Herbivore biocontrol and manual removal successfully reduce invasive macroalgae on coral reefs

Abstract

Invasive macroalgae pose a serious threat to coral reef biodiversity by monopolizing reef habitats, competing with native species, and directly overgrowing, and smothering reef corals. Several invasive macroalgae (Eucheuma clade E, Kappaphycus clade A and B, Gracilaria salicornia, and Acanthophora spicifera) are established within Kāne‘ohe Bay (O‘ahu, Hawai‘i, USA), and reducing invasive macroalgae cover is a coral reef conservation and management priority. Invasive macroalgae control techniques, however, are limited and few successful large-scale applications exist. Therefore, a two-tiered invasive macroalgae control approach was designed, where first, divers manually remove invasive macroalgae (Eucheuma and Kappaphycus) aided by an underwater vacuum system (“The Super Sucker”). Second, hatchery-raised juvenile sea urchins (Tripneustes gratilla), were outplanted to graze and control invasive macroalgae regrowth. To test the effectiveness of this approach in a natural reef ecosystem, four discrete patch reefs with high invasive macroalgae cover (15–26%) were selected, and macroalgae removal plus urchin biocontrol (treatment reefs, n = 2), or no treatment (control reefs, n = 2), was applied at the patch reef-scale. In applying the invasive macroalgae treatment, the control effort manually removed ∼19,000 kg of invasive macroalgae and ∼99,000 juvenile sea urchins were outplanted across to two patch reefs, totaling ∼24,000 m2 of reef area. Changes in benthic cover were monitored over 2 years (five sampling periods) before-and-after the treatment was applied. Over the study period, removal and biocontrol reduced invasive macroalgae cover by 85% at treatment reefs. Our results show manual removal in combination with hatchery raised urchin biocontrol to be an effective management approach in controlling invasive macroalgae at reef-wide spatial scales and temporal scales of months to years.

Modulating CRISPR gene drive activity through nucleocytoplasmic localization of Cas9 in S. cerevisiae

“…The total percentage of colonies sensitive to the SD-HIS condition was quantified across multiple trials. As predicted, a NLS SV40 tag and a tandem NLS SV40 -NLS SV40 tag allowed for >95% activity at 5 h of Cas9 induction (1,2).…”

“…Control of biological populations is critical to agriculture, ecological conservation, and human health. Numerous methods have been employed to remove invasive species 1,2 , cropdamaging pests [3][4][5][6] , or metazoans that harbor diseases 7,8 including physical barriers, chemical agents, and/or natural predators or competitors. However, the ability to genetically modify an entire species has been hindered by the natural laws of segregation-introduction of a genetic element through natural breeding would require an unattainable number of modified individuals to be released into the wild.…”

Can Herbivore Management Increase the Persistence of Indo-Pacific Coral Reefs?

“…While the impacts of management on herbivorous fishes have been relatively well studied, with a few exceptions, there has been much less focus on the direct and indirect effects of management on other coral reef herbivores, such as sea-urchins. This is in spite of the fact that sea-urchins can become the dominant herbivores on some reefs (O'Leary and McClanahan, 2010;Humphries et al, 2014), and are such effective grazers they have even been used as macroalgal biocontrol agents (Neilson et al, 2018). As we describe above, release from predation pressure and competition with other herbivores led to the explosion of seaurchin abundance on fished reefs in Kenya (McClanahan, 2000).…”

Coral Resilience at Malauka`a Fringing Reef, Kāneʻohe Bay, Oʻahu after 18 years

“…The invasive species G. salicornia was introduced to Kāne'ohe Bay in the 1970 s and quickly spread, overgrowing and smothering reef-building corals [36]. The invasive algae has since decreased over the past few years as a result of biocontrol [37], manual removal [38], and increased grazing from Chelonia mydas, the green sea turtle [39]. The management efforts and return of C. mydas to Kāne'ohe Bay likely explain why the once dominant macroalgae was not observed during the 2018 survey.…”

“…were assessed in 2002 [42]. Divers used an underwater vacuum cleaner and outplanted juvenile urchins (Tripneustes gratilla) to remove and control the species in 2011-2013, leading to an 85% decrease in invasive macroalgae across sites [38]. Management efforts have continued to be successful as K. alvarezii was not observed at the study site during the 2018 survey.…”