Benthic macroinvertebrates include invertebrates (animals without a backbone) that live on or in the sediment and can be seen with the naked eye. They include a large variety of organisms such as sponges, crabs, shrimp, clams, oysters, barnacles, insect larvae, and worms. Almost 400 species from 10 phyla have been identified in the LSJRB.
18.104.22.168. Sponges (Phylum Porifera)
Sponges are stationary filter feeding organisms consisting of over 5,000 species with about 150 freshwater species. They do not have organs or tissues, but the cells specialize in different functions. They reproduce both sexually and asexually (Myers 2001c). In the LSJRB, five taxa have been recorded and are found in fresh, marine, and estuarine waters (i.e., Spongilla fragilis and Craniella laminaris) (Mattson et al. 2012).
22.214.171.124. Sea Stars and Sea Cucumbers (Phylum Echinodermata)
There are approximately 7000 marine species. They can range in size from 1 cm to 2 m. Food habits vary among the different species, anything from filter feeders to scavengers to predators. Sea stars can regenerate missing arms, and sea cucumbers and urchins are also able to regenerate certain parts of their anatomy (Mulcrone 2005).
126.96.36.199. “Moss Animals” (Phylum Bryozoa)
This group of animals lives in colonies (Collins 1999). They have tentacles which they use to filter phytoplankton out of the water (Bullivant 1968). Five non-native species have been recorded in the LSJRB (see Section 4.5 Non-native Aquatic Species; Mattson, et al. 2012).
188.8.131.52. Jellyfish, Sea Anemones, and Hydrozoans (Phylum Cnidaria)
All the species in this phylum have stinging cells called nematocysts. They have two basic body forms – medusa and polyp. Medusae are the free-moving, floating organisms, such as jellyfish. Polyps are benthic organisms such as the hydrozoans (Myers 2001a). In the LSJRB, hydrozoans are more common than jellyfish and sea anemones. Eight taxa have been recorded in the LSJRB, with three taxa found in freshwater including Corylophora lacustris (Mattson et al. 2012). The non-native freshwater jellyfish Craspedacusta sowerbyi has been recorded in the LSJRB (see Section 4.5 Non-native Aquatic Species).
184.108.40.206. Ribbon Worms (Phylum Nemertea)
The common name “ribbon worm” relates to the length of many species with one species being 30 m. Marine species are more common than freshwater species (Collins 2001). Besides long length, these worms have an elongated appendage from the head called a proboscis that they use to capture prey. (Collins 2001; Graf 2013). One ribbon worm was recorded by Evans et al. 2004 that was salt and pollution tolerant
220.127.116.11. Snails, Mussels, and Clams (Phylum Mollusca)
The Mollusca are very diverse with >50,000 species, ranging in size from less than a millimeter to more than twenty meters long (giant squids). Over 150 taxa have been identified in the SJRB, including more than 3 invasive taxa (see Section 4.5 Non-native Aquatic Species) and others endemic to the SJR drainage (Elimia sp.) (Mattson et al. 2012). Representative taxa include Mytilopsis leucophaeata, Gemma gemma, Littoridinops, Boonea impressa, Nassarius obsoletus, and the non-native Rangia cuneata (Cooksey and Hyland 2007). Six taxa were recorded by Evans et al. 2004 from 2002-2003 collections in the LSJRB. Each taxon was pollution tolerant and two taxa were gastropods and the other four were bivalves.
18.104.22.168. “Peanut Worms” (Phylum Sipuncula)
The common name “peanut worm” relates to their shape. Over 320 marine species have been described and they are found in sand, mud, and crevices in rocks and shells (Collins 2000).
22.214.171.124. “Horseshoe worm” (Phylum Phoronida)
Approximately 12 marine species have been identified with some species having horseshoe-shaped tentacles (Collins 1995). They are most common in shallow sediments. Phoronis has been recorded from Clapboard Creek (Cooksey and Hyland 2007).
126.96.36.199. Insect larvae (Phylum Arthropoda, Supbphylum Crustacea, Class Insecta)
Most insect larval forms look differently from their adult stage. Those larvae associated with aquatic habitats can be found under rocks and in the mud (Myers 2001b). Representative genera include Coelonypus and Chrionomus (Cooksey and Hyland 2007). Sixteen taxa were recorded by Evans, et al. 2004 from 2002-2003 collections in the LSJRB. These taxa were found in freshwater, and six were pollution tolerant.
188.8.131.52. Isopods, Amphiphods, and “shrimp-like” crustaceans (Phylum Arthropoda, Subphylum Crustacea, Class Malacostraca, Superorder Peracarida)
It has been estimated that there are over 54,000 species in this group (Kensley 1998). They all possess a single pair of appendages (maxillipeds) extending from their chest (thorax) and mandibles. The maxillipeds assist in getting food to their mouth. For this superorder, the carapace (the exoskeleton protecting the head and some to all of the thorax is reduced in size and does not cover all of the thorax. The carapace is also used to brood eggs (UTAS 2013). Over 60 taxa have been recorded in the LSJRB (Mattson et al. 2012). In the LSJRB, eleven taxa were recorded, of which all were salt-tolerant, and four taxa were pollution-intolerant (Evans et al. 2004). Example taxa are Paracaprella pusilla, Apocorophium lacustre, and Protohaustroius wigleyi (Cooksey and Hyland 2007). Two species are non-native to the SJRB (see Section 4.5 Non-native Aquatic Species).
