high levels of grazing close to AOI. Moreover, we recommend that areas with hard substrate and high structural complexity should be avoided when farming non-indigenous strains of E. denticulatum.

A Retrospective Review of Global Commercial Seaweed Production—Current Challenges, Biosecurity and Mitigation Measures and Prospects

“…For instance, “tip nippers” was given to fish that ate thalli tips, and “pigment pickers” were mainly juveniles consuming pigmented cell layers, while “thalli planers” were primarily sea urchins and green turtles that eat whole seaweed propagules [ 90 ]. Another approach was identifying the grazers according to the bite mark morphology; small holes on the thallus could have been caused by invertebrates, whereas irregular, jagged edges on the thallus are bite marks from sea urchins [ 100 ]. Herbivory grazing in eucheumatoid farms in China was reported with Siganus fuscescens (rabbitfish) being the dominant grazer, exhibiting a preference for red and green K. alvarezii and E. denticulatum due to their delicate morphological structures [ 92 ].…”

Habitat selection by invaders: Avoiding natural habitats by the red‐whiskered bulbul Pycnonotus jocosus

“…Furthermore, action against invaders is often hindered by a lack of relevant ecological information. Therefore, knowing the habitat preferences of invasive species, predicting their demography and occupancy evolution in invaded areas is the first step towards successful environmental, social, and economic management (Eggertsen et al, 2021; Strubbe & Matthysen, 2007; Walters et al, 2016). Predicting species' habitat occupancy and habitat modeling has been a major focus in ecosystem management, aimed at protecting endangered or declining species and preventing habitat destruction (Bernat‐Ponce et al, 2018; Hahn et al, 2011; López‐Iborra et al, 2011).…”

“…Predicting species' habitat occupancy and habitat modeling has been a major focus in ecosystem management, aimed at protecting endangered or declining species and preventing habitat destruction (Bernat‐Ponce et al, 2018; Hahn et al, 2011; López‐Iborra et al, 2011). But, they also become relevant to control and manage the early invasion stages of non‐native species (Eggertsen et al, 2021; Hallstan et al, 2010; Pietrek & González‐Roglich, 2015; Strubbe & Matthysen, 2007). Different habitat selection patterns in invasive species might suggest the existence of natural barriers to their presence and expansion in new colonized territories, especially in continental areas (Clout & Williams, 2009; Haran et al, 2015).…”