DOI: 10.5061/dryad.4qrfj6qdh
title: Break-through fish diversity and locations

description: Aim: While marine debris is entering the ocean at unprecedented rates,
 little is known about how biological communities engage with this
 introduced substrate. This study analyzes the community composition of
 debris-associated fishes and explores the role of plastics in transferring
 fish across biogeographic barriers. Location: Pacific Ocean, including
 North Pacific Garbage Patch. Results: Fish communities around marine
 debris have low diversity, individual debris items have highly dissimilar
 species compositions, and species composition is affected by horizontal
 debris item size. Debris items in Group I have significantly higher fish
 species diversity and differ in community composition from Group II. We
 observed four species (Abudefduf vaigiensis, Histrio histrio, Oplegnathus
 punctatus, and Petroscirtes spp.) surviving east of the Hawaiian Islands,
 where they have not been previously reported. While we have not yet
 detected juveniles of these “break through” species east of the Islands,
 the earlier transport by debris of A. vaigiensis and H. histrio to Hawaii
 in the 1990s and their subsequent successful establishment there suggest
 that these Indo-Pacific fish have found hospitable thermal regimes east of
 the Hawaiian Islands matching their original reproductive ranges. Main
 conclusion: We suggest that marine debris acts as a mechanism for fish to
 cross biogeographic barriers, such as the Eastern Pacific Barrier. While
 natural flotsam has long been a potential vector, long-lived and
 increasingly abundant plastic debris may set the stage for altering fish
 biogeography.
description: Five cruises were conducted between 2018 and 2020 by The Longest
 Swim (TLS), The Vortex Swim (TVS), Greenpeace (GP), and Ocean Voyages
 Institute (OVI, 2019 and 2020) (Table S1, Fig. 1). Each cruise had
 different research goals and photographic sampling methodologies; cruise
 tracks thus do not necessarily represent equal sampling intensity. In
 chronological order, TLS was a 189-day voyage from Japan to Hawaii; GP a
 104-day cruise from Mexico to Hawaii; OVI-2019 a 31-day out-and-back
 cruise between Hawaii and the NPGP; TVS a 71-day cruise from Hawaii to San
 Francisco, and OVI-2020 a 59-day out-and-back cruise between Hawaii and
 the NPGP. Thus, TLS included samples from both the Western Pacific Ocean
 (west of 180 degrees longitude) and the Eastern Pacific Ocean; all other
 cruises were restricted to the Eastern Pacific Ocean.
 We analyzed approximately 1,500 underwater photographs of marine
 debris taken during the cruises. In addition, we analyzed two videos,
 which were processed into individual images using Adobe Photoshop at 3
 frames per second. Together, 49 debris items were analyzed. Spatial and
 temporal data (precise location and dates of photographs) were available
 for TVS and OVI cruises; precise data were not available for the other
 cruises (Table S1). ​​We recorded debris item
 attributes as follows: Type: hollow (barrels, bins,
 boats, bottles, boxes, and pallets; total number of hollow items, n = 10),
 solid (buoys, spools/reels, and plastic pieces; n = 12), and nets (n =
 21) Size: using objects of estimated known size (such
 as a diver) for comparison, we recorded horizontal (item width) and
 vertical (penetration below the water’s surface) sizes as: small (20-50
 cm; horizontal n=16, vertical n=15), medium (50-500 cm; horizontal n=15,
 vertical n=24), large (500-1000 cm; horizontal n=8, vertical n=3), and
 mega (1000+ cm; horizontal n=4, vertical n=1) Material:
 hard plastic (n = 17), soft plastic (styrene; n = 3), wood (n = 1),
 plastic fabric (tarps; n = 5), rope (n = 14), and plastic and rope (mixed
 material items; n = 3). Color: dark (brown; n = 4),
 light (white, yellow, light blue, gray, tan, or clear; n = 25), and
 multicolor (multiple colors, including dark and light components; n =
 14) Biofouling:  the presence (n = 26) or absence (n =
 17) of the pelagic gooseneck barnacle Lepas, an ocean rafter and often
 foundation species for flotsam-associated invertebrate
 communities. Only items with associated fish (n = 43)
 were analyzed. The six excluded items were from two cruises (GP and TVS)
 and included two bottles and four nets ranging from small to large,
 consisting of plastic and rope; five of these items had no Lepas
 biofouling. Live fish were identified to the lowest
 taxonomic level possible. Dead fish (n = 4) were not recorded. Most
 individual debris items had multiple photos. Fish species diversity and
 maximum abundance per species were quantified for each debris item. To
 determine maximum abundance and reduce the likelihood of double counting,
 we recorded the maximum number of each fish species seen in a photo within
 a given item’s photoset. Fish identifications were verified or made by
 ichthyologists Giacomo Bernardi and Bruce Mundy.