184.108.40.206. Crabs and Shrimp (Phylum Arthropoda, Subphylum Crustacea, Class Malacostraca, Order Decapoda)
This is one of the most well-known groups since many people eat crabs, shrimps, and lobsters. Decapoda refers to the five pairs of legs. This group has an exoskeleton, which they periodically have to shed (molt) so they can continue to grow. Their body is divided into three sections – the head, thorax and abdomen. The head and thorax are fused together and covered by the carapace. In crabs, the abdomen is curved under the carapace (Humann and Deloach 2011). Approximately 55 taxa of crabs and shrimp have been reported in estuarine, marine, and freshwater in the LSJRB (Appendix 3.3.2a-3.3.3b). In the SJRB, five species are commercially and/or recreationally (Mattson et al. 2012) harvested. In 2002-3, Evans et al. 2004 recorded two taxa in salt waters, of which Rhithropanopeus harrisii was pollution intolerant. Four species are non-native to the SJRB (see Section 4.5 Non-native Aquatic Species).
220.127.116.11. Barnacles (Phylum Arthropoda, Subphylum Crustacea, Class Malacostraca, Infraclass Cirripedia)
There are approximately over 1,400 species. Size can range from a few centimeters to slightly greater than 10 cm. Barnacles are attached to a hard substrate or other organisms. The carapace completely encloses their soft body. They do not possess compound eyes or appendages. For most, their habitat is along rocky shoreline in the intertidal zone (Newman and Abbott 1980). Two taxa were recorded by Evans et al. 2004 that were salt and pollution tolerant in the LSJRB. Five non-native taxa have been recorded in the LSJRB (see Section 4.5 Non-native Aquatic Species).
18.104.22.168. Worms (Class Polychaeta, Phylum Annelida)
This phylum consists of worms that have segmented bodies, including earthworms. Polychaete means “many bristles” and members of this class look like feathered worms. Over 200 taxa have been recorded in the SJRB (Mattson et al. 2012). Example taxa are Streblospio benedicti, Mediomastus, Neanthes succinea, Nereis, Sabellaria vulgaris, Paraonis fulgens, Nephtys picta (Cooksey and Hyland 2007). Streblospio benedicti and N. succinea are pollution tolerant and representative of impaired environmental conditions (Cooksey and Hyland 2007). Seventeen taxa were recorded by Evans et al. 2004, of which two taxa were pollution intolerant (Orginiidae sp. and Scolopolos rubra) and another two species that were freshwater tolerant (Aulodrilus pigueti and Limnodrilus hoffmeisteri) (Evans et al. 2004).
Benthic macroinvertebrates are an important component of the river’s food web. Indeed, many of the adults of these species serve as food for commercially and recreationally important fish and invertebrate species. Their microscopic young can also be very abundant, providing food resources for smaller organisms, such as important larval and juvenile fish species. Benthic activities in the sediment or bioturbation can result in sediment turnover, changes in oxygen and nutrient availability, and distribution of grain size. The presence of stress-tolerant species can serve as an indicator of river health (Table 4.2; Pearson and Rosenberg 1978; Gray et al. 1979). For more information on pollution in benthic invertebrates, see Section 5 Contaminants.
4.3.3. Data Sources
Macroinvertebrate community data used to assess long-term trends were obtained from the Florida Department of Environmental Protection (DEP), Florida’s Inshore Marine and Assessment Program (IMAP), and the St. Johns River Water Management District (SJRWMD) from 1973-2000 with supplemental data from DEP’s “Fifth Year Assessments” (DEP 2013k). No dataset has been compiled within the past three years.
4.3.4. Current Status (UNCERTAIN)
The current STATUS is rated as Uncertain due to lack of data.
4.3.5. Trend (UNCERTAIN)
Community shifts are expected in response to the natural changes in water quality, salinity, and temperature in addition to biological factors that can include recruitment and predation variability (Cooksey and Hyland 2007). It is important to recognize that the mechanism by which many of these organisms may be affected is by either direct impact to adults or to the offspring that spend part of their time in the water column as plankton. During the planktonic stage of these organisms’ lives, environmental gradients (i.e., salinity, temperature, dissolved oxygen) within the river can affect where young are and how they are transported to adult habitat.
The current trend is rated as UNCERTAIN. The lack of recent surveys and monitoring of benthic macroinvertebrates makes it difficult to identify trends, especially since microhabitat variability can be as high as site variability. Yet, low species richness, diversity, and abundance are representative of impaired benthic conditions (Cooksey and Hyland 2007). The health of the SJR is linked to the health of benthic macroinvertebrates. A potential concern is if macroinvertebrate communities change in a large area within the river, and then affect abundances of ecologically, commercially or recreationally important species (for example, red drum, spotted sea trout, or flounder).