Ecologically significant shallow-water (0–30 m) marine animal forests in central New Zealand

Abstract

Marine animal forests are habitats formed by dense aggregations of suspension-feeding invertebrates that are increasingly being recognised as biodiversity hotspots with key roles in ecosystem functioning. Despite being found across the world, these ecologically important ecosystems remain understudied in temperate seas. Furthermore, while temperate animal forests are typically associated with deeper water, they can also occur in the shallows (< 30 m). This study is the first to describe the diversity of shallow-water (0–30 m) marine animal forests in the Wellington Region of New Zealand using a combination of SCUBA, ROVs, and citizen science surveys. Through qualitative and quantitative surveys, we identified nine distinct biotic communities dominated by sessile invertebrates, including sponges, cnidarians, bivalves, brachiopods, and polychaetes. In Wellington Harbour, the most common communities were sponge beds formed by the massive sponge Suberites australiensis, often occurring with other sponges, the brachiopod Magasella sanguinea, and the bivalve Atrina zelandica. The S. australiensis beds occurred between 7 and 17 m, with densities up to 19 sponges per m2 and specimens up to 40 cm in diameter. Based on pumping rate measurements, we estimated the average filtration capacity of S. australiensis in the sponge beds to range between 1240 and 19,996 L m−2 day−1. Along Wellington’s open coasts, diverse sponge gardens were dominated by massive morphologies, such as Ecionema alata, together with fan, and branching sponges between 20 and 30 m deep. Community composition varied spatially, likely due to heterogeneity in currents, sedimentation, and food availability. Anthropogenic impacts on animal-dominated ecosystems in the harbour included widespread marine debris (e.g., plastics, fishing gear, and tyres), and substrate alteration from coastal development. The open-coast communities were comparatively undisturbed but might be vulnerable to anchoring and fishing activities. Our study revealed ecologically important marine animal forests in the shallow waters of Wellington, which are largely unprotected urban ecosystems. Conservation through mapping, monitoring, and strategic marine spatial planning is urgently needed to preserve these underappreciated biodiversity hotspots worldwide